the micropaleontology of critical boundaries file473 the micropaleontology of critical boundaries...

473

The Micropaleontology of Critical Boundaries

Chaired by Ellen Thomas and Robert Speijer

Overall, the Earth’s biosphere has shown a strong increase in diversityover the Phanerozoic, although the pattern of this increasing diversity is beingdebated: did diversity increase logarithmically (although interrupted by massextinctions), or were there periods of stability? Microfossils offer an unrivaledopportunity to study the patterns of change in diversity and assemblagecomposition at times of major faunal turnover throughout the Phanerozoic,including periods of mass extinction and recovery, and intervals of major climatechange. We call such intervals ‘critical boundaries’; they include the Frasnian-Famennian, Permo-Triassic, Triassic-Jurassic, Cretaceous-Paleogene,Paleocene-Eocene, Eocene-Oligocene boundaries as well as Oceanic AnoxicEvents. In microfossil studies, large populations can be sampled across suchevents, and possible relations between evolutionary and environmental changecan be evaluated statistically. The study of microfossils also offers theopportunity to compare patterns of extinction in planktic and benthic forms,and in shallow and deep water forms. Contributions present information onshort-term or long-term patterns of change in diversity and assemblagecomposition across periods of rapid (e.g., K/P) or more gradual (e.g, E/O)environmental change, including comparisons between variations in faunaland geochemical (including isotope) proxies.

Anuár io do Inst i tu to de Geociências - UFRJISSN 0101-9759 Vol . 29 - 1 / 2006

FORAMS 2006

475

The Cretaceous/Paleogene boundary event in the deep sea:Inferences from the Caribbean and the Gulf of Mexico

Laia Alegret & Alfonso Meléndez

Dept. Ciencias de la Tierra, Universidad de Zaragoza, Zaragoza, Españ[email protected]

The impact of an asteroid at Chicxulub (Yucatan Peninsula, Mexico) incoincidence with the Cretaceous/Paleogene (K/Pg) boundary is the mostplausible hypothesis to account for the mass extinctions recorded worldwide,and the deposition of the so called “K/Pg boundary cocktail unit” in the Gulf ofMexico, Caribbean and North Atlantic. In these areas, the Chicxulub impactcaused mass wasting processes, submarine landslides and extensive slumpsrelated to the destabilization of the continental margins, leading to the depositionof a mixture of impact-derived materials, heterogeneous lithic fragments andreworked fossils. Nevertheless, there is still some controversy as to this singlecatastrophic scenario, and the origin and model of deposition of the K/Pgboundary deposits from the Gulf Coast and Caribbean need more research.The study of K/Pg boundary deposits from Cuba, which was located relativelyclose to the impact site, is of great importance to investigate the K/Pgboundary event.

At the Loma Capiro section (central Cuba; Alegret et al., 2005. Geology,33: 721-724), the K/Pg boundary is located within the Santa Clara Formation,at the base of a 9.6m-thick, fining-upward clastic complex that overlies theuppermost Maastrichtian marls and underlies the lower Paleogene siltysediments. In addition to the sedimentological analysis, the study of the abundantmicrofossils that are present through the whole section may provide someadditional information on the origin and deposition of the clastic complex, andon its relationship with the K/Pg boundary event.

Analysis of benthic foraminiferal assemblages from Loma Capiro showsa close similarity to Upper Maastrichtian and lower Paleogene assemblagesfrom bathyal sections in Mexico. They contain abundant representatives of thebathyal and abyssal Velasco-type fauna, such as Aragonia velascoensis,Gyroidinoides globosus, Nuttallides truempyi, Stensioeina beccariiformis.At Loma Capiro, upper Maastrichtian and lower Danian sediments below andabove the clastic complex contain benthic foraminiferal species typical frombathyal settings. The clastic complex itself, in contrast, contains a mixture of

Anuár io do Inst i tu to de Geociências - UFRJISSN 0101-9759 Vol. 29 - 1 / 2006 p. 165

FORAMS 2006

476Anuário do Instituto de Geociências - UFRJISSN 0101-9759 - Vol. 29 - 1 / 2006 p. 475-476

FORAMS 2006The Cretaceous/Paleogene boundary event in the deep sea:

Inferences from the Caribbean and the Gulf of MexicoLaia Alegret & Alfonso Meléndez

benthic foraminifera and other fossils from different ages and differentenvironments, including taxa typical from shallow and deep-water settings.Assemblages from the clastic complex at Loma Capiro probably resulted fromreworking and down-slope transport triggered by the K/Pg boundary impact. Asimilar scenario was reported from the Mexican sections, where the K/Pgclastic complex contains mixed neritic-bathyal faunas that indicate redepositionin the deep basin by mass-wasting processes resulting from the K/Pg boundaryimpact in the Gulf of Mexico (Alegret et al., 2001. Geology, 29: 891-894).

Moreover, the comparison of the benthic foraminiferal turnover in sectionsfrom Cuba and Mexico constitutes an important tool to reconstructpaleoenvironmental changes across the K/Pg boundary. At Loma Capiro, as inthe Mexican sections, lowermost Paleogene sediments immediately above theclastic complex contain assemblages dominated by oligotrophic taxa such asCibicidoides hyphalus, N. truempyi, and S. beccariiformis, with lowpercentages of infaunal taxa. These data indicate a decrease in food supply tothe seafloor in this area, probably related to the collapse of surface primaryproductivity that occurred immediately after the K/Pg boundary impact event.

L.A. holds a Ramón y Cajal contract from the Spanish Ministerio deEducación y Ciencia. This research was funded by project CGL2004-00738/BTE.

477

The Paleocene/Eocene boundary event:Inferences from the benthic foraminiferal turnover

Laia Alegret & Silvia Ortiz

Dept. Ciencias de la Tierra, Universidad de Zaragoza, Zaragoza, España - [email protected]

A global extinction event of deep-sea benthic foraminifera at thePaleocene/Eocene (P/E) boundary was coeval with a period of rapid globalwarming that has been called the Initial Eocene Thermal Maximum (IETM),and with a several per mille negative excursion in marine and terrestrial 13Cvalues (Carbon Isotope Excursion, CIE). Whereas deep-sea benthicforaminifera from many bathyal through upper abyssal sites suffered majorextinction, benthic foraminifera from marginal and epicontinental basins showlesser extinctions or temporary assemblage changes. Evidence from shallowseas indicates increasing productivity and low oxygen conditions during theIETM, but data from open ocean sites do not support the presence of globalhypoxia, and are not consistent as to globally increasing or decreasingproductivity. Further studies are thus needed to look into the cause/s of the extinctions.In order to investigate the cause/s of the benthic foraminiferal turnover across theIETM, we compared the faunal turnover in the outer neritic Dababiya Quarrysection (Egypt), where the Global Stratotype Section and Point (GSSP) for the P/E boundary was defined, with existing records from the deep sea.

The extinction of Angulogavelinella avnimelechi at the P/E boundaryat Dababiya, making up only 2.2% of the species, confirms that extinctions inshallow settings were considerably less severe than in the deep sea. Thisextinction was coeval with the main phase of extinction of deep-sea benthicforaminifera, and with the extinction of Stensioeina beccariiformis. Moreover,dramatic changes in the composition and in the diversity of the assemblageshave been identified in bathyal sections from the northeastern Atlantic andTethys at the base of the CIE, as in Dababiya. Benthic foraminiferal assemblagesfrom the lower part of the CIE in all these sections are dominated by opportunistictaxa that indicate environmental stress and, in some sections, increaseddissolution of calcite (Alegret et al., 2005. Terra Nova, 17: 526-536; Alegret& Ortiz, submitted to Marine Micropaleontology). The comparison of thefaunal turnover, and the analysis of the paleoecological preferences of the taxathat dominated the assemblages across the CIE, are thus of great importanceto infer the paleoenvironmental changes that caused the benthic foraminiferalturnover across the IETM.

L.A. holds a Ramón y Cajal contract from the Spanish Ministerio deEducación y Ciencia. S.O. thanks the Gobierno de la Rioja for the predoctoralfellowship. This research was funded by project CGL2004-00738/BTE.


FORAMS 2006

478

Deep-sea environments across the Cretaceous/Paleogeneboundary in the SE Atlantic Ocean

(ODP Leg 208 Hole 1262C, Walvis Ridge)

Laia Alegret1 & Ellen Thomas2

1Dept. Ciencias de la Tierra, Universidad de Zaragoza, 50009 Zaragoza, Españ[email protected]

2Dept Geology & Geophysics, Yale University. New Haven, CT 06520-8109, U.S.A.

Benthic foraminifera did not suffer significant extinction across theCretaceous/Paleogene (K/Pg) boundary, one of the largest mass extinctions inthe Phanerozoic, at a time when planktic foraminifera and calcareousnannoplankton underwent severe extinction. In lowermost Paleocene sedimentsplanktic microfossil groups thus have a low abundance and their assemblagesare strongly affected by the extinction, whereas benthic foraminifera showchanges in assemblage composition but remain common. Analysis of thismicrofossil group can therefore provide information on the changes in deep-sea environments.

A continuous, well-preserved Cretaceous/Paleogene transition wasrecovered on ODP Leg 208 (Site 1262, Walvis Ridge, eastern South AtlanticOcean, present depth 4755m). The K/Pg boundary is marked by a sharptransition from Maastrichtian clay-bearing nannofossil ooze with abundantplanktic foraminifera to Danian dark reddish to brown, clay-rich nannofossil-ooze and clay. In the lowermost cm of the Danian, green microspherules(interpreted as microtektites) occur, and clays and mineral oxides are abundant.Up-section, sediments grade into brown clays with abundant nannofossils andplanktic foraminifera, but the carbonate content of sediments did not return toMaastrichtian values for several million years. Detailed quantitative analysisof benthic foraminifera from the uppermost 5m of the Maastrichtian (a:A.mayaroensis Zone) and the lowermost 1.6m of the Paleogene (Zone Pα andlower P1a) in Hole 1262C indicates an upper abyssal paleodepth.

