8. site 978
TRANSCRIPT
Comas, M.C., Zahn, R., Klaus, A., et al., 1996Proceedings of the Ocean Drilling Program, Initial Reports, Vol. 161
8. SITE 9781
Shipboard Scientific Party2
HOLE 978A
Date occupied: 1600, 15 June 1995
Date departed: 0230, 21 June 1995
Time on hole: 5 days, 10 hr, 30 min
Position: 36°13.867'N, 2°3.424'W
Drill pipe measurement from rig floor to seafloor (m): 1941.0
Distance between rig floor and sea level (m): 11.6
Water depth (drill pipe measurement from sea level, m): 1929.4
Total depth (from rig floor, m): 2639.0
Penetration (m): 698.0
Number of cores (including cores having no recovery): 53
Total length of cored section (m): 504.2
Total core recovered (m): 406.66
Core recovery (%): 80.7
Oldest sediment cored:Depth (mbsf): 698.0Nature: ClaystoneAge: Miocene
Comments: Drilled from 0.0 to 213.0 mbsf spot coring Core 1R (110.3-119.9 mbsf) and Core 2R (168.4-178.0 mbsf).
Principal results: Site 978 (proposed Site Alb-4) is located in the EasternAlboran Basin to the south of Cabo de Gata and 24 km north of Site 977.The site lies in an small east-west-trending basin within the same 35-km-wide graben as Site 977, but north of the Al-Mansour Seamount. Site 978was selected because, like Site 977, seismic data at this site show a lowersequence that may represent the synrift sediments that filled the EasternAlboran Basin, overlain by uniform, flat-layered sediments. We drilledSite 978 to complete objectives that were not achieved at Site 977: (1) topenetrate a major unconformity, which we were unable to penetrate at Site977; and (2) to sample the underlying synrift sequence, in order to deter-mine the age and nature of these deposits and to identify the relative pro-portions of synrift and postrift subsidence. In addition, Site 978 results,like Site 977, will permit accurate seismic correlation between the Albo-ran Sea Basin and the South Balearic Basin.
A continuous sequence of 485.3 m (from 213 to 694.3 mbsf) of upperMiocene (Zone NN11) to Pleistocene (Subzone NN19) sediments was re-covered at Site 978. The Pliocene/Pleistocene boundary, as approximatedby the first occurrence of Gephyrocapsa oceanica, is between 222.77 and223.35 mbsf; the Miocene/Pliocene boundary occurs between 607.51 and611.39 mbsf. All Miocene cores are assigned to Zone NN11 (Messinianor uppermost Tortonian). In the Pliocene interval, foraminifers are abun-dant and preservation is generally good. Miocene foraminifers are moder-ately to poorly preserved. Using foraminiferal and nannofossil ages andgeomagnetic polarity events, sedimentation rates are 127 m/m.y. for the
'Comas, M.C., Zahn, R., Klaus, A., et al., 1996. Proc. ODP, Init. Repts., 161:College Station, TX (Ocean Drilling Program).
2 Shipboard Scientific Party is given in the list preceding the Table of Contents.
Pleistocene, 111 m/m.y for the upper Pliocene, 120 m/m.y. for the lowerPliocene, and 156 m/m.y. for the upper Miocene.
The sedimentary sequence sampled at Site 978 was divided into threelithologic units:
Unit I (213.0-620.9 mbsf). This unit consists of early Pleistocene toPliocene grayish olive nannofossil clay to claystone that is variably bio-turbated. Foraminifers and shell fragments are dispersed throughout theunit. The carbonate fraction consists predominantly of nannofossils, mi-crite, bioclasts, and foraminifers. Terrigenous components include quartz,feldspar, mica, sedimentary and low-grade metamorphic rock fragments,and accessory minerals such as garnet and zircon. Minor amounts of or-ganic debris (up to 5%) and diagenetic opaque minerals (up to 3%) arepresent. On the basis of their distinct color, lithological associations, andsedimentary structures, three subunits have been distinguished withinUnit I.
Unit II (620.9-630.67 mbsf). This unit consists of an upper Miocenegravel-bearing interval containing pebbles of volcanic and sedimentaryrocks. The contact between Units I and II was not recovered. Some peb-bles have smooth, rounded, weathered? surfaces and some are partly coat-ed by a thin microcrystalline calcareous laminae (zeolites and smectite),possibly representing matrix or cement. The pebbles are formed of andes-itic basalt to andesite, chert, limestone, quartzite, and metamorphic rocks.
Unit III (630.67-694.3 mbsf). This unit consists of Miocene sandy andsilty layers that exhibit parallel and cross lamination, and are inverse tonormal grading. Sparse bioturbation and in situ brecciation and clasticdikes are observed throughout this unit.
Sediment bedding is mostly horizontal and occasional slump foldingand small synsedimentary faults occur. Slump folds are well preservednear the base of the Pliocene. Late Miocene sediments are significantlymore consolidated than the Pliocene sequence above. Bedding in the Mi-ocene section is also mostly horizontal, but some units are cut by numer-ous dilational fractures with irregular orientations. The fractures possiblyrepresent hydraulic fractures formed by overpressured and underconsoli-dated horizons within the sequence.
Carbonate content varies between 10% and more than 60% in thePliocene sediments. Miocene sediments are distinctly lower in carbonatecontent. Total organic carbon (TOC) averages 0.3% and reaches values upto 0.9% in some organic-rich layers. Organic C/N ratios are mostly be-tween 4 and 8. From Rock-Eval analysis we infer that the organic matterhas been heavily oxidized, probably by microbial reworking.
Concentrations of headspace methane are high in sediments at Site978. The source of the methane is probably in situ microbial fermentationof marine organic matter. Concentrations of propane, wo-butane, and iso-pentane exceed or equal those of ethane in sediments from about 300 mbsfto 500 mbsf. These C3, C4, and C5 gases were probably produced by ther-mal degradation of sedimentary organic matter.
Interstitial water salinity, chloride, sodium, and calcium increasedownhole with a steepening of the concentration gradients below 450mbsf. Sulfate concentrations are close to zero until 450 mbsf and increasesteeply below 500 mbsf. Because no halite salts are known at depth in thisarea, the high concentrations of these elements are likely derived from pa-leo-seawater or lateral migration of saline fluids from the Messinian halitedeposits that are known to occur in the South Balearic Basin, about 30 kmeast of Site 978. The downhole lithium increase may also be partly relatedto "evaporitic" fluids. Alkalinity shows a maximum of 3.5 mM at 269.5mbsf that corresponds to the highest ammonia concentrations, indicatingthat organic matter decomposition is most extensive at that depth. Magne-
355
SITE 978
sium concentrations are consistently below seawater concentrations, indi-cating precipitation of high-magnesium calcite or dolomite in thesediments. Strontium shows a maximum at 492.20 mbsf, likely indicatingcarbonate recrystallization.
At least 11 magnetic polarity zones are identified between 390 and610 mbsf at Site 978. Correlation with biostratigraphic data suggests thatthese represent polarity subchron C2An.2n through subchron C3n.4n(3.22 to 4.98 Ma). A sharp increase in intensity occurs at 440 mbsf, about50 m below the last well-defined polarity change. A similar increase in in-tensity was observed at Site 977 at 420 mbsf indicating good correlationbetween the two neighboring sites. Remanent directions, however, aresubstantially different between the sites, probably because of differentcoring techniques. RCB drilling at Site 978 resulted in the only reasonablemagnetostratigraphy obtained during Leg 161, as well as better preserva-tion of sediment structures and less intense biscuiting than at Site 977,which was drilled using XCB.
The post-Messinian stratigraphy established at Site 978 supports ourresults and interpretations from Site 977, and an accurate correlation be-tween the post-Messinian sequence at both sites is feasible. The upper-most-Miocene gravel-bearing interval containing pebbles of volcanicrocks in Unit II, encountered at 620.9 mbsf at this site, can be seismicallycorrelated with the gravel interval sampled at 598.5 mbsf at Site 977. Thisconfirms not only that this gravel-bearing sedimentary interval corre-sponds to the "M"-reflector, but that this reflector represents a major ero-sional event in the Eastern Alboran Basin, possibly from the earlyPliocene flooding of the Mediterranean.
Drilling at Site 978 was successful in sampling the postrift and the up-permost part of the synrift sequence of the Eastern Alboran Basin and indetermining that late synrift sediments correspond to the upper Miocene(Tortonian). Post-cruise studies will help to clarify the paleodepth of dep-osition for this upper Miocene facies and will allow us to evaluate the rateof synrift to postrift subsidence for the Eastern Alboran Basin.
BACKGROUND AND OBJECTIVES
Site 977 Background and Objectives section was written for bothSites 977 and 978. See "Background and Objectives" section, "Site977" chapter.
OPERATIONS
Transit Site 977 to Site 978 (Alb-4B)
After the short, 13-nmi (1.5 hr, 8.67 nmi/hr) transit to Site 978, wedeployed two beacons at 1600 hr and 1840 hr, respectively, on 15June. No site survey was performed since existing seismic data weresufficient to select the site and to correlate coring results throughoutthis part of the Eastern Alboran Basin. The elevation of the DESabove sea level was 11.60 m for Hole 978A.
