marine geology

Marine Geology

Paleoceanographic Changes During the Late-Holocene in the Adriatic Sea (Central Mediter-ranean)

A. Piva1, A. Asioli2, F. Trincardi3, R.R. Schneider4, L. Vigliotti31, ENI E&P Division, Sedimentology, Petrography & Stratigraphy Dpt., S. Donato Mi-lanese, Italy2, Institute of Geosciences and Earth Resources, CNR, Padova, Italy3, Institute of Marine Sciences, CNR, Bologna, Italy4, Institute of Geosciences, Christian-Albrechts-Universitat zu Kiel, Kiel, [email protected]

Abstract

Sub-millennial scale variability during the last 6000 years is recognized in theplanktic and benthic foraminifera records from sediment cores retrieved from theCentral Adriatic shelf and the Southern Adriatic deep basin. The δ18O shift of ben-thic foraminifer B. marginata suggests an increase of dense water production around7500 years BP with the onset of the modern routing of the North Adriatic DenseWater occurring before the end of Mediterranean Sapropel S1. After 5500 years BP,the northward intrusion of the salty Levantine Intermediate Water (LIW) in the MidAdriatic slope basin (MAD) is recorded by the δ18O of intermediate-water dwellerG. bulloides. During the late Holocene, short-lived episodes of increased runoff areindicated by δ18O values of G. bulloides in the MAD with concurrent drops in G.sacculifer concentration, suggesting either increased fresh water input impacting theentire water column (thereby forcing the LIW to a deeper level) or reduced LIWformation failing to intrude the MAD slope basin. Repeated abundance peaks of theplanktic foraminifer Globigerinoides sacculifer represent warm-dry intervals, amongwhich the Medieval Warm Period, the Roman Age, the late Bronze Age and the Cop-per Age. Moreover, the Little Ice Age (LIA) is approximated at the base by the LastOccurrence of G. sacculifer (550 years BP), and its two main (coldest) phases arerecorded on all the shelf cores by two peaks of the benthic foraminifer Valvulineriacomplanata.

1 IntroductionThe recent literature on short-term climatechange during the Holocene revealed tim-ing, amplitude and possible mechanismsof sub-Milankovitch millennial to centen-nial fluctuations. Although the originof this forcing is not fully understood,some authors suggest that, at least in the

North Atlantic region, the weak quasi-periodic forcing (1500±500 years) of cli-mate changes during the Holocene mirrorsthe Dansgaard-Oeschger oscillations doc-umented during glacial intervals, thoughwith a substantially attenuated expression[1, 2, 3]. Three of the eight warm-coldevents recognized during the Holocene oc-

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Marine Geology

curred during the last 5500 years [1, 4].Among these events the Little Ice Age(LIA) is the coldest (ca. 1500-1880 AD),the best chronologically constrained anddocumented by historical reports, artis-tic production, economical and societalchanges. The goal of this paper is to re-view Adriatic Sea records studied withinthe framework of the two EC projects EU-RODELTA AND EUROSTRATAFORMand showing high resolution short-term(century- to millennial-scale) climatic os-cillations during the last 6000 years withinthe context of the climate variability athemispheric scale [5]. The Adriatic Seais one of the key areas of deep water for-mation in the Mediterranean [6], it is aland-locked basin providing an excellentrecord of terrestrial proxies (pollens andmagnetic properties) related to soil compo-sition and erosion [7], it provides a con-tinuous (slope) and very expanded (mudbelt on the inner shelf) sedimentary recordof the late Holocene [8, 9], and it is con-strained by refined geochronological con-trol, including tephra layers [10]. Eightsediment cores between 55 m and 1126 mwater depth and located along the path im-pinged by the North Adriatic Dense Wa-ters (NAdDW) are here presented at suffi-cient resolution to recognize regional-scaleevents and to evaluate the impact of thesame environmental signals within shallowand deeper-water settings.

2 Study area

The Adriatic Sea is a narrow epicontinen-tal basin with a low axial topographic gra-dient in the North, and a narrower andsteeper shelf further South (Figure 1). Onthe shelf, the late Holocene mud wedge isup to 35 m in thickness above the max-

imum flooding surface (mfs), dated ca.5500 cal. years BP [11, 8, 9]. High-resolution seismic-stratigraphic correlationand integrated stratigraphy indicate a re-duced deposition between 5500 and 3700cal. years BP over much of the shelf andbasin [11, 7, 9, 10]. Above this interval,sediment accumulation rates increased toup to 1.5 cm·yr−1 [12]. These data indicatean overall shore-parallel advective compo-nent controlling sediment dispersal and asignificant decrease of the sediment accu-mulation rates during the last century com-pared to the Little Ice Age interval [8, 9].The Mid Adriatic Deep (MAD) is a slopebasin about 260 m deep providing an ex-cellent paleoenvironmental record throughthe last deglaciation [13, 14]. Cores fromthis area reflect atmospheric forcing, riverrunoff and water mass intrusion from theopen Mediterranean basin.

3 Material and methods

The cores selected for this review are de-scribed in Piva et al. ([5] and referencetherein) and their results are compared withthe ones published for core RF93-30, col-lected on the seaward pinch-out of the35-m-thick Late Holocene mud wedge re-vealing century to millennial-scale envi-ronmental changes over the last 6000 years[7]. Additional cores from slope settings,where sediment accumulation rates arehigh, complement the paleoenvironmentalreconstructions from shallow-water sites.Foraminifera. Cores AN97-15, SA03-9,SA03-11 and PRAD1-2 were sampled ev-ery 10 cm, and core AMC99-1 every 6 cm.For the sample processing and countingmethod the reader is referred to Piva et al.[5]. All taxa are quantified as percentagesof the total number of planktic and benthic

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foraminifera, respectively, while the con-centration is reported as number of speci-mens per gram of dry sediment. Regardingplanktic foraminifera Globigerinoides exgr. ruber includes Globigerinoides ruberand Globigerinoides elongatus; while Glo-bigerinoides sacculifer comprehends Glo-bigerinoides trilobus, Globigerinoides sac-culifer and Globigerinoides quadrilobatus[15]. Oxygen and carbon stable isotopes.Oxygen and carbon stable isotope analyseswere obtained from selected monospecificforaminifera specimens, planktic speciesGlobigerina bulloides in cores SA03-9,SA03-11, PRAD1-2, G. sacculifer for coreAMC99-1 and the benthic species Bulim-ina marginata for PRAD1-2 from the size

fraction > 0.180 mm [5]. All the iso-topic records discussed are expressed asper mil (�) deviation with respect to theinternational V-PDB standard with no cor-rection for the ice-volume effect. Radio-carbon dates. The 14C AMS dates wereperformed in cores AMC99-1 and SA03-9 on (mixed) planktic and benthic samples(monospecific Cibicidoides pachyderma,mixed with Uvigerina peregrina in onesample) at the Poznan Radiocarbon Lab-oratory, Poland, from the size fraction >0.250 mm. The data were then calibratedusing Calib 5.0.2 Radiocarbon CalibrationProgram [16]. For further details the readeris referred to Piva et al. [5]. Magnetic mea-surements. Measurements of the Secular

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Variation of the magnetic field were car-ried out for core AMC99-1 on u-channelsamples collected from each section of thecore and measured on an automated 2Gcryogenic magnetometer at the Universityof California at Davis [17].

4 ChronologyThe chronologic framework relies on theintegration of several and independentmethods, such as: regional bioevents (LOof the planktic species Globorotalia inflatamarking the end of the post-glacial sea-level rise), 14C AMS dates, secular varia-tion and tephra layer correlation. Fine tun-ing of the core-top ages relies on the defi-nition of the activity depth of 210Pb short-lived radionuclide [18]. The chronology ofthe reference core RF93-30 is described inOldfield et al. [7]. Full details about theage-depth model adopted for the cores arereported in Piva et al. [5].

5 New biostratigraphic re-sults from the Adriaticreg

G. sacculifer presents a consistent distribu-tion in all the cores (Figure 2), although itsabundance is inversely related to the wa-ter depth, because planktic foraminifers in-crease in abundance with the increase ofthe water column [19, 20]. Core AMC99-1 shows three major long-term increasesof G. sacculifer at 5200-4000, 3800-2400and 2100- 600 years BP, respectively [5](Figure 2, dashed line for cores SA03-9 and AMC99-1). This latter peak ap-pears double phased in core SA03-9, be-cause of the higher resolution consequent

to the higher sediment accumulation rate.Moreover, the age of the main frequencyminima of G. sacculifer in core AMC99-1 (2200-2400 and 3800-4100 years BP)are in good agreement with the minima inthe other cores from both deeper and shal-lower water (SA03-9 and RF93-30) (Fig-ure 2 dashed line). The age of the LO ofG. sacculifer is about 550 years BP and itis the average among the values obtainedfrom the chronologically best constrainedcores RF93-30, AMC99-1 and SA03-9 [5].Moreover, the LO of G. sacculifer wasrecognised also in the Eastern Mediter-ranean slope off Israel [21, 22] and, al-though occurring slightly earlier (between800 and 850 years BP), still representsthe planktic foraminifers’ bioevent best ap-proximating the base of the LIA in thewhole Eastern Mediterranean. The shallowcores AN97-15 and RF93-30 record twopeaks of the benthic foraminifer Valvuline-ria complanata (Figure 2) dated at 1865ADand 1689AD according to Oldfield et al.[7]. Although the record of V. complanatais peculiar of the inner-shelf mud-belt envi-ronment, it is significant that the peaks canbe recognized over at least 300 km, show-ing that this benthic feature can be used foradditional stratigraphic correlation at a re-gional scale [5].

6 Paleoenvironmental in-ferences

G. sacculifer is an oligotrophic, shallowwater, symbiont-bearing dweller, typical ofwarm, tropical environments [23, 15, 24].As this species lives only in the West-ern Mediterranean at the end of summer[24] the main peaks of this species dur-ing the last ca. 6000 years are inter-

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Figure 2: Major climatic oscillations during the last 6 ka: warm planktic foraminiferasum, G. sacculifer abundance, C. laevigata carinata, Brizalina spathulata, trees sum,aquatic+hygrophytes curve (Pinus excluded) (from [7]). In cores SA03-9 and AMC99-1a 3-point average smoothed curve (dashed bold line) is plotted for G. sacculifer, in orderto better highlight the major long-term increases. Grey and dotted stripes indicate warm-dry intervals and the Little Ice Age, respectively. W (1-4) are warm-dry events, C (1-3)are cool-wet events. LIA=Little Ice Age; MWP=Medieval Warm Period; DACP=DarkAge Cold Period; RWP=Roman Warm Period; IrA=Iron Age; LBA=Late Bronze Age;ABA=Ancient Bronze Age; CA=Copper Age (from [5] modified).

preted as indicative of relative climatic op-timum with low turbidity of the water col-umn and reduced river runoff [5]. Ac-cording to the age-depth model adopted,the main peaks of G. sacculifer correspondto warm intervals recognised by archaeo-logical studies in the regions surroundingthe Mediterranean: the Medieval Warm Pe-riod, the Roman Age, the late Bronze Ageand the Copper Age (Figure 2). Amongthe benthic foraminifers, the opportunis-tic species V. complanata presently livesin the mud belt environment, character-ized by large availability of organic mat-ter, mainly brought by river runoff andleading to a poorly oxygenated sea floor[25, 26, 27]. The two peaks of this speciespresent in the shallowest cores RF93-30

and AN97-15, occur above the LO ofG. sacculifer, therefore they represent theenvironmental conditions during the Lit-tle Ice Age (LIA). Moreover, the ages ofthese two peaks are consistent with thecoldest phases of the LIA: Fernau (1590-1630 AD) and Napoleon (1810-1820 AD)[28, 29]. Consequently, high frequenciesof V. complanata record two cold and hu-mid intervals, characterized by substan-tially increased river discharge [5]. In thedeeper-water cores the abundances of themain benthic taxa show a generally con-stant trend, except for minor oscillations.In core AMC99-1 the decrease of Brizalinadilatata (Figure 2) points out an improve-ment of bottom floor oxygenation, whilethe Cassidulina laevigata carinata trend

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indicates increased bottom water salinity[30]. Moreover, in the two deeper-watercores benthic taxa do not clearly paral-lel G. sacculifer oscillations. Therefore,the causes responsible of the changes reg-istered in surface waters did not impactthe deeper environment. At last, addi-tional high frequency oscillations are vis-ible within the main trend observed forG. sacculifer, as well as for the warmspecies (Figure 2 solid lines for G. sac-culifer in AMC99-1 and SA03-09 cores).The minima of these high frequency os-cillations parallel the pollen record ofcore RF93-30 [7], which shows a concur-rent increase in humidity-related aquaticherbs/hygrophytes pollen (Figure 2), con-firming the cool and rainy conditionsinferred by the planktonic foraminiferarecord.

7 The main paleoceano-graphic steps

In Figure 3 all the δ18O records availableand indicative of surface, intermediate andbottom water are plotted against calibratedage according to the adopted age depthmodel [5]. The B. marginata δ18O recordis available for three cores from the MAD.The three curves are distributed in a quitenarrow range of values up to 7500-7000years BP, after which the isotope compo-sition of core RF93-77 becomes lighter upto the modern time, while the two recordsin slightly deeper waters (PRAD1-2 andCM92-43) show substantially higher val-ues. This “permanent separation” betweenthe shallower and deeper records occursclose to the end of the deposition of theSapropel 1 (ca. 7000 years) and it is in-terpreted to reflect an increased production

of the dense bottom waters forming in theNorthern Adriatic [5]. According to Arte-giani et al. [31, 32] the dense water, formedduring winter time, moves from the Northfollowing the western coast of the Adriatic,where it is mixed and stored in the MADbecoming the Middle Adriatic Deep Wa-ter. This dense water seems to contribute,together with the inflowing LIW, to theformation of dense water in the SouthernAdriatic. The modern δ18O composition ofthe dense bottom water indicates a changetowards relatively higher values proceed-ing southward ca. from 1.00� in north-ernmost part of the Adriatic to 1.36-1.48�in the MAD and to higher values in theSouthern Adriatic [33]. Our isotope recordsuggests that the shallow site (RF93-77)is not affected by the dense water flowresponsible of higher oxygen values inthe deepest site (CM92-43). PRAD1-2site, showing a similar record to CM92-43, would locate at the upper limit of thearea impacted by the dense bottom waterpath (Figure 3a). The G. bulloides δ18Ocurves from the Central and Southern Adri-atic show almost overlapping trends up to5500 years BP (Figure 3b). Later, theCM92-43 record shifts towards higher val-ues, while all records from the other coresremain constant and overlapping up to themodern time. G. bulloides is an interme-diate dwelling species occurring in winterand spring in the Mediterranean [24] downto 200 m and is prolific below the thermo-cline. Artegiani et al. [31] and Stenni etal. [33] indicate that the Modified Lev-antine Intermediate Water (MLIW) entersin the Southern Adriatic basin on the east-ern side during spring and the shallowestcomponent of this water mass reaches theMiddle and Northern Adriatic. Stenni etal. [33] describe this water mass as charac-terized by an oxygen isotope composition

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Figure 3: Major paleoceanographic turnovers in the Adriatic basin during the Holocene.Stripes mark cold-wet intervals. Grey circles mark critical time intervals of the mainδ18O events: a) NAdDW dense bottom water achieve the modern route some 7000 yearsBP; b) Modified LIW intrude the Central Adriatic around 5500 years BP and c) Closely-spaced cool/wet events during the last 5500 years (from [5] modified).

heavier than the surrounding surface andbottom waters. Therefore, the shift to rel-atively higher values in CM92-43 recordsthe intrusion of MLIW in the Central Adri-atic around 5000-5500 years BP, creatinga circulation pattern similar to the mod-ern one. The occurrence of higher val-ues in CM92-43 does not mark a decreasein temperature, because they correspond towarm intervals (G. sacculifer peaks). Thesurface-water record of G. ruber for theCentral Adriatic shows overlapping trendsup to 5500 years BP, regardless of majordepth or distance from the coast (Figure3c). After 5500 years the core in deeperwater and more distal location shifts to-wards higher values compared to the prox-imal core. Moreover, the more distal sitebecomes less affected by fluvial runoff, re-flecting the increased distance of the rivermouths at the end of the sea level rise [34].The oscillations towards lower isotope val-

ues during the last 5500 years in CM92-43 mark short intervals of increased rain-fall, which match the minima in G. sac-culifer (Figure 3d and dotted stripes in Fig-ure 3). In the upper part of the cores, theinterval corresponding to the LIA is char-acterized by a heavier isotope composition(in particular for core RF93-77), that re-flects primarily the temperature decreaserather than a salinity change, in contrastwith all the preceding wet/cool intervals,as suggested by the pollen record and bythe sum of warm planktic species (Figure2). The Adriatic stratigraphic record canbe compared with several other climaticrecords based on different proxies in sev-eral locations worldwide suggesting that anatmospheric connection is the most likelylink among these distant areas. A gen-eral correspondence between the observedclimate oscillations and recognised archae-ological intervals confirms the major role

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exerted by climate change in determiningrises and declines of civilizations. Old-field et al. [7] recognised the impact ofan anthropogenic signal in proximal (in-ner shelf) cores. The abundance of treepollen from Oldfield et al. [7]) in coreRF93-30 and the derived intervals of for-est clearance around 3600, 2400 and 700years BP are reported in Figure 2, as thebest expression of a possible anthropogenicimpact on sedimentation. Human impactduring these intervals, however, probablyaffects only relatively proximal environ-ments and does not extend in deeper-watercores AMC99-1, in the MAD slope basin,and SA03-9, in the South Adriatic slope.

In these distal contexts the surface-waterplanktic foraminifers display subtle but co-herent oscillations in relative abundances,which appear to match the climate variabil-ity on super-regional extents.

8 AcknowledgementsThis study was supported by the EC-EURODELTA, EC-EUROSTRATAFORMand EC-PROMESS1 projects. Nils Ander-sen performed the isotope analysis and toAnna Maria Mercuri helped on the inter-pretation of pollen records of core RF93-30. This is the ISMAR-Bologna (CNR)contribution n. 1697.

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[31] A. Artegiani, E. Bregant, D.and Paschini, N. Pinardi, F. Raicich, and A. Russo.The Adriatic Sea general circulation. Part I: air-sea interactions and water massstructure. Journal of Physical Oceanography, 27:1492–1514, 1997.

[32] A. Lascaratos, W. Roether, K. Nittis, and B. Klein. Recent changes in deep waterformation and spreading in the eastern Mediterranean sea: a review. Progress inOceanography, 44:5–36, 1999.

[33] P. Stenni, B.and Nichetto, P. Bregant, D.and Scarazzato, and A. Longinelli. The18O signal of the northward flow of Mediterranean waters in the Adriatic Sea.Oceanologica Acta, 18(3):319–328, 1995.

[34] F. Trincardi, A. Asioli, A. Cattaneo, A. Correggiari, and L. Langone. Stratigra-phy of the late-Quaternary deposits in the Central Adriatic basin and the record ofshort-term climatic events. Memorie dell’Istituto Italiano di Idrobiologia, 55:39–70, 1996.

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328

Paleoceanographic Evolution of the Central Adri-atic During the Last Four Glacial-Interglacial Cy-cles (Promess1 borehole PRAD1-2)

A. Piva1, A. Asioli2, N. Andersen3, J.O. Grimalt4, R.R. Schneider5, F.Trincardi61, ENI E&P Division, Sedimentology, Petrography & Stratigraphy Dpt., S. Donato Mi-lanese, Italy2, Institute of Geosciences and Earth Resources, CNR, Padova, Italy3, Leibniz Laboratory for Radiometric Dating and Stable Isotope Research, CAU, Kiel,Germany4, Department of Environmental Chemistry, Institute of Chemical and EnvironmentalResearch (IIQAB-CSIC) Girona, Spain5, Institute of Geosciences, Christian-Albrechts-Universitat zu Kiel, Kiel, Germany6, Institute of Marine Sciences, CNR, Bologna, [email protected]

Abstract

The paleoenvironmental history of the central Adriatic basin is here reconstructedfor the last 360 ka BP, based on an integrated approach (planktic and benthic foraminifera,alkenone SST and O and C stable isotope records). There seems to be a general in-phase trend in the paleoclimatic changes between the central Adriatic and the northAtlantic climate system, except for the intervals related to the deposition of the sapro-pel layers in the eastern Mediterranean; in particular, the time period between MIS7.5and MIS5 results to be strongly influenced by the monsoonal regime. Compared toother Mediterranean records, it can be inferred that the Adriatic was affected by verylow SST during glacial times (down to 2°C for MIS2), which is uncommon for theMediterranean basin. The SST record points out that the Adriatic was not capableto maintain interglacial/interstadial conditions for a duration similar to the westernMediterranean. The landlocked position of this shallow basin, in fact, makes it par-ticularly sensitive to factors such as the strong exposure to atmospheric forcing (e.g.Siberian High), and the strong influence of the nearby land mass, producing a lag inthe demise of glacial intervals. Moreover, the progressively higher values of the δ18Orecords of the glacial intervals, consistently with the SST record and the foraminiferaassemblage, imply an increasing impact of the formation of cold and dense water inmore recent times.

1 Introduction

The Mediterranean Sea is a mid-latitude,land-locked marginal basin, switched, dur-

ing the Quaternary, between intervals moredominated by the high-latitude obliquity(41 ka)-driven climate system or by thelower-latitude North African climate sys-


Marine Geology

tem, tightly linked to the precession cy-cle (21 ka). To address the stabilityof the Mediterranean climatic scenario,high-resolution paleoceanographic studieshave been carried out, unravelling recordsretrieved from broad shelves and upperslopes, where thick sedimentary sequencesdeposited during the last 500 ka. This inter-val encompasses several orders of cyclic-ity (100, 41, and 21 ka) that are charac-teristic of past Quaternary climate regimes,with the chance of identifying centennial tomillennial-scale episodes of abrupt climatechange.Borehole PRAD1-2 is the first continu-ous and almost undisturbed marine recordspanning the last 370 ka retrieved in theAdriatic Basin [1, 2], in order to studythe paleoenvironmental changes of the lastfour glacial-interglacial cycles in a key areafor the oceanographic setting of the wholeMediterranean.Even if the borehole was drilled in ashallow-water and proximal location (186m water depth), Piva et al. [1] pro-vided a multi-proxy high-resolution inte-grated stratigraphy for PRAD1-2, docu-menting a robust chronologic correlationwith other oceanic records within and out-side the Mediterranean.This paper aims at reviewing the cli-matic trends of glacial and interglacialintervals during the last 370 ka in ahigh resolution Adriatic setting, integrat-ing independent proxies, such as plank-tic and benthic foraminifera assemblages,foraminifera-derived O and C stable iso-tope composition, and alkenone-derivedSST records. Comparison with otherMediterranean records provides informa-tion for the recognition of the role thissmall basin played in the past for cold anddense water production.

2 Materials and Meth-ods and ChronologicalFramework

Borehole PRAD1-2 yielded a continuous,71.2 m long sediment sequence, collectedon the western slope of the Mid-AdriaticDeep (Figure 1). The methods adoptedfor each proxy considered in the paper fol-lowed a standard procedure and are fullydescribed by Piva et al. [2]; the reader isreferred to Piva et al. [1] for a complete de-scription of all the other proxies taken intoaccount in the integrated stratigraphy.A comprehensive description of the agemodel for PRAD1-2 was provided by Pivaet al. [1]. The borehole was ascribedto the last 370 ka, ranging from MIS11.1to MIS1, by means of an integrated ap-proach, based on Oxygen stable isotopestratigraphy (both on planktic foraminiferGlobigerina bulloides and on benthic Bu-limina marginata), calcareous nannoplank-ton biostratigraphy, foraminifera bioevents,magnetostratigraphy, radiocarbon dates,sapropel stratigraphy, and the recognitionof Dansgaard-Oeschger events.

3 PRAD1-2 General Cli-mate Trends

PRAD1-2 interglacial and interstadial in-tervals are characterized by peaks of warm-water planktic foraminifera species, (Fig-ure 2) paralleled by significant shifts inthe oxygen stable isotope and alkenone-derived SST curves. MIS5.5 is the warmestsubstage of the entire record (about 22°C).Similarly high SST values are found ininterglacials MIS7 and 9. Most glacial-interglacial transitions exhibit rapid andlarge SST increases, as for the 19.5°C

330


10o

40o

35o

0o 10o 20o

Site 977A

KC01-Breference cores PRAD1-2 borehole

MD01-2443

MD01-2444

Pelagosa sill

Figure 1: Location of borehole PRAD1-2 (star) and of the core records (circles) discussedin the text.

warming during Termination II.An overall cooling trend characterizes bothMIS9 and MIS5, while MIS7 shows the op-posite. Substages 7.3 and 7.1 are warmerthan MIS7.5, based on both SST values andthe planktic assemblage composition. Thissuccession of climatic changes matcheswith the integrated sea-land records (ma-rine and pollen data) described by Rou-croux et al. [3], and Desprat et al. [4, 5] onthe western Iberian margin. These authorssuggested an insolation maximum duringMIS7.3 similar to the one in MIS7.5 and amild stadial of MIS7.2, the latter character-ized by reduced ice caps compared to theother stadials [6], and by only a slight de-crease of Atlantic sea-surface temperatures[7].The planktic foraminifera assemblage in-dicates dominant oligotrophic conditionsin the surface water during warm inter-vals. Higher productivity conditions, ei-ther related to the development of a DeepChlorophyll Maximum or concentrated inthe uppermost water column, mainly corre-

spond to the deposition of sapropel equiv-alent layers. Globorotalia inflata, a win-ter deep dweller species requiring verticalmixing and a cool and homogeneous wa-ter column [8], is generally present dur-ing warm substages and also at the onsetand/or at the end of cold substages (5.4 and7.4, Figure 2), but not during the deposi-tion of sapropel equivalents, confirming thestrong stratification of the water mass dur-ing these events. Therefore, when present,G. inflata can be considered an indicator ofdeep water production, assuming that dur-ing past interglacials and interstadials thenorthern Adriatic deep-water formation oc-curred through mechanisms similar to themodern interglacial [9].The difference between planktic and ben-thic foraminifera oxygen isotope values(∆18O B. marginata-δ18O G. bulloides) isan indicator of the water mass homogene-ity. When ∆values approach zero the watermass tends to become more uniform, whileincreasing δ values reflect a stronger strati-fication of the water column. Consistently,

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Marine Geology

5.5 4.5 3.5 2.5 1.5 0.5 -0.5

1

2

3

4

5.1

5.25.3

5.55.4

6.4

7.27.1

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8.59.1

10.2?

11.1?

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δ18O vs VPDB G. bulloidesδ18O vs VPDB B. marginata

S1 eq.

S3 eq.

S4 eq.

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S7 eq.

S9 eq.

S’ eq.

S10 eq.

S8 eq.

S6 eq.

0

4

8

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16

20

24

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36

mLO G. in�ata

LO S. sellii

Lithology

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stratig

raphy

S. sellii

40

44

48

52

56

60

64

68

71.2

cal age (ka BP)

reversalG. caribbeanica-small Gephyrocapsa

FO E. huxleyi

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modern timeLO G. i.S1 eq.top Y. D.

S3 eq.

S4 eq.

S5 eq.T II

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S10 eq.

06

8.512

81

101

124130

172188

195

216

239243

264288

331

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364

Control points

17.319.2

14C AMS 14C AMS

14C AMS 27.7

LCO G. in�atain MIS3

LCO G. i. in MIS3 43.1

LGM Chronozone

homogenuos mudsilty mudsilty laminaesandtephra layer

di�used bioturbation

organic matterbiosomebioclast

burrow

erosional surfaceMIS10.2?

MIS11.1?

H. balthica

I. islandica

E. excavatum f. clavata

9.39.2

6.56.3

6.2

7.0

MIS5.2 91

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MIS7.0

MIS7.2

MIS7.4

111

135152.5

189.5

200.5

225

D-O events

Foram + nannopl. bioevents

Figure 2: PRAD1-2 stratigraphic framework. Grey arrows indicate the control points ofDansgaard-Oeschger events (see [1] for details).

the ∆18O curve for PRAD1-2 shows thehighest values (up to 2.5�) during the de-position of the Adriatic sapropel equivalentlayers, while minima in ∆18O are mainlyrecorded during cold intervals. G. inflata isabsent during the acme of glacial intervals(MIS10.2, 8.4, 6), when ∆18O minima areextreme and the water depth was too shal-low to allow the appropriate depth habitatof this intermediate water dweller (Figure2). Excluding the sapropel-equivalent in-

tervals, the benthic assemblage indicates anupper slope mesotrophic environment dur-ing all interglacials and interstadials, char-acterized by the accumulation of organicmatter on the seafloor and relatively lowoxygenation. However, in this mesotrophicenvironment a small amount of epifaunalspecies is indicative of well oxygenatedbottom waters. This occurrence thereforesuggests seasonal bottom ventilation, com-parable with modern conditions, character-

332


ized by winter production of oxygenated,dense water in the north Adriatic.Glacial stages show distinctive featuresboth in terms of paleodepth and climatetrends. MIS10 shows the shallowestglacial sea level of the whole borehole,as testified by the near-absence of plank-tic foraminifera and by the high percentageof Elphidium + Ammonia, reflecting a veryshallow environment. In contrast, MIS4 ischaracterized by the deepest glacial basinconditions.

4 Comparison with otherrecords: westernMediterranean

We compare PRAD1-2 δ18O G. bulloidesand alkenone-derived SST records to thetime equivalent succession from ODP Site977A (Figures 1-2), the western Mediter-ranean Sea record with the highest res-olution for the last 250 ka [10]. TheUk′

37 SST record reported by Martrat etal. [10] for the Alboran Sea indicatesSSTs quite similar to those reported dur-ing warm substages in PRAD1-2 (Figure2). Intervals of abrupt warming are de-tected in PRAD1-2 by concurrent peaks ofδ18O, SST and warm planktic foraminifera(Figure 2), in particular during MIS9.3(12°C shift), 9.1 (7°C), 7.5 (13°C), 5.5(18.5°C) and 1 (8°C), confirming the con-clusion made by Martrat et al. [10] thatcold stadials had only limited duration, im-mediately followed by well-defined returnsto interstadials with accelerated warmingby positive feedback mechanisms once athreshold was passed. However, PRAD1-2 reveals several exceptions, with regardto the exact timing of the highest SSTvalues: maximum warming is differently

recorded by Uk′

37 SST or warm plankticforaminifera frequency. Frequency peaksof warm planktic species and minima ofδ18O values are not in phase with coevalpeaks of Uk′

37 SST. These phase lags seemto reflect decrease in productivity before orafter the maximum Uk′

37 SST, producing apoorer total flux of planktic foraminiferaassemblage but a relative increase in warmspecies. All these observed trends lead tothe conclusion that the Adriatic basin isnot capable to maintain interglacial and in-terstadial conditions with a duration simi-lar to the western Mediterranean and east-ern Atlantic [10, 11], as suggested by threeobservations: (1) during MIS7.3, 7.1, 5.3and 5.1, the decreasing SST trend towardcold substages starts earlier in the AdriaticBasin than in the Alboran Sea; (2) simi-larly, the subsequent SST increase in warmsubstages is slower and delayed in PRAD1-2, resulting in prolonged intervals with lowSST and (3) in PRAD1-2 the maximumUk′

37 SST within MIS7.3 is achieved later(Figure 2). The overall very low SST, un-common for the Mediterranean Sea, andthe shorter duration of warm intervals doc-umented for the Adriatic, may be explainedby three interacting causes, which are herelisted on the basis of their inferred rel-ative importance: (1) the landlocked na-ture of this shallow basin, especially dur-ing the glacial stages, when sea level wasmore than 100 m lower than at present,probably amplified the SST excursion andincreased the atmospheric forcing, e.g.,through outbreaks of northerly polar con-tinental air masses (Siberian High), as al-ready argued by Rohling et al. [12] for theHolocene cold oscillations; (2) the vicinityof the basin to large Alpine and Apennineglaciers, conveying cold air, an uncommoncondition for the Mediterranean and (3)the location at a latitude at least 3° higher

333

Marine Geology

than the best documented Mediterraneansites. Glacial intervals like MIS10, 8.4,6.2 and 2 experienced the lowest temper-atures (2-4°C) and MIS4 was just slightlywarmer (5°C). These central Adriatic SSTare typically 3-4°C lower than at the Alb-oran site [10] both during glacial and sta-dial intervals. Greatest SST differences(up to 5-7°C) between the two sites arerecorded during MIS6.2–6.3, MIS4 andMIS2. The comparison of the SST recordbetween PRAD1-2 and the Iberian Mar-gin [11], Figures 1, 2) for the last fourclimate cycles confirms differences as rec-ognized between the Alboran and AdriaticSites also for MIS8 as well as for the inter-stadials MIS9.1 and 9.3.

5 Comparison with otherrecords: easternMediterranean

Sanvoisin et al. [13] analyzed the oscil-lations in the planktic foraminifera assem-blage in the Ionian Basin. Core KC01-Bwas retrieved in 3643 m water depth (Fig-ure 1), and spans the last circa 1.1 Ma BP.The correlation between PRAD1-2 recordand the last circa 340 ka BP of the Io-nian core allowed the identification of ma-jor similarities and differences between thetwo basins, reflecting local processes in theAdriatic region. Warm planktic speciesin core KC01-B allow, despite the lowerstratigraphic resolution, recognition of allthe major warm oscillations documented inthe more detailed PRAD1-2 record, in par-ticular for MIS5 and MIS7, with MIS5.3,5.5, 7.1 and 7.3 as the warmest intervals.Moreover, planktic deep-dweller species,requiring a well developed winter verti-cal mixing, peak in both records during

MIS5.1, 5.3, 7.1, 7.5 and 9.3, suggest-ing an enhanced seasonal contrast duringthese interstadials. Consequently, duringMIS5.5 and MIS7.3, a prolonged summerwarm season and a weaker winter cool-ing are inferred. It seems that the cli-matic evolution of the two areas particu-larly matched within the time interval fromMIS7.3 to MIS5.3. This interpretation issupported by the δ18O data (Figure 2),indicating a higher intensity of sapropel-equivalent events from S8 to S4, and re-inforced by the presence of deep infaunaltaxa only during these sapropel equivalentbeds (ODS curve), suggesting that in thetime interval between S8 and S4 the con-ditions of the central Adriatic were moresimilar to those of the eastern Mediter-ranean, at least during the sapropel depo-sition. The stronger surface water dilutionalong with the relatively large thickness ofPRAD1-2 sapropel-equivalent intervals S8to S4 (typically 50 to 100 cm each) sug-gest enhanced precipitation over the cen-tral Adriatic brought about by a strongerinfluence of the monsoon system over theMediterranean. The Adriatic and Ionianmicrofaunistic records differ more signif-icantly during glacial intervals than dur-ing interglacials, but this fact is mainlya consequence of the shallow depth ofthe central Adriatic, where sea level fallshampered the intrusion of deep-dwellingplanktic taxa, leaving a planktic associationdominated by shallow- and intermediate-water dwellers.

6 Bottom Water Forma-tion

Sanvoisin et al. [13] analyzed the oscil-lations in the planktic foraminifera assem-

334


ADRIATIC vs ALBORAN

0 5 10 15 20

-0.51.53.55.5

25

PRAD1-2ODP Site 977A (after Martrat et al., 2004)

0 5 10 15 20 25

Alkenone SST (°C)

ADRIATIC vs WEST IBERIAN MARGIN

MD01-2443 + MD01-2444 (after Martrat et al., 2007)Alkenone SST (°C)

0.5 1.5 2.50 1 2

∆(δ18O)warm pl. spec. %

0 20 40 60 80

0 5 10 15 20 25

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50

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400

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δ18O

more stratification

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0 10 20 30G. inflata %

12

3

4

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5.55.4

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10.2?

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δ18O G. bulloides

Alkenone SST (°C)

S1 eq.

S10 eq.

S’ eq.

S9 eq.

S8 eq.S7 eq.

S6 eq.

S5 eq.

S4 eq.S3 eq.

ADRIATIC

(B. marg.- G. bull.)

Figure 3: Synthesis of the main proxies of borehole PRAD1-2 against eccentricity(Be91). The alkenone-derived SST parallels significantly the δ18O records. On the right,comparison between δ18O G. bulloides records of the last 250 ka of the ODP site 977Aand PRAD1-2 records; comparison between Uk′

37 SST records of the ODP site 977A andPRAD1-2. ODP 977A records are plotted according to the age-depth model by Martratet al. [10]; comparison between Uk′

37 SST records of the composite Western Iberian siteby Martrat et al. [11] and of PRAD1-2. Grey areas indicate the sapropel equivalent layersdetected in PRAD1-2.

blage in the Ionian Basin. Core KC01-Bwas retrieved in 3643 m water depth (Fig-ure 1), and spans the last circa 1.1 Ma BP.The correlation between PRAD1-2 recordand the last circa 340 ka BP of the Io-nian core allowed the identification of ma-jor similarities and differences between thetwo basins, reflecting local processes in theAdriatic region. Warm planktic speciesin core KC01-B allow, despite the lowerstratigraphic resolution, recognition of allthe major warm oscillations documented inthe more detailed PRAD1-2 record, in par-ticular for MIS5 and MIS7, with MIS5.3,5.5, 7.1 and 7.3 as the warmest intervals.Moreover, planktic deep-dweller species,

requiring a well developed winter verti-cal mixing, peak in both records duringMIS5.1, 5.3, 7.1, 7.5 and 9.3, suggest-ing an enhanced seasonal contrast duringthese interstadials. Consequently, duringMIS5.5 and MIS7.3, a prolonged summerwarm season and a weaker winter cool-ing are inferred. It seems that the cli-matic evolution of the two areas particu-larly matched within the time interval fromMIS7.3 to MIS5.3. This interpretation issupported by the δ18O data (Figure 2),indicating a higher intensity of sapropel-equivalent events from S8 to S4, and re-inforced by the presence of deep infaunaltaxa only during these sapropel equivalent

335

Marine Geology

-0.50.51.52.53.54.55.50

50

100

150

200

2500.5 1.5 2.50 1 2

‰

0 20 40 60 80

H. balthica

C. laevigata-carinata%

intensified sapropelicconditions in the A

driatic

‰

ka

∆(δ18O) (B. marginata-G. bulloides)

-1.5 -1.0 -0.5 0.0 0.5 1.0 ‰δ18O G. bulloides δ13C B. marginata

cold

er, s

altie

r,m

ore

oxyg

enat

ed w

ater

more hom

ogenized water

Figure 4: PRAD1-2 integrated proxies showing the overall trend for the last 250 ka. Lightgrey stripes mark glacial and stadial intervals. The dotted area indicates the interval whenthe central Adriatic was more influenced by the monsoon regime.

beds (ODS curve), suggesting that in thetime interval between S8 and S4 the con-ditions of the central Adriatic were moresimilar to those of the eastern Mediter-ranean, at least during the sapropel depo-sition. The stronger surface water dilutionalong with the relatively large thickness ofPRAD1-2 sapropel-equivalent intervals S8to S4 (typically 50 to 100 cm each) sug-gest enhanced precipitation over the cen-tral Adriatic brought about by a strongerinfluence of the monsoon system over theMediterranean. The Adriatic and Ionianmicrofaunistic records differ more signif-icantly during glacial intervals than dur-ing interglacials, but this fact is mainlya consequence of the shallow depth ofthe central Adriatic, where sea level fallshampered the intrusion of deep-dwelling

planktic taxa, leaving a planktic associationdominated by shallow- and intermediate-water dwellers.

7 Conclusions

The analysis of PRAD1-2 multiproxyrecord provides new evidence for pale-oenvironmental trends that appear consis-tent with those typical for western andeastern Mediterranean basins, apart fromsome peculiar characteristics like a higher-amplitude temperature excursion duringmajor Terminations (up to 19.5°C during TII) and minor climate transitions, and thedeepening trend of glacial intervals fromMIS10 to MIS4. Three general conclu-sions can be drawn from the analysis of the

336


results of PRAD1-2 and their comparisonto other paleoceanographic records in theMediterranean and north Atlantic.

1. The central Adriatic reflects paleocli-matic changes during the last 370 kathat appear in phase with the north At-lantic climate system, except for theinterval between MIS7.5 and MIS5.3when the Adriatic basin was more influ-enced by the monsoon regime.

2. The Adriatic Basin does not seem ca-pable of maintaining interglacial and in-terstadial warm conditions over an inter-val comparable to that reconstructed inthe western Mediterranean. The reasonsare probably the landlocked position ofthis shallow basin and the response toother factors such as (1) a greater ex-position to atmospheric forcing, partic-ularly through northerly polar continen-tal air outbreaks, (2) a higher influence

of the surrounding landmass, includingthe occurrence of glaciers on its west-ern side, when the sea level was morethan 100 m lower than at present dur-ing glacial intervals, resulting in a lagin the demise of glacial conditions, and(3) a higher-latitude position comparedto other Mediterranean sites.

3. During the modern interglacial theAdriatic basin is a site for dense deeperwater formation and was so also dur-ing past interglacials, contributing to theventilation of the deep MediterraneanSea, except when sapropelic conditionsbecame established.

8 AcknowledgementsThis study was supported by EC-PROMESS 1 project. This is ISMAR-Bologna (CNR) contribution no. 1698

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[11] B. Martrat, J.O. Grimalt, N.J. Shackleton, L. de Abreu, M.A. Hutterli, and T.F.Stocker. Four climate cycles of recurring deep and surface water destabilizationson the Iberian Margin. Science, 317(5837):502–507, 2007.

[12] E.J. Rohling, P.A. Mayewski, R.H. Abu-Zied, J.S.L. Casford, and A. Hayes.Holocene atmosphere–ocean interactions: records from Greenland and the AegeanSea. Climate Dynamics, 18:587–593, 2002.

[13] R. Sanvoisin, S. D’Onofrio, R. Lucchi, D. Violanti, and D. Castradori. 1 Ma paleo-climatic record from the eastern Mediterranean- Marflux project: First results of amicropaleontological and sedimentological investigation of a long piston core fromthe Calabrian Ridge. Il Quaternario, 6(2):169–188, 1993.

338

Bottom Water Production Variability in the RossSea Slope During the Late Pleistocene-Holocene asRevealed by Benthic Foraminifera and SedimentGeochemistry

A. Asioli1, L. Langone2, F. Tateo1, F. Giglio2, D. Ridente3, V. Summa3,A. Carraro5, M.L. Giannossi4, A. Piva6, F. Trincardi21, Institute of Geosciences and Earth Resources, CNR, Padova, Italy2, Institute of Marine Sciences, CNR, Bologna, Italy3, Institute of Environmental Geology and Geoengineering, CNR, Roma, Italy4, Institute of Methodologies for Environmental Analysis, CNR, Potenza, Italy5, Department of Geosciences, University of Padova, Italy6, ENI E&P Division, Sedimentology, Petrography & Stratigraphy Dpt., S. Donato Mi-lanese, [email protected]

Abstract

The Antarctic area produces bottom waters that ventilate the vast majority of thedeep basins in the rest of the world ocean. The rate of formation in the source areaand the strength of these cold bottom waters are key factors affecting the GlobalThermohaline Circulation during modern and past climate conditions. We presentthe results of a multidisciplinary study carried out on a sediment core collected onthe slope off the Drygalski Basin (Ross Sea) for the Late Pleistocene-Holocene. Theresults obtained allow the following main observations: 1) two main intervals (15-10and 7.5-6 cal kyr BP) mark subsequent enhanced nutrient supply because of a higherefficiency in the Upper CDW upwelling; 2) within this general context, an oscillatorytrend is present from 15 kyr BP to present time, indicated by the measured param-eters. A possible hypothesis to interpret these oscillations is that foraminifers con-centration minima, corresponding to minima in %OC and to reversal of 14C (relativeincrease of older carbon) and to colder (atmospheric) condition, reflect dilution in thesediment because of rapid accumulation of fine sediment re-suspended at the shelfedge by the cascading currents. The minima may represent higher rate of bottomwater formation; 3) the detected oscillations (minima) seem to correlate to colderconditions in Adelie Land record where increased sea-ice cover and bottom waterformation were suggested.

1 Introduction

The Antarctic area produces bottom watersthat ventilate the vast majority of deep wa-

ters in the rest of the world ocean. Thestrength of the source of these cold bot-tom waters and their flow toward the equa-tor are key factors affecting Global Ther-


Marine Geology

mohaline Circulation during present andpast climate. Most Antarctic Bottom Wa-ter (AABW) is thought to be produced inthe Weddell Sea [1, 2], while less con-strained is the amount from other Antarc-tic areas, such as the Ross Sea. Accordingto several authors [3], the Ross Sea con-tribution may be greater than presently es-timated. Moreover, whether AABW pro-duction was in a steady state during theHolocene is still debated [3, 4]. The west-ern Ross Sea is considered a formation sitefor a particularly salty variety of AABW[5, 2] as well as an important area of off-shelf transfer of water. In detail, the exportof Ross Sea shelf water onto the continen-tal slope occurs within plumes (100-250mthick) descending at moderate angle to iso-baths (35°), entraining in Lower Circumpo-lar Deep Water (CDW). The export is punc-tuated by rapid downhill cascades (60°) togreater depths. The former (moderate an-gle) is far more persistent and thus may beof greater significance to ocean ventilation,as a precursor of AABW [6, 7]. The re-sults here presented were obtained withinthe frame of the PNRA project 4.8 “Bot-tom water production in the Ross Sea dur-ing the late Quaternary: a geochemical andmicropaleontological study”. Among thegoals of the project, the main is to detecta qualitative signal of possible changes inthe rate of bottom water production dur-ing the Late Pleistocene-Holocene, on theventilation of bottom water and, indirectly,on sea ice cover variability by integratingdata on modern assemblages with sedimentgeochemistry (bulk mineralogy, Total Or-ganic Carbon, biogenic silica, C and N sta-ble isotopes, Ice Rafted Debris). To satisfythis goal a core was collected at 2377m wa-ter depth off Drygalski Basin on the slopeadjacent the western continental shelf ofthe Ross Sea, along the pathway of bottom

water spreading [6, 7] (Figure 1).

2 Materials and methods

The gravity core AS05-10 has been re-trieved during the XX Antarctic ItalianCruise (2005) on the slope off Cape Adare.The core was scanned on board by meansof a Bartington ring sensor for whole-coremagnetic susceptibility. A provisional es-timate of the time interval spanned by theentire core is proposed on the basis of theexisting literature of the slope area. Cec-caroni et al. [8] studied a core (ANTA91-8) collected very close (Lat. 70°47’S,Long. 172°50’E, 2383 m water depth) tocore AS05-10 (Figure 2). The chronologyof this reference core was obtained by a230Thex profile, the isotope stage bound-aries and ages were set according to theδ18O record of Martinson et al. [9] af-ter tuning with biogenic parameter con-tents [8]. According to Ceccaroni et al.[8]) and Quaia and Cespuglio [10], coreANTA91-8 spans at least the last two cli-mate cycles. Ceccaroni et al. [8] re-port also the magnetic susceptibility curveof core ANTA91-8, which allows a cor-relation with our core AS05-10 (Figure1, from [11]), resulting, for the MIS1and 2, in an almost double sedimentationrate in core AS05-10 than in ANTA91-8. The core was frozen at -20°C to en-sure the preservation of sediments for mi-cropaleontological investigation. Indeed,the general scarcity or lack of agglutinatedforaminifera in Antarctic sediments shouldnot only be ascribed to their low preserva-tion potential or to ecological factors alone,as also the routine use of often aggres-sive laboratory techniques (such as sedi-ment desiccation or the use of peroxide)can be, at least partially, responsible. The

340


Figure 1: Above: location map of the core AS05-10 (open circle) along with the pub-lished core ANTA91-8 (star). Below: 3-D map showing the path of the High SalinityShelf Water forming in Drygalski Basin and flowing in the continental slope. Persis-tent plumes descend at moderate angle to isobaths (35°, up to 1 m/s speed), while rapiddownhill cascades flow at ca. 90° to isobaths at 1.4 m/s speed (from [6]).

sections of the core have been subsequentlycut and frozen in slices ca. 1cm thick,then each slice has been divided in twohalves (one for foraminifera analysis andthe other for geochemical and mineralogi-cal analysis). To get a high temporal reso-lution the study has been performed on allthe slices, and the 182 samples of the up-permost two sections have been analysed.Samples for foraminifers analysis weresoaked in ethanol, never dried, washedwith a 0.063mm sieve, split into aliquotswith a wet-splitter [12], and examinedwith a stereomicroscope. Whole aliquotswere counted until at least 300 benthicforaminifers were reached. Foraminiferswere determined at specific levels andhere expressed as concentration (numberof specimens per 10cc). The IRD content

has been determined counting at light mi-croscope all the grains excluding the onesof biologic origin. The counting has beenperformed on three fractions: larger than2mm, between 1 and 2mm, and between0.5 and 1mm. Samples for TOC, δ13C andδ15N were dried at 60°C, finely poundedin an agate mortar. TOC and Nitrogencontents were obtained using a FISONSNA2000 Element Analyzer after removalof the carbonate fraction in Ag capsules in1.5N HCl. Stable isotope analyses werecarried out on the same samples using aFINNIGAN Delta Plus mass spectrome-ter directly coupled to the Elemental Ana-lyzer by means of a CONFLO interface forcontinuous flow measurements. The IAEAstandards NBS-19 (+1.95�) and N-1(0.4�) were used as calibration material for

341

Marine Geology

C and N stable isotope analysis, respec-tively. Biogenic silica was determined fol-lowing the progressive dissolution methodof DeMaster [13, 14] and the colorimetricanalysis of Strickland and Parsons[15]; 0.5M NaOH was used as extracting agent andthe uncertainty is about 10%. Total rockanalysis: the semi-quantitative estimationof crystalline phases in the bulk rock wasperformed using an X-ray Philips diffrac-tometer, based on the area measurements[16]; the bulk rock was grounded by handin agate mortar and pressed with a frozenglass into an alluminium holder.

3 Chronology

Twenty-two 14C AMS datings were per-formed on the bulk organic carbon atNational Ocean Sciences AMS Facility(Department of Geology and Geophysics,Woods Hole Oceanographic Institution,USA). Two datings were spent to datethe core top of the box-core AS05-10bc(4710±30 yr BP) and of the core AS05-10 (6160±35 yr BP), to get a reservoir agefor this area. To obtain calibrated ages wesubtracted 450 years (average ocean reser-voir) to the age of the core top AS05-10bc,then we run CALIB 5.0.2 online [19] us-ing a =4260±30 yr. Among the twenty-one datings available for the core AS05-10 ten levels were discarded, including thecore top. The age of the core top is surelyyounger than 100-150 yr BP since 210Pbanalysis carried out in the topmost levelsof core AS05-10 revealed the presence ofexcess 210Pb. Then, an age of 50 yearshas been ascribed to the core top of AS05-10. The other nine discarded levels presentage reversal. In summary, the age-depthmodel is based on the best fitting of twelvecontrol points grouped in three clusters of

levels because of the presence of a possi-ble condensed interval around 29 cm coredepth. This level corresponds to a sharpcolour change (from grey to red-brownish)and it is lithologically composed by weaklycemented silty clay (crust). The age modelsuggests that this short interval (cm 29.8-29) spans about 500-600 years.

4 DiscussionThe data obtained for the last 15,000 yearsBP are shown in Figure 3. Although thisstudy is still in progress, the trend of the pa-rameters allows the following preliminaryobservations:1. two main intervals around 15-10 kyr BP

and 7.5-6 calib kyr BP mark a subse-quent enhanced nutrient supply. Indeed,∆15N variations depend on the utiliza-tion degree of nitrates, which in turncan reflect productivity or nutrient sup-ply changes. The concurrent increaseof the paleoproductivity proxies OC andbiogenic silica suggests that the respon-sible of ∆15N major variations is an in-crease of the nutrient availability. TheUpper CDW is a water mass rich in nu-trients; therefore we interpret the abovecited two time intervals as character-ized by a higher efficiency in the UpperCDW upwelling ;

2. around 7.5-7kyr BP (part of the MiddleHolocene Climatic Optimum, Domacket al.[20]) the IRD content drops, and itis interpreted as an evidence of the re-treat of sea-ice/icebergs or a change ofthe iceberg path.

Within this general context, an oscilla-tory trend testified by all the parametersis present from 15 kyr BP to presenttime. The benthic foraminifera assem-blage is composed only by agglutinated

342


Figure 2: Whole core magnetic susceptibility correlation between core AS05-10 and ref-erence core ANTA91-8 [8]. The 14C AMS age in core ANTA91-8 are uncorrected (yrBP) and were performed on bulk organic carbon [10]. The grey areas mark the time in-terval investigated in core AS05-10 (last 15 cal kyr BP). Note that the sedimentation ratein core AS05-10 is higher (ca. twice) compared to one of the reference core ANTA91-8.

foraminifera (inorganic carbon contents in-dicate negligible calcareous components)and it is strongly dominated by one species(Trochammina multiloculata, Figure 3).Two hypotheses are proposed to interpretthese oscillations:a) minima in foraminifera concentra-tions reflect relatively stronger dissolu-tion, weaker bottom currents (testified byminima in dry density indicating higheramount of fine fraction) and lower nutri-ent supply (lighter values of δ15N ). There-fore, these intervals may reflect a lowerrate of bottom water formation, consid-ering that these latter spill out of theshelf as plumes or cascading currents ;Consequently, the intervals correspondingto maxima in foraminifers concentrationshould indicate better preservation, higherbenthic productivity and/or better oxygena-tion at bottom, stronger bottom currents(maxima in dry density) and relativelyhigher nutrient supply reflecting a rela-tively higher rate of bottom water forma-

tion.b) alternatively, minima in foraminifers,corresponding to minima in %OC and toreversal of 14C (relative increase of oldercarbon), reflect dilution in the sediment be-cause of rapid accumulation of fine sedi-ment re-suspended at the shelf edge by thecascading currents. Therefore, the min-ima represent higher rate of bottom wa-ter formation. We compared our recordswith the climatic trend proposed by Mas-son et al. [17] for the Ross Sea sec-tor and represented by the D/H ratio ofice-cores. The comparison of this atmo-spheric signal, the chronology of whichis completely independent from the oneadopted for our marine core, with the os-cillatory trend of core AS05-10, indicatesthat the foraminifers minima always cor-respond to colder (atmospheric) condition,at least from 0 to 12kyr. If this interpre-tation is correct, the higher rate of bottomwater formation occurs within cold inter-vals. This scenario is coherent with the

343

Marine Geology

10 30 70

1 3 40 2 0-0.5 0.5

Neoglacial

Late Holocene

Mid Holocene

Hypsithermal 2

Hypsithermal 1

Early Holocene

Cool

D/H (‰)

ψ

F. curtaF. kerguelensis

cal. age (kyr BP) E8

E7

E6

E5

E4

E3

E2

E1

?

core MD03-2601 Adelie Land (w.d. 746 m)

from Denis et al. (2009)

colder

ice free

higher lateral sedimentary input

0 10 20155 25>1mm<2mm

IRD (n. grains/10cc)total n. benthic

foram. spec./10cc

0 600300 900OC (%)

0.80.4 0.60.2

δ15N (‰)

63 910 3020

biogenic silica (%)sheet silicates (%)

8040 6050 70

cal k

yr B

P

core AS05-10 (w.d. 2377 m)

Ross Sea SectorD/H (‰) *

0-0.5 0.5

0.80.4 0.6 1.0

dry density (g/cm3)

control points

10

0

5

15

* from Masson et al (2000)

?

total n. T. multi-loculata spec./10cc

14C reversal

colder

warmer

0

2

4

6

8

10

12

condensed interval (colour change)

Figure 3: Some of the main parameters measured for the uppermost 120cm of core AS05-10 studied for the Holocene and plotted vs calibrated age. Sheets silicates, δ15N and OCare plotted with a 3-point average smoothed curve. The open arrows mark the controlpoints selected for the age-depth model, while the black ones indicate age reversals.On the right, in sequence, the climatic trend (D/H) for the Ross Sea sector calculated byMasson et al. [17] and three parameters (ratio diatomsFragilariopsis curta/Fragilariopsiskerguelensis, the focusing factor and the climatic trend for the Eastern Antarctic plateauby [17]) are shown from the core MD03-2601 collected off Wilkes-Adelie Land (mod-ified by [18]). The grey stripes in core AS05-10 indicate the intervals correspondingto minima in foraminifers abundance and are correlated with the cold events (E1-E8)detected for the core MD03-2601 by Denis et al. [18].

record reported by Denis et al. [18] for acore (MD03-2106) retrieved on the slopeoff Wilkes-Adelie Land, where increasedsea-ice cover (=colder conditions) corre-sponds to enhanced bottom water forma-tion, on the basis of different parametersamong which the diatom composition (ra-tio Fragilariopsis curta/Fragilariopsis ker-guelensis as proxy of the sea-ice cover) andthe focusing factor, as indicator of lateralsedimentary input (Figure 3). On the ba-sis of the above inferences, we prefer thehypothesis b), although both the two hy-pothesis support the non-steady state rate

of bottom water production of AABW dur-ing the Holocene proposed by Harris et al.[4] in a study carried out on cores and seis-mic stratigraphy off George V Land. Atlast, the condensed/hiatus interval centeredat ca. 3.5-4 kyr BP does not seems tomark a major change in the general patternof our variables, apart from biogenic silicaand sheets silicates which show an increaseof the oscillation amplitude. Nevertheless,this feature is coeval to the base of theNeoglacial and it is time-equivalent to thebeginning of major changes in the Antarc-tic environment: for instance, in the circu-

344


lation pattern in Antarctic Peninsula (oscil-lations between Upper Circumpolar DeepWater and shelf water-dominated states,[20], and in glacier advance and sea-ice ex-pansion off Wilkes-Adelie Land [18].