Both Maastrichtian and Danian assemblages consist of about 50%infaunal (suggestive of higher food supply) and 50% epifaunal (suggestive oflower food supply) morphotypes, with common trochospiral taxa includingParalabamina lunata, P. hillebrandti, Nuttallides spp., Nuttallinella spp.,Oridorsalis umbonatus, and Stensioeina beccariiformis. Infaunal taxa suchas buliminids show more substantial differences in Maastrichtian and Paleogene

Anuár io do Inst i tu to de Geociências - UFRJISSN 0101-9759 Vol. 29 - 1 / 2006 p. 478-479

FORAMS 2006


FORAMS 2006Deep-sea environments across the Cretaceous/Paleogene boundary in the SE Atlantic Ocean

(ODP Leg 208 Hole 1262C, Walvis Ridge)Laia Alegret & Ellen Thomas

sediments. In the Maastrichtian, buliminid species such as Bolivinoidesdecoratus and Praebulimina reussi were common. Their abundance as wellas the heterogeneity of the assemblages start to decrease a few cm below theK/Pg boundary. At the boundary, diversity and heterogeneity drop dramatically,but there are no major changes in morphogroup composition. The interval directlyabove the boundary has low abundances of laevidentalinids, and high abundancesof Paralabamina spp. and Quadrimorphina allomorphinoides; the relativeabundance of buliminid taxa decreases drastically and does not recover in thestudied interval. About midway into Zone Pα the agglutinated taxaSpiroplectammina spectabilis and Clavulinoides spp. increase in abundance.The former bloomed after the K/Pg boundary at many locations, and is seen asa disaster taxon, which may indicate increased organic carbon flux (Kaminski& Gradstein, 2005. Grzybowski Found. Spec. Publ. 10). Diversity andheterogeneity of the assemblages fluctuate throughout the studied interval abovethe K/Pg boundary. These data suggest that the food supply to the deep-seafloor started to decline slightly before the K/Pg boundary, decreased morestrongly at the boundary, and started to recover in the upper part of Zone Pα,as suggested by the increase in diversity of the assemblages and in thepercentage of S. spectabilis The drop in calcium carbonate delivery, probablyresulting from the extinction of calcareous planktic groups, may have influencedthe benthic faunal composition, leading to the replacement of infaunal carbonatetaxa (buliminids) by agglutinated groups when the food supply recovered.Benthic foraminiferal assemblages did not stabilize throughout the studiedPaleogene interval, suggesting that food supply to the seafloor remained unstablein quality and/or quantity.

L.A. holds a Ramón y Cajal contract (Spanish Ministerio deEducación y Ciencia).

480

Maastrichtian-Paleocene depositionin the Paraíba Basin, NE Brazil

José Antonio Barbosa1; Gerta Keller2; Thierry Adatte3;Virgínio Henrique Neumann1 & Mário Lima Filho1

1Department of Geology, Federal University of Pernambuco, Recife, PE 50740-530, [email protected]

2Department of Geosciences, Princeton University, Princeton, NJ 08544, U.S.A.3Institut de Géologie, 11 Rue Emile Argand, 2007 Neuchatel, Switzerland

The Paraíba Basin, located along the Atlantic margin of NE Brazil, issubdivided into three sub-basins: Olinda (south), Alhandra (middle) and Miriri(north). Only the Olinda sub-basin contains a complete Maastrichtian-Paleocenecarbonate sequence. This sequence is relatively unknown, except for the K-Tboundary transition at the Poty Quarry and Ponta do Funil, which are amongthe best K-T sections in South America. Previous studies have detailed the K-T transition in the Poty Quarry, but the physical aspects and geological natureof this record and its correlation with the Chicxulub impact are still under debate.

A US-Brazil funded cooperative project between GeosciencesDepartments at Princeton University and the Federal University of Pernambuco(CNPq/NSF) drilled the Paleocene through Maastrichtian sequences in threelocalities (Poty, Olinda, Itamaraca). The main objectives include the evaluationof environmental changes during the Maastrichtian and the K-T boundarytransition. The wells span the carbonate sequences from the Maria Farinha(Paleocene) to the base of the Gramame (Maastrichtian) Formations. TheItamaracá-core is located in the deepest part of the Olinda sub-basin, withPoty and Olinda in the shallower flanks. The deep basin location of the Itamaracácore is evident by the presence of small slumps (50-100cm). These slumps areprobably related to gravity flows. In addition, we examined and sampledseveral K-T outcrops.

Preliminary results from sedimentology, biostratigraphy and physicalstratigraphy suggest that the carbonate deposition began after a maximumflooding surface, which produced a phosphate-rich layer. This phosphatic layermarks a sequence boundary at the top of the Itamaracá Formation (transitionalsequence). The Gramame Formation shows a monotonous sequence of marls,marly limestones and limestones. Deposition occurred in a shallow low-energyenvironment, resulting in intermittent reworking, erosion and shell bed


FORAMS 2006


FORAMS 2006Maastrichtian-Paleocene deposition in the Paraíba Basin, NE Brazil

José Antonio Barbosa; Gerta Keller; Thierry Adatte; Virgínio Henrique Neumann & Mário Lima Filho

accumulations. Upper Maastrichtian sediments show a strong reduction in themacrofossil components compared with the underlying high diversityassemblages at the base of the Gramame Formation. Ammonites disappeartwo meters below the K-T transition. Observed Ichnofossils suggest theCruziana ichnofacies, with low diversity dominated by large Thalassinoidesand Planolites.

The top of the Gramame Formation is separated from the Maria FarinhaFormation by a conglomeratic bed that marks the K-T transition. Thisconglomerate was observed in all three wells and in outcrops. The origin ofthis conglomerate is still under debate and under intensive study. It has beenvariously interpreted as impact-generated tsunami deposit, storm deposit, tectonicbreccia or sea level lowstand. Our preliminary investigation of this conglomeratereveals a 40-50cm thick mass flow deposit consisting mainly of phosphate andglauconite pebbles, occasionally graded, and floating in a micrite matrix. Thiscoarser material probably derives from the dislocation of the uppermostMaastrichtian phosphatized hardground that developed in more proximal areasand can be observed in outcrops. Such sedimentological features are not uniqueand frequently associated with the sea-level fall and/or local tectonic activity,which mark the uppermost Maastrichtian. The age of deposition of this massflow is still in question. Although previous studies have placed it at or below theK-T boundary, the presence of Danian planktic foraminifera puts this age inquestion. It remains to be determined whether their presence is the result ofburrowing or whether the breccia is of early Paleocene age. Above the K-Ttransition, the cores reveal gradual shallowing, marked by glauconitic andphosphatized beds and shell layers. The presence of Ostrea sp. and a largenumber of callianaseadean crabs suggests the proximity of estuaries ortidal conditions.

482

Paleoenvironmental interpretation of theDanian-Selandian transition (Paleocene)

in the North Sea Basin based on foraminifera

Anne Clemmensen & Erik Thomsen

Department of Earth Sciences, University of Aarhus, Building 1120,DK-8000 Århus C, Denmark

[email protected]

The Danian–Selandian boundary (~60 Ma) marks the cessation of 40million years of carbonate deposition in the North Sea Basin and a shift tosiliciclastic deposition. On the basis of variations in lithology, benthic andplanktonic foraminifera and calcareous nannofossil assemblages in three coresfrom Storebælt in the eastern part of the North Sea Basin, we havereconstructed the paleoenvironmental changes across the boundary. The benthicforaminiferal faunas belong to the “Midway-type fauna”. They are extremelyrich and more than 260 species have been recognized. Q-mode cluster analysisgroups the benthic assemblages into four biofacies, which correspond fairlyclosely to lithological units. Correlation of the Storebælt records with marinepaleorecords from the Danish Basin and the North Sea Basin indicates that thetransformation of the North Sea from a carbonate- to a siliciclastic basinoccurred in four steps. The most important external factors involved in thechange was, firstly, a major fall in the relative sea level during the late Danianleading to the disappearance of bryozoans from the North Sea Basin and anincrease in the proportion of marginal marine coccoliths and to non-depositionand erosion in many areas. The relative abundance of the planktonic foraminiferadecreased, whereas the benthic foraminifera show very little change. Secondly,coinciding with the Danian–Selandian boundary, an uplift of the Scotland–Shetland area resulted in a massive input of siliciclastic material into the NorthSea Basin, and the sediments changed from carbonate to marl. The marginalmarine coccoliths disappeared, indicating a return to more normal marineconditions. In the foraminiferal faunas, the boundary marks an increase in thedensity of both planktonic and benthic foraminifera and an increase in theproportion of epifaunal morphotypes. Thirdly, during the early Selandian, inversion


FORAMS 2006


FORAMS 2006Paleoenvironmental interpretation of the Danian-Selandian transition (Paleocene)

in the North Sea Basin based on foraminiferaAnne Clemmensen & Erik Thomsen

of the Sorgenfrei–Tornquist Zone and Mesozoic basins in the southern andeastern part of the North Sea Basin resulted in a huge influx of reworkedCretaceous chalk and an almost complete stop of carbonate production. Theinflux of both planktonic foraminifera and in situ coccoliths showed a drasticdecline. The proportion of infaunal benthic morphotypes increased. Finally, laterin the early Selandian, in connection with a general sea-level rise and a reductionin the gateway between the North Sea Basin and the Tethys Sea, the seabottom conditions became colder and more acidic. This resulted in partialdissolution of the carbonates. Despite the great environmental andsedimentological changes, the species composition of the benthic foraminiferaremained remarkably similar during the Danian-Selandian transitional interval.Very few species appeared or disappeared. The changes consisted almostexclusively of variations in their relative abundance. Comparison with recordsfrom the Western Pyrenees, the Nile Basin, and the eastern North Americasuggests that sea-level changes across the Danian–Selandian boundary wereprimarily of eustatic nature.