Hole 978A (Alb-4B)
We offset the ship 100 m northwest of the beacon to ensure thatwe were >0.5 nmi away from the known coordinates of a telecommu-nication cable. Hole 978A was drilled at 36°13.867'N, 2°03.424'W.The same RCB BHA was run as was used in Hole 977A, except thatwe added a new MBR and drill bit. To save time and reach the deepobjectives as quickly as possible, the scientists requested the bit belowered to the seafloor without using the VIT to determine the exactseafloor depth. The seafloor depth was determined to be at 1954 mbrf(1942.4 mbsl) based on the drill string weight indicator as the bit en-tered the seafloor. (Note: The seafloor depth was later adjusted to1941 mbrf or 1929.4 mbsl; see below). Hole 978A was spudded at2100 hr, 15 June.
The hole was drilled with a center bit in place to 110.3 mbsf(2064.3 mbrf) where the first RCB core was taken (Table 1; see also
Table 1. Site 978 coring summary.
Core
161-978A-
Date(June 1995)
Time(UTC)
Drilled from 0.0 to 110.3 mbsf1R 16 0000
Drilled from 119.9 to 168.4 mbsi2R 16 0315
Drilled from 178.0 to 213.0 mbsi3R4R5R6R7R8R9R
10R11R12R13R14R15R16R17R18R19R20R21R22R23R24R25R26R27R28R29R30R31R32R33R34R35R36R37R38R39R40R41R42R43R44R45R46R47R48R49R50R51R52R53R
Coring totals:Drilled:Total:
1616161616161616161616161616161617171717171717171717171717181818181818IS181818181819191919191919191920
063007200755083509201020112012201330144015501715183520152140230000150115022003300450062008051000120014051630181522000000020003400510070009001100134016201900212023450145030004550900122016001835202022300130
Depth(mbsf)
110.3-119.9
168.4-178.0
213.0-222.7222.7-232.3232.3-236.2236.2-245.9245.9-255.5255.5-265.1265.1-274.8274.8-284.3284.3-293.9293.9-303.6303.6-313.1313.1-322.8322.8-332.5332.5-342.2342.2-351.8351.8-361.4361.4-371.0371.0-380.6380.6-390.2390.2-399.8399.8-409.3409.3-418.9418.9-428.5428.5-438.1438.1-447.8447.8-457.5457.5-467.1467.1-476.7476.7-486.3486.3-495.9495.9-505.5505.5-515.2515.2-524.9524.9-534.5534.5-544.1544.1-553.7553.7-563.3563.3-572.8572.8-582.5582.5-592.1592.1-601.7601.7-611.3611.3-620.9620.9-630.6630.6-640.3640.3-649.9649.9-659.6659.6-669.2669.2-678.8678.8-688.4688.4-698.0
Lengthcored(m)
9.6
9.6
9.79.63.99.79.69.69.79.59.69.79.59.79.79.79.69.69.69.69.69.69.59.69.69.69.79.79.69.69.69.69.69.79.79.69.69.69.69.59.79.69.69.69.69.79.79.69.79.69.69.69.6
504.2193.8698.0
Lengthrecovered
(m)
0.02
0.02
1.637.293.488.848.868.998.958.176.759.038.489.558.037.819.819.129.579.178.639.879.839.439.879.969.849.919.207.019.359.889.859.898.619.029.859.269.559.689.467.928.985.810.090.034.578.809.778.022.262.995.90
406.66
Recovery(%)
0.2
0.2
16.875.989.291.192.393.692.286.070.393.189.298.482.880.5
102.095.099.795.589.9
103.0103.098.2
103.0104.0101.0102.095.873.097.4
103.0102.0102.088.793.9
102.096.499.5
102.097.582.593.560.50.90.3
47.191.6
101.083.523.531.161.4
80.7
Note: See also detailed coring summary on the CD-ROM, back pocket, this volume.
detailed coring summary on the CD-ROM, back pocket, this vol-ume). The hole was then advanced (without coring) from 119.9 to168.4 mbsf where a second RCB core was attempted. Recovery inCores 978A-1R and 2R was almost zero (0.2%). The hole was thendrilled from 178.0 to 213.0 mbsf where we started continuous RCBcoring. At this depth, the formation was firm enough to be recoveredwithout being washed away. Core 5R was advanced only 3.9 m fordrilling convenience; the driller then could work with a full kelly.
RCB Cores 3R to 53R were taken from 213.0 to 698.0 mbsf(2154.0 to 2629.4 mbrf). Recovery from the interval from 213.0 to611.3 mbsf was 364.19 m (91%). Recovery was poor in the interlay-ered sands and gravels. The total recovery for Hole 978A was 406.7m (80.7%; Table 1). Coring parameters were 4-25,000 lb WOBwhile rotating at 50-70 rpm with 100-200 amps torque, circulatingseawater at 30-50 spm with pressures ranging from 150 to 400 psiwith the core barrel installed.
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SITE 978
A bit change was required to complete the hole, so we deployed afree-fall funnel (FFF) at 0530 hr, 20 June. When pulling out of theseafloor, several attempts were required before the bit would clear theFFF without dragging the FFF up. The back-reaming buttons on thebit were apparently catching the lower lip of the FFF. We rotated thepipe approximately one-quarter turn with chain tongs on the rig floorbefore we saw on the VIT that the FFF had dropped off,and the pipewas then withdrawn from the FFF.
Upon clearing the FFF it was noted that the drill pipe depth wasshallower (-17 m; 1937 mbrf) than first reported. After attaching anew bit, we ran it back to the seafloor and reentered the FFF, whileobserving with the VIT. The accurate seafloor depth was 1929.4 mbsl(1941 mbrf). All previous depths were changed to reflect this correctdepth.
The FFF was entered at 1530 hr, 20 June. The drill pipe was runinto the hole to 33.27 mbsf (1974.27 mbrf) where it met resistancefrom the formation, suggesting that we probably did not reenter theprevious borehole. Several attempts were made to find the same holeby raising and lowering the drill pipe. We picked up the circulatinghead and attempted to wash down and hopefully locate the hole; how-ever, the bit met with the same amount of resistance. Finally, the topdrive was picked up, and we unsuccessfully attempted to find the holeby rotating and washing to 150.21 mbsf (2090.21 mbrf). After 6.5 hrof unsuccessful attempts to reenter the same hole, we decided to ter-minate the hole and move on to the next site. A slug of heavy mudwas placed in the hole prior to pulling out. The drill pipe cleared theseafloor at 2300 hr, 20 June. The beacons were released and recov-ered while the drill pipe was being pulled. The bit cleared the rotarytable at 0230 hr, 21 June 1995.
Hole 97 8A exhibited similar hydrocarbon patterns as Hole 977A.Core 978A-18R contained the maximum methane recorded for thehole of 20,710 ppm. This was accompanied by 10 ppm of C2,77 ppmof C3, 9 ppm of IC4, and 8 ppm of IC5. Gas content began to decreasebelow Core 978A-25R. No gas trends were observed that were con-sidered reason to abandon the hole.
LITHOSTRATIGRAPHY
Unit Descriptions
Site 978 is located within the Eastern Alboran Basin in a smallnortheast-southwest-trending sub-basin flanked to the north by theMaimonides Ridge and to the south by the Al-Mansour Seamount. Asingle RCB hole (Hole 978A) was drilled at this site. The uppermostsection (213 m) was drilled without coring except for two spot cores(Cores 978A-1R [110.3-119.9 mbsf] and 978A-2R [168.4-178.0mbsf]) of which all recovery (2 cm per core) was given to the paleon-tologists. As we did not describe samples from Cores 978A-1R and2R, they are not included in our discussion of the lithostratigraphy(see "Biostratigraphy" section, this chapter). Continuous coring be-gan at 213 mbsf (Core 978A-3R) and continued to 698 mbsf (Core978A-53R). Based on composition and sedimentary structures, wehave subdivided the 485-m sedimentary sequence recovered at Hole978A into three Lithologic Units (I, II, III), and further subdividedUnit I into three subunits (Table 2; Fig. 1).
Unit I: Pleistocene to Pliocene
Hole 978A, 213.0-620.9 mbsf, Core 978A-3R, 0 cm to Section978A-45R-CC, 0 cm.
The main lithology within Unit I is grayish olive nannofossil clayto claystone. A diverse suite of minor lithologies is present and theseare listed in Table 2. The color changes for each lithology are present-ed in Figure 2.
Unit I is variably bioturbated with common Planolites, Chon-drites, and Zoophycos, and less frequent halo, composite, andSkolithos burrows (Figs. 3, 4). Locally, burrows are partly to wholly
infilled by pyrite. Foraminifers and shell fragments are dispersedthroughout the unit, with some local concentrations in burrow fillsand as discrete sandy/silty beds/laminae. The latter foraminifersandy/silty layers range in thickness up to a few centimeters, haveabrupt upper and lower contacts, and are locally parallel-laminated(Fig. 5). Concentrations of dark gray, mm-sized fecal pellets arepresent in Cores 978A-15R through 19R and Core 978A-27R (Fig.6).
Smear-slide data from Unit I indicate similar components but invariable proportions throughout the unit, resulting in a large range ofminor lithologies, as listed in Table 2. The main components are clay-sized material and carbonate. The carbonate fraction consists pre-dominantly of nannofossils, micrite, bioclasts, and foraminifers. Themicrite component includes recrystallized nannofossils, rhombs, andirregular granular carbonate. Other terrigenous components arequartz, feldspar, mica, sedimentary and low-grade metamorphic rockfragments, and accessory minerals such as garnet and zircon. Minoramounts of organic debris (up to 5%) and diagenetic opaque minerals(up to 3%) are also present.
Downhole variations in selected components from smear-slideanalyses, along with measured carbonate data are given in Figures 2and 7. Compositional shifts shown in Figures 2 and 7, along withdownhole variations in sedimentary structures, have been used to dif-ferentiate several subunits within Unit I (IA, IB, and IC; Table 2).The boundaries between subunits are somewhat gradational, hencethe dashed lines in Table 2.