5 Acknowledgements

This study was supported by the PNRAproject 4.8. This is ISMAR-Bologna(CNR) contribution no. 1696.

References[1] T. Whitworth III, A.H. Orsi, S.J. Kim, W.D. Nowlin, and R.A. Locarnini. Water

masses and mixing near the Antarctic slope front. In: Jacobs, S.S. e Wiess R.F.(Eds.): Ocean, Ice and Atmosphere. Interactions at the Antarctic Continental Mar-gin. Antarctic Research Series, 75:1–27, 1998.

[2] A.H. Orsi, G.C. Johnson, and J.L. Bullister. Circulation, mixing and production ofAntarctic Bottom Water. Progress in Oceanograph, 43:55–109, 1999.

[3] W.S. Broecker, S.L. Peackock, S. Walker, R. Weiss, E. Fahrbach, M. Schroeder,U. Mikolajewicz, C. Heinze, R. Key, T.H. Peng, and S. Rubin. How much deepwater is formed in the Southern Ocean? Journ. Geophys. Res., 103(C8):15833–15843, 1998.

[4] P.T. Harris, G. Brancolini, L. Armand, M. Busetti, R. Beaman, G. Giorgetti,M. Presti, and F. Trincardi. Continental shelf drift deposit indicates non-steadystate Antarctic bottom water production in the Holocene. Marine Geology, 179:1–8, 2001.

[5] S. Jacobs, R. Fairbanks, and Y. Horibe. Origin and evolution of water masses nearthe Antarctic continental margin: Evidence from H218O/H216O ratio in seawater,in Oceanology of the Antarctic Continental Shelf. Antarct. Res. Ser., 43:59– 85,1985.

[6] A.L. Gordon, E. Zambianchi, A. Orsi, M. Visbeck, C.F. Giulivi, T. Whitworth III,and G. Spezie. Energetic plumes over the western Ross Sea continental slope.Geophysical Research Letters, 31, 2004.

[7] A.L. Gordon, A. Orsi, R. Muench, B.A., Huber, E. Zambianchi, and M. Vis-beck. Western Ross Sea continental slope gravity currents. Deep-Sea ResearchII, 56:796–817, 2009.

[8] L. Ceccaroni, M. Frank, M. Frignani, L. Langone, M. Ravaioli, and A. Mangini.Late Quaternary fluctuations of biogenic component fluxes on the continental slopeof the Ross Sea, Antarctica. Journal of Marine Systems, 17:515–525, 1998.

[9] D.G. Martinson, N.G. Pisias, J.D. Hays, J. Imbrie, T.C. Moore, and N.J. Shackleton.Age dating and the orbital theory of the ice ages—Development of a high-resolution0 to 300,000-year chronostratigraphy. Quaternary Research, 27:1–29, 1987.

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[10] T. Quaia and G. Cespuglio. Stable isotope records from the Western Ross Sea conti-nental slope (Antartica): considerations on carbonate preservation. Terra AntarticaReports, 4:199–210, 2000.

[11] A. Piva, A. Asioli, L. Langone, D. Ridente, F. Tateo, and F. Trincardi. Cruise resultsand preliminary study of living benthic foraminifera assemblages in the westernRoss Sea (XX Antarctic Expedition, 2004-2005). Terra Antartica Reports, 14:247–254, 2008.

[12] D. B. Scott and J.O.R. Hermelin. A device for precision splitting of micropale-ontological samples in liquid suspension. Journal of Paleontology, 67:151–154,1993.

[13] D.J. DeMaster. The marine budgets of silica and 32 Si. JPhD Thesis, Yale Univer-sity, New Haven., 1979.

[14] D.J. DeMaster. The supply and accumulation of silica in the marine environment.Geochim. Cosmochim. Acta, 45:1715–1732, 1981.

[15] J.D.H. Strickland and T.R. Parsons. A practical handbook of seawater analysis.Bull. Fish. Res., 167:311, 1972.

[16] E. Barahona. Arcillas de ladrilleria de la provincia de Granada: evaluacion dealgunos ensayos de materias primas. Ph.D. Thesis, University of Granada, Spain.,1974.

[17] V. Masson, F. Vimeux, J. Jouzel, V. Morgan, M. Delmotte, P. Ciais, C. Hammer,S. Johnsen, Y. Lipenkov, V.E. Mosley-Thompson, J.R. Petit, E.J. Steig, and M.R.V.Stievenard. Holocene climatic variability in Antarctica: what can be inferred from11 ice core isotopic records? Quaternary Research, 54:348–358, 2000.

[18] D. Denis, X. Crosta, S. Schmidt, D.S. Carson, R.S. Ganeshram, H. Renssen,V. Bout-Roumazeilles, S. Zaragosi, B. Martin, M. Cremer, and J. Giraudeau.Holocene glacier and deep water dynamics, Adelie Land region, East Antarctic.Quaternary Science Reviews, 28:1291–1303, 2009.

[19] M. Stuiver and P. Reimer. Extended 14C data base and revised CALIB 3.0 14C agecalibration program. Radiocarbon, 35:215–230, 1993.

[20] E. W. Domack, A. Leventer, S. Root, J. Ring, E. Williams, D. Carlson, E. Hirshorn,W. Wright, R. Gilbert, and G. Burr. Marine sedimentary record of natural envi-ronmental variability and recent warming in the Antarctic Peninsula. In: “Antarc-tic Peninsula climate variability; historical and paleoenvironmental perspectives.Antarctic Research Series, 79:205–224, 2003.

346

River Pattern and Shore Bars Migration in LateQuaternary Regression-Trasgression ContinentalDeposits, Salerno Bay, Southern Italy

A. ConfortiInstitute for Coastal Marine Environment, CNR, Napoli, [email protected]

Abstract

The evolution of the northern Sele coastal plain during the Late Quaternary is out-lined on the base of the stratigraphic reconstruction of the Late-Quaternary sequenceof Salerno Bay. To this purpose thickness and stacking patterns of latest Pleistocene-Holocene stratigraphic units and associated erosional – depositional features havebeen obtained, which record the relative sea level variation between ca.100 ky BPand the present.In the above study area depositional-erosional features in paralic-continental areas,prograding seaward during slow sea level fall (from about 100 ky BP) have beenrecognised. Sedimentary structures linked to the development of a fluvial systemon the presunt inner continental shelf have been also individuated. After the low-stand and during sea level rise occurred between ca. 18 ky BP and 7-5 ky BP, thestacking transgressive units and progradational paralic deposits, forming elongatedprisms, locally are preserved at morphological steps below the transgressive ravine-ment surface. These bars are mostly represented by sandy bodies deposited during astill standing phase of landward coast line shift.

1 Introduction

The marine “forced regression” deposits[1, 2, 3] are widely studied in the recognis-able stratigraphic features and, often in thelast 4th order eustatic cycle a “sharp basedshoreface” system occurs [4]. In the Adri-atic the stratigraphic evolution of forcedregressive marine deposits has been com-pared with the Late Holocene HST progra-dational wedge [5, 6]. However the coastalcontinental deposits of the late Quater-nary regression are relatively poorly stud-ied on Mediterranean shelves [7]. Regres-sive continental and transitional depositshave been prevented from being eroded in

the inner-middle shelf sector, due to a slowsea level variation during regression andrapid sea level rise. These deposits arenot easy to indentify due to the overburdenof thick transgressive and high stand unitsclose to the coast that inhibits coring; thesestrata can only be reachedby geophysics.Normally the migration of the erosionalsurface erases these thin deposits, and onlysome terminations are visible. The con-tinental deposits are too thin to be read-able at low resolution in seismic config-urations. However, with high resolutionseismics, the coarser sediments, typical ofthis environment, absorb the signal. Inthe same way the transgressive deposits are


Marine Geology

Figure 1: Salerno Bay, Eastern Thyrrhenian margin.

normally thin and not clearly recognisable,due to a rapid landward shift of the coastline, on a low inclination coastal plain.This study area provides an expanded sec-tion of Late Quaternary deposits [8], withwell developed regression and transgres-sion units. High resolution seismic pro-files allow to read thin strata terminationsand to recognize sedimentary bodies in par-alic continental facies. The distinction ofthese bodies allows to map fluvial pat-terns and continental deposits, down step-ping during regression, and the develop-ment of coastal ridges in late regressionand lowstand phases. Above the transgres-sive units, erosive surfaces are also rec-ognizable, as well as some shore depositstrapped between the transgressive and theravinement surfaces. Also these bodies thatare normally thin in the Late QuaternarySequence, are well developed here in the

Salerno Bay, preserved in morphologicalsteps below the transgressive ravinementsurface.

2 Regional setting

The study area is located in the northernsector of the Salerno Gulf, Eastern Tyrrhe-nian Sea (Figure 1). The Salerno Gulfand the Sele coastal plain are part of aPery-Thyrrenian Basin (Bartole et al 1984),whose evolution is linked to the Late Neo-gene – Quaternary tectonics of the Appen-ninian arc [9, 10, 11, 12]. The half grabenthat forms the Salerno Gulf has a WSW-ENE trend [13]. The northern block ischaracterized by a steep homocline slopedue to the main listric fault, where thecontinental platform is almost absent. Inthe Positano and Amalfi Bays, a portion

348


Figure 2: Tectonic sketch of study area, in land and offshore. 1) faults, 2) trascurrentfaults, 3) thrusts.

Figure 3: Location of studied seismic reflection profiles, unbroken line represents thelocation of chirp profiles.

of the continental shelf is preserved. Inthe Salerno Bay the shelf break widens tothe South close to the Tusciano and Selemouths. The Pleistocene tectonic evolu-tion of this sector shows a reactivation ofsome deep lineaments [14] and these re-cent faults are recognized, testifying of theresurgence of tectonics in recent times. Themain among these recent NW-SE trend-ing faults has a transcurrent component;other NE-SW trending faulting adjusts thismain rotation, displacing Late Quaternaryregression deposits [8] (Figure 2), and pro-viding a large accommodation space forpost glacial sediments (Figure 8). A large

scale tilting of the Salerno Gulf margin alsooccurred in the middle Pleistocene [15].The continental shelf is mainly formedby a Pleistocenic sedimentary succession[16, 14]. The general progradation of theseunits is SW ward, near to the Sele Rivermouth. Finally the middle Pleistocene suc-cession is truncated by a sharp erosionalsurface formed during the last regression,of the Late Pleistocene. Thick Holocenedeposits drape the entire continental shelf.

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Marine Geology

Figure 4: Chirp profiles showing strata geometry and termination of continental-transition facies as well as regression and transgression deposits; ch: channel fill; cb:coastal bars; du: dunal cordons; la: lateral accretion; md: marine deposits (TST+HST).


3 Materials and Methods

3.1 Geophysic DataMore than 200 km of very high-resolutionseismic reflection data were collected inSalerno Bay on the continental shelf area.Data were acquired with the Chirp Cap IISubbottom profiler and the ship positioningwas done by a DGPS system; this seismicsystem has a frequency modulation source(FM) pinging in a frequency band of 3 to7 kHz; the bathymetry was acquired byan ATLAS single beam echo sounder anddata where linearly interpolated by trian-

gulation (Figure 1). Lines have a preva-lent NNW-SSE orientation, interspaced inabout 300-500 m and some cross lines wereacquired with an ENE-WSW orientation(Figure 3). Conversion of two way traveltime to real depth in meters in marine sed-iments, was obtained assuming an averagevelocity of about 1600 ms-1 within the first100 ms of the seismic record below the seafloor [17].

350



3.2 Seismic and sequencestratigraphy

The terminations and the stratigraphic ar-chitecture of the Late Quaternary Sequencedeposits have been recognized previouslyin the Salerno Bay [8], and the stackingpattern of Systems Tracts marine units hasbeen clearly defined (Figure 7). Howeverthe main difficulties of continental-paralicfacies recognition in high resolution seis-mics data are due to coarse sediment sig-nal absorbance and the recognition of thinstrata termination. The Chirp seismic sys-tem allows for a sufficient penetration incoarse (sandy) sediment and a good reso-lution of terminations. The closely spaceddataset allows to interpolate thin and lim-ited bodies and to map the distribution ofacoustic facies corresponding to variouscontinental and transitional deposits.The main continental-paralic facies recog-nized are the following:• fluvial sedimentary elements [18, 19],

channel cut and channel fills deposits(ch) that are characterized by concavelyshaped reflectors, testifying of erosion ,and filling corps, mainly with parallel re-flectors. Lateral accretions (la) are char-acterized by progradational clinoforms

growing laterally to channel facies, rec-ognized in seismics by thin reflectors anda prolongated acoustic facies signal, dueto coarser (probably sandy) sediments(Figure 4, 5, 6).

• coastal dunes (du) [20], a clear reflec-tor defines these bodies with a total ab-sorbance of the signal (due to sandy sedi-ments). Morphology and lateral continu-ity are recognizable in seismic data (Fig-ure 4).

• estuarine microtidal wave dominatedsystems [21, 22], coastal bar corps (cb)are clearly defined by prograding sea-ward clinoforms with great lateral con-tinuity, and prolongated acoustic faciesdue to coarser sediments (sandy) (Figure4).

4 DiscussionIn seismic profiles the geometrically deep-est unit (Figure 7) called c FSST representscontinental deposits of sea level fall; thisunit is characterized by a sharp truncationsurface at the top and organized in conti-nental parasequences of coastal plain de-posits and river facies; these bodies pro-gressively prograde seaward on the FSST

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Figure 7: Schematic section of Late Quaternary Sequence in Salerno Bay. FSST: FallingStage Systems Tract. LST: Lowstand Systems Tract; TST: Transgressive Systems Tract;HST: Highstand Systems Tract; sb: sequence boundary; mfs: maximum flooding sur-face; c FSST: continental deposits of Falling Stage; s TST: shore bars of TransgressiveSystems Tract.

marine clinoforms truncated at the top.A coastal prograding wedge of lowstand(LST) stacks on the Late Quaternary Se-quence boundary (sb) and is located at theshelf break. The transgressive units aremainly marine (TST). Two main coastalbars also formed prograding wedges (sTST) during sea level rise. The High standunits (HST) are characterized by prograda-tional deposits located close to the coastand a thick drape of sediments along theshelf. Post glacial deposits, (transgressiveand highstand units) reach a high thick-ness particularly in the western sector ofSalerno Bay, where accommodation spacewas larger due to recent tectonics (Figure8).Mapping of marine and continental facieslinked to sea level variation stages, allowedto delineate the depositional environmentevolution in Late Quaternary as follows:• After 100 ky bp, with a fluctuant sea-

ward migration of the coast line, pro-grading marine parasequences were de-

posited. The morphology of the con-tinental shelf had a low gradient pen-dency and the top of the offlap breaks ofthese units were eroded by slow sea levelfall and the relative displacement of theshore and transitional environments; theprogradation of the coastal plain on ma-rine sediments is recognizable by map-ping of alluvial deposits and fluvial fa-cies; the lowering of the base level andthe seaward migration of fluvial patternscaused a cutting of coastal plain bodiesand progressive resedimentation of allu-vial deposits (c FSST, Figure 7).

• On this alluvial plain the probable paleo-channel pattern of the Picentino Riverand the Tusciano River in the South, thatprobably became one stream (Figure 9),are recognizable. During the slowingdown of sea level fall some dune cordonswere formed on the coastal plain at about-105 m, maximally 6 m high. The eu-static minimum was reached at about -120 m, which allowed for the deposition

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Figure 8: Isopaches of postglacial sediments in Salerno Bay (thickness is expressed inmetres).

of a prograding wedge (LST) (in Fig-ure 10, D0). Due to sea level standingstill, the shore environment formed anerosional flat surface. The coastal andalluvial plain had some wide terraces atabout -115 m (E2), -105 m (E3), and -95m (E4). The rapid sea level rise after theeustatic minimum (about 18ky bp), al-lowed the coast line to shift rapidly land-ward, also due to the low inclination ofthe plain. A few coastal deposits are pre-served during sea level rise (D3), trappedin some morphologic steps; close to theterrace at -95 m (E4) a large progradingshore body was deposited (D5) proba-bly during a reduction of sea level rise

velocity (Younger Dryas). Other ter-races are recognizable higher up at -60m (E6), -50 m (E7) and -30 m (E8); theE6 terrace also preserves a well devel-oped shore body (D7). After D5 deposi-tion, mainly aggradation is recognizablein marine deposits up to the present sealevel reached at about 5-6 ky bp. Sedi-mentation rates became exceedingly lowin periods around deposition of the max-imum flooding surface (mfs, Figure 7).The first downlaps are recognized in theeastern coastal sectors, and shore pro-grading bodies developed in these areaswith high sedimentation rates.

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Figure 9: Reconstruction of river pattern during regression; td thyrrenian dunal cordonon land cutted by actual rivers; ch paleoriver pattern on continental shelf, dashed linesuncertain pattern; ld late regression and lowstand coastal dunes

Figure 10: Morphology of transgressive surface in study area, reconstruction of the land-ward coastal shift.

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5 Conclusions

The attempt of correlating acoustic faciesin geophysics with sedimentary continen-tal facies, in a defined and constrained se-quence stratigraphy, provided the outlineof the evolution of a depositional environ-ment, during the Late Quaternary. Theconsequent river pattern and alluvial plaindeposits during regression, are probablymore developed close to the present coast.The presence of recognisable fluvial fa-cies preserved along the inner shelf tes-tify of a probably slow and fluctuatingsea level fall during early stages of re-gression. Also strong river activity and agreat sediment supply are also suggestedby the thickness of preserved continen-tal deposits. High sediment accommoda-tion space in the western sector was prob-ably induced by recent mainly transcurrenttectonics, that were active until regression

stages. In transgressive stages a rapid sealevel rise was recognizable allowing forpreservation of coastal deposits , exceptfor coastal bars, that are probably corre-lated to a slowing down of the sea levelrise velocity in the Younger Dryas. In high-stand stages the sedimentation rate mainlyincreased in the eastern sector close to rivermouths.

6 AcknowledgementsI would like to mention CA.R.G. P. (exper-imental marine geologic mapping project)carried out by the IAMC CNR (Institute forthe Marine Coastal Environment, NationalResearch Council) of Naples for the ItalianGeological Survey (ISPRA); all the datawere acquired in the frame of this projectbetween 1998-2000. I would also like tothank Prof. B. D’Argenio, who substainedthis study with insightful suggestments.

References[1] H.W. Posamentier, G.P. Allen, D.P. James, , and M. Tesson and. Forced regressions

in a sequence stratigraphic framework: Concepts, examples, and exploration signif-icance. American Association of Petroleum Geologists Bulletin, (76):1687–1709,1992.

[2] D. Hunt and M.E. Tucker and. Stranded parasequences and the forced regres-sive wedge systems tract: deposition during base-level fall. Sedimentary Geology,(81):1–9, 1992.

[3] H.W. Posamentier and W.R. Morris. Aspect of the stratal architecture of forced re-gressive deposits. Sedimentary responses to forced regressions, (172):19–46, 2000.

[4] A.G. Plint. Sharp-based shoreface sequences and offshore bars in the CardiumFormation of Alberta; their relationship to relative changes in sea level. Sea LevelChanges––An Integrated Approach; SEPM Special Publication,, 42(42):357–370.,1988.

[5] F. Trincardi and A. Correggiari. Quaternary forced-regression deposits in the Adri-

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atic basin and the record of composite sea level cycles. Geological Society SpecialPublication, 172:247–271, 2000.

[6] D. Ridente and F. Trincardi. Pleistocene “muddy” forced-regression deposits on theAdriatic shelf: a comparison with prodelta deposits of the late Holocene highstandmud wedge. Marine Geology, (222–223):213–233, 2005.

[7] A. Amorosi, M.L. Colalongo, and F. Fusco. Glacio-eustatic control of continental-shallow marine cyclicity from Late Quaternary deposits of the south-eastern PoPlain (Northern Italy). Quaternary Res., 52:1–13, 1999.

[8] A. Conforti. Stratigrafia integrata della Sequenza Tardo-Quaternaria nel settoresettentrionale del Golfo di Salerno ed in quello meridionale del Golfo di NapoliPhd Thesis. Universita Federico II di Napoli, 2003.

[9] I.R. Finetti & A. Del Ben. Geophysical study of the thyrrenian opening. Boll. Geof.Teor. Appl., (28):75–155, 1986.

[10] A. Malinverno & W.B.F. Ryan. Extension in the Tyrrenian Sea and shortening in theAppennines as a result of arc migration driven by sinking of the litoshere. Tectonics,(5), 1986.

[11] E. Patacca and R. Sartori & P. Scandone. Tyrrhenian basin and Appennic arc:cinematic relations since late Tortonians time. Mem. Soc. Geol. It, 45:425–451,1990.

[12] L. Ferranti, P. R. Gialanella, A. Incoronato, and F. Heller. Localized strain zone dur-ing polyphase non coaxial deformation in the Lagonegro rochs, southern apennines:inferences from structural and palaeomagnetic data. Structures and Properties ofHigh Strain Zones in Rocks. Ric. Sc. Educ. Perm, (107), 1996.

[13] M. Marani, F. Gamberi, and E. Bonatti. From seafloor to deep mantle: architectureof the Tyrrhenian backarc basin. Mem.Descr.Carta geol.d’Italia, Vol.LXIV, 2004.

[14] M. Sacchi, S. Infuso, and E. Marsella. Pleistocene compressional tectonics in off-shore Campania. Bollettino di geofisica ed Applicata, Vol. XXXVI:141–144, 1994.

[15] F. Budillon, T. Pescatore, and M.R. Senatore. Cicli deposizionali del Pleistocenesuperiore-Olocene sulla piattaforma continentale del golfo di Salerno (TirrenoMeridionale). Boll. Soc. geol. It., (113):303–316, 1994.

[16] R. Bartole, D. Salvelli, and M. Tramontana & C. Forese. Structural and sedimentaryfeatures in the tyrrenian margin off campania , southern Italy,. Marine Geology,(55):163–180, 1984.

[17] R.L. Carlson, A.F. Gangi, and K.L. Snow. Empirical reflection travel time ver-sus depth and velocity versus depth functions for the deep sea sediments column.Journal of Geophysical Research, (91):8249–8266, 1986.

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[18] A.D Miall. Architectural-element analysis: a new method of facies analysis appliedto fluvial deposits. Earth Science Rewiews, (22):261–308, 1985.

[19] A.D. Miall. Reservoir heterogeneities in fluvial sandstones . ;AAPG , Bulletin,(72):682–297, 1988.

[20] G. Einsele and S.K. Chough & T. Shiki. Depositional events and their records-anintroduction. Sedimentary Geology, (104):1–9, 1996.

[21] G.M. Ashley and M.L. Zeff. Tidal channel classification for a low-mesotidal saltmarsh. Marine Geology, (82):17–32, 1988.

[22] G.E. Reison. Transgressive barriers Island and Estuarine systems. Facies Models:Response to Sea level Changes., QE 651:179–194, 1992.

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358

The Tectono-Stratigraphic Evolution of the East-ern Tyrrhenian Sea (from Calabria to CampaniaMargins) and its Geodynamic Implications

A. Milia,Institute for Coastal Marine Environment, CNR, Napoli, [email protected]

Abstract

The interpretation of seismic reflection profiles is a fundamental step in the anal-ysis of sedimentary basins. Over the last two decades we studied the basins offCampania and Calabria located in the Eastern Tyrrhenian Sea. The application ofthe sequence stratigraphy and structural geology methodologies permitted us to rec-ognize tectonically enhanced unconformities, uplifting and subsiding areas, fault ar-chitecture and kinematics to reconstruct a detailed chronostratigraphic framework.For the first time we identified the main tectonic and sedimentary events that char-acterize the Eastern Tyrrhenian Sea margin. Because the opening of the Tyrrhenianbasin is linked to the formation of the Apennine thrust belt, the results of this workhave important implication for the tectonic history and geodynamic evolution of theTyrrhenian Sea-Apennine thrust belt system. In conclusion the post-700 ka geologicevolution of the Eastern Tyrrhenian Sea features an intense Quaternary volcanism inCampania the coeval activity of NNE and NE-trending normal faults off Campaniaand NW-trending right lateral faults active off Calabria. Such faults are compatiblewith the Southeast migration of the Calabria Arc occurred in the last 700 ka.

1 Introduction

Plate reconstructions of the centralMediterranean region have always beencontroversial due to the lack of well-defined oceanic magnetic anomalies andto a complex tectonic history. The open-ing of the Tyrrhenian Basin has been thesubject of numerous papers. However,these kinematic models have to be con-firmed by the structural and stratigraphicevidence derived from marine geologyand field data. The Tyrrhenian Basin isa Neogene back-arc basin formed by ex-tensional tectonics within the overridingplate of the eastward migrating subduc-

tion system, giving rise to the arcuate foldand thrust belt running from the central-southern Apennines to Sicily (Figure 1).According to several authors [2, 3, 4],the extensional processes in the SouthernTyrrhenian Sea started during the Torto-nian stage and took place in a region pre-viously affected by contractional tecton-ics and by the stacking of tectonic unitsnow belonging to the Southern AppenineBelt. Nevertheless, a possible Serravallianage for extension onset has been recentlysuggested by stratigraphic and structuralstudies carried out by Mattei et al. [5]in the Amantea area along the TyrrhenianMargin of the Calabrian Arc. The East-


Marine Geology

Figure 1: Seafloor morphology of the Thyrrenian Sea and location of the study areas(from [1]). NB=Naples Bay, PB=Paola Basin, AB=Amantea Basin The upper insetshows a schematic structural map of Italy. TS=Thyrrhenian Sea; NAA=Northern Apen-nine Arc; SAA=Southern Apennine Arc; AF=Adriatic Foreland.

ern Tyrrhenian Sea Margin off Campa-nia and Calabria is characterized by thepresence of deep peri-Tyrrhenian basins(Figure 1) filled by an up to 5000 m thicksedimentary succession deposited duringthe Serravallian-Pleistocene. In particu-lar the Paola Basin (off Calabria) featuresan older Serravallian-Pleistocene sedimen-tary infill, whereas the younger Naples BayBasin (off Campania) was filled by clas-tic sediments and volcanics Lower Pleis-tocene to Present in age. The study ofthe stratigraphic succession of these peri-

Tyrrhenian basins revealed the signatureof the tectonic events responsible for theopening of the Tyrrhenian Sea. The studyof the Eastern Tyrrhenian Basins is crucialfor the kinematic analysis of the opening ofthe Tyrrhenian Sea as this area lies betweenthe Southern Apennine and Calabrian Arcsand records the sedimentary and tectonichistory from the Serravallian to the Present.The four-dimensional structural analysisof the area reveals a complex frameworkresulting from the superposition of differ-ent tectonic events, the ages of which are

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constrained by stratigraphic analysis. Ourstudy was based on a high quality cover-age of two dimensional seismic data, coresand boreholes. We integrated high resolu-tion seismic reflection profiles, CROP seis-mic lines [6] and detailed bathymetric map[1, 7] to provide a three-dimensional imageof the geological units. The basin analysisof the deepest pery Tyrrhenian basins re-vealed a geologic evolution characterizedby the opening of the southeast Tyrrhenianmargin (off Calabria) starting in the Ser-ravallian stage and successively affectedby transcurrent faulting. Instead, the open-ing of the Campania margin occurred inthe Pleistocene and from the Middle Pleis-tocene both basins migrated toward south-east [8, 9, 10, 11, 12, 13]. These resultsprovide fundamental geological constrainson the geodynamic evolution of the Tyrrhe-nian – Apennine system.

2 Methodology

Seismic reflection profiles of different res-olution and penetration together with deepstratigraphic logs and piston cores wereused to investigate the Eastern Tyrrheniancontinental margin (Figure 1). In particu-lar, our work is based on the CROP seismicprofiles that were acquired for the Italiandeep crust project, characterized by deeppenetration and low resolution (for furtherdetails see [6]), and Sparker data, acquiredwith a Multispot Extended Array System.The output power of the MEAS, transmit-ted through a 36-tip array, was 16 kJ. Ver-tical recording scales were 2.0 sec with amaximum vertical resolution of 6 m. Ourinterpretation of the seismic data set in-cludes the recognition of individual seis-mic units that were characterized on the ba-sis of the contact relations and internal lay-

ering properties [14]. Structures were cor-related between seismic profiles with con-fidence. A stratigraphic framework wasestablished using unconformity boundedunits and key reflectors traced across thedeformation zone. In addition, a detailedseismic facies analysis of the undeformedsuccession was carried out using the se-quence stratigraphy approach. The seismicinterpretation was calibrated by deep wells,piston cores and the stratigraphic succes-sion outcropping in the coastal area. Themapping of structures and isopachs of thesedimentary units were carried out[8, 9,10, 11, 12, 13]. The seismic stratigraphyinterpretation permitted the individuationof unconformity-bounded units that corre-spond to tectono-stratigraphic units (Fig-ure 2). During the late Quaternary, sealevel fluctuations occur with a cycle of100 ky as a response to climatic varia-tions. Compared to the tectonic events,the eustatic sea level fluctuations display ahigher frequency. This is reflected in thestratigraphic succession where it is possi-ble to distinguish the high frequency depo-sitional sequences associated with the eu-static sea level fluctuations. Several depo-sitional sequences were recognized. Basedon the number of recognized depositionalsequences and on the age constraints pro-vided by the age of volcanoes, well dataand dated geologic events on the coastalarea, we tentatively attributed an age to therecognized seismic units (Figure 2). Themain results of this work will be schemat-ically illustrated for the Paola Basin andNaples Bay Basin (Figures 1-3)

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3 Geologic evolution of theCalabria Margin

The structural and stratigraphic analyses ofthe basins along the Margin of Calabria(Figure 2 [13]) reveal the presence of twosedimentary depocenters, the Paola Basinand the St. Eufemia Trough, that corre-spond to the oldest basins of the EasternTyrrhenian margin.Stage 1: The first deposits overlying themetamorphic substrate (Unconformity U1)corresponds to Unit SU1, Serravallian-Tortonian in age. This sedimentary unitindicates the onset of basin formationwhereas the onlap of the strata overly-ing the metamorphic substrate indicates theprogressive filling of the basin. This unitcan be interpreted as the stratigraphic sig-nature of the opening of the TyrrhenianBasin. This Stage is well documented on-shore at Amantea [5].Stage 2: The Messinian stage is repre-sented locally by sediments and by an ero-sional surface (unconformity U2). Theseismic interpretation and well data indi-cate lateral changes in the thickness of theMessinian succession. Because the thick-ness increases on hangingwall fault blocks,we suggest that the E-W trending normalfaults have been active since the Messinianage. Besides the lateral juxtaposition oftwo approximately N-S substrate blockswith different stratigraphic successions isin agreement with the presence of a transferfault during the Tortonian and Messinianstages.Stage 3: Unit SU3 (Pliocene-Lower Pleis-tocene) corresponds to deposits overlyingthe Messinian horizon. This unit witnessesa period of subsidence that is associatedwith the E-W trending normal fault activ-ity. At the end of this stage the sediments

completely filled the basin as suggested bythe upper strata characterized by the devel-opment of prograding unit in a shallow wa-ter environment.Stage 4: The occurrence of the unconfor-mity U4 is interpreted as an abrupt changein the basin sedimentation. The deposi-tion of SU4, characterized by the presenceof deep water turbidites and slumps on theslope, indicates a rapid deepening of thebasin. The deposition of a wedge seismicunit thinning toward the West on an uplift-ing area indicates the formation of synsed-imentary growth folds with a source areafor the sediments from the West and North.The map of these fold axes indicates anen-echelon geometry approximately N-S.During this stage the Paola Basin physiog-raphy changes, assuming approximately aN-S trending orientation.Stage 5: Unit SU5 indicates a dramaticchange in the basin fill. The occurrenceof the unconformity U5 indicates an abruptchange in the stratigraphic architecture ofthe basin. This event occurs in correspon-dence to the sequence boundary 700 kaB.P.. The distal stratal termination onlapsthe slope of the fold and indicates the in-fill of the basin corresponding to the previ-ously formed syncline. In the stratigraphicsuccession we distinguish two substages,represented by SU5 and SU6 units. Atthe beginning the parallel seismic config-uration indicates a horizontal infill of thebasin. Successively in the eastern part ofthe basin, the strata were folded , whereasthe deposition of the thicker depositionalsequences, made up mainly of turbidites,forms a front fill. These features indicate,for the first time in the evolution of thebasin, the presence of a continental slopeand an important sedimentary source to theEast. At the same time, the post-700 ka up-lift of Calabria is documented by the up-

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lift of the marine terraces along the coast,whereas offshore the activity of the NW-SEdextral faults is documented.

4 Geologic evolution of theCampania Margin

The structural and stratigraphic analysisof the Bay of Naples permitted the re-construction of the Quaternary tectono-stratigraphic evolution of this sector of theEastern peri-Tyrrhenian margin. A five-stage scenario of this evolution will now bepresented (Figure 2).Stage 1: The oldest sedimentary unit, UnitA, corresponds to the first deposits overly-ing the Meso-Cenozoic substrate. This unitmarks the beginning of a period of sub-sidence associated with the activity of theNW-SE trending normal faults. The seis-mic configuration and distribution of unitA suggest that the rate of sediment supplywas high enough to fill the accommodationspace creation.Stage 2: At 700 ka the formation of theunconformity U1 and the rapid variationin the physiographic configuration of thebay is related to a tectonic event. The NE-SW oriented normal faults are character-ized by segments linked by relay zones andresponsible for the basin formation. Thefault blocks tilting and the relative posi-tion of the sea level produced an emergedarea and deep hangingwall basins: the Bayof Salerno Basin, the Campi Flegrei Basin,and the Capri Basin. The distribution ofsediments was affected by the structuralpattern. Indeed sediments produced by theshelf erosion are directly deposited in theadjacent basin west of Capri via the re-lay zone and Campi Flegrei area via slopebasin.

Stage 3: During this stage the overall con-figuration of the shelf and basin determinesthe architecture of the sedimentary infill.The latter corresponds to three depositionalsequences (B1, B2, B3; Figure 2) that forma prograding unit in the shelf slope area andan aggrading unit in the basin. The trans-gressive trend of the first unit is related tothe creation of accommodation space dur-ing the rapid basin subsidence associated tothe tectonic activity [8]. At that time thecontinental margin was characterized byhigh tectonic subsidence related to the faultactivity and low sediment supply. This lat-ter was enable to fill the accommodationspace and as a result the basin was mainlyfilled with water.Stage 4: The end of fault activity is markedby a rapid decrease in the accommodationspace creation. This implies that the de-pocentre of sequence set C migrate later-ally from the shelf toward the basin fillingthe previously formed basin. This stagewas characterized by a relatively tectonicstability and high sediment supply that wasresponsible for the formation of a regres-sive trend [8].Stage 5: After the deposition of the se-quence set C the physiography of the baywas similar to the present day one. Ap-proximately 100 ky ago the formation ofthe unconformity U2 in the shelf repre-sent a tectonic event. Indeed the reacti-vation of the pre-existing faults occur con-temporaneously to an intense volcanic ac-tivity [10]. An aggradational depositionalsequence (D) successively formed in theshelf area documenting a rapid increase inthe accommodation rate, coeval with thelarge volume pyroclastic eruptions [11].

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5 Conclusion

The structural and stratigraphic analysisof the deeper basins located in the East-ern Tyrrhenian Margin permitted the recon-struction of a detailed basin evolution al-lowing tectonic and eustatic signatures tobe identified. It was seen that, tectonicscontrolled basin formation, whereas the in-teraction between tectonic structures andrelative sea level position controlled theenvironment of sedimentation and uncon-formities. In the Eastern Tyrrhenian Seaoff Calabria we document the presence ofthe oldest stratigraphic unit, Serravallian-Tortonian in age, that onlaps the substrate.Successively a N-S extension took placegiving rise to the Paola Basin and St. Eu-femia Trough (Figure 3) that were com-

pletely filled by sediments. This sedimen-tary succession witnesses the onset of theTyrrhenian basin opening. Successivelythe activity of NW-SE left lateral faultsare related to the opening of the Marsilibasin (Figure 3). Starting approximately at700 ka, the formation of pull-apart basins,that overprint en-echelon folds, documentsa change in the slip sense of the NW-SEtrascurrent faults from a left-lateral to aright-lateral (Figure 3). The opening of thedeep basins in the Campania Margin occursapproximately 700 ka. The SE oriented ex-tension, the intense volcanism and the ac-tivity of the NW-SE oriented right lateralfault off Calabria suggest a jump towardthe north in the extension and the migrationof the eastern Tyrrhenian margin sector to-ward SE (Figure 3).

References[1] M.P. Marani and F. Gamberi. Distribution and nature of submarine volcanic land-

forms in the Tyrrhenian Sea: the arc vs the backarc. 2004.

[2] A. Argnani and F. Trincardi. Paola slope basin: evidence of regional contraction onthe eastern tyrrhenian margin. 1988.

[3] K.A. Kastens, J. Mascle, et al. Leg 107 in the Tyrrhenian Sea: insights into passivemargin and back-arc basin evolution. 1988.

[4] R. Sartori. Main results of ODP Leg 107 in the frame of Neogene to Recent geologyof perityrrhenian areas. 1990.

[5] M. Mattei, P. Cipollari, D. Cosentino, A. Argentieri, F. Rossetti, F. Speranza, andL. Di Bella. The Miocene tectono-sedimentary evolution of the southern TyrrhenianSea: stratigraphy, structural and paleomagnetic data from the on-shore AmanteaBasin (Calabrian Arc Italy). 2002.

[6] D. Scrocca. et al. Crop Atlas. Seismic reflection profiles of the Italian crust. 2003.

[7] M. P. Marani et al. Seafloor morphology of the Tyhhernian Sea. Plate 1. 2004.

[8] A. Milia. Aggrading and prograding infill of a pery-tyrrhenian basin (Naples Bay,Italy). 1999.

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[9] A. Milia and M.M. Torrente. Tectonics and stratigraphic architecture of a pery-Tyrrhenian half-graben (Bay of Naples, Italy). 1999.

[10] A. Milia and M. Torrente. Late Quaternary volcanism and transtensional tectonicsat the Campania continental margin Bay of Naples, Italy. 2003.

[11] A. Milia and M. Torrente. The influence of paleogeographic setting and crustalsubsidence on the architecture of ignimbrites in the Bay of Naples (Italy). 2007.

[12] A. Milia et al. Tectonics and crustal structure of the Campania continental margin:relationships with volcanism. 2003.

[13] A. Milia et al. Four-dimensional tectonic-stratigraphic evolution of the Southeasternperi-Tyrrhenian Basins (Margin of Calabria, Italy). 2009.

[14] R.M.Jr. Mitchum, P.R. Vail, and J.B. Sangree. Seismic stratigraphy and globalchanges of sea level Part 6, Stratigraphic interpretation of seismic reflection patternsin depositional sequences. 1977.

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Figure 2: Tables showing the results of the seismo-stratigraphic interpretation in thebasins offshore Calabria and Campania.

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Figure 3: Three evolutionary steps (based on the structural and stratigraphic data, re-gional geology) linked to the geodynamics of the region (modified from [8]). A: TheNS extension is the result of the different orientation and similar magnitude of the ve-locity vectors of the Southern Appenine and Calabrian Arcs. B: NW left lateral faultsis the result of the decrease in the magnitude of the the velocity vectors of the SouthernAppenine Arc. C: The NW right lateral faults in the Eastern Tyrrhenian Margin and thestop of the Southern Appenine Arc towards NE indicate a movement of this latter towardSE. In particular the complex tectonic evolution can be interpreted as the response in thevelocity variation between the Southern Apenninic Arc and the Calabrian Arc during thethrust belt formation.

368

The Role of Marine Geology in the Reconstructionof Vesuvius Volcano History

A. Milia1, A. Raspini2, M.M. Torrente3

1, Institute for Coastal Marine Environment, CNR, Napoli, Italy2, Institute of Geosciences and Earth Resources, CNR, Firenze, Italy3, Department of Geological and Environmental Studies, University of Sannio, Ben-evento, [email protected]

Abstract

Vesuvius in southern Italy has been one of the most active volcanoes in the world.Although its eruptions have been recognized through several geologic studies of sub-aerial exposures, recent marine geological investigations that documented offshoreVesuvius products greatly improved the reconstruction of the volcano history. Indetail, three thick stratigraphic units and criptodomes were identified and mappedfor the first time on the continental shelf of the Bay of Naples through the interpreta-tion of high-resolution seismic reflection profiles calibrated by offshore gravity cores.These stratigraphic units are genetically linked to three plinian volcanic eruptions andinterlayered between the systems tracts of the last depositional sequence. Two units,coeval with the 18 ka-old Pomici di Base eruption and 3.5 ka-old Avellino eruptions,correspond to debris avalanches resulting by flank collapses whereas the third unit,coeval with the 79 A.D. Pompei eruption, represents submarine pyroclastic flow de-posits. The documentation of the rapid entrance of debris avalanches and pyroclasticflows originating from Vesuvius into the sea-water may be relevant for studies ofvolcanoes in close proximity of coastlines and imply that debris avalanche-generatedand pyroclastic flow-generated tsunamis need to be taken into account for hazardevaluation in the management of the densely populated coastal zone of Naples Bay.

1 Introduction

The Somma-Vesuvius volcanic complex islocated in a highly populated area on thenortheastern coast of the Bay of Naplesthat is characterized by crustal thinningand severe rifting processes affecting theNeogene southern Apennines thrust belt.The Bay of Naples is a Middle Pleis-tocene NE-trending half graben with itsdepocenter located in the north-west. Itis filled by fourth-order depositional se-quences that are arranged in sequence

sets displaying long-term aggradational-progradational stacking patterns [1, 2]. TheMesozoic-Cenozoic carbonate substratum,cropping out on the Sorrento Peninsula,dips towards the NW and is overlain byQuaternary sediments and volcanic prod-ucts [3]. The Somma-Vesuvius edifice cor-responds to the breached crater of the Mt.Somma stratovolcano and the recent coneof the active Vesuvius, which grew withinMt. Somma. It began its eruptive ac-tivity at least 35 ka BP [4]. The vol-canic succession of the Somma-Vesuvius


Marine Geology

complex mainly consists of lava flows andminor scoria fall deposits [4] overlain bythe products of four main plinian eruptions(e.g., [5]): the Pomici di Base (18 ka BP),the Mercato Pumice (8 ka BP), the Avel-lino Pumice (3.5 ka BP) and the PompeiiPumice (AD 79). The last eruption of thevolcanic complex occurred in 1944 after aperiod (1631-1944) of semi-persistent ac-tivity. At the present, the volcano showsa moderate seismic and fumarolic activity.The region around Vesuvius has been in-vestigated by means of a lithostratigraphicanalysis of boreholes drilled by privatecompanies and local authorities, and/or bythe reinterpretation of data from the liter-ature [6, 7, 8, 9]. Locally, seismic reflec-tion data have been calibrated using grav-ity cores whose sediment description wascarried out at centimetre scale using both a10x hand lens and microscope observationsof sieved–dried sediment [10]. The inter-pretation of high-resolution seismic reflec-tion profiles carried out on the continen-tal shelf of the Bay of Naples and cali-brated by gravity cores, allowed the iden-tification, for the first time, of cryptodomesand of three thick stratigraphic units (Fig-ure 1) that are interlayered in the systemstracts of the depositional sequence follow-ing the Last Glacial Maximum. Two unitsare coeval with, respectively, the 18 ka-old Pomici di Base eruption and 3.5 ka-old Avellino eruptions, and correspond todebris avalanches resulting by flank col-lapses. The third unit, instead, representsthe underwater components of the onshorepyroclastic current deposits that buried theRoman town of Herculaneum during theAD 79 Pompeii eruption of Vesuvius. Thestatigraphy offshore Vesuvius is character-ized by the Campania Ignimbrite (CI, 39ka) covered by the Late Quaternary depo-sitional sequence. Between the systems

tracts of the depositional sequence differ-ent volcanic features are present [11, 12, 7,10].

2 Cryptodomes andFaults

Mounds characterized by reflection freeand chaotic reflection configuration wererecognized off Vesuvius. They are posi-tioned at water depths ranging between 80and 110 m and result aligned parallel tothe NW-SE coastline (Figure 1). The earlyLowstand Systems Tract deposits overly-ing these mounds appear warped and theirupper strata were eroded and re-depositedduring the Lowstand of the sea level suc-cessively the deposits of the Transgressiveand Highstand Systems Tracts (character-ized by parallel configuration) draped theprevious morphology. These deposits weregently folded, disrupted and pierced by themounds. This overall stratigraphic archi-tecture suggests a localized uplift in cor-respondence of the mounds that were con-sequently interpreted as cryptodomes [11].These cryptodomes result characterized byat least two events of uplift during theLowstand and Highstand of the sea level.Moreover, a tectonic uplift offshore Pom-peii predates the deposition of the 79 ADpumice fall [14]. These stratigraphic con-straints suggest that the cryptodome intru-sions correspond to repeated events possi-bly coeval with Vesuvius plinian eruptions(Pomici di Base, 18 ka; Avellino, 3.5 ka;A.D. 79). Our cryptodome interpretationwas recently confirmed as the four moundsmapped off Vesuvius (Figure 1) exactlycorrespond to positive anomalies (up to300 nT) of the magnetic map of Naples Bay[15]. A 34 km-long NE-SW trending re-

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Figure 1: Physiography of Naples Bay and map distribution of the DA1 (yellow), andDA2 (light blue) debris avalanches, the submarine volcanoclastic fan associated to the79 AD eruption (green) and the cryptodomes (red). Dashed lines mark the presumedonshore boundaries of these units. Tectonic framework is from [11] and [13].

gional section from the slope and shelf ofthe Bay of Naples to the southern Cam-pania Plain was reconstructed [13] by fit-ting offshore seismic stratigraphy [11, 3]and drill hole stratigraphy [6, 16] in thesouthern Campanian Plain. The sequenceconsists of Middle Pleistocene marine sed-iments overlain by Upper Pleistocene ig-nimbrites (pre-CI tuffs and CI) and post-25 ka Somma-Vesuvius products. Tracingof the Upper Pleistocene ignimbrite markerhorizons from the shelf to the southernCampania Plain permitted the imaging oftwo normal faults (one located on the coastand another below the Vesuvius cone).

Both normal faults displace the pre-CI tuffsand the top of the Campania Ignimbrite.They downthrow to the southwest. Thethicknesses of the pre-CI tuffs and CI unitis greater in the footwall than in the hang-ingwall block and fault throws are greaterfor older marker levels. On the basisof these features we maintain that normalfault activity started during the emplace-ment of the Upper Pleistocene ignimbrites.An evidence of the recent activity of theNW-SE Vesuvius faults comes from his-torical data. Indeed an earthquake, whichseriously damaged Pompeii, occurred onFebruary 5th 62 AD, with a Magnitude of

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5.9. Because of the high value of the mag-nitude and of the NW–SE trend of the iso-sists it was suggested a tectonic origin forthe earthquake and hypothesized that thetectonic event triggered an upward surge ofnew magma, that 17 years later was respon-sible of the 79 AD Plinian eruption [17].

3 The DA1 debrisavalanche (18ky-old)

The Campana Ignimbrite is capped by anunconformity covered by an approximately20 m thick younger unit showing parallelreflectors and a tabular external form. Thisunit, made up of sediment deposited dur-ing the fall of the sea level between 39and 18 ka ago [12], is covered landwardby Unit DA1 that features a chaotic seis-mic facies. A younger seismic unit, charac-terized by parallel reflectors with low am-plitude and low frequency and a thicknessof approximately 30 m, onlaps unit DA1.At its seaward margin Unit DA1 is cov-ered by a progradational seismic unit cor-responding to the Late Lowstand SystemsTract. The seismic unit DA1 shows chaoticfacies and hummocky surfaces, and is in-terlayered within the systems tracts of theLate Quaternary depositional sequence oncontinental shelf between Portici and TorreAnnunziata, until 100 m of water depth(Figure 1). Its top features a staircase mor-phology with flat surfaces overlain by ma-rine sediments. The seaward terminationdisplays a steep 60 m scarp with an irregu-lar pattern characterized by elongated lobesthat lie perpendicular to the coast. UnitDA1 has an areal distribution of 36 km2,with a volume of approximately 2.9 km3,and, assuming a mean velocity of 1600m/s for the depth conversion, its thickness

ranges from 100 m close to the volcanoto 60 m far from the coast [12]. As UnitDA1 lies above the unconformity overly-ing the 39 ka Campana Ignimbrite and be-low the wedge that formed during the sealevel lowstand, [12] suggested that it set-tled about 18 ka ago in a subaerial environ-ment (see also [18]). Unit DA1 cannot beassociated with normal sedimentation thatoccurred on the continental margin or withany Somma-Vesuvius eruption because ofits unusually large thickness, lateral exten-sion and internal and external seismic fa-cies. Reflection-free seismic facies (sug-gesting a massive sedimentary body), hum-mocky external seismic facies and a 60 m-high terminal scarp of unit DA1 are typi-cal of a dry debris avalanche with a poorlysorted mixture of brecciated debris (e.g.,[19, 20, 21, 12]). Based on 1) the good spa-tial correlation between the offshore lateralboundary of unit DA1 (depositional area)and the presumed onshore scarp of the Mt.Somma breached crater (source area); 2)the stratigraphic relationships between thedebris avalanche products and the systemstracts of the Late Quaternary depositionalsequence; 3) the ages of the dated Somma-Vesuvius plinian eruptions, [12] associatedthe debris avalanche to the collapse of Mt.Somma at 18 ka shortly before the Pomicidi Base eruption.

4 The DA2 debrisavalanche (3.5 ka-old)

The deposits related to the Avellino erup-tion show a chaotic seismic facies, reacha water depth of 150 m, have a totalvolume exceeding 1 km3 and are sand-wiched by marine sediments [7, 8, 9],(Figure 1). They consist of a 15–20 m-

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thick basal loose gravels and sands withsubangular pumice, lava and scoria frag-ments overlain by 5 m-thick deposit con-sisting of yellow to green lithoid tuff in-cluding pumice, scoriae and mainly cal-careous lithic fragments. The volcanoclas-tic deposits are interpreted as the productof a debris avalanche related to the col-lapse of the western seaward-facing flankof the Somma–Vesuvius, while the tuff de-posits are related to pyroclastic gravity cur-rents. Locally, the latter deposit is abruptlycovered by a 2 m-thick layer consisting ofsand and gravel rich in marine shell frag-ments and rounded pumice. The succes-sion terminates with shallowing and coars-ening upward marine sediments consist-ing of muds, silts and sands. A compa-rable stratigraphic succession of the Avel-lino unit as detected on the eastern coastof Naples is also present near the ventat Novelle [22] and at the Herculaneumexcavation site [6]. The correlation be-tween the offshore geological section, re-constructed by means of the interpretationof seismic reflection profiles, and the on-shore geological section, reconstructed bythe interpretation of borehole data, revealsa physical continuity between the Avellinounit recognized offshore, consisting of adebris avalanche covered by deposits re-lated to pyroclastic gravity currents, andthe previously recognized thick tuff de-posits, in places overlying breccia depositsin the Volla plain [6]. Offshore, the dis-tribution of the Avellino unit documentsa debris avalanche that travelled westwardover a distance of approximately 10 km be-fore entering the sea and the subsequentwestward flow of pyroclastic currents. Theemplacement of this voluminous unit in-duced an instantaneous inner shelf progra-dation which resulted in an abrupt shift ofthe inner shelf edge off San Giovanni a

Teduccio, where the mound-shaped Avel-lino unit reaches thicknesses ranging from50 to 70 m [9]. Here the Avellino unit isbounded at the top by a surface that dis-plays an irregular morphology with troughsand highs of up to 20 m relief. This, in turn,is abruptly overlain by an approximately2 m-thick layer consisting of loose sandand gravel with abundant marine shell frag-ments and rounded pumice. These featuresdocument a high-energy event in coastalareas which produced a deep erosion ofthe substratum up to a water depth of 30m and the winnowing of fine sedimentsacross the coastal setting before the settle-ment of the coarse-grained bioclastic de-posit. Such high-energy depositional con-ditions have been correlated to a tsunamiwhich was induced by the displacement ofseawater away from the shore after the sud-den entrance into the sea of the volumi-nous Avellino volcanoclastic unit [7, 9].Below 40 m water depth, a slump affectsthe volcaniclastic debris avalanche and theoverlying marine sediments. Although pa-rameters that generally favour or triggerslope instabilities include seismic activity,angle of slope of the margin, basement ar-chitecture, sea current and high pore-fluidpressure [23], it cannot be excluded that,in such a scenario, the slump may havebeen triggered by tsunami-induced pore-pressure changes of the voluminous vol-caniclastic deposit that was instantaneouslyemplaced under the sea, producing a rapidphysiographic change and a potential areaof disequilibrium [9].

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Figure 2: Cartoon depicting the syn-eruptive sedimentary processes associated to the en-trance of hot pyroclastic flows into the sea during the A.D. 79 eruption of Vesuvius. Forfurther explanations see text.

5 The AD 79 submarinevolcaniclastic fan

During the Pompeii Pumice plinian erup-tion the deposition of the products of thesubaerially-generated pyroclastic currentsrapidly entered the sea. They formed awide volcaniclastic fan that is located offHerculaneum, at 10-140 m water depth[10],( Figure 1), and induced a coastalprogradation of approximately 400 m (cf.[24]). The fan, 0.3 km3 in volume, dis-plays a chaotic seismic facies that grad-ually changes seaward to parallel reflec-

tors and then to wavy reflectors. Wavy fa-cies form dunes that are aligned roughlyparallel to the coast and feature bedformsdisplaying marked asymmetry and irreg-ular pattern, passing seawards to parallelreflectors. Gravity cores reveal a succes-sion consisting of cm-thick sand/silt-sizedash couplets followed by an up to 180 cm-thick graded gravely sand-sized bed withshell fragments and beach-derived pebblesthat is overlain by dm-thick graded andlaminated bioclastic sandy ash layers [10].The depositional textures and sedimentarystructures of the volcaniclastic fan imply

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that high-energy events repeatedly and se-quentially affected the shallow continentalshelf where they settled. Such an orga-nization in multiple scour-and-graded lay-ers of the topmost part of the AD 79 erup-tion deposit have been also documented inthe southern sector of the Bay of Naples,while it is lacking in the adjacent Bay ofSalerno [14]. This confirms that the afore-mentioned stacking pattern has to be re-lated to an exceptional process that in-terested the Bay of Naples only, rework-ing substantially the AD 79 pyroclastic de-posits [10]. Also, seismic interpretationshowed that most of the pyroclastic prod-ucts forming the submarine fan are ar-ranged in minor units forming a retrogra-dational stacking pattern and wavy stratifi-cation [10]. In particular, the occurrence ofdunes and the observed sedimentary struc-tures reflect events of rapid deposition un-der the effect of tractive currents and excessof suspended sediment load. The featurescharacterizing the volcaniclastic fan havebeen interpreted as the product of the in-teractions between hot pyroclastic densitycurrents entered into the sea and tsunami-induced water waves [10]. Such event wasalso observed and described by Pliny theYounger during the 79 AD eruption: “theseashore withdrew and fishes and other ma-rine faunas laid on the emerged seafloor”.Based on our findings, the geological liter-ature (e.g., [24, 25, 26, 27, 28, 29]), andthe description of Pliny the Younger, weput forward a speculative model of syn-eruptive sedimentary processes that oc-curred off the city of Herculaneum duringthe AD 79 plinian eruption (Figure 2). Inthe morning of 25 August, hot (350/500 °C[30, 31], pyroclastic currents transited overthe city of Herculaneum and entered thesea. Near shore steam explosions and, pos-sibly, ash fountains and convectively ris-

ing fine ash plumes were generated, as usu-ally produced experimentally with hot ashflows into water [28]. Due to the den-sity contrast at the air/water interface andhigh velocity (∼100 km·h−1), the currentslikely segregated into a basal dense portion,that continue subaqueously, and a more di-lute turbulent finer ash upper fraction, thattravelled on water for a great distance fromthe volcano [32, 27, 28]. Once the lat-ter sinking and interacting with seawater,finally deposited, the fractionation of thecomponents, according to their settling ve-locities, led the formation of coarser ashunder traction currents with excess of sus-pended sediment load, while the finer por-tion settled from suspension under calmerconditions. It allowed couplets consistingof multiple laminated-and-graded coarserlayers overlying by finer material to be de-posited. Further pyroclastic flows were de-livered towards the sea. The denser basalportion of the flows sank and a degree ofinteraction between its surface and seawa-ter developed, giving rise to density cur-rents. As a result, chaotic seismic uniton the inner-middle continental shelf pass-ing seaward to parallel reflector facies werelaid down. Massive facies also characterizethe 79 AD eruption deposits cropping outon roman Herculaneum beach suggesting arapid fall-out of dense pyroclastic currentswhen they arrived on the beach and enteredthe sea (e.g., [33]). Later in the morning of25 August, tsunami waves induced by theentrance into the sea of a coarse grainedpyroclastic flow struck the coast of NaplesBay. The waves partly reworked the previ-ously deposited volcaniclastic material andredistributed it to deeper areas as a ma-rine gravity flow, inducing the settlement ofgraded gravely sand-sized deposit overlainby dm-thick graded and laminated bioclas-tic sandy ash layers.