484

Foraminiferal, ostracode and radiolarian biostratigraphyof the Campanian–Maastrichtian and K/P boundary

of synorogenic basins of Cuba

María Lizette Díaz Collell

CEINPET/CUPET, La Habana, [email protected]

Late Cretaceous (Campanian – Maastrichtian, main subject of thisstudy) and Paleogene microfaunal assemblages from synorogenic basins ofcentral and western Cuba have been investigated on the basis of 133 samplesfrom 9 outcrop sections. Foraminifera and ostracodes are scarce and/or poorlypreserved in these strata. Nevertheless, systematic analyses in this study reveal50 genera and 65 species of foraminifera. Ostracodes are particularly rare,with only 13 genera and 11 species determined. The main biohorizons evidencedby microfossil successions are characterized, and biostratigraphic,paleoecological and biogeographic implications of the various microfaunas arere-evaluated, thus contributing to the overall update of Cuban micropaleontology.In spite of their low diversity (13 genera and 15 species identified), radiolariansare frequent in most sections. They permit to erect a regional biozonation ofthe lower to possibly middle Eocene (Stylosphaera coronata Taxon RangeZone) at La Conchita section, western Cuba, where the Paleocene-Eoceneboundary is recorded. Occurrences of Late Cretaceous larger foraminiferaare documented, and correlated with FADs and LADs of Tethyan zonal taxadescribed in the international literature. Three Maastrichtian planktonicforaminiferal biozones of regional applicability are identified (in ascending order):Globotruncanella minuta (new), Trinitella scotti and Racemiguembelinafructicosa Interval Zones. Planktonic foraminifera also permit recognition ofthe undifferentiated P0/Pα-P1b zonal succession within an interval less than 4m thick at Loma Capiro (Santa Clara Formation), central Cuba, thus confirmingthe correlation of these strata with the K/P boundary global event.Micropaleontological results from another K/P boundary section in westernCuba (Miracielo locality, Cacarajícara Formation) point to the regionalprevalence of shallow neritic paleoenvironments and inextricable mixing ofpre-Campanian and Maastrichtian shallow water assemblages (e.g.: larger andsmaller benthic foraminifera, rudists and calcareous algae). These have beenpartly remobilized from coeval end-Cretaceous sediments, and partly reworked


FORAMS 2006


FORAMS 2006Foraminiferal, ostracode and radiolarian biostratigraphy of the Campanian–Maastrichtian

and K/P boundary of synorogenic basins of CubaMaría Lizette Díaz Collell

from older Cretaceous carbonate platforms exhumed at that time. Theoccurrence of an important earliest Danian unconformity in the synorogenicbasins of Cuba is once again demonstrated. A probable late Campanian – earlyMaastrichtian age span is inferred for the end of Cretaceous volcanism inCuba, based on lithological and paleontological evidence from Loma Capirolocality (micropaleontological dating of Late Cretaceous marine depositsassociated with tuffitic materials, tectonically recurrent onto Danian strata).The remarkable endemism and restricted geographic distribution of somewestern Tethyan marine ostracode genera during the Senonian permit todistinguish a coeval biogeographic unit (the Caribbean Subprovince) within thebroader American Province. The distribution pattern of Late Cretaceous largerforaminifera also supports the endemism of Caribbean benthic microfaunas inthe Campanian – Maastrichtian.

486

Cenomanian/Turonian benthic foraminiferal faunas ofthe Demerara Rise depth transect (ODP Leg 207)

Oliver Friedrich1; Jochen Erbacher1 & Jörg Mutterlose2

1Bundesanstalt für Geowissenschaften und Rohstoffe, Stilleweg 2, 30655 Hannover, Germany [email protected]

2Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum,Universitätsstrasse 150, 44801 Bochum, Germany

This study is based on Cenomanian to early Turonian sediments of OceanDrilling Program (ODP) Sites 1258, 1259, 1260, and 1261 from DemeraraRise (Leg 207, western tropical Atlantic, off Suriname) that are oriented alonga paleodepth transect. Studied sediments include the Cenomanian/TuronianBoundary Event (CTBE) or Oceanic Anoxic Event 2 (OAE 2) and consist oflaminated black shales with TOC values between 5 and 10% below and aboveOAE 2 and up to 29% within the OAE 2 interval. Benthic foraminiferalassemblages in this eutrophic environment are generally characterized by lowdiversities and strong fluctuations of abundances, indicating oxygen depletionand high organic matter fluxes. Dominant taxa at all sites are Bolivina anambra,Gavelinella dakotensis, Tappanina sp., Praebulimina prolixa , andNeobulimina albertensis. Based on the stable carbon isotope excursionparalleling OAE 2 we subdivided the studied successions into three intervals:

1) the interval below the OAE 2;2) the carbon isotope excursion reflecting the OAE 2; and3) the interval above the OAE 2.

In the bathymetrically shallower Sites 1260 and 1261 benthic foraminiferalfaunas indicate anoxic to sometimes slightly dysoxic bottom-waters conditionsbelow the OAE 2. The bathymetrically deepest Site 1258, in contrast, reflectsmore oxygenated bottom waters with an almost continuous occurrence ofbenthic foraminifera. It is therefore suggested that the shallower sites werelocated amidst the oxygen minimum zone (OMZ), whereas the sediments ofSite 1258 were deposited below the OMZ. During OAE 2 anoxic conditionsprevail at the shallower sites. At Site 1258 benthic foraminifera indicate severedysoxic but not anoxic conditions. This pattern is proposed to reflect astrengthening of the OMZ possibly related to increasing primary productionduring OAE 2. A short-termed repopulation event of benthic foraminifera locatedin the lower third of the OAE 2 was observed at all sites, reflecting a brief


FORAMS 2006


FORAMS 2006Cenomanian/Turonian benthic foraminiferal faunas of the Demerara

Rise depth transect (ODP Leg 207)Oliver Friedrich; Jochen Erbacher & Jörg Mutterlose

bottom-water oxygenation event within the OAE 2. This event parallels asurface-water cooling and is probably equivalent to the “Plenus Cool Event” inEurope and the “benthic zone” in the Western Interior. The benthic foraminiferaof a ~0.5 Ma interval following the OAE 2 still indicate oxygen depletion ofbottom waters. Subsequently, however, a strong increase in benthic foraminiferalabundance and diversity reflects a better oxygenation of the bottom-watermasses, probably related to a weakening of the OMZ.

488

Small Benthic Foraminifera extinction and turnover acrossthe Cretaceous/Tertiary boundary in a low latitude marine

bathyal environment (e.g. Melah section: Tunisia)

Njoud Gallala¹ & Dalila Zaghbib-Turki²

Faculté des Sciences de Tunis, Département de Géologie Campus universitaire, 2092Tunis, Tunisia

[email protected]

The benthic foraminiferal assemblages, in contrast to those of planktonicforaminifers, did not suffer severe mass extinction at the K/T boundary (Keller,1988. Palaeogeography, Palaeoclimatology, Palaeoecology, 66 (3-4): 153-171; Karoui-Yaakoub & Zaghbib-Turki, 1998. International Workshop onCretaceous-Tertiary Transition (Mai 1998, Tunis), Abstracts, 61; Zaghbib-Turki et al., 2000. Sciences de la Terre et des planètes, C.R. AcadémieSciences. Paris, 33: 141-149.; Alegret et al., 2003. Marine Micropaleontology,48: 251-279).

Taxonomic and statistic analyses of small benthic foraminifera speciesin K/T transition deposits of the Melah section in northern Tunisia, supportedby Benthic/Planktonic ratios, reveal that this faunal group was very diversified(136 species) and dominated by deep-sea species (e.g. Anomalinoides acuta,A. midwayensis, A. welleri, Gaudryina pyramidata, Bulimina midwayensis,B. trinitatensis, Cibicidoides alleni). The successive assemblages werecomposed of about 50 to 80% of endobenthic ecological morphotypes.

Among all the Maastrichtian benthic species (109 species), 37 speciesbecame extinct at the K/T boundary. This extinction bioevent concerned 34%of the total Maastrichtian assemblage, and especially 30% of the total eutrophicspecies. Throughout the P0 zone, the extinction is considerably less severe andonly three survivor species disappeared: two of buliminids and A. welleri. Incontrast, through this earliest Danian zone, seven species appeared, amongthem the oligotrophy tolerant Gavelinella danica. From those initially survivingand becoming extinct within P1a subzone, a consistent cluster (27 species)was diminished. This cluster was composed of calcareous (buliminids, bolivinids,anomalinoids, marginulinids) and agglutinated (spiroplectaminids andsaccaminids) species. Most of them (67%) were endobenthic. In contrast,across the P1a subzone interval, 13 endobenthic species appeared butGavelinella danica thrived. Throughout the P1b subzone, 15 other species


FORAMS 2006


FORAMS 2006Small Benthic Foraminifera extinction and turnover across the Cretaceous/Tertiary boundary in a

low latitude marine bathyal environment (e.g. Melah section: Tunisia)Njoud Gallala & Dalila Zaghbib-Turki

became progressively extinct which were mainly endobenthic and botholigotrophic and low oxygen tolerant versus 7 other species which appeared.

Globally, the species richness marks a negative shift at the K/T boundary.In the detail, among those disappearing at the Melah section, few of themsurvived in shallower environments of El Kef, Elles and Selja area (e.g.Cibicidoides alleni, Lenticulina comptoni, Nodosaria limbata, Bolivinadecoratissima, Tritaxia midwayensis, Bulimina quadrata andPseudoglandulina manifesta). This species disappearance may be related tothe decrease of oceanic organic matter flux to the sea floor which wassimultaneous to the primary productivity decrease in the upper water columnprevailing at the K/T boundary in response to the meteorite impact. Such ascenario had generated a sudden climate cooling.

After this mass extinction event a clear turnover was established at theearliest Danian. An almost complete recovery was achieved at the lower partof the P1a subzone. However, a less severe species richness decrease close toP1a/P1b boundary coincided with the eustatic curve excursion included in thechron 29n (Haq et al., 1987. Science, 235:1156-1167) and may be related to asea-level fall. After this temporary crisis the small benthic foraminifers speciesrichness mark a progressive increase, then remains almost stable.