Subunit IA: Pleistocene to Pliocene
213.0-342.2 mbsf, Core 978A-3R, 0 cm to Section 978A-17R-1,0 cm).
Subunit IA is characterized by the presence of slightly darker lay-ers that alternate with the dominant lithology of olive gray (5Y 4/1)to dark greenish gray (5GY 4/1) nannofossil clay. The darker beds(Type 1) range in thickness up to 65 cm, and commonly begin with amedium-dark gray (N4) sand to silt interval above an abrupt base(Fig. 8). The basal sandy/silty intervals range in thickness up to 10 cmand often exhibit normal grading and parallel lamination. Thesecoarser sediments pass up into bioturbated finer grained ones thatmake up the remainder of the dark layer (e.g., olive gray (5Y 4/1)nannofossil clay; dark greenish gray (5GY 4/1) nannofossil-rich siltyclay; dark greenish gray (5GY 4/1) calcareous silty clay; grayish ol-ive (10Y 4/2) calcareous clay). Some dark layers have abrupt basalcontacts and bioturbated tops, but lack a sandy/silty basal interval(e.g., Fig. 4).
A unique semi-indurated calcareous bed (packstone) is present inSubunit IA (Fig. 9; Core 978A-8R at 60-97 cm). As determined mac-roscopically during core description and microscopically in smearslide and thin section, the main allochems are bioclastic debris in-cluding foraminifers and fragments of red algae, molluscs, and wormtubes?. Other minor components include fragments of echinoderms,coral, bryozoans, and siliciclastic debris. The rock has a grain-sup-ported fabric, with microsparite matrix and rare carbonate cementwithin intra-allochem pores (e.g., foraminifer chambers) and as mi-nor overgrowths on echinoderm fragments. Microborings within al-lochems are commonly filled with pyrite?. This packstone bed hasabrupt basal and upper contacts, and shows a crude upward-finingtrend from granule- to sand-sized material.
Subunit IB: Pliocene
342.2-409.3 mbsf, Core 978A-17R, 0 cm to Section 978A-24R-1,0 cm.
Subunit IB is a fairly homogeneous transitional subunit that con-tains a few, poorly developed versions of the dark beds found in Sub-unit IA (Type 1), and those present in Subunit IC (described below).
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SITE 978
Table 2. Unit and subunit summary for Site 978.
Unit Series LithologySedimentary
structures OccurrenceInterval(mbsf)
IA late Pliocene Major:to Pleistocene Nannofossil clay
Minor:Nannofossil-rich clay, nannofossil-rich silty clay,
nannofossil silty clay, calcareous clay, calcareoussilty clay, foraminifer sand, sandy silt, silt, sandysilty clay, nannofossil ooze, packstone
IB late Pliocene Major:Nannofossil clay
Minor:Nannofossil silty clay, foraminifer silt to sand
IC early Pliocene Major:to late Nannofossil claystone, calcareous claystone,Pliocene calcareous silty claystone
Minor:Nannofossil silty claystone, nannofossil chalk,
foraminifer siltstone to sandstone, sandy siltyclaystone
II early Pliocene Pebbles of volcanic and sedimentary rocksto?
III Miocene Calcareous siltstone, calcareous silty claystone,calcareous silty sandstone, silty claystone,claystone, clayey silty sandstone, clayeysandstone, nannofossil-rich claystone
Structureless, bioturbation (Planolites,Chondrites, and Zoophycos), rare color banding,mottling, lamination, and graded bedding
Bioturbation (Chrondrites, Planolites, andZoophycos), rare laminations, localconcentrations of shell fragments anddisseminated pyrite
Bioturbation (Zoophycos, Chondrites, andPlanolites) mottling, lamination, soft-sedimentdeformation (slump?), local concentrations ofshell fragments and disseminated pyrite
None (poor recovery)
Normal grading and upward coarsening, inversegrading, parallel lamination, cross-lamination,mottling, minor bioturbation, in situ breccia
Core 978-3R-CC, 0 cm, toCore 978A-17R-1, Ocm
Core 978A-17R-1, 0 cm, toCore 978A-24R-1, Ocm
Core 978A-24R-1, 0 cm, toCore 978A-46R-1, Ocm
Core 978A-45R-1, 0 cm, toCore978A-47R-l,7cm
213.0-342.2
342.2-409.3
409.3-620.9
620.9-630.67
Core 978 A-47R-1, 7 cm, to 630.67-694.3Core 978A-53R-CC, 13 cm
It is characterized by rather uniform color and composition (Table 2;Figs. 2, 7), minor bioturbation, and the presence of at least one thinforaminifer silt/sand layer per core.
Subunit IC: Pliocene
409.3-620.9 mbsf, Section 978A-24R-1, 0 cm to Section 978A-46R-l,0cm.
The top of Subunit IC marks where the sediments are sufficientlyindurated to use the suffix "stone" and the term "chalk." Subunit ICis characterized by the presence of thick alternating dark and lightbeds of nannofossil claystone, calcareous claystone, nannofossil siltyclaystone, and calcareous silty claystone. The lighter beds are com-monly greenish gray to light olive gray to dusky yellow green (5GY5/1; 5GY 6/1; 5Y 6/1; 5Y 5/2; 5GY 5/2; 5Y 5/1), whereas the darkerbeds are commonly dark greenish gray to grayish olive to olive gray(5GY 4/1; 10Y 4/2; 5Y 4/1). The darker beds are progressively lesscalcareous and the lighter beds become progressively more rich incarbonate content (chalk) with depth (Fig. 7). The darker beds (Type2) have common Chondrites burrows; sharp bases (Fig. 10) are com-monly obscured by bioturbation (Fig. 11), are gradational, and havebioturbated upper contacts (Fig. 12). The lighter, more intensely bio-turbated intervals have abundant Planolites burrows. The major com-positional distinction between light and dark intervals is theproportion of nannofossils: the lighter layers commonly contain 15%more than darker intervals in the same core, hence the somewhat bi-modal distribution of carbonate and nannofossil content in SubunitIC (Fig. 7).
The downhole occurrences of dark beds with sharp basal contacts(Type 1, Subunit IA) vs. those with gradational- or bioturbated-basalcontacts (Type 2, Subunit IC) is summarized in Figure 13. The thick-ness distribution of these intervals is shown in Figure 14, and thedownhole variation in thickness is pictured in Figure 15. In general,Type 1 beds are more common in the upper 200 m of Unit I, whereasType 2 beds are prevalent in the lower 200 m of Unit I. The frequency
of these intervals can be calculated using the sediment accumulationrates presented in the "Biostratigraphy" section, this chapter. Thesediment accumulation rate for the interval 223.03-375.57 mbsf, azone with 114 Type 1 beds, is 143 m/m.y., whereas the sediment ac-cumulation rate for the interval 398.69-570.2 mbsf, a zone with 87Type 2 beds, is 93 m/m.y. The calculated recurrence interval for theType 1 beds is 9357 yr, whereas the recurrence interval for the Type2 beds is 20,116 yr.
An interval of laminated nannofossil chalk exhibits soft-sedimentfolding (slump?) from Sample 978A-43R-4,39 cm to 43R-5,110 cm.The folded sediment is crosscut by burrows (Fig. 16). The base of theslump is marked by a shear zone where darker burrow fills have beensmeared out; this interval is also associated with dewatering veinlets(Fig. 17). A silty clay layer directly overlying the slumped interval(Core 978A-43R-4, at 23-26.5 cm; Fig. 18) contains approximately15% zeolite minerals and relict microlitic textures in grains, suggest-ing that it may be an altered tuff.
Unit II: Lower Pliocene to Upper Miocene
Hole 978A, 620.9-630.67 mbsf, Section 978A-46R-CC, 0 cm toSection 978A- 47R-1, 7 cm).
Unit II constitutes a gravel-bearing, low-recovery interval. Thecontact between Units I and II was not recovered. The lithologiespresent in the short interval recovered in Core 978A-45R are similarto those found in Unit I (calcareous chalk and nannofossil silty clay-stone). Because of low recovery (0.9%) in this interval (611.3-620.9mbsf) and the resultant uncertainty as to the position of the recoveredmaterial within the cored interval, the top of Unit II is placed justabove the first occurrence of gravel at 0 cm in Section 978A-46R-CC.The base of this unit is placed in Core 978A-47R, at 7 cm, just belowthe lowermost interval containing loose pebbles, and above a severe-ly disrupted zone with fragments similar to underlying coherentlithologies of Unit III. (Note that some pebbles were lodged along theliner in this disrupted zone and they were placed in the uppermost
358
SITE 978
Figure 1. Simplified stratigraphic column for Site 978.
pebble-rich interval.) The ODP convention of sliding recovered inter-vals to the top of the cored interval, coupled with the moderate recov-ery in Core 978A-47R (47.1%), implies that the lower contact couldbe a few meters lower within the cored interval. Therefore, the totalthickness of the gravel-bearing interval (Unit II) may be greater than10.23 m, up to maximum of 24.97 m, with the addition of unrecov-ered intervals in Cores 978A-45R (9.51 m) and 47R (5.13 m).
The material recovered in Unit II consists of pebbles of volcanicand sedimentary rocks. They range in size from 14×11×8 mm to 40× 28 × 28 mm, and are well-rounded to angular in shape. The totalvolume of material recovered is approximately 143 cm3, with threepebbles recovered in Section 978A-46R-1 and 96 pebbles recoveredin Section 978A-47R-1. Some pebbles have smooth, rounded, weath-ered surfaces and some are partly covered by a thin coating of micro-crystalline calcareous material, zeolites, and smectite, possiblyrepresenting matrix or cement.