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6 ConclusionsRecent marine geology investigations al-lowed us to document cryptodomes andoffshore volcaniclastic deposits related tothe Vesuvius volcanic activity. Threethick stratigraphic units were identified andmapped for the first time on the conti-nental shelf of the Bay of Naples throughthe interpretation of high-resolution seis-mic reflection profiles calibrated by off-shore gravity cores. Two units, coeval withthe 18 ka-old Pomici di Base eruption and3.5 ka-old Avellino eruptions, correspondto debris avalanches resulting by flank col-lapses whereas the third unit, coeval withthe A.D. 79 Pompeii eruption, representsa submarine volcaniclastic fan related tocomplex interactions between hot pyro-clastic density currents entered into the sea

and the induced tsunami waves. The con-temporaneous occurence of normal faults,cryptodomes and debris avalanches in theVesuvius history suggests a genetic linkbetween these processes. It is possiblethat normal faulting and cryptodome intru-sion were responsible of the volcano in-stability producing lateral collapse and de-bris avalanche. The results of our researchdemonstrate that marine geology may offera fundamental contribution for greatly im-proving the reconstruction of coastal vol-canoes’ activity. In particular, our find-ings imply that voluminous mass-flow en-tering into the sea may generate tsunamisthat have to be taken into account for haz-ard evaluation and disaster managementplanning of the densely populated regionaround the coastal active Vesuvius volcano.

References[1] A. Milia. Aggrading and prograding infill of a peri-Tyrrhenian Basin (Naples Bay,

Italy). Geo-Marine Letters, 19:237–244, 1999.

[2] A. Milia and M.M. Torrente. Tectonics and stratigraphic architecture of a peri-Tyrrhenian half-graben (Bay of Naples, Italy). Tectonophysics, 315:301–318, 1999.

[3] A. Milia, M.M. Torrente, and A. Zuppetta. Offshore debris avalanches at Somma-Vesuvius volcano (Italy): implications for hazard evaluation. Journal of the Geo-logical Society, London, 160:309–317, 2003.

[4] R. Santacroce and A. Sbrana. Carta geologica del Vesuvio. 2003.

[5] D. Andronico, G. Calderoni, R. Cioni, A. Sbrana, R. Supplizio, and R. Santacroce.Geological map of Somma-Vesuvius Volcano. Periodico di Mineralogia, 64:77–78,1995.

[6] F. Bellucci. Nuove conoscenze stratigrafiche sui depositi effusivi ed esplosivi nelsottosuolo dell’area del Somma-Vesuvio. Bollettino della Societa’ Geologica Ital-iana, 117:385–405, 1998.

[7] A. Milia, A. Raspini, and M.M. Torrente. The dark nature of Somma-Vesuviusvolcano as evidenced from the 3.5 ka, B.P. Avellino eruption. Quaternary Interna-tional, 173-174:57–66, 2007.

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[8] A. Milia, A. Raspini, and M.M. Torrente. The dark nature of Somma-Vesuviusvolcano: evidence from the 3.5 ka, B.P. Avellino eruption. Reply. QuaternaryInternational, 192:110–115, 2008b.

[9] A. Milia, A. Raspini, and M.M. Torrente. Evidence of slope instabilities andtsunami associated with the 3.5 ka Avellino eruption of Somma-Vesuvius volcano,Italy. The Geological Society, London, Special Publications, 322:105–119, 2009.

[10] A. Milia, F. Molisso, A. Raspini, M. Sacchi, and M.M. Torrente. Syneruptive fea-tures and sedimentary processes associated to pyroclastic flows entering the sea:the AD 79 eruption of Vesuvius, Bay of Naples, Italy. Journal of the GeologicalSociety, London, 165:839–848, 2008a.

[11] A. Milia, L. Mirabile, M.M. Torrente, and J.J. Dvorak. Volcanism offshore of Vesu-vius Volcano in Naples Bay. Bulletin of Volcanology, 59:404–413, 1998.

[12] A. Milia, M.M. Torrente, M. Russo, and A. Zuppetta. Tectonics and crustal struc-ture of the Campania continental margin: relationships with volcanism. Mineralogyand Petrolology, 79:33–47, 2003.

[13] F. Bellucci, A. Milia, G. Rolandi, and M.M. Torrente. Structural control on the Up-per Pleistocene ignimbrite eruptions in the Neapolitan area (Italy): volcano tectonicfaults versus caldera faults. Elsevier, B.V., pages 165–182, 2006.

[14] M. Sacchi, D. Insinga, A. Milia, F. Molisso, A. Raspini, M.M. Torrente, andA. Conforti. Stratigraphic signature of the Vesuvius 79 AD event off the Sarnoprodelta system, Naples Bay. Marine Geology, 222-223:443–469, 2005.

[15] G. Aiello, A. Angelino, E. Marsella, S. Ruggieri, and A. Siniscalchi. Carta magnet-ica di alta risoluzione del Golfo di Napoli (Tirreno meridionale). Bollettino dellaSocieta’ Geologica Italiana, 123:333–342, 2004.

[16] F. Brocchini, C. Principe, D. Castratori, M.A. Laurenzi, and L. Gorla. Quaternaryevolution of the southern sector of the Campanian Plain and early Somma-Vesuviusactivity: insights from the Trecase well. Mineralogy and Petrology, 73:67–91, 2001.

[17] A. Lima, B. De Vivo, L. Fedele, F. Sintoni, and A. Milia. Geochemical variationsbetween the 79 AD and 1944 AD Somma-Vesuvius volcanic products: Constraintson the evolution of the hydrothermal system based on fluid and melt inclusions.Chemical Geology, 237:401–417, 2006.

[18] A. Milia and M.M. Torrente. The influence of paleogeographic setting and crustalsubsidence on the architecture of ignimbrites in the Bay of Naples (Italy). Earthand Planetary Science Letters, 263:192–206, 2007.

[19] H. Glicken. Criteria for identification of large volcanic debris avalanches. EOSTransactions, AGU, 63:1141, 1982.

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[20] P.F. Ballance and M.R. Gregory. Parnell Grift - Large subaqueous volcanoclasticgravity with multiple particle-support mechanisms. SEPM Special Publications,45:189–200, 1991.

[21] T.B. Fortuin, A.R. Roep, P.A. Sumususastro, T.C.E. van Weering, and W. van derWerff. Slumping and sliding in Miocene and Recent developing arc basins, onshoreand offshore Sumba (Indonesia). Marine Geology, 108:345–363, 1992.

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[23] B.C. Vendeville and V. Gaullier. Role of pore-fluid pressures and slope angle intriggering submarine mass movements: natural examples and pilot experimentalmodels. Kluwer, Dordrecht, pages 137–144, 2003.

[24] H. Sigurdsson, S. Carey, W. Cornell, and T. Pescatore. The eruption of Vesuvius inAD 79. National Geographic Research, 1:332–387, 1985.

[25] N.S. Carey, H. Sigurdsson, C.W. Mandeville, and S. Bronto. Pyroclastic flows andsurges over water: an example from 1883 Krakatau eruption. Bulletin of Volcanol-ogy, 57:493–511, 1996.

[26] C.W. Mandeville, S.N. Carey, and H. Sigurdsson. Sedimentology of the Krakatau1883 submarine pyroclastic deposits. Bulletin of Volcanology, 57:512–529, 1996.

[27] F. Legros and T.H. Druitt. Shoreline displacement as a mechanism for the emplace-ment of ignimbrite in shallow marine environments. Journal of Volcanology andGeothermal Research, 95:9–22, 2000.

[28] A. Freundt. Entrance of hot pyroclastic flows into the sea: experimental observa-tions. Bulletin of Volcanology, 65:144–164, 2003.

[29] M. Edmonds and R.A. Herd. Inland-directed base surge generated by the explosiveinteraction of pyroclastic flows and sea. Geology, 33:245–248, 2005.

[30] D.V. Kent, D. Ninkovitch, T. Pescatore, and R.S.J. Sparks. Paleomagnetic deter-mination of emplacement temperature of Vesuvius, A.D. 79 pyroclastic deposits.Nature, 290:393–396, 1981.

[31] G. Mastrolorenzo, P.P. Petrone, M. Pagano, A. Incoronato, P.J. Baxter, A. Can-zanella, and L. Fattore. Ercolano victims of Vesuvius in AD 79. Nature, 410:769–770, 2001.

[32] H. Sigurdsson, S. Cashdollar, and R.S.J. Sparks. The eruption of Vesuvius in AD79: reconstruction from historical and volcanological evidence. American Journalof Archeology, 86:39–51, 1982.

[33] L. Gurioli, R. Cioni, A. Sbrana, and E. Zanella. Transport and deposition of pyro-clastic density currents over an inhabited area: the deposits of the AD 79 eruptionof Vesuvius at Herculaneum, Italy. Sedimentology, 49:929–953, 2002.

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Volcanism, Sedimentation and Tectonics in theCampi Flegrei Area (Italy): an Outlook from Ma-rine Geology

A. Milia1, M.M. Torrente2

1, Institute for Coastal Marine Environment, CNR, Napoli, Italy2, Department of Geological and Environmental Studies, University of Sannio, Ben-evento, [email protected]

Abstract

The interpretation of a strictly spaced seismic grid (made up of several deep-lowresolution multichannel seismic lines and shallow-very high resolution monochan-nel seismic lines) permitted us to investigate the offshore counterpart of the CampiFlegrei. For the first time we outlined: 1) the interplay between clastic and vol-canic units in the stratigraphic succession; 2) numerous previously unknown vol-canic units; 3) the fault architecture and kinematics. We identified distribution andtypologies (monogenetic volcanoes, ignimbrite units and volcanic domes) of thesevolcanic units and the three-dimensional architecture of inter-eruptive stratigraphicsuccession. We detected faults and folds and we recognized fault kinematics, sliprates and fold uplift rates. We were able to reconstruct the paleogeographic evolutionand calculate the accommodation curves of this region. The structural pattern fea-tures NE-trending normal faults, left-lateral E-W faults and right lateral NW-trendingfaults. Our work documents the enormous capability of marine geology to investigatesubmarine volcanic fields as well it has important implications for the identificationof the active tectonic structures of Campi Flegrei and for the interpretation of thebradyseism episodes. Finally our basin analysis can play a role in the site selectionand lithostratigraphic interpretation of the ICDP Campi Flegrei project.

1 Introduction

Volcanism at Campi Flegrei has been ac-tive over the past several hundred thou-sand years and a huge amount of pyro-clastics and lavas was erupted (Figure 1).This volcanism is associated with Quater-nary extension along the Eastern Tyrrhe-nian margin. Although this region hasbeen the target of intense research, the ori-gin of the volcanism and the geodynamicframework remain a matter of spirited de-

bate. Approximately three million peo-ple reside in the greater Naples area, rep-resenting one of the most densely popu-lated volcanically active regions on Earth.Of particular interest regarding volcanic,seismic and geodetic hazards at CampiFlegrei is the phenomenon of slow, ver-tical ground movements and earthquakesreferred to as bradyseism that have af-fected Campi Flegrei since before Romantimes. The Tyrrhenian Sea is an exten-sional back-arc basin formed at the rear of


Marine Geology

the Neogene Apennine thrust belt. Dur-ing the Quaternary the eastern Tyrrhe-nian margin was affected by normal faultsthat controlled basin architecture and vol-canism. Milia [1] and Milia and Tor-rente [2] reconstructed a detailed chronol-ogy of faults characterized by LowerPleistocene NW-SE normal fault followedby Middle Pleistocene NE-SW normalfaults and NW-SE reactived transfer faults.The NE-trending extensional fault gener-ated the Naples Bay half graben filledby fourth order depositional sequencesarranged in sequence sets that displaylong term aggradational-progradational-aggradational stacking patterns[3]. Amongthe controversial themes concerning theCampi Flegrei are the ignimbrite sourceareas, the occurrence of a Caldera, therelationships between regional faults andignimbrite emission, the meaning of thebradyseismic episodes as precursor of vol-canic eruption. The submerged part ofCampi Flegrei was investigated by meansof more than 4000 km of single-channeland multi-channel seismic reflection pro-files (for technical details and interpreta-tion methodologies of the seismic data see[4]). The interpretation of the seismic re-flection profiles permitted us to investi-gate the relation between the volcanism,stratigraphy and tectonics, a fundamentalapproach that reveals a new complex evo-lution of the volcanic area. In particular adetailed seismo-stratigraphic interpretationpermit:1. to investigate the stratigraphic succes-

sion in terms of syn-eruptive and inter-eruptive units;

2. to recognize global and local processes;3. to interpret the origin of the volcanic

units;4. to individuate faults and folds;5. to reconstruct their kinematics;

6. to find the link, in term of space andtime, between faulting and volcanism.

2 Volcanic succession

Our marine geological studies of the sub-marine part of Campi Flegrei [8, 9, 10, 7,11, 12, 4, 13, 14, 2, 5, 6, 15] documentedand mapped for the first time the oc-currence of several syn-eruptive volcano-clastic units mainly formed by voluminousignimbrite deposits and monogenic volca-noes (Figure 1, Figure 2). These depositswere cross-correlated to the stratigraphicsuccession outcropping at Naples and tothe boreholes drilled on the coast. In partic-ular four superposed wedge-shaped unitscharacterised by a chaotic seismic facies(units Pre-CI, CI, F and NYT) occur inthe Eastern part of Campi Flegrei and taperseaward. Unit Pre-CI was linked to the Pre-Campania Ignimbrite tuffs; it has a max-imum thickness of approximately 550 m.Unit CI corresponds to the Campania Ig-nimbrite (39 ka) that reaches a maximumthickness of approximately 200 m. Unit Fhas a variable thickness between 60 and 10m and features diapiric mounds. Unit NYTcorresponds to the Neapolitan Yellow Tuff(15 ka) and is approximately 100 m thick.The overall pyroclastic wedge thicken to-ward Campi Flegrei reaching a maximumthickness near the coast where a 850 m-thick succession of tuffs was drilled bya geothermal deep well. Monogenic vol-canoes of the Campi Flegrei offshore arecharacterized by chaotic or non-coherentreflections seismic facies and by a moundexternal form; they will be described fromolder to younger. The oldest volcanicmound (V5) reposes on a subparallel pre-volcanic sedimentary unit (C3a). It is ap-proximately 150 m high, has a diameter

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Figure 1: Fisiographic map illustrating the distribution of the syn-eruptive units (mono-genic volcanoes and ignimbrites) and faults off Campi Flegrei. GB: Gaia Bank, PB:Mariapia Bank, PP: Penta Palummo Bank, NB: Nisida Bank, MB: Miseno Bank, MD:Monte Dolce Dome, MV: Mirabile volcano, WV: Walther volcano (modified from[5, 6, 7].

of ca 1 kilometre and lies in the PentaPalummo area. Volcanic mounds (150 ka)correspond to the Gaia, Walther, Mariapia,Mirabile and V4 volcanoes and are locatedin the southern part of the continental shelf.These volcanoes share similar dimensionsfeaturing diameters on the order of 2 km,average heights of approximately 150-200m and slopes ranging between 18° and40°. Two volcanic mounds located in themiddle part of the continental shelf corre-spond to the Penta Palummo (V3, 100 ka-old) and the Miseno Bank (39 ka) volca-noes. During the same eruptive period ofthe Neapolitan Yellow Tuff (15 ka) several

small mounds (NYTtcs, YT1, YT2, YT3)formed in the northern part of the conti-nental shelf. The youngest volcanic units(≤ 6 ka V1, PF; 4.1 ka Nisida bank, [16]occur in the northern part of the continen-tal shelf and correspond to pyroclastic flowdeposits. The Monte Dolce volcano (V1)reaches the sea floor and locally emergeswith up to 60 m-high relief; it was in-terpreted as shallow magmatic body over-lain by a lava-sediment breccia [7]. Py-roclastic flows (Unit PF) younger than 5ka where present off Capo Miseno and offMonte Spina. The Nisida Bank volcano,the Nisida shoal and the Nisida island form

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the Nisida Complex volcano. In conclusionoff Campi Flegrei, various types of sub-marine monogenetic volcanoes were rec-ognized. The specific environmental con-ditions suggest that they were generated byphreatomagmatic eruptions. Indeed, ex-ternal water is easily the most importantenvironmental factor influencing the vari-ous evolutionary stages of magma/volcanicsystems. Based on (1) the internal and ex-ternal seismic configuration, (2) the sub-marine environment of volcano formation,(3) the dimensions of the volcanoes and(4) the comparison with younger volcanoesformed in shallow water in Campi Flegrei,we argue that the submarine volcanoes thatlie off Campi Flegrei are scoria cones. GaiaBank, Mariapia Bank, Walther, Mirabile,Miseno Bank and Penta Palummo volca-noes are characterized by a lateral over-lap along an E-W direction, similar dimen-sions (in the order of 2 km in diameterand 150-200 m in height), and the pres-ence of normal faults along the base of thevolcanoes. Positive magnetic anomaliescorresponding to these volcanoes suggestthe presence of cooled lava bodies. Thesesubmarine volcanoes are similar to that ofMonte Nuovo, a volcano that formed in1538 during a one week-long hydromag-matic eruption. Nisida Bank is an exampleof a submarine stratified volcano. It has adiameter of 1.6 km and height of 80 sug-gesting diffusely bedded, water-settled ashand lapilli. The top of Nisida Bank Volcanois characterized by a flat, wave-cut surface,where rounded gravel were dredged, indi-cating the position of the sea level at thetime of the volcano formation. The NisidaComplex includes the emergent Nisida is-land, 600 m in diameter and 110 m inheight, which is a tuff cone. The evolu-tion of the Nisida Complex tuff cones canbe compared with that of the well studied

case of Surtsey (Iceland), a subaqueous toemergent tuff cone [17]. After the erup-tion ceases, the volcanic cone is rapidlydestroyed by subaerial and or wave ero-sion. Removal of the top of these vol-canic centers produces a fairly flat, wave-cut plateau and widens the volcanic edi-fice through the deposition of a surround-ing apron of volcaniclastic and bioclastictalus and mass-flow deposits. Dikes anddomes are present below a water depth of115 m and form minor volcanic units. Thechaotic facies at the lateral margin of thesills can be interpreted as a texturally com-plex lava-sediment breccia (peperite) pro-duced by the mixing of domes with subja-cent wet sediments. A partially extrusivecryptodome may locally break through thecover and emerge at the surface. In partic-ular the Monte Dolce extrusion occurs inassociation with normal faults downthrowntoward the northeast and southeast.

3 Eustatism and Inter-eruptive sedimentarydeposits

Climatic cycles during the Quaternary af-fected all the continental margins with astepwise fall in eustatic sea level that cul-minated in the Last Glacial Maximum ofoxygen isotope stage 2; a much faster sealevel rise occurred after 18 ka [18]. Sed-imentary deposits on continental marginscan readily be subdivided on their internalgeometry and stacking pattern and referredto distinct phases of sea level fluctuations(e.g. [19]). Our marine geological stud-ies of the submarine part of Campi Flegrei[8, 9, 10, 1, 7, 11, 12, 4, 13, 14, 2, 5, 6, 15]reported for the first time the occurrence ofseveral clastic units (Figure 2). Epiclastic

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processes are extremely significant in vol-canic terrains, both in terms of their dura-tion and the volume of sediments that maybe transported. The interpretation of theseismic reflection profiles off Campi Fle-grei reveals that volcanoes are covered byinter-eruptive volcaniclastic units. Theseunits present an extremely lateral variabil-ity due to the isolated source areas, theirlocation and their influence on the hydro-dynamic currents. Indeed these latter influ-ence the direction of the transported sedi-ment and the deposition of the suspendedsediments that occurs in low energy envi-ronments. Slope instability processes havesculpted numerous morphological featureson the flanks of the submerged volcanoes inthe Bay of Naples off Campi Flegrei. Thetiming and spatial evolution of sedimentfailures were defined using seismic profilesand multibeam bathymetry [20, 21]. Rota-tional slump complexes occur immediatelyafter the growth of volcanoes, with some ofthem remaining active for a long time af-ter their formation. The depth of the mainscars occurring on the volcano flanks aredeeper than 150 m. The volcanic land-slides that developed above a depth of 150m were characterized by different trigger-ing factors (angle of slope margin, seis-mic activity, basement architecture, rapidsea level change, sea currents and highpore-fluid pressure). Instead below a waterdepth of 150 m, the main factor controllinginter-eruptive erosional/depositional pro-cesses is probably gravity. Indeed, theflanks of the volcanoes were seen to be in-stable, and slumps eroded deposits on theslope and deposited material in the adja-cent basin at the slope base. Concern-ing the erosional-depositional processes af-fecting volcanoes above a water depth of150 m, the major controls on offshoreclastic facies were sediment supply, wa-

ter depth, relative sea level fluctuation,and hydraulic regime. The developmentof the volcanoes in the northern part ofNaples Bay basin created E-W alignedrelief and seaways between these volca-noes. The part of each volcano above wavebase was affected by erosion. Shorefaceerosion is reflected by flat erosional sur-faces located on the flanks or at the topof these volcanoes. The occurrence ofthe prograding wedge adjacent to the ero-sional surface suggests that the eroded sed-iments were contemporaneously depositedbelow the wave base level. Thicker clas-tic wedges develop radially from PentaPalummo and Mirabile volcanoes alongan approximately 15-km-long coastal areaand prograde toward the sea. The thick-ness of these wedges reaches a maximumof 120 m and extends approximately 4 kmaway from the volcano, suggesting volu-minous source areas. The wedges filledthe isolated basins between the volcanoesand formed the continental shelf. Weath-ering and erosion of pre-existing, poorlyor non welded, syn-eruptive deposits cansimply release the original pyroclasts orautoclasts and rapidly provide large vol-umes of recycled material. Consequentlythe great amount of volcaniclastic prod-ucts suggests that the original dimensionsof Penta Palummo and Mirabile volcanoeswere much larger than at present. The se-quence stratigraphic framework is impor-tant for establishing both the relationship ofprograding wedges to continuous shorefaceareas and the significance of bounding ero-sional surfaces in relation to relative sealevel changes. The paleo-geographic en-vironment, stratal architecture and plau-sible physical mechanism of sand trans-port and deposition suggest that the initialdeposition of the sedimentary banks wasaccompanied by a relative sea level fall

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(FST/LST), as documented by the down-ward shift of the toplap surfaces. Thiscaused a sudden and rapid influx of coarsegrained sediment. The mechanism of sandemplacement included direct fluvial supplyand reworking by coastal currents within anarrow seaway. The growth of the sedi-mentary banks was marked by a very rapid(750 cm·yr−1) basinward shift in the fore-sets. The rapid rise of relative sea levelproduced a rapid landward shift of sedi-mentation toward the volcanic centers andconsequently the wide surface at the topof the FST/LST prograding wedge, which,at this stage, corresponds to the maximumflooding surface. The TST is formed byup to 30-m-thick minor wedges that on-lap on the volcano craters and overlie theFST/LST. The sedimentary input dimin-ished and formed a condensed section inthe distal area. When the sedimentary unitscovered the volcanoes, all of the continen-tal shelf simultaneously experienced non-deposition due to the absence of source ar-eas and was rapidly drowned. This anal-ysis leads us to conclude that relative sealevel fluctuations were the main processcontrolling the architecture of the inter-eruptive sedimentary units. This recon-struction, based on the assumption that ero-sion occurred gradually during sea levelfall and rise, suggests that, during the inter-eruptive periods, sediment delivery dimin-ished and non-volcanic sediment transportand deposition processes dominated. Newvolcaniclastic particles created solely bysurface weathering and erosion (epiclasts),and biogenic particles, may also have beendeposited at this time.

4 Tectonics

The structure of the Campi Flegrei offshoreis characterized by folds and faults (Fig-ure 1) that formed during Late Quaternary[8, 9, 10, 1, 7, 11, 12, 4, 13, 14, 2, 5, 15]. InPozzuoli Bay three NW-SE folds (two an-ticlines and an intervening syncline) havebeen identified: the syncline controls thephysiography of the deepest part of the bay,the northern anticline extends along thecoast of Pozzuoli (Figure 1). The foldingbegan 8 Ka ago and calculated uplift ratesare up to 20 mm·yr−1 [5, 6]. Three mainfault systems occur: northeast-southwest,east-west, and northwest-southeast trend-ing faults (Figure 1). The NE-trendingfault swarm off Posillipo Hill and south-east of Campi Flegrei features a normalthrow and down throw the southeast block.It displace the 150 ka-old Gaia Bank vol-cano, the strictly controlled the location ofboth the Pia Bank volcano and the MonteDolce dome and offset the Neapolitan Yel-low Tuff with a cumulative throw is ap-proximately 50 m. The east-trending faultsare left lateral. One of these structuresoccurs in the northern part of the PentaPalummo continental shelf (Figure 1) andabruptly offsets the 12-9 Ka old prograd-ing wedge of the TST unit. The northwest-southeast faults display normal and right-lateral slip components. In the Bay ofPozzuoli northwest-southeast-trending enechelon segments of right-lateral normalfaults downthrow the central area of thebasin by a few meters at the same timeas the deposition of the first sedimentaryunit above the Neapolitan Yellow Tuff.One of the northwest-southeast faults dis-plays a dextral offset of the oldest vol-canic unit V4. The activity of this faultwas contemporaneous with the depositionof the 12-9 Ka old prograding wedge of the

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TST unit. In conclusion East-trending left-lateral faults, Northeast-trending normalfaults, Northwest-southeast right-lateralfaults and Northwest- trending folds arecompatible with the activity of an east-trending left-lateral transtensional shearzone [5, 6].

5 Discussion

The architecture of the Campania Ign-imbrites in the Bay of Naples is charac-terised by a thick wedge that overlies Mid-dle Pleistocene marine sediments. In theEastern part of Campi Flegrei the superim-position of the volcanoclastic wedges oc-curred in the slope/basin area. The lat-ter resulted from three geologically instan-taneous episodes that produced dramaticchanges in the physiographic environment.In particular, the syn-eruptive and inter-eruptive products of the Pre-CI tuffs and CItuffs completely filled the accommodationspace in the slope/basin area. In successionthe products of the NYT were initially de-posited in shallow water and in a sub-aerialsetting, where the thickness of the volcanowas greater than the water depth. Withinthe Bay of Pozzuoli the pyroclastic wedgedeposited in the slope/basin environmentthickens toward ENE, and its base dips byapproximately 11° landward. We main-tain that the volcano-tectonic subsidence iscontrolled by the activity of a NW-trendingfault indicated by the elongation of the Pre-CI tuffs depocenter at Campi Flegrei. Thisarchitecture suggests an increase in the ac-commodation space balanced by the depo-sition of the syn-eruptive and inter-eruptiveproducts of the volcano. In this case thepaleo-basin (approximately 350 m deep be-fore the deposition of the ignimbrite units)results filled. Consequently, we conclude,

that in area West of Naples the thick sin-eruptive and inter-eruptive ignimbrite de-posits fill both the accommodation spaceof the basinal environment and that createdby a tectonic-controlled subsidence. In or-der to understand the relationship betweenvolcanic activity and tectonic subsidenceduring the Late Quaternary, the authors re-constructed the accommodation curve fortwo specific points of the Naples Bay basin(Penta Palummo and Pozzuoli Bay). Theaccommodation space curve is the resultof the algebraic sum of the eustatic curve(Martinson et al., 1987), the curve of spacefilled by volcanics and sediments (calcu-lated assuming in the depth conversion avelocity of 1600-1800 m·s−1 compatiblewith very shallow mainly medium-grainedsediments and pyroclastic rocks) and thesubsidence curve (associated with faultingand folding). A basin analysis was per-formed [1, 22, 6, 13, 14] for the last 200 kaand the paleobathymetry was estimated byreconstructing the stratigraphic architec-ture and depositional environments. Sedi-ment accumulation is plotted through time.In the Penta Palummo area there was notectonic subsidence and the rate of the ac-commodation space changes according tothe eustatic curve minus the space filledby volcanics and sediments. Here MiddlePleistocene sedimentary strata extend hor-izontally from the intraslope basin north-ward, thus supporting a paleogeographicscenario preceding volcanism. The latteris characterized by a paleo-water depth ofapproximately 520 m (top of C2 sequence).The space between the paleo-sea-floor andthe sea level was filled by isolated mono-genetic volcanoes (V5, V4, V3) and clas-tic marine sediments until the present wa-ter depth of 75 m. Sedimentary units pro-grade north- and southward from these vol-canoes, indicating that the latter became

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the source areas for the sediments duringthe intervals of volcanic standstill. The ver-tical aggradation of both volcanic and clas-tic deposits gave rise to the emersion of thisarea during the last glacial maximum andto subaerial erosion when the curve dis-playing the vertical aggradation of the vol-canic and sedimentary deposits intersectedthe accommodation curve. The paleogeog-raphy of Pozzuoli Bay before the onset ofvolcanism is that of the adjacent intras-lope basin and Penta Palummo area char-acterized by a paleowater depth of approxi-mately 520 m. The subsidence curve showsa negligible value until 15 ka. Afterward aninstantaneous increase of subsidence dueto faulting and the Holocene enucleationof the syncline can be seen. The accom-modation curve presents a rapid increaseover the last 15 ka corresponding to basinsubsidence. The space filled by sedimentsincreased linearly producing a gradual de-crease in the water depth until this curveintersected the accommodation curve dur-ing the last glacial maximum producing anemersion of the area and subaerial erosion(documented by the unconformity at thetop of the Forced regression system tractLowstand system tract, FST-LST, [13]).The mean rate of sedimentary supply in-creased over the last 15 ka as indicatedby the thick Holocene succession (G3, G2,G1). Repeated volcanic events and a rapidinfill of the basin were documented forthe Penta Palummo area that experienceda dramatic physiographic change, from a

slope-basin (in the Middle Pleistocene) to ashelf (during Late Quaternary) due to vol-canic vertical aggradation. A more gradualphysiographic change from a slope-basinto a shelf occurred in Pozzuoli Bay wherethe basin infill, caused by clastic verticalaggradation, was later followed by a local-ized tectonic subsidence.

6 ConclusionsThese marine geological studies producedkey results for the understanding of the ge-ologic evolution of Campi Flegrei. We pro-vided a very detailed picture of the volcanicactivity in the marine area, started 200 ka,that records the underwater component ofonshore flows entering the sea.We question the existence of a caldera col-lapse on the basis of our structural andstratigraphic findings (the presumed ringfault is absent whereas a complex faultpattern does occur and the computed lo-cal volcano-tectonic subsidence coeval tothe CI and NYT eruptions resulted muchsmaller than that postulated for the subsid-ing caldera block).We fornished geological constrains (strati-graphic sequence characterized by imper-meable layers and active compressionalstructure at Pozzuoli producing fluid over-pressures) to a quantitative model forbradyseism at Campi Flegrei with implica-tions for future volcanic eruptions [23, 24,25].

References[1] A. Milia. Aggrading and prograding infill of a pery-tyrrhenian basin (Naples Bay,

Italy). Geo-Marine Letters, 19:237–244, 1999.

[2] A. Milia and M.M. Torrente. Tectonics and stratigraphic architecture of a pery-

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Tyrrhenian half-graben (Bay of Naples, Italy). Tectonophysics, 315:297–314, 1999.

[3] A. Milia and F. Giordano. Holocene stratigraphy and depositional architecture ofeastern Pozzuoli Bay (Eastern Tyrrhenian Sea margin, Italy): the influence of tec-tonics and wave-induced currents. Geo-Marine Letters, 22:42–50, 2002.

[4] A. Milia and M.M. Torrente. The influence of paleogeographic setting and crustalsubsidence on the architecture of ignimbrites in the Bay of Naples (Italy). Earthand Planetary Science Letters, 263:192–206, 2007.

[5] A. Milia and M.M. Torrente. Fold uplift and syn-kinematic stratal architectures ina region of active transtensional tectonics and volcanism, Eastern Tyrrhenian Sea.Bulletin of the Geological Society of America, 112:1531–1542, 2000.

[6] A. Milia and M.M. Torrente. Late Quaternary volcanism and transtensional tec-tonics at the Campania continental margin Bay of Naples, Italy. Mineralogy andPetrology, 79:49–65, 2003.

[7] A. Milia. The stratigraphic signature of volcanism off Campi Flegrei (Bay of NaplesItaly). Geological Society of America SP Pubbl., 464:155–170, 2010.

[8] A. Milia. Evoluzione tettono-stratigrafica di un bacino peritirrenico: Il Golfo diNapoli. PhD Thesis, page 184 p, 1996.

[9] A. Milia. Le unita piroclastiche tardo-quaternarie nel Golfo di Napoli. GeografiaFisica Dinamica Quaternaria, 21:147–153, 1998.

[10] A. Milia. Stratigrafia, strutture deformative e considerazioni sull’origine delle unitadeposizionali oloceniche del Golfo di Pozzuoli (Napoli). Bolletino Societa Geolog-ica Italiana, 117:777–787, 1998.

[11] A. Milia, F. Giordano, and G. Nardi. Stratigraphic and structural evolution ofNaples Harbour over the last 12 ka. Giornale di Geologia, 60:41–52, 1998.

[12] A. Milia, M.M Torrente, and G. Nardi. Recent tectonic and magmatic features offthe coast of Naples. Giornale di Geologia, 60:27–39, 1998.

[13] A. Milia, M.M. Torrente, and L. Giordano, F. and. Mirabile. Rapid changes of theaccommodation space in the Late Quaternary succession of Naples Bay, Italy: theinfluence of volcanism and tectonics. Development in volcanology, 9:53–68, 2006.

[14] A. Milia, M.M. Torrente, and F. Giordano. Active deformations and volcanismoffshore Campi Flegrei, Italy: new data from high resolution seismic reflectionprofiles. Marine Geology, 171:61–73, 2000.

[15] F. Bellucci, A. Milia, G. Rolandi, and M.M. Torrente. Structural control on the Up-per Pleistocene ignimbrite eruptions in the Neapolitan area (Italy): planar volcanotectonic faults versus caldera faults. 9:165–182, 2006.

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[16] L. Fedele, D. Insinga, A.T. Calvert, V. Morra, A. Perrotta, C. Scarpati, and S. Lep-ore. 40Ar/39Ar dating of tuff vents in the Campi Flegrei caldera: towards a newchronostratigraphic reconstruction of the volcanic activity during the Holocene.Epitome Geoitalia, (3):445, 2009.

[17] B.P. Kokelaar. The mechanism of Surtseyan volcanism. Journal of the GeologicalSociety of London, 140:939–944, 1983.

[18] D.G. Martinson, N.G. Pisias, J.D. Hays, J. Imbrie, T.C. Moore, and N.J. Shackleton.Age dating and orbital theory of the Ice Ages: Development of a high resolution 0to 300 000 year chronostratigraphy. Quaternary Research, 27:1–29, 1987.

[19] H.W. Posamentier and P. Vail. Eustatic control on clastic deposition. II. Sequenceand system tract models. SEPM, 42:125–154, 1988.

[20] A. Milia, F. Giordano, G. Nardi, and M.M. Torrente. Submarine slides off PosillipoHill (Naples, Italy). Giornale di Geologia, 60:17–25, 1998.

[21] A. Milia, M.M. Torrente, and F. Giordano. Gravitational instability of submarinevolcanoes offshore Campi Flegrei (Naples Bay, Italy). Development in volcanology,9:69–83, 2006.

[22] A. Milia and M.M. Torrente. Evoluzione tettonica della Penisola Sorrentina(margine peritirrenico campano). Bolletino Societa Geologica Italiana, 116:487–502, 1997.

[23] R.J. Bodnar, B. DeVivo, A. Lima, H.E. Belkin, C. Cannatelli, and A. Milia. Quan-titative evaluation of magma degassing and ground deformation (Bradyseism) atCampi, Flegrei, Italy. Geology, 35(9):791–794, 2007.

[24] B. De Vivo, A. Lima, R.I. Bodnar, A. Milia, and F.J. Spera. Il rischio eruzione neiCampi Flegrei. Le Scienze, (settembre):96–103, 2009.

[25] A. Lima, B DeVivo, F.J. Spera, R.J. Bodnar, A. Milia, C. Nunziata, H.E. Belkin, andC. Cannatelli. Thermodynamic model for uplift and deflation episodes (bradyseism)associated with magmatic–hydrothermal activity at the Campi Flegrei (Italy). EarthScience Review, 97:44–58, 2009.

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Figure 2: Description and interpretation of the eruptive and inter-eruptive units of CampiFlegrei.

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Research of Marine Sand Resources for BeachNourishment: an Applied result of Geological Mapof the Adriatic Sea (1:250000)

A. Correggiari1, M. Aguzzi1, F. Foglini1, A. Gallerani1, A. Remia1

1, Institute of Marine Sciences, CNR, Bologna, Italy2, ARPA Environmental Agency of Emilia Romagna, Bologna, [email protected]

Abstract

Shorelines and coastal development will be even more vulnerable to hazards inthe future. Need for offshore sand for nourishment will increase but volumes for sus-tainable shore protection are uncertain for many regions. Beach nourishment withsand derived from river or coastal borrow sites has been the preferred most commonmethod of shoreline stabilization method in Italy for several decades. This practicehas increased rapidly over the last decade to the point that the search of alternativesources of sand became an issue. Better understanding of the shelf geology can aidour ability to plan for sustainable use of offshore sands. Since the ’80 the Adriaticshelf has been studied to identify potential sand deposits available for extraction. In-formation about the geology of adriatic shelf regions, the character of the seafloor,and samples comprising the seafloor and subbottom have been aquired by ISMAR-CNR-Bologna as the result of several national and international projects includedthe Geological Adriatic Map (at the 1:250000 scale). Pleistocene/Holocene relativesea level rise submerged a wide portion of the northern and central Adriatic paleo-alluvial plain has been progressively drowned. For each step of the relative sea levelrise a barrier lagoon system has been identifed and the amount of sand has beenquantified.The potentially sand resources are available to a confined area in the cen-tral portion of the basin. The average grain size is fine sand, well to moderately wellsorted.

1 IntroductionSeveral factors may cause beach erosion,most of which are natural. Beachesare constantly moving, building up hereand eroding there, in response to oceano-graphic factors (waves, winds, storms, rel-ative sea level change and supply fluctu-ation). Some beaches are also destroyedby human activity when harbors or anyother anthropic structure disrupt the frag-ile balance of erosion and deposition in the

coastal environment. Out of the 5961 kmcoastline referred to in the Italian CoastalAtlas, 3612 km are sandy beaches, ofwhich more than 960 km are classifiedas subject to erosion [1]. Many coastalareas are facing chronic long-term shore-line erosion problems and eroding beachesrequire periodic beach replenishment tomaintain stable berms for coastal protec-tion and recreation. This paper reportson sand search investigations offshore as



strategic resources for beach restoration.Geologic factors control the location ofoffshore sand resources. For this reason,putting sand resource studies in the con-text of the geological setting of the areais critical for developing an ability to pre-dict sand potential availability. Demand isgrowing in Mediterranean and worldwidefor information about the geology of off-shore continental shelf regions, the charac-ter of the seafloor and sediments, compris-ing the seafloor and subbottom. The Adri-atic shelf, particularly offshore Emilia- Ro-magna and Veneto regions, has been the fo-cus of these studies for the past 25 yearswith widely varying results. Geophysi-cal studies to locate potential borrow ar-eas, identify sediment quantities, inves-tigate sediment characteristics, and rankcandidate sites are usually undertaken inmultiple phases. The method draws to-gether local geological information anddata to generate the final sand search de-liverables.

2 Adriatic coastal setting

On much of its extent the Adriatic coasthas been steadily eroding in the recent past.Sediment transport by the Po and otherApennine rivers between 1960-1980, wasreduced to about 30% of its previous values[2], due to the hydrogeological control ofthe catchment areas and to dam construc-tion (artificial lakes, etc.) accompained byintense quarrying of graveland sand fromriverbeds. These factors have led to an en-hanced erosive activity in the coastal envi-ronment. The decrease of land erodibilityresulting from reforestation of the Italianpeninsula after the second Word War con-tributed to a reduced sediment supply tothe sea. Growing shores are “nourished”

by material that has been eroded fromsomewhere else. Any attempt to reducecoastal erosion in one area will result in re-duced deposition elsewhere, “starving” an-other shoreline. Erosion and accretion aretherefore two faces of the same process,and their balance may change at extremelyslow rates or make dramatic changes in theshoreline within a human lifetime. Sandbedload that used to flow down rivers con-tributing to beach maintenanceis no longerreaching the coast, resulting in a substan-tial narrowing of the beach area therebyaffecting also the recreational opportuni-ties. Since the 1960s several strategies toprevent beach erosion have been appliedon the Italian coasts. Attached and de-tached breakwaters, groins, jetties built onthe coast have changed the natural phys-iography of the shoreline partially inhibit-ing the flow of beach sand by longshoredrift. These features may actually accel-erate erosion or change the ways in whichthe shoreline can be used. In fact in someareas of the north Adriatic coast, the break-waters installed to stop beach erosion havebeen so effective that the beach has becomea mud flat with severe environmental pol-lution problems [3]. Along the Adriaticcoast, in addition to the construction of sta-ble beach protections, nourishment opera-tions contributed to preserve beaches fromerosion. Protective structures occupy about35% of the 1630 km of the Italian Adri-atic coast and large supply of suitable sandused for beaches accretion was mined fromriver beds until 1984 when this activity wasalmost forbidden. In a period of decreas-ing sediment supply a good strategy is tosearch an alternative source of sand outsidethe coastal and river system. In Italy onlyin the recent years offshore sand becomethe main source for beach nourishment.

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Figure 1: Wide portion of the northern and central Adriatic alluvial plain of the glacialtime has been progressively drowned during the late Pleistocene/Holocene relative sealevel rise with concurrent widening of the continental shelf area of the Adriatic. Thedepth/time plot is referred to the most importat drowned barrier lagoon systems in theAdriatic basin.

3 Late Quaternary Geo-logical setting of theAdriatic

The Synthetic geological mapping pro-vides the basis for any applied environ-mental or natural resources study by mak-ing basis information available to widerange of end users. In offshore geologi-cal mapping, extensive areas can be cov-ered at much smaller scale than those usedfor geological mapping on land becauseof the large costs implied. We must im-

prove knowledge about the marine envi-ronment in order to understand the impactof human activities on the sea and to en-sure that various human projects are im-plemented in a sustainable way. Most Eu-ropean countries have extensive geologicalmapping project for their offhore ExclusiveEconomic Zone. With the Geological map-ping project of the Italian Seas, in collabo-ration with ISPRA (ex APAT) Servizio Ge-ologico d’Italia, ISMAR CNR Bologna ex-tended the geological mapping to the en-tire italian portion of the Adriatic basin.The modern Adriatic Sea is a narrow epi-

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Figure 2: Schematic evolution of a barrier lagoon system during trangressive erosionalprocesses.

continental basin with a low longitudinaltopographic gradient (ca 0.02°), whereasthe maximum shelf gradient along the cen-tral Adriatic is on the order of 0.5°. Dur-ing the late Pleistocene/Holocene relativesea level rise (between ca 18 and 5.5 kyrBP) [4, 5, 6, 7, 8] wide portion of thenorthern and central Adriatic alluvial plainof the glacial time has been progressivelydrowned, with concurrent widening of thecontinental shelf area of the Adriatic (Fig-ure 1). Across the low-gradient northernshelf, the stepwise, high-amplitude relativesea-level rise favoured the deposition andin-place drowning of different generationsof transgressive barrier–lagoon systems.Along the western side of the Adriaticshelf and seaward of the modern shoreline,the late-Holocene mud wedge, a continu-

ous belt of deltaic and shallow-marine de-posits, overlies the available transgressivesand deposits. The exploitable trangressivesand bodies comprising old beach deposits,are outcrop only in the axial part of thebasin far from the recent muddy sediment.

4 Description of potentialbeach compatible de-posits

The comprehensive review and analysisof geological, geophysical, and geospa-tial data provides new insight into sandsearch methodologies for offshore sand re-sources [9]. Using the Adriatic shelf ge-ological mapping project, benefits of thereview and analysis of acquired geological

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Marine Geology

Figure 3: The ravinement surface, a peculiar sedimentary shell debris in the transgres-sive deposit caused by waves erosion as relative sea level rises and the shoreline moveslandwards. The vibracores were sampled in a drowened barrier lagoon system marinesand offshore Emilia-Romagna region. ([8], Correggiari et al. in press)

datasets become manifest. During the lastdecades the increasing amount of data ac-quired by ISMAR CNR Bologna providesunique opportunities to summarize knowl-edge of geology and shelf geomorphologywith existing geotechnical and geophysicaldata that facilitate identification of sand re-sources. This kind of understanding ab-breviates the need to conduct random geo-physical and sampling surveys over largeexpanses of the seabed and is more efficientand economical because only potential de-posits are targeted. Some types of offshoresites can be described as linear sand bod-ies, including remnant shoal features, ebbor flood tidal shoals, drowned barrier is-lands, oblique sand ridges, longshore bars,trough sand accumulations, and migratory

sand spits attached or unattached to tidalinlets. In the northern Adriatic coastal ar-eas several morphological and sedimento-logical investigations have been carried outalong active barrier islands in order to eval-uate the sand reservoir potential associatedwith ebb-tidal deltas [10].The preservation potential of a trangressivebarrier/lagoon system in the low gradientadriatic shelf is limited to its basal portionand is function of its original thickness advolume. The Figure 2 shows the schematicevolution of a barrier lagoon system andpoints out the importance of sediment fa-cies characterisation of each sand deposit[11]. The ravinement surface, a pecu-liar sedimentary signature in the transgres-sive deposit, forms through waves erosion

394


Figure 4: Chirp sonar profiles, and vibracore of a sand deposit in the central Adriaticaround 80-90 metres water depth. In yellow the sand available. The deposit thicknessriches up to 4 m and is considerably homogeneus in terms of composition and grain sizeas shown in plots and map.

as relative sea level rises and the shore-line moves landwards, causing reworkingof both older and newly deposited sedimenton the shoreface, and separating non ma-rine (below) from marine (above) deposits(Figure 2). The ravinement surface is typ-ically associated to shelly sands and hashdeposits largely made up by mollusc re-main sourced from paralic to fully marineenvironments. In the transgressive sanddeposit used for nourishment this bioclas-tic lag may create some problems duringdredging operations: the high shells con-centration can block the fluidized sedimentduring the pumping process. [8].The Adriatic available borrow sand de-posits lays in patches inside paleo-barrier

lagoon systems and comprise sedimentclassified as fine sand (D50=0,160 mm)well to moderately well sorted. The min-eralogical and chemical composition ofAdriatic sand deposits classifies them aslitharenites, with a variable mixture ofcabonates, and silicates. Carbonates oc-curred in sediments as detrital granules ofcalcite or dolomite frequently associatedwith shell fragments [8, 12, 13]. Three ex-ample of sand research results are shownin Figure 4 and Figure 5. The first onecomprise several patches of transgressivedeposits with positive bathymetry at 80-90m water depth in central Adriatic (Figure4). They represent a reworked complexcoastal wedge with barriers lagoon envi-

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Figure 5: In the map 3 examples of transgressive deposits where borrow sites for sandextraction have been identified. The number 1 is described in Figure 4. The number 2 isrelated to offshore of Emilia-Romagna region and identified with A and C, while number3 describes the starved northern shelf were asymmetric large sand waves contribute tothe sand reservoir of the Adriatic basin.

ronment dated around 14-16 calibrated kyrBP [14, 15]. The second one is representedby another group of transgressive depositsoffshore Emilia-Romagna region studiedby ARPA Ingegneria Ambientale Emilia-Romagna and ISMAR since 1984 alreadyused as borrow sites for beaches nourish-ment [16, 17, 18, 19]. Several outcropsof trangressive lithosomes, located from 36m to 42 m water depth, has been datedbetween 8 to 12 calibrated kyrs BP (Fig-ure 5). The third relict system of starvedand reworked sand deposits is located off-shore northern coast of the Adriatic basinand has been studied by a collaborativeproject by Regione del Veneto and ISMARCNR Bologna with geophysical and geog-nostic surveys [6, 20, 13]. It is importantto note that while the majority of potential

Adriatic borrow deposits identified consistof ridges and remnants of barrier lagoonalsystem, in the future it is likely that therange of deposit types will be expanded toinclude paleo-channels, paleo-deltas, andother buried sand deposits.The volume of the entire potental fine sandavailable reservoir outcropping in the ital-ian portion of the adriatic shelf seafloor hasbeen extimated in ca. 240 x106 cubic me-tres.

5 Conclusions

Compilation of the surficial marine geo-logical maps, using high-resolution seismicprofiles, with the addition of new narrowgrid detailed geophysical suveys an sedi-

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ment vibracores in targeted locations, is aneffective way to evaluate potential borrowsites on any continental shelf.Offshore sand resource, as any other non-renewable resource, must be managed ona long-term, large scale, wide basis to en-sure that environmental damage will notoccur as a result of continual and prolongeduse. Sand sources that are to be used re-

peatedly may require additional biologicaland physical monitoring to avoid unaccept-able impacts to the marine and coastal en-vironments. For these reasons it is neces-sary to address future efforts through im-proving monitoring protocols to evaluatethe long-term impact of offshore dredgingoperations on the marine environments.

References[1] E. Valpreda and U. Simeoni. Assessment of coastal erosion susceptibility at the

national scale: the Italian case. J Coastal Conserv, 9(1):43–48, 2003.

[2] AQUATER. Studio generale per la difesa delle coste prima fase. Rapporti di settore.Regione Marche. II, 1984.

[3] A. Correggiari, F. Frascari, S. Miserocchi, and D. Fontana. Breakwaters and eu-trophication along the Emilia-Romagna coast. pages 277–290, 1992.

[4] F. Trincardi, A. Correggiari, and M. Roveri. Late Quaternary transgressive erosionand deposition in a modern epicontinental shelf: The Adriatic semienclosed basin.Geo-Marine Letters, 14(1):41–51, 1994.

[5] F. Trincardi, A. Cattaneo, A. Asioli, A. Correggiari, and L. Langone. Stratigra-phy of the late-Quaternary deposits in the central Adriatic basin and the record ofshort-term climatic events. Palaeoenvironmental Analysis of Italian Crater Lakeand Adriatic Sediments. Memorie dell’Istituto Italiano di Idrobiologia,, 55:39–70,1996.

[6] A. Correggiari, M.E. Field, and F. Trincardi. Late-Quaternary Transgressive largedunes on the sediment-starved Adriatic shelf. in M. De Batist and P. Jacobs, (eds.)Geology of Siliciclastic Shelf Seas Geological Society of London Special Pubbl.,117:155–169, 1996.

[7] A. Correggiari, M. Roveri, and F. Trincardi. Late Pleistocene and Holocene evo-lution of the north Adriatic sea. II Quaternario - Italian Journal of QuaternarySciences AIQUA, 9(2):697–704, 1996.

[8] A. Correggiari, D. Carra, A. Cattaneo, D. Penitenti, and F. Trincardi. Caratter-izzazione delle aree di prelievo dei sedimenti a mare. Programma di messa in si-curezza dei tratti critici del litorale Emiliano-Romagnolo mediante ripascimentocon sabbie sottomarine. Arpa Ingegneria Ambientale - Regione Emilia Romagna,Relazione Specialiastica, page 71, 2001.

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[9] C.W. Finkl, J.L. Andrews, T.J. Campbell, L. Benedet, and J.P. Waters. Applyinggeologic concepts coupled with historical data sets in a MIS framework to prospectfor beach-compatible sands on the inner continental shelf: the eastern Texas Gulfcoast. Journal of Coastal Research, 20(2):533–549, 2004.

[10] G. Fontolan, S. Pillon, F.Delli Quadri, and A. Bezzi. Sediment storage in the north-ern Adriatic ebb-tidal deltas, Italy: sand use potential and GIS database. Journal ofCoastal Research, 50:917–921, 2007.

[11] S. Penland, R. Boyd, and J.R. Suter. Transgressive depositional systems of theMississipi delta plain: a model for barrier shoreline shelf sand evolution. Journalof Sedimentary Petrology, 58(6):932–949, 1988.

[12] A. Correggiari, A. Remia, and F. Foglini. Progetto di caratterizzazione dei depositisabbiosi sommersi presenti sulla piattaforma alto adriatica potenzialmente sfrut-tabili come cave di prestito per il ripascimento costiero nell’ambito del progettoPRASTAVO. Primo SAL stato avanzamento lavori. Relazione tecnica, page 38,2007.

[13] A. Correggiari, A. Remia, and A. Gallerani. Esecuzione di analisi granulometrichee di suscettivita magnetica nell’ambito di Progetti per il ripascimento costiero. Re-lazione finale, 2008.

[14] A. Correggiari and A. Remia. Ricerca ed individuazione di depositi sabbiosi inAdriatico Centrale. Relazione Tecnica CNR, page 51, 2005.

[15] A. Correggiari and A. Cattaneo. Quality and quantity of sand deposits on the Adri-atic continental shelf. EMSAGG-CRIA Conference 7-8 Maggio 2009, Roma, 2009.

[16] P. Colantoni, M. Preti, and B. Villani. Sistema deposizionale e linea di rivaolocenica sommersi in Adriatico al largo di Ravenna. Giornale di Geologia,52(1):1–18, 1990.

[17] M. Preti. Ripascimento di spiagge con sabbie sottomarine in Emilia-Romagna.Studi Costieri, 5:107–134, 2002.

[18] Various Authors. BEACHMED-e http://www.beachmed.it/Beachmede/Pubblications/tabid/115/Default.aspx. 2008.

[19] A. Correggiari, M. Aguzzi, A. Remia, and M. Preti. Caratteristiche sedimento-logiche e stratigrafiche dei giacimenti sabbiosi in Mare Adriatico Settentrionaleutilizzabili per il ripascimento costiero. Studi costieri, in press, 2011.

[20] G. Cecconi and G. Ardone. La protezione delle spiagge della laguna di Venezia. inAtti seminario Riqualificazionee salvaguiardia dei litorali: idee proposte confrontitra esperienze mediterranee, pages 58–65, 2003.

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http://www.beachmed.it/Beachmede/Pubblications/tabid/115/Default.aspx

http://www.beachmed.it/Beachmede/Pubblications/tabid/115/Default.aspx

Influence of Seawater Circulation on the Evolutionof Ultramafic Spreading Ridges

C. Boschi1, A. Dini1, G. Frueh-Green2

1, Institute of Geosciences and Earth Resources, CNR, Pisa, Italy2, Department of Earth Sciences, ETH-Zurich, Zurich, [email protected]

Abstract

A mid-oceanic ridge is an underwater mountain range formed by the divergingmotion of tectonic plates that triggers the production of new lithosphere and thespreading of seafloor. The mid-ocean ridges of the world are connected and forma single global ridge system. It represents the longest mountain chain in the world,totaling 60,000 km. Mid-ocean ridges are geologically active, with new magma con-stantly intruded, and erupted onto the ocean floor, along the ridge axes. If for somereason the magma supply stops for a period of time, the crust must stretch to matchthe plate motion producing multiple cracks (i.e. faults) in the lithosphere and largeexposure of deeper mantle rocks at the seafloor. These rocks, known as abyssalperidotites, due to the continuous interaction with seawater, are variably hydratedand transformed in serpentinite. Low-angle detachment faults, exposing the serpen-tinized mantle rocks at the seafloor, act as pathways for seawater allowing complexinteractions with ultramafic/mafic rocks at depth with formation of serpentinitic andtalc-rich rocks. Here, we illustrate our recent petrographic, geochemical and isotopicstudies on a peridotite-dominated underwater massif, the Atlantis Massif, located at30°N on the Mid-Atlantic Ridge. The consequences of its hydratation and alterationin relation to the geochemical and geodynamical evolution of this area are discussedin details.