490

The mid-Pleistocene “Stilostomella extinction event”in the southeast Pacific Ocean: A review

Igor J. C. Gavriloff

Facultad de Ciencias Naturales e Instituto Miguel Lillo, Universidad Nacional de Tucumán,Miguel Lillo 205, 4000 San Miguel de Tucumán, Tucumán, Argentina

[email protected]

During the mid-Pleistocene several important geological events occurredglobally and/or regionally (hemispheric), including: polarity reversal of the Earth’smagnetic field at 0.78 Ma (Brunhes/Matuyama Boundary); changes in theamplitude of the glacial/interglacial cycles (from a dominance of 40 ka to thatof 100 ka cycles) between 0.9-0.6 Ma (called Mid-Pleistocene Transition); at0.793 Ma the Australasian Impact Event covered ~1/10 of the Earth’s surfacewith its tektites strewn-field; and at 0.788 Ma the first super-eruption of theToba Caldera Complex in Sumatra expelled c. 1000km3 of equivalent rock-volume into the atmosphere. There are several global and/or regional changesin the marine biota in the mid-Pleistocene: the extinction of 30% of Plio-Pleistocene coral fauna in the Caribbean Basin between 0.9-0.5 Ma; and theglobal extinction of elongate and/or uniserial deep-sea! benthic foraminiferabetween 0.9-0.6 Ma (called the “Stilostomella Extinction Event”, SEE). Asrecently described by several authors, the SEE comprises the diachronousextinction of two families and a subfamily (partim) of benthic foraminifera (32cosmopolitan species plus several endemic forms) in the world ocean. In thePeru-Chile Trench area, however, a modern benthic foraminiferal bathymetriczone (upper limit 3257m), defined in the 1960s, is characterized by theStilostomella antillea group, containing some living Stilostomella forms (e.g.Stilostomella antillea). This species was recently listed as extinct and thereforeit should be considered as a “living fossil”. In the Southeast Pacific, the SEE ispresent in the ODP Site 861 (45º 51’S, 75º 41’W, depth water 1652m), whereit occurs at the upper boundary (1.3/3 Ma) of the Pliocene to lower-PleistoceneStilostomella cf. S. consobrina Assemblage Zone. At Site 861, the SEE thusoccurred earlier than elsewhere in the world’s oceans (0.9-0.6 Ma). The SEEin the Southeast Pacific Ocean can also be recognized in Eltanin Core 3-9 (23º15´S, 72º 49´W, depth water 3512m). At this site, the SEE occurred at 5.52mbsf, where the genera of the Stilostomella extinction group have their LastOccurrence. The S. cf. S. consobrina Assemblage Zone is recognized between


FORAMS 2006


FORAMS 2006The mid-Pleistocene “Stilostomella extinction event” in the southeast Pacific Ocean: A review

Igor J. C. Gavriloff

5.52 mbsf and the core bottom (7.54 mbsf) and it is characterized by thefollowing species: S. cf. S. consobrina, S. ex gr. S. lepidula, Orthomorphinacf. O. challengeriana and Pleurostomella alternans. The two benthic deep-sea foraminiferal species Epistominella exigua and Eponides weddellensisare the dominant components of the fauna in core E3-9 from the top down to5.52 mbsf. In this core section, both species alternatingly are dominant. Belowthe SEE level (5.52 mbsf), these two species are no longer dominant in thefauna and E. exigua is always more abundant than E. weddellensis. The co-occurrence of the mid-Pleistocene global and hemispheric/regional geologicalevents, such as paleoclimatic changes, impacts of extraterrestrial bodies andsuper-vulcanism, suggest that the SEE might be a smaller-scale event similarto greater Phanerozoic extinction events.

492

Response of foraminiferal faunas to paleoceanographicchanges in the Gulf of Guinea from the late Paleocene to the

Initial Eocene Thermal Maximum (IETM)

Holger Gebhardt1; Olabisi Adekeye2 & Samson Bankole3

1Geologische Bundesanstalt, Neulinggasse 38, A-1030 Wien, [email protected]

2University of Ilorin, Dept. of Geology and Mineral Sciences, PMB 1515, Kwara State, Nigeria3Technische UniversitŠt Berlin, ACK14, Ackerstrasse 71-76, Germany

Foraminiferal assemblages from Shagamu in southwestern Nigeria wereinvestigated to gain stratigraphic and environmental data from epicontinentalpaleoenvironments of Late Paleocene to earliest Eocene age (plankticforaminiferal zones P4b to P5). The Paleocene-Eocene boundary is indicatedby a distinct δ13C excursion. Exceptionally well preserved calcareousmicrofossils in the unweathered portion of the investigated section result inreliable stable isotope data, ranging approximately from -4 to -1‰ δ13C, -1.5 to-2.5‰ δ18O for benthic foraminifera, or -1 to 4‰ δ13C, around -3.5‰ δ18Ofor planktic foraminifera. Paleowater-depths changed from 50 to 300 m withthe maximum during the P4b/P4c-transition. Surface water paleotemperaturescalculated from δ18O values vary around 290C without a prominent trend.Bottom water temperatures however increase from 19 to 230C already duringzone P4b, coincident with the appearance of Gavelinella and Nonionella.Benthic and planktic foraminiferal concentration was very low (5 to 10individuals/gram sediment), pointing to oligotrophic conditions during deposition.The generally good oxygenation of the bottom water was interrupted by periodsof reduced oxygenation during zone P4c and oxygen deficiency during theIETM. Benthic assemblages changed from Gyroidinoides/Lenticulina toGavelinella/Nonionella-associations during the period investigated.

Canonical correspondence analyses of benthic and planktic assemblagespoint to bottom water temperature and type of food as the most importantfactors for the distribution of benthic species, or amount of food and temperatureof the lower mixed layer for planktic genera.

The early increase of the bottom water temperature is in contrast todeep sea sections, which show almost contemporary increase of bottom andsurface paleotemperatures. Our results may indicate differentialpaleoceanographic processses on tropical shelves and deep seas during thelatest Paleocene.


FORAMS 2006

493

Foraminiferal and calcareous nannofossil events and thestratigraphic record across the Cretaceous-Paleogene

boundary in Campos Basin, southeastern Brazil

Eduardo A. M. Koutsoukos1 & Alexandre de Azevedo Grassi2

1PETROBRAS-CENPES, Cidade Universitária, Quadra 7, Ilha do Fundão, 21941-598Rio de Janeiro, RJ, [email protected]

2PETROBRAS-E&P/EXP, Centro, Rio de Janeiro, RJ, Brazil

An almost complete Cretaceous-Paleogene boundary sequence wasrecovered in a core section, drilled in the outer shelf (145m of water depth) ofthe central-south region of Campos Basin, in Rio de Janeiro. The boundarybetween the uppermost Maastrichtian (Micula prinsii (CC26) nannofossilZone) and the lowermost Paleocene Danian (Thoracosphaera acme-Zone)is clearly undisturbed, non-bioturbated, and marked by the sharp appearanceof a 2.5cm thick layer composed of microtektite-like spherules (at 2,166.6m).Iridium concentrations peak to a maximum value of 0.937ng/g, about 50 timeshigher the background levels, 4cm above the spherule layer. The benthicforaminifera assemblage recovered from the uppermost Maastrichtian sectionis chiefly composed of Anomalinoides aragonensis, Gavelinellabeccariiformis, G. dayi, Gyroidinoides globosus, Nuttallinella coronula,Pullenia bulloides, Ammodiscus cretacea, A. glabratus, Ammoglobigerinaglobigeriniformis, Arenobulimina sp., Cribrostomoides trinitatensis,Gaudryina pyramidata, Haplophragmoides sp., Hormosinella trinitatensis,Recurvoides sp., Reticulophragmium sp., Reophax globosus, Repmaninacharoides corona, Bathysiphon sp. and Rhizammina indivisa, among othertypical deep slope dwellers, which suggests a middle bathyal environment. At2,166.3m there is the first occurrence of Danian planktonic foraminifera(Eoglobigerina edita, E. eobulloides, Guembelitria irregularis,Parvularugoglobigerina eugubina, Woodringina claytonensis and W.hornerstownensis), which mark the base of the Pα foraminiferal zone. Nocalcareous nannofossils and foraminifera have been recovered between 2,166.75and 2,166.55m. Benthic assemblages from the Danian mark a community shift,with the decrease of deep-slope calcareous and agglutinated specimens, andreplacement by a typical transitional “Velasco/Midway-type” fauna, such asAnomalinoides alazanensis, A. chiranus, Bolivina midwayensis, Gyroidinabandyi, Gyroidinoides dissimilis, G. girardianus, Hoeglundina sp. ,


FORAMS 2006


FORAMS 2006Foraminiferal and calcareous nannofossil events and the stratigraphic record across the

Cretaceous-Paleogene boundary in Campos Basin, southeastern BrazilEduardo A. M. Koutsoukos & Alexandre de Azevedo Grassi

Osangularia plummerae, O. velascoensis, Clavulinoides plummerae,Arenobulimina sp., and variable numbers of nodosariids and vaginulinids, amongothers. The Danian foraminiferal assemblage suggests an upper bathyalenvironment, which is consistent with the record of a sharp sea-level dropacross the boundary transition. A similar sea-level fall, in the order of magnitudeof 100 to 300m, was also suggested for the coeval boundary deposits of thePoty section, near Recife, in northeastern Brazil (Koutsoukos, E.A.M., 2005.Applied Stratigraphy, Chapter 7: 147-161, Springer, Dordrecht).

495

Messinian benthic foraminifera from the Mediterranean

Tanja J. Kouwenhoven1 & G. J. Van Der Zwaan1, 2

1Department of Earth Sciences, Utrecht University, Utrecht, [email protected]

2Department of Ecology / Biogeology, Radboud University Nijmegen, Nijmegen, Netherlands

The Messinian salinity crisis (MSC), affecting the Mediterranean areaaround 6 Ma may be considered a critical boundary on a regional scale, althoughevidence exists that its effects were more far-reaching. Integrated stratigraphyallows us to place the event within a well-constrained time frame. The sequenceof events preceding this late Messinian evaporative phase, however, is still notfully resolved. It has proven problematic to derive reliable paleoenvironmentalinformation from Messinian Mediterranean sediments. A generally acceptedscenario is that severance of the Betic and Rif Corridors (SE Spain and NWMorocco, respectively) isolated the Mediterranean more or less completelyfrom the Atlantic. Different stages in the Messinian restriction of theMediterranean are tentatively correlated with uplift in different areas of theCorridors. It is still not clear what the precise effects were of this restriction,for instance, whether surface- and/or deep-water salinity rose long before theactual MSC, and if so, when, and to what extent.

We will present data derived from benthic foraminiferal faunas, coveringthe Messinian up to the start of the evaporative phase. Paleoenvironmentalreconstructions were made at several locations and at different paleowaterdepths, aiming at development of a more accurate scenario of the pre-MSC events.


FORAMS 2006

496

Foraminiferal turnover at the Eocene-Oligoceneboundary in Tanzania and Java

Paul N. Pearson1; Ian K. Mcmillan1; Bridget S. Wade2 & Helen K. Coxall1

1School of Earth, Ocean and Planetary Sciences, Cardiff University,Main Building, Park Place, Cardiff CF10 3YE, U.K.

[email protected] of Geological Sciences, Rutgers University, New Brunswick, New Jersey 08903, U.S.A.