The pebbles were first subdivided into two groups based on initialmacroscopic inspection: one group from Core 978A-46R-1 (Group1) and the other from 978A-47R-1 (Group 2). The group from Core978A-47R-1 was further subdivided into three subgroups (Subgroups2a, 2b, 2c). Thin sections of representative samples from each of thegroups were prepared and described in detail. The first group (Group1) consists of three rounded to subangular pebbles with an averagesize of 37 × 27 × 21 mm. These pebbles likely have similar composi-tion in that they macroscopically have porphyritic texture with gray-ish green hypohyaline fine-grained matrix. In thin section, onespecimen exhibits a spherulitic to microlitic (plagioclase, pyroxene,olivine) glass matrix containing subhedral to euhedral olivine, euhe-dral pyroxene (orthopyroxene, clinopyroxene), subhedral plagioclasephenocrysts. Fe-oxides are included in the matrix and in olivine phe-nocrysts.
Group 2 is composed of mostly subrounded to subangular (round-ed 19%, subrounded 39%, subangular 27%, angular 15%) pebbleswith an average size of 14×11×8 mm. The pebbles can be divided(macroscopically) into three subgroups of probably similar composi-tion. The first subgroup (2a; Fig. 19) consists of grayish light to darkolive, primarily subangular pebbles with aphanitic and porphyritictextures. In thin section, the hypocrystalline, fine-grained, microlitic(plagioclase, pyroxene) groundmass contains subhedral pyroxene(clinopyroxene), euhedral olivine, and amphibole. A patch of vitricgroundmass is enriched in phenocrysts of pyroxene. Based on petro-graphic observations, the Subgroup 2a pebbles are likely andesiticbasalt to andesite in composition. Subgroup 2b (Fig. 20) consists ofgrayish, mostly subrounded pebbles. Petrographic examination ofone pebble from Subgroup 2b shows that it is holocrystalline and finegrained, with a seriate texture of a microlitic to spherulitic ground-mass of pyroxene and plagioclase. This groundmass contains anhe-dral phenocrysts of orthoclase, biotite, olivine, pyroxene, amphibole,quartz, and iron oxide. The amphibole and biotite phenocrysts arepartly altered to chlorite. Based on petrographic observations, theSubgroup 2b pebbles have a dacitic or trachytic composition. Thethird subgroup (2c; Fig. 21) consists of a diverse suite of nonvolcanicpebbles, with variable color and composition. They range fromrounded to subangular and are predominantly aphanitic. Macroscop-ically, this group contains pebbles of chert, limestone, quartzite, andmetamorphic rocks. A thin section produced from one pebble showsit to be a dolomicrosparite with possible ghosts of recrystallized al-lochems in a microsparite matrix.
Unit III: Miocene
Hole 978A, 630.67-694.3 mbsf, Section 978A-46R-1, 0 cm toSection 978A-53R-CC, 13 cm).
The Miocene sediments that constitute Unit III are very differentfrom the overlying marine sequences in Unit I in terms of color, com-
359
SITE 978
Munsell indexLight <s > Dark
Mica + feldspar + quartzcontent (%)
2000 1 2 3 4 5 0
Figure 2. Graphs of Munsell color variations, and %mica + feldspar + quartz and sand + silt content atHole 978A vs. depth.
60 0
Sand + siltcontent (%)
40 80 unit
1: 5Y6/1, 5GY6/1, 5Y5/22: 5Y5/1, 5GY5/1, 10Y4/2, 5GY5/23: 5Y4/1, 5GY4/1, 5Y4/4, N44: 5Y3/2, 5GY3/2, N3
cm130-i
132-
134-
136-
138-
140 - 1
Figure 3. Tree-like Skolithosl burrow. Core 978A-39R-3, 130-140 cm(558.0-558.1 mbsf).
position, and sedimentary structures. The dominant lithologies aresilty claystone, clayey siltstone, silty sandstone, claystone, sandysilty claystone, and clayey sandstone all with variable, but generallylow (14%-32%; average = 22%) carbonate content. Colors of theselithologies range from (1) light olive-, olive- to dark-greenish gray,(2) grayish olive, to (3) moderate olive brown (5Y 4/1; 5GY 4/1;5GY 5/2; 10Y 4/2; 5Y 3/2; 5Y 4/4). These lithologies are moderatelyto thinly interbedded to interlaminated. The sandy and silty sequenc-es commonly overlie sharp basal contacts that are locally scoured(Fig. 22), and exhibit parallel and cross lamination (Figs. 22, 23), andinverse (Fig. 24) to normal grading (Fig. 25). The bases of the sandyintervals are sometimes inversely graded, but then pass up into nor-mally graded sequences with cross-lamination, parallel lamination,and abrupt to gradational tops (Fig. 24). Very fine sub-millimeter-scale lamination similar to varves is locally present within the clay-rich intervals (Fig. 26). Types of sediment couplets observed includesandy siltstone and silty claystone; siltstone and claystone; and sand-stone and siltstone. Amalgamation is very common, often resulting indecimeter sequences of sharp-based siltstone and sandstone beds.Sparse burrows are present throughout the sequence (Figs. 23, 25).Other structures present in this unit include possible dish structures,in situ brecciation (Fig. 27), boudinage, faulting (Fig. 22), and clasticdikes (Figs. 28, 29). This deformation, coupled with drilling-inducedbiscuiting, inhibited detailed description of some intervals.
The primary components of the sediments in Unit III are, in de-creasing order of abundance, clay-sized material, micrite and inor-ganic carbonate, mica, quartz, nannofossils, and feldspar. Thecarbonate fraction exhibits a wide range of crystal morphologies, in-cluding needles, rhombs, and zoned rhombs. The mica category in-cludes fragments of biotite, muscovite, and chlorite. Other lessercomponents include foraminifers, bioclasts, iron oxides, rock frag-ments, accessory minerals, and plant debris. Identified accessoryminerals include zircon, sphene, and garnet. The rock fragmentspresent include quartz-mica schist, chlorite schist, shale, and lime-stone (micritic). The iron oxides are commonly associated with clayminerals in discrete particles and as coatings on feldspar grains. Pos-sible detrital gypsum was observed in a smear slide at 978A-47R-1,47 cm.
SITE 978
cm95 -i
100-
105-
110 —
cm5-
Figure 4. Sharp-based dark silty layer with abundant Chondrites burrows.Note biscuit margins at 98.5 and 103.5 cm. Core 978A-15R-4, 95-113 cm(328.25-328.43 mbsf).
7 -
9~
Figure 5. Dark gray (N4) laminated layer of foraminifer-rich sandy siltexhibiting abrupt lower and upper contacts. Core 978A-9R-3, 6-10 cm(268.16-268.2 mbsf).
Interpretation of Sediments Recovered at Site 978Unit I
The pelagic to hemipelagic sediments of Unit I contain calcareousnannofossil and foraminifer assemblages that are consistent withopen marine conditions and deposition in upper mesobathyal to lowermesobathyal depths (1000-4000 m), above the carbonate compensa-tion depth (CCD), with common reworking from shallower depths(see "Biostratigraphy" section, this chapter). Ichnofacies present inUnit I sediments (e.g., Chondrites, Zoophycos, and Planolites) alsosupport deposition in this depth range. There is some variation in car-bonate content among subunits of Unit I, particularly a tendency to-wards bimodality in Subunit IC, associated with alternating dark (lesscarbonate; 40%) and light (more carbonate; 55%) layers. As dis-cussed below, this bimodality may be linked to climatic variations.
The thin, laminated foraminiferal and bioclastic sandy/silty layersthat occur throughout Unit I are probably the product of winnowingby contour currents. Supporting evidence for this interpretationcomes from their uniform thickness (commonly 1-2 cm), their abruptbasal and upper contacts, their composition (mostly foraminifers andbioclasts, commonly dispersed in underlying lithologies), and thepresence of parallel lamination. Verification of this interpretation re-quires more detailed work, particularly grain-size analysis.
The abrupt basal contacts of the Type 1 dark beds, in addition totheir laminated to cross-laminated sandy/silty bases and bioturbatedtops, are consistent with deposition by low-density turbidity currents(Pickering et al., 1989). Alternatively, given the frequent occurrenceof the proposed foraminifer contourite layers in Unit I, the Type 1dark beds could also be the product of deposition from muddy con-tour currents. Again, detailed grain-size analysis is needed to helpdifferentiate the origin of these deposits.
The calculated recurrence interval of approximately 20,100 yr forType 2 dark beds in Subunit IC suggests that their apparent cyclicitymay be tied to climate change related to the precession of the Earth'sorbit during the Pliocene. The presence of moderately to intenselybioturbated tops and bottoms of these intervals implies that they rep-resent gradual shifts in sediment composition, rather than discreterelatively instantaneous depositional "events." The compositionalvariation between the light and dark beds is mostly a function of nan-nofossil content. In smear slides, there is no distinct difference be-tween the proportion of terrigenous silt and sand-sized componentsin the dark vs. the light layers. This would suggest that perhaps thevariations in nannofossil content are a function of surface-water pro-
361
SITE 978
2 0 -
2 5 -
3 0 -
3 5 -
4 0 -
Figure 6. Intensely bioturbated nannofossil clay with common dark millime-ter-sized fecal pellets. Core 978A-17R-3, 18-42 cm (345.38-345.62 mbsf).
ductivity, or alternatively, fluctuations in the local CCD. The recur-rence interval of the Type 1 beds, approximately half that of the Type2 beds, suggests that they could also be linked to climatic change.Somewhat coincidentally, the switch from dominantly Type 2 toType 1 dark beds is located at a change in slope of the sediment ac-cumulation curve (between 375.57 and 398.69 m; Fig. 30), at approx-imately 3 m.y., the time of initial glaciation in the northernhemisphere (Raymo et al., 1992).