1 Introduction

Following the theory of plate tectonics,the lithosphere is broken up into what arecalled tectonic plates that move in relationto one another at one of three types of plateboundaries: convergent (or collisional),divergent (also called spreading centers)and transform boundaries. Earthquakes,volcanic activity, mountain-building, andoceanic trench formation occur along plateboundaries.At divergent boundaries, two plates moveapart from each other and the space that

this creates is filled with new lithospheresourced from magma that forms below,forming a massive underwater mountainrange, the oceanic ridge system. If forsome reason the magma supply stops fora period of time the crust must stretch tomatch the plate motion. If the crack is notvertical, it almost never is, the lower part ofthe crust can be pulled sideways out fromunder the upper layer along a dipping fault(so called detachment fault) and exposedeeper mantle rocks at the seafloor, theabyssal peridotite. This type of rocks cropout frequently in slow to ultraslow spread-


Marine Geology

Figure 1: Schematic representation of the history of oceanic lithosphere, from its birth atspreading ridge to the ”grave” at convergent margin (subduction zone). Major processesdiscussed in the text are reported.

ing ridge environments that are character-ized by low magma supply and/or com-plex tectonic processes related to spread-ing. In these environments, they maycomprise ∼20% or more of the oceaniccrust. Oceanic lithosphere newly formedat spreading ridges is variably geochemi-cally and mineralogically modified by in-teraction with seawater. Then it moves, asa belt conveyor, for hundreds of kilome-ters to the convergent boundaries, whereduring subduction, it releases several ele-ments to the upper plate (Figure 1). Forthis reason, the understanding of seawater-oceanic lithosphere interaction is funda-mental not only for processes occurring atspreading ridges (hydration of lithosphere,changes in lithosphere rheology, modifi-cation of ocean chemistry, formation ofblack-smokers and ore deposits, etc.), butalso for the spectacular geological pro-cesses that take place where the oceanic

plates subduct into the mantle (hydration ofupper plate by fluids released from the sub-ducted lithosphere, production of arc mag-matism, formation of giant metal deposits,etc.).Taking into account this scenario, the in-teraction with seawater and the consequenthydration of the abyssal peridotites at slowspreading ridges is a fundamental process(so called serpentinization) that has signifi-cant geophysical, geochemical and biolog-ical importance for both the global marinesystem and the subduction zone environ-ments. Hydration is accompanied by a de-crease in bulk density and a change in rhe-ology that directly affect the strength andphysical properties of the mantle, the mag-netic and gravity signatures, and the seis-mic velocities [3].The depth to which serpentinization mayoccur is controlled by the depth to whichseawater can penetrate into the oceanic

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Figure 2: Plate boundary geometry and seafloor morphology near the intersection of theMid-Atlantic Ridge (MAR) and the Atlantis Transform Fault. Broad, elevated massifswith spreading-parallel corrugations in this area are interpreted as oceanic core com-plexes (modified from [1]).

crust and upper mantle. Tectonic processesand fracture permeabilities largely controlthe depth of seawater circulation.Extreme extension of oceanic lithosphereduring seafloor spreading at slow to ul-traslow spreading ridges creates oceaniccore complexes (OCCs) that are broad,elevated massifs (few tens of kilometersacross) where deep crustal and/or uppermantle rocks have been unroofed, upliftedand consequently altered. One of the moststudied oceanic core complex is the At-lantis Massif, located at 30°N at the inter-section of the Mid-Atlantic Ridge (MAR)and the Atlantis Transform Fault (Figure2). This dome-like massif has been thesubject of different oceanic expeditions:

in particular, the southern and the LCHFwere mapped and sampled during threecruises: AT3-60 (MARVEL expedition,2000, [4]) and AT7-34 [5] using the sub-mersible Alvin with the R/V Atlantis andin 2005 using the remotely operated vehi-cles (ROV) Hercules and Argus onboardthe R/V R.H. Brown.The multidisciplinary project, led by Deb-bie Kelley in collaboration with differentinstitutes of research including IMP-ETH(Switzerland) and IGG-CNR (Pisa, Italy)focused on the geological and biologicalconsequences of the interaction betweenseawater and the Atlantis massif. One ofthe aspects that we investigated concernsthe interaction between seawater and peri-

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Figure 3: Hydrothermal vents in white and black. Photomosaic (courtesy of M. Elendand D. Kelley, U. Washington) of a structure, composed of carbonate and over 10 m inheight, typical of those at Lost City identified by [2]. Water depth here is 700–800 m(modified from [2]).

dotites along the 100 m thick detachmentfault responsible for the uplift of the mas-sif. Here, we summarize our results high-lighting the importance of our research.

2 The Atlantis Massif

The dome-like Atlantis Massif is locatedat 30°N at the intersection of the Mid-Atlantic Ridge (MAR) and the AtlantisTransform Fault [6]. The central dome

of the massif shows a distinct corrugatedmorphology, which is interpreted as thesurface expression of a low-angle detach-ment fault that led to uplift and expo-sure of lower crustal and upper mantle se-quences over the past 1.5–2 Myr. Thedomed morphology and exposure of vari-ably altered and deformed gabbros andperidotites during phases of asymmetricextension and detachment faulting are con-sidered key components that define oceaniccore complexes (OCCs). To the south,

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the Atlantis Massif is truncated by a steep,faulted escarpment with >3800 m of reliefadjacent to the Atlantis Transform Faultvalley. The southern ridge has experi-enced significantly greater uplift than thecentral portion of the massif and shoalsto 730 m below sea level. An impres-sive hydrothermal field, the so called LostCity Hydrothermal Field (LCHF), lies ona terrace at the top of this southern ridgeand hosts numerous active and inactivecarbonate-brucite chimneys that tower upto 60 m above the seafloor (Figure 3).The LCHF is the surface expression ofwarm (40–90°C), high pH (9–11) fluidsemanating from fault zones that tap a re-gion of active serpentinization in the un-derlying peridotites [2, 5]. The southernridge of the massif consists primarily ofvariably altered and deformed peridotites(70% of total samples) that have been in-truded by smaller bodies of gabbro, pyrox-enite, and minor basalt, and are coveredwith a flat-lying, 1–2 m thick sedimen-tary sequence. The peridotites are primar-ily depleted spinel harzburgites, consistingof olivine, orthopyroxene, and chromiumspinel with minor clinopyroxene. Therocks are highly serpentinized (from 70%to 100%) primary olivine and orthopyrox-ene are replaced by serpentine and mag-netite, and minor (<5 vol%) chlorite, am-phibole and talc. Field studies in 2003provided detailed observations and sam-ples of a well-defined, continuous, low-angle detachment fault at the top of thesouth wall of the AM [1]. The fault zoneis 100 m thick and is marked by vari-ably deformed, talc- and/or amphibole-richfault rocks. The alteration to form talc-and amphibole-rich rocks occurs locallythroughout the southern wall but is a keyaspect of the detachment fault (Figure 4).

3 The detachment zone

The detachment fault zone is a fracturedzone in which rocks on one side of thefracture move with respect to rocks on theother side. This is also a locus where flu-ids are focused and rock alteration is perva-sive. Deformation along detachment shearzones is intimately connected to the tec-tonic evolution of the core complex and tothe evolving geometry of the shear zone.The Atlantis detachment fault zone is char-acterized by the occurrences of a pecu-liar rock types mostly made by a very softmineral, the talc (Mg3Si4O10(OH)2). Thisdistinctly mechanically weak phase facili-tates the dislocation along the detachmentand lowers the shear strength. Recently,new experiments to characterize the me-chanical behavior of talc show that thepresence of even small amounts of talccan substantially weaken the volumes ofrock, affecting its behavior and evolutionof shear zones [8]. Our petrological andgeochemical studies revealed those talc-rich rocks are resulting from a dehydrationand Si-metasomatism of previous serpen-tinized peridotite rocks [7], following thereaction:

Serpentine + 2SiO2 = Talc + H2O (1)

Such a reaction is generally considered aprograde reaction taking place in the pres-ence of SiO2-rich fluids at temperaturesof about 300-350°C ([9] and referencestherein). Furthermore, [10] presented ex-periments of the permeability evolution ofan actively dehydrating serpentinite andshowed that dehydration of serpentiniteleads to a large transitory increase in poros-ity and permeability, an observation thathas important implications for naturallydehydrating systems in subducting slabs

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Figure 4: Interpretative cross section of the Atlantis Massif (no vertical exaggeration),with detailed areas showing fluid pathways, metasomatic zones, and extent of serpen-tinization (light green shaded region) related to detachment faulting and steep normalfaults (modified from Boschi et al. [7]). Box A: detail of the narrow shear zone (<100m) along the detachment surface (in red-yellow) characterized by heterogeneous, vari-ably altered and deformed gabbroic and peridotite lithologies and with extensive synk-inematic metasomatism. Fluids were focused along the detachment and through discreteductile shear zones triggering metasomatism of serpentinites and gabbros. The result-ing talc-amphibole schists enclose lenses of relic, locally less deformed serpentinite andgabbroic rocks. The footwall was affected by a diffuse and static metasomatism mainlydriven by a cataclastic network of fractures.

and in middle to lower-crustal metamor-phic regimes. Together with these pecu-liar rocks, the Atlantis detachment zoneis characterized by amphibole-rich rocks(with mafic protolith). These close spa-tial association of talc- and amphibole-richrocks suggested a local hydrothermal re-action between mafic rocks (gabbros) andseawater under greenschist-facies condi-tions along the detachment forming the am-phibole schist, releasing silica and causingSi metasomatism and talc formation in the

neighboring serpentinites (forming the talcschist Figure 4A and 5).

4 Boron isotope studyDuring the last 20 years boron isotopeshave increasingly been used as geochem-ical tracers in petrogenetic and ore depositstudies, and for modeling geochemical cy-cles in the Earth’s mantle, crust and oceans.In spite of the increasing interest in un-derstanding serpentinites geochemistry, the

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Figure 5: Three-dimensional representation of major element distribution of talc-rich(blue) and amphibole-rich (red) rocks together with Atlantis Massif serpentinites (green)and gabbros (yellow, see Boschi et al.[7] for details). The talc and amphibole schistsshow MgO and Al2O3 between those of serpentinites and gabbros. In the binary plotMgO versus Al2O3 (projection xz), there is a clear inverse correlation between the twoelements. Moreover, concentrations of amphibole-rich samples are closer to the AtlantisMassif gabbros and concentrations of talc-rich samples to the Atlantis Massif serpen-tinites. By contrast, SiO2 shows no correlation with the other two elements (projectionsxy and yz), suggesting strong remobilization during the metasomatism. Talc-rich rocks,due to the elevated stoichiometric concentration of Si in the crystal structure, are mostenriched in SiO2.

B-isotope composition of oceanic serpen-tinites remains poorly documented. Iso-topic data on this potentially importantboron reservoir is crucial to properly modelboron isotope systematics during metaso-matic/magmatic processes in subductionzones and to estimate the global flux ofboron and its isotopic fractionation duringseawater-rock interaction in oceanic envi-ronments. Since the 1990’s, researchersof IGG-CNR (Pisa) developed an analyth-ical method for the determination of boronisotopes. Boron isotope compositions are

measured at IGG-CNR (Pisa) using a VGIsomass 54E positive thermal ionizationmass spectrometer, following separation ofboron by ion-exchange procedures as de-scribed by [11]. Boron isotope composi-tion is expressed by the notation:

δ11B =[

(11B/10B)sample

(11B/10B)stdSRM951− 1

]× 103,

where(11B/10B

)stdSRM951

indicates theisotopic ratio of the international stan-dard NIST SRM 951 (4.04362 ± 0.001372s). During serpentinization of peridotites,

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Marine Geology

part of the boron contained in seawater(ca. 4.5 µg · g−1 most of it as trigonalspecies with δ11B = +39.5�) is incor-porated in serpentine minerals as tetrahe-dral species, producing variably enrichedserpentinites (boron in the range 34-91µg · g−1) with a fractionated isotopic com-position (δ11B = +11 ÷ +16�). Inthis way, the originally boron-poor peri-dotites (ca. 0.05-1 µg · g−1) were trans-formed in a strongly enriched boron reser-voir. Our studies [12] indicate that ex-tensive serpentinization of abyssal peri-dotites was a seawater-dominated processthat occurred predominately at tempera-tures of 150–250 °C and at high inte-grated water/rock ratios. Talc and amphi-bole formation along the detachment faultwas controlled by the access of Si-rich flu-ids derived through seawater–gabbro in-teractions. Replacement of serpentine bytalc and amphibole resulted in boron loss(talc- and amphibole-rich fault rocks con-tain only 3-30 µg · g−1) and significantlowering of δ11Bvalues(9to10�), whichwe modeled as the product of progres-sive extraction of boron. Completion ofthese processes produced the peculiar fea-ture of the Atlantis Massif, where seawa-ter continued to circulate through the ser-pentinitic basement introducing additionalcomplexities. In fact, present-day seawa-ter circulation is responsible for the for-mation of the spectacular low-temperature(max. 90°C), high-pH (up to 11) LostCity Hydrothermal Field [13]. These pe-culiar fluids form carbonate-brucite veinsand fissures into the serpentinitic base-ment and, when discharged at seafloor, pro-duce beautiful carbonate-brucite chimneysup to 60 m in height (Figure 3). Flu-ids issued at Lost City display the low-est boron concentrations ever measured inmarine hydrothermal fluids (0.4 µg · g−1

with respect to the average 5 µg · g−1

of ”normal” black smokers) coupled withsignificantly low boron isotope composi-tion (δ11B = +25�). This behaviour iscontrolled by the precipitation of brucite,an efficient sink for boron, that is sta-ble only under particular physico-chemicalconditions. Our results have strong im-plications on understanding differences be-tween chemistry of hydrothermal fluids atslow- and fast-spreading ridges that seemsto be controlled respectively by the pres-ence/absence of serpentinized peridotitesat seafloor. Marine hydrothermal vents rep-resent one of the main inputs to the oceansand the observed chemical differences maysignificantly influence the secular chemicalvariations of oceans.

5 Concluding remarks

The integrated field, petrological, geo-chemical and isotopic study of maficand ultramafic rocks exposed on thesouth wall of the Atlantis Massif pro-vides new insights into how major de-tachment shear zones evolve during thedevelopment of oceanic core complexesand demonstrates the interplay of flu-ids, mass transfer, and metamorphism instrain localization associated with this pro-cess. The talc-amphibole-chlorite-mineralassemblages and microstructures in thefault rocks indicate multiple stages of fluidinfiltration and high strain deformation inlimited domains. These minerals maycontribute to softening and lubricate my-lonitic fault zones, facilitate dislocationalong the detachment and lower its shearstrength, concentrate movement along thefaults, and allow these faults to remain ac-tive as “detachment faults”. Seawater/rockinteraction at ultramafic spreading ridges,

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like Atlantis Massif, produces a com-plex geochemical evolution of the origi-nal abyssal peridotites characterised by aninitial boron content enrichment and iso-tope composition increase (serpentiniza-tion) followed by a later boron contentdepletion and isotope composition low-

ering (Si-metasomatism along detachmentzone). Our research provides new knowl-edge on the geological evolution of oceaniclithosphere, how it is affected by seawatercirculation and how it affects the geochem-istry of marine hydrothermal vents.

References[1] J. A. Karson, E. A. Williams, G. L. Frueh-Green, D. S. Kelley, D. R. Yoerger, and

M. Jakuba. Detachment Shear Zone on the Atlantis Massif Core Complex, Mid-Atlantic Ridge 30°N. G3, 7(6), 2006.

[2] Kelley D.S. and et al. An off-axis hydrothermal vent field near the Mid-AtlanticRidge at 30°N. Nature, 412:145–149, 2001.

[3] G.L. Frueh-Green, J.A.D. Connolly, D.S. Kelley, A. Plas, and B. Grobety. Serpen-tinization of oceanic peridotites: Implications for geochemical cycles and biologicalactivity. The Subseafloor Biosphere at Mid-Ocean Ridges, Geophys. Monogr. Ser.,144:119 – 136, 2004.

[4] D. K. Blackman and et al. Geology of the Atlantis Massif (Mid-Atlantic Ridge,30°N): Implications for the evolution of an ultramafic oceanic core complex. Mar.Geophys. Res., 23:443–469, 2004.

[5] D.S. Kelley and et al. A serpentinite-hosted ecosystem: The Lost City Hydrother-mal Field. Science, 307:1428 –1434, 2005.

[6] J.R. Cann, D.K. Blackman, D.K. Smith, E. McAllister, B. Janssen, S. Mello,E. Avgerinos, A. R. Pascoe, and J. Escartın. Corrugated slip surfaces formed atNorth Atlantic ridge-transform intersections. Nature, 385:329–332, 1997.

[7] C. Boschi, G.L. Frueh-Green J.A. Karson, D.S. Kelley, and A. Delacour. Masstransfer and fluid flow during detachment faulting and development of an oceaniccore complex, Atlantis Massif (MAR 30°N). G3, 7, 2006.

[8] J. Escartın, M. Andreani, G. Hirth, and B. Evans. Relationships between the mi-crostructural evolution and the rheology of talc at elevated pressures and tempera-tures. Earth and Planetary Science Letters, 268:463–475, 2008.

[9] C. Boschi, G.L. Frueh-Green, and J. Escartın. Occurrence and significance ofserpentinite-hosted, talc-rich fault rocks in modern oceanic settings and ophiolitecomplexes. Ofioliti, 31(2):123–134, 2006.

[10] E. Tenthorey and S.F. Cox. Reaction-enhanced permeability during serpentinitedehydration. Geology, 31(10):921–924, 2003.

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[11] S. Tonarini, M. Pennisi, and W.P. Leeman. Precise boron isotopic analysis of com-plex silicate (rock) samples using alkali carbonate fusion and ion-exchange separa-tion. Chem. Geol., 142:129–137, 1997.

[12] C. Boschi, A. Dini, G.L. Fruh-Green, , and D.S. Kelley. Isotopic and elementexchange during serpentinization and metasomatism at the Atlantis Massif: Insightsfrom B and Sr isotope data. Geochim. Cosmochim. Acta, 72:1801–1823, 2008.

[13] G.L. Fruh-Green, D.S. Kelley, S.M. Bernasconi, J.A. Karson, K.A. Ludwig, D.A.Butterfield, C. Boschi, , and G. Proskuroski. 30,000 years of hydrothermal activityat the Lost City vent field. Science, 301:495–498, 2003.

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Tephrochronology of Deep Sea Marine Succes-sions: Unlocking the Last 1 Myrs of Explosive Vol-canic History in the Central Mediterranean Area

D.D. Insinga1, S. Tamburrino1, M. Sprovieri21, Institute for Coastal Marine Environment, CNR, Napoli, Italy2, Institute for Coastal Marine Environment, CNR, Capo Granitola (TP), Italy

[email protected]

Abstract

Tephrochronological research at IAMC is currently focusing on the study of deepsea marine successions cored in the southern Tyrrhenian Sea, the Sicily Channeland the Ionian Basin. The composite record results in a 1 Myr long successionwith a high-resolution and refined dating framework. The main scientific objec-tive of the work is to extract timing and consequences of volcanic activity in thecentral Mediterranean area from the marine record, by integrating accurate datingtechniques: tephrochronology, astronomical tuning and radiometric methods (40Ar-39Ar). Advanced analytical approaches to tephrostratigraphy that include chemicalcharacterisation through WDS-EPMA and LA-ICP-MS on single glass shards havebeen used and preliminary results were obtained on a number of the most recenttephra layers (<200 kyr) among the 70 recovered along the composite succession.This allowed us to start off with a new reference database of chemical analyses tocharacterize the distal products of major volcanic events occurred during the latePleistocene-Holocene and related to the explosive activity of the Campania Plain,the Aeolian islands, Pantelleria island and Mount Etna.

1 Introduction

Tephra layers originate from explosive vol-canic eruptions and are distributed by windor current action over wide areas. As thedeposition of a tephra layer is essentiallyinstantaneous on a geological timescale,these deposits are of major importancein stratigraphy because they provide asound basis for dating (tephrochronome-try) and also for correlation (tephrostratig-raphy). Tephrochronology (tephrostratig-raphy + tephrochronometry; [1]) can be ap-plied in several geological settings where

fresh volcaniclastic materials are interbed-ded in continental, lacustrine, marine plat-form and deep sea sedimentary sequences.In particular, the study of these horizons isa powerful tool to correlate and provide ab-solute ages in marine successions and toestablish a high-resolution event stratigra-phy and chronology in the framework ofbasin evolution. Tephra (from the Greekword meaning “ash”) is actually used asa collective term for all airborne pyro-clasts, including both airfall and pyroclas-tic flow material. Tephrochronologists whogenerally work with materials that are de-


Marine Geology

posited at considerable distance away fromthe volcanic source (distal tephras) are pri-marily concerned with tephra in ash-sizefragments (<2 mm). Tephrochronologi-cal research at the IAMC is currently fo-cusing on the study of deep sea marinesuccessions cored in the southern Tyrrhe-nian Sea (core MD012474G), in the SicilyChannel (ODP Leg 160 Site 963A) andin the Ionian Basin (core KC01B) (Figure1). The main scientific objective of thiswork is to “extract” the timing and con-sequences of volcanic activity in the cen-tral Mediterranean area from the marinerecord since the middle Pleistocene. Thegreat potential of these cored successionsin terms of tephrochronology is given bythe 1.1 My-long composite record with ahigh-resolution and refined dating frame-work, the downwind position of the coreswith respect to the major volcanic sourcesof the area and the recognition of about 70tephra layers suitable for chemical analysesand radiometric dating. This type of workcould lead to several implications that in-clude, for example:1. the availability of a new analytical ref-

erence database;2. the possibility of unravelling the history

of poorly known or unknown explosiveactivity on land from the marine record;

3. the patterns of ash dispersal in the cen-tral Mediterranean;

4. the intercalibration of independent ra-dioisotopic and astronomical datingmethods.

Here we present some preliminary resultsconcerning the chemical characterisationof five tephra layers that are found in thestudied record and have correlated withmajor events occurred during the last 200kyrs in the Campania Plain, at the AeolianIslands, at Pantelleria island and at MountEtna.

2 Tephra layers in the cen-tral Mediterranean area

The central Mediterranean area is an out-standing natural laboratory for tephra stud-ies because of the occurrence of a numberof highly explosive volcanoes active duringthe late Cenozoic. These vents are mostlyknown from the central-southern Italy, theHellenic arc (e.g. Santorini) and CentralAnatolia in Turkey. The tephra falloutof Hellenic and Anatolian volcanic erup-tions is dispersed only in the very east-ern part of the Mediterranean [5, 4] whilethe Italian volcanoes provide a more likelysource for tephras in the central Mediter-ranean area due to their relative proximityand the favourable westerly blowing winds(Figure 1). The Plio-Quaternary magma-tism in Italy occurred: a) along a NW-SEtrending extensional zone on the Tyrrhe-nian border of the Italian Peninsula that in-cludes the Roman Province (Vulsini, Vico,Sabatini and Colli Albani volcanoes), theErnici-Roccamonfina Province, the Cam-pania Province (Somma-Vesuvius, CampiFlegrei, Procida and Ischia volcanoes) andMount Vulture, located east of the south-ern Apennines ; b) in the southern Tyrrhe-nian sea with the Aeolian volcanic arcand seamounts ; c) in the Sicily Province,which includes Mount Etna and Pantelleriaisland in the Sicily channel ([2] and refer-ences therein).A chronogram of the activity of the vol-canic centers is shown in Figure 2. Theerupted products range from subalkaline(tholeiitic and calc-alkaline) to alkaline(sodic, potassic and ultrapotassic), frommafic to silicic, and from oversaturated tostrongly undersaturated in silica. Calc-alkaline and shoshonitic rocks are concen-trated in the Aeolian arc, Na-alkaline rocks

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Figure 1: Location of the studied cores and volcanic centers of the central Mediterraneanarea.

occur at Etna and Pantelleria while potassicand ultrapotassic rocks represent the mosttypical composition in the Roman, Roc-camonfina and Campania provinces. Sil-ica undersaturated rocks rich in both K2Oand Na2O are found in the Mount Vul-ture products [6]. These different rocks ofdifferent magmatic series developed in re-sponse to the various geodynamic settingsand mantle sources in the central Mediter-ranean region. Since the 1970s-1980s,numerous studies have produced tephros-tratigraphic frameworks for the last 200kyrs in the Ionian and Tyrrhenian sea (e.g.[5, 7, 8, 9, 10]). They have been pro-gressively refined over the years [11] (Ta-ble 1) with the most recent papers deal-ing with very high-resolution tephrostrati-graphic studies of deep basin [12, 13,14], shallow water [15] and lacustrine [16,17, 18, 19, 20, 21, 22] archives. Re-cently, tephrostratigraphic studies in thisregion have been addressed towards therefinement of palaeoclimatic studies (e.g.[23, 24, 25, 13, 26]). At the present,

there is no geochronological method bet-ter than a tephra marker for synchronisingpalaeoenvironmental records across the re-gions and for integrating different “eventstratigraphies”. Eruptive centers from theItalian volcanic regions, particularly ac-tive over the last 200 kyrs, have pro-duced very numerous pyroclastic depositson land and off-shore that are well suitedfor 40Ar/39Ar dating (sanidine-bearingtephras). Some of them are of particu-lar interest as they are contemporaneous tomajor climatic changes. This is especiallytrue for the Campanian Ignimbrite (CI),dated at 39 ka on proximal deposits [27,28] and 40 ka in the marine setting [25].This major volcanic event has produced amarker layer throughout the central-easternMediterranean Sea (tephra layer Y5, Table1), and possibly as far as the Greenland icecap, as testified by the marked peak in SO4found in GISP2 at the end of interstadial 9(just after the Laschamp event coincidingwith interstadial 10) [29]. Furthermore, alarge number of tephras are interbedded in

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Figure 2: Chronogram of the volcanic activity in the central Mediterranean area duringthe last 1.1 Myrs. Data from [2] and references therein. CVZ: Campania Volcanic Zoneafter [3].

the Mediterranean sediments ranging from0 to 50 Ka. These tephras were not datedbefore with the highly precise 40Ar/39Armethod, [30, 13]. The direct 40Ar/39Ardating of these young ash layers (<100 ka)will open the way for the high-resolutiontephrochronologic study of proximal anddistal volcanic deposits interlayered withincontinental and marine sequences used inpaleoclimatic reconstructions.Finally, tephras have proved to provide ro-bust absolute tie points for astronomicallyderived core chronology in several areas, inparticular in the Mediterranean region (e.g.CT 85-5 core, Ton-That et al., 2001), thenortheast Indian Ocean (e.g. OPD site 758,[31]) and the New Zealand margin (DSDP594, [32]).

3 Materials and methods

The sample set of this work is representedby three sedimentary successions cored inthe southern Tyrrhenian Sea, in the SicilyChannel and in the Ionian basin down toa maximum depth of ∼3600 meter. Thecomposite record results in a 1.1 Myrlong succession with a high-resolution andrefined dating framework mostly yieldedby the combination of astronomical tun-ing, environmental magnetism, stable iso-tope stratigraphy and radiometric meth-ods. About 70 tephras, mostly composedof pumices and glass shards were foundalong the entire sequence (Figure 3). Thetephrochronological results here presenteddeal with five layers of which three are

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Table 1: Tephrostratigraphic framework for the Mediterranean during the last 200 kyrs.Modified from [4].

from the Ionian basin (tephras I1, I3 andI9), one from the Sicily Channel (tephraSC1) and one from southern TyrrhenianSea (tephra T22). They were labelled fol-lowing an alpha numerical code indicatingthe location of the drilling site and theirstratigraphic position with respect to theother tephras recognised in the core. Pistoncore KC01B (37.04 m long) is consideredto be a reference core for the Pleistocenerecord in the Mediterranean. It was col-lected by the French R/V Marion Dufresnein 1991 (MD69 cruise) at a small ridge (thePisano Plateau-36°15.25’N, 17°34.44’E,3643 m depth) from the lower slope ofthe Calabrian Ridge in the Ionian Basin.Lithology [38], paleoclimatic record (San-voisin et al., 1993), high-resolution iso-

tope stratigraphy [39], magnetostratigra-phy [40] and astronomical calibration forthe last 1.1 Myrs [33] were performedon the cored succession. Coring distur-bances did not allow to study the upper-most 231 cm corresponding to the last 14kyr. An attempt of tephrochronology wasproposed by [33]: the author correlated 33tephra layers found in the core with knownevents on land or with other distal mark-ers just on the basis of their astronomi-cal age (Table 2). Recently, core KC01Bwas entirely re-sampled and more than 33tephras were recognised. Preliminary geo-chemical data obtained from several lay-ers of the last 200 kyr, allowed to clas-sify them for the first time thus recognisingtheir source event, [41]. Mixed geochemi-

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Table 2: Tephrochronology of core KCO1B proposed by [33].

cal populations related to two different vol-canic sources, moreover, have been oftendetected in the same tephras. Gravity coreMD01-2474G (13.9 m long) was retrievedby the French R/V Marion Dufresne in2001 at a structural high from the border ofthe Marsili Basin (39°10.44’N, 15°2.72’E,2131 m depth) in southern TyrrhenianSea. Ecobiostratigraphy, isotope stratig-raphy, 14C AMS dating and paleomag-netism were performed on the top 9 me-ters of core MD01-2474G and an age-depth model was constructed for the last70 kyr [34]. ODP site 963 (37°02.148’ N,13°10.686’ E 470.5 m depth) was drilled inthe Sicily Channel on a short ridge betweenthe Adventure Bank to the northwest and

the Gela basin to the southeast. The agemodel was assessed through oxygen iso-tope data of the 963 Site composite section[42] coupled with high resolution ecobios-tratigraphy studies [35, 36] for the last 430kyr.

3.1 Sampling and chemistry oftephra layers

Tephra samples were disaggregated in wa-ter and wet sieved at intervals of 63,90, 125 and 250 µm. Glass concen-trates were obtained through hand-pickingwith a microscope after a lithological anal-ysis of the materials, avoiding sampleswith vesicles, crystalline intergrowth and

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alteration. Mineral phases were takenmainly from those tephra layers wherefresh glass was not found. All thesegrains were then rinsed in distilled water,cleaned with an ultrasonic probe for twoto three minutes and mounted on epoxyresin and then polished. The major ele-ment content was obtained through elec-tron probe micro-analysis (EPMA). Thisenables grain-discrete determinations ofthe major elements within an individualglass shard. Measurements were made us-ing a CAMECA SX-50 electron micro-probe (WDS) at the IGAG-CNR (Istitutodi Geologia Ambientale e Geoingegneria-Consiglio Nazionale delle Ricerche) inRome. The accelerating voltage was 15kV, the beam current 15 µA and the spotsize 10 µm. Peak counting times for ma-jor elements were 20 seconds except for Fewhich was analysed for 30 seconds. In-strument calibration was based on interna-tional glass and mineral standards. Individ-ual analyses of glass shards with total oxidesums lower than 95 wt% were excluded.The data of accepted analyses of individ-ual tephra layers were then recalculatedto 100 wt%. Although WDS requires ahigher beam current and a longer countingtimes than EDS (energy dispersive spec-trometry), the former offers the advantageof sequential acquisition of elemental data,so that the degree of sodium loss (frequentduring EDS acquisition) can be tracked.Actually, this methodology is the most rec-ommended tool for determining the geo-chemical spectra of samples [30]. DuringEPMA analysis, back-scattered electronimages are usually taken to record the po-sition of each shard analysed and to carryout morphological observations which canbe used as correlation tools. Trace ele-ment analysis on each single shard was ob-tained through Laser Ablation-Inductively

Coupled Plasma-Mass Spectrometry (LA-ICP-MS) methodology using a Q-switchedNd:YAG laser, model Quantel (Brilliant)at the IGG (Istituto di Geoscienze eGeorisorse)-CNR in Pavia. The spot sizewas 25µm.Several criteria were used to identify theprimary origin of the studied tephras andthey include: (1) well-recognisable peakabundance of the glass fraction above thewhole lithic, crystal and bioclastic contentcoarser than 63 µm and (2) the identifica-tion, within each layer, of sizeable glasspopulations (>10 measurements) from themajor element content.

4 Results and discussion

4.1 Tephrochronology:tephrostratigraphy andtephrochronometry of thestudied layers

The analysed tephras are represented bymedium-to-fine dark grey ashes where theglass fraction is dominant. According totheir major element content and by usingthe TAS diagram and the CIPW norms,these layers have compositions rangingfrom rhyolites to trachytes (qz-norm) andtrachyphonolites with tephra T22 showinga wide range of variability (Table 3 andFigure 4). The recognition of the sourcearea for each analysed tephra was mainlybased on the comparison with publishedSEM-EDS and WDS (wavelength disper-sive spectrometry) data on single glassshards. In those cases where single glassshard chemical data were lacking, XRF (X-ray fluorescence) and ICP-MS whole rockdata were used. The combination of EPMAand LA-ICP-MS results finally allowed tobetter characterise the source event. This

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procedure can be considered still pioneeris-tic when dealing with tephrostratigraphicanalyses of marine successions. The “clas-sical” type of investigation takes only themajor oxide content into account. This ap-proach has often proved to be inadequateto explain the complexity of some eruptiveproducts and may lead to incorrect con-clusions. Otherwise, the availability of adatabase composed by more than 40 ele-ments for a single shard, may provide amuch wider range of information from asingle tephra than previous studies, allow-ing, for example, (1) to detect magmaticevolution of the sources and (2) to rec-ognize chemically different populations ofshards within one deposit which sometimesmay not be easily distinguishable just fromthe electron probe data alone. This ap-proach to the study of tephra layers fromthe cored successions might be necessary,if we consider that in the central Mediter-ranean area magmatic sources exhibit avery large compositional range of eruptedproducts.

4.1.1 Ionian Basin

Tephra I1 is a 4 cm-thick layer composedof light grey micropumices, black poorlyvesiculated obsidian, brown blocky glassshards and loose crystals of clinopyrox-ene and plagioclase. The glass fractionhas a trachytic (qz-normative) composi-tion with a Na-alkaline affinity (Figure 5).REE (Rare earth Elements) are fraction-ated while a Ti trough and a Pb spike canbe observed in the incompatible elementpatterns normalised to the primitive man-tle (Figure 5). These chemical featuresstrongly suggest an origin for tephra I1from the Mount Etna volcano. This re-sult, combined with an astronomical ageof 16.7 ka B.P. for I1 [33], allowed to

correlate this tephra with the Y1 distalmarker [5] or Et-1 [9], widespread bothin marine [12, 13] and lacustrine [16, 18]archives. The source event is retained tobe the Biancavilla Montalto Ignimbrite (orUnit D [43]) dated at ca. 15-16 ka B.P.(14C age [43]). Tephra I3 is about 4cm-thick layer formed of tubular and Y-shaped glass shards and subordinate mi-cropumices. Loose crystals of k-feldspar,biotite and clinopyroxene are also present.Tephra I3 has a trachytic-trachyphonoliticcomposition which is typical of the potas-sic series erupted in the Campania Plainduring the Late Pleistocene-Holocene (Fig-ure 6). The overall REE pattern analysedfor these deposits is characterised by a highdegree of fractionation with a (La/Yb)n ra-tio (where the subscript ”n” indicates nor-malization to chondritic abundances) rang-ing from ∼10 to∼17. Light rare earth el-ements (LREE) are strongly fractionatedwhilst heavy rare earth elements (HREE)give almost flat patterns (Figure 6). Eushows marked variations, with both posi-tive and negative anomalies [Eu/Eu*=0.30-1.4; Eu/Eu*=Eun/(SmnGdn)1/2] whichis typical in these rocks, where frac-tional crystallisation of K-feldspar is dom-inant (e.g.,[28]). The primitive mantle-normalised diagram (Figure 6) shows pro-gressively higher incompatible elementabundances in the analysed samples anddeeper Ba, Sr, and Ti troughs as the de-gree of differentiation increases. TephraI3, dated at 39.1 ka B.P. in core KC01B[33], can be correlated with the Y5 distalmarker [5] related to the Campanian Ign-imbrite event that occurred at Campi Fle-grei (∼39 ka B.P. [27, 28]). This erup-tion is considered to be the most catas-trophic eruption during the Quaternary inthe Mediterranean area. Analysis of singleshards allowed us to distinguish in tephra

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I3 between a “primitive” and “evolved” tra-chytic composition which indeed occurs inthe proximal outcrops [28]. Tephra I9 isa very pronounced layer in core KC01B(8 cm thick) and it is represented by thinelongated, tubular and platy glass shards.Loose crystals of biotite, clinpyroxene andK-feldspar are present. This layer has atrachytic composition and the major, traceand rare element content indicates a Cam-pania Plain provenance (Figure 7). Thisresult, combined with an age of 110.5 kaB.P. for the studied layer, suggest a cor-relation with the X6 tephra [5] dated ap-proximately at 110 ka B.P. [52, 24]. Thisdistal marker, widespread in the southernItaly domain [53, 19, 45], has been relatedto a major event occurred in the CampaniaPlain which experienced intense explosivevolcanism during that period [27].

4.1.2 Southern Tyrrhenian Sea

Tephra T22 (8 cm thick) is formed mainlyof dark scoria, light brown curvy, elon-gate and pumiceous glass shards. Theshards representative of this layer fall intoa large compositional field ranging frombasaltic trachy-andesite to rhyolite with ahigh-potassium calc-alcaline affinity (Fig-ure 8). REE of mafic and intermediaterocks are fractionated with a flat HREEpattern. Incompatible elements values nor-malized to primordial mantle give patternswith troughs at Nb and Sr, and peaks atTh, La, Nd and Gd. These chemical fea-tures suggest Lipari island (Aeolian Arc)as the source area for tephra T22 (40.6 ka)which might be related to the Brown Tuffunits [54, 55] and, in particular, with the“Punta del Perciato” formation (ca. 41 kaB.P. [56]).

4.1.3 Sicily Channel

Tephra SC1 (tephra ODP1 in [57], inpress), 4 cm thick, is represented mostlyby light grey tubular and Y-shaped glassshards and loose crystals (feldspar). Themajor element content of the glass fractionshows a bimodal composition: peralkalinerhyolites (Agpaitic Index >1) for the bot-tom samples and trachytes for the top sam-ples (Figure 9). Rhyolitic glass is pantel-leritic in composition. Overall, these fel-sic volcanic products are characterised byan enrichment in LREE, Rb, Th, Nb andZr (Figure 9). The main features of thechondrite-normalized REE patterns as thedifferentiation increases, are representedby the increase of total concentration ofREE, a slight increase of LREE/HREE ra-tios ([La/Yb]n=8.8) and a marked Eu neg-ative anomaly (Eu/Eu∗ = 0.6). Thesefeatures are typical of Pantelleria productsto which tephra SC1 can easily be corre-lated. In detail, this layer, dated at 42.5ka B.P. in the ODP record, may representthe signature in the Sicily Channel of theGreen Tuff event [58, 59] that occurred atca. 45-50 ka B.P. [60]. According to this,tephra SC1 corresponds to the distal ma-rine tephra layer Y6 [5], Table 1). Depositsrelated to this major event have been foundextensively in lacustrine archives towardsthe northeast [50].

5 Conclusion

The tephrochronological analysis of a 1.1Myr-long deep sea record, characterised bya refined dating framework, allowed us torecognise and correlate a number of tephralayers, out of the 70 found within the com-posite succession, with volcanic events onland. In this work we presented, in partic-

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ular, results concerning the major and traceelement content detected on single glassshards from five tephra layers that span thetime period ranging from ∼16 ka B.P. to∼110 ka B.P.. This allowed us to start offwith a new reference database of chemicalanalyses to characterize the distal productsof major volcanic events that occurred dur-ing the late Pleistocene-Holocene and thatare related to the explosive activity of theCampania Plain, the Aeolian islands, Pan-telleria island and Mount Etna.The main conclusions can be outlined asfollows:• the most recent tephra I1, dated at 16.7

ka B.P. in the KC01B astronomically-tuned succession, was related to Mount

Etna activity and correlated with theBiancavilla Montalto Ignimbrite event;

• tephra I3, dated at 39.1 ka B.P., has beencorrelated with the major event of theCampanian Ignimbrite eruption occurredat Campi Flegrei in the Campania Plain;

• tephra T22, dated at 40.6 ka B.P., hasbeen correlated with Lipari activity in theAeolian arc;

• tephra SC1, dated at 42.5 ka B.P., hasbeen correlated with the Green Tuff erup-tion occurred at Pantelleria island;

• tephra I9, dated at 110.5 ka B.P., rep-resents the most ancient layer here pre-sented. It has been correlated with a pre-ignimbritic event occurred in the Campa-nia Plain during the Late Pleistocene.

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Figure 3: Depth and age of tephra layers recovered in the KC01B, MD 012474G andLeg 160 ODP site 963 successions. Tephra layers presented in this work have been high-lighted. (1): after[33]; (2): after [34]; (3) after [35] and [36].

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Figure 4: Classification of the studied tephra layers from the composite record of thecentral Mediterranean according to TAS (total alkali/silica) diagram [37].

Figure 5: (a) Tephra I1 interbedded in marine deposits of core KC01B; (b) classificationof tephra I1 and comparison with the average compositional fields of tephra Y1 and theonland deposits of Biancavilla Montalto Ignimbrite eruption; (c) Na2O/K2O diagram toshow the sodic affinity of tephra I1; (d) primitive mantle normalised and chondrite nor-malised diagrams for tephra I1. Compositional range of proximal deposits are reportedfor comparison. Data from: [5, 9, 12, 18, 43, 2] and references therein.

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Table 3: Major (wt%), trace and rare-element (ppm) composition of glasses from thestudied tephras. All analyses recalculated water-free to 100. s: scoria; gs: glass shard;alk: Na2O+K2O; AI (Agpaitic Index): molar (Na2O+ K2O/Al2O3); n: number of shardsanalysed for each tephra; σ: standard deviation; T: trachyte; TP: trachyphonolite; BTA:basaltic trachyandesite; TA: trachyandesite; A: andesite; TD: trachydacite; D: dacite;Rhy: rhyolite; P: pantellerite.

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Figure 6: (a) Tephra I3 interbedded in marine deposits of core KC01B; (b) classificationof tephra I3 and comparison with the average compositional fields of tephra Y5 and theonland deposits of the Campanian Ignimbrite eruption; (c) primitive mantle normalisedand chondrite normalised diagrams for tephra I3. Compositional range of proximal de-posits are reported for comparison. Data from: [5, 18, 19, 28] and references therein.

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Figure 7: (a) Tephra I9 interbedded in marine deposits of core KC01B; (b) classificationof tephra I9 and comparison with the average compositional fields of tephra X6; (c) prim-itive mantle normalised and chondrite normalised diagrams for tephra I9. Compositionalrange of proximal deposits are reported for comparison. Data from: [5, 44, 18, 19, 45].

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Figure 8: (a) Tephra T22 interbedded in marine deposits of core MD 012474G; (b) clas-sification of tephra T22 and comparison with the average compositional fields of Lipariproximal deposits; (c) primitive mantle normalised and chondrite normalised diagramsfor tephra T22. Compositional range of Lipari proximal deposits are reported for com-parison. Data from [2] and references therein.

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Figure 9: (a) Tephra SC1 interbedded in marine deposits of ODP site 963; (b) classifi-cation of tephra SC1 and comparison with the average compositional fields of the GreenTuff proximal deposits and tephra Y6; (c) FeOtot-Al2O3 diagram (after [46]) wheretephra SC1 samples have been plotted for the geochemical discrimination between pan-tellerites and trachytic comendites; (d) primitive mantle normalised and chondrite nor-malised diagrams for tephra SC1. Compositional range of Pantelleria proximal and distaldeposits (pantellerites) are reported for comparison. Data from [5, 47, 48, 49, 50, 51].

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Volcanic Islands: the Tips of Large SubmergedVolcanoes that only Marine Geology May Reveal(Examples from W-Pontine Archipelago, Ischia,Stromboli and Pantelleria)

A. Bosman1, M. Calarco2, D. Casalbore1, A.M. Conte3, E. Martorelli1, A.Sposato1, F. Falese2, L. Macelloni4, C. Romagnoli5, F.L. Chiocci1,2

1, Institute of Environmental Geology and Geoengineering, CNR, Roma, Italy2, Department of Earth Sciences, University of Roma “La Sapienza”, Roma, Italy3, Institute of Geosciences and Earth Resources, CNR, Roma, Italy4, Center for Marine Resources and Environmental Technology, University of Missis-sippi, MS, USA5, Department of Geo-Environmental and Earth Sciences, University of Bologna, Bologna,[email protected]

Abstract

Submarine portions of volcanic islands are several times (up to an order of magni-tude) larger than subaerial ones but very poorly known. Their knowledge about themis essential for the reconstruction of eruptive history and volcano-tectonic evolution,which are more difficult to be fully witnessed on-land. The offshore investigation ofa number of Italian volcanic islands led to the identification of key outcomes, such asthe widespread occurrence of mass-wasting features ranging across different scalesand occurrence frequency. Large-scale features (i.e. debris avalanche deposits) occurboth at Stromboli and Ischia islands, whereas morphologies and deposits related tominor slides and density flows (e.g. debris flows, grain flows, and turbidity flows)are very common in all the study areas. Moreover, several primary volcanic featureshave been identified, such as volcanic cones, eruptive fissures and lava fields. The re-sults highlight the complex evolution of volcanic edifices, through the alternation ofconstructive phases, due to magma emission, and destructive processes, with masswasting at different scales, including flank collapse. Thus, the achieved scientificresults also provide a relevant contribution to the instability hazard assessment.

1 Introduction

Marine research is essential to gain acomplete geological reconstruction of in-sular volcanoes, as it enables the char-acterization of the submarine sectors ofthe edifices, usually much wider than the

subaerial ones. Moreover, the underwa-ter environment usually displays a finerrecord of eruptive events compared tothe subaerial counterpart, where erosiveand anthropic processes may often oblit-erate the outcrops. In the last decade,the availability of new high-resolution re-


Marine Geology

mote sensing techniques for the investi-gation of marine areas, such as multi-beam echosounder and side scan sonar,has provided a great improvement to mor-phological studies. Furthermore, the cou-pling of such surveys with other geophys-ical methodologies (e.g. seismic survey)and petrographyc-petrological analysis ofseafloor samples greatly contributed to theknowledge of insular and oceanic volca-noes. This contribution aims to show therelevant results of a decade of studies car-ried out offshore some Italian volcanic is-lands characterized by different volcanicactivity and physiographic setting. Fourstudy-cases are here described followingan order that takes into account their dif-ferent settings with respect to the continen-tal margin, i.e. two isolated island vol-canoes (Stromboli and Pantelleria Islands)and two other ones lying on the continentalmargin (Ischia Island and Western PontineArchipelago). The data were collected dur-ing over ten oceanographic cruises carriedout onboard research vessels Urania, Tethisand Universitatis between 1998 and 2008.The results are more detailed for Pontine,Ischia and Stromboli that have been studiedfor a longer time than Pantelleria, where in-vestigations began in 2006. Particular em-phasis is given to those results that haveimproved the knowledge of geological set-ting, previously based only on subaerialdata. Notably, these studies also improvethe overall understanding of volcanologi-cal evolution of studied apparata and, par-ticularly, provide relevant implications onvolcano-tectonic events reconstruction.

2 Stromboli Island

Stromboli Island is located in the NE partof the Aeolian Arc and it is known world-

wide for its persistent Strombolian activ-ity. It consists of periodic low-energy ex-plosions of incandescent scoriae, magmalumps, ashes and blocks with heights of afew tens to hundreds of meters. The islandrepresents the tip of a steep and mostlysubmerged (98% of the entire area [1])stratovolcano that rises for ∼3000 m fromthe seafloor. New high-resolution multi-beam bathymetry and long-range side scansonar data allowed the characterization ofthe morpho-structural setting of the edi-fice [1]. On the whole, this is defined bya quasi-bilateral symmetry of the subma-rine flanks with respect to the main SW-NErift axis, similarly to what observed for thesubaerial portion, although a more com-plex structural pattern can be depicted onthe basis of new marine evidence. For in-stance, a N64°E structural trend controlsthe alignment of Strombolicchio Canyon(Figure 1), a flat-bottomed erosive feature,8 km long and 500-700 m wide, boundedby steep (up to 45°) and very rectilinearscarps with a relief of about 200 m.Marine studies have also shown the occur-rence of widespread mass-wasting featuresthat affect about the 90% of its submergedextension [2]. These events range frommedium-scale submarine landslides (es-timated volume of a few 106 m3) up tolarge-scale sector collapses (estimated vol-ume of each being 1-2 km3). The lattercatastrophic events drove the developmentof large and well-marked scars on the Eand NW submerged flanks and to the em-placement of related debris avalanche de-posits at the base of the edifice. In par-ticular, buried chaotic deposits and a largemegablocks field (Figure 1) have been rec-ognized at the foot of the older easternflank [3]. These features testify the oc-currence of at least two large-scale sectorcollapses in this side of volcano, where

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Figure 1: 3D perspective view of the eastern flank of Stromboli vocano TOBI data aredraped over bathymetry. a) Reference map; b) Bathymetric map (equidistance: 200 m,the grey area corresponds to the tridimensional view). Vertical Exaggeration: 1.2

landslide events were previously consid-ered a minor process. Differently, a largevolcaniclastic fan-shaped bulge has beenidentified on the NW slope, representingthe sum of the four nested lateral collapsesthat affected the NW sector of the Strom-boli in the last 13 ka [4, 5]. Despite theirlow frequency of occurrence (in the orderof thousands of years), these large-scalesector collapses pose a major threat to thecoastal settlement, as they are able to gen-erate important tsunami waves [6].However, medium-scale submarine land-slides represent a major and possibly moresignificant (with respect to large-scalesector collapses) hazard as they occur athigher frequencies [7, 8], and may be-come important at human timescales, asdemonstrated by the 30 December 2002tsunamigenic slide [9]. Thus, the Strom-boli 2002 landslide represented a uniqueopportunity to characterize tsunamigenic

medium-scale submarine mass failures atStromboli, providing useful insights forhazard assessment [7, 10].Finally, a large spectrum of ero-sive/depositional features related to theflowing of density currents were identi-fied on Stromboli submerged flanks. Grainflows seem to dominate the upper slopethat is characterized by very high gradi-ents (up to 35°), whereas turbidity currentsevolve on the lower slope [2].

3 PantelleriaPantelleria Island is located in the SicilyChannel Rift Zone (SCRZ) and representsthe emergent tip of an underwater volcanostructure with 72% lying below sea level,down to a depth of ∼1200 m. Pantelle-ria geology is characterized by a bimodalsuite of widespread lavas and tuffs, domi-nated by silicic peralkaline volcanism and

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Marine Geology

Figure 2: DEM of Pantelleria volcanic edifice. a) Reference map; b) 3D perspective viewof the NW offshore volcanic area. Vertical Exaggeration: 1.5.

subordinated mafic lavas. The volcanic his-tory started 300 ka ago and alternated be-tween periods of less energetic activity orquiescence and large explosive eruptions,which caused two caldera collapses the lat-ter being related to the Green Tuff eruption(e.g. [11, 12]). The most recent volcanicevent occurred in 1891, four km offshorethe NW coast [13, 14] with a submarinebasaltic eruption (i.e. the Foerstner volcanoeruption).Until recent marine surveys, little wasknown about the submarine portions ofthe volcano. The main results of ma-rine surveys led to: i) the identification ofabout thirty new submarine eruptive vents,at depth ranging between ∼250 to ∼800

m; ii) the accurate re-location of the 1891eruptive vent and iii) the recognition of awide submerged shelf in the NW sectorwith recent lava flows.Most of the newly discovered eruptivevents consist of cones and eruptive fissuresthat rise from the NW submarine flank ofthe edifice (Figure 2), with the farthestone located 8.5 km offshore the coastline.The morphology of the cones is similarto the emerged scoria-cones, with heightsup to 350 m and basal widths of 0.5-2.3 km. Sometimes, the coalescence of afew cones along an eruptive fissure createselongated or complex structures that aremainly aligned with the SCRZ trend. Theeruptive centres exhibit a well-preserved

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volcanic morphology; two centers presentsmall-scale sector collapses with smallercones inside (Figure 2b).Samples collected from the eruptive ventsas well as core samples from the NWsector encompass a variety of productswhich include highly scoriaceous lava frag-ments, glass-rich lapilli, and coarse ashes.This highlights the complexity of eruptivemechanisms that characterized the volcanichistory of this area. However, all samplesrevealed a nearly homogeneous basaltic-hawaiitic composition, similar to that of re-cent volcanic products on-land reported byCivetta [15]. This evidence significantlyextends the areal distribution of basalticmagmatism known on the island.Marine data also enabled the accurate re-location of the 1891 eruptive event, whichwas identified only through floating lavabombs emission [13]. The most likelyeruptive vent for the 1891 eruption is asmall centre located four km northwest ofPantelleria harbour (Figure 2). Samplesrelated to this eruption were collected aswell; they are fragments of highly scoria-ceous lava bomb that display a porphyriticand holocrystalline-textured portion and aglassy inner layer. They are hawaiithic incomposition, as the other eruptive productsfrom the NW area [16]. Of particular inter-est is the eruptive style of the 1891 eventthat represents a peculiar case of shallow-intermediate submarine eruptions. Similarvolcanic events have been rarely observed(i.e. Socorro Island, Mexico [17] and Ter-ceira Island, Azores [18]), and at present,they are still not fully explained. Moreover,the submarine investigation led to the char-acterization of the wide shelf that extendsoffshore about 4 km in the NW direction(Figure 2). This submarine shelf was likelybuilt up by lava flows and other volcani-clastic deposits of different ages, with the

sources localized on-land (Mursia, and P.taSan Leonardo basalts) or submerged at thepresent-day. Contemporary, over this time,the shelf underwent subaerial and marineerosion due to different stages of eustaticsea level fluctuations.It deserves to mention that most of thediscovered volcanic vents occur in theNW area of Pantelleria and show well-preserved morphologies, whereas the SEsector of the edifice mainly consists oferosional remnants of old volcanic out-crops. Indeed, this last sector was affectedby severe and widespread dismantling pro-cesses. These morphological differences,as well as the occurrence of the historicaleruption in the NW sector, indicate that,during time, the focus of volcanic activityhas been propagating northwestward. Thesubmarine evidence for this migration isin agreement with the hypothesis of [12]based on subaerial volcanological data.

4 Ischia

Ischia Island is an active alkalitrachyticvolcanic edifice located at the western endof the Bay of Naples. Excluding the M.Epomeo Green Tuff ignimbritic eruption,that occurred around 55 ka, the large part ofthe activity consisted of small-scale erup-tions, the latest of which occurred in 1302AD [19]. A notable characteristic of thisvolcanic edifice is the rapid uplift of Mt.Epomeo, that has been raised ∼700-800m in the past 33 kyr [20]. The strongvolcano-tectonic uplift caused oversteep-ening and morphologic disequilibrium that,combined with seismicity and hydrother-mal rock weathering, produced diffuseslope instability.With the exception of the southern flank,the island is surrounded by a continental

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Figure 3: 3D perspective view of the southern flank of Ischia Island offshore. TOBI dataare draped on the DEM. a) Reference map; b) Bathymetric map (equidistance 200 m, thegrey area corresponds to the tridimensional view); c) detailed view of megablocks of thedebris avalanche deposit.Vertical Exaggeration: 1.5.

shelf that partially merges with the con-tinental margin facing the Volturno Plainand the Gulf of Naples. Our research re-vealed that in the southern flank a steepslope, locally cut by near vertical scarpsand canyon heads, connects the coastlineto deep areas. In this area it is also evi-dent the continuation, below the sea level,of the 2.2-km-wide horseshoe scar, carv-ing the Mt. Epomeo. This has been inter-preted as a sector collapse scar; related de-bris avalanche deposit (DA) lies at the toeof the southern slope of Ischia. Between550 m and 1100 m w.d., collected datashow a field of thousands of mega blocks,dispersed over an area of ∼200 km2, as faras 50 km from the island (Figure 3). Thewidth of individual blocks in the DA varyfrom several meters to more than 200 m,while the height of the larger blocks rangeup to 30-50 m. The deposit has a curved

areal distribution, partly following the localpre-collapse topography. However, on itseastern side it extends up over a ridge 80 mhigh and down into the Magnaghi Canyon(Figure 3). This debris avalanche deposithas been related to the catastrophic failureof the southern flank of the island [21].Samples of the DA matrix and associateddebris flow (DF) deposit were recoveredthrough dredging and, in the interblock re-gions, by gravity coring. The DA ma-trix consists of a mixture of clasts rang-ing in size from centimeters to millime-ters and an interclast groundmass with avery low clay fraction; the resulting tex-ture is that of a slightly consolidated sandydeposit. On the contrary, the DF is amud-supported deposit with a significantclay fraction. Cores also recovered a post-avalanche hemipelagic mud drape thinnerthan 1 m.