The Eocene-Oligocene stage boundary (as currently defined) is markedby the disappearance of the Hantkeninidae, a distinctive group of tubulospinoseplanktonic foraminifera. The boundary is generally accepted to pre-date thewell-known phase of rapid ice accumulation on Antarctica and associatedclimate and sea-level change (which occurred in the early Oligocene). Therehas been little detailed study of foraminifer turnover at the Eocene-Oligoceneboundary proper, because good expanded sections with abundant and well-preserved foraminifera are rare.

We have obtained three new drill-cores through the Eocene-Oligoceneboundary in Tanzania and (at the time of writing) one new drill-core from Java,Indonesia. Both were deposited in shelf-slope settings and are now exposed onland. These sites are important in recording tropical events through the boundaryinterval in mudstone facies with exceptionally well-preserved foraminifera. Thepresence of common allochthonous shallow-water debris in the sites also permitscorrelation with large benthic foraminifer extinction events as well as nannofossilbiostratigraphy.

The Tanzanian sites are highly expanded (with sedimentation rates higherthan 10cm / kyr). Five morphospecies of Hantkeninidae are recognized, all ofwhich disappear simultaneously in an interval of less than 30cm. There is noevidence of a hiatus at this level. The hantkeninid morphospecies (Hantkeninaalabamensis, H. nanggulanensis, H. primitiva, H. compressa andCribrohantkenina inflata) are too dissimilar to realistically belong to a singlebiospecies, hence the extinction appears to have been coordinated event involvingseveral closely related species. To date we have been unable to identify aprobable cause for the extinction.

The Eocene-Oligocene boundary extinction is distinctly preceded by asimilar coordinated extinction within the genus Turborotalia. Several


FORAMS 2006


FORAMS 2006Foraminiferal turnover at the Eocene-Oligocene boundary in Tanzania and Java

Paul N. Pearson; Ian K. Mcmillan; Bridget S. Wade & Helen K. Coxall

morphospecies belonging to the T. cerroazulensis group disappear in the top10m of the Eocene in Tanzania (Turborotalia cerroazulensis, T. cocoaensisand T. cunialensis). A similar short interval between the extinctions of thesetwo groups has also been observed at the GSSP in Massignano, Italy (wherethe estimated interval between the events is about 60 kyr), and otherTethyan sections.

An interesting feature of the new sections is the record of smaller andlarger benthic foraminifera. The Eocene-Oligocene boundary is associated withthe extinction of several important groups of larger foraminifera. Our dataindicate that the turnover event(s) at or very near the stage boundary weresignificant and affected very widely distributed taxa (particularly among thelarger foraminifera), implying a severe global perturbation that preceded themajor climate shift in the early Oligocene.

498

High resolution planktonic foraminifera analyses across thePaleocene/Eocene boundary at Shatsky Rise, Pacific Ocean

Maria Rose Petrizzo

University of Milano, Milano, [email protected]

The latest Paleocene to earliest Eocene sediments from two OceanDrilling Program Holes 1209B (water depth 2387m) and 1210B (water depth2573m) recovered from Shatsky Rise were studied to obtain a detailed planktonicforaminifera record across the Paleocene-Eocene transition in the subtropicalPacific Ocean. At these sites the Paleocene yellowish brown calcareous oozeis overlain by a thin dark brown clay seam (~ 2mm) at 196.42 mbsf in Hole1209B and at 184.31 mbsf in Hole 1210B which corresponds to the base of thePaleocene-Eocene Thermal Maximum (PETM) and to the Paleocene/Eoceneboundary. The PETM was an interval of rapid global warming ~55 Ma agoassociated with transformation of fauna and flora ecosystems and changes incarbon cycling. At Shatsky Rise, the onset of the PETM is marked by theabrupt onset of the negative carbon isotope excursion (CIE) which lies justbelow the sharp lithologic contact between more carbonate-rich ooze overlyingclay-rich ooze. In the upper part of the PETM interval, the clay-rich oozegradually becomes more carbonate rich and carbon isotope valuesgradually increase.

A high-resolution centimeter-scale quantitative analysis of the planktonicforaminiferal assemblages was performed in order:

1) to document the composition of the planktonic foraminiferalassemblages and their variations at centimeter scale, and

2) to provide a high resolution bio-chemostratigraphic correlation acrossthe Paleocene/Eocene boundary.

Quantitative analyses well document the similarity in composition of theplanktonic foraminiferal assemblages between the two sites. In general,Morozovella dominates the assemblages and its maximum relative abundanceis coincident with the carbon isotope excursion. Subbotinids show an oppositetrend and are absent in the interval of maximum abundance of Morozovella. Adecrease in abundance of about 10% in average is observed within the Acarininagroup from the base to the top of the studied sections. The excursion taxa (A.sibaiyaensis, M. allisonensis, and A. africana) first appear at the CIE and


FORAMS 2006


FORAMS 2006High resolution planktonic foraminifera analyses across the Paleocene/Eocene

boundary at Shatsky Rise, Pacific OceanMaria Rose Petrizzo

rich their maxima abundance (10%) at the beginning of the morozovellidsdecline. SHE diversity indices, used to evaluate changes in planktonicforaminiferal species composition through the studied interval, show similartrend at both sites. Species diversity varies between 21 to 34 species in thedeeper Site 1210, and from 15 to 29 in the shallower Site 1209, with the minimumdiversity values occurring in the carbonate-rich ooze below the CIE, andpreceding the FO of A. sibaiyaensis. This diversity minimum is followed by ageneral increase in the number of species, reflecting the progressive appearanceof igorinids and globanomalinids, and of the excursion taxa. Equitability isrelatively high at both sites with average values of 0.5-0.6 that reflects minorchanges in composition, as most of the species are present in the same proportion.The maximum diameter of largest specimens of surface-dwelling (Morozovellavelascoensis, M. pasionensis, M. subbotina, M. occlusa and Acarininasoldadoensis), and deep-dwelling planktonic foraminifera (Subbotinavelascoensis, and S. triangularis) were measured in each sample. Resultsshow that during the warming event the test size Morozovella has a maximum,and A. soldadoensis shows no significant change in size throughout the studiedinterval. Within the morozovellids several specimens of M. velascoensis showdiameter close to 800µm in the interval containing the CIE.

Lithology, planktonic foraminiferal distribution and abundances, planktonicand benthic foraminifera tests size, calcareous plankton and benthic events,and the negative carbon isotope excursion allow precise correlation of databetween sites.

500

Correlation of the Thanetian-Ilerdian turnover of largerforaminifera and the Initial Eocene thermal maximum

(IETM) confirming evidence from the Campo area(Pyrenees, Spain)

Victoriano Pujalte1; B. Schmitz2; J. I. Baceta1; G. Bernaola1; J. Dinarès-Turell3;X. Orue-Etxebarria1 & A. Payros 1

1Dept. of Stratigraphy and Paleontology, Fac. of Science and Technology,Univ. of the Basque Country, P.O. Box 644, E-48080 Bilbao, Spain

[email protected]. of Geology, Univ. of Lund Sölvegatan 12, SE-22362 Lund, Sweden

3Inst. Nazionale Geofisica-Vulcanologia, Lab. Paleomagnetismo,Via Vigna Murata, 605, I-00143 Roma, Italy

It has long been known that a major larger foraminifera turnover (LFT)occurred at the boundary between the Thanetian and Ilerdian stages (Hottinger& Schaub, 1960. Eclog. Geol. Helv. 53). However, its possible correlationwith the IETM was unsuspected until the re-study of the Campo section in theSpanish Pyrenees by Orue-Etxebarria et al. (2001. MarineMicropaleontology, 41). Orue-Etxebarria et al.’s correlation was laterreinforced with data from additional sections in the Pyrenees (Urrobi, Mintxate,Ermua, Esplugafreda) and in the Galala Mountains of Egypt (Scheibner, 2005.Geology 33). However, although the combined evidence from all these sectionsis compelling, the information provided separately by any one of them is notwithout ambiguities: in deep-water settings, such as Ermua or the GalalaMountains Sections, the location of the Carbon Isotopic Excursion (CIE) thatmarks the IETM is well established, but the position of the LFT relies upon therecord of re-sedimented larger foraminifera. Conversely, in shallow-watersections such as Urrobi or Campo, in which the LFT is well constrained, theisotopic signature is either obliterated or unclear. In point of fact, therefore, theproposed temporal concurrence of the LFT and the CIE hinges on a correlationbetween sections at different settings and, perhaps because of that, somespecialists on larger foraminifera are still reluctant to accept it.

Here we present new information from two shallow-water sections thatconclusively resolve the issue, Sections Campo and St Martin, situated lessthan 2km from each other in the Pyrenees. At St Martin, a ca. 7 meter-thickintercalation of continental deposits rich in pedogenic carbonate nodules is


FORAMS 2006


FORAMS 2006Correlation of the Thanetian-Ilerdian turnover of larger foraminifera and the Initial Eocene thermal

maximum (IETM) confirming evidencefrom the Campo area (Pyrenees, Spain)Victoriano Pujalte; B. Schmitz; J. I. Baceta; G. Bernaola; J. Dinarès-Turell;

X. Orue-Etxebarria & A. Payros

sandwiched between shallow marine carbonates of late Thanetian and earlyIlerdian age. Analysis of 35 of these nodules has shown that their s:δ13Ccomposition ranges between –11.4/-14.3‰ and averages –12.9‰, values thatunquestionably record the CIE and, for the first time, are reported in a sectionwhere the LFT is clearly represented. That crucial evidence is coupled withnew calcareous nannofossil and magnetostratigraphic data from Campo, thatdemonstrate that no sizeable break exists in the upper Thanetian/lower Ilerdiansuccession and, therefore, that the spatial coincidence of the LFT and the CIEat St Martin is not an artifact. Larger foraminifera were major rock builders inthe extensive early Paleogene marginal seas of the Tethys Ocean. Our newdata thus confirm that the ecological impact of the IETM was much greaterthan earlier thought, having also affected low- and mid-latitude shallow marinebiota. The exact mechanisms bringing about the LFT, however, remain elusive.

Contribution to Projects CGL2005-02770/BTE, CGL2005-01721/BTEand 9/UPV00121.310-1455/2002.

502

The evolution of late Paleocene-early Eocenecarbonate platforms of the Tethys

Christian Scheibner1; Robert P. Speijer2 & Maria Mutti 3

1Department of Geosciences, University Bremen, Germany2Department of Geography and Geology, K.U.Leuven, Belgium

[email protected] of Geosciences, University Potsdam, New York, U.S.A.