Alternatively, the change in sedimentation style and frequency ofterrigenous input to the basin could be tied to basin margin tectonism.However, given the strong correlation between climate variation andthe style of sedimentation at Site 978, climatic change appears tohave exerted the most control on the Pliocene sedimentary sequenceat this site.
Lastly, the origin of the semi-indurated calcareous deposit (pack-stone) in Subunit IA (Fig. 9; Core 978A-8R at 60-97 cm), bears somediscussion. The suite of shallow-water allochems in this unit suggeststhat it was derived from a carbonate bank or reef developed on theMaimonides Ridge or the Al-Mansour Seamount. The grain-support-ed fabric, abrupt basal and upper contacts, and crude upward-finingtrend from granule- to sand-sized material are consistent with thisunit being a high concentration debris-flow deposit.
Unit II
Volcanic rocks with compositions similar to the pebbles fromUnit II (andesitic basalt to andesite, dacite, and trachyte) are knownonshore to the west of Cabo de Gata near Almeπa, Spain and fromseamounts in the Eastern Alboran Basin (volcanic Alboran Ridge).These pebbles may represent channel facies associated with a "paleo-Almeria" channel (Alonso and Maldonano, 1992). The modern Al-merfa channel presently heads in the Cabo de Gata region, and alsopasses near the Alboran Ridge before entering the sub-basin in whichSite 978 was drilled. Hence either source is plausible for the volcanicgravel in Unit II.
Unit III
The dominance of terrigenous silt- and sand-sized material withinUnit III, as well as the sedimentary structures observed, including fre-quent amalgamation of beds, are consistent with submarine fan lobeor apron deposits. The presence of inverse grading at the base of oth-erwise normally graded sandstone to siltstone intervals could be at-tributed to traction carpets, produced by shearing at the base of highconcentration turbidity currents (Pickering et al., 1989). However,the sparse ichnofacies and varve-like lamination in some intervalsmay correspond to anoxic marine bottom-water conditions or, alter-natively, to marginal brackish or possibly even lacustrine deposition.The calcareous nannofossil assemblages indicate open marine condi-tions, at least for the uppermost cores (Cores 978A-47R to 978A-50R), with poorer preservation in Cores 978A-51R to 978A-53. Incontrast, the foraminiferal assemblages, usually good indicators ofmarine environment, are poorly preserved in Unit III, and, in the caseof the planktonic foraminifers, are likely reworked. Unit III at Site978 is similar to the Miocene sediments of Unit III at Site 974, par-ticularly in terms of sedimentary structures and gross sediment com-position (see "Lithostratigraphy" section, "Site 974" chapter, thisvolume, for relevant discussion of possible depositional environ-ments).
BIOSTRATIGRAPHY
Calcareous Nannofossils:Abundance and Preservation
All samples examined from Hole 978A contain common to abun-dant calcareous nannofossils, except Samples 978A-49R-CC, 51R-
SITE 978
200
Nannofossil content (%) CaCO3 content (wt%)
0 30 60 0 30 60
£400-
α.CD
Q
600 -
Micrite content (%) £
10 20 30 E
= v • : • ; •
• : : " 1 .
•. \
• *•
. ' " 5 "• * *t
# *
s i • i •1 ' i
: i
?\ ''' : : i .
IA
IB
IC
II
4-
iii
Figure 7. Graphs of % nannofossil, CaCO3, and
micrite content at Hole 978A vs. depth. See text for
discussion.
CC, 52R-CC, and 53R-CC, in which nannofossils are few. Nannofos-sil preservation is good in Cores 978A-1R-CC to 8R-CC; preserva-tion is moderate or moderate to good in all other cores.
BiostratigraphyHole 978A (Fig. 31)
Coring was intermittent down to 213.00 mbsf, after which coringwas continuous. The strati graphic interval recovered ranges from up-per Miocene (Zone NN11) to Pleistocene (Subzone NN19F). Allzones and subzones in the Pliocene except Zone NN17 were identi-fied. Because of intermittent coring, only Pleistocene SubzonesNN19B, NN19D, and NN19F were found. The biozonal assignmentof each core and the distribution of marker species are shown in Fig-ure 31.
The Pliocene/Pleistocene boundary, as approximated by the firstoccurrence of Gephyrocapsa oceanica, lies between Samples 978A-4R-1, 6-8 cm (222.77 mbsf) and 4R-1,64-66 cm (223.35 mbsf). Thelower/upper Pliocene boundary lies between Samples 978A-28R-CC(457.71 mbsf) and 29R-2, 74-77 cm (459.75 mbsf).
The Miocene/Pliocene boundary occurs between Samples 978A-44R-CC (607.51 mbsf) and 978A-45R-CC (611.39 mbsf). All Mi-ocene cores are assigned to the Rotaria Subzone (Messinian) basedon the presence of Reticulofenestra rotaria. Also present are rare Am-arolithus delicatus down to Core 987A-53R.
Planktonic Foraminifers:Abundance and Preservation
Planktonic foraminifers are abundant and well preserved in thePleistocene in Hole 978A. In the Pliocene interval, foraminifers areabundant and preservation is generally good. From Samples 978A-33R-CC to 45R-CC, foraminifers show signs of enhanced dissolutionor fragmentation with variable amounts of deformed or flattenedtests. Miocene samples in Cores 978A-47A through 53A (641.29-694.3 mbsf) mostly yield very small (<150 µm), fragmented, or en-crusted foraminifers.
Biostratigraphy
Biozones, distribution of marker species, and sampled intervalsare shown in Figure 32.
Hole 978A (Fig. 32)
A lowermost Pliocene (MPLl)-Pleistocene sedimentary se-quence (533 m thick) was recovered from the seafloor through628.27 mbsf (Sample 978A-45R-CC). Below this, a 7-cm-thick grav-el interval was recovered, which likely indicates an unconformity in
the sedimentary sequence. The sequence from Cores 978A-47R to53R contain foraminifers of late Miocene age.
The Pleistocene was discontinuously cored and, therefore, it is notwell documented. Globorotalia truncatulinoides excelsa Zone wasrecognized only in Sample 978A-1R-CC (110.30 mbsf) and the Glo-bigerina cariacoensis/Globorotalia inflata zonal boundary(Pliocene/Pleistocene boundary) was recognized between Samples978A-3R-CC (214.25 mbsf) and 4R-1, 64-66 cm (223.35 mbsf).
The Pliocene is represented by all biozones (MPL6 throughMPL1). Globorotalia bononiensis is consistently present also inZone MPL4b. Globorotalia margaritae is discontinuously present inboth Zones MPL3 and MPL2. Within Zone MPL3, from Sample978A-29R-CC (466.70 mbsf) to 35R-3, 7-9 cm (518.27 mbsf), it iscommon only in few samples. Within Zone MPL2 G. margaritae wasnot detected from Sample 978A-39R-7, 53-55 cm (563.25 mbsf) toSample 978A-42R-CC (590.42 mbsf). This irregular distribution ofG. margaritae is believed to be controlled by ecologic factors. Anoth-er hypothesis explaining such an absence of G. margaritae could beinterpreted as a repetition of the sequence caused by the commonslumps in this interval. Zone MPL1 was identified from Sample978A-44R-CC (607.28 mbsf), in which the poorly diversified assem-blage characterized by Orbulina universa, Globigerinoides obliquus,Globigerinoides extremus, and the Globigerina bulloides group areabundant. This assemblage, which is commonly recorded at the verybase of the Pliocene in the Mediterranean, is similar to that in MPL1at Site 977.
Below Sample 978A-45R-CC (611.30 mbsf), planktonic foramin-ifers are no longer biostratigraphically reliable because they are con-sidered reworked. However, rare specimens of Globorotalia suterae,Globorotalia miotumida, Globorotalia cf. conomiozea occur fromSample 978A-47R-CC (634.93 mbsf) to Sample 978A-53R-CC(694.17 mbsf) and are indicative of Messinian age. Evidence for re-working is based on the following considerations: (1) the foramini-fers are a minor component of the residue, (2) they have the same sizeas the detrital components, and (3) the finest sediment fraction doesnot provide any residue or is barren in foraminifers. The assemblagerecorded in these samples is similar to that recorded in the Messinianinterval of Site 975.
Benthic Foraminifers
Benthic foraminifers at Site 978 (present-day water depth 1942.4m) are larger in size, more abundant, and more diverse than at Sites974 or 975, and are comparable in size and diversity to Sites 976 and977. They are diagnostic of upper mesobathyal to lower mesobathyal(1000-4000 m) depths as defined by Wright (1978). They generallycomprise <1%—2% of the total foraminiferal assemblage, exceptwhere there is evidence for downslope contamination by shelf taxathat are often abraded and mixed with deeper water assemblages.
SITE 978
cm30-
cm
3 5 -
4 0 -
4 5 -
5 0 -
5 5 -
6 0 -
6 5 -
7 0 -
7 5 -
8 0 -
8 5 -
9 0 -
9 5 -
60- 1
Figure 8. Dark silty interval with an abrupt lower contact (55 cm) overlain by athin laminated bioclastic sandy/silty layer (54-55 cm) that passes up into bio-turbated nannofossil clay. Burrow types include Planolites and Chondrites.Core 978A-15R-2, 30-60 cm (324.6-324.9 mbsf).