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A reliable estimate of the DA volumewould require knowledge of its overallthickness (i.e. blocks + matrix + DF)while an estimate based only on the volumeof “outcropping” blocks that are acousti-cally detectable (numbering around 5000)results in an extremely conservative value.Therefore the minimum estimated volumeof the deposit is 1.5 km3, whereas the pos-sible mobilized volume in the scar arearanges between 0.3 km3 and 0.7 km3.The age of the collapse is constrainedboth by the occurrence of Mt. EpomeoGreen Tuff (55 kyrs BP) fragments in-side the avalanche deposit and by two14C-AMS datings of Posidonia oceanicafragments (4254-4520 and 5050-5480 cal-ibrated years BP, i.e. Neolithic time), atabout 5 kyrs BP. The most recent dating[22] gives an age between ∼2,3 cal. kaB.P. and ∼3 cal. ka B.P. Finally, the re-sulting morphostructural setting of Ischiahighlights a significant geo-hazard for theIschia-Bay in the Naples area.

5 Western Pontine Archi-pelago

The Western Pontine Archipelago (Ponza,Zannone and Palmarola Islands) is locatedalong the central sector of the EasternTyrrhenian Margin at the tip of a morpho-structural high, facing the Vavilov Basin.Ponza and Zannone are mainly made upof rhyolitic volcanites of calcalkaline affin-ity emplaced during the Pliocene, whereasPalmarola is made up of alkaline to peral-kaline rhyolites emplaced during the Pleis-tocene. Pleistocene trachytic to peralka-line products also outcrop on the South-ern portion of Ponza Island (e.g., [23, 24].The rhyolites occur either as hyaloclastic

domes or massive lava dykes in responseto different degrees of water-magma in-teraction in a shallow environment (e.g.[25]). Erosion mainly dismantled thehyaloclastite, while dykes form headland,cliffs and submarine shoals. Over time,such a process has been producing an ex-tremely complex morphology on the nar-row (2-8 km) continental shelf (e.g. NWand SW Palmarola offshore). On the outershelf, the morphology becomes more regu-lar, as the rocky substrate is mainly coveredby Late Quaternary deposits, forming a de-positional terrace.Marine studies include remote sensing in-vestigation as well petrographyc and petro-logical studies. In particular analysis ofsubmarine rock samples provided new el-ements, i.e.: the presence offshore Ponzaof limestone bedrock (previously describedonly on-land at Ponza and Zannone); theoccurrence, in the SW sector of PalmarolaIsland, of Pliocene calc-alkaline rhyolitessimilar to those located at Ponza and Zan-none Islands. This latter result is rel-evant for the general volcanological set-ting, as Palmarola was previously known tobe constituted only of Pleistocene alkalineproducts. Therefore, this new setting sig-nificantly extends the distribution of calc-alkaline magmatism in the area. In addi-tion, submarine investigations have showna compositional linkage between the Pleis-tocene volcanics of Palmarola and thoseof South Ponza. This finding reinforcesthe hypothesis that a progressive changeof magmatism from calc-alkaline towardsalkaline character occurred in the West-ern Pontine Archipelago during the Pleis-tocene, probably in response to a tectonicevolution defined by stronger extensionalprocesses at that time [26, 24].Beyond the shelf break at 120-150 m w.d.,the continental slope is characterized by

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Marine Geology

Figure 4: 3D perspective view of the Western Pontine Islands offshore. TOBI data aredraped on the offshore DEM. a) Reference map; b) Bathymetric map (equidistance 200m, the grey area corresponds to the tridimensional view). Vertical Exaggeration: 2.

a suite of massive instability-erosive phe-nomena (Figure 4). The cannibalization(slope retreat) of most of the margin (98%)is a consequence of extremely high seafloorgradients (5°-10°, locally up to 30°), aswell as the presence of tectonic features[27]. Instability-erosive processes differ indimension (from less than one km2 to sev-eral tens of km2) and typology (e.g. slides,debris and grain flows). A well defined cor-relation between the mass movements dis-tribution and the slope gradient exists, infact, the steepest areas (∼10° up to 30°),such as the upper continental slope and theflanks of main ridges, are characterized bypervasive slides and erosive channels whilegentler sloping areas, such as the lowercontinental slope, are dominated by grainflow and debris flow deposits (Figure 4).Grain flow deposits (high backscatter fa-cies in Figure 4) are formed by coarse

grained debris (e.g. sands and gravels) de-livered by a large amount of linear chan-nels. They develop on a quite steepseafloor (3°-20°) and seem to disappearwhen the gradient decreases below roughly3°, reaching however a huge extent (about150 km2). Debris flow deposits (mediumbackscatter facies in Figure 4) are consti-tuted by relatively finer sediments; they aredeveloped on low gradient seafloor (typ-ically 0.5-2.5°) and cover a smaller area(about 65 km2) than that of grain flows.Aside from the well known differences insediments and transport mechanisms, den-sity flows of the Western Pontine conti-nental slope show different feeding sys-tems. Grain flow deposits are fed by sev-eral punctual sources (i.e. the channels andgullies) so that the deposit is the result ofamalgamated debris. In contrast, debrisflows originate from a singular and distinct

440


point source; actually, it is an area of coa-lescing scars.The pervasive character of instability-erosive phenomena affecting the continen-tal slope enables the local crop out of thebedrock. Such outcrops are mainly lo-cated in areas affected by severe erosion oralong fault escarpments. The petrographic-petrochemical characterization of collectedsamples evidences that most of them arevolcanites comparable to the Pliocene cal-calkaline rhyolites cropping out on-land atPonza and Zannone. Taking into accountthe aforementioned volcanic outcrops ob-served on the continental shelf, a furthersignificantly wider extent of calcalkalinerhyolites in this area is highlighted by off-shore data.

6 Conclusive Remarks

The reported case-studies prove the im-portance of marine investigations to con-strain the geology and evolution of insularvolcanoes since these often represent thetip of very large edifices that are mostlydeveloped underwater. In this regard,long range side scan and swath bathymetryseafloor mapping enable the detection ofmain volcano-tectonic features and mass-wasting processes at very high detail, alsoin deep water areas. Thus, marine geol-ogy unveils part of the evolution of volca-noes that is often difficult to recognize onthe basis of the sole terrestrial geology. Asan example, at Stromboli the recognition ofthe structurally-controlled StrombolicchioCanyon in the NE side of the edifice de-picts a tectonic pattern more complex thanthe quasi-bilateral symmetry observed onthe edifice. Furthermore, multistage lat-eral collapses have been reconstructed forthe eastern Stromboli flank. Their volume

is an order of magnitude higher than pre-viously thought, and comparable to thatof the younger collapses affecting the NWflank (Sciara del Fuoco). Similarly, off-shore the southern coast of Ischia Island,the recognition of a large debris avalanchedeposit testifies the occurrence of large-scale instability related to the resurgenceof M.te Epomeo. This leads to reconsiderthe geological interpretation of the Ischiasouthern coast as due to a lateral collapse.On the NW part of the Pantelleria edifice,marine studies identified a previously un-known large volcanic field, which includesthe vent related to the last eruptive event(occurred in 1891). This evidence seems toindicate a northwestward migration of theactivity over time.Overall, the possibility to enlarge the viewof a volcanic edifice allows to correlatethe development of instability processesand volcano-tectonic structures to the lo-cal physiographic and structural setting. Inthis regard, the presence of a regional mainfault system with NE-SW direction in theStromboli area results in the NE-SW elon-gated shape of the edifice due to a strongtectonic control. Such setting determinesthat the NW and SE flanks are prone tocollapse as they are steep and structurallyunbuttressed. Similarly, at Ischia the struc-tural control plays a major role, since thecoalescence with the Campanian continen-tal margin prevents the collapse of but-tressed flanks.As well as Stromboli, Pantelleria is a maincentral volcano with a prominent structuralcontrol due to the SCZR; however, its elon-gated shape is also due to the aforemen-tioned northwestward migration of erup-tive centers.In the case of old and inactive volcanicedifices, such as the Western PontineArchipelago, morphological evolution of

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Marine Geology

submerged flanks is mainly related to ero-sion and mass wasting as constructive vol-canic processes ended. On the Pontinecontinental slope dismantling processes arestrengthened by tectonics that gives rise tovery steep gradients.Besides a fundamental role in the morpho-structural reconstruction of insular volca-noes, marine studies also provide important

insights for the assessment of geo-hazardsthrough the recognition, mapping and char-acterization of widespread mass-wastingfeatures occurring at different scale andfrequencies. As most of the instabilityphenomena evolve upslope, they may af-fect coastal infrastructures and may alsogenerate tsunamis, as demonstrated by theStromboli 2002 event.

References[1] A. Bosman, F.L. Chiocci, and C. Romagnoli. Morpho-structural setting of Strom-

boli volcano, revealed by high-resolution bathymetry and backscatter data of itssubmarine portions. Bulletin of Volcanology, 71(9):1007–1019, 2009.

[2] D. Casalbore, C. Romagnoli, F.L. Chiocci, and V. Frezza. Morpho-sedimentarycharacteristics of the volcaniclastic apron around Stromboli volcano (Italy). MarineGeology, in press, 2010.

[3] C. Romagnoli, D. Casalbore, F.L. Chiocci, and A. Bosman. Offshore evidenceof large-scale lateral collapses on the eastern flank of Stromboli, Italy, due tostructurally-controlled, bilateral flank instability. Marine Geology, 262:1–13,2009a.

[4] A. Tibaldi. Multiple sector collapses at Stromboli volcano, Italy: how they work.Bulletin of Volcanology, 63:112–125, 2001.

[5] C. Romagnoli, P. Kokelaar, D. Casalbore, and F.L. Chiocci. Lateral collapses andactive sedimentary processes on the northwestern flank of Stromboli volcano, Italy.Marine Geology, 265:101–119, 2009b.

[6] S. Tinti, E. Bortolucci, and C. Romagnoli. Computer simulations of tsunamis dueto sector collapse at Stromboli, Italy. Journal of Volcanology and Geothermal Re-search, 96:103–128, 2000.

[7] F.L. Chiocci, C. Romagnoli, P. Tommasi, and A. Bosman. Stromboli 2002 tsunami-genic submarine slide: Characteristics and possible failure mechanisms. Journal ofGeophysical Research, 113:1–11, 2008a.

[8] P. Tommasi, P. Baldi, F.L. Chiocci, M. Coltelli, M. Marzella, and C. Romagnoli.Slope failures induced by the December 2002 eruption at Stromboli volcano. Learn-ing from Stromboli and its 2002–03 eruptive crisis, 182:129–146, 2008.

[9] S. Tinti, A. Manucci, G. Pagnoni, A. Armigliato, and F. Zaniboni. The 30 December2002 landslide-induced tsunamis in Stromboli: sequence of events reconstructed

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from the eyewitness accounts. Nat. Hazards and Earth System Sciences, 5:763–775, 2005.

[10] F.L. Chiocci, C. Romagnoli, and A. Bosman. Morphologic resilience and depo-sitional processes due to the rapid evolution of the submerged Sciara del Fuoco(Stromboli Island) after the December 2002 submarine slide and tsunami. Geomor-phology, 100:356–365, 2008b.

[11] L. Civetta, Y. Cornette, G. Crisci, P. Gillot, G. Orsi, and C. Requejo. Geology,geochronology and chemical evolution of the island of Pantelleria. GeologicalMagazine, 121(6):541–562, 1984.

[12] G.A. Mahood and W. Hildreth. Geology of the peralkaline volcano at Pantelleria,Strait of Sicily. Bulletin of Volcanology, 48(2-3):143–172, 1986.

[13] A. Ricco. Terremoti, sollevamento ed eruzione sottomarina a Pantelleria nella sec-onda meta’ dell’ottobre 1891. Boll. Soc. Geogr. Ital., pages 1–31, 1892.

[14] H.S. Washington. The submarine eruption of 1831 and 1891 near Pantelleria. Amer-ican Journal of Science, 27:131–150, 1909.

[15] L. Civetta, M. D’Antonio, G. Orsi, and G.R. Tilton. The geochemistry of volcanicrocks from Pantelleria Island, Sicily Channel: petrogenesis and characteristics ofthe mantle source region. Journal of Petrology, 39(8):1453–1491, 1998.

[16] A. Bosman, M. Calarco, D. Casalbore, F.L. Chiocci, M. Coltelli, A.M. Conte,E. Martorelli, C. Romagnoli, and A. Sposato. New insights into the recent sub-marine volcanism of Pantelleria Island. Abstract 26 Convegno Nazionale GNGTS13-15/11/2007, pages 177–178, 2007.

[17] C. Siebe, J.C. Komorowski, C. Navarro, J. McHone, H. Delgado, and A. Cortes.Submarine eruption near Socorro Island, Mexico: Geochemistry and scanning elec-tron microscopy studies of floating scoria and reticulite. Journal of Volcanology andGeothermal Research, 68(4):239–271, 1995.

[18] J.L. Gaspar, G. Queiroz, J. M. Pacheco, T. Ferreira, N. Wallenstein, M.H. Almeida,and R. Coutinho. Basaltic lava balloons produced during the 1998-2001 SerretaSubmarine ridge eruption (Azores). Subaqueous Explosive Volcanism, AmericanGeophysical Union, Geophysical Monograph, 140:205–212, 2003.

[19] L. Vezzoli. Island of Ischia. Quaderni de La Ricerca Scientifica, 114(10):122, 1988.

[20] G. Orsi, G. Gallo, and A. Zanchi. Simple shearing block-resurgence in calderadepressions. A model from Pantelleria and Ischia. Journal Volcanol. Geoth. Res.,47:1–11, 1991.

[21] F.L. Chiocci and G. de Alteriis. The Ischia debris Avalanche: first clear submarineevidence in the Mediterranean of a volcanic island prehistorical collapse. TerraNova, 18:202–209, 2006.

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[22] G. de Alteriis, D. Insinga, S. Morabito, V. Morra, F.L. Chiocci, F. Terrasi,C. Lubritto, C. Di Benedetto, and M. Pazzanese. Age of submarine debrisavalanches and tephrostratigraphy offshore ischia Island, Tyrrhenian Sea, Italy. Ma-rine Geology (Submitted), 2010.

[23] A.M. Conte and D. Dolfi. Petrological and geochimical characteristics of Plio-Pleistocene Volcanics from Ponza Island (Tyrrhenian Sea, Italy). Mineralogy andPetrology, 74:75–94, 2002.

[24] A. Cadeaux, D.L. Pinti, C. Aznar, S. Chiesa, and P.Y. Gillot. New chronologicaland Geochemcal constraints on the genesis and geological evolution of Ponza andPalmarola Volcanic Islands (Tyrrhenian Sea, Italy). Lithos, 81:121–151, 2005.

[25] D. De Rita, G. Giordano, and A. Cecili. A model for submarine rhyolite domegrowth: Ponza Island (central Italy). Journal Volcanol. Geotherm. Res., 107:221–239, 2001.

[26] A.M. Conte, D. Dolfi, E. Martorelli, and F.L. Chiocci. Aspetti petrologici deiprodotti magmatici delle Isole Pontine occidentali in relazione all’ambiente geo-dinamico. Atti del 4 Forum Italiano di Scienze della Terra - FIST GEOITALIA2003, Bellaria, 16-18 settembre, 2003.

[27] F.L. Chiocci, E. Martorelli, and A. Bosman. Cannibalization of a continental mar-gin by regional scale mass wasting: an example from the central Tyrrhenian Sea.Submarine Mass Movements and their consequences, 19:409–416, 2003.

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The Bathymetry of the Adriatic Sea

F. Foglini1, E. Campiani1, A. Cattaneo3, A. Correggiari1, A. Remia1, D.Ridente2, F. Trincardi11, Institute of Marine Sciences, CNR, Bologna, Italy2, Institute of Environmental Geology and Geoengineering, CNR, Roma, Italy3, French Research Institute for Exploration of the Sea, Brest, [email protected]

Abstract

The Istituto di Scienze Marine (ISMAR-CNR) conducted several research projectsin the Italian side of the Adriatic Sea over more than 15 years collecting bathymet-ric, geophysical, and sediment core data and performing multidisciplinary studiesto reconstruct paleoenvironmental changes and sediment dynamics during the lasteustatic cycle. A key issue in any marine dataset is the construction of a detailedbathymetry. The Adriatic Sea bathymetry is unique because, due to the shallow wa-ter depth of large areas of the basin, standard hydrographic surveys to obtain a com-prehensive Multi Beam bathymetry are not applicable. The Adriatic Sea bathymetricmap is necessarily based on heterogeneous data with uneven spatial distribution andincludes both Single Beam echo-soundings and Multi Beam surveys in key studyareas. The main objectives of this work are to illustrate the methodology appliedto compile a new bathymetric map of the Adriatic Sea integrating Single Beam andMulti Beam data, to describe the morphological units reflecting the main geologicalfeatures, and to discuss the limits of reliability of the data when a bathymetric mapis to used by oceanographic modellers

1 Introduction

The bathymetry plays a key role not onlyin geological, geomorphological and geo-physical studies, but also in the fields ofphysical oceanography and habitat map-ping in submarine areas. In particular, thebathymetry represents a crucial constrainfor oceanographic models in basin-scalecirculation and in bottom-boundary-layerstudies, and for the simulation of tsunamipropagation across continental margins andin shallow areas. The seafloor morphol-ogy has been investigated for more than acentury, but only with the technologies de-veloped during the last decades it revealed

world-wide scale physiographic featuressuch as mid-ocean ridges, transform faultsand deep-sea trenches [2]. Heezen et al. [2]represented the morphology of the seafloorin a semi-pictorial way based on continu-ous echosoundings profiles together withan intelligent interpretation of the seafloorfeatures to fill-in areas where no suchsoundings existed. Their purpose was to il-lustrate the morphology rather than to offera precise measure of the water depth at anygiven point.In 1922, De Marchi provided the first rep-resentation of the Adriatic Sea bathymetrygiving, in particular, a conceptual imageof the network of fluvial valleys incising


Marine Geology

Multi Beam

systems

Water depth range

surveyed

Frequency

kHz

Beam

width

N°

of Beams

Total area

surveyed

Reson Seabat 8160 100-1200m 50 1.5°X1.5° 126

Kongsberg EM300 100-1000m 30 1°x 2° 135

Kongsberg EM710 100-900m 70-100 1°X1° 258

Konsberg EM3000 30-100 300 1.5° x 1.5° 127

7700 km2

Konsberg EM3002D 30-100 m 300 1.5° x 1.5° 508

Reson Seabat 8125 30-100 455 0.5°x1° 240 1600 km2

Tab. 1 - Technical characteristics of the Multi Beam echo sounders used to survey the South West Adriatic

Margin and some selected areas of the Adriatic continental shelf.

Fig. 1 - General morphology of the Adriatic Sea from Giorgetti and Masetti, 1969 (Mercator Projection -

Scale 1:750.000). Compiled from O.G.S Trieste from 1966-67 cruises with the CNR oceanographic vessel

“Bannok” and integrated with I.I.M published data.

Figure 1: General morphology of the Adriatic Sea from Giorgetti and Masetti [1] (Mer-cator Projection - Scale 1:750.000). Compiled from O.G.S Trieste from 1966-67 cruiseswith the CNR oceanographic vessel ”Bannok” and integrated with I.I.M published data.

the alluvial plain during the Last GlacialMaximum and drowned during the fol-lowing sea level rise. Later, Giorgettiand Mosetti [1], constructed a map of thegeneral morphology of the Adriatic basinbased on a great number of echosounderrecords taken during several geophysicalcruises that covered nearly the entire Adri-atic Sea. The morphological map of Gior-getti and Mosetti [1] was drawn with thepurpose of representing a pictorial view ofthe seafloor structures (Figure 1). Over thelast 15 years, the Istituto di Scienze Ma-rine (ISMAR-CNR) conducted several re-search projects in the Italian side of theAdriatic Sea collecting bathymetric data inorder to obtain a high resolution map of

the seafloor features [3]. This map rep-resented a key step for multidisciplinarystudies aimed to reconstruct paleoenvi-ronmental changes and sediment dynam-ics during the last glacial-interglacial cy-cle. The bathymetric map is necessar-ily based on heterogeneous data with un-even spatial distribution and includes bothSingle Beam echo-soundings and variable-frequency Multi Beam surveys in key studyareas such as the South West Adriatic Mar-gin and part of the continental shelf on theItalian side. The aim of this paper is topresent the new bathymetric map of theAdriatic Sea compiled by CNR-ISMAR forthe Italian side of the Adriatic Sea and to il-lustrate the main geological features of the

446


Western Adriatic Basin. In this framework,we will examine the methodological ap-proaches applied to process and to integratesingle beam and multi beam echosound-ings and we will discuss the limits of re-liability of the data when the bathymetricmap is to used by oceanographic modellersinterested either in basin-scale circulationor in bottom-boundary-layer studies.

2 Methodology

2.1 Single Beam bathymetry -Data acquisition and pro-cessing

Single Beam sonar data were collected us-ing an hull mounted Echo sounder (At-las Deso25 operating at frequencies of12, 100, 33 and 210 kHz) along about17.830 km of seismic profiles during 22cruises performed by ISMAR from 1991to 2005 on board R/V Urania in the Ital-ian side of the Adriatic Sea (Figure 2). Theecho sounding profiles are unevenly dis-tributed and the seafloor coverage is withinthe range of one sounding every 20-40m, along track. The Echo sounder At-las Deso25 was merged with the naviga-tion system NAV PRO from Communica-tion Technology and with DGPS position-ing system with metrical accuracy. Thesound speed was set at 1500 m·s−1. In ar-eas where the sound speed profiles werehighly variable, as for example in frontof the Po River Delta, local values ob-tained from CTD (Conductivity, Temper-ature, and Depth) measurements were ap-plied. The navigation and water depth datawere stored every 2 seconds in a Databaseand filtered to correct positioning errorsand to delete null values using filteringprocedures implemented by ISMAR (e.g.

Kalman filter). Afterwards, the bathymet-ric data were migrated in a GIS (Geo-graphic Information System) Database andplotted as water depth points in maps atdifferent scale depending on the soundingsdensity, dividing the Adriatic in subset ar-eas from north to south. The bathymetriccontours were manually drawn and digi-tised as vector data in a GIS, with variablespace according to water depth range (con-tour every 1 m from 5 to 150 m and every20 m from 150 m to 1200 m). The con-tours were used to generate a uniform grid(200 m) applying computing technology(KRIGING algorithm with variable resolu-tion depending on the soundings density)in order to give a more flexible product forvisualisation and manipulation of data.

2.2 Multi Beam bathymetry -Data acquisition and pro-cessing

The Multi Beam data were collected witha variety of Multi Beam Echo. with vari-able frequency, beam number and beam an-gles, according to the scientific objectivesor to the instruments available. The MultiBeam acquisition strategy comprised a fullcoverage survey of the entire South Adri-atic Continental slope on the Italian side(from 200 to 1200 m) and the investigationof selected areas of the continental shelf(from 10 to 150 m) characterised by com-plex seafloor morphology. Table 1 sum-marizes the Multi Beam Echo. technicalcharacteristics and the water depth rangesurveyed. The Multi Beam data process-ing was carried out using both PANGEAMulti Beam System and CARIS HIPS andSIPS 7.0. The processing methodologyapplied implies the creation of a 2D and3D best-fit interpolated surface using dif-

447

Marine Geology

Fig. 2 – Single Beam data (grey lines) collected by ISMAR from 1991 to 2005 on board R/V Urania in the

Italian side of the Adriatic Sea. The blue boxes represent the areas surveyed with high frequency Multi Beam

systems on the continental shelf, the red boxes represent the areas surveyed with low frequency Multi Beam

systems on the Adriatic continental slope.

Figure 2: Single Beam data (grey lines) collected by ISMAR from 1991 to 2005 on boardR/V Urania in the Italian side of the Adriatic Sea. The blue boxes represent the areas sur-veyed with high frequency Multi Beam systems on the continental shelf, the red boxesrepresent the areas surveyed with low frequency Multi Beam systems on the Adriaticcontinental slope.

ferent algorithms and grid resolutions. Thefirst processing step is the analysis of thedata errors and the definition of a strat-egy to solve them. The latter includes: 1)the correction of the sensor angles (multibeam patch-test); 2) the sound speed cor-rection applying the ray-tracing techniqueafter data acquisition; 3) the manual clean-ing of the spikes (beam remove) only inthe area where they are visible on the 2Dand 3D surface; 4) the automatic filteringfor a depth window, by beam number or

slope between points. The second process-ing step is the creation of a new surface af-ter the data correction and cleaning using adifferent resolution grid for a given waterdepth range and for geologically relevantseafloor features. The processing method-ology applied is based on an interpreta-tive approach instead of a traditional lineto line cleaning system. The role of thedata processing is to understand the relia-bility of the seafloor features detected onthe grid surface and to identify all kinds of

448


Fig.3 - Single Beam bathymetry contour map of the Italian side of the Adriatic (contour lines every 1 m from

5 to 150 m and contour every 20 m from 150 to 1200 m). A) Incised valleys on the north Adriatic shelf,

offshore Ancona, between 75 and 100 m of water depth formed during the subaerial exposure of this area

during the Last Glacial Maximum and the early stages of the post-glacial sea-level rise; B) Sand dunes on the

north Adriatic shelf are located 20 km SE of Venice between 20 and 24 m water depth.

.

Figure 3: Single Beam bathymetry contour map of the Italian side of the Adriatic (con-tour lines every 1 m from 5 to 150 m and contour every 20 m from 150 to 1200 m). A)Incised valleys on the north Adriatic shelf, offshore Ancona, between 75 and 100 m ofwater depth formed during the subaerial exposure of this area during the Last GlacialMaximum and the early stages of the post-glacial sea-level rise; B) Sand dunes on thenorth Adriatic shelf are located 20 km SE of Venice between 20 and 24 m water depth.

noise and their origin. The interpretativeapproach leads to achieve a high resolutionbathymetry focusing the processing effortin revealing the geologically most signifi-cant seafloor features. This method is lesstime consuming in terms of manual datacleaning and implies a change in the per-spective of the entire processing work flow.

2.3 Multi Beam and SingleBeam data integration

The Single Beam and Multi Beam datawere integrated at regional scale using thesoftware PANGEA MB Manager and its“Tuning filter” tool. The “Tuning filters”represent special areas, drawn by the op-erator as polygons with variable shapes,where it is possible to apply a specific res-olution. The software assigns an ID num-ber to each Tuning filter with its associ-ated resolution value. The Single Beam

449

Marine Geology

Multi Beam

systems

Water depth range

surveyed

Frequency

kHz

Beam

width

N°

of Beams

Total area

surveyed

Reson Seabat 8160 100-1200m 50 1.5°X1.5° 126

Kongsberg EM300 100-1000m 30 1°x 2° 135

Kongsberg EM710 100-900m 70-100 1°X1° 258

Konsberg EM3000 30-100 300 1.5° x 1.5° 127

7700 km2

Konsberg EM3002D 30-100 m 300 1.5° x 1.5° 508

Reson Seabat 8125 30-100 455 0.5°x1° 240 1600 km2

Tab. 1 - Technical characteristics of the Multi Beam echo sounders used to survey the South West Adriatic

Margin and some selected areas of the Adriatic continental shelf.

Fig. 1 - General morphology of the Adriatic Sea from Giorgetti and Masetti, 1969 (Mercator Projection -

Scale 1:750.000). Compiled from O.G.S Trieste from 1966-67 cruises with the CNR oceanographic vessel

“Bannok” and integrated with I.I.M published data.

Table 1: Technical characteristics of the Multi Beam echo sounders used to survey theSouth West Adriatic Margin and some selected areas of the Adriatic continental shelf.

and the Multi Beam DTM (Digital Ter-rain Model, respectively 200 m and 20 mresolution) were loaded in the software assoundings. According to the sounding den-sity, at a given water depth range, the op-erator drawn Tuning Filters including ar-eas with homogenous characteristics. Foreach areas a different resolution was as-signed in order to emphasize the most rel-evant seafloor features and to maintain thedetails of the Multi Beam DTM. At the bor-der between the Multi Beam surveys andthe Single Beam ones, several Tuning fil-ters were drawn increasing progressivelythe resolution, going from the Single Beamto the Multi Beam data, in order to mini-mize the differences between the two areasand to avoid the creation of morphologi-cal steps. The Tuning filters allowed thecreation of a DTM with variable resolutiondepending on the operator choice, permit-ting to merge Single Beam and Multi Beamdata maintaining the high resolution of thearea surveyed with Multi Beam E.


3.1 Single Beam bathymetry ofthe Western Adriatic Sea

The new contour map of the Western Adri-atic Sea resulting from the acquisition, pro-cessing and interpretation of data collectedby ISMAR over the last 15 years showsin detail the seafloor morphology of theAdriatic from the northern shelf to southernslope (Figure 3). The bathymetry showsthat the Northern Adriatic has a low lon-gitudinal topographic gradient (ca 0.02°),whereas the maximum shelf gradient alongthe central Adriatic is on the order of 0.5°.The central Adriatic is characterised bya narrower shelf and localised bathymet-ric irregularities that are the expression ofstructural highs offshore Punta Penna, theTremiti Islands and the Gargano promon-tory, and reaches a maximum depth of 260m in two remnant slope basins aligned ina SW-NE direction. The Southern Adri-atic, beyond the Pelagosa Sill, reaches thedepth of ca 1200 m and is flanked by asteep slope. In this area, the shelf is gen-erally narrow except in the Gulf of Man-

450


Fig. 4 - Slope map of the Late Holocene clinoform on the Adriatic shelf. The offlap break (yellow and red

slope values) occurs in progressively deeper waters from the Po Delta (few meters water depth) to the area

offshore Gargano The geometry of the clinoform varies between Ancona and Ortona where the gradient

gradually increases.

Fig. 5 - Subsurface undulations between 28 m and 93 m water depth the foreset region of the late Holocene

progradational clinoform in the area offshore Ortona (Location in Fig 2 - Area 1). The undulations

(maximum slope of 2°) are associated with mud reliefs that occur further seaward (60 m water depth).

Figure 4: Slope map of the Late Holocene clinoform on the Adriatic shelf. The offlapbreak (yellow and red slope values) occurs in progressively deeper waters from the PoDelta (few meters water depth) to the area offshore Gargano The geometry of the clino-form varies between Ancona and Ortona where the gradient gradually increases.

fredonia, south of the Gargano Promon-tory, where it broadens to about 80 km.The main morphological features detectedon the Single Beam bathymetry reflect thefollowing main geological elements of thearea:

• The Late Holocene mud wedge clino-form extending over 600 km along thecoast of Italy from the modern Po Deltato the area south of the Gargano Promon-tory, with a characteristic subaqueous of-flap break, marking the transition be-tween topset and foreset deposits (Fig-

ure 4). The Late Holocene clinoform onthe Adriatic shelf reaches up to 35 m inthickness with a volume of 180 km3 andrests above the maximum flooding sur-face (mfs), a regional downlap surfacedated ca. 5.5 cal kyr BP [4, 5, 6];

• Several incised valleys on the NorthAdriatic shelf, offshore Ancona, between100 and 75 m of water depth formed dur-ing the subaerial exposure of this areaduring the Last Glacial Maximum and inthe early stages of the post-glacial sealevel rise (Figure 3A). The valleys are

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Marine Geology

Fig. 4 - Slope map of the Late Holocene clinoform on the Adriatic shelf. The offlap break (yellow and red

slope values) occurs in progressively deeper waters from the Po Delta (few meters water depth) to the area

offshore Gargano The geometry of the clinoform varies between Ancona and Ortona where the gradient

gradually increases.

Fig. 5 - Subsurface undulations between 28 m and 93 m water depth the foreset region of the late Holocene

progradational clinoform in the area offshore Ortona (Location in Fig 2 - Area 1). The undulations

(maximum slope of 2°) are associated with mud reliefs that occur further seaward (60 m water depth).

Figure 5: Subsurface undulations between 28 m and 93 m water depth the foreset regionof the late Holocene progradational clinoform in the area offshore Ortona (Location inFigure 2 - Area 1). The undulations (maximum slope of 2°) are associated with mudreliefs that occur further seaward (60 m water depth).

up to 20 km long, several hundred me-tres to a kilometre wide and between 4and 15 m deep. The orientation of thevalleys is predominantly north-south andtheir sinuosity is low [7]. The valleys arespatially associated to preserved barrier-lagoon deposits, which originated duringthe Late Pleistocene and Holocene sea-level rise [8, 9];

• Sand dunes on the North Adriatic shelfare located 20 km SE of Venice between20 and 24 m water depth (Figure 3B)[10]. The sand dunes rest on a broadshore-parallel mound bounded landwardby an elongated trough. The dunes areup to 2 km long, characterised by low

sinuosity and extend across the entirewidth of the underlying mound to theedge of the shoreline parallel trough [10].The sand dunes off shore the Venice La-goon are formed from the reworking of adrowned coastal lithosome accompaniedby secondary erosion in the troughs andrecycling of low stand fluvial sand [10].

452


Fig. 6 – DTM (20 m grid) of the South West Adriatic Margin showing the extreme geological and morphological complexity of the slope. A) Areas with enhanced bottom-current features in the upper slope. B) The Gondola Slide representing the largest mass failure deposit on the SAM. c) The Bari Canyon System, the main sediment conduit active since the Last Glacial Maximum

Figure 6: DTM (20 m grid) of the South West Adriatic Margin showing the extremegeological and morphological complexity of the slope. A) Areas with enhanced bottom-current features in the upper slope. B) The Gondola Slide representing the largest massfailure deposit on the SAM. C) The Bari Canyon System, the main sediment conduitactive since the Last Glacial Maximum.

3.2 Multi Beam bathymetry ofthe Italian side of the centralAdriatic continental shelfoffshore Ortona

The Multi Beam map the Adriatic Con-tinental shelf offshore Ortona (Figure 5.location in Figure 2) defines the seafloorexpression of subsurface undulations be-tween 30 m and 75 m water depth (typi-cally 300 m wide, 2.5 m high, and severalkm long, parallel to the bathymetric con-tour) affecting the foreset region of the lateHolocene progradational clinoform abovea regional downlap surface (the mfs) inareas where it shows evidence of defor-

mation and fluid escape [5, 11, 12, 13].The undulations are associated with mudreliefs that occur farther seaward in elon-gated swarms perpendicular to the regionalslope and to the crests of the undulations.Cattaneo et al. [11], suggested that theseseafloor undulations evolved in responseto sediment deformation and were succes-sively amplified by differential depositionfrom bottom currents crossing an irregu-lar seafloor. Recently Sultan et al. [14]demonstrated that the basal unit of theHolocene mud wedge immediately abovethe mfs has coarser grain size than the un-derlying and overlying units. The latterrepresents a weak layer where liquefaction

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Marine Geology

can occur during earthquake of M1≤4.5,typical of this area.

3.3 Multi Beam bathymetry ofthe South West Adriaticslope

The high resolution Multi Beam map ofthe South West Adriatic Margin (SAM)shows the extreme geological and morpho-logical complexity of the slope and allowsdetailed description of the seafloor fea-tures (Figure 6). The SAM slope is gener-ally characterised by: 1) widespread mass-failure features including slide scars up to10 km wide and extensive slide depositswith runout distances greater than 50 km[15]; 2) a large variety of bottom-currentfeatures [16, 17]; 3) the Bari Canyon Sys-tem (BCS), the main sediment conduit ac-tive since the Last Glacial Maximum inter-val [17]; 4) the Dauno Seamount, the mainstructural feature on the slope, with a clearmorphologic expression. A large variety ofbottom current features (Figure 6A) char-acterises a confined sub-triangular slopearea suggesting the constructive interactionbetween two distinct southerly bottom wa-ter masses: the contour-parallel LevantineIntermediate Water and the North AdriaticDense Water, cascading seasonally acrossthe slope. By analyzing the large varietyof bottom-current features, it was possibleto identify areas in the upper slope stronglyswept by bottom currents and characterisedby predominant erosion. Seaward and east-ward of the main current path, the bottomcurrent progressively loses energy, througha field of progressively more continuousand aggradational sediment waves [16, 18].The Gondola slide (Figure 6B) is one ofthe largest mass failure deposits on theSAM. It is 10 km wide on the slope, up to

35 m thick, it has a total runout of about54 km [15] and a volume of the depositof about 30 km3. The evacuation zoneincludes a crescent-shaped headscarp lo-cated at the shelf edge with a maximumheight of 250 m with several sub-parallelsecondary scarps [15]. The morphologicalpattern reflects the interaction between thecomplex relief created by down-slope grav-ity flows and along-slope bottom currents[15, 18]. The Bari Canyon System (Fig-ure 6C) is a peculiar erosional-depositionalfeature characterised by two main, almostparallel, conduits emanating from a broadcrescent-shaped upper slope region [17].This setting is consistent with the flow ofbottom currents along the shelf from theNorth entering the canyon and interactingwith its complex topography, leading topreferential deposition on the up-currentside of pre-existing morphological relief[17]. Today, density-driven bottom cur-rents cascade off shelf and flow both acrossthe open slope and through the BCS, reach-ing velocities greater than 60 cm·s−1 [19].

3.4 Bathymetry and Oceanog-raphers - Multi Beam andSingle beam combined map

In the case of basin scale circulation mod-els, the Single Beam bathymetry of theItalian side of the Adriatic compiled byISMAR can be applied in oceanographicnumerical model as a uniform resolutiongrid. The main limitation in using this gridcomes from the heterogeneity of the bathy-metric data in terms of distribution andquality, and the possible errors generatedduring the interpolation procedures appliedto derive a grid with homogeneous resolu-tion. The Multi Beam bathymetry is moresuitable for bottom boundary layer appli-

454


cations and for tsunami-propagation sim-ulation models in specific areas. The re-liability of Multi Beam data is higher be-cause the Multi Beam Sys. guarantee a fullcoverage of the seafloor ensuring an ho-mogeneous data quality. The processingof this kind of data leads to the reductionof instrumental noises and to the genera-tion of a high resolution DTM where theuncertainty, given by the interpolation pro-cedures, is extremely reduced. The inte-gration of Single Beam with Multi Beambathymetry, using a variable resolutiongrid, allows the generation of a completebathymetric map functional at differentscales. The resulting combined bathymetryis useful for the oceanographers in detect-ing areas of maximum strength of bottom-hugging currents and defining the regionalmorphological trends; for example in areasof flow restriction caused by the presenceof narrow passageways or shallow shoals.

4 ConclusionsDue to its large extent (200 x 800 km) andits physiographic setting with a wide shelfarea in the North and a slope basin in theSouth, the Adriatic bathymetric map is theresult of a merger of dataset from numer-ous oceanographic surveys performed dur-ing the last decades with variable tools. Inparticular, large areas at shallow depth havebeen mapped with Single Beam tools andinterpolated, because an extensive MultiBeam mapping would have been too timeconsuming in such conditions. The Sin-gle Beam contour map of the Italian sideof the Adriatic Sea compiled by ISMAR-CNR shows, at basin scale, the follow-ing main geological features: 1) the coast-parallel extent of the late Holocene mud

wedge; 2) the occurrence of incised valleyson the north Adriatic shelf; 3) the distribu-tion of sand ridges and sand dunes of vari-able size on the north Adriatic shelf. TheMulti Beam maps of the South AdriaticContinental slope on the Italian side (from200 to 1200 m water depth) and of some se-lected areas of the continental shelf (from10 to 150 m) show: 1) the complexityand variability of the progradational clino-forms of the late Holocene prodelta wedge;2) widespread mass-failure features on theslope; 3) a large variety of bottom-currentfeatures; 4) the Bari Canyon System ac-tive during the Last Glacial Maximum, butstill impinged by shelf density currents; 5)the Dauno Seamount, the main structuralfeature on the slope, with a clear morpho-logic expression. The Multi Beam dataprocessing was based on an interpretativeapproach instead of a traditional line to linecleaning system. This approach allows toachieve a high resolution bathymetry fo-cusing the processing effort in revealingthe geologically most significant seafloorfeatures. The integration of Single Beamwith Multi Beam bathymetry using a vari-able resolution DTM (Tuning filter tool) al-lows the generation of a complete bathy-metric map useful at different scales. Theresulting combined bathymetry is usefulnot only for marine geologists, but alsofor oceanographers in detecting areas ofmaximum strength of bottom-hugging cur-rents and defining regional morphologi-cal trends. In perspective, the methodol-ogy illustrated here could be furthered withthe acquisition of the bathymetry on theEast side of the Adriatic Sea, through in-ternational scientific projects in collabora-tion with eastern Adriatic countries such asCroatia, Slovenia, Montenegro and Alba-nia.

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References[1] G. Giorgetti and F. Masetti. General morfology of the Adriatic Sea. Bollettino di

Geofisica teorica ed applicata, 11:44–56, 1969.

[2] B.C. Heezen, M. Tharp, and M. Ewing. The floors of the oceans, Part I, The NorthAtlantic. Geol. Soc. America Special Paper, 65:122, 1959.

[3] A. Correggiari, D. Penitenti, D. Ridente, M. Roveri, and F. Trincardi. La batimetriaad alta risoluzione del Mare Adriatico: una base di lavoro per studi multidisci-plinari. Primo Workshop SINAPSI Roma 6-8 aprile. 1998.

[4] A. Asioli. High resolution foraminifera biostratigraphy in the Central Adriatic basinduring the last deglaciation: a contribution to the PALICLAS Project. In: Guiliz-zoni, P., Oldfield, F. (Eds.), PalaeoenvironmentalAnalysis of Italian Crater Lakeand Adriatic Sediments (PALICLAS). Memorie del’Istituto Italiano di Idrobiolo-gia, 55:197 – 218, 1996.

[5] A. Correggiari, F. Trincardi, L. Langone, and M. Roveri. Styles of failure in heavily-sedimented highstand prodelta wedges on the Adriatic shelf. Journal of Sedimen-tary Research, 71(2):218–236, 2001.

[6] A. Cattaneo, A. Correggiari, L. Langone, and F. Trincardi. The Late-HoloceneGargano subaqueous delta, Adriatic shelf: sediment pathways and supply fluctua-tions. Marine Geology, 193:61–91, 2003.

[7] J.E.A. Storms, G.J Weltije, G.J. Terra, A. Cattaneo, and F. Trincardi. Coastal dy-namics under conditions of rapid sea-level rise: Late Pleistocene to Early Holoceneevolution of barrier-lagoon systems on the Northern Adriatic shelf (Italy). Quat.Sci. Rev., 27:1107–1123, 2008.

[8] F. Trincardi, A. Correggiari, and M. Roveri. Late Quaternary transgressive erosionand deposition in a modern epicontinental shelf: The Adriatic semienclosed basin.Geo-Marine Letters, 14:41–51, 1994.

[9] A. Cattaneo and F.Trincardi. The late-Quaternary transgressive record in the Adri-atic epicontinental sea: basin widening and facies partitioning. Isolated ShallowMarine Sand Bodies: Sequence Stratigraphic Analysis and Sedimentologic Inter-pretation. SEPM Spec. Publ, 64:127–146, 1999.

[10] A. Correggiari, M.E. Field, and F. Trincardi. Late Quaternary transgressive largedunes on the sediment-starved Adriatic shelf. Geology of Siliciclastic Shelf Seas.Geological Society Spec. Publ, 117:155–169, 1996.

[11] A. Cattaneo, F. Trincardi, L.Langone, A. Asioli, and P. Puig. Clinoformation gen-eration on Mediterranean Margins. Oceanography, 17(4):104–117, 2004.

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[12] T. Marsset, B. Marsset, Y. Thomas, A. Cattaneo, E. Thereau, F. Trincardi, andP. Cochonat. Analysis of Holocene sedimentary features on the Adriatic shelf from3D very high resolution seismic data (Triad survey). Marine Geology, 213:73–89,2004.

[13] F. Trincardi, A.Cattaneo, A. Correggiari, and D. Ridente. Evidence of soft-sedimentdeformation, fluid escape, sediment failure and regional weak layers within theLate-Quaternary mud deposits of the Adriatic Sea. Marine Geology, 213:91–119,2004.

[14] N. Sultan, A. Cattaneo, R. Urgeles, H. Lee, J. Locat, F. Trincardi, S. Berne,M. Canals, and S. Lafuerza. A geomechanical approach for the genesis of sedimentundulations on the adriatic shelf. Geochemistry Geophysics Geosystems, 9(4):1–25,2008.

[15] D. Minisini, F. Trincardi, and A. Asioli. Evidence of slope instability in the South-western Adriatic Margin. Natural Hazards Earth System Sciences, 6(1):1–20, 2006.

[16] G. Verdicchio and F. Trincardi. Short-distance variability in slope bed-formsalong the southwestern Adriatic margin (central Mediterranean). Marine Geology,234(1/4):271–292, 2006.

[17] F. Trincardi, F. Foglini, G. Verdicchio, A. Asioli, A. Correggiari, D. Minisini,A. Piva, A. Remia, D. Ridente, and M. Taviani. The impact of cascading currentson the Bari Canyon System, SW-Adriatic Margin (Central Mediterranean). MarineGeology, 246(2-4):208–230, 2007.

[18] G. Verdicchio, F. Trincardi, and A. Asioli. Mediterranean bottom-current deposits:an example from the Southwestern Adriatic Margin. Geological Society, London,Special Publications, 276:199–224, 2007.

[19] M. Turchetto, A. Boldrin, L. Langone, S. Miserocchi, T. Tesi, and F. Foglini. Par-ticle transport in the Bari canyon (southern Adriatic Sea). Marine Geology (VanWeering and Heussner, Eds.)., 246(Issues 2-4):231–247, 2007.

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458

Early Diagenesis of Carbon and Nutrients in Sedi-ments of the Gulf of Manfredonia (Southern Adri-atic Sea)

F. Spagnoli1, G. Bartholini1, E. Dinelli2, M. Marini1, P. Giordano3

1, Institute of Marine Sciences, CNR, Ancona, Italy2, Interdepartmental Research Centre for Environmental Sciences, University of Bologna,Ravenna, Italy3, Institute of Marine Sciences, CNR, Bologna, [email protected]

Abstract

The aims of the research presented here were to investigate the carbon and nu-trient cycles in sediments of the Gulf of Manfredonia and to understand their rolein the water column chemistry. Four cores were collected in two sites of the gulf inearly fall 2002 and late winter 2003. The cores were extruded for pore water (TCO2,DOC, alkalinity, nutrients, Si(OH)4, sulphate, Fe, Mn, Ca and Mg) and solid (grainsize, organic and total C, total N, 210Pb excess, 137Cs, 234Th) analyses. Further-more, fluxes at sediment-water interface have been measured by benthic chambersand calculated from pore water concentration profiles for O2, TCO2, DOC, alkalinity,nutrients, Si(OH)4, sulphate, Fe and Mn. Pore water data evidenced high inputs ofreactive organic matter in the two stations, diagenesis of organic matter progressesthrough oxygen consumption, denitrification, Mn-Fe-oxy-hydroxide reduction andweak sulphate reduction. Degradation processes are more intense during the warmseason. Bio-irrigation seems to be a consistent transport mechanism in both stations,with more evident effects in early fall in the outer station. Measured benthic fluxesshowed no clear difference between sites with slight higher values in the offshore sitein the warm season. Benthic flux comparison of the Gulf of Manfredonia with thenorthern Adriatic allowed evaluating the role of the gulf sediments in the chemistryof the south-western Adriatic Sea waters.

1 Introduction

The sediment-water interface is a site of in-tense chemical, physical and biological re-actions that can lead to the formation ofnew mineralogical phases, alteration of ex-isting minerals and to changes in the com-position of pore water and water columnthemselves. Reactions involving the ox-idation of organic matter are carried out

largely by bacteria that use a sequence ofelectron acceptors at decreasing redox po-tentials and increasing depth in the sedi-ment. It is well know that different ter-minal acceptors are used by the microbialcommunity in the order of decreasing freeenergy production per mole of organic car-bon oxidized [1]. These reactions are con-trolled by external factors, such as tem-perature, sedimentation rate, organic mat-


Marine Geology

ter inputs, sea bottom water chemistry andhydrodynamics, bioturbation and irrigation[1]. In coastal marine environments, withshallow waters and fine sediments, earlydiagenesis processes play an important rolein the biogeochemical cycling of nutrients,i.e. they determine the amount of nutrientsburied versus the amount of nutrients recy-cled to the water column as benthic fluxes[2, 3]. Such benthic fluxes can represent aninput comparable to, or higher than, inputsfrom terrestrial sources. Hence, nutrient in-puts and consequently the primary produc-tivity in shallow coastal ecosystems can beclosely associated with sea-floor biogeo-chemical processes [4].In this paper the results of a study regard-ing the interactions between sediments andwater column carried out in the PITAGEMProject [5] are presented. The study fo-cuses on early diagenesis processes andbenthic flux measurements in the Gulf ofManfredonia, a shallow basin in south-western Adriatic Sea (Figure 1), where sea-sonal variation of nutrient inputs and co-existence of multiple nutrient sources canproduce diagenetic process variations andinfluence quality and quantity of decom-posing matter. By studying the early dia-genesis processes and the benthic fluxes itwas also possible to evaluate organic mat-ter and nutrient regeneration in surface sed-iments and their role in the chemistry ofthe coastal waters of a confined area of thesouth-western Adriatic Sea.

2 Study area

The Gulf of Manfredonia is located in thewestern side of the southern Adriatic Sea(Figure 1). The gulf is delimited to theNorth by the Gargano Peninsula, whichmorphologically marks the northern bor-

der of the southern Adriatic.The general Adriatic Sea hydrodynamicpresents a cyclonic circulation in the south-ern sub-basin with a strong seasonal vari-ability [6] and a southward coastal cur-rent, enriched in nutrients, flowing alongthe western coast of the Adriatic basin(Western Adriatic Current, WAC, [6]). TheWAC connects the northern and southernecosystems and affects the biogeochemicalproperties of the whole western Adriaticbasin. However, in the southern AdriaticSea, open waters show clearly oligotrophiccharacteristics and the nutrient supply tothe euphotic zone depends strongly on thevertical stratification and mixing processes[7].This general hydrodynamic patternstrongly affects the biogeochemical prop-erties of the Gulf of Manfredonia that rep-resents a transition zone between the mid-dle and the southern Adriatic circulation.The gulf presents a main cyclonic gyre [8]that may reverse depending on wind direc-tion: cyclonic and anticyclonic gyres arerespectively generated by N-NW and S-SEwinds (Signell, personal communication);this circulation is slower in the inner sideof the gulf where a high sedimentation rateis present [9]. Furthermore, the inner areaof the gulf is characterised by high watercolumn nutrient contents and high primaryproduction (Spagnoli, unpublished data).As regards bottom sediments, previousstudies based on grain size analyses insurface sediments recognized 3 sedimenttypes: silt-sandy, silt and clay [10, 11].The distribution of these sediment typesis essentially the result of wave influence:grain-size in fact decreases with increasingwater depth and distance from the shore.Silt-sandy sediments are common in zonesadjacent to the shoreline between 2 and 4mdepth. Silty and clay sediments are found

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15.0 15.2 15.4 15.6 15.8 16.0 16.2 16.4 16.6 16.8 17.041.0

41.1

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41.4

41.5

41.6

41.7

41.8

41.9

42.0

42.1

0 20 40

Vieste

Manfredonia

Barletta

BariProjection ED50

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Candelaro

Ofanto10 20

50

100

120200

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Figure 1: Study area with early fall 2002 and late winter 2003 stations. S1 is the innerstation, S2 is the outer station.

in the central part of the gulf (> 8m ofdepth) and in the deeper zones. Further-more biogenic clastic fragments are foundin some coastal sites (> 6m of depth) dueto breaking of biogenic concretions.

3 MethodsDuring two oceanographic cruises carriedout in early fall (October 2002) and latewinter (March 2003) gravity cores werecollected in two stations (Figure 1) by us-ing a SW-104 corer, a device which assuresthe collection of undisturbed sediment-water interfaces [12]. The stations arelocalised in the inner side of the gulf at16 m depth (S1), supplied by mixed finesediments coming from northern Apulian

rivers (mainly the Ofanto River) and fromthe northern Adriatic Sea, and in the outerside of the gulf at 17 m of depth (S2),fed mainly by northern fine-grained sedi-ments [8]. The waters overlying the coreswere generally clear, suggesting minimaldisturbance and the sediment surface wasgenerally uneven. On board, cores weresectioned and centrifuged in inert atmo-sphere for pore water and solid phase sep-aration and analyses. Each core was sec-tioned in a nitrogen-filled glove-box andpunch in pH and Eh measurements weremade during the sectioning. In order toextract pore waters, the mud was trans-ferred into plastic tubes and centrifugedfor about 15 min at 5500 rpm in a re-frigerated centrifuge at the in situ temper-

461

Marine Geology

atures. Pore waters were filtered undera nitrogen atmosphere in plastic syringeholders (hydrophilic PTFE 0.45 µm mem-brane). Four not acidified splits were savedfor alkalinity, TCO2 (total dissolved inor-ganic carbon), DOC (Dissolved OrganicCarbon), NH+

4 , NO−3 , PO3−4 , Si(OH)4 and

SO2−4 measurements, another aliquot was

acidified (to about pH 1.5) and used forthe analysis of dissolved Fe, Mn, Ca andMg. Pore water extraction and filtrationwas generally completed within 6 hoursfrom core collection. The centrifuged mudwas frozen and subsequently dried at roomtemperature for analysis of solid phases(organic carbon (C-org), total carbon (C-tot) and total nitrogen (N)). Another mudaliquot was stored at 4°C and used forgrain-size analysis. In the first cruise repli-cate cores have been collected to estimatesedimentation rates and bioturbation coef-ficients by 210Pb excess, 137Cs and 234Thmeasurements. The excess activities of210Pb were calculated from 226Ra sup-ported 210Pb deduced from the activitiesof 214Pb and 214Bi. Radionuclides werecounted using an HPGe (30-60% relativeefficiency, 2 KeV of resolution). In the sec-ond cruise replicate cores were collectedto measure dissolved oxygen penetrationdepth by a microelectrode profiler.Furthermore,in situ benthic flux chamberswere deployed in each site to measure thedissolved fluxes of O2, TCO2, DOC, alka-linity, NH+

4 , NO−3 , PO3−4 , Si(OH)4, Fe and

Mn. Two chambers were deployed in eachsite to replicate the measurements. Ben-thic chambers capture approximately 39 lof water in contact with 0.25 m2 of seabottom. Each chamber was sampled sixtimes during deployments of about 24h.The incubation time of 24h was sufficientto generate measurable changes in concen-tration, but not enough to produce signifi-

cant changes in fluxes. A CsCl spike wasinjected in the incubations after the firstsampling and the observed dilution of thisspike in subsequent sample drawings wasused to calculate chamber volume and alsoas tracer for chamber-water exchanges withpore waters. Chambers were stirred by arotating paddle so that the diffusive bound-ary layer thickness was unaffected by theincubation.In sediment solid phase, porosity was cal-culated by wet loss after drying each sam-ple at 60°C, total and organic carbon andtotal nitrogen (all expressed as weight %)were measured by CHN elemental analyzer(Carlo Erba 1500) after removal of the in-organic carbon with HCl [13]. Organic ni-trogen was assumed equal to total nitrogen[14].Dissolved phosphate, ammonia, nitrate andsilicate were measured on pore water andbenthic chamber samples by colorimetricautoanalyser technique. Alkalinity was de-termined by Gran titration [15] and TCO2

was determined from alkalinity, pH, salin-ity and temperature. Additionally, in thesecond cruise, an aliquot of 5ml was col-lected for the analyses of TCO2 by mano-metric measurements [16]. Fe, Mn and Cswere determined on the acidified aliquotsby Flame-AAS. Ca and Mg were deter-mined by HPLC. For each parameter anal-ysed benthic fluxes were calculated as theproduct of the slope of concentration vs.incubation time and chamber height, with-out including bottom water data in the cal-culation. As the incubation time increases,there is the possibility that chamber chem-istry or other artefacts do not produce con-stant fluxes and this is recognizable by datatrends. For this reason benthic flux calcu-lations were determined only from the lin-ear portion of the concentration vs. timeplots [17] and no flux was reported if we

462


had fewer than 4 data points. Using twodeployments, fluxes were averaged and theuncertainty in the mean was calculated intwo ways: (a) as the standard error of themean; (b) as the square root of the sum ofthe variance of each flux value, divided bythe number of flux measurements. We re-port the larger of these two uncertainties,following the procedure described by [18].