We present an overview on platform evolution data from several latePaleocene-early Eocene carbonate platforms from the Tethys. We focus onplatform evolution in Egypt and Spain as these regions are biostratigraphicallybest defined and integrate data from other areas in the Tethys. These dataindicate that the late Paleocene–early Eocene interval was a time of profoundchanges in shallow-water carbonate settings. A comparison of time-equivalentcarbonate platforms in the low and middle latitudes shows a threefold Tethyan-wide carbonate platform evolution in the late Paleocene to earliest Eocene:

1) a late Paleocene (shallow benthic zone 3) coralgal-dominatedplatform stage;

2) a latest Paleocene (shallow benthic zone 4) transitional platformstage, where coralgal reefs thrived only at middle latitudes while thelow latitudes were dominated by larger foraminifera (Miscellanea,Ranikothalia, Assilina) and

3) an early Eocene (shallow benthic zone 5/6) platform stage dominatedat all paleolatitudes by larger foraminifera (Alveolina, Orbitolites,Nummulites).

The causes for the stepwise change from coral-dominated platforms tolarger foraminifera-dominated platforms are multilayered. The early Paleogenewas the time of the most pronounced long-term warming during the Cenozoic.During this time interval a calcite sea prevailed with very low Mg/Ca ratios,high CO2 concentrations, and highly oligotrophic regimes. While the transitionfrom stage I to stage II does not seem to correlate to a discrete global event,the transition from platform stage II to stage III coincides with the short-termPaleocene-Eocene Thermal Maximum that is characterised by increased globalwarming, a massive input of CO2 and eutrophic conditions on shelf areas. Theresponse of corals and larger foraminifera as the most important platform-building organisms to these long- and short-term trends resulted in these twosteps of Tethyan platform evolution around the Paleocene/Eocene boundary.


FORAMS 2006

503

Foraminiferal transition across the K-P boundaryin the Gulf of Mexico and the Chicxulub crater

Jan Smit1; S. Galeotti2 & H. Brinkhuis3

1Sedimentology Group, Faculty FALW, Vrije Universiteit,de Boelelaan 1085, 1081HV Amsterdam, Netherlands

[email protected] di Geologia, Università degli Studi di Urbino, 61029 Urbino, Italy

3Laboratory of Palaeobotany and Palynology, Utrecht University, Budapestlaan 4, 3584 CDUtrecht, Netherlands

The K-P transition of planktic and benthic foraminifers in the Gulf ofMexico and the Chicxulub crater is stratigraphically complicated because ofthe occurrence of impact-ejecta rich clastic deposits at the K-P boundary.Preservation of foraminifers in all outcrops of the Mexican Gulf coastal plainsis poor, although the species richness is high, in particular in the deep watersections like Coxquihui. The Texas coastal plain outcrops near Brazos River(Brazos-1 is studied here) offer a better preservation, but the species richnessis low. Large, specialized species like Gt. stuarti, R. fructicosa, C. contusaand A. mayaroensis are absent. Faunas are dominated by heterohelicids andrugoglobigerinids. Yet the uppermost Maastrichtian can be demonstrated onthe basis of nannofossils (Jiang & Gardner, 1986. Micropaleontology, 32:232-255). The specimen abundance of planktic foraminifers drops spectacularlyin the uppermost beds of the clastic deposits, represented by 21cm of gradedsemi-lithified silt-mudstones in the Brazos-1 section (units F-G of Hansen, 1987.Cretaceous Research, 8: 229-252). These beds contain enhanced abundancesof iridium, smeared over the same 21cm. The first (very scarce) Paleoceneforaminifers appear about 1.3m above the lithological marker bed F. We couldnot confirm earlier reports of Paleocene foraminifers occurring in the clasticbeds (Montgomery et al., 1992. EPSL, 109: 593-600), or their first occurrencenear bed H (Keller, 1989. Paleoceanography, 4 (3): 287-332). The sequenceof FADs is similar to El Kef (levels from base of bed F, the first iridiumenrichment): first G. minutula (+1.25m), followed by G. fringa (+1.4m), G.eugubina (var. longiapertura) and Eoglobigerina spp. (+2.1m). Their FADshave been used for a biozonal scheme of the basal Paleocene (Smit &Nederbragt, 1997. Marine Micropaleontology, 29: 94-100).


FORAMS 2006


FORAMS 2006Foraminiferal transition across the K-P boundary in the Gulf of Mexico and the Chicxulub crater

Jan Smit; S. Galeotti & H. Brinkhuis

Benthic foraminifers suddenly change in Bed G. Their abundancesdecrease dramatically, and species richness is low in units F-I. Infaunal species(Fursenkoina) become dominant at three different levels (0.15-0.4m, 1.4mand 2.3m), following a spike of agglutinated foraminifers (0.12m). These threeabundance peaks agree very well with three cooling episodes documented inthe El Kef section at identical chronostratigraphic levels (Galeotti et al., 2004.Geology: 529-532).

The Yaxcopoil-1 core in the Chicxulub crater shows a similar sequence,but a significant portion (upper part of magnetic anomaly 29R) is missing. Alsoiridium enriched deposits are missing, probably by erosion and dissolution onthe seafloor, as shown by stylolite-like horsetail laminations in a thin clay toppinga graded and cross-bedded dolomitic sand unit capping the suevitic ejecta.Reports of in situ Maastrichtian foraminifers in the dolomitic sand unit (Kelleret al., 2004. Meteoritics and Planetary Science, 39 (7):1127–1144) are basedon erroneous misidentifications of fortuitous combinations of zoned dolomitecrystals (Smit et al., 2005. Meteoritics and Planetary Science, 39:1113-1126),and cannot be used to demonstrate a Maastrichtian age of the Chicxulub impact.

All combined evidence strongly indicates a single impact triggering amassive extinction and radiation event at the K-P boundary.

505

Planktonic Foraminifera biostratigraphy at the Jerissa area,(CES section in north-western Tunisia), and the impact of the

Cenomanian-Turonian Oceanic Anoxic Event (OAE-2)on their assemblages

Mohamed Soua & Dalila Zaghbib-Turki

Faculté des Sciences de Tunis, Département de GéologieCampus universitaire, 2092 - Tunis, Tunisia

[email protected]

During the late Cenomanian–early Turonian Oceanic Anoxic Event(OAE-2), organic-rich black shales were deposited worldwide. This eventcoincides with the strongest eustatic Uppermost Cenomanian transgressiveperiod. Induced by this sea-level rise, the Oxygen Minimum Zone (OMZ)impinged onto the South Tethyan margin where the organic-rich BahloulFormation indicates the record of OAE-2 in central Tunisia as well as northeastern Algeria.

At the CES section in the Jerissa area, a closer sampling along a 24mthick interval in this formation allows a high resolution biostratigraphic analysisbased on planktonic Foraminifera. It shows that this event was extendedthroughout the upper part of the Rotalipora cushmani Zone and across theWhiteinella archaeocretacea Zone. There, five subzones are recognized whichare correlated with those of the Pueblo global boundary stratotype section andpoint (GSSP). In the upper part of the R. cushmani Zone, the Dicarinellaalgeriana subzone coincides with the onset of the organic-rich deposits. TheW. archaeocretacea Zone is divided into three subzones: theGlobigerinelloides bentonensis, D. hagni and Heterohelix moremanisubzones coincide with maximum TOC contents (up to 1.91%). At the top ofthe Bahloul Formation where the marls and limestones become impoverishedin organic matter the Helvetoglobotrunana helvetica Zone starts.

Immediately below the Bahloul Formation in the upper part of theFahdene Formation, samples have yielded diversified foraminiferal assemblages,containing more than 70% planktonic taxa. They are dominated by unkeeledsurface dwellers such as of Gl. bentonensis associated with rare keeled deeperwater dwellers (e.g. Rotalipora cushmani , R. greenhornensis, rare R.montsalvensis) and weakly-keeled lower photic zone dwellers (e.g.Praeglobo-truncana stephani P. gibba, P. delrioensis) and primitivedicarinellids. This assemblage points to an outer shelf to bathyal and


FORAMS 2006


FORAMS 2006Planktonic Foraminifera biostratigraphy at the Jerissa area, (CES section in north-western Tunisia), and

the impact of the Cenomanian-Turonian Oceanic Anoxic Event (OAE-2) on their assemblagesMohamed Soua & Dalila Zaghbib-Turki

oxygenated marine environment. Such an assemblage is preserved inorganic-poor (0.2% TOC) light shales and marls with 30% CaCO3 content.The first occurrence (FO) of the unkeeled surface dwellers of W.archaeocretacea is observed at this level. There, also the benthicforaminifera are diversified and dominated by bathyal species such as ofCassidella, Gavelinella, Lenticulina , Frondicularia, Gaudryina,Buliminella and Textularia.

From the upper part of the R. cushmani Zone (D. algeriana subzone),where the Bahloul Formation starts, the black shales are dominant andenriched in organic matter. There, an increase in the Planktonic/Benthicratio is observed. It coincides with a major decline in the number of keeledRotalipora species resulting from the disappearance of R. montsalvensisfollowed by the extinction of R. cushmani and R. greenhornensis (the LOof R. cushmani at -93.90 + 0.2 Ma). This particular coincidence of eventsis correlated in both Tethyan and Boreal realms. Throughout the middle partof the Bahloul Formation, where the Whiteinella archaeocretacea zone isdeveloped, a drastic change in the benthic assemblage is also observed. Thisbioevent coincides with a positive shift of heterohelicids (Heterohelixmoremani, H. reussi, H. aff. pulchra and H. navaroensis), then guembelitriids(Guembelitria cenomana, G. albertensis). Especially, heterohelicids areconsidered as low oxygen tolerant surface dwellers. Throughout the Gl.bentonensis subzone, their frequencies increase is related to the OMZ setting.Later, across the D. hagni subzone, guembelitriids mark a positive shift.They are considered as eutrophic surface dwellers. Their thriving coincideswith maximum TOC values (2% TOC) and CaCO3 contents (up to 80%).It may be related to the OMZ expansion.

The FO of the keeled Helvetoglobotruncana helvetica (-93.29 +0.2 Ma) was noted at the top of the Bahloul Formation followed byMarginotruncana spp. above through the Kef Formation where the TOCvalues again decrease.