100- 1
Figure 9. Packstone interval with abrupt upper and lower contacts. Thematrix-rich intervals in the coarser base of the unit are probably muddy intra-clasts. The unit exhibits a crude upward-fining trend. See text for furtherdescription and discussion. Core 978A-8R-5, 56-100 cm (262.06-262.5mbsf).
364
SITE 978
cm
8 5 -
9 0 -
cm115-
120-
125-
130-
95 - 1
Figure 10. Bioturbated, abrupt lower contact of thin clay-rich darker intervalat 83-86 cm, with common Zoophycos and Chondrites. This contact wasclassified as "abrupt," making it a Type 1 dark interval. Millimeter-sizedblack spots are hollow foraminifer tests cut in half by the saw when the corewas split. Core 978A-43R-2, 82-95 cm (594.42-594.55 mbsf).
This is more frequent at Site 978 than Site 977 and occurs in discreteintervals.
In the Miocene interval, benthic foraminifers are poorly preservedand the assemblage is not indicative of a definite environment. Rarespecimens of Brizalina dentellata and Bulimina echinata, typicalMediterranean benthic species of the Messinian interval (Colalongoet al., 1979), are discontinuously present throughout the entire inter-val.
Biozonal Correlation
Correlation of the calcareous nannofossil and planktonic foramin-iferal zonations for Hole 978A is shown in Figure 33. The placement
135-
140 - 1
Figure 11. Bioturbated contact between a darker and lighter interval in Sub-unit IC. Millimeter-sized black spots are hollow foraminifer tests cut in halfby the saw when the core was split. Core 978A-28R-3, 115-140 cm (451.95-452.2 mbsf).
365
SITE 978
cm5-1
1 0 -
1 5 -
2 0 -
Number of Type 1 beds Number of Type 2 beds2 Q 0 15 30 0 15 30
300^
Figure 13. The downhole occurrence of dark beds with sharp basal contacts(Type 1) vs. those with gradational- or bioturbated-basal contacts (Type 2).
Accumulatednumber of dark beds
0 30
Figure 12. Bioturbated upper contact of a darker bed exhibiting Chondritesand composite burrows. Core 978A-36R-6, 5-24 cm (532.45-532.64 mbsf).
Figure 14. Thickness distribution of the Type 1 (abrupt base) and 2 (grada-tional- or bioturbated-base) dark beds.
of the Pliocene/Pleistocene boundary is based primarily on the cal-careous nannofossils. Miocene calcareous nannofossils and plank-tonic foraminifers are indicative of Messinian age.
Paleoenvironment
The Pleistocene-Pliocene interval is pelagic to hemipelagic withminimally greater amounts of detrital material and displaced faunathan nearby Site 977. Planktonic and benthic foraminifers are indic-ative of an open-marine environment with planktonic dominant overbenthic foraminifers. However, the regular presence of echinoid
366
SITE 978
200
Thickness of dark beds (cm)Type 1 Type 2
0 100 200 0 100 200
400
fCDQ
600
Figure 15. Downhole variation in thickness of Type 1 and Type 2 dark beds.
spines and a few inner neritic benthic foraminifers suggest weak, butcontinuous, sediment input from shallower waters.
The foraminiferal assemblage and associated sediment of the Mi-ocene interval is indicative of a depositional environment close to asignificant terrigenous source. Further, the detrital component is arelatively immature mixture of quartz, feldspars, and micas, the lattercomprising 10%—15% of the sediment (see "Lithostratigraphy" sec-tion, this chapter). Small bathyal and a few neritic benthic foramini-fers are represented. The foraminiferal assemblage shows a typicalpattern of turbiditic sediments: barren samples alternate with fossilif-erous ones. There are no clear indications of indigenous fauna of dif-ferent size fractions. On the contrary, calcareous nannofossilsindicate normal marine conditions.
Sedimentation Rates
Figure 30 shows the sedimentation rates for Hole 978A. Age dataused for calculations (Table 3) are based on first and last appearanceevents of selected nannofossils and planktonic foraminifers, and onmagnetostratigraphic chrons. Average sedimentation rates in Hole978A were 127 m/m.y. for the Pleistocene, 111 m/m.y for the upperPliocene, 120 m/m.y. for the lower Pliocene, and 156 ni/m.y. for theupper Miocene.
PALEOMAGNETISM
Fifty RCB cores were measured with the cryogenic magnetome-ter. Blanket AF demagnetization was routinely applied at 15 mT. Wecould identify several geomagnetic polarity zones in the interval be-tween 390 and 610 mbsf.
Remanent Magnetization
Declination, inclination, and intensity before and after AF demag-netization are shown in Figures 34 and 35 together with low-fieldmagnetic susceptibility (K) measured on the MST. From 210 to 440mbsf intensities (15 mT) and K are as weak as 10̂ * A/m and lO~4 SI,respectively (Fig. 35). Below 440 mbsf a sharp increase is observed,up to intensities of about 10~2 A/m and up to susceptibilities of about
cm46 - i
5 0 -
55-
6 0 -
6 5 -
7 0 -
7 5 -
80 - 1
Figure 16. Soft sediment slump folding of laminated nannofossil chalk nearthe top of a slumped interval in Subunit IC. The apparent laminations may bestretched darker burrow fills. Upper fold limb at 52-55 cm is crosscut byburrow traces. Core 978A-43R-4, 46-80 cm (597.06-597.4 mbsf).
367
SITE 978
cm
125-
130-
1 3 5 -
cm10-1
1 5 -
2 0 -
2 5 -
140"
Figure 17. Shear zone near base of slump pictured in Figure 16. Dark streaksat 125-127 cm may be sheared burrow fills. Note that this interval is alsoassociated with faint dewatering veinlets at 137-140 cm. Core 978A-43R-6,122-141 cm (600.82-601.01 mbsf).
3 0 -
Figure 18. Silty clay layer (23-26.5 cm) above the slumped interval picturedin Figure 16. Smear-slide analysis shows that it is likely an altered tuff,because it contains approximately 15% zeolite minerals and relict microliticvolcanic textures in some grains. The upward change in color from 23 to 16cm probably reflects pelagic input followed by deposition of a darker (biotur-bated) terrigenous layer (Type 1 dark layer[?] base is biscuited). Core 978A-43R-4, 10-31 cm.
368
SITE 978
cm2-
4 -
6 -
8 -
1 0 -
1 2 -
1 4 -
1 6 -
Figure 19. Close-up photograph of volcanic pebbles from Subgroup 2a. Grid spacing is 0.5 cm.
2 x 10^ SI. From 630 to 700 mbsf, K rises again but the intensityshows little change.
Declinations are considerably scattered before demagnetizationwith very slight clustering around 0° below 390 mbsf, implying aweak radial overprint (Fig. 34). After AF demagnetization at 15 mT,declinations are equally scattered below 390 mbsf (Fig. 35). Abovethis, declinations cluster around 200°.
Before demagnetization inclinations are almost entirely positive.Application of AF of 15 mT significantly changes inclinations be-
tween 390 and 610 mbsf (Fig. 35). We can identify at least 11 polarityzones based on systematic change in inclinations as shown in Figure36. Shallow and scattered inclinations between each polarity zonemay indicate a transitional geomagnetic field or, more likely, insuffi-cient removal of the positive overprint. Intervals from 210 to 390mbsf and 630 to 700 mbsf are still dominated by positive inclinations.
We find that the change in inclination record does not correspondwith the significant change in intensity or susceptibility at this site.The termination of the zone with well-defined polarity (390 mbsf) oc-
369
SITE 978
Figure 20. Close-up photograph of volcanic pebbles from Subgroup 2b. Grid spacing is 0.5 cm.
370
SITE 978
cm0-
2 -
4 -
6 -
8 -
1 0 -
1 2 -
1 4 -
1 6 -
Figure 21. Close-up photograph of nonvolcanic pebbles from Subgroup 2c. Grid spacing is 0.5 cm.
371
SITE 978
cm100-
1 0 5 -
110 —
Figure 22. Scoured base of fine sandstone layer truncates laminated siltyclaystone at 104-107 cm. Small-scale ripple cross laminations are presentfrom 100 to 101 cm. The sequence is probably crosscut by a reverse fault thatextends from the lower left corner of the photograph at 112.5 cm up to theright of the core at 107 cm. The fault places older silty claystone on the left,adjacent to younger (repeated) fine sandstone on the right. Core 978A-53R-4, 100-114 cm (693.9-694.04 mbsf).
curs at a much shallower depth than the sharp change in intensity andK (440 mbsf). Change in />-wave velocity, porosity, and lithologycorresponds with this significant change in inclination attitude. P-wave velocities indicate Stepwise increase at 390 mbsf from 1.73 to1.78 km/s (see "Physical Properties" section, this chapter). Thesechanges may indicate an increase in consolidation and may controldegree of sediment deformation during coring. LithostratigraphicUnit IC almost coincides with this interval.
cm
132-
134-
136-
138-
140-
Figure 23. Cross-laminated fine sandstone from 131 to 135 cm, overlyingcomplexly bedded/laminated interval at 135-138 cm. Note that thin dark,silty claystone laminae at 137 cm are crosscut by the faint oval burrow on theright. Core 978A-52R-1, 131-141 cm (679.11-680.21 mbsf).