4.1 General setting and porewater profiles

In early fall 2002 the water column washomogeneous with a mean temperature ofabout 21°C in both stations.In the late winter 2003 the water columnwas characterised by homogeneous tem-perature at 11°C in the inner station and aweak stratification in the upper 2 m in theouter station (bottom water at 12°C).Water column productivity in the gulf hasbeen shown to be higher in summer months(Spagnoli unpublished data).Dissolved oxygen, in continental slope andrise sediments underlying well-oxygenatedbottom waters, is the most important elec-tron acceptor for the organic matter decom-position. In sediments of these environ-ments anoxic conditions occur from fewmillimetres to few centimetres of depth de-pending on the balance between sedimen-tation rates and organic matter inputs. Forthis reason the sedimentary oxygen con-sumption rate is a good indicator of organicmatter oxidation rates in most of thesesites. In the sampled stations dissolvedoxygen decreases exponentially below thesediment-water interface and at a depth ofabout 1 cm suboxic conditions [20] occurin both sites (Figure 2). Higher oxygen

concentration at the sediment-water inter-face and sharper gradient are displayed atS2 station. Nitrate pore water profiles (Fig-ure 3 and 4, plot A) show decreasing val-ues up to about zero in the first centime-tre of the sediment after an early increasenear the sediment-water interface in bothstations and seasons. The peaks are weaklyhigher in early fall. These nitrate concen-tration trends indicate that already at 1 cmof depth the suboxic conditions prevails forthe degradation of the organic matter. Athigher depth, up to about 20 cm, someweak and irregular nitrate increases takeplace; they could be due to nitrificationor irrigation processes related to biologicalactivity. Instead initial nitrate peaks are at-tributed to nitrification processes that ori-gin for the ammonium migration towardsthe sediment-water interface where it ox-idizes for the oxic conditions present nearthe surface. Down to the nitrate peak a den-itrification process take place by bacteriathat use the nitrate as final electron accep-tor and that produce a nitrogen (N2) loss inthe system.Furthermore, immediately below the ni-trate peaks, suboxic diagenesis takes placeas indicated by the pore water concentra-tion profiles of dissolved manganese andiron (Figure 3 and 4, plots B and C). Thisagrees with the well-established diageneticreaction depth sequence that are governedby the preferential use of Mn and Fe ox-ide phases as electron acceptors after thenitrates because they provide the highestamount of free energy for the bacteriallymediated oxidation of organic matter [13].Dissolved manganese profiles exhibit, inboth stations, near surface peaks (between0.5 cm and 1 cm of depth), just below theoxygen penetration depth and nitrate peak.A secondary peak in Mn pore water profileis observed in S2 site at 13 cm in early fall.

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Figure 2: Microprofiles of dissolved oxygen measured in the inner (S1) and outer (S2)stations of the Gulf of Manfredonia in late winter 2003.

The dissolved Fe shows, in all profiles, asharp increase just below the depth rangein which Mn concentrations reach maxi-mum values. At higher depth dissolvediron concentrations decrease rapidly downto 10–20cm and then increase in both fallcores and in the S2 winter core. The in-crease of dissolved Fe below the first peaksuggests a complexation with dissolved re-fractory organic matter that prevents theprecipitation of dissolved Fe with sulphurto form FeS, thermodynamically preferred,or with carbonate, as siderite. The peaksof dissolved Mn and Fe near the interfaceare attributed to the dissimilated reduc-tion of manganese and iron oxy-hydroxidesby bacteria activity in anaerobic condition:these oxide phases are used as terminalelectron acceptors by bacteria for the or-ganic carbon oxidation.About the sulphate pore water profiles(Figure 3 and 4, plot D), the trends are

rather constant displaying a weak decreasebelow 40 cm in S1 station (Figure 3, plotD) and below 20 cm in S2 station (Fig-ure 4, plot D). These trends indicate thata slight organic matter mineralization bysulphate reduction takes place down thesedepths without however reaching suboxicsulphidic conditions.The organic matter decomposition using,in order, dissolved oxygen, nitrates, Mnand Fe oxy-hydroxides and sulphates aselectron acceptors, results in the release ofammonia and TCO2 into the pore waters,other than the phosphate which concentra-tions are affected also by other complexprocesses. Pore water data (Figure 3 and4) reflect this process, as they show NH+

4

and TCO2 concentration increases below20 cm for S1 station and below 10 cmfor S2 station. From the sediment-waterinterface to 10-20 cm of depth, the dis-tribution of both organic matter degrada-

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Figure 3: Pore water profiles of electron final acceptors (NO−3 , Mn2+, Fe2+ and SO2−4 )

and main organic matter degradation products (NH+4 , TCO2 and phosphate) and silica

in cores collected in Gulf of Manfredonia in S1 station in early fall 2002 (yellow) andlate winter 2003 (red). Depth intervals were 0.5 cm for the first four layers, 1 cm for thenext 4 layers, 3 and 5 cm for the subsequent data; data are plotted at the mid-point of thesampling layer. Data at −1 cm indicate bottom water values.

tion products are scattered suggesting irri-gation and bio-mixing processes. In thiscase macrofauna activity deepens, channel-izes and increases the solute fluxes acrossthe sediment-water interface. At greaterdepths the constant increase of ammoniumand TCO2 indicates that only diffusive pro-cesses take place. The NH+

4 released to thepore waters by suboxic diagenesis diffusesupwards in the sediment column, wherepart of it is oxidized in the first millime-tres before reaching the sediment-water in-terface giving rise to the nitrate peaks.On the whole the organic matter degrada-

tion product concentrations (range valuesbetween 2.3 and 11 mM for TCO2 and0.004 and 0.8 mM for ammonium) andtheir distributions in the pore waters high-light high reactive organic matter inputsinto the sediments without a strong differ-ence between the two stations. The higherdegradation product concentrations in earlyfall in both stations (Figure 3 and 4, plotsE and F) suggest stronger degradation pro-cesses driven by the higher temperature;this is inferred both from the high depthsof the higher concentrations and also fromsatellite data that exclude important fresh

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Marine Geology

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Figure 4: Pore water profiles of electron final acceptors (NO−3 , Mn2+, Fe2+ and SO2−4 ),

main organic matter degradation products (NH+4 , TCO2 and phosphate) and silica in

cores collected in Gulf of Manfredonia in S2 station in early fall 2002 (yellow) and latewinter 2003 (red). Depth intervals were 0.5 cm for the first four layers, 1 cm for thenext 4 layers, 3 and 5 cm for the subsequent data; data are plotted at the mid-point of thesampling layer. Data at −1 cm indicate bottom water values.

marine organic matter inputs.The phosphate concentrations in pore wa-ters in all cores have similar trends (Fig-ure 3 and 4, plot G): they show a rapidand irregular increase near the surface(about 3 cm depth) and a second strongerpeak at about 17-20 cm, at higher depththe profiles approach the analytical detec-tion limit. The higher values are shownin S1 cores. These variable trends aredue to the complexity of the phospho-rous cycle: the low concentrations nearthe sediment-water interface are due to theco-precipitation of the phosphate with the

Fe oxy-hydroxides in the oxic environmentpresents near the sediment-water interface;the phosphate concentration increases fromthe sub-surface to about 20 cm depth arethe result of release by organic matter de-composition and Fe-oxy-hydroxide disso-lution in suboxic environment; at higherdepths the phosphate decreases result fromthe authigenic mineral phosphate precipita-tion (apatite or fluoroapatite).The silica concentration profiles presentdistinctive and always similar patternssince they reflect a different process re-spect to the degradation of organic matter:

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Figure 5: Dissolved benthic fluxes measured by benthic chamber in Gulf of Manfredo-nia in S1 (a) and S2 (b) stations in early fall 2002 (yellow) and late winter 2003 (red).Units are µmol·m−2 · d−1 for NO−3 , Mn2+, Fe2+, NH+

4 , PO3−4 , Si(OH)4 and SO2−

4 andm·mol·m−2 · d−1 for O2 and TCO2.

mainly they are the consequence of the dis-solution of the diatom silicatic exoskele-tons. The silica profiles in both stations andseasons show a sharp increase below thesediment-water interface up to values thatremain constant with depth (Figure 3 and4, plot H). This is due to the diatom skele-ton dissolution that produces dissolved sil-ica up to the reaching of the equilibrium be-tween the solid and liquid phase at depth.

4.2 Chamber data

Benthic chamber fluxes were measured foroxygen, nitrate, Mn, Fe ammonium, TCO2,phosphate and silicate, in both sites and

seasons (Figure 5a and Figure 5b).In the case of oxygen a general similar up-take (negative fluxes) occurred in both sta-tions with a slight increase in early fall.These patterns confirm the aerobic organicmatter degradation near the sediment-waterinterface with the higher values in early falldue to the higher temperatures that promotethe bacterial activity.Nitrate fluxes were very low and directedinto the sediment in S1 site and higher andout of the sediment in S2, greatest vari-ability is evident in S2. This complex be-haviour is connected with the nitrificationand denitrification processes that take placenear the interface and inside the benthic

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Marine Geology

-20,00

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Figure 6: Comparison of benthic fluxes measured in the Gulf of Manfredonia and in theNorthern Adriatic Sea [19]. Fluxes are in m·mol·m−2 · d−1.

chamber: in case of low fluxes, as our case,nitrification and denitrification mask thefluxes due to diffusion and irrigation. Dis-solved manganese and iron show positivefluxes with stronger seasonality in S1 site.These fluxes are produced by the dissolu-tion of Mn and Fe oxy-hydroxides at thechange from oxic to suboxic conditions.Organic matter degradation products (Am-monium and TCO2) fluxes were alwaysdirected out of the sediment, with higherfluxes occurring in early fall, this is afurther confirmation of the higher organicmatter degradation in the warmer season.Furthermore, in the case of the ammonium,calculated fluxes are always higher than themeasured ones. This difference can be ex-plained with a nitrification processes near

the oxic sediment-water interface (as sup-ported by the strong nitrate peaks near theinterface) that remove part of the ammo-nia produced by the organic matter degra-dation.As regards the phosphate, positive fluxeswere always measured, they are mainly dueto the anoxic Fe-oxy-hydroxide dissolutionnear the sediment-water interface that re-leases the phosphate co-precipitated withFe-oxy-hydroxides in oxic environment.Also the silica shows positive fluxes gener-ated by the dissolution of the silicatic ex-oskeleton of diatoms.Other major findings can be deduced bythe comparison between the measured andthe calculated fluxes (Table 1). By com-paring the measured and calculated TCO2

468


Stations S1 S1 S2 S2 Benthic fluxes (mmol/m2 d) Early fall Late winter Early fall Late winter TCO2 Measured by chamber 17.95±2.05 4.84±1.49 46.94±8.58 4.65±0.56 Calculated diffusive Constant Rz 22.62 7.67 15.04 8.22 Exponential Rz - 9.76 16.77 8.08 Diffusive/Measured % 126 202 36 174 Ammonium Measured by chamber 0.19 0.15 1.05 0.12 Calculated diffusive Constant Rz 0.71 2.16 2.45 0.56 Exponential Rz Diffusive/Measured % 374 1440 233 467 Phosphate Measured by chamber 0.01 0.001 0.02 0.002 Calculated diffusive Constant Rz 0.005 0.003 0.01 -0.003 Exponential Rz Diffusive/Measured % 50 300 50 -150 Silica Measured by chamber 1.02±0.05 1.01±0.08 2.47±0.37 1.07±0.24 Calculated diffusive Constant Rz 0.66 0.42 0.51 1.24 Exponential Rz 1.06 0.81 0.99 1.64 Diffusive/Measured % 104 80 40 153

Table 1: Comparison of measured and calculated benthic fluxes in the S1 and S2 stationsin early fall 2002 and late winter 2003.

fluxes it raises that diffusive fluxes pre-vail in both stations and seasons (diffusivefluxes higher or equal to measured fluxes)except for the outer stations (S2) in fall,where the lower calculated flux respect tothe measured one suggest the presence ofirrigation processes.Also in the case of the silica and phosphatethe irrigation clearly prevails in the earlyfall outer station (lower calculated flux re-spect to the measured ones). Finally, mea-sured benthic fluxes in the Gulf of Man-fredonia and in the northern Adriatic Seahave been compared (Figure 6) to establishthe role of the sediments of the gulf in thechemistry of the western Adriatic Sea wa-ters. From this comparison it results thatthe benthic fluxes of nutrients and of oxy-gen in the Gulf of Manfredonia are lowerthan those of the northern Adriatic Sea andthis is attributed to the higher inputs offresh marine organic matter, fresh and old

continental organic matter and inorganicsolid inputs to the sediments in the northernAdriatic Sea connected to the higher dis-solved and solid load of the Po River.In any case the results indicate that also inthe Gulf of Manfredonia the fluxes of nu-trients to the water column and the oxy-gen consumption are able to affect the wa-ter column chemistry contributing to theeutrophication and dystrophic processes ofthe southern Adriatic Sea.

4.3 Solid phaseIn the two sites surface sediments have aporosity of 0.75-0.8 with decreasing valuesup to 0.60-0.65 at 25-30 cm depth (Fig-ure 7, plot A and D). The excess activ-ity of 210Pb, decreasing exponentially be-low the interface in both stations (Figure 8,plots A and D), may be used to estimatethe sediment accumulation rates. Applying

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Marine Geology

late winterearly fall

late winterearly fall

Figure 7: Porosity (A and D), C-org (B and E) and C-org vs. N total (C and F) fromcores collected in Gulf of Manfredonia in early fall 2002 (red triangles) and late winter2003 (yellow squares) in S1 and S2 stations.

Constant Flux-Constant Supply (CF-CS)model to the 210Pb excess profiles [21],sedimentation rates (w) from each stationswere estimated to be 0.52 cm·y−1 in sta-tion S1 and 0.49 cm cm·y−1 in station S2.These values are similar to those calculatedby [19] and by [22] in the northern AdriaticSea. In order to check sedimentation ratesthe vertical profile of 137Cs (Figure 8, plotsB and E) is used. It is well know that asignificant input of this radionuclide in theenvironment occurred in the 1963 relatedto atmospheric weapon tests. Hence max-

ima concentrations in caesium vertical pro-files correspond to sediments buried in thistime [23], supporting the dating calculatedby 210Pb excess.Thorium activities were also measured asuseful tracer of sediment mixing (Figure8, plots C and F). The mixing of the up-per 10 cm of sediment caused by macro-fauna is referred to as bioturbation; it canalter the physical and chemical propertiesof sediment affecting both particle and so-lute transport [24, 2, 25]. In order to cal-culate bioturbation coefficients (Db) the re-

470


Figure 8: Profiles of solid phase parameters in the inner station (S1: A, B and C) andouter station (S2: D, E and F) of the Gulf of Manfredonia. The solid line shows theexponential function fit of excess 210Pb vs. mass depth.

lation calculated by [26] was applied to234Th exponential profile (S2 station) andDb was estimated to be 0.2 cm2 ·y−1. Thisvalue falls at the low end of the compila-tion of [27] relating Db to w for similarenvironments; this could be explained bythe episodic presence of low oxygen bot-tom water. The profiles of 234Th in sta-tion S1 is constant from sediment-water in-terface down to 5 cm, suggesting a biotur-bated layer too.Organic carbon concentrations in all cores(Figure 7, plots B and E) rapidly decreasefrom the sediment-water interface to 5-7cm, at greater depths C-org reaches lowconstant values and exhibits a regular trendinterrupted only by relatively high values atabout 20 cm in both sites. Total N concen-trations also show a down-core decreasingtrend. These trends indicate the degrada-tion in the first centimetres of the more la-

bile fraction of the total organic matter con-tent of the sediments.Marine continental margin sediments are amixture of terrestrial and marine compo-nents. As regards the C-org/N, the Red-field ratio of C:N:P in marine sediments,106:16:1 (C/N=7), is considered repre-sentative of settled marine phytoplankton,whereas higher values may reflect inputs ofterrestrial derived particulate organic car-bon or the breakdown marine organic mat-ter. For these reasons the C-org/N ratiomight be used to identify the source of theorganic matter undergoing diagenesis [13].The C-org/N ratios range from 5±2 to 7±2in late winter and in early fall cruises re-spectively (Figure 7, plots C and F), withhigher values shown by surface sedimentscollected in early fall that are similar thosecalculated in North Adriatic Sea by [22].Therefore, the origin of organic matter in

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Marine Geology

the gulf is prevalently marine.

5 ConclusionsPore water concentration profiles of fi-nal electron acceptors for organic car-bon oxidation indicate that in the Gulf ofManfredonia early diagenesis progressestrough oxygen consumption, denitrifica-tion, manganese and iron oxy-hydroxidereduction and slight sulphate reductionwhile methanogenesis does not takes place.The high concentrations of the organicmatter degradation products in the gulfsupport high inputs of reactive organic mat-ter without a strong difference among thetwo areas. In the warmer season the degra-dation processes are more intense in bothstations for the higher temperature that en-hances microbial activity.Pore water concentration profiles also indi-cate the presence of other processes nearthe sediment-water interface such as thecoupled phosphorous and iron cycling, byrepeated iron oxy-hydroxide dissolutionand precipitation in anoxic and oxic envi-ronment, the nitrification and denitrifica-tion processes, the irrigation processes and,at greater depths, the phosphorous, man-ganese and iron precipitation in authigenicminerals.Solid phase concentration profiles high-light inputs of prevalently marine organicmatter (low C-org/N ratio) in both stationsand high sedimentation rate in the gulf.The measured benthic fluxes disclosed an

important role of the sediments in the Gulfof Manfredonia as supplier of nutrientsto the water column, in particular for theTCO2, and as sinker of dissolved oxygen,contributing in this way to increase the eu-trophication and anoxic processes and toaffect the carbon dioxide dynamics in thewater column.From the comparison between the mea-sured and calculated benthic fluxes it raisedthe confirmation of the irrigation processesin the outer station in the warmer sea-son and the nitrification processes near thesediment-water interface.Finally, by comparing measured benthicfluxes of the Gulf of Manfredonia and ofthe northern Adriatic Sea it follows thatlower organic matter degradation processesin Manfredonia Gulf take place respect tothe North Adriatic Sea mainly for the lowerorganic matter and inorganic solid inputs tothe sediments in the southern Adriatic Sea,however these fluxes are able to affect thewater column chemistry.

6 Acknowledgements

We wish to acknowledge Giovanni Ca-solino for the invaluable assistance to carryout the on-board operations and PieroTrentini and R. Belastock for the help re-spectively in metal and TCO2 analyses. Fi-nancial support for this research was pro-vided by the Consiglio Nazionale delleRicerche trough the PITAGEM project.

References[1] R.A. Berner. Early Diagenesis: A Theoretical Approach. page 241, 1980.

[2] R.C. Aller. Quantifying solute distribution in the bioturbated zone of marine sed-

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iments by defining an average microenvironment. Geochimica et CosmochimicaActa, 44:955–1965, 1980.

[3] D.E. Hammond, C. Fuller, D. Harmon, B. Hartman, M. Korosec, L. Miller, R. Rea,W. Berelson, and S. Hager. Benthic fluxes in San Francisco Bay. Hydrobiologia,129:69–90, 1985.

[4] J.E. Cloern. Phytoplankton bloom dynamics in coastal ecosystems: a review withsome general lessons from sustained investigation of San Francisco Bay, California.Reviews of Geophysics, 34:127–168, 1996.

[5] A. Specchiulli, F. Spagnoli, F. Dicembrini, and A. Conversi. The PITAGEMProject: an example of integrated, continuous and punctual coastal monitoring inthe Gulf of Manfredonia, adjacent to the Gargano National Park. Bollettino di ge-ofisica teorica ed applicata, 44:69–77, 2003.

[6] A. Artegiani, D. Bregant, E. Paschini, N. Pinardi, F. Raichic, and A. Russo. TheAdriatic Sea general circulation. Part II: Baroclinic Circulation Structure. Journalof Physical Oceanography, 27:1515–1532, 1997.

[7] D. Vilicic, Z. Vucak, A. Skrivanic, and Z. Grzetic. Phytoplankton blooms in olig-otrophic open South Adriatic waters. Marine Chemistry, 28:89–107, 1989.

[8] F. Spagnoli, G. Bartholini, E. Dinelli, and P. Giordano. Geochemistry and particlessize of surface sediments of Gulf of Manfredonia (Southern Adriatic Sea). Estuar-ine Coastal and Shelf Science, 80:21–30, 2008.

[9] V. Damiani, C.N. Bianchi, O. Ferretti, D. Bedulli, C. Morri, M. Viel, and G. Zurlini.Risultati di una ricerca ecologica sul sistema marino pugliese. Thalassia Salentina,18:153–169, 1988.

[10] W. Sigl. Der Golf von Manfredonia (Sudliche Adria). I. Die fazielle Differenzierungder Sedimente. Senckenbergiana marittima, 5:3–49, 1973.

[11] M. Viel, V. Damiani, and M. Setti. Caratteristiche granulometriche e composizionemineralogica dei sedimenti della piattaforma pugliese. pages 127–147, 1986.

[12] A. Magagnoli and M. Mengoli. Carotiere a gravita SW-104. (27):1–45, 1995.

[13] P.N. Froelich, G. Klinkhammer, M.L. Bender, N.A. Luedtki, G.R. Heath, D. Cullen,P. Dauphin, D. Hammond, and B. Hartman. Early oxidation of organic matter inpelagic sediments of the eastern equatorial Atlantic: suboxic diagenesis. Geochim-ica et Cosmochimica Acta, 43:1075–1095, 1979.

[14] P. Giordani and L. Angiolini. Chemical parameters characterizing a NW Adriaticcoastal area. Coastal Shelf Science, 17:159–167, 1983.

[15] J.M. Gieskes and W.C. Rogers. Measurements of total carbon dioxide and alkalin-ity. Journal of Sedimentary Petrology, 43:272–277, 1973.

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[16] D.C. McCorkle and S.R. Emerson. The relationship between pore water carbonisotopic composition and bottom water oxygen concentration. Geochimica et Cos-mochimica Acta, 52:1169–1178, 1988.

[17] W.M. Berelson, D. Heggie, A. Longmore, T. Kilgore, G. Nicholson, and G. Skyring.Benthic Nutrient Recycling in Port Phillip Bay, Australia Estuarine. Coastal ShelfScience, 46:917–934, 1998.

[18] D.E. Hammond, J. McManus, W. Berelson, T. Kilgore, and R. Pope. Early dia-genesis of organic carbon in the equatorial Pacific: rates and kinetics. Deep SeaResearch, 43:1365–1412, 1996.

[19] P. Giordani, D.E. Hammond, W.M. Berelson, R. Poletti, G. Montanari, A. Milandri,M. Frignani, L. Langone, M. Ravaioli, and E. Rabbi. Benthic fluxes and nutrientbudgets for sediments in the Northern Adriatic Sea: burial and recycling efficien-cies. Science of the Total Environment, 5:251–269, 1992.

[20] R.A. Berner. A new geochemical classification of sedimentary environments. Jour-nal of Sedimentary Petrology, 51:359–365, 1981.

[21] C. Lalou. Sediments and sedimentation processes. pages 384–406, 1982.

[22] D.E. Hammond, P. Giordani, W. Berelson, and R. Poletti. Diagenesis of carbon andnutrients in sediments of the Northern Adriatic Sea. Marine Chemistry, 66:53–79,1999.

[23] J.K. Cochran. Particle mixing rates in sediments of the eastern equatorial Pa-cific: evidence 15 from 210Pb, 239,240Pu, and 137Cs distributions at MANOP sites.Geochimica et Cosmochimica Acta, 49:1195–1210, 1985.

[24] D.R. Schink and N.L.J. Guinasso. Redistribution of dissolved and adsorbed mate-rials in abyssal marine sediments undergoing biological stirring. American Journalof Science, 278:687–702, 1977.

[25] J.Y. Aller and R.C. Aller. Evidence for localized enhancement of biological activityassociated with tube and burrow structures in deep-sea sediments at the HEBBLEsite, western North Atlantic. Deep-Sea Research, 33:755–790, 1986.

[26] H.P. Pope, D.J. Demaster, C.R. Smith, and H. Seltman. Rapid bioturbation in equa-torial Pacific sediment: evidence from excess 234Th measurements. Deep Sea Re-search II, 43:1339–1364, 1996.

[27] T.K. Tromp, P. Van Cappellen, and R.M. Key. A global model for the early diage-nesis of organic carbon and organic phosphorus in marine sediments. Geochimicaet Cosmochimica Acta, 59:1259–1284, 1995.

474

Deep Sea Depositional Systems: Processes, Archi-tecture and Controls

F. Gamberi, G. Dalla Valle, M. Marani, M. Rovere, F. Trincardi, F. FogliniInstitute of Marine Sciences, CNR, Bologna, [email protected]

Abstract

Due to the needs for exploration and exploitation of resources in the deep ma-rine environment and thanks to the development of new investigation techniques,the study of deep sea depositional systems has flourished in the last years. ISMARhas contributed to this field of research through the acquisition of a large amountof high resolution data (multibeam, sidescan sonar, high resolution profiles, seafloorsamplings) and through their integrated interpretation aimed at defining the char-acteristics of the deep sea environments. In this paper, we present the results ofrecent researches carried out at ISMAR dealing with the geomorphological analysisof canyons, channel levee complexes, mass transport complexes, depositional lobesand countourite drifts that are the main architectural elements of deep sea deposi-tional systems. Their large scale geometry and the distribution of their componentsand facies are reconstructed and defined with a process sedimentology approach todetermine the character of their genetic sedimentary processes. Studies are also fo-cussed at the definition of the factors that influence the transfer of sediment from thecoastal areas to the deep sea. Recent studies have pointed out the relative impor-tance of the characteristics of the source area, of sea level variations, of the initiatingmechanisms of sediment gravity flows, of seafloor topography and gradient on theevolution of deep sea depositional systems on a range of margins with largely differ-ent geological setting. The results of the studies have applications in the definition ofanalogues for hydrocarbon reservoir characterization and for the study of geomarinehazards.

1 Introduction

In the recent years, the comprehensionof deep-sea depositional systems has ad-vanced significantly. Much of the newideas come from studies of outcrops, of3-D seismic volumes with the develop-ment of the concepts of the seismic geo-morphology interpretation, of drilling dataand of modelling of the processes thatcontrol sediment transport and deposition.Also, the study of modern systems hasmuch contributed to the revitalization of

the researches dealing with deep-sea de-positional systems. Although ISMAR isactively working in many of the abovefields of research, its main contributions tothe understanding of deep-sea depositionalsystems come from the study of the modernenvironment, in particular in the marine ar-eas surrounding the Italian peninsula. Inthis paper, we describe the methodologyused to acquire and interpret data in thedeep-sea environment. Then we focus onthe studies aimed at the characterization ofsedimentary processes and at the definition


Marine Geology

Figure 1: Shaded relief map from multibeam bathymetric data showing the extent ofacquired data in the Tyrrhenian Sea [1] and in the in the southern Adriatic margin [2].

of the geomorphic elements that representthe basic components of the deep-sea depo-sitional environment. Finally, we describehow the spatial and temporal arrangementof the basic geomorphic elements can beused to infer variations of controlling fac-tors.

2 Imaging and interpreta-tion of the deep-sea de-posit

In the recent year, ISMAR has acquireda large amount of multibeam data in theItalian Sea [1, 3] (Figure 1). The multi-beam acquisition technology furnishesbathymetry data and gives images of theseafloor topography with a detail compa-rable to the observations possible on land(Figure 1). The multibeam technology also

offers the possibility of acquiring seafloorreflectivity data that are used to qualita-tively map sediment grain size and textureat the seafloor (Figure 2). Deep-tow sides-can sonars furnish data that are also usedto map sediment distribution at the seafloorbut they give a much higher resolution thanmultibeam reflectivity often allowing theinterpreter to map features at a metric scale(Figure 3). Subbottom profiles gives im-ages of the first tenth of ms below theseafloor with a vertical resolution whichcan be below 1 m and are used to recon-struct the distribution of depositional bod-ies and erosional surfaces in the near sub-seafloor section (Figure 3). Finally, seis-mic data that image subseafloor stratigra-phy down to kms below the seafloor, areused to extend the scale of temporal obser-vation and to analyze the evolution of deepsea depositional environments at a basinscale and for temporal interval that can

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Figure 2: Mulibeam seafloor reflectivity draped over bathymetric data. In the Gioia basina meandering channel is flanked by a straight one. The bathymetric data show the fine-scale detail of meandering channel evolution in a way similar to rivers. Crevasse splaysare located on the outer side of bends along the channel courses.

span millions of years (Figure 4). Seafloorsamples are used to groundtruth the obser-vations made with all the above geophysi-cal data and through bio-stratigraphic anal-ysis to date particular events.

3 Sedimentary processesin the deep-sea deposi-tional

A variety of gravity-driven flows is re-sponsible for the transfer of sediment fromthe shallow water, coastal and shelf ar-eas though the continental slope to thebasin plain. Debris/rock fall consists inthe free downslope tumbling of hard sed-iment or fragmented bedrocks that fail sud-denly from steep slopes. They usually re-

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Figure 3: Deep towed sidescan sonar data on the Stromboli slope valley. The resolutionof the image allows to define a series of small scale intra-channel erosional and deposi-tional features. The corresponding subbottom profile gives an high resolution image ofthe near subseafloor stratigraphy. In particular, it enables to define a fine grained areawith parallel reflectors and good penetration to west (left) of the coarse grained channelfloor characterized by low penetration.

sult in local, small areal extent deposits.Debris/rock avalanches are similar to de-bris/rock falls but are larger flows in whichclasts collide and share their momen-tum. Submarine debris/rock avalanches aremostly observed in steep volcanic slopes,such as that studied in the Stromboli Is-land submarine flank that was at the ori-gin of a tsunami in 2002 [4]. Slumps andslides are movement of coherent sedimentmasses above discrete basal shear surfaces.Many examples of slumps and slides are

currently studied at ISMAR; they are notdescribed here since they are the focus ofa dedicated contribution in this volume [5].Debris flows have plastic rehology and arepoorly sorted mixtures in which clasts floatin a fine-grained matrix with finite shearstrength. Debris flow result in chaotic orpoorly organised depositional bodies thatare found along many tracts of deep seadepositional systems recently being recog-nized as a component of frontal splay basinplain deposition [6, 7]. Turbidity currents

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Figure 4: Seismic data showing the Milazzo and Niceto channels and their levee wedgewith a train of bedforms. Some portion of the levee wedge area affected by incipientinstability.

are flows of mixed sediment that are main-tained in suspension by fluid turbulenceand can have strong erosional character.Deposition from turbidity currents can beassociated with traction at the seafloor orto rapid fall out from suspension depend-ing on seafloor gradient and on the degreeof flow confinement (Figure 5). Sedimentgravity flows are often part of a continuumwhere one flow can transform into another.The investigations of the causes that drivethe various type of flow transformation inthe deep-sea environment is part of the on-going research at ISMAR [8, 4, 9].

4 Deep-sea depositionalsystems: basic geomor-phic elements

Depending on the character of sedimentgravity flows, six main key geomorphic el-ements are recognized in the deep-sea de-positional environment: canyons, leveedchannels, channel overbank levees, frontalsplays, contourite mounds and drifts, masstransport complexes. The recent researchescarried out at ISMAR on mass-transportcomplexes are not included in the follow-ing description since they will be treatedelsewhere in this volume [5].Canyons. Submarine canyons, the prox-imal trunk of deep sea depositional sys-tems, are amongst the largest features onthe earth and are mainly sites of sediment

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Figure 5: Reconstruction of longitudinal and transversal variations in channel floor fea-tures and grain-size in the Stromboli slope valley. The arrangement of erosional andtraction fuatures and featureless seafloor portions is due to different flow behaviour inresponse to variation in confinement degree and seafloor gradient.

transport and erosion. Usually they arelocated in the continental slope, that con-nects the shelf with the basin plain, wherethe steep gradient allow flows to maintainan erosional behaviour. In the continen-tal slope, the locations of canyons is oftencontrolled by river distribution on land [9],simple v-shaped or flat bottomed canyonsare typical river-connected features. How-ever, canyons can also develop away fromriver mouths in areas affected by seafloorinstability resulting in highly degraded fea-

tures forming complex embayments oftenindenting the shelf-break [10]. Recentstudies carried out at the Institute haveshown that canyons can also form awayfrom the continental slope where steep es-carpments are present along topographi-cally complex margins [11, 12]. In thiscases, canyons can also propagate upwardin relatively flat area where headward ero-sion induced by downslope eroding sedi-ment gravity flows causes knickpoint ret-rogradation [12] (Figure 6).

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Figure 6: Gradient variations (solid line) and depth of incision (crosses) along the Strom-boli slope valley. The steeper sectors (III and IV) correspond with tracts with canyonmorphology and are controlled by fault (F) crosscutting the slope valley course. Theycorrespond with knickpoihat

Leveed channels. At the base of the conti-nental slope or elsewhere where a suddendecrease in seafloor gradient occurs, thesediment gravity flows that are funnelledwithin canyons lose energy, become depo-sitional and result in the formation of chan-nels. Channel have a large variety of di-mension and planform depending on thecharacter, size and grain size of the flowsand on seafloor gradient. A recent studyof leveed channels in the Calabrian mar-gin has shown that straight and meanderingchannels run parallel in a slope sector with-out gradient variation, pointing to a relativemajor impact of flow character and grain-

size on channel planform [13] (Figure 2).It also highlights that the gradient thresh-old for the transition from straight to sin-uous channel planform much depends onthe grain size of the flows [13]. Erosionalscours, inner levees, longitudinal barforms,inner meander bars are all features that de-velop within the floor of submarine chan-nels (Figure 5). Their distribution is con-trolled by longitudinal and transversal vari-ations in flow behaviour that are mainlycontrolled by channel planform, degree offlow confinement, and seafloor gradient(Figure 5). Researches in the Adriatic seahave shown that submarine channels can

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also be affected, or in the extreme case fedmainly by geostrophic currents (Figure 7)[10].Channel overbank levees. Overbank lev-ees are wedges of sediment constructedalongside channels through the depositionof the finer, upper part of sediment-gravityflows that overspill the channel banks (Fig-ure 4). Flows are mostly unconfined andresult in the deposition of thin bedded tur-bidites with thickness wedging away fromthe levee crest (Figure 4). Sediment waveswith trend perpendicular to the channel arefrequent on levee flanks (Figure 4). Re-cent studies carried out at ISMAR haveshown that however, also erosional pro-cesses are frequently associated with over-banking flows. Particularly in the outsideof channel bends, chutes, scours and over-bank channels can develop and can giverise downslope to crevasse splay deposits(Figure 2, 8) [13, 3]. The size and in-ternal character of the crevasse splay de-posits is mainly dependent on the size ofthe breach in the levee and thus correlatedwith the grain size of the flows that exitthe cahnnel [13]. Beside constructionalprocesses levee are also affected by insta-bility processes of largely variable dimen-sions, from small local failure (Figure 4)to margin-wide large collapse often facil-itated by lithologic boundaries developedduring period of channel inactivity [7].Frontal splays. At the mouth of chan-nels, sediment-gravity flows lose confine-ment and become strongly depositional re-sulting in the formation of frontal splaydeposits. Frontal splay deposits stack to

originate lobate features that are the mainconstituent of the basin plain environment.They can be featureless lobes or be char-acterized by a distributary channel pattern[9]. They are mainly made up by tur-bidites but also debris flow lobe are present[9]. Beside basin plain environment frontalsplay deposit can be also developed in theslope where low efficiency hyperpycnal de-rived turbidite currents are unable to crossthe whole length of the slope (Figure 9)[13].Contourite mounds and drifts. Deepcontour-parallel currents develop wheredifferences in temperature and salinitycharacterize different water masses. Wherecurrents intersect the basin margin or in-teract with bottom-topography they mayerode rework transport and deposit sedi-ment. Sediment mounds and drifts andmigrating very large bedforms (Figure 10)are the most frequently observed geome-try of contourite deposits [14, 15]. A aparticular case of the interaction of mar-gin morphology and water masses has beenrecently evidenced in the southern Adri-atic margin where currents developed in thenorthern Adriatic shelf are forced downs-lope and originate large bedform fields andcontourite mounds and drifts (Figure 7)[10, 16]. In the same area the impor-tance of seafloor topography in determin-ing the location of counturite deposits hasalso been shown [14]. Data interpretationin the Sicily channel an Adriatic sea havein addition shown that countourite deposi-tional bodies are frequently affected by in-stability and failure [15].

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Figure 7: A submarine channel is fed mainly by cascading current in the southern Adri-atic sea. It develops above a canyon that formed through repeted slope and shelf in-stability and resulted inan embayment along the margin. The temporal evolution of thedepositional system are linked with sea level variations and related changes in the char-acter of the sediment feeding mechanism.

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Figure 8: An erosional chute feeds a crevasse splay deposit in the Caprera deep sea fan.

5 Deep sea depositionalsystems in space and intime

The spatial arrangement of geomorphicelements in the deep-sea environment ismainly the result of the geology of thesource area, of the initiating mechanisms ofsediment gravity flows, of geostrophic cur-rents and of seafloor gradient and topogra-phy. The Italian peninsula and its continen-tal margins comprise different geodynamicprovinces and thus the depositional sys-tems of the Italian deep water regions arecharacterized by source areas with highlyvariable dimensions, type and volume ofriver sediment transport, variable rate ofrelative vertical movements and differentdegree of tectonic activity and seismicity.The large variability of the geodynamicsetting of the Italian region has also a di-

rect impact on the deep sea depositionalenvironment controlling the gradient of theseafloor, the dimensions and shape of thecontinental slope, of intraslope basins andof basin plain regions and the ultimate baselevel for sediment-gravity flows. Thus theItalian sea offers an unique setting thathas allowed ISMAR to investigate the fac-tors that control the evolution of deposi-tional systems under a large variety of ge-ologic scenarios. A variety of initiatingmechanism of sediment gravity flows hasbeen determined to feed sediment to thedeep sea areas of the Italian Sea. In thesouthern Adriatic margin, sediment supplyis at present mainly derived from cascad-ing currents (Figure 7) [10, 16]. In theSardinian margin where a wide shelf trapmuch of the sediment, along shore cur-rents deflected by across shelf ones feedthe Caprera channel [3]. Direct dischargeof river hyperpycnal flows has been inter-

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Figure 9: Geomorphic element reconstruction in the Gioia basin as a function of sourcearea character.

preted to feed the Gioia basin where thelack of the continental shelf allow a di-rect connection between rivers and sub-marine canyons. However, a basin-widechannel/canyon system is developed onlyin connection with large rivers whereassmall channels that die out in the slopeface small rivers (Figure 9) [13]. Shelfwidth has also been determined to con-trol the shape and dimensions of intraslopebasin fans shown in the Sardinian marginwhere a large fine-grained fan is developedexclusively in the areas where the shelfis wide and can trap coarse-grained sedi-ment and contrasts with small fans madeup of coarser grained material where theshelf is narrower [11]. In the Sicilian mar-gin, differential rates of vertical uplift havebeen determined to control the locationof submarine leveed channels and moreimportantly to influence their destructionthrough mass-wasting processes that par-

ticularly affect the portions of channel-levee complexes facing areas with high up-lift rates [17]. Slope gradient has beenrecognized as the main factor that controlthe location of canyon and channel tractsalong single basin-wide sedimentary path-ways in topographically complex slopes.Canyon and channel tracts alternate alongthe length of the Stromboli and Sardiniaslope valley in response to gradient vari-ations due to the presence of active faults(Figure 6) [11, 12]. The importance of gra-dient has also been recognized in relativelyflat basin plain areas where slight increaseof seafloor dip cause rechannelization offlows downslope from area where they areunconfined (Figure 11) [9]. Within subma-rine channel, gradient reduction has beenrecognized as driving deposition with de-velopment a multi-thalweg floor and barsand inner levees (Figure 5). The temporalarrangement is a function of all the above

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factors that however, to a large extent arecontrolled by cyclic nature of sea level vari-ation. The Gioia mesisma system showboth the importance of sea level in control-ling the deactivation of submarine channelswhere the shelf is wide [13] In the GioiaBasin, only the channels facing the areaslacking the continental shelf are active dur-ing the present-day high stand. In the Sar-dinia Caprera fan lower efficiency flowsduring the present-high stand result in theretrogradation of the fan that also pass to adepositional phase in regions previously af-fected by erosion [3]. Sea level variationshave also demonstrated to be instrumentalin controlling the activation of geostrophicand cascading currents thus impacting onthe temporal evolution of continental mar-gin as shown in the southern Adriatic Sea(Figure 7) [10, 16].

6 Concluding remarksISMAR is actively involved in the studiesof deep-sea depositional systems. Largedata set have been acquired in many of thesubmarine areas of the Italian seas. Impor-tant results of the recent researches carriedout at ISMAR are meaningful steps towardthe understanding of the sedimentary pro-cesses that occur in the deep sea environ-ment and how they contribute in the shap-ing of the deep-water landscape. They alsoshow how the deep marine environmentrepresent an archive of a variety of pro-cesses that occur in the surrounding areasand of climatic oscillations. Furthermorethe results of the researches represent keyissue when considering the exploitation ofdeep sea resources, the action needed forthe preservation of the environment and thedefinition of the geological hazard.

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Figure 10: Shaded relief (left) and deep towed sidescan sonar of a sediment wave fieldformed due to downslope cascading currents in the southern Adriatic Sea. In the samearea, chirp profiles (below) show contourite drifts with variable shape often controlledby preexisting seafloor topography are also formed.

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Figure 11: Reconstruction of basin plain deposition at about 300m depth in the Tyrrhe-nian Sea. The influence of the geological character of the different margins of the Tyrrhe-nian Sea is reflected in the architecture of the two basin plain.

References[1] M. Marani, F. Gamberi, and E. Bonatti. From seafloor to deep mantle: architecture

of the Tyrrhenian backarc basin. Memorie descrittive della carta geologica d’Italia,44, 44:1–194, 2004.

[2] F. Foglini, E. Campiani, A. Cattaneo, Correggiari A., et al. The bathymetry of theAdriatic Sea. this volume, 2011.

[3] G. Dalla Valle and F. Gamberi. Erosional sculpting of the Caprera confined deep-seafan as a result of distal basin-spilling processes (eastern sardinian margin, Tyrrhe-nian Sea). Marine Geology, 268:55–66, 2010.

[4] M.P. Marani, F. Gamberi, M. Rosi, A. Bertagnini, and A. Di Roberto. Subaque-ous density flow processes and deposits of an island volcano landslide (StromboliIsland, Italy). Sedimentology, 56:1488–1504, 2009.

[5] M. Rovere, G. Dalla Valle, F. Foglini, F. Gamberi, M. Marani, and F. Trincardi.Submarine landslides: case studies in the Mediterranean Sea. This volume, 2011.

[6] F. Gamberi, M. Marani, V. Landuzzi, A. Magagnoli, et al. Sedimentologic andvolcanologic investigation of the deep Tyrrhenian Sea; preliminary results of cruiseVST02. Annals of Geophysics, 49:767–781, 2006.

[7] F. Gamberi, V. Marani, M. Landuzzi, A. Magagnoli, et al. Sedimentologic andvolcanologic investigation of the dep Tyrrhenian Sea: preliminary results of cruiseVST02. Annals of Geophysics, 49(2/3):767–781, 2006.

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[8] F. Gamberi. Volcanic facies associations in a modern volcaniclastic apron (Lipariand Vulcano offshore, Aeolian island arc). Bulletin of Volcanology, 63:264–273,2001.

[9] F. Gamberi and M. Marani. Regional geology control on the style of basin plaindepositional systems in the Thrrenian Sea. SEPM Special Puplication, Externalcontrols on deep water depositional systems, 92:221–232, 2009.

[10] F. Trincardi, G. Verdicchio, and S. Miserocchi. Seafloor evidence for the interactionbetween cascading and along-slope bottom water masses. Journal of GeophysicalResearch, (112):1450–1467, 2007.

[11] F. Gamberi and M. Marani. Deep-sea depositional systems of the Tyrrhenian Basin.Memorie descrittive della carta geologica d’italia, 44:127–146, 2004.

[12] F. Gamberi and M. Marani. Downstream evolution of the Stromboli slope valley(southeastern Tyrrhenian Sea). Marine Geology, 243(1-4):180–199, 2007.

[13] F. Gamberi and M. Marani. Controls on Holocene deep-water sedimentation in thenorthernGioia Basin, Tyrrhenian Sea. Sedimentology, 55:1889–1903, 2008.

[14] G. Verdicchio and F. Trincardi. Short-distance variability in slope bed-formsalong the Southwestern Adriatic Margin (Central Mediterranean). Marine Geol-ogy, 234:271–292, 2006.

[15] G. Verdicchio and F. Trincardi. Mediterranean shelf-edge muddy contourites: ex-amples from the Gela and South Adriatic basins. Geo-marine Letters, 28:137–151,2008.

[16] F. Trincardi, F. Foglini, G. Verdicchio, A. Asioli, et al. The impact of cascadingcurrents on the Bari Canyon System, SW-Adriatic Margin (Central Mediterranean).Marine Geology, (246):208–230, 2007.

[17] F. Gamberi and M. Marani. Hinterland geology and continental margin growth:the case of the Gioia Basin (southeastern Tyrrhenian Sea). Special publicationgeological society of London, 262:349–363, 2006.

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Deep Marine Record from Sentinelle Valley (Sar-dinia Channel): Integrated Stratigraphy of AKey Site for Western Mediterranean Paleoceano-graphic and Geological Reconstruction

F. Budillon1, F. Lirer1, M. Iorio1, P. Macrı2, L. Sagnotti1, M. Vallefuoco1,L. Ferraro1, S. Innangi1, G. Di Martino1, R. Tonielli11, Institute for Coastal Marine Environment, CNR, Napoli, Italy2, National Institute of Geophysics and Volcanology, Roma, [email protected]

Abstract

Biotic, petrophysical, paleomagnetic proxies combined with 14C AMS data al-lowed us to produce, for deep marine record of Sentinelle Valley (Sardinia Channel),a detailed integrated stratigraphic time-framework for the last 80 kyr.Major planktonic foraminiferal changes in quantitative distribution of selected cli-mate sensitive species allowed the identification of 10 eco-biozones and the mainclimatic global events (Sapropel S1, Younger Dryas, Greenland Isotope Interstadial1, Greenland Isotope Stadial 2, Heinrich events H1-H6).An accurate age-depth profile has been proposed for the studied record which spansbetween 2 and 83 kyr cal. BP. The adopted age model was successively confirmed bycomparing the colour reflectance data of the studied record with the astronomicallytuned deep marine record ODP-Site 964 from the Ionian Sea. Three turbidite eventlayers were chronologically constrained within the relative low stand and loweringsea level phases associated to the MIS 4 and MIS 3.

1 Introduction

Since climate excursions recorded inNorthern Hemisphere in the GreenlandGISP and GRIP ice cores [1] over the last100 kyr had more or less synchronous ef-fects in the Mediterranean area, many re-searches have focused on Mediterraneanmarine cores, with the aim to detect theirintensity and the impact on the marine en-vironment. During the last glacial pe-riod the Mediterranean region experiencedrapid modifications in hydrographic con-ditions in response to fast climatic excur-

sions, known as Heinrich events (HE) andDansgaard-Oeschger (D-O) Stadials (cold)and Interstadials (warm) [2, 3]. In partic-ular, [4, 5] and [6] have proved that themillennial scale D-O and HE directly con-trol the winds and precipitation system onthe Northern Mediterranean basin. Evenduring the Holocene the principal climaticevents and oscillations of the NorthernHemisphere were clearly traceable in dif-ferent sectors of the Mediterranean Basinsedimentary records [5, 6, 7, 8, 9, 10, 11,12, 13].A detailed outline of the paleoenviron-


Marine Geology

mental changes and their control on ma-rine communities, calibrated by severalindependent proxies (tephra, sapropel,14C geochronology), is available for theMediterranean area (i.e. [14, 15, 16, 17,18, 19, 9, 10], and reference therein). Sev-eral codified eco-bioevents, if clearly de-tected in marine records, can be used astie points to chronologically constrain thelate Pleistocene-Holocene Mediterraneanmarine sequences. Nevertheless, evenif many reference records are availablefrom deep-sea sites, most of them spana short time interval and lack a high res-olution detail of the paleo-environmentaland paleo-ecological changes before 40kyr. Recently, [11, 12] carried out a high-resolution study of the tuned ODP-Site977, located in the Western part of the Alb-oran Sea, and identified several planktonicforaminiferal eco-bioevents occurred dur-ing the marine isotope stages (MIS) 1 to 5.These eco-bioevents represent the best toolto correlate deep marine records from dif-ferent Mediterranean sites.Many recent studies emphasize the chal-lenge when studying deep sea records toestablish a reliable chronology even forthe deposition of turbidites [20, 21, 15]and underline the utility to support con-ventional dating methodologies with dif-ferent constraints. It is widely acceptedthat one of the main factor controlling andenhancing turbidite deposition along deepsea fan is the fall and lowstand of sea-level, whereas sea-level rise and highstandphases reduce terrigenous supply to deepsea systems [20, 22, 23].The studied CIESM core C08 is locatedin the Sardinia Channel in a key posi-tion of paleoceanographic and geologicalsignificance. In fact, the Sardinia Chan-nel connects the Alboran to the TyrrhenianBasin and offers a stratigraphic record with

the potential to link the eco-stratigraphicand paleoceanographic observations be-tween the Western, the Central and EasternMediterranean late Pleistocene Holocenemarine records [12, 24, 13, 25, 26]. In fact,a portion of the Modified Atlantic Water(MAW) coming from the Strait of Gibraltar[27], diverges from the part that enters theEastern Mediterranean and flows throughthe Sardinia Channel into the TyrrhenianSea along the northern Sicilian coast [28],forming a secondary circulation gyre. Thecirculation system in this sector of theTyrrhenian Sea is counter-clockwise withthe Levantine Intermediate Water (LIW)inflows lapping on the northern Siciliancoast and the outflow occurring along theeastern Sardinia coast ([29] and referencestherein).The core site is even in a strategic posi-tion to check the efficiency of a submarinecanyon in driving density flow to the deepsea environment, even if not directly con-nected to any emerged sector nor to conti-nental shelf areas [30]. Thus the possibil-ity that such a type of canyon would forma fan can be evaluated, even verifying thesignificance and the timing of the turbiditedeposition.The aim of this study is to provide a recordof integrated stratigraphic data spanningthe last 80 kyr, relatively to a deep basinarea, based on eco-biozones, 14C-datedages, Event Stratigraphy, lithostratigraphyand petrophysical properties.This work represents a short version ofthe article “Integrated stratigraphic recon-struction for the last 80 kyr in a deepsector of the Sardinia Channel (West-ern Mediterranean)” published on Deep- Sea Research II, v°56, 725-735 -doi:10.1016/j.dsr2.2008.07.026, by Budil-lon et al. (2009, [31]).

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Figure 1: A) Location map of CIESM Core C08. Bathymetry from The General Bathy-metric Chart of the Oceans (GEBCO, 1997); B) bathymetric detail of core site, close toa channel South-North oriented (green arrow).

2 Geological setting

The core C08 was collected in the Sen-tinelle Valley of the Sardinia Channel (Fig-ure 1), during the cruise CIESM Sub2 on-board the R/V Urania in December 2005(38°38.5364’N, 10°21.5576’E - 2370 mbelow sea level), and it recovered about5.40 m of hemipelagic mud interlayeredwith three fine to medium sand turbiditelayers of increasing thickness towards thetop of the core (Figure 2). In the stud-ied area a 400 km long submerged sec-tor of the Apennine-Maghrebian branch ofthe Alpine orogen separates the Tyrrhe-nian (Plio-Pleistocene in age) and the Al-gero Provencal (Miocene in age) oceanicbasins. This sector of the chain was notcompletely fragmented during the open-ing of the basins [32]. Due to the rela-tively minor post-orogenic extension andthe good preservation of morpho-structuralfeatures, the Sardinia Channel is an impor-tant area for the reconstruction of the geo-dynamic evolution of the Western Mediter-ranean sector and was recently investigated

through submersible surveys [33, 32]. Thetriangular shaped valley is bounded bya NE-SW oriented Median Ridge on itsnorth-western side and by the South Cor-naglia slope on the south-eastern one. Thesouth- western sector of the Sentinelle Val-ley receives the sedimentary contributionof the Bizerte Canyon, which engraves theTunisian Plateau and the south margin ofthe Sentinelle Bank [34]. The canyon headappears disconnected from the Tunisianshelf margin and extends over an area ofabout 1000 km2 at an average depth ofabout 500 m (Figure 1). It represents a par-ticular type of canyons since it is not fedby an emerged areas or by a fluvio-deltaicsystems (Reading and Richards, 1994, [35,36], but it drains a wide submarine plateau.

3 Material and methodsThe physical properties of the core weremeasured at 1 cm step in a fully auto-mated GEOTEK Multi-Sensor Core Log-ger (MSCL), in the petrophysical laborato-

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Figure 2: The core CIESM 08: photography, lithologic log, petrophysical propertiescurves (magnetic susceptibility, Grape density, reflectance 550 nm %) plotted againstdepth (cm below sea floor).

ries of IAMC in Naples (Italy). The MSCLsystem includes a Bartington MS2E Pointsensor, to measure the low-field magneticsusceptibility (MS) with a spatial resolu-tion of 0.4 cm and a Minolta Spectropho-tometer CM 2002 which records at 0.8cm step, the percentage of reflected energy(RSC) at 31 wavelengths in 10-nm steps,over the visible spectrum (from 400 to 700nm).The analysis of planktonic foraminifera

was conducted on 216 samples. Samplingspacing was 2 cm from the top of the coredown to the base. Each wet sample ofabout 20 g was dried at 50° C and washedover sieves with mesh-width size of 63microns. Quantitative planktonic analyseswere carried out on the fraction >125µm.The adopted taxonomic units were thosereported by [37, 38]. According to [37]and [38], we introduced some supraspecificcategories (which remain unchanged even

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Figure 3: Relative abundance of selected planktonic foraminifera from core C08 plot-ted vs depth (m bsf). Eco-biozones 1 to 10 are pointed out, according to the Ecozonalscheme of [9] slightly modified. Grey bands show the selected eco-bioevents proposedby [11, 12]. Event Stratigraphy according to GRIP scheme. MIS and age scale accordingto [11, 12]. Associated to G. ruber curve, two grey bands interbedded with the black onecorrespond to the position of sapropel 1 equivalent with the two interval S1a and S1b.The three banded areas indicate the position of the turbidite layers.

under bad preservation conditions), reduc-ing the number of species actually occur-ring in the planktonic foraminiferal assem-blages.The AMS 14C radiocarbon analysis, wasperformed at the CIRCE (Centre for Iso-topic Research for Cultural and Envi-ronmental heritage) laboratory in Caserta(Italy). In particular, two AMS 14Canalysis (at the core top and at 0.44mbsf) were carried out on mixed plank-tonic foraminifera (Globigerina bulloidesand Globorotalia inflata). All radiocarbondates were corrected using a reservoir ageof 48 ± 21 yr (a mean DR value calculatedamong six of the Tyrrhenian Sea) and cal-ibrated using the marine data base and theCALIB 5.0 Program of [35].

4 Results: lithostratig-raphy and planktonicforam

The sediment consists of hemipelagic mud,ranging in colour from reddish and ochreto light, olive and dark grey, punctuated bythree turbiditic sand layers (Figure 2) from1.82 to 2.08 m (T1), from 3.10 to 3.17 m(T2), and from 4.33 to 4.34 m (T3). Theturbidite layer T1 is marked by a sharp ero-sive contact and consists of a thin layer ofoxidized sand, and then of a massive fine tomedium sand with high percentage of shellfragments; the upper boundary is sharp andthe grain size populations comprised be-tween fine sand and clay, that usually per-tain to “b, c, d, e” divisions of the classicalBouma sequence [39], are missing, as ev-idenced by the abrupt decrease of MS andGrape density values, which are a functionof grain size and lithology. A sharp contactmarks the onset of the turbidite layer T2

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which contains a thin layer of well sorteddark fine sand passing to a massive, wellsorted bioclastic fine sand; also in this casethe upper boundary is sharp and the pas-sage from massive and structureless sandto the hemipelagic mud is abrupt. Turbiditelayer T3 has well defined sharp boundariesand starts at the base with a thin layer ofdark sand passing to light grey bioclasticsand. The thickness of the turbidites in-creases upward, but no sand layers occurin the uppermost 0.18 m of the core.The planktonic foraminifera, character-ized by modern assemblages, are abundantand well-preserved and the percentages offoraminiferal fragments are very low anddo not alter the composition of the plank-tonic assemblage.In terms of quantitative distribution ofplanktonic foraminifera a number of 13species or groups of species were distin-guished: Globigerina bulloides (includ-ing extremely rare specimens of G. fal-conensis), Globigerinoides quadrilobatus(including G. trilobus and very subordi-nate G. sacculifer), G. ruber white andpink (always extremely rare), G. elongatus(very rare) and G. gomitolus (very rare),Globigerinoides tenellus (rare), Globoro-talia truncatulinoides sl. right (very rare)and left coiling, Neogloboquadrina pachy-derma right and left coiling (extremelyrare), N. dutetrei right and left coiling(extremely rare), Globigerinita glutinata,Orbulina universa, Turborotalita quin-queloba, Globigerinatella siphoniphera(rare) including G. calida (very rare),Globoturborotalita rubescens (rare).The long-term trend in planktonicforaminifera reveal that the faunal com-position of the studied interval does notshow drastic changes in the abundancepatterns (Figure 3). In particular, amongthe taxa that have a continuous distribu-

tion patterns, G. bulloides, G. ruber, G.inflata left coiled, G. scitula right coiled,N. pachyderma right coiled and T. quin-queloba show long-term oscillation (trend)superimposed on short-term fluctuationspossibly related to high-frequency climaticoscillations (Figure 3). Among the plank-tonic species having discontinuous dis-tribution, G. quadrilobatus, G. truncat-ulinoides left coiled and G. tenellus onlyoccasionally reach significant percentages(Figure 3).