507

Benthic foraminiferal change and sea level across theCretaceous/Paleogene boundary at Brazos River, Texas

Robert P. Speijer1; Peter Schulte2; Hartmut Mai3 & Christoph Meisen3

1Department of Geography and Geology, K.U.Leuven, 3001 Leuven, [email protected]

2Institut für Geologie und Mineralogie, Universität Erlangen-Nürnberg,D-91054 - Erlangen, Germany

3Department of Geosciences, Bremen University, 28334 Bremen, Germany

It is often suggested that late Maastrichtian eustatic sea-level changecaused particular sedimentary features of the K/P boundary and contributed tobiotic turnover prior to or at the boundary. Benthic foraminiferal distributionsprovide excellent opportunities to reconstruct changes in water depth throughtime and thus to unravel sea-level histories. In this study, we investigate twocores drilled close to the Brazos River outcrops, together constituting anexpanded succession of 15 m of the uppermost Maastrichtian (Biozones CF2to CF1) and lower Danian (Biozone P0 to P1a). The quantitative benthicforaminiferal record shows a succession of three distinct assemblages. TheCorsicana assemblage is dominated by Clavulinoides trilatera, Anomalinoidesspp. and Planulina nacatochensis, together consistently constituting 70-80%of the benthic assemblage (fraction >125µm). This late Maastrichtian benthicfauna is stable up to the base of the Chicxulub-ejecta-rich K/P event bed, withfew first or last appearances. Planktic/benthic ratios vary between 75 and90%, but remain high and stable up to the top of the Corsicana Fm. The stabilityof the fauna indicates a constant paleodepth of ~ 100m during the latestMaastrichtian. The K/P event bed marks an abrupt faunal change in the benthicforaminiferal assemblage. The post-event assemblage during Zone P0,immediately above the event bed constitutes a new fauna with a subordinatecomponent of Corsicana taxa. The four most common Corsicana taxa composebetween 1-18% of the new fauna. Pseudouvigerina naheolensis is the firstnew species to appear, composing up to 42% of the assemblage. It is followedby other common species such as Eponides elevatus, and Cibicidesnewmanae. P/B ratios in this interval gradually drop from a peak value of 80%just above the event bed to just a few percent during Zone P0. It is remarkablethat within this interval there is a one-to-one match with samples that contain arelatively large proportion (8-18%) of Corsicana benthic taxa. This relationship


FORAMS 2006


FORAMS 2006Benthic foraminiferal change and sea level across the Cretaceous/Paleogene

boundary at Brazos River, TexasRobert P. Speijer; Peter Schulte; Hartmut Mai & Christoph Meisen

strongly suggests that a significant proportion of both foraminifera groups isreworked (washed in) within this interval. At the same time the total number offoraminifera is extremely low directly above the event bed (~20 specimens pergram), but gradually increases to 100 specimens/g in the upper part of ZoneP0. Paleobathymetric estimates of this interval are uncertain, because the faunais quite unusual, reflecting variations in food and/or oxygenation rather thanchanges in paleodepth. However, sedimentologic and mineralogic parameterssuggest neither shallowing nor deepening during the lowermost Danian. Withthe appearance of the benthic taxa Alabamina midwayensis andAnomalinoides midwayensis during Zone Pα-P1a, a typical benthic Midway-fauna was established; other common taxa are Anomalinoides acutus andGyroidina subangulata. Only a few other species, such as Pulsiphoninaprima, and Cibicidoides alleni, are observed in this interval. Only scatteredsingle specimens of the Corsicana taxa are observed within this Midwayassemblage, suggesting that there was limited – if any – erosion of upperMaastrichtian beds into this interval. The gradual formation of the Midwayassemblage coincides with increasing P/B ratios, up to ~50% at the top of theLittig Member. The Midway fauna typifies deposition in a middle to outer shelfsetting (50-100m), so the depositional environment at Brazos during BiozonePα-P1a appears to have shallowed somewhat relative to the latestMaastrichtian, a scenario that is also supported by sedimentological mineralogicaldata. In conclusion, there is no indication of sea-level change prior to the K/Pboundary and the Danian record merely suggests gradual shallowing, probablyreflecting a late high-stand systems tract. The Brazos data do not supporteustatic sea-level change as an important controlling parameter in the globalbiotic turnover across the KP boundary.

509

PETM in a shallow marine environment: Benthic foraminiferalTurnover and echinoid bloom (Sidi Nasseur, Tunisia)

Peter Stassen1; Christian Dupuis2; Roberto Magioncalda2; Peter Schulte3;Etienne Steurbaut4; Johan Yans2 & Robert P. Speijer1

1Department of Geography and Geology, K.U.Leuven, 3001 Leuven, Belgium2Faculte Polytechnique de Mons, B-7000 Mons, Belgium

3Institut für Geologie und Mineralogie, Universität Erlangen-Nürnberg,D-91054 - Erlangen, Germany

4Department of Paleontology, Royal Belgian Institute of Natural Sciences,Brussels, B-1000, Belgium

[email protected]

Despite a large number of studies on the Paleocene/Eocene thermalmaximum (PETM) in continental margin sections, our knowledge of the PETMin inner to middle neritic environments remains quite poor. In order to unravelfaunal and paleoenvironmental changes in shallow marine settings during thePETM, we investigated the Sidi Nasseur (NAS) section in Tunisia. The sectionexposes upper Paleocene to lower Eocene shales and marls of the El HariaFormation. The lower 9 m of the NAS section is marked by moderately rich,fairly diversified nannofossil associations, containing the typical pre-PETM taxaof the middle part of NP9 (Discoaster multiradiatus, D. falcatus,Rhomboaster cuspis, Fasciculithus alanii, F. schaubii, etc.). The upper halfof the section (10.50 - 17.50 m) is very poor in nannofossils (Coccolithuspelagicus and a few D. multiradiatus are present), partly because of selectivedecalcification, excluding refined age attributions. The lower 9m of the NASsection contain a benthic foraminiferal assemblage with numerous largeFrondicularia, Nodosaria, Lenticulina, many small calcareous andarenaceous species, but only rare planktic foraminifera, pointing to inner tomiddle neritic deposition (~ 50 m paleodepth). A faunal turnover is situatedwithin a carbonate-poor interval interpreted as a decalcified zone, rich inarenaceous foraminifera. From 10.50 to 17.50 m the foraminiferal assemblagesconsist of many minute trochospiral and bi-/triserial benthic taxa. Frondiculariaand Nodosaria do not reappear above the carbonate-poor interval. Plankticforaminifera become frequent above the carbonate-poor interval and consistto a large extent of flat-spired species of Acarinina, including the multi-chambered variety of Acarinina sibaiyaensis. This planktic assemblage typifies


FORAMS 2006


FORAMS 2006PETM in a shallow marine environment: Benthic foraminiferal Turnover and echinoid bloom

(Sidi Nasseur, Tunisia)Peter Stassen; Christian Dupuis; Roberto Magioncalda; Peter Schulte; Etienne Steurbaut4; Johan Yans2 & Robert P. Speijer

the well-known planktic excursion assemblage observed within the PETMworldwide. From 12m onwards, spines and shell fragments of burrowingechinoids become increasingly abundant in the foraminiferal residues, aphenomenon not previously observed in Tethyan PETM sections. Parallel tothe main twofold benthic foraminiferal succession, also two different ostracodassemblages are identified: a diverse Paracosta kefensis assemblage (up to 9m), typical of Paleocene neritic deposits in Tunisia, followed by an oligotaxicReticulina sangalkamensis assemblage in the upper part of the section (10.15- 17.50 m). Faunal parameters suggest more stressed, probably food-rich sea-floor conditions during the PETM. SEM observations provide information ofthe preservation of microfossils including the echinoid spines. In the lowerpart, Frondicularia specimens show signs of partial re-crystallization.Nodosaria and the echinoid spines, however, appear excellently preservedwith only infilling by diagenetic calcite, separable from the shells. Stable isotopicstudies are conducted on Nodosaria, echinoid spines and organic carbon (TOC).The foraminiferal δ13Ccarb record of the uppermost Paleocene (Nodosaria) isfairly stable, with individual measurements varying between -1 and 0.5‰.Isotopic data from the echinoid spines (δ13Ccarbonate) show a very wide scatter,which may reflect undetected diagenetic overprint or vital effects. Only theTOC δ13Corg record provides a continuous sequence and reveals a 4‰ negativeexcursion (from -24.5‰ to -28.5‰) very similar to the δ13Corg record ofDababiya, the GSSP of the basal Eocene in Egypt. Surprisingly however, theonset of the excursion shows an enigmatic 1-2m lag relative to all faunalindications (particularly the Acarinina excursion assemblage) of the positionof the onset of the PETM. Further study should clarify the reasons behind thisapparent decoupling between the faunal and δ13Corg record.

511

Faunal changes of Oligocene benthic foraminifera in theEastern Equatorial Pacific sites of ODP Leg 199

Hiroyuki Takata1; Ritsuo Nomura2 & Koji Seto1

1ReCCLE, Shimane Univ., [email protected]

2Faculty of Education, Shimane Univ., Japan

Deep-sea paleoceanographic conditions during the transition from theEocene into the Oligocene varied considerably, under the influence offluctuations in volume of the Antarctic ice sheets and of deep water formationin the Southern Ocean. As an example, the Calciumcarbonate CompensationDepth (CCD) dropped precipitously close to the Eocene/Oligocene boundary(e.g. Coxall et al., 2005. Nature), and there were several increases in valuesof benthic foraminiferal oxygen isotope values in the Oligocene (Oi events,e.g., Miller et al., 1991. JGR). Benthic foraminiferal faunal assemblages duringthe Oligocene are expected to record these paleoceanographic changes. TheOligocene faunal succession of benthic foraminifera at various water depthshas been summarized for the Atlantic Ocean (Katz & Miller, 2003.Micropaleontology) and the Indian Ocean (Nomura, 1995.Micropaleontology). These authors documented the paleobathymetricdistribution of benthic foraminiferal species and the relationship between theirdistribution and paleoceanographic changes, including the Oi events. An outlineof Oligocene benthic foraminiferal faunas for the eastern equatorial PacificOcean was presented by Thomas (1985. DSDP Init. Rep.), but our knowledgeof short-term fluctuations in the assemblages of Oligocene benthic foraminiferalfaunas in the Pacific Ocean remains limited. Sites 1218 (4826m water depth)and 1219 (5063m water depth) of ODP Leg 199 in the East Equatorial PacificOcean provide the opportunity for conducting a detailed study of faunal change,because the drilled sections contain well-preserved foraminifera in almost allsamples. The objectives of our study are to investigate the Oligocene faunalsuccession of benthic foraminifera and to consider their relation topaleoceanographic changes at abyssal depths in the East Equatorial Pacific Ocean.