The sharp increase in intensity and K was also observed at Site977 at 420 mbsf, suggesting good correlation between two neighbor-ing sites. Remanent directions, however, are quite different betweenSites 977 and 978. This also suggests that the magnetic mineralogychange (abundance and mineral assemblage) is not the only factorcontrolling the reliability of paleomagnetic data. Substantial differ-ences between these two sites may be due to coring methods used(XCB at Site 977 and RCB at Site 978). Although recovered by usingRCB, the cores were less deformed and less biscuited in Lithostrati-graphic Unit IC at this site. The influence of coring methods on coremagnetism needs to be studied carefully.
Magnetostratigraphy
Eleven polarity zones are identified between 390 and 610 mbsf(Fig. 36). There is still some ambiguity (gray zones in Fig. 36), pos-sibly indicating insufficient demagnetization. Several age-diagnosticmicrofossils were found in this interval; first common occurrence ofG. margaritae (606 mbsf), first occurrence of P. lacunosa (505mbsf), last common occurrence of G. margaritae (466 mbsf), and lastoccurrence of G. puncticulata (436 mbsf; see "Biostratigraphy" sec-tion, this chapter). Correlation of the biostratigraphic data and the po-larity zones indicate they are mostly subchrons in Chron 3n.Correlation of polarity zones with the geomagnetic polarity time
372
SITE 978
1 3 0 -
cm
1 3 5 -
Figure 24. Silty clay stone at 135 cm is overlain at a scoured contact by sandysilty claystone with clay rip-up clasts at 133 cm, that passes up into normallygraded sandstone. This is an example of a unit with poorly developed basalinverse grading. Upper contact of sandstone with overlying silty claystoneappears to have been modified by soft-sediment deformation. Note abruptcontact of silty claystone and dark siltstone at 126 cm. Core 978A-53R-2,125-136 cm (691.15-691.26 mbsf).
scale (GPTS: Cande and Kent, 1995) is shown in Figure 36. Depth ofchron and/or subchron boundaries based on this correlation are givenin Table 4.
STRUCTURAL GEOLOGY
Site 978 is located between Al-Mansour Seamount and the Mai-monides Ridge in the Eastern Alboran Basin, in an east-northeast- towest-southwest-trending trough about 15 km wide. The basin has apre-Pliocene fill that shows evidence of tilting and internal unconfor-mities, overlain by flat-lying Pliocene to Pleistocene sediments. Thislack of deformation is reflected in the Pliocene to Pleistocene coresfrom Site 978. The bedding is for the most part horizontal, with localvariations in dip that probably result from slump folding. An open 10-cm east-vergent slump fold is well preserved near the base of the
1 0 -
1 5 -
Figure 25. A bed consisting of normally graded sandstone to laminated silt-stone with irregular but abrupt upper and lower contacts with adjacent siltyclaystone. Dark silty claystone patches within lighter graded interval may betrace fossils or, alternatively, rip-up clasts. Core 978A-53R-4, 7-17 cm(692.97-693.07 mbsf).
Pliocene in Section 978A-43R-4 (597.1 mbsf). This fold is cut byburrows, demonstrating that it formed not far below the sediment-water interface (Fig. 16). Just below, the clay has been deformed bythe slumping, and the burrows have been sheared with respect to bed-ding and stretched (Fig. 17). There are also a few normal faults withdisplacement on the order of 1 cm (Fig. 37).
The late Miocene rocks below the zone of low recovery in Cores978A-45R through 47R are significantly more lithified than thePliocene to Pleistocene sequence, and show some remarkable defor-mational features. Although the bedding is horizontal, the rocks arecut by numerous dilational fractures (Fig. 38). These have very irreg-ular orientations, but are generally at a high angle to the bedding.They vary considerably in width, branch, and form networks (Fig.39). They are filled by pale green or gray clay, and by numerous an-gular fragments of the surrounding consolidated mudstone. Locally,the fracturing is so intense that the rock has been turned into an in-traformational breccia (Fig. 27). The clay filling the fractures resem-bles the surrounding rock except that it appears to be lessconsolidated. In places the mud fill can be traced from a fracture to abedding-parallel layer of the same material. A possible explanation
373
SITE 978
cm
6 -
1 0 -
1 2 -
cm
1 4 -
Figure 26. Finely laminated (cm- to mm- to sub-mm scale) to thinly beddedsilty claystone. Small oval burrows are present at 5.5 cm and 13.5 cm. Core978A-49R-7, 5-15 cm (658.98-659.01 mbsf).
for these features is that they are hydraulic fractures formed in con-solidated clay by overpressured and underconsolidated horizonswithin the sequence. They are present down to the bottom of the hole.
ORGANIC GEOCHEMISTRY
Calcium carbonate and organic carbon concentrations were mea-sured on samples obtained regularly from Hole 978A. Organic matteratomic C/N ratios and Rock-Eval analyses were employed to deter-mine the type of organic matter contained within the sediments. Ele-vated amounts of headspace gases were encountered, and routinemonitoring of these gases was done for drilling safety.
Inorganic and Organic Carbon Concentrations
Concentrations of carbonate carbon vary between 1.3% to 8.0%in sediments from Site 978 (Table 5; Fig. 40). These carbonate car-bon concentrations are equivalent to 11 % to 66% sedimentaryCaCO3, assuming that all of the carbonate is present as pure calcite.The Miocene sediments in the lowermost lithologic unit are distinctlylower in carbonate contents (Fig. 40). The range in carbonate contentreflects varying combinations of fluctuating biological productivity,dilution by non-carbonate sedimentary components, and post-deposi-tional carbonate dissolution driven by oxidation of organic carbonduring Miocene to Pleistocene times.
Sediments at Site 978 average 0.3% TOC, which is the same asthe ocean-drilling average compiled by Mclver (1975) from DSDP
1 3 0 -
1 3 5 -
1 4 0 -
Figure 27. In situ brecciation in upper late Miocene claystone to silty clay-stone. The fragments all appear to be locally derived by hydraulic fracturing.Core 978A-49R-3, 128-141 cm (654.18-654.3 mbsf).
Legs 1 through 33. TOC concentrations fluctuate between 0% and1.27% (Table 5; Fig. 40). Some of the Pleistocene sediments in whichTOC concentrations are elevated resemble those referred to assapropels at Sites 974 and 975. As such, their occurrence at Site 978confirms the westward extension of Mediterranean sapropel deposi-tion discovered at Site 977 (see "Site 977" chapter, "Lithostra-graphy" section, this volume).
Organic Matter Source Characterization
Organic C/N ratios were calculated for Site 978 samples usingTOC and total nitrogen concentrations to help identify the origin oftheir organic matter. Site 978 C/N ratios vary from <5 to 45 (Table5); most values are between 4 and 8, which is diagnostic of marineorganic matter (e.g., Emerson and Hedges, 1988; Meyers, 1994).
Sediment samples having relatively elevated TOC concentrations(>0.5%) were selected for Rock-Eval characterization of the type andthermal maturity of their organic matter contents (Table 6). A vanKrevelen-type plot of the hydrogen index (HI) and oxygen index (OI)values suggests that the sediments contain mostly Type III (land-de-
374
SITE 978
cm
3 5 -
4 0 -
4 5 -
Figure 28. Example of fine clastic dikes with crosscutting relationships, par-ticularly in the interval 37-40 cm. Core 978A-53R-2, 34-49 cm (690.24-690.39 mbsf).
rived) organic matter (Fig. 41). This source assignment for the organ-ic matter conflicts, however, with the marine-type C/N ratios forthese samples. The contradiction between the Rock-Eval source char-acterization and the elemental source characterization is evidencethat the marine organic matter has been heavily oxidized, probably bymicrobial reworking. Well-preserved Type II organic matter has highHI values (Espitalié et al., 1977).
Headspace Gases
Concentrations of headspace methane are relatively high in sedi-ments from Hole 978A (Fig. 42). Two sources of the gas are possible.
cm
9 6 -
9 8 -
1 0 0 -
1 0 2 -
1 0 4 -
Figure 29. Several funnel-shaped clastic dikes crosscut silty claystone andsiltstone; bedding is offset in a normal sense along the dikes. Core 978A-50R-1, 95-105 cm (660.58-660.63 mbsf).
Age (Ma)
Pleistocene
Piacenzianlate
Pliocene
Zancleanearly
Pliocene
Messinianlate
Miocene
Sedimentationrate
(m/m.y.)
200
200
£400
600 Hiatus? - - - - ' ? i 2 - 0 -late Miocene X
I 156 m/m.y.
Figure 30. Age-depth model and sedimentation rates at Hole 978A.
First, gas from some deeper origin may have migrated into the unit.Evidence for migration of methane into porous sediments from deep-er sources has been found at Sites 762 and 763 on the Exmouth Pla-teau (off northwest Australia) where a known thermogenic sourceexists in underlying Jurassic rocks (Meyers and Snowdon, 1993). Nocomparable source of gas is known in the Alboran Basin. A second
375
SITE 978
DrilledOto 110.3
1 1U ;120-=1 6 0 -
Drilled ^119.9 to168.4"
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1R-CC
2R-CC
3R-CC4R-1.6-B
4R-1,64-66
11R-4, 19-20
11R-5, 20-21
15R-1, 20-2115R-2, 18-19
15R-3, 20-21
20R-1, 20-2120R-3. 20-21
20R-CC
27R-4, 30-3227R-CC
29R-2, 19-2029R-3, 19-20
31 R•2, 20-2131R-3, 20-21
34R-CC35R-3, 7-8
38R-CC
45-CC, 6-8
46R-CC
47R-1, 8-9
Nanno.zone
NN19F
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NN19A
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T.D. 698.0 mbsf
Figure 31. Calcareous nannofossil zonation of Hole 978A. Bold lines repre-
sent acme intervals. Lack of a short horizontal line at the end of a species'
vertical range line indicates that the range of that species is incomplete.