5 Planktonic foraminiferaleco-biozonation

Significant changes in quantitative dis-tribution of the planktonic foraminiferaspecies allowed several authors [40, 25, 38,41, 17, 9, 15] to define eco-biozones use-ful for fine subdivisions of the stratigraphicrecord. The eco-biozone boundaries arecharacterized by temporary appearance ordisappearance and/or evident abundancepeaks of different taxa. In the presentwork, we refer the stratigraphic record toeco-biostratigraphic classification of [9],slightly modified. At present, the eco-biostratigraphic classification of [9]) pro-poses 9 eco-biozones over the last 23 kyr.In this work, we propose to mark the baseof eco-biozone 9 with the strong increaseof G. inflata, occurring in the Mediter-ranean area at about 30 ka [15, 13], and toextend the eco-biozone 10 back to∼80 kyr.Actually, using the quantitative distributionpattern of the most abundant planktonicforaminifera species counted throughoutthe C08 core, we identified 10 evident eco-biozones from top to bottom (Figure 3).The uppermost part of the studied recordattributed to the eco-biozone 1, which

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Table 1: Tie-points used for age-depth profile of core C08. The Globigerina bulloideseco-bioevents B3 to B11 are coded according to [11, 12].

bases at 0.08 m, is characterized by a de-crease in abundance of G. quadrilobatusand the end of G. truncatulinoides rightcoiled. This attribution is also supportedby a 14C – AMS calibration, which dates2.18 ka cal. BP (Figure 3, Table 1).The eco-biozone 2 is defined by the con-comitant abundance of G. quadriloba-tus and G. truncatulinoides left and rightcoiled and by low abundance values of N.pachyderma right coiled in the lower part.Besides, the strong increase of G. truncat-ulinoides left coiled marks the base of theeco-biozone (Figure 3).The short interval represented by eco-biozone 3, whose base is at 0.31 m, ismarked by the end of micropaleontologicalsignature of sapropel S1 and is character-

ized by low abundance values of T. quin-queloba, G. quadrilobatus, and G. truncat-ulinoides left coiled.The eco-biozone 4 corresponds to the timeinterval of sapropel S1 deposition, al-though no lithological evidence was found,but for colour shades (Figure 2). G. ru-ber oscillations allowed a reliable identi-fication of the faunal signature of the cli-matic events associated to the depositionof sapropel S1 (Figure 3). In particular,two distinct peaks in G. ruber mark the twoshort-term warm oscillations (S1a and S1b,[9]), separated by a cold phase betweenthem (Figure 3). The event is supported bya 14C-AMS datum at 0.44 mbsf (within thecold phase) with an age of 8.79 ka cal. BP(Table 1) as well as an increase in abun-

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dance of G. tenellus and G. quadrilobatus[9].The eco-biozone 5 is defined by the con-comitant occurrence of G. ruber and G. in-flata, by a distinct peak of G. truncatuli-noides left coiled and absence of N. pachy-derma right coiled and very low value of T.quinqueloba. The eco-biozone 6 is markedby the absence of G. ruber and G. in-flata left coiled, by a distinct peak of T.quinqueloba and of N. pachyderma rightcoiled. This eco-biozone corresponds tothe Younger Dryas event, according to [9].The eco-biozone 7 is defined by the in-crease in abundance of G. ruber and G.inflata, by the absence of T. quinquelobaand by a distinct peak of G. quadriloba-tus and corresponds to the warmer (inter-stadial) GI-1. According to [9] in the eco-biozone 8 the persistent high abundance ofcold species permit correlation of this in-terval with the GRIP GS-2 period. In par-ticular this eco-biozone is dominated by T.quinqueloba, N. pachyderma right coiled,G. scitula and by absence of G. inflata leftcoiled and rare G. ruber. The base of thiseco-biozone approximates to the base ofMIS 2 [11] (Figure 3).The eco-biozone 9 is characterized bythe concomitant absence of G. inflata leftcoiled and G. ruber, by low abundancevalue of N. pachyderma right coiled andhigh abundance of T. quinqueloba and G.scitula right coiled. The eco-biozone 10 isclearly marked by the progressive down-ward increase in abundance of G. inflataleft coiled and G. ruber and the progressivedecrease of G. scitula right coiled, T. quin-queloba and N. pachyderma right coiled(Figure 3). No distinctive or drastic eventsin the planktonic faunal patterns are visibletowards the base of the studied record butonly short-term oscillation in G. bulloides(B3-B11 eco-bioevents; the adopted sam-

pling resolution does not allow the recog-nition of G. bulloides B8 eco-bioevent),G. inflata left coiled (I3-I5 eco-bioevents),T. quinqueloba (Q4-Q9 eco-bioevents) andN. pachyderma right coiled (P5-P7 eco-bioevents), clearly associated to the mil-lennial climate oscillations occurring in thelast 80 kyr [12]. According to [12] close tothe G. bulloides eco-bioevents B7 and B10are placed the MIS 4/MIS 3 and MIS4/MIS5a transition, respectively. Finally, accord-ing to [12] the lowermost part of the stud-ied record lies within the eco-bioevent B11and within the uppermost part of MIS 5b(Figure 3).

6 Age model

The identified foraminiferal marker events,regarded as to reflect major changesin oceanographic conditions and alreadyrecognised for the Central and WesternMediterranean [37, 38, 25, 24, 9, 12, 13]were used, in combination with two 14C –AMS data (Table 1), to constrain the age ofcore CIESM-C08 and strengthen the corre-lations between the Mediterranean sites. Inparticular, we used the age model proposedby [11, 12] for the Alboran Sea, to recog-nize the top and base of the eco-bioeventsrecorded in the core C08, the age modelproposed by [25] for the Adriatic Sea, toidentify the Younger Dryas and the base ofthe Greenland isotope interstadial 1 (GI-1)and the age model of [43] for the NGRIPrecord to distinguish the Greenland isotopestadial 2 (GS-2) (Table 1). The turbiditelayers T1, T2 and T3 have been taken intoaccount to construct the age model curveand to estimate the sedimentation rate. Asecond-order polynomial is needed to de-scribe the age-depth relationship for thestudied record, indicating an average sed-

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Figure 4: From left to right: comparison in time domain between the distribution patternof G. bulloides from ODP-Site 977 [12] and the studied core CIESM C08 (the red curverepresents a 3-points average). The grey bands and the labels B1 to B11 are from [12].Age-Depth profile and Sedimentation Rate of core CIESM C08. The adopted tie-pointsby eco-bioevents and by 14C – AMS data are shown respectively with black boxes andgrey boxes.

imentation rate of ∼7 cm·kyr−1 from thebase to the top and four main excursions(Figure 4).In order to confirm the reliability of theproposed age model, a three step validationprocess have been performed. First, the vi-sual comparison, in time domain, betweenG. bulloides distribution pattern of [12] forthe Alboran Sea and the patterns in coreCIESM C08 (Figure 4), which confirmedthe tuning accuracy.The second step consisted of the compari-son of the colour reflectance record at 550nm (%) of the core CIESM C08, withthe record of the ODP-Site 964 (Figure5), drilled in the Ionian Sea at 3650 mbsland astronomically calibrated [16]. This

comparison shows that the large-scale re-flectance fluctuations in core CIESM C08not only have similar pattern to those re-ported in the Ionian sea record but also en-compass absolute values in the same range(±10 nm). Remarkable is also the strongsimilarity between the colour reflectancesignature of the sapropel S1 equivalent,recorded in the studied core, with thesapropel S1 colour reflectance signaturein the Ionian basin. On the whole, thegood visual correlation obtained betweenthe two records supports the validity ofthe age model based on the identified eco-bioevents and 14C AMS calibrations.Finally, the third control step consistedin the comparison of the G. ruber distri-

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Figure 5: Comparison in time domain of colour reflectance data of core CIESM C08(black curve, with 3 points average, red dotted curve) with reflectance data after[33] forODP-Site 964 (thin black curve) in the Ionian Sea. The numbers I1-I6 indicate tephralayers in ODP-Site 964 and the code 1 and X indicate the position of the sapropel 1 andX, respectively.

bution pattern chronology with the δ18ONGRIP ice core record. The ecologicalfeatures of G. ruber associated to warmand oligotrophic surface waters has beenestablished in several oceanographic set-tings [44, 45, 46, 47] and it is considered anuseful tool as recorders of climatic variabil-ity [48, 49, 9, 10]. The G. ruber and δ18ONGRIP ice core records exhibit a remark-able agreement, with the identification ofthe Heinrich events (H1 to H6) and of theYounger Dryas (YD) in the studied recordwhich further support the reliability of ourtuning (Figure 6).

7 Ages and provenance ofturbidite events

The size population of grains, the grain fab-ric, the high content in bioclasts (gastro-

pod, bivalve and echinoderm debris) andthe features of the surfaces bounding T1,T2 and T3 turbidites lead us to infer a dis-tant source of transported material, since itseems to be remobilized from high produc-tivity areas. Both the slope of the medianRidge, and the southern Cornaglia slopecan be ruled out as possible source areasfor this bioclastic sand rich density cur-rents, since their top is located respectivelyat about 1300 and 1000 m bsl. Namely,Sartucya 6 diving survey [33] showed thatthe base of the southern slope of the medianRidge (investigate from 2270 to 1940 mbsl)is draped with mud, shaped by current bed-forms, while the upper slope (investigatedfrom 1990 to 1640 m bsl) is character-ized by conglomerates and sandstone lay-ers outcropping from the mud, then vol-canic rocks. The lithology pertaining tothe southern Cornaglia slope has been de-

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Figure 6: Distribution pattern of G. ruber (thin black line) with 3 points average (redline) of core CIESM C08 plotted versus δ18O NGRIP [42] record, with 7 points average,in time domain. Labels H1 to H6 indicate the position of Heinrich events and the labelYD the position of the Younger Dryas.

scribed during the Sarcya 2 submersiblediving [33], which evidenced the occur-rence of pelagic mud along the plain (sur-veyed from 2500 to 2250 mbsl) and ce-mented coarse material in correspondenceof the steep slopes (from 2250 to 2060mbsl). Although the occurrence of sev-eral canyons along the Southern Cornagliaslope was evidenced by the bathymetricsurveys [51], nevertheless they enter theSentinelle Valley seaward to the core siteand thus they possibly fed a deepest sec-tor of the basin. Thus, we have to inferthat the Bizerte Canyon may have acted asthe main conduit to transport the bioclas-tic sand from the high productivity areas ofthe Tunisian plateau (Figure 1); then theflows had to cover more than 50 km be-fore settling. As highlighted by many au-thors over the years [52, 53, 30] gentle gra-dient slopes or pre-existing slope conduitscan drive very efficient density currents

[54, 22] able to cover long distances in rel-atively “instantaneous” time and to “segre-gate the original grain populations into dis-tinct and relatively well-sorted facies typeswith distances” [55]. The beds occurringin C08 core and in particular T1 and T2,could correspond to the facies tract F7 in[55], composed predominantly of mediumto fine grained well sorted sand. In fact inthis model, which associates the horizontalgrain size partition of the deposit with thedifferent degrees of flow efficiency, the F7facies tract consists of medium to fine sandoverlying a mm thick traction carpet thataccounts for the development of an erosionsurface at the base. This model may ex-plain why T1 and T2 turbidites lack paral-lel and ripple lamination and pelitic divi-sions.The turbidite layers in CIESM core C08 areconfined in the lower 4 m of the core andtheir thickness increases upward peaking

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Figure 7: The inferred age of turbitite sand beds is plotted on curves of sea level varia-tions over the last 100 kyr (from [50], modified). T2 and T3 turbidites occur during tworelative lowstand phases of the MIS 4 and MIS 3, while the T1 turbidite falls during thelast dropping phase of sea level of MIS 3.

at T1 (Figure 2) and pointing to a generalregressive trend. Through the age modelscheme of CIESM C08 core here proposed,it is possible to date T layers respectively at28 ka cal. BP (T1), 48 ka cal. BP (T2) and63 ka cal. BP (T3) (Figure 5), thus duringthe MIS 4 and MIS 3. The emplacement ofT1 event bed caused the removal of an un-defined thickness of hemipelagic mud cor-respondent to a time span of about 4 kyr(Figure 4).Plotting their inferred age on the sea levelvariation curve relative to the last 100 kyr[56, 57], a strong correlation of T2 and T3turbidite event beds deposited in this sectorof the Sentinelle Valley emerges with tworelative sea level low stand phases, while

the T1 corresponds to the falling stage ofsea level that led to the maximum sea levellow stand at about 20 ka BP (Figure 7).This observation seems in agreement withthe most accepted stratigraphic models ofdeep sea deposition [23]. Thus, the partof the basin fan intercepted by the CIESMcore C08 was active and fed with bioclas-tic sand deposition during the relative sealevel minimum and increased its transportefficiency following the sea level lowering.Nevertheless the CIESM core C08 does notrecord any further event of sand depositionduring the maximum sea level low stand,relative to the MIS 2. A rapid starvation indetritus supply occurred in this area start-ing from 28 kyr and the middle fan fos-

502


silized below a drape of hemipelagic mud.It is reasonable to suppose that during thisphase, this sector of the fan acted mainly asbypass area. In this hypothesis any possiblesand flow would have been deposited bas-inward moving possibly through the chan-nel showed in Figure1b.

8 ConclusionsThe multidisciplinary study of core C08,recovered from the deep sector of theSardinia Channel, based on planktonicforaminiferal assemblages and petrophys-ical data, provides an integrated strati-graphic reference record for the WesternMediterranean Sea that spans back forabout 83 kyr. The most important eco-bioevents widely used for large scale cor-relation in the Western Mediterranean areawere recognized providing a detailed cor-relation with the eco-stratigraphic recon-struction proposed by [11, 12] for the Alb-oran Sea.According to [11, 12], the documentedshort-term oscillations in the planktonicforaminiferal fauna are clearly associatedto the stadial/interstadial excursions occur-ring over the last 80 kyr and allowed theidentification in core C08 of the S1, YD,GI-1 and GS-2 climatic events in the last23 kyr. Furthermore, the comparison be-tween the δ18O NGRIP ice core recordwith G. ruber oscillation of core C08, sug-gests the identification in the studied recordof the Heinrich events (H1 to H6) and of

the Younger Dryas (YD).The eco-bioevents chronology combinedwith 14C – AMS data were used to definea detailed age model which was comparedby means of reflectance parameters to theastronomically tuned age model proposedfor the Ionian Sea ODP-Site 964 [16].The similarity between the two reflectancerecords, validated the age model of thestudied record especially in the time inter-vals between 2-25 kyr and 60-83 kyr. Thismethodology, if confirmed with further ev-idences, proved a powerful tool for reliablycorrelating marine records between com-parable deep sea environment settings. Thesector of the Sentinelle Valley interceptedby the CIESM core C08 has been sporad-ically fed by sand turbidite flows, likelydriven along the Bizerte Canyon from thenorthern sector of the Tunisian Plateau,during relative sea level minimum and sealevel drop of MIS 4 and 3. This sector ofthe basin was reached by three sand depo-sition events of increasing thickness in thetime interval from 64 to 28 kyr cal. BPfollowing a regressive trend. Starting fromabout 28 kyr this part of the fan was de-activated and fossilized beneath a carpet ofhemipelagic mud at a sedimentation rate ofabout 7 cm·kyr−1.The combined logging of sedimento-logical and petrophysical data of coreCIESM-C08, integrated with the ecobio-zone stratigraphy could provide an impor-tant source of information useful to im-prove the confidence of correlations in theMediterranean for the last 83 kyr.

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Holocene Palaeo-Geographical Evolution of theSele River Alluvial-Coastal Plain: New Morpho-Sedimentary Data from Poseidonia-Paestum Area

B. D’Argenio1, V. Amato2, E. Anzalone1, P.P.C. Aucell3, M. Cesarano2,A. Cinque4, S. Da Prato5, G. Di Paola2, L. Ferraro1, G. Pappone3, P.Petrosino4, C. M. Rosskopf2, E. Russo Ermolli41, Institute for Coastal Marine Environment, CNR, Napoli, Italy2, Department of Science and Technology for the Environment and Territory, Universityof Molise, Pesche (IS), Italy3, Department of Environmental Sciences, University of Napoli “Parthenope”, Italy4, Department of Earth Sciences, University of Napoli “Federico II”, Napoli, Italy5, Institute of Geosciences and Earth Resources, CNR, Pisa, [email protected]

Abstract

The Sele river plain is located along the western Tyrrhenian margin of the south-ern Apennine Chain and is defined seawards by a straight sandy coast formed duringthe Last Interglacial (Tyrrhenian stage, OIS 5e) and the Holocene. It is character-ized by the presence of beach-dune ridges which to the rear interfinger with lagoonaland fluvio-palustrine deposits. This belt was accreted progressively and representsthe evolution of a barrier-lagoon system shifted alternatively landward and seaward.In this work, we summarize the main results relative to the Holocene evolution ofthe Sele river coastal plain along the coast in front of the archaeological area ofPoseidonia-Paestum, where the knowledge has been improved by two new coresand by many collected archaeo-tephro-stratigraphical data. The area was affectedby the Holocene marine transgression that formed cliffs that cut the travertine de-posits. During the second part of the Holocene the shoreline shifted seaward and alagoonal-beach bar system (Fossa Lupata) formed. The archaeological remains ofPoseidonia (VI cent. B.C.) and the Agnano Monte Spina tephra layer (4.1 ky BP)confirm the presence of this morpho-sedimentary system during this time interval.After this period, and mostly after the deposition of the A.D. 79 tephra, the shore-line shifted seaward and an additional beach ridge was formed, while the flat area ofFossa Lupata, was rapidly aggraded and dried up.

1 Introduction

The Holocene glacio-eustatic sea level riseafter the Last Glacial Maximum (LGM)led to a worldwide flooding of shelf areasand controlled the evolution of marine em-

bayments, fluvial mouths and rocky coasts,while its significant deceleration in mid-Holocene times resulted in the overcom-pensation by sediment yields and shore-line progradation in many Mediterraneanalluvial-coastal plains. The shoreline shifts


Marine Geology

Figure 1: Schematic geological and geomorphological maps of the Sele river alluvialcoastal plain. A: Simplifed geomorphological map; B– Simplifed geological map ofsouthern Apennine with in evidence the Tyrrhenian graben of the Sele-plain. 1) Neo-gene clastic and volcanic deposits; 2) Eboli Conglomerates (Pleistocene); 3) Miocenedeposits; 4) Ligurian Units (Cretaceous-Oligocene); 5) Meso-Cenozoic apennine carbon-atic shelfs; 6) Lagonegro Units (Trias-Miocene); 7) Meso-Cenozoic apulian carbonaticshelfs; 8) Thrusts; 9) Main faults; 10) Somma-Vesuvius volcano.

forced ancient societies to continuouslyadapt their lives and infrastructures to everchanging natural factors. These rapidchanges of sedimentary environments havebeen investigated throughout the Mediter-ranean in detail, combining methods andresearch designs of a great number of dis-ciplines, including geomorphology, geol-ogy, palaeobiology, archaeology (e.g. [1,2, 3, 4, 5, 6, 7, 8]). All the studies as-sert that the Holocene sea level rise caused,firstly, a general marine transgression intothe alluvial-coastal plains of the Mediter-ranean Sea, and successively, a strong

progradational trend of shorelines. Thecoastal progradation is relative to the de-crease in the rate of sea level rise and tothe increase in the sediment load of rivers.It was more marked during the last 2.5ky, because favored by the increase in an-thropic impacts on vegetation and rivers[9, 10, 11, 12]. Similarly, it is knownthat the Tyrrhenian alluvial-coastal plain ofthe Sele river was interested by the samemorpho-sedimentary behavior during theHolocene, with a transgressive trend dur-ing the early Holocene and with a progra-dational trend of shorelines starting from

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middle Holocene ([13, 14, 15, 16, 17, 18]and references herein). The plain, locatedalong the western Tyrrhenian margin of thesouthern Apennine Chain, is defined sea-wards by a straight sandy coast formedduring the Last Interglacial (Tyrrhenianstage, OIS 5e) and the Holocene. It ischaracterized by the presence of beach-dune ridges which to the rear interfin-ger with lagoonal and fluvio-palustrine de-posits. This belt was accreted progres-sively and represents the evolution of abarrier-lagoon system shifted alternativelylandward and seaward (Figure 1a). Thecoastal belt shows the geomorphologicalevidences (dune ridges and flat depres-sion areas) of the late-Quaternary glacio-eustatic sea level changes and in particularof the sea level high stand of the last inter-glacial periods: Tyrrhenian High Stand SeaLevels - HSSLs of MIS 5 - and HoloceneHigh Stand Sea Level – HSSL of MIS1. In fact, the coastal belt was accretedprogressively during the late Quaternaryand represents the evolution of a barrier-lagoon system shifted alternatively land-ward and seaward as a result of the eustaticsea level changes. In the SE portion ofthe Sele Plain, near the archeological areaof Poseidonia-Paestum, numerous genera-tions of travertine deposits crop out. Thedepositional system of the “Travertini diPaestum” was active during the late Qua-ternary, especially during the Last Inter-glacial period and the Holocene [19], form-ing a plateaux hanging over the plain. Inthis sector of the coastal plain the mor-phologies linked to the eustatic changesare not recognizable, because absent and/orinterfingered and/or covered by traver-tine deposits. Using geomorphologicaland stratigraphic methods, integrated bygeo-archeological and tephro-stratigraphicdata, we focused the researches on the

Holocene morpho-stratigraphy changes ofthis sector of the Sele plain, in order to de-cipher the local sea level rise history andhorizontal shoreline changes. Sedimentaryevidence is presented for the Holocene ma-rine transgression due to Postglacial sealevel rise and the shoreline progradation,respectively, resulting from reduced eu-static effects and, to a minor extent, in-creased sediment loads.


As regards the Vektor-Vulkost Project (the-matic line 2), a multidisciplinary approach,based on a detailed sedimentological, geo-morphological and structural characteriza-tion of the Sele plain, was carried out in or-der to reconstruct the paleoenvironmentaland landscape changes that occurred dur-ing the Holocene, and the related chrono-logical framework. The sedimentary in-filling of the SE sector of the Sele plainwas studied in detail through two newcores, 15 m long, which were drilled in thecoastal sector in front of the archaeologicalarea of Poseidonia-Paestum. Further strati-graphic data were obtained from the inter-pretation of ca. 200 stratigraphic logs ofcores drilled for geotechnical purposes andfrom some archaeological trenches. On thebasis of lithofacies, unconformities, pres-ence of tephra layers and paleosoils, thecore and trench successions were subdi-vided into sedimentary units, by using theUnconformity Boundary Stratigraphic Unitmethod (UBSU, after Salvador, 1994). Themost important layers of the cores weresampled and subjected to laboratory anal-yses such as pollen and fossil content andtephra-stratigraphy, in order to reconstructthe UBSU chronology. Contemporary, alarge scaled geomorphologic analysis of

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the study area, based on field surveys andon airphoto and topographic map inter-pretation (CasMez 1:5.000 and I.G.M.I.1:25.000), was carried out. This analysisallowed us to identify landscape features ofdifferent types and ages and to define thepresent-day geomorphologic setting.

3 Geological and geomor-phological setting

The Sele plain derives from the aggrada-tion of a Pliocene-Quaternary depressionlocated along the western Tyrrhenian mar-gin of the southern Apennine Chain (Fig-ure 1b). It is about 400 km2 wide andpresents a triangular plan outline, which isdefined seawards by a straight sand coaststretching between the towns of Salernoand Agropoli. The boundaries of the plainare defined by NW-SE and NE-SW trend-ing faults, active during the Early and Mid-dle Pleistocene. The easternmost portionof this structural depression was charac-terised by continental conditions as testi-fied by the huge phases of clastic sedimen-tary aggradation of the “Eboli Conglomer-ates” auct., which compensated the Qua-ternary tectonic subsidence [20, 13, 21,22]. Further seawards, there is a strip ofcoastal plain formed during the Last Inter-glacial (MIS 5e) characterized by the pres-ence of three orders of beach-dune ridgeswhich to the rear interfinger with lagoonaland fluvio-palustrine deposits (Figure 1a).Only the youngest and most external ofthe Tyrrhenian coastal ridges still has agood morphological evidence (Gromola-Arenosola palaeo-ridges). The present el-evation a. s.l. of these Tyrrhenian de-posits proves that the plain has been moder-ately uplifted since the last interglacial pe-

riod [13, 23, 14, 15, 16, 17, 18]. Betweenthe Tyrrhenian sandy-coastal ridge and thepresent shoreline, a younger coastal sectoroccurs, which is elevated up to 5 m a.s.l.This belt was accreted progressively andrepresents the evolution of a barrier-lagoonsystem shifted alternatively landward andseaward during the Holocene. It includes acomposite sandy ridge which is partly ex-posed along the present coast and disap-pears inland under a muddy, substantiallyflat depression. After being exposed to sub-aerial conditions during the last glacial re-gression, this belt gradually entered brack-ish water conditions at the beginning ofthe Holocene, when transgressive trend oc-curred as the effect of rapid sea level rise.The inversion of tendency, from retrogra-dational to progradational, most probablycan be ascribed to a decline of the rate ofsea level rise under the threshold of bal-ance with the progradation due to fluvialsedimentation. The progradational trendwas interrupted by at least three phases offormation of sandy coastal ridges, knownas Laura ridge (dated from 5.3 to 3.6 kyBP) and Sterpina ridges (I and II, datedto before 2.6 ky BP and to about 2.0 kyBP, respectively) [23, 15, 16, 17]. Duringthese intervals the flat depression behindthe ridges was interested by palustrine con-ditions which persisted partially until veryrecent times, when it was interested by an-thropic reclamations. In the southern sectorof the Sele plain, near the Greek-Roman ar-chaeological area of Poseidonia-Paestum,lobate and self-terraced morphologies ofthe Paestum Travertine (Figure 2), com-posed by several polyphasic deposits oftravertine, derived by in situ carbonateencrustation of vegetables and/or by flu-vial reworking, and then lithified phyto-clasts. They were generated by highlycharged calcium carbonate waters of the

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Figure 2: Litho-facies map (1:5.000) of the coastal sector of the southern Sele river plain

springs located at the base of the SopranoMt. The recognized lithofacies of traver-tine (stromatolitic travertines, microhermaltravertines, phytohermal travertines, phyto-clastic travertines and calcareous tufa) al-lowed us to refer the depositional systemof Paestum Travertine to fluvial marshyconditions that favored the emergence ofa large sector hanging over the surround-ing plain [24, 25]. In this sector ofthe coastal plain the morphologies linkedto the eustatic changes are not recog-nizable, because absents and/or interfin-gered and/or covered by travertine de-posits. Recently, [19] have provided a

detailed chronological reconstruction ofthe various stages of the Paestum deposi-tional system, based on radiometric dating,archeo-tephra-stratigraphic data, and geo-morphological constraints (Figure 2). Theages of the deposits show that the deposi-tional systems have migrated from NE toS from the Pleistocene to the Holocene,up to deposit thick travertine successionsin the valley of Capodifiume river even inmodern times. In particular, the deposi-tion was active during the Last Interglacial(Tyrrhenian) and the early Holocene untilabout 5000 years ago, and in the historicalperiod during the Late-Ancient and Mid-

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Figure 3: Schematic geological and geomorphological map of the coastal sector of thesouthern Sele river plain, in front of the archaeological area of Poseidonia-Paestum

dle Ages (V-IX century AD). Further sea-ward, downstream of the hanging traver-tine plateaux, a low coastal belt is present.It is constituted by a continuous sandydune ridge (of not more than 6 m a.s.l.),which characterize the sector near the ac-tual beach. The dune belt stands behind adepressed area, situated at an altitude notexceeding 3 m, only recently reclaimed bya complex system of anthropic drainage.In the coastal sector, in front of the ar-chaeological area of Poseidonia-Paestum,Lippmann-Provansal (1987) proposed, onthe basis of finds of pottery fragments atPorta Marina (the port of the Greek-Romantown of Paestum looking to the sea), thata coastal lagoon had already establishedin the Iron Age (3.0 ky ago) while Guy(1990), on the basis of surveys and the in-terpretation of satellite images and aerialphotographs, suggested that, during theClassic period (2.5 ky ago), there was onlya small lagoon (pond or artificially pre-served and open to the sea). Preciselyin this area of the Sele River alluvial-coastal plain we have focused the morpho-stratigraphic investigations in order to un-derstand how the Holocene sea level risechanged the environments and the coastal

landscape.

4 New morpho-stratigraficaldata

The coastal strip in front of the archae-ological area of Paestum presents a veryarticulated landscape, consisting in an in-ner area situated at an altitude between10 and 20 m a.s.l., some meters higherthan the average level of the plain, thatdoes not exceed 5 m a.s.l. (Figure 3).Such morphological high, slightly slop-ing to the sea, appears to be composedof travertine deposits, belonging to differ-ent depositional bodies (as previously de-scribed). These polyphasic depositionalbodies, generated during the late Quater-nary, now form self-terraced bodies hang-ing above the average level of the plain.For this reason the travertine plateaux de-veloped above the tracks and remains of ar-chaeological settlements, particularly thoseof the Greek-Roman town of Poseidonia-Paestum. Landward, the hanging traver-tine bodies are connected to the piedmontbelt of the Capaccio hills and seaward tothe coastal strip by a steep escarpment cut

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Figure 4: Stratigraphic logs of the S2 and S3 cores

into travertine, whose remains are still vis-ible at Porta Marina of Paestum. Thissteep escarpment gently downgrades to adepressed area, situated at an altitude ofabout 4 m a.s.l. (Fossa Lupata), located be-hind a large sand dune ridge, which reachsan altitude of about 6 m a.s.l., located about1 km from Porta Marina (Figure 3). In ad-dition to the numerous data from archaeo-logical excavations, collected during mul-tidisciplinary geoarchaeological collabora-tions, and to new stratigraphic data derivedby collected cores, two new cores (Vek-tor S2 and S3) were drilled that reachedthe depth of 15 m. S2 and S3 were per-formed, respectively, in the area immedi-ately located westwards of the escarpmentcut into travertine of the Porta Marina (5.5m a.s.l.), and in the outer dune ridge, im-mediately behind the coastal road (2.5 m

a.s.l.) (for location see Figures 2 and 3).The deposits of the S2 core are constitutedof, from the top to the bottom (Figure 4):

• Unit 1: (5 m thick) Colluvial deposits,buried soils, anthropogenic restores andsilt-clay layers of continental environ-ments, subject to marshy episodes. Inthis unit the tephra of 79 AD Vesuviuseruption is intercalated at a depth ofabout 2 m.

• Unit 2: (4,5 m thick) Peaty silt and claylayers of marshy and lagoon environ-ments. At the top of the unit, potteriesof the VI cent. B.C. are present, whileat 7 m of depth (-1,5 a.s.l.) the fall de-posits (pumices and ashes) of the Ag-nano Monte Spina eruption (4.1 ky BP,Di Vito et al, 1999) are present.

• Unit 3: (4 m thick) Coarse sand andgravel layers of high-energy environ-

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Figure 5: Schematic geological section passing through S2, S3 and other cores.

ments (cliff toe with proximity of rivermouths).

This succession covers the travertine de-posits with a clear unconformity markedby an abrasion surface at -7,5 m a.s.l. Thedeposits of the S3 core are constituted of,from the top to the bottom (Figure 4):

• Unit 1: (6 m thick) Coastal dunesand layers. This unit be divided intotwo sub-units (1a for the sandy lay-ers of the upper part and 1b for thesandy layers of the lower part) ac-cording to the presence of a buriedsoil, at the depth of 3 m. Thispalaeosoil, in some archaeologicalexcavations close to the core, holdsarchaeological materials of the VI-Vcent. B.C. and is partly covered bythe fall deposits of the 79 AD erup-tion.

• Unit 2: (9 m thick) Alternating lay-

ers of clays and peaty silts, sandsand calcareous tufa and gravels offluvial-marshy environments. In thisunit the fall volcanoclastic depositsof the Neapolitan Yellow Tuff (15ky BP, Deino et al, 2004) and of theY3 (30 ky BP Munno and Petrosino,2004) are intercalated at a depth of 8m (-5,5 m a.s.l.) and 11 m (-8,5 ma.s.l.), respectively.

5 DiscussionThe schematic geological section of Figure5, that passes through the S2, S3 and othercores, was drawn perpendicular to the ac-tual shoreline, from the sea to the escarp-ment of Porta Marina, where the remainsof the Greek-Roman walls of Poseidonia-Paestum are located. Correlating tephralayers, such as the 79 AD tephra, the Ag-nano Monte Spina tephra (4.1 ky BP),

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Figure 6: Paleogeographical sketchs of holocene morfo-sedimentary trends of coastalarea of Paestum.

the Neapolitan Yellow Tuff tephra (15 kyBP), the Y3 tephra (30 ky BP), the lay-ers with archaeological remains, and re-ferring the data to the known Holocenemorpho-sedimentary trends, it was possi-ble to scan the late Quaternary palaeogeo-graphical evolution of this sector:

• The sea level low-stand of the LastGlacial Maximum (20 ky BP) led toa strong progradation of the shoreline.Therefore, the whole studied area wasinterested by continental environments,represented in the S3 core by deposits(Unit 2) containing the Neapolitan Yel-low Tuff tephra and the Y3 tephra. In theS2 core, the deposits of this phase mayhave been eroded by subsequent trans-gressive trend and/or have been obliter-ated by the deposition of travertine bod-ies.

• The rapid sea level rise of the first part

of the Postglacial period led to a rapidsubmergence of the area of Porta Marinaof Paestum, modeling a steep cliff. Atthe foot of the latter the deposits of clifftoe of Unit 3 of the S2 core were accu-mulated. The presence of fluvial clustersin the Unit 3 of the S2 core could wit-ness the proximity of one or more rivermouths.

• As soon as the rate of the Holocenesea level rise decreased, a rapid shore-line progradational trend started, and abarrier-lagoon coastal system formed. Infact, the sands of Unit 1 of the S3core represent the barrier beach that iso-lated the depressed area of Fossa Lupata,where the lagoon-marshy clays and siltsof Unit 2 of the S2 core were deposited.Pollen analysis revealed the presence ofa rich and diversified forest in which thedominant trees and shrubs (Alnus, Cory-

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lus, Quercus, Carpinus, Vitis) are indica-tive of high soil moisture. The presenceof the Agnano Monte Spina Tephra (4.1ky BP) and the archaeological remains ofthe VI cent B.C. in Unit 2 of the S2 core,allowed us to hypothesize the presence ofthe barrier-lagoon coastal system duringthis period. The collected chrono-dataare in agreement with the dating of theLaura paleoridge coastal deposits (5.3-2.5 ky BP) [15, 16].

• During the period between the foun-dation of the Greek-Roman town ofPoseidonia-Paestum (540 B.C.) and the79 AD, the area of S2 core was interestedby continental environments subject tomarshy episodes (Unit 1) while the areaof S3 core was interested by coastal duneenvironments (Unit 1). During this pe-riod the shoreline prograded a few hun-dred meters because an additional sandydune ridge was generated seaward.

• After 79 AD and up to now, the progra-dational trend of shoreline was empha-sized through the addition of anothersand dune ridge, testified in the S3 coreby the deposits of sub-Unit 1a. In thearea of the S2 core, a strong aggradationof the ground level took place due to an-thropogenic fills, reworked volcanoclas-tic deposits of 79 AD and historical de-position of travertines.

6 Conclusion

The stratigraphic data, obtained throughthe study of the cores, and the chronologi-cal framework, derived from the archaeol-ogy and tephro-stratigraphy and supportedby geomorphological indications, allowedus to outline some important stages of theHolocene palaeogeographical evolution ofthe SE sector of the alluvialcoastal plain of

the Sele River. The main results of the re-search are relative to the Holocene evolu-tion of the plain along the coast in frontof the archaeological site of Poseidonia-Paestum, where the knowledge has beenimproved by two new cores. In particu-lar, by integrating geomorphological andarcheo-tephro-biostratigraphical studies, itwas possible to characterize the Holoceneevolution of this sector with more detail forthe last 6.0 ky BP (Figure 6). In partic-ular, the research shows that the sea levelchanges and shoreline shifts character-ized the morpho-sedimentary trend of thecoastal areas: during the early Holocenethe morpho-sedimentary trend shows aclear transgressive trend, while the lateHolocene shows a progradational trend. Inthe area of Paestum, the transgressive trendhas favored the formation of a cliff cutin travertine, now partly buried by traver-tine deposits of mostly medieval age. Theprogradational trend started when an exten-sive sandy dune ridge (Laura Paleoridge)was generated, now located about 0.6 kmfrom the Porta Marina palaeocliff. Thisridge isolated a large depression at its back(Fossa Lupata depression). The archaeo-logical remains related to the VI-V cent.B.C. and the Agnano Monte Spina tephra(4.1 ka BP) confirm the presence, duringthis period, of a barrier-lagoon morpho-sedimentary system that shifted alterna-tively landward and seaward. The FossaLupata depression may have been con-nected with the sea through fluvial mouths,and it was probably used as a natural portand/or sea port of the Greek city. Afterthis period, and mainly after the deposi-tion of the 79 AD volcanoclastic fall de-posits, the shoreline shifted seaward a fewhundred meters through the formation ofanother dune ridge (Sterpina ridge). TheFossa Lupata depression, no longer con-

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nected with the sea, was filled by fluvial-marshy deposits and slowly dried up.

7 AknowledgmentsWe thank the Soprintendenza Archeolog-ica of Avellino-Salerno (Paestum Office),

in particular Dr. Marina Cipriani to havekindly granted the permission for the cor-ing within the Porta Marina archaeologi-cal area and Dr. Alfonso Santoriello of theSalerno Universita (Beni Culturali Depart-ment) for the interpretation of the ceramicmaterials of the cores.

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[4] P.A. PIRAZZOLI. Sea-Level Changes. The Last 20.000 Years. page pp.211, 1996.

[5] J. La Borel, C. Morhange, R. Lafont, J. Le Campion, and F. Laborel Deguen. Bio-logical evidence of sea level rise during the last 4500 years on the rocky coasts ofcontinental France and Corsica. Marine Geology, 120:203–223, 1994.

[6] G. Leoni and G. Dai Pra. Variazioni di livello del mare nel tardo Olocene lungo lacosta del Lazio in base ad indicatori geoarcheologici (pubblicazione ENEA-CNR).page 127, 1997.

[7] K. Lambeck, F. Antonioli, A. Purcell, and S. Silenzi. Sea level change along theItalian coast for the past 10,000 years. Quaternary Science Reviews, 23:1567–1598,2004.

[8] K. Lambeck, M. Anzidei, F. Antonioli, A. Benini, and A. Esposito. Sea level inRoman time in the Central Mediterranean and implications for recent change. Earthand Planetary Science Letters, 224:563–575, 2005.

[9] G. Vita-Finzi. The mediterranean valleys: geological changes in historical times.Cambridge University Press. page 186, 1969.

[10] R.S. Bradley. Palaeoclimatology. International Geophysic Series 64, Harcourt Aca-demic Press. page 325, 1999.

[11] B. Messerli, M. Grosjean, T. Hofer, L. Nunez, and C. Pfister. From nature-dominated to human-dominated environmental changes. Quaternary Science Re-views, 19:459–479, 2000.

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[12] V. Amato. La risposta di alcuni tipici sistemi morfodinamici della Campania (Italiameridionale) alle variazioni climatiche oloceniche. PhD thesis www.fedoa.unina.it,page 405, 2006.

[13] A. Cinque. Guida alle escursioni geomorfologiche(Penisola Sorrentina, Capri, Pi-ana del Sele e Monti Picentini). Gruppo Nazionale Geografia Fisica e Geomorfolo-gia, Amalfi 1986. page 119.

[14] L. Brancaccio, A. Cinque, G. D’Angelo, F. Russo, N. Santangelo, and I. Sgrosso.Evoluzione tettonica e geomorfologica della Piana del Sele (Campania, Appenninomeridionale). Geogr. Fis. e Dinam. Quat., 10:47 – 55, 1987.

[15] L. Brancaccio, A. Cinque, F. Russo, N. Santangelo, M. Alessio, L. Allegri, S. Im-prota, G. Belluomini, M. Branca, and L. Delitala. Nuovi dati cronologici sui de-positi marini e continentali della Piana del F. Sele e della costa settentrionale delCilento (Campania, Appennino meridionale). Atti del 74.mo Congr. Naz. della Soc.Geol. It., A:55 – 62, 1988.

[16] D. Barra, G. Calderoni, A. Cinque, P. De Vita, C. Rosskopf, and E. Russo Ermolli.New data on the evolution of the Sele River coastal plain (Southern Italy) duringthe Holocene. Il Quaternario, 11:287–299, 1998.

[17] D. Barra, G. Calderoni, M . Cipriani, J. De La Geniere, L. Fiorillo, G. Greco,M. Mariotti Lippi, M. Mori Secci, T. Pescatore, B. Russo, M.R. Senatore, G. ToccoSciarelli, and J. Thorez. Depositional history and palaeogeographic reconstructionof Sele coastal plain during Magna Grecia settlement of Hera Argiva (SouthernItaly). Geologica Romana, 35:151–166., 1999.

[18] A. Cinque and P. Romano. Note illustrative della Carta Geologica d’Italia alla scala1:50.000 foglio 486 Foce del Sele. ISPRA-Servizio Geologico d’Italia. page 83,2008.

[19] V. Amato, G. Avagliano, A. Cinque, M. Cipriani, G. Di Paola, A. Pontrandolfo,M. C. Rosskopf, and A. Santoriello. Geomorphology and geoarchaeology ofthe Paestum area: modification of the physical environment in historical times.Mediterranee, 112:129–135, 2009.

[20] M. Lippmann-Baggioni and G.Gars. La bordure sud des Monts Picentini: un jalondans l’evolution neotectonique et paleoclimatique de l’Apennin Meridional. Geogr.Fis. Dinam. Quat., 7:49–58, 1984.

[21] A. Cinque, F. Guida, F. Russo, and N. Santangelo. Dati cronologici e stratigraficisu alcuni depositi continentali della Piana del Sele (Campania): i ”Conglomerati diEboli”. Geogr. Fis. e Dinam. Quatern., 11:39 – 44, 1988.

[22] A. Zuppetta and A. Sava. Pleistocene brittle deformation in the Eboli Conglom-erates (Sele Plain – Campanian Apennines). Boll. Soc. Geol. It., 111:273 – 281,1992.

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[23] L. Brancaccio, A. Cinque, G. Belluomini, M. Branca, and L. Delitala. Isoleucineepimerization dating and tectonic significance of upper Pleistocene sea level fea-tures of the Sele Plain (Southern Italy). Zeit. Geomorph. N.F., Suppl. Bd.,, 62:159– 166, 1986.

[24] B. D’Argenio, V. Ferreri, and C. Violante. Travertine in the rise and decline of theancient town of Paestum (2500-1000 BP). GEOBEN Torino. page 16, 1999.

[25] B. D’Argenio, V. Ferreri, and E. Anzalone. I travertini di Paestum: breve guidaal periplo geoarcheologico della citta. Guida all’escursione della IX Borse delTurismo Mediteraneo di Paestum, page 25, 2007.

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Facies Analysis of Flood-Dominated Fan-Deltas offthe Amalfi Coast, Eastern Tyrrhenian Sea

F. Molisso1, E. Esposito1, D. Insinga1, C. Lubritto2, S. Porfido1, M.Sacchi1, T. Toth3, C. Violante1

1, Institute for Coastal Marine Environment, CNR, Napoli, Italy2, Department of Environmental Sciences, Second University of Napoli, SUN, Caserta,Italy3, Eotvos Lorand University, Budapest, [email protected]

Abstract

A stratigraphic study of marine gravity cores, complemented by high-resolutionseismic profiles acquired off the Amalfi coast, a rocky coastal area on the southernflank of the Sorrento peninsula (Italy), documents the facies associations and theinternal stratigraphic architecture of a series of small fan-deltas that develop at themouth of major bedrock streams. Integrated stratigraphy and correlation of gravity-cores allowed for a bed-to-bed calibration of seismic reflectors. Accurate dating andcorrelation have been essential for the construction of reliable models of the sedi-ment architecture and influx rates in this area, as well as for establishing the linksbetween changes in sedimentation and palaeoenvironmental events. Our research in-dicates that the Amalfi fan-delta system largely postdates the Plinian eruption of theVesuvius of AD 79 and displays various phases of development that were ostensi-bly associated with periods of high sediment supply from the adjacent river basins,under varying climatic conditions. During these periods landscape-mantling loosepyroclastic deposits were quickly eroded and delivered to the continental shelf bysheet wash and flash floods events. This in turn created favourable conditions forseafloor instability, soft sediment failure, slumping and sliding that characterize thedeltaic stratigraphic architecture.

1 Introduction

The aim of the study is the detailed recon-struction of stratal architecture of the fan-deltas and the interpretation of seismic fa-cies in terms of depositional processes andenvironmental setting off the Amalfi coast,eastern Tyrrhenian Sea. In recent years,deltaic depositional settings at the mouth ofsmall rivers of the Mediterranean and othertemperate regions have received growingattention, due to the relevance of these fa-

cies associations in the understanding ofthe late Quaternary evolution of inner shelfdepositional systems and their interactionwith fluvio deltaic processes, seafloor in-stability of delta slopes, coastal volcanism,active tectonics, and the climatic regime[1, 2, 3]. Sediment dispersal underwa-ter is directly related to supply by rivers.In the case of bedrock rivers and streamsof temperate regions that form fan deltasalong high-relief seacliffed coasts [4, 5, 1],the fluvial regime is basically controlled by


Marine Geology

Figure 1: Tectonic sketch-map of the Campania continental margin (Eastern TyrrhenianSea) and location of the study area.

episodic, and sometimes catastrophic dis-charges which cause flooding of the fans.Long-term development of fan deltas ob-viously reflects a wide range of processesbut variations in sediment supply and in themorphoclimatic regime appear to be ma-jor controls (e.g., [6]). Among the fac-tors that may have significant impact onfan delta construction, are, hence, the fre-quency of recurrence of exceptional riverfloods, mudflows and explosive eruptions(pyroclastic falls, surges and flows) fromcoastal volcanoes. All these processes caninduce the supply of large volumes of looseor poorly consolidated sediment into thedelta system and over vast areas of the con-tinental shelf [2, 7, 8, 9].

2 Geological frameworkThe study area is located on the south-ern slope of the Sorrento Peninsula. Thepeninsula is a major Quaternary morpho-

structural unit of the western flank ofSouthern Apennines and forms a narrowand elevated mountain range (up to 1444m) that separates two major embaymentsof the eastern Tyrrhenian margin, namelythe Naples and Salerno Bays (Figure 1).It is mostly formed by a pile of Meso-zoic carbonate rocks, covered by Tertiaryto Quaternary siliciclastic and pyroclasticunits and is deeply cut by a complex pat-tern of bedrock rivers and channels char-acterized by relatively small catchment ar-eas and pronounced disequilibrium of thestream profiles. These rivers show a dis-tinct seasonality and a torrential regime[10, 11]. Coarse-grained coastal alluvialfans confined by narrow valleys at themouth of the major streams are relativelycommon in this setting (Figure 2). Theyare formed by deposition from flash floods,that occur during heavy rain storms. Thedelivery of sediments towards the coastalfans is favoured by the steep slopes andthe loose material of a wide size range

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Figure 2: Shaded relief map of the Sorrento Peninsula and location of the fan delta sys-tems fed by the main streams of the Amalfi coast. Location of some of Seistec profilesand gravity cores used in this study (see Figure 1 for location)

that includes, bedrock river gravel, slope-weathering products, soil, and unconsoli-dated volcaniclastics deriving from the ex-plosive activity of the Vesuvius and CampiFlegrei Volcanoes [12, 13, 8].


This study is based on integrated stratig-raphy and correlation of gravity-cores al-lowed for a bed-to-bed calibration ofseismic reflectors and interpretation ofvery high-resolution (IKB-Seistec), single-channel reflection seismic survey carriedout on the Amalfi inner shelf, betweenSalerno and Amalfi, in July 2004 (Figure 2)[14, 15]. The overall control for the stratig-raphy and depositional setting of the lateQuaternary depositional sequence comesfrom facies analysis of sediment cores(Figure 3), integrated biostratigraphic (Fig-ure 4) and chronologic data (Figure 5),analysis of an extended dataset that in-

cludes multibeam bathymetry, Side ScanSonar imagery, single-channel Sparkerand Chirp-sonar profiles, acquired bythe IAMC-CNR between 1997 and 2004.The sequence stratigraphic nomenclatureadopted for seismic interpretation is after[16](1992).

4 Data and results

4.1 Gravity-core stratigraphy,14C chronology and tephralayers

Gravity-cores C90, C106, C106 12 werecollected on the outer shelf of Salerno Bay,between Capo d’Orso and Amalfi and pro-vide a calibration of the entire last postglacial succession. Stratigraphic correla-tion of the gravity-cores from the sedi-mentological analysis is robust, thus al-lowing the construction of a compositestratigraphic section that represented the

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Figure 3: Lithology, textures, sedimentary structures, magnetic susceptibility, calciumcarbonate content and facies associations of gravity cores C90 and C106 12. Grain sizestatistical parameters: Mz: mean; s: sorting; SK: skewness; KG: kurtosis. See text formore information on chronology and nature of event beds.

base for the geological calibration adoptedin the seismic stratigraphic interpretation.The cored succession consists of c. 5 mthick transgressive sequence that overliesthe major erosional surface (ES) associatedwith the sea-level drop and lowstand of thelast glacial maximum. Below this uncon-formity, core C106 12 sampled a sandy siltsuccession older than 50 ka, within UpperPleistocene deposits (Figures 6 and 7). Thecored sequence is punctuated by at leastten tephra layers, we have labelled fromtop to bottom as tS1, tS1-α, tS1-β, tS1-γ, tS2, tS3, tS3-α, and tS4 to tS6 (Figure3). Tephra nomenclature is after Insingaet al. [17], Sacchi et al.[15] and Molissoet al. [14]. On the basis of sedimento-logical analysis and quantitative changesin benthic foraminiferal assemblages of the

core samples, three main lithofacies as-sociations can be recognized (Figures 3and 4). A composite stratigraphic section,from bottom to top consists of: a) Shelfmud with volcaniclasts and bioclasts, b)Shoreface sand and pebble, c) Bioturbatedprodelta mud.

4.1.1 Facies A) - Shelf mud with vol-caniclasts and bioclasts (UpperPleistocene > c. 50 ka BP)

This facies is represented only in coreC106 12 and displays a thickness of c. 110cm. From base to top, it consists of poorlysorted olive gray (5Y4/2) clayey sandysilt and dark gray (5Y4/1) sandy clayeysilt with very thin volcaniclastic lenses in-terbedded. At 612 cm and 580 cm bsf

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two pyroclastic layers occur, namely a 4cm thick tephra (tS6) and a 9 cm thicktephra (tS5), respectively. The sandy frac-tion is represented by volcaniclasts andbioclasts and displays a gradual increase,especially in the volcaniclastic componenttowards the top (Figure 3). The benthicforaminifera assemblage (Figure 4) and theoccurrence of epipelagic boreal guest (Li-macina retroversa) suggest a cold periodof the glacial Pleistocene. The upper-most 20 cm of unit A) is characterizedby sparsely-branching burrows of ichno-genus Thalassinoides. Burrows have well-defined circular boundaries, with diame-ter ranging from 1 to 2 cm, and are pas-sively infilled with the above lithofacies B).This ichnofabric corresponds to the Glos-sifungites ichnofacies [18]. The unit isbounded at the top by an erosional surfacethat correlates with the unconformity (ES)of seismic profiles, and is characterized bythe occurrence of shell debris. Glossifun-gites ichnofabric is commonly taken to in-dicate a firmground. In this context it likelyrepresents colonisation of the Pleistoceneeroded substrate during minor breaks insedimentation following storm events, be-low storm wave base in the foreshore-offshore transition zone, during the earlyTST. The lithofacies assemblage of thissuccession, coupled with the seismic evi-dence of thick Upper Pleistocene forestep-ping parasequences beneath unconformity(ES), suggests that this unit may be inter-preted as a progradational deltaic sequencecharacterised by shelf mud deposit withvolcaniclasts and bioclasts.

4.1.2 Facies B) – Shoreface sand andpebble (Uppermost Pleistocene c.18.0 – 10.2 ka BP)

These deposits directly overlies facies A)and consist of a 70 cm thick unit in coreC106 12. The grain-sizes of this unit rangefrom silty sand to pebble, with very poorsorting. The lowermost 10 cm are repre-sented by medium sandy pebble with in-verse gradation that is bounded at the topby an erosive surface that correlates withthe ravinement surface recognized on seis-mic profiles. Towards its top, the de-posit is characterized by coarse-grainedconstituents represented by volcaniclasts,lithoclasts and bioclasts often fragmented.Among bioclasts are bivalve and gastropodshell fragments, sometimes abraded, bio-eroded and encrusted, solitary corals, bry-ozoans and echinoid fragments. Plant de-bris (Posidonia oceanica) are also found(Figure 3). The foraminifers assemblages(Figure 4) along with the occurrence ofrhodolith-bearing pebbles and shells indi-cate a infralittoral to circalittoral zone as-sociated with relatively low-salinity con-ditions. On the basis of lithofacies as-semblages and the seismic-stratigraphic ar-chitecture this unit can be interpreted asa transgressive lag containing reworkedmaterial from the substrate and/or theearly shoreface deposits (“healing phasedeposits”) (e.g. [19]). A negative peakof the CaCO3 curve in the interval be-tween 495 and 505 cm (C106 12), whichsuggests a relatively low water tempera-ture, may be tentatively correlated with theYounger Dryas [20]. Analogously, the un-derlying interval between 505 and 525 cm(C106 12), marked by a positive peak ofthe CaCO3, may be taken as correspondingto the Bolling–Allerød event (Figures 3 and4 and 7).

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Figure 4: Relative frequency (%) of selected benthic foraminifera and event beds of coreC106 12. See text for more information on chronology and nature of event beds.

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Figure 5: Stratigraphic depth versus calibrated radiocarbon ages plots for gravity coresC90 (a) and C106 12 (b).

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Figure 6: Seistec profile 3006 showing the general architecture of the continental shelfoff the Amalfi coast and the location of C106 12 core site. See the insert for location ofprofile.

Figure 7: Geological calibration and labelling of seismic reflectors of Seistec profile atC106 12 core site. See text and Figures 3 and 4 for more information on chronology andnature of event beds.

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4.1.3 Facies C) – Bioturbated prodeltamud (Uppermost Pleistocene –Holocene < c. 10.2 ka BP)

Facies C) is represented in all the studycores. It consists of a mud-supportedlithofacies characterized by a gray to olivegray homogeneous, bioturbated clayey siltwith at least eight tephra (or cryptothepra)and a few thin layers of fine-grained tur-bidites interbedded. The sandy fractionis rare and consists of fine to very finevolcaniclasts, sub-rounded to sub-angulargrey pumices, minerals, scoriae and glass,and bioclasts, represented by fragments ofgastropod, bivalves, bryozoans and echi-noid. Turbidite layers are a few centimetresthick and consist of volcaniclasts (roundedpumice, locally reddened scoriae, frag-ments of minerals), subrounded lithics andreworked bioclasts (fragments of bivalves,gastropods, bryozoan, phanerogamous sea-grass remains) (Figure 3). Facies C) marksa significant change in the relative abun-dance of many benthic taxa, accompaniedby the disappearance and/or abrupt de-crease of some species and the parallel in-crease of others (Figure 4). Peaks of max-imum abundance of some taxa, along witha relative maximum in the CaCO3 curve,seem to concentrate around 450 cm, at astratigraphic horizon we interpret as themaximum flooding surface (mfs) (Figures3 and 4). The AD 79 Pompeii tephra bed(tS2) represents a marked environmentalchange in the faunistic assemblage (Figure4). In general, the benthic assemblage ofthis unit indicates a rapid increase in sed-imentation rate with respect to the under-lying facies B and a predominantly muddysetting, characterized by relatively high or-ganic matter and low oxygen concentra-tion, typical of the modern “mud belt” [21].Correlation with seismic profiles suggests

that this lithofacies corresponds to prodeltamud deposits associated with the modernfan-delta system of the Amalfi shelf. Ac-cording to the 14C calibrated age-depthplots we get interpolated ages that pro-vide chronologic reference for the recog-nized event beds and can be used for ten-tative correlation of the studied tephra lay-ers with age dated volcanic events onland(Figures 5 and 7). 14C AMS datings wereobtained on carbonate specimens of plank-tic foraminifera, mollusc shells and woodremains [15, 14]. Tephra layers tS1 to tS4are interbedded within the last post-glacialsuccession, while tS5 and tS6 are interbed-ded within the Upper Pleistocene depositsunderlying unconformity ES ((Figures 6and 7). Most tephras have a sharp base,normal or inverse grading, poor sorting andtypically a gradual transition to the over-lying deposits. All cored tephras layersdisplay a thickness in the order of 3-10cm, with exception of tephra tS2 that cor-respond to a 80-100 cm thick pyroclasticbed deposited during the AD 79 Plinianeruption of the Vesuvius. This teprha canbe subdivided into three major horizons,namely a) white pumice, b) gray pumiceand c) gray lapilli [2, 17] that correspondto different phases during the AD 79 erup-tion (Figures 3 and 7).