The common constituents of the benthic foraminiferal association at Sites1218 and 1219 are Nuttallides umbonifer, Globocassidulina subglobosa,Pseudoparrella exigua, Oridorsalis umbonatus and Cibicidoidesmundulus0(Takata & Nomura, 2005. ODP Sci. Results). Based on factor


FORAMS 2006


FORAMS 2006Faunal changes of Oligocene benthic foraminifera in the Eastern Equatorial Pacific sites of ODP Leg 199

Hiroyuki Takata; Ritsuo Nomura & Koji Seto

analysis, three factor assemblages were recognized. The Factor 2 assemblageis characterized by Cibicidoides spp. and O. umbonatus, and is common inthe lower part of the lower Oligocene, whereas the Factor 1 assemblage,characterized by N. umbonifer, is abundant mainly in the upper part of thelower Oligocene and the upper Oligocene. The Factor 3 assemblage, dominatedby P. exigua, is common around the Oligocene/Miocene boundary.

In addition, the Factor 1 and 2 assemblages show several relatively short-term fluctuations throughout the Oligocene, mainly associated with Oi events(Miller et al., 1991; Pekar et al., 2002. Geology). The Factor 2 assemblageoccurred abundantly around Oi1a, Oi1b and Oi2, whereas peak abundances ofthe Factor 1 assemblage were observed around Oi2a, Oi2b and Oi2c. Thus,relatively short-term fluctuations of these benthic foraminifera at abyssal depthsof the Eastern Equatorial Pacific Ocean are likely related to Oi events. N.umbonifer, the dominant species of the Factor 1 assemblage, is related toSouthern Ocean deepwater flow and/or carbonate undersaturation of deepwaters. Therefore we suggest that changes in the characteristics of the deepwatermasses may be responsible for such relatively short-term fluctuations inforaminiferal assemblages. In addition, the down-hole distribution of planktonicforaminiferal abundance is negatively correlated to the Factor 1 assemblage.Relatively short-term occurrences of benthic foraminifera in the EquatorialPacific Ocean may be related not only to the corrosivity of deep waters butalso to the production of calcareous materials in the surface waters.

513

How soon was food delivery to the sea floor restored after theCretaceous/Paleogene plankton extinction?

Ellen Thomas

Department of Geology and Geophysics, Yale University, New Haven, CT 06520-8109, [email protected]

At the Cretaceous/Paleogene boundary deep-sea benthic foraminifera,in stark contrast to planktic forms, did not suffer significant extinction, but theirassemblages underwent temporary restructuring commonly attributed to collapseof the pelagic food web. It seems improbable that such minor net changescould have been the response to a major, several-million-year-long, collapse ofoceanic productivity and the ‘biological pump’ (“Strangelove Ocean”), assuggested by the collapse of the gradient in carbon isotope values betweenbenthos and plankton (foraminiferal and/or bulk carbonate). Productivity (interms of biomass, not diversity) could have recovered as soon as light returnedafter the impact: calcareous nannoplankton suffered severe extinction, butdiatoms and prokaryote photosynthesizers survived, and the dinoflagellatecalcareous cyst Thoracosphaera bloomed post-extinction. The extinction ofsome groups lessened competition for nutrients, with blooms of survivors leadingto local/regional anoxia (e.g., Southern Spain). The lack of benthic-planktongradient in carbon isotope records persisted for several millions of years,suggesting that transfer of organic matter to the sea floor (thus benthicforaminifera) remained low as the result of extinction of fecal pellet producersand/or a shift to smaller-celled primary producers (‘living ocean model’; d’Hondtet al., 1998). The lack of extinction of benthic foraminifera, however, arguesfor a faster recovery of both productivity and food transfer to the sea-floor.Transport of organic matter to the sea-floor may have recovered, becauseother processes of transport to the sea-floor than incorporation in fecal pelletsmay have worked, such as coagulation of organic particles by sticky diatomsand cyanobacteria, various methods of ballasting with biogenic silica orterrigenous dust. If atmospheric CO2 levels were high after the impact,decreased calcification of the surviving calcareous nannoplankton may haveled to increased delivery of organic matter to the sea floor because of increasedformation of sticky polysaccharides. A rapid recovery of both productivity andthe carbon pump leaves the persistent collapse of benthic-planktic carbon isotope


FORAMS 2006


FORAMS 2006How soon was food delivery to the sea floor restored after the

Cretaceous/Paleogene plankton extinction?Ellen Thomas

gradients to be explained. First, light carbon isotope values in bulk carbonateand planktic foraminiferal tests, reflecting the carbon isotope values of totaldissolved carbon in surface waters, may not represent a drop in productivity. Anegative carbon isotope anomaly has also been observed in terrestrial materials,indicating that a marine-productivity explanation is not sufficient. The excursionto lower values might (at least in its early, more extreme part) have been causedby an input of light carbon in the surface ocean-atmosphere system (notpenetrating into the deep sea), either as the result of biomass burning or bymethane liberated from dissociation of gas hydrates due to massive slumpingon continental margins. Second, at least part of the surface isotope signal mayreflect ‘vital effects’. The carbon isotope values reflecting isotope values oftotal dissolved carbon in surface waters must by necessity be measured oncalcareous nannofossils (bulk records) and/or planktic foraminifera. Both groupsunderwent severe extinction, so that post-extinction records are derived fromdifferent species than the pre-extinction records. Post-extinction calcareousnannoplankton is dominated by bloom species such as Thoracosphaera, andrelated Cretaceous and Recent species have light carbon isotopesignatures.Third, the bulk record at some sites may be affected by diagenesis,as common in low-carbonate sediments. The three possibilities are not mutuallyexclusive, and the Cretaceous/Paleogene surface-bottom carbon isotope gradientcollapse thus may reflect a more complex signal than one of collapsedproductivity only. If both productivity and food transfer to the deep sea floorrecovered faster than assumed earlier, the recovery of marine ecosystems (asto biomass, not as to diversity) would be similar to the rapid recovery postulatedfor terrestrial ecosystems.

515

Record of the Paleocene/Eocene boundary global warmingimpact on deep-sea benthic foraminifers at low latitudes

(Kharrouba section: Tunisia)

Lamia Zili & Dalila Zaghbib-Turki

Faculté des Sciences de Tunis, Département de Géologie Campus universitaire, 2092 Tunis, [email protected]

The rapid global warming across the Paleocene/Eocene (P/E) inducedchanges in the benthic foraminiferal assemblages, and caused a destabilizationof the benthic assemblages resulting in drastic extinction. This bioevent hasbeen labelled the Benthic Foraminiferal Extinction Event (BFEE), and is welldocumented in some sections in the Tethyan realm, e.g., in Spain (Zumaya,Alamedilla, Caravaca sections), in Egypt (Dababiya section) and in Tunisia(section Ellès). In Tunisia, the P/E transition occurs in the upper part of the ElHaria Formation, at a transition from a clay-rich to a limestone-rich facies. Inthe Kharrouba section in northern Tunisia, about 200 km to the North of theEllès section, this part of the El Haria Formation is well exposed. We collectedand investigated 81 samples across a 31.40 m thick interval into the P/Etransition. Samples were spaced at 10 cm intervals close to the P/E transition,at 30 cm and then 70cm above and below the transition. Our investigationsincluded high resolution biostratigraphic studies and paleoecological analysis.The deposits interval is rich in high diversified assemblages of small benthicforaminifers associated, as well as abundant Planktonic specimens. The samplesrange from late Paleocene to early Eocene in age, including the P5 and P6planktonic foraminiferal Biozones. The high Planktonic/Benthic ratio valuesand the estimated depth range of benthic species (e.g., Tappanina selmensis,Gaudryina pyramidata, Bulimina midwayensis, and Nuttallinella coronula)in the Kharrouba section indicate that the environment was bathyal throughoutthe P/E transition period. Statistical analysis of the benthic Foraminifera (73species) shows a severe temporary disappearance of the majority of species,with a low-diversity in the benthic assemblages present just after this temporarydisappearance in an interval of about 30cm thick. This bioevent, probably thelocal expression of the global BFEE, occurred after the Last Appearance (LA)of M. velascoensis, within the M. subbotina Zone. Throughout the 30cminterval, benthic foraminifers are rare, and their assemblages are dominated by


FORAMS 2006


FORAMS 2006Record of the Paleocene/Eocene boundary global warming impact on deep-sea benthic

foraminifers at low latitudes (Kharrouba section: Tunisia)Lamia Zili & Dalila Zaghbib-Turki

bolivinids. The onset of this interval is marked by temporary disappearance ofall the epibenthic species and many endobenthic ones.

The relative abundance of bolivinids increases at this interval, from 16.5%to 40% average. The bolivinid assemblages also contain common endobenthicmorphotypes such as the calcareous Tappanina (11.1- 14.3%) and Dentalina(7-22%) and Aragonia (11.1-21.4%), with scarce and sporadic Oolina,buliminids, Zeauvigerina and Fursenkoina. During this bioevent in the lowerpart of the Morozovella subbotinae Zone (P6b), among the planktonicforaminifers’ surface dwellers Acarinina species increased in relative abundance.

Immediately above as well as below the BFEE interval, the assemblagesare more diverse, and bolivinids are less abundant (i.e., 16.5% below, 12.5%above the BFEE).

Hollis et al. (2005. Palaeogeography, Palaeoclimatology,Palaeoecology, 215: 313–343) estimated the sedimentation rate for the earlyEocene at 1.4 cm/kyr to 2.7 cm/kyr. So, considering that the BFEE interval is30cm thick in the Kharrouba section, we estimate the duration of the smallbenthic foraminifers’ temporary disappearance event between 11.1 kyr to 21.4kyr. These values are included within the duration of the carbon isotopeexcursion (CIE), which was estimated by Röhl et al. (2000. Geology, 28: 927-930) at about 220 Kyr.

the micropaleontology of critical boundaries file473 the micropaleontology of critical boundaries...

Documents