4.2 Seismic interpretationThe interpretation of the IKB–Seistecseismic profiles acquired off the Amalficoast was conducted according to se-quence stratigraphic principles. Termi-nology adopted for sytems tracts is after[16], 1992. Core-to-seismics correlationallowed for calibration of the major se-quence stratigraphic surfaces on seismicprofiles (e.g. transgressive surface, ravine-ment surface, maximum flooding surface).

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Figure 8: Detail of Seistec profile 3012 showing the slumping of the Pompeii tephra bed(AD 79). See Figure 7 for key to reflectors labels.

Moreover, it indicated that tephra lay-ers tend to correspond to high amplitude,well developed seismic reflectors. This isclearly the case, for instance, of the Vesu-vius early Medieval tephra tS1-γ, the tS2(AD 79) pumice fall layer, the tS3 and tS3-α, AP inter-Plinian deposits), and tephratS4 (Astroni-Averno). Seistec profiles in-dicate that unconformity ES separates twomain seismic stratigraphic units (Figures6 and 7). The lower one is representedby a prograding succession truncated atthe top by a dramatic erosional surfaceand mostly consists of Upper PleistoceneForced Regressive Wedge Systems Tracts(FRWST) deposits. Above unconformityES, seismic profiles show relatively con-tinuous, parallel and sub-parallel reflectors,gently inclined towards SE, as result oflow-angle backstepping and aggrading oflayers. This unit is represented from bot-tom to top by the Transgressive Systems

Tract (TST) and Highstand Systems Tract(HST) deposits which formed in responseto the time-transgressive landward shift ofthe coastline during the rapid sea-level risethat accompanied the last deglaciation (c.18-6 ka). The thickness of the uppermostPleistocene-Holocene shelf wedge variesin the study area from 35-40 m in theinner-mid shelf, to a minimum of 4-2 mat the shelf edge. The HST deposits ofthe southern shelf of the Sorrento Penin-sula between Amalfi and Capo d’Orso, arecharacterized by the occurrence of a num-ber of remarkably developed reflectors thatcan be correlated with different pyroclas-tic layers interbedded mostly within the up-per Holocene succession. Seismic profilesshow that the late HST (Upper Holocene)succession of the Amalfi shelf is charac-terized by a number of small progradingdeltas that develop at the mouth of thesmall bedrock rivers with torrential regime.

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Figure 9: Detail of Seistec profile 5006 off the Canneto stream, Amalfi, showing approx-imate correlation of prograding subaqueous delta units with major climatic changes ofthe last 2000 years. See insert and Figure 2 for location.

The best developed deltaic wedges in thestudy area occur offshore Maiori at themouth of the Reginna Major torrent offthe village of Minori at the mouth of theReginna Minor at the mouth of Canneto,Dragone and Cappuccini torrents (Figure2). These deltaic bodies represent the sub-aqueous components of the confined al-luvial fans that developed in the narrowcoastal plain and pocket beaches of theAmalfi coast. Seistec profile 3012 (Figure8) documents the occurrence of sedimen-tary structures at the base of the ReginnaMajor delta front that may be associatedwith a general gravity-driven instabilityand soft sediment deformation above dis-tinct stratigraphic surfaces, namely rep-resented by reflector H (base of AD 79pumice layer) and reflector I. Minor, butstill clear evidence of seafloor instabilitycan be recognized above reflectors L and E(Figure 8). Seismic interpretation suggeststhat soft sediment deformation above the

base of tephra tS2, mostly involves the py-roclastic layer itself and consists of slump-slide folding and slump-fault rupture of thetephra layer (Figure 8).

5 Discussion and Conclu-sion

The IKB-Seistec seismic reflection pro-files and gravity-core data used in thisstudy have revealed unprecedented detailedviews of the inner-mid shelf depositionalsystem of the northern Salerno Bay, al-lowing for the recognition of a numberof fan-deltas that developed mostly dur-ing the last two thousand years, at themouth of small rivers of the Amalfi cliffedcoast. During this time interval of c. 2000yrs, both sea-level oscillation and tectonicsubsidence/uplift were practically negligi-ble in terms of influence on the overallstratigraphic architecture of the inner shelf

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system ([22] and references therein) andthe main factor controlling stratal geome-tries and patterns, were likely the rates andmodes of sediment supply. The deltaicbodies imaged by seismic interpretationrepresent the underwater counterparts ofcoastal alluvial fans fed by small bedrockrivers with torrential regime that are partof the hydrographic network of the Sor-rento Peninsula. In this context subaerialdelta-plain components are practically ab-sent and the narrow space at the exit of thevalleys is filled up with a coarse-grainedalluvial prism up to a few tens of me-tres thick, whereas at the seashore the al-luvial deposits are reworked into pocket-beach settings. Most of the stratigraphicsequence imaged by seismic profiles is rep-resented by HST deposits and the gen-eral stratigraphic architecture of the studiedfan-deltas is of two main types. The deltaicbodies off Maiori and Minori display rel-atively steep and long sigmoidal foresets,commonly associated with topset layers.The fan-deltas off the Amalfi-Atrani coastshow a clear variation in the dip angleof foresets and a very reduced or absenttopset towards the delta fronts. All thefan-deltas described in this study startedto develop above the pyroclastic bed de-posited by the Vesuvius during the “Pom-peii” Plinian eruption of AD 79 which cor-responds to a major downlap surface. Asignificant change in the stratal architec-ture of the fan-deltas occurred after an-other eruption of the Vesuvius, during theearly Medieval period (c. AD 512-685).This is documented by the development ofanother remarkable downlap surface thatcan be correlated with the oldest Medievalproducts of the Vesuvius preserved in theSalerno Bay (tephra layer tS1-γ). Seismicreflector (E) that correlates with these prod-ucts consistently separates the fan-deltas

of all the study areas into two sub-unitsshowing distinct stratal patterns (Figure 9).Seistec profiles reveal evidence of gravity-driven instability at various stratigraphiclevels within the fan-deltas. Likely, morethan one mechanism of sediment deforma-tion or failure is behind the variety of thefeatures described in the fan-deltas of theAmalfi coast. The available data allow forthe recognition of (1) crenulation in mud-dominated prodelta slopes, possibly asso-ciated with shear deformation of sedimentsby creeping, (2) slide/slump deformationof the AD 79 pyroclastic deposits (3) grav-ity (inertia/turbidity/debris) flow depositsassociated with selected stratigraphic inter-vals. Seismic stratigraphic interpretationshowed that most of the gravity-driven in-stability processes are not diffused acrossthe fan-delta but indeed concentrated ona few stratigraphic horizons that invari-ably correspond to major tephra layers ortephra clusters. This observation, coupledwith the recognition that the sediment sup-ply to the fan-delta system is largely af-fected by high-energy river floodings sug-gests a direct relationship between the ratesof erosion of the river basin slopes that fol-low deposition of landscape-mantling vol-caniclastic deposits and the rates of under-water sediment that are delivered to thefan-deltas. The interpretation proposed inthis study, implies that the growth ratesof the fan-deltas of the Amalfi coast wereprimarily controlled by the average re-currence and magnitude of river floodingepisodes that have provided conspicuoussediment yields to the delta system, con-comitant with periods during which abun-dant, erosion-prone (volcani)clastic mate-rial was available on the slopes of the feed-ing river basins. Accordingly it may beproposed that the amount of sediments de-livered to the coastline and hence the rates

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of development of the Amalfi fan-deltas inthe last 2000 years were possibly dictatedby the interplay of the availability of loosepyroclastic covers on the slopes of the allu-vial basins, on one hand, and on the otherby the varying erosional rates on the slopesdue to the climatic oscillations that haveoccurred during the last millennia. Theillustration of the fan delta developing atthe mouth of the Canneto stream (Amalfi)(Figure 9), shows an attempt of correlationbetween the seismic stratigraphic frame-work described in this study and the ma-jor climatic fluctuations of the last millen-nia (e.g. [23]). This tentative correlation,derived from mere chronologic basis, sug-

gests that the major change detectable inthe stratal geometries of the fan-deltas oc-curring in the early Medieval time (tephratS1-γ) may be associated with the onsetof a period of climatic cooling, known asEarly Medieval cool period (c. AD 500-AD 800), that developed immediately afterthe Roman Warm period. Similarly, furtherminor changes in the stratal patterns of thedelta foresets, that are consistently imagedby the seismic record in all the individualfan-deltas of the Amalfi coast may be cor-related, in turn, with the Medieval WarmPeriod (c. AD 900-AD 1100) and the Lit-tle Ice Age (c. AD 1400-AD 1850).

References[1] F.J. Lobo, L.M. Fernandez-Salas, I. Moreno, J.L. Sanz, et al. The sea-floor mor-

phology of a Mediterranean shelf fed by small rivers, northern Alboran Sea margin.Continental Shelf Research, 26:2607–2628, 2006.

[2] M. Sacchi, D. Insinga, A. Milia, F. Molisso, et al. Stratigraphic signature of theVesuvius 79 AD event off the Sarno prodelta system, Naples Bay. Marine Geology,222-223:443–469, 2005.

[3] T.S. McConnico and N. Bassett Kari. Gravelly Gilbert-type fan-delta on the Con-way Coast, New Zealand: Foreset depositional processes and clast imbrications.Sedimentary Geology, 198:147–166, 2007.

[4] L.M. Fernandez-Salas, F.J. Lobo, F.J. Hernandez-Molina, et al. High-resolutionarchitecture of late Holocene highstand Prodeltaic deposits from southern Spain:the imprint of high-frequency climatic and relative sea-level changes. ContinentalShelf Research, 23:1037–1054, 2003.

[5] T. Hasiotis, M. Charalampakis, A. Stefatos, G. Papatheodorou, et al. Fan-deltadevelopment and processes offshore a seasonal river in a seismically active region,NW Gulf of Corinth. Geo-Marine Letters, 26:199–211, 2006.

[6] A. Colella and B.D. Prior, (Eds.). Coarse-grained deltas. International Associationof Sedimentologists. Special Publication, 10:357 pp., 1990.

[7] R. Sulpizio, G. Zanchetta, F. Demi, M. Di Vito, et al. The Holocene syneruptivevolcaniclastic debris flowin theVesuvian area: geological data as a guide for haz-

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ard assessment. In: Siebe, C.and Macias, J.L. and Aguirre-Diaz, G.J. (Eds.) Neo-gene–Quaternary continental margin volcanism: a perspective from Mexico. Geol.Soc. Am. Special Paper, 402:203–221, 2006.

[8] M. Bisson, M.T. Pareschi, G. Zanchetta, R. Sulpizio, et al. Volcaniclastic debris-flow occurrences in the Campania region (Southern Italy) and their relation toHolocene–Late Pleistocene pyroclastic fall deposits: implications for large-scalehazard mapping. Bulletin of Volcanology, 70:157–167, 2007.

[9] E. Esposito, G. Foscari, F. Molisso, S. Porfido, M. Sacchi, et al. Flood risk estima-tion through document sources analysis: the case of the Amalfi Rocky Coast. Thisvolume, 2010.

[10] E. Esposito, S. Porfido, and C., (Eds.) Violante. Il nubifragio dell’ottobre 1954 aVietri sul Mare-Costa di Amalfi Salerno. CNR GNDCI, 2870:381, 2004.

[11] C. Liquete, P. Arnau, M. Canals, and S. Colas. Mediterranean river systems ofAndalusia, southern Spain, and associated deltas: a source to sink approach. MarineGeology, 222–223:471–495, 2005.

[12] H. Sigurdsson, S. Carey, W. Cornell, and T. Pescatore. The eruption of Vesuvius inAD 79. National Geographic Research, 1:332–387, 1985.

[13] R. Sulpizio, G. Zanchetta, F. Demi, M. Di Vito, et al. The Holocene syneruptivevolcaniclastic debris flowin theVesuvian area: geological data as a guide for hazardassessment. Geol. Soc. Am. Special Paper, 402:203–221, 2006.

[14] F. Molisso, D. Insinga, F. Marzaioli, M. Sacchi, et al. Radiocarbon dating versusvolcanic event stratigraphy: age modelling of Quaternary marine sequences in thecoastal region of the Eastern Tyrrhenian Sea. Nucl. Instr. and Meth. in Phys. Res.B., 268(7-8):1236–1240, 2010.

[15] M. Sacchi, F. Molisso, C. Violante, E. Esposito, et al. Insights into flood-dominatedfan-deltas: very high-resolution seismic examples off the Amalfi cliffed coasts,eastern Tyrrhenian Sea. The Geological Society London, Spec. Publ., 322:33–71,2009.

[16] D. Hunt and M. E. Tucker. Stranded parasequences and the forced regressive wedgesystems tract: deposition during base-level fall. Sedimentary Geology, 81:1–9,1992.

[17] D. Insinga, F. Molisso, C. Lubritto, M. Sacchi, I. Passariello, and V. Morra. Theproximal marine record of Somma–Vesuvius volcanic activity in the Naples andSalerno bays (eastern Tyrrhenian Sea) during the last 3 kyrs. Journal of Volcanologyand Geothermal Research, 177:170–186, 2008.

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[18] M.K Gingras, S.G Pemberton, and T. Saundners. Bathymetry, sediment texture andsubstrate cohesiveness their impact on modern Glossifungites trace assemblagesat Willapa Bay, Washington. Palaeogeogr. Palaeoclimatol. Palaeoecol., 169:1–21,2001.

[19] H.W. Posamentier and G.P. Allen. Variability of the sequence stratigraphic model:effects of local basin factors. Sedimentary Geology, 86:91–109, 1993.

[20] N. Kallel, M. Paterne, L. Labeyrie, J.C. Duplessy, and M. Arnold. Temperature andsalinity records of the Tyrrhenian Sea during the last 18000 years. Paleogeography,Paleoclimatology, Palaeoecology,, 135:97–108, 1997.

[21] F. J. Jorissen. Benthic foraminifera from the Adriatic Sea principles of phenotypicvariation. Utrecth Micropaleontol. Bull., 37:176, 1988.

[22] C. Caiazzo, A. Ascione, and A. Cinque. Late Tertiary–Quaternary tectonics of theSouthern Apennines (Italy): New evidences from the Tyrrhenian slope. Tectono-physics, 421:23–51, 2006.

[23] R. Brazdil, C. Pfister, H. Wanner, H. von Storch, and J. Luterbacher. Historicalclimatology in Europe–the state of the art. Climatic Change, 70:363–430, 2005.

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538

The Coastal Depositional Systems along the Cam-pania Continental Margin (Italy, Southern Tyrrhe-nian Sea) since the Late Pleistocene: New Informa-tion Gathered in the Frame of the CARG Project

F. Budillon1, G. Aiello1, A. Conforti1, B. D’Argenio1, L. Ferraro1, E.Marsella1, L. Monti2, N. Pelosi1, R. Tonielli11, Institute for Coastal Marine Environment, CNR, Napoli, Italy2, Regione Campania, Settore Geotecnica, Geotermia e Difesa del Suolo, Napoli, [email protected]

Abstract

Extensive high-resolution mapping of the continental margin off the southernCampania region (eastern Tyrrhenian Sea) has revealed significant morphologicaland geological features which allowed us to outline the gradual modification of thecoastal domains since the Late Pleistocene. Swath bathymetry, acoustic images ofthe seafloor, seismic acquisition, core and bottom samples were used to implement alarge database.Shore bodies ranging in age from pre- to post- last-glacial times have been identifiedin the uppermost 100 ms of the seismic stratigraphic record off the Sele and Bussentoriver mouths. The oldest bodies formed during the seaward retreat of the shorelineduring the Late Pleistocene sea level drop. The peak of the retreat accounts forthe growth of a shelf-margin, in the Salerno and Policastro Bays, and a mid-shelf,off Cilento, littoral body, at least 100 km long, during the last maximum lowstandphase. At that time, the River Sele flowed directly on the upper slope and formed achannel drainage system, still preserved between a depth of 180 and 500 m, due todensity flows that have transferred sediment from the coastal area directly into theSalerno Valley, an intraslope basin of the Eastern Tyrrhenian Margin. The postglacialsea level rise caused the fast drowning of the shelf and a partial preservation of thetransgressive deposits. However a prograding wedge 1.5 km long and about 10 msthick, which lies above the transgressive surface (90/60 m below the present day sealevel), could represent a trace of the Younger Dryas climatic event. The rapid shoreprogradation during the ∼12 ky B.P. cold event testifies the sensitivity of the Selecoastal system even to minor climatic oscillations.

1 Introduction

The geological mapping Project of theCampania offshore (CARG project) al-lowed us to gather new geological (Chirpsonar Subbottom and Uniboom profiles,

gravity cores and grabs) and morphological(Swath-bathymetric soundings and Sides-can Sonar images of seafloor) information,valuable to create maps of the seafloor atscales of 1:10000 and 1:25000, down to the200 m isobath. The project was commis-


Marine Geology

sioned to the IAMC- CNR by the RegioneCampania (Settore Geotecnica, Geotermiae Difesa Suolo) about 8 years ago, to berealized according to the steering lines ofthe Italian Geological Survey, now ISPRA,Institute for Environmental Protection andResearch.Mapping criteria focussed mainly on thephysiographic features of the shelf/slopesector, the lithology and textures of sedi-ment at the seafloor, the stratigraphic stack-ing pattern within the Late Quaternary de-positional sequence (SDTQ).This project has been a valuable oppor-tunity to investigate the morphology andstratigraphy and to map the southern Cam-pania offshore thoroughly, implementingthe high resolution geological and morpho-logical data set of the CNR-IAMC.This report summarizes the main outcomeof the surveys.

2 Geological settingThe surveyed marine area is about 1500km2 and falls within four sheets of the Na-tional Geological Map of Italy (n. 486 Focedel Sele, n. 502 Agropoli, n. 519 Pal-inuro, n. 520 Sapri, Figure 1). It per-tains to the Tyrrhenian side of the SouthernApennine range, which has been formingsince the Late Pliocene- Early Pleistocene,along with the opening of the Marsili basin,within the Tyrrhenian Sea back-arc basin[1]. The Tyrrhenian border of the chainachieved most of its actual configurationby the Early Pleistocene, when NE-SW ori-

ented alternating structural depressions andhighs began to delineate. A set of low-angle, south-east verging faults, and asso-ciated minor faults, led to the extensionaldeformation of the Meso-Cenozoic car-bonate basement and the Miocene nappesand the formation of asymmetrical half-grabens [2, 3]. Throughout the Mid- andLate Pleistocene the extensional regimeproduced high-angle NW-SE oriented nor-mal faults and trans-tensional faults thatenhanced the vertical displacement of themargin of the chain with respect of its ax-ial portion [4], [3]. A thick syn-tectonicPleistocene sedimentary succession madeof continental, volcanoclastic and marinedeposits filled the structural depressions[5, 6]. The Sele Plain-Salerno Gulf half-graben is a ENE-WSW oriented structuraldepression, which displays up to 2400ms of post-orogenic sediment infill [5]and about 1000 m of Pleistocene sedi-ment documented by offshore well stratig-raphy. Seismic reflectors’ geometries showlocal evidences of transpressive deforma-tion and tectonic inversion due to the effectof strike-slip faulting [7]. The deepest por-tion of the gulf, the Salerno Valley, sits atthe foot of the Sorrento-Amalfi Peninsulaand exceeds a depth of 1000 m to the southof Capri Island [8].The shelf areas of the Salerno Gulf containthe seaward front of the Sele, Tusciano, Pi-centino and Solofrone alluvial plains whichprograded seaward by about 15 km start-ing from the MIS 5a and following the gen-eral retreat of the sea level during the LatePleistocene [9, 10], (Figure 2).

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Figure 1: The continental margin off southern Campania region, between Salerno andSapri, extensively surveyed by IAMC –CNR since the 2003, to accomplish the CARGproject aims (bold numbers refer to the geological maps of Carta Geologica d’Italia, scala1:50000). Submarine topography is by swath bathymetry. 1) submerged beach; 2) con-tinental shelf; 3) upper continental slope; 4) intraslope ridges; 5) acoustic substratum; 6)Infreschi canyon-fan system; 7) slope failure; 8) dismantling slope areas ; 9) intraslopebasin; 10) gas charged sediment; 11) sediment waves field; 12 ) water escape features andplastic deformation of subbottom reflectors; 13) outer shelf marine erosional surface; 14)paleo-drainage system; 15) physiographic shelf margin; 16) buried lowstand deposits;17) relic features; 18) withdrawing slope; 19) last glacial sea level terrace; 20) furrows.

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Figure 2: Schematic line drawing of Uniboom line off the River Sele, showing the re-gressive trend of shore deposits during Late Pleistocene sea level fall (modified after[9]).

The offshore area included in the Agropoliand Palinuro sheets is the result of thePleistocene evolution of the Cilento mar-gin. The shallow position of the acous-tic basement, and therefore the scarce ac-commodation space for sediment deposi-tion [11], accounts for the formation ofseaward prograding wedges, bounded bymarine and subaerial erosive unconformi-ties [12]. The basement consists of sili-ciclastic sequences pertaining to the inter-nal Ligurides and Cilento Group units andoutcrops mainly along the Cilento coast[13, 14] and across the shelf [7].The acoustic substratum outcrops off Mt.Bulgheria coast (Palinuro and Sapri sheets)

consist of carbonate rocks, Upper Triassicto Lower Miocene in age, unconformablycovered by Lower Miocene siliciclastic de-posits [3]. On land this succession forms aN-verging fold thrust over the internal Lig-urides nappe [15], cut by a complex pat-tern of faults. A major NE– SW trend-ing fault borders Mt. Bulgheria towardsthe Gulf of Policastro graben, where theMeso-Cenozoic basement is downthrownto about 3000 m below the sea level [16].The shelf area (about 1200 km2) betweenSalerno and Sapri underwent drowning,following the Holocene transgression [9,17, 10, 18].

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Figure 3: Subbottom chirp line across the Salerno Bay shelf and slope (from [10], modi-fied).

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3 The shelf

The continental shelf widens roughly fol-lowing the coastline, while it enlarges bymore than 23 km seaward off the Licosaand Palinuro promontories (Cilento coast)(Figure 1). Off the Sele and Bussento al-luvial plains loose and smooth seabed pre-vails, whereas off the Cilento coast, therocky substratum largely controls the mor-phological features and the seafloor lithol-ogy. Two rocky ridges crop out off LicosaCape and Acciaroli, respectively E-W andN-S oriented (Figure 1). Several orders ofterraces shape the seabed at various depthintervals: 160/140 m, 44/46 m, 18/24 m,12/14 and 7/8 m [19, 20, 11]. The lastthree surfaces have been largely reportedby scuba dive surveys and have been tenta-tively related to Tyrrhenian sea-level stages[20].The shore belt is affected by both erosiveand depositional processes, due to wave ac-tion and alongshore currents and is gen-erally characterized by the occurrence ofwell sorted sand deposits. They extenddown to a water depth of 10-12 m and in-clude the outermost sand bars. Three dif-ferent types of submerged beach can bedistinguished along the Sele shore, basedon the topographic profile: shoal bar, bar-trough and mixed types with cells lessthan 100 m wide [21]. The Alento sub-merged shore displays a bar-trough sys-tem and the Marina di Ascea shore a shoalbar [22]. These features are controlledby the coastal morpho-dynamics and there-fore may change rapidly. Sediments con-sist of coarse to medium, well sorted sanddown to 3 m and, medium to fine, well-sorted fine sand down to10-12 m. Thefine-grained fraction is less than 20 Fine-grained, poorly sorted deposits occur be-tween the outer limit of the submerged

shore and water depth of 40-50 m andform the inner shelf depositional systemwhere sandy pelite lithofacies prevails. Thefine-grained fraction increases beneath theCymodocea nodosa meadows which trapthe loose sediment at the seabed and withCaulerpa racemosa, recently introduced inthe Tyrrhenian Sea [23]. Posidonia ocean-ica meadows occur down to 25 m in sectorswhere terrigenous supply is scarce.The seismic acoustic profiles off the mainriver mouths show beneath the seabed ashallow unit with fluid escape and plas-tic deformation features (Figure 3). Thisunit is bounded at the base by a regularand conformable reflector lying halfwaybetween the 79 A.D. Vesuvius tephra andthe present-day seabed, between 40 and 70m bsl (Figure 3). The unit, which liesseaward of shallow biogenic gas pocketscan be associated to the estuarine deposi-tional environment and possibly marks theboundary between the silty and the muddyprodelta system.The outer shelf environment ranges be-tween 40-50 m bsl and the shelf break.Fine grained textures prevail, however avariable but valuable fraction of fine sand,mostly pumices, scoria and bioclasts, iscommon at the seabed where sedimentwaves and terraced areas occur (Figures1 and 2). Conversely, in the same depthrange off the Cilento Promontory authi-genic bioclastic coarse sand and gravel lieseteropically to siliciclastic deposit. Shellfragments, bioclasts and rhodholits formthe coarse fraction that largely tapers therocky seabed and the terraced surfaces.The bioclastic and organogenic coarse sandand fine gravel (maerl facies) pertain to the“coastal detritus assemblage” Auct., andform decimetre thick patches at a waterdepth between 25 and 70 m; this lithofa-cies changes seaward into mud supported

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Figure 4: Subbottom chirp line across the Cilento shelf and slope.

organogenic gravel and bioclastic sand typ-ical of the “muddy coastal detrital assem-blage” and may occur down to a depth of90 m. Organogenic mounds, made of foul-ing organisms, encrust the travertine out-crops in the Salerno Bay and build up pin-nacles on the rocky seabed off Acciaroliand Palinuro offshore.The outermost sector of the shelf, south ofthe River Sele to the Acciaroli Cape, cor-responds to a morpho-structural high thatlacks a modern terrigenous supply fromthe mainland. High resolution seismic sec-tions show that the most shallow units per-tain to the distal marine segment of thewedge which prograded seaward duringthe Late Pleistocene sea level fall and low-stand phases. They lie conformably on ma-rine units possibly Middle Pleistocene inage (Figure 3). A set of furrows scratchedinto the seabed parallel to the isobathscould be due to present day seabed currentswhich border the shelf margin.Pleistocene relic morphologies outcrop atthe seabed along the Cilento shelf (Figures1 and 4) and consist of large irregular re-liefs in the first 80 m of depth or regu-

lar ridges sub-parallel to the isobaths andoverlying the prograding reflectors of theouter shelf (Figure 1). Sediment textureconsists of well sorted, coarse to mediumsand and contains Arctica islandica shellsand corals. These morphologies have beeninterpreted as relic ridges and bars formedduring the maximum glacial lowstand [19,12, 11].The most evident morphological elementof the Campania margin is the physio-graphic edge of the shelf, which occurs be-tween 100 m and 230 m bsl Figure 1; be-yond it, lies the slope sector with a gradi-ent of more than 1.5°. The varying exten-sion, the different depth and gradient of theshelf could be accounted for by the stack-ing pattern of the systems tract pertainingto the Middle - Late Pleistocene deposi-tional sequences, which allowed this sec-tor of the Campania margin to expand. In-deed Sparker seismic profiles in the Cilentooffshore show a deep stratigraphic uncon-formity below the Tyrrhenian marine unit,which develops down to a depth of 180 mand is largely affected by sub-vertical fault-ing [11], therefore possibly pertaining to

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Figure 5: Relict channel system at the paleo-mouth of the Rivers Sele andSolofrone/Capo di Fiume, carved during the last lowstand phase of sea level.

the Middle Pleistocene lowstand phase.

4 The slopeSlope morphologies, with gradients of be-tween 1.3° and 6° are quite uneven andinclude large erosive sectors shaped byslides or deeply engraved by gullies andcanyon heads, alternating to slope ridgesbordered by structural lineaments (Figure1). Dismantling slope sectors are evidentoff Salerno and Sapri, where erosional pro-cesses produced a dense network of down-stream gullies with herringbone patternsand caused the shelf retreat (Figure 5).The slope sector which forms the southernboundary of the Salerno Valley is shapedby several slide headscarps, whose depositsreached great distances due to the high gra-dient of the slope. Off the Cilento coast,slide scars are confined to the upper slope

and relative deposits accumulated into theelongated depocentres which are boundedseaward by intra-slope ridges [24, 25].Seaward of the 180 m isobath (where theHST wedge thins out) a paleo-channel sys-tem, possibly engraved by the outflowsof the Sele, Solofrone/Capo di Fiume andAlento rivers, is still preserved. Indeed,during the lowstand stage of sea level theserivers flowed directly at the shelf edgeforming small shelf-margin deltas and sed-iment underflows were transferred alongthe upper slope down to the Salerno Val-ley and Cilento offshore intraslope basin(Figures 1 and 5). A wavy unit devel-oped at the bend of the upper slope in theSalerno Gulf (Figures 1 and 3). The ge-ometries of the wavy reflectors and the lo-cation of the unit point to sediment driftstructures and thus possibly to depositionalprocesses related to bottom current dynam-ics [26]. It has been observed that the strati-

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graphic discontinuity within this unit maycause sediment failures along weak layers.A slope canyon-fan system with meander-ing thalwegs, levees, overflowing channelsand fan lobes has been developing on thesouthern slope of Monte Bulgheria (Figure1), possibly being fed by coastal sedimentdrift alongshore (Budillon et al., in press).

5 Depositional environ-ments within the SDTQ

Several key elements for a sequence strati-graphic rendering were recognized andmapped within the SDTQ, from the coast-line down to the water depth of 250m, based on submarine morphology in-terpretation, sediment core stratigraphy,high resolution seismic records and bot-tom samples analysis. In particular, still-forming and completely-formed units weredistinguished, according to analogous in-land mapping criteria and steering linesof Servizio Geologico d’Italia. The firstcorresponds to the highstand systems tract(hst), which has been developing since 5-6 kyr BP, while the second represents thetransgressive, lowstand and falling-stagesystems tracts (TST, LST and FST) [27],stacked following the Late Pleistocene –Holocene sea level variations. Specifically,three still-forming depositional environ-ments (beach, shelf and upper slope), twocompletely-formed depositional environ-ments (relic shelf and relic slope) and onecompletely-formed unit, continental in ori-gin, (a relic tabular plate of travertine, cor-related with the inland outcrop of Traver-tini di Paestum) have been mapped. Themost represented unit within the SDTQ isthe highstand systems tract. It includes,landwards, the present-day coastal system

and typically consists of a tapering seawardwedge. The maximum thickness is reachedon the inner shelf off the river mouths (Fig-ure 3). In the Salerno Bay the HST de-pocentre is located off the Sele River 40m deep, where its thickness exceeds 10 mand rapidly thins out seaward to less than 1m, about 20 km off the coast (Figure 6). Ittherefore goes beyond the shelfbreak in thenorthern sector, while it tapers in the south-ern part of the bay at about 160 m, onto therelict outer shelf off Licosa Cape, due tothe low sediment supply. Pre- and post-glacial shore units, featuring progradinggeometries with offlap terminations, wereidentified off the Sele and Bussento rivermouths. The oldest ones (Figure 2), lyingbelow the maximum glacial unconformity,formed as a consequence of the seaward re-treat of the shoreline during the last stagesof the Late Pleistocene sea level drop andtherefore show a regressive trend [9]. Theregression of the shore system culminated,as largely reported at a global scale, dur-ing the 20-18 ky lowstand stage, which ac-counts for the prograding units commonlystacking at the shelf margin. Neverthe-less the depositional terrace linked to thelast glacial maximum is not always evi-dent, since shore deposits relative to thisphase are preserved in morphological steps(green dashed line, Figure 1) [12]. A mid-shelf prograding wedge marks the low-stand stage of the last glacial peak off theAgropoli, Licosa and Acciaroli coasts. Onthe whole, relic deposits and coastal mor-phologies related to the last glacial maxi-mum form a discontinuous belt, croppingout or draped by Holocene sediments, thatcan be followed for more than 100 kmalong the southern Campania margin (Fig-ure 1). The post-glacial sea level rise re-sulted in a rapid drowning of the shelf, witha limited preservation of the transgressive

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Figure 6: Schematic block diagram of the main stacking pattern and morphologies in theSalerno Bay (from [10] modified).

units. Transgressive lithosomes are poorlyrepresented and resolvable due to their lowthickness. However, a shore system, 1.5km wide and 5-10 m thick (Figures 3 and6), which lies above the transgressive sur-face, 90/60 m below the sea level, couldbe the remains of the Younger Dryas cli-matic event [28]. These bodies consist ofa continuous set of prograding reflectors,with offlap and downlap lateral termina-tions, overlain by onlapping sub-horizontalreflectors, topped in turn by the maximumflooding surface. Other lithosomes relativeto the transgressive systems tract occur sea-ward to the shelf break and represent thehealing phase of postglacial transgression[27]; besides they occur in morphologicalsteps on the shelf between the transgres-sive and the ravinement surfaces, showingacoustic facies typical of transitional shoredeposits.

6 Conclusions

The CARG Project allowed the acquisitionof regularly spaced, high resolution data setvaluable for geological, morphological andcartographic purposes. The large amountof data led to the redaction of four geo-logical sheets in the Southern Campaniamarine area down to the upper slope en-vironment, yet published [10] or in press.In particular, within the Late PleistoceneDepositional Sequence, still-forming unitsand completely-formed units were distin-guished. The first ones correspond to thehighstand wedge (HST), which has beendeveloping since 5-6 kyr BP, while thesecond ones represent the transgressive,lowstand and falling-stage systems tracts,stacked following the Late Pleistocene –Holocene sea level variations. Pre- andpost-glacial shore units, featuring prograd-ing geometries with offlap terminations,were identified off the Sele and Bussento

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river mouths. The one lying above thetransgressive surface, 90/60 m below thesea level, could be the effect of the YoungerDryas climatic event. A paleo-channel sys-tem along the upper slope indicates the po-sition of Sele, Solofrone/Capo di Fiumeand Alento river mouths during the glacial

maximum retreat of the sea level and testifythe density flows passage down to the in-traslope basins. However, if the main targethas been achieved by mapping the seabedfeatures and lithologies, a large number offurther scientific questions remain, to beaddressed at a later date.

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[17] G. Buccheri, G. Capretto, V. Di Donato, P. Esposito, et al. A high resolution recordof the last deglaciation in the southern Tyrrhenian Sea: environmental and climaticevolution. Marine Geology, 186:447–470, 2002.

[18] M. Iorio, J. Liddicoat, F. Budillon, P. Tiano, et al. Paleomagnetic secular varia-tion time constraints on late Neogene geological events in slope sediment from theeastern Tyrrhenian Sea. In Kneller, et. al (eds.) External Controls on DeepwaterDepositional Systems, SEPM. (92):33–243, 2009.

[19] M.G. Coppa, M. Madonna, M. Putignano, P. Russo, et al. Elementi geomorfologicie faunistici del margine continentale tirrenico tra P.ta Campanella e P.ta degli In-freschi (Golfo di Salerno). Soc. Geol. It., Atti del74° Congresso, pages 203–207,1988.

[20] F. Antonioli, A. Cinque, L. Ferranti, and P. Romano. Emerged and submerged ma-rine terraces of Palinuro Cape (Southern Italy). Mem. Desc. Carta Geol. D’Italia,LII:237–260, 1994.

[21] E. Cocco and S. Iuliano. L’erosione della fascia costiera tra Foce Sele e Paestum(Salerno): dinamica evolutiva ed ipotesi di intervento a difesa e tutela della spiaggiae della pineta litoranea. Il Quaternario, 12(2):125–140, 1999.

[22] E. Cocco and F. Musella. Variazioni della linea di riva e dinamica dei sedimentifra Marina di Casalvelino e Marina di Ascea (Cilento, Campania). Atti del XIICongresso AIOL (Isola di Vulcano, 18-21 settembre 1996), II:341–350, 1998.

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[23] M.C. Gambi and A. Terlizzi. Record of a large population of Caulerpa racemosa(Forsskal) J. Agardh (Clorophyceae) in the Gulf of Salerno. (Southern TyrrhenianSea, Italy). Biologia Marina Mediterranea, 5:553–556, 1998.

[24] F. Trincardi, A. Cattaneo, A. Correggiari, S. Mongardi, et al. Submarine slidesduring sea level rise: Two examples from the eastern Tyrrhenian margin, in Subma-rine Mass Movements and Their Consequences, edited by J. Locat and J. Mienert.Kluwer Acad., Dordrecht, Netherlands, page 469– 478, 2003.

[25] A. Bellonia, F. Budillon, F. Trincardi, D. Insinga, et al. Licosa and Acciaroli sub-marine slides, Eastern Tyrrhenian margin: characterisation of a possible commonweak layer. Rendiconti online Soc. Geol. It., 3:83–84, 2008.

[26] G. Verdicchio and F. Trincardi. Mediterranean shelf-edge muddy contourites: ex-amples from the Gela and South Adriatic basins. Geo-Mar Lett., 28:137–151, 2008.

[27] D. Hunt and M.E. Tucker. Stranded parasequences and the forced regressive wedgesystems tract: deposition during base-level fall. Sedimentary Geology, 81:1–9,1992.

[28] R.G. Fairbanks. A 17,000 year glacio-eustatic sea-level record: Influence of glacialmelting rates on the younger Dryas event and deep ocean circulation. Nature,342:637–642., 1989.

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3D Seismic Geomorphology: the Enigma Project,an Encounter between Academia and Industry

G. Dalla Valle1, F. Gamberi1, F. Trincardi1, P. Rocchini21, Institute of Marine Sciences, CNR, Bologna, Italy2, ENI E&P Division, Sedimentology, Petrography & Stratigraphy Dpt., S. Donato Mi-lanese, [email protected]

Abstract

The advent of the 3D seismic technology has represented a major revolution forthe Earth Sciences, in the development of interactive interpretation systems. 3D seis-mic technology, through the transition from a two-dimensional, cross-section analy-sis to a real three-dimensional visualization of the entire sedimentary basin, has led toa unique opportunity for the study of submarine geological processes. 3D seismicsprovide the opportunity to image the geological elements in plainview, furnishinga detailed morphology of the seafloor at any given time/depth. Studies are aimedat tracing the signature of sedimentary processes from shallow water to the deep-water realm, easing the evaluation of architectural elements distribution, their faciescomponents and the making of lithological predictions. The imaging of a variety offeatures related to the mass-transport complexes (MTCs) and fluid migration offersalso the possibility to improve geohazard studies.The coupling of modern seafloor observations, a field in which ISMAR has a longlasting tradition of researches, with industry-derived three-dimensional seismic datafurnished by eni, creates a positive feedback that leads to exciting results regard-ing the characterization of depositional systems and the develop of sedimentologicalmodels.

1 Introduction

Three dimensional (3D) seismic has repre-sented one of the most important revolu-tion in the Earth Sciences of the last fortyyears. Originally developed by industry tomitigate risk in hydrocarbon exploration,nowadays the 3D seismic is an indispens-able tool earth scientists for understandingcomplex geological phenomena. Seismicgeomorphology, that consists in the extrac-tion of geomorphic insight using 3D seis-mic data, allows the researchers to studythe subsurface using plain view image and

making possible the reconstruction of theevolution of the landscapes through time.Thanks to the powerful spatial resolutionfurnished by the 3D seismic, comparable,at least for the shallower portion of the sed-imentary basin, to that obtainable throughmodern swath bathymetry, it has been pos-sible to characterized complex geologicalstructures with unprecedent detail. Amongthese are the investigation of buried sinu-ous deep-water channels, with a detail thatwas virtually impossible with the 2D seis-mics. The advent of 3D seismics increas-ingly document the wide variety in mor-


Marine Geology

phology and internal organization of largemass-transport complexes (MTCs) on con-tinental margins. The ISMAR-Bologna hasstarted a collaboration with eni-Milan inorder to develop a sedimentological con-ceptual model of continental margin devel-opment coupling the industrial-derived 3Dseismic database and the know-how of IS-MAR regarding the modern seafloor sedi-mentary processes.

2 3D seismic: historicalbackground

It was as early as 1970 when G.G. Waltonpresented the concept of three dimensionalseismic (3D seismic) in the seminal pa-per “Three Dimensional Seismic Method”[2], that was the cornerstone for an ex-traordinary revolution in the Earth Sci-ences, both in the industrial and in theacademic realm. In this paper, in fact,were first presented the concepts that un-derlie the 3D seismic technology and itspossible applications in term of hydrocar-bon exploration. Only three years after,in the 1975, the new technology was ap-plied to the real world with the first 3Dcommercial survey performed in the NorthSea. In the early years, the use of the 3Dseismic technology was restricted to thepetroleum industry realm due to the veryhigh costs of operation both in the planningand in implementation of the seismic sur-vey phase, and in the processing phase, ob-tainable only through high-expensive per-formance computing. Whereby the clas-

sical 2D surveys consisted of 100 to 200lines and cross lines, a 3D survey require anhigher number of closely spaced crossingseismic traces with a high-precision nav-igation system. Due these requirements,an important limitation of the early sur-veys was the small areal coverage due toprohibitive costs per unit area. With theadvance of 3D technology, cost was low-ered gradually and nowadays is not un-common to deal with up to 10.000 km2

single surveys, or mega-surveys, obtainedto the merging of multiples surveys as inthe North Sea Basin, with a coverage ofover 100.000 km2. The resolving powerof 3D seismic technology, both in term ofvertical and horizontal resolution, and interm of accuracy and precision has pro-moted an enormous boost on the abilityof interpret and characterize complex ge-ological structures at the scale of the en-tire basin or wider. Until the advent ofthe 3D technology in fact, the limitationof the spatial resolving power of the 2Dseismic technology was the greatest obsta-cle for the accurate reconstruction of hy-drocarbon traps, reservoir continuity andintegrity [3]. Despite with the use of 2Dseismic, it was possible to delineate the ba-sic framework of the sedimentary basins,and to recognize the main sedimentary andtectonic structures, the detailed reconstruc-tion of the morphology of the depositionalsystems and the three-dimensional geome-tries of the fault systems and other tectonicstructures (thrust systems, relay ramp, etc)it is possible only with the 3D seismic tech-nology.

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Figure 1: a) Example of a 3D seismic amplitude cube. The green reticulate is achievedby the picking of a key horizon on the seismic cube (Courtesy of ENI). b). In a sesmiccube each amplitude trace consists of an array of amplitude samples that is representedas a series of voxels. The gray level associated with each voxel denotes the amplitudeintensity of the sample (Modified from [1]).

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Figure 2: Example of a deep-water channel imagined on the same time-slice throughthree different seismic attributes: a). Amplitude; b). Coherence; c). Sweetness (Imagecourtesy of ENI).

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3 3D seismic technology

Whereas initially 3D seismic data was dis-played and interpreted in a 2D view, withthe advent of graphic interactive worksta-tions the interpretation was made into afully real 3D environment. Some special-ized software allows infact to visualize theacquired seismic data as three-dimensional“cube” consisting of millions of voxels,that represents the smallest unit in a 3Ddataset that can display a colour corre-sponding to the seismic sample value. A3D cube, or volume (Figure 1) is not a sim-ple closer staking of 2D lines, but differsgreatly from this: there is no the spatialaliasing as in the 2D data, and the greaterdensity of spatial sampling guarantee a lat-eral resolution similar to the vertical one.The sophisticated 3D migration techniques(3D dip move-out as example), permit toimage geological structures characterizedby steep dips and strong lateral velocityvariations with a detail that would be im-possible with the 2D seismic. The seismiccube, or volume, can be interrogated bythe interpreter using a wide range of math-ematical operations as rotation to any an-gle, flattening, enlarging and zooming. Theinterpreter may need infact to “stretch” or“shrink” the view, or to squeeze the 3D datato show sedimentary features or tectonicdiscontinuities in more detail, and this canbe accomplished also by changing the ver-tical and horizontal exaggeration. One ofthe most useful application of the 3D seis-mic technology is the ability to incorporateopacity and transparency values in the dis-play of a three-dimensional volume, andthe possibility to render the 3D volume orprobe. In this way the interpreter can iso-late specific range of data values within thevolume in order to see exclusively thosedata within the probe, rather than just see

the data on the faces of the probe.The interpreter has the possibility to createa variety of seismic volumes using differentseismic attributes (Figure 2). A seismic at-tributes normally provide informations as-sociate to the amplitude, shape, and posi-tion of the seismic waveform and permit toresolve geological features and their rela-tionship that otherwise would be omitted,such as channels pathway, channel infill,and presence of fluids or gas. Attributesas envelope, instantaneous phase, and in-stantaneous frequency allows to discern thepresence of gas (bright spots), and changesin lithology. Coherency attribute is usedto evidence the lateral continuity of the re-flectors, and the presence of numericallyseparated surfaces, as faults, and fractures.Nowadays the production of various reflec-tion attributes such as amplitude, dip mag-nitude, dip azimuth, time/depth structure,polarity sweetness, etc. is increased ex-ponentially; however there is not an all-purpose seismic attribute, but these must becarefully chosen by the interpreter on thebasis of his experience and on the basis ofthe expected goal.

4 3D seismic geomorphol-ogy

The study of geological features usingplain view images generated through themanipulation of 3D seismic data is calledseismic geomorphology [4]. The oppor-tunity to visualize geological features inmap view has represent the most valuableprogress that the 3D technology has pro-vide to the geological prediction, establisha marked step beyond the seismic stratigra-phy mindset.

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Figure 3: Example of the same sinuous deep-water channel and its main architecturalelements, investigated trough the traditional 2D seismic (a), and imaged using plan viewimages with the 3D seismic technology (b) (Image courtesy of ENI).

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Figure 4: a) An example of the resolution obtainable with the 3D seismic on a seriesof buried deep-water channels (Image courtesy of ENI); b) Modern deep-water channelimagined with multibeam swath bathymetry by ISMAR Bologna.

Figure 5: Example of a slope channel developed on a topographically complex slope.The channel pathway is controlled by a series of topographic highs, related to tectonicstructures. In this case is the paleo-seafloor is imagined with a series of time-equivalent,coherence probes (Image courtesy of ENI).

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4.1 Methodologies

Various planes, surfaces and time slicescan be extracted from the different typesof 3D volume. The interpreter can slice aplane surface through the depth/time direc-tion of the 3D cube, without reference toany stratigraphic horizon. In this way, atime-slice surface is extracted from a 3Dcube at a constant depth/time coordinate,and permits to the interpreter to looking forgeological features, above or below the sur-face event.However, geological features rarely showup completely at a spatially consistenttime/depth within the seismic volume, andthey could be also deformed by post-depositional structural events, which makethem even more complex. To outflankingthese limitations, the interpreter can createa series surfaces, through the picking (man-ually or automatically) of spatially consis-tent reflectors such as thick shale horizons,in order to obtain a time-equivalent sur-face from the 3D cube. The interpreter cananalyze the spatial variations of any seis-mic attribute data along the selected sur-faces and through time. Moreover, in thecase of tectonic deformation, the pickedtime-equivalent horizon can be flattened,and the resulting image is an approxima-tion of the morphology as it existed at thetime of deposition. Through the seismicgeomorphologies methods, the interpreterhas a more realistic view of the sedimen-tary environments, and can directly iden-tify the process-derived facies distributionon map view [5]. When used in conjunc-tion with seismic stratigraphy, and withcorrelated borehole data, seismic geomor-phology, represent the state of the art ap-proach to extracting stratigraphic insightsfrom 3D seismic data of subsurface sedi-mentary bodies [6].

4.2 Submarine channels

One of the most striking success of the seis-mic geomorphology was the imagining ofburied sinuous submarine channels (Figure3). Before the advent of the 3D seismic infact, no imaging of the planform of the de-positional systems was available, and onlyqualitative 2D description of seismic re-flection geometries and terminations cap-tured planview distributions of depositionalelements. A further advantage furnished bythe 3D seismics is that the planview imageof the submarine channels and others sed-imentary elements can be extracted at anygiven depth. As a consequence the inter-preter can observe the morphological evo-lution of the depositional elements throughtime, and examine the response of the sed-imentary systems to the changes of the de-positional environment. Using a geomor-phic approach, the sedimentary architec-tural elements can be mapped accuratelyboth in time and space, observing the vari-ations of the depositional systems at in re-sponse of controlling factors changes.It can be evaluated how submarine chan-nels evolve in topographically complexslopes (Figure 5) resulting from shale/salttectonics or from tilted basement fault-blocks, during the infilling of the receiv-ing basin. The progressive healing ofthe seafloor topography drives the evolu-tion and the pathway of the channel, bychanging in the slope gradient, basin ge-ometry and the degree of confinement,and eventually, in promoting fill-and-spillprocesses from upper intra-slope basinsto lower ones. The availability of large3D surveys has been also very useful inshowing that those who were consideredponded turbidite systems, in some cases,do not terminate in intra-slope basins, butthey have continuous but very convoluted

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courses which takes them through and be-yond complex slope topography. Intra-channel knickpoints, meandering cut-off,meander-loop migration or abrupt channelavulsions due to variations in the surround-ing seafloor topography can be not onlyobserved and described, but they can alsoquantified in space and in time. The evo-lution of these sedimentary architecturalelements that characterize the submarinechannels can be afforded also by statisticalanalysis of different parameters, as varia-tions of the sinuosity index, the numbers ofbend and their radius of curvature, the me-ander length and width, the ratio betweenchannel depth and width, levee heights andwidth during the whole evolution of thesystems.These parameter variations can be usedto predict the nature and the distributionof the deposits, obtaining important infor-mation in the reservoir heterogeneity andlithological prediction [7].

4.3 Mass Transport Complexes(MTCs)

3D seismic geomorphology has been re-cently also used on the imaging of mass-transport complexes (Figure 6)([8]). Thepossibility of study and analyze from a ge-omorphic perspective, large-scale events inthe off-shore environment, has lead to abetter comprehension of the mechanismscontrolling the initiation and the propaga-tion of the MTCs. In particular, throughthe characterization of the external geome-tries and internal distribution of deforma-tional structures that forms in headwall, inthe sidewalls and in the toe-region of theMTCs, with the imaging of complex imbri-cate thrusts and fold systems. Through therecognition of specific kinematic indicators

along the basal shear surface, it can be alsoreconstructed the type and direction of mo-tion and the model of emplacement of thevarious MTCs [9].The study of MTCs through 3D seismicgeomorphological analysis has been use-ful for those researcher who seek to un-derstand the mechanisms of submarineslope failures that can generate tsunamisin coastal regions. The 3D seismic geo-morphology has bought to light the com-plex behaviour of large mass transport de-posits, often characterized by multiple fail-ure events, showing different rheology andmechanisms of initiation. Submarine fail-ures along the continental margins canalso affect and destroy submarine cables,pipeline and other engineered structures forhydrocarbon exploration, and the increas-ing studies lead with a seismic geomor-phological approach is gradually improv-ing our ability to predict and mitigate theimpact of these events.

4.4 Other research avenues

The 3D seismic have made great contribu-tion to a wide range of additional avenuesof research ranging from structural geol-ogy, fluid-rocks interactions and the studyof igneous systems. Three-dimensionalanalysis has allowed to study how faultsgrow and link [10] and to discover newtype of fault systems as polygonal faults[11]. Other application of 3D seismic re-gard the study of subsurface plumbing sys-tems as gas-blow out pipes and mud volca-noes [12], and the imaging of large-scalesand intrusions and collapse craters, thatplays a significant role in controlling andaffecting reservoir geometry and perme-ability [13].

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Figure 6: Example of a buried slope failure imaged through time equivalent, coherenceprobes (Image courtesy of ENI).

5 The Enigma Project: anoverview

In the last year, the ISMAR of Bolognahas started a collaboration with the Ex-ploration& Production division of ENIi(Ente Nazione Idrocarburi) of San Do-nato Milanese. The intent of this joinventure (Enigma Project) is to couple theknowledge of the two institutions in or-der to develop a sedimentological concep-tual model on silicoclastic continental mar-gins. ISMAR has provided its data set ofmodern seafloor of the Adriatic sea thatconsist of multibeam swath bathymetry,sidescan sonar and sedimentological andstratigraphic coresm whereas eni has fur-nished its large, high-resolution 3D seis-mic dataset acquired in recent years alongthe Adriatic basin. This approach has pro-vided the exciting opportunity to investi-gate an industrial-oriented data set with anacademic point of view. The wide cover-

age of eni 3D seismic dataset make pos-sible to obtain morphometric observationsand to trace the signature of sedimentaryprocesses, at the scale of the entire basin,from shallow to deep-water areas, outflank-ing the spatial limitation linked to tradi-tional 2D seismic data (Figure 7).

6 The Enigma project:main results

The eni 3D seismic volume has been ac-quired along the central Adriatic conti-nental margin, focussing in particular inthe Plio-Pleistocene sedimentary succes-sion that consists mainly of progradingslope clinoforms. The seismic geomor-phology techniques has allowed to asseshow sediment is dispersed and partitionedacross the slope clinoforms during their de-velopment. The changes of the clinoformscharacteristics during the infilling of the

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Figure 7: Example of a series of regional scale surfaces with different ages, obtainedthrough the interpolation of selected horizons in order to approximate the paleo-lanscapesat the time of deposition.

sedimentary basin form the basis for theconstruction of the conceptual model. Anexamination of the geometries of the slopeclinoforms and of their internal stackingpatterns has allowed to in order to shedlight on the morphological differences andthe linkages between the different sectorsof the clinoforms and the related sedimen-tary bodies.By comparison with similar geomorphicelements present on the modern seafloor ofthe Adriatic and Tyrrhenian basin, that can

provide indications on the geological pro-cesses responsible for their formation, ithas been possible to develop a conceptualtool to predict when sands are likely to beconnected or disconnected along slope seg-ments of the different types of shelf-marginclinoforms. The model has been succes-sively generalized as much as possible inorder to be exported and applied in differ-ent but similar contexts, with the aim of re-duce uncertainties in exploration and reser-voir evaluation.

References[1] D. Gao. 3D seismic volume visualization and interpretation: An integrated work-

flow with case studies. Geophysics, 74:W1–W12, 2009.

[2] G.G. Walton. Three dimensional seismic method. Geophysics, 37(3):418–430,1972.

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[3] H.W. Posamentier. Application of 3D seismic visualization techniques for seismicstratigraphy, seismic geomorphology and depositional systems analysis. 29:11–24,2004.

[4] H.W. Posamentier. Seismic stratigraphy into the next millennium. A focus on 3Dseismic data. Abstract from AAPG Annual conf. New Orleans, April 16-19, 2000,page A118, 2000.

[5] J. Cartwright and M. Huuse. 3D seismic technology: the geological ‘Hubble’.Basin Research, 17(1):1–20, 2005.

[6] H.W. Posamentier and V. Kolla. Seismic geomorphology and stratigraphy of de-positional elements in deep-water settings. Journal of Sedimentary Research,73(3):367–388, 2003.

[7] L.J. Wood and K.L. Mize-Spansky. Quantitative seismic geomorphology of a qua-ternary leveed-channel system, offshore eastern Trinidad and Tobago, northeasternSouth America. AAPG Bullettin, 93(1):101–125, 2009.

[8] J. Frey Martinez, J. Cartwright, and B. Hall. 3D seismic interpretation of slumpcomplexes: examples from the continental margin of Israel. Basin Research,17(1):83–108, 2005.

[9] S. Bull, J. Cartwright, and M. Huuse. A review of kinematic indicators frommass-transport complexes using 3D seismic data. Marine and Petroleum Geology,26(7):1132–1151, 2009.

[10] C. Mansfield and J.A. Cartwright. Fault growth by linkage: observation and impli-cations from analogue models. Journal of Structural Geology, 23:745–763, 2001.

[11] J.A. Cartwright. Episodic basin-wide expulsion from geopressured shale sequencesin the North Sea Basin. Geology, 22:447–450, 1994.

[12] R.J. Davies and S.A. Stewart. Emplacement of giant mud volcanoes in the SouthCaspian basin: 3D seismic reflection imaging of their root zone. Journal of theGeological Society, 162:1–4, 2005.

[13] M. Huuse, D. Duranti, N. Steinsland, C.G. Guargena, P. Prat, K. Holm, J.A.Cartwright, and A. Hurst. Seismic characteristics of large-scale sandstone intru-sions in the Paleogene of the South Viking Graben, UK, and the Norwegina NorthSea. Memoirs of the Geological Society of London, 29:262–277, 2004.

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