Dashed vertical lines below the Mediterranean bases of H. sellii indicate its
irregular global occurrence.
T.D. 698.0 mbsf Suspected hiatus
Figure 32. Planktonic foraminiferal zonation of Hole 978A. Shaded areas
represent intervals not sampled.
376
SITE 978
300-
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600-
700
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Core,section,
interval (cm)
1R-CC
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11R-4, 19-20
11R-5, 20-21
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20R-3, 20-21
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14R-2, 82-84
22R-5, 111-113
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Figure 33. Summary of nannofossil and foraminiferal zonations of Hole 978A. Bold lines represent acme intervals.
possibility is in situ formation by methanogenic bacteria. High C,/C2
ratios (Table 7) indicate that the methane is biogenic, as opposed tothermogenic, in origin. The source of the methane is probably fromin situ microbial fermentation of the marine organic matter present inthe sediments at Site 978. Similar microbial production of methanefrom marine organic matter has been inferred from high biogenic gasconcentrations in Pliocene-Pleistocene sediments from Site 532 onthe Walvis Ridge (Meyers and Brassell, 1985), Sites 897 and 898 onthe Iberian Abyssal Plain (Meyers and Shaw, in press), Sites 976 and
977 nearby in the Alboran Sea (this volume), and also in middle Mi-ocene sediments from Site 767 in the Celebes Sea (Shipboard Scien-tific Party, 1990). A biogenic origin of the methane is supported bythe marked decrease in headspace methane concentrations at approx-imately 500 mbsf (Fig. 42), the same sub-bottom depth at which in-terstitial sulfate reappears (see "Inorganic Geochemistry" section,this chapter). As noted by Claypool and Kvenvolden (1983), the pres-ence of interstitial sulfate inhibits methanogenesis in marine sedi-ments.
377
SITE 978
Table 3. Age of calcareous nannofossil and planktonic foraminiferal biostratigraphic events and depth of their occurrence in Hole 978A.
1
23456
7
910111213141516
171819202122
Biostratigraphic event/magnetostratigraphic data
FO
FOLOLOLOLOBaseTopLOBaseLCOFCOTopBaseTopFOBaseLO
TopBaseTopFCOLOFO
G. oceanic a >4.0 µm
Pliocene/Pleistocene boundary
G. inflataG. bononiensisD. pentaradiatus/D. surculusD. tamalisSphaeroidinellopsis spp.C2An2nC2An3nG. puncticulataC2An3nG. margaritaeD. asvmmetricusC3nlnC3nlnC3n2nG. puncticulataC3n2nH. intermedia (very rare
occurrence)C3n3nC3n3nC3n4nG. margaritaeR. rotariaR. rotaria
Age(Ma)
1.75
1.83
2.132.452.522.783.223.223.333.573.583.944.134.184.294.484.524.624.67
4.804.894.985.106.126.62
Top
222.76
268.64315.42323.00371.20397.31400.70408.40435.06436.00465.93478.40490.60503.10515.40518.27535.10542.40
550.30559.20570.20605.44611.39694.30
Depth (mbsf)
Bottom
223.30
(calculated)
273.38318.42324.49374.21400.07400.70408.40438.46436.00466.70479.91490.60503.10515.40522.54535.10544.35
550.30559.20570.20606.74620.93694.30
Mean
223.03
233.13
271.01316.92323.74372.70398.69400.70408.40436.76436.00466.31479.15490.60503.10515.40520.41535.10543.38
550.30559.20570.20606.09616.16694.30
Notes: FO = first occurrence, LO = last occurrence, LCO = last common occurrence, FCO = first common occurrence; also indicated are the main chronostratigraphic boundaries. Thistable is also on the CD-ROM, back pocket, this volume.
200
300
O 400in
500
600
700
Declination (°) Inclination (°) Intensity (mA/m)0 90 180 -90 0 90 1 10 100
< V*.
. ‰<
Figure 34. Declination (core-coordinate), inclination, and intensity beforedemagnetization at Hole 978A.
Higher molecular weight thermogenic headspace gases are alsopresent at Site 978. Concentrations of propane, /so-butane, and iso-pentane exceed or equal those of ethane in sediments from -300 to500 mbsf (Table 7). Ethane is typically the second most abundantcomponent of biogenic gases (Claypool and Kvenvolden, 1983). Theunusual gas compositions at Site 978 therefore suggest that the C3,C4, and C5 gases were produced by thermal degradation of sedimen-tary organic matter during some former period of elevated heat flowin this sub-basin of the Alboran Sea.
INORGANIC GEOCHEMISTRY
Fifteen interstitial water samples were obtained from Hole 978Abetween 225.60 mbsf to 692.75 mbsf, one sample every five coresuntil 317.5 mbsf and one every three cores below. Because coringstarted only below 200 mbsf, early diagenetic processes could not bedocumented at this site. The most important process influencing theinterstitial water composition at Site 978 appears to be upward diffu-sion of a saline brine.
Evaporite-Related Fluxes
The clearest pattern observed at this site is a downcore increase insalinity, chloride, sodium, and calcium, with a steepening of the con-centration gradients below 450 mbsf (Table 8; Figs. 43-46). Sulfateconcentrations are close to zero until 450 mbsf and increase steeplybelow 500 mbsf to reach a constant value of approximately 19 mMbelow 600 mbsf. Chloride should behave conservatively because it isnot involved in any common diagenetic reactions within the sedi-ments. Therefore, chloride concentration gradients are only influ-enced by fluid diffusion and advection processes and can help todetermine the composition of the brine. The linear correlation be-tween sodium and chloride (Fig. 47) suggests that sodium also be-haves almost conservatively. The average molar Na/Cl ratio of all theinterstitial water samples is 0.82, close to the seawater ratio of 0.86.If halite dissolution were the principal cause of the salinity increase,the Na/Cl ratio would be expected to increase because halite dissolu-tion would move the ratio closer to the stoichiometric ratio of 1. Theabsence of an increase in this ratio (Fig. 47) indicates that halite dis-solution is not responsible for the salinity increase with depth (Fig.44). Also, because halite salts do not underlie this area, it is possiblethat the high concentrations of the salt components (Figs. 43-45) areat least partly caused by trapped Messinian-age paleo-seawater. Inthis basin evaporation may not have been intense enough to cause ha-lite precipitation, but waters with elevated salinities may have seepedinto the underlying strata and been preserved in the Pliocene-Pleis-tocene sediments. Another possible explanation for the high salinitiesobserved at this site is large-scale fluid migration. Important Messin-
SITE 978
200
300
400
CL
Q 500
600
700
Declination Inclination
0 90 180 -90 0 90
Intensity Magnetic(mA/m) susceptibility (10~4 SI)
0.1 1 10 1 5
Figure 35. Declination, inclination, and intensity inHole 978A after AF demagnetization at 15 mT. MSTlow-field susceptibility after smoothing (20 point).
-90
400 -
Inclination (c
0GPTS
90 (Cande and Kent, 1995)
C2An.2n
C2An.3n
Table 4. Chron and subchron boundaries.
£ 500 -Q.ΦQ
600 -
Figure 36. Polarity zones in Hole 978A identified for the interval from 390 to610 mbsf and possible correlation with GPTS (Cande and Kent, 1995). Grayzones indicate ambiguous polarity intervals after AF demagnetization at 15mT.
ian halite deposits are known to occur 25 to 30 km east of Site 978 inthe South Balearic Basin (Mauffret et al., 1992). Brines produced bythe dissolution of these deposits might have migrated along perme-able sediment units and influenced the interstitial water compositionat this site.
The downcore lithium increase may also be partly related toevaporitic fluids as suggested by the near-linear relationship betweenLi+ and Cl~ in the upper part of the section (Fig. 44). Below 500 mbsfthese concentration profiles diverge, however, suggesting that lithi-
Depth(mbsf)
400
436491503515535550559570
Section
22R-723R-626R-5/26R-632R-333R-535R-137R-138R-539R-440R-5
Boundary
C2An.2n/C2An.2rC2An.2r/C2An.3nC2An.3n/C2ArC2Ar/C3n.lnC3n.ln/C3n.lrC3n.lr/C3n.2nC3n.2n/C3n.2rC3n.2r/C3n.3nC3n.3n/C3n.3rC3n.3r/C3n.4n
Age(Ma)
3.223.333.584.184.294.484.624.804.894.98
Notes: Depth (mbsf) and section that includes each chron/subchron boundary is given.Age is after Cande and Kent (1995).
um abundance is affected by other sources and sinks. Lithium re-placement in clays by ammonia may be responsible for some of theincrease. The potassium concentrations are constant and below sea-water values, indicating that no major potassium source is present atdepth.
Sulfate concentration in the interstitial waters is also influencedby the postulated brine, but in addition it is controlled by two addi-tional factors: bacterial sulfate reduction and in situ dissolution ofgypsum. The absence of sulfate above 450 mbsf can be ascribed tobacterial sulfate reduction, which completely depleted interstitial wa-ter sulfate at some time in the past. Down to this depth, organic matterdegradation is presently mediated by methanogenic bacteria, as evi-denced by the presence of high headspace methane concentrationsdown to 468 mbsf (see "Organic Geochemistry" section, this chap-ter). Methanogenic bacteria can favorably compete with sulfate re-ducers only when sulfate is completely depleted from theenvironment (Claypool and Kvenvolden, 1983). The constant sulfateconcentration below 600 mbsf possibly reflects in situ dissolution ofgypsum, although this mineral has been found only in minor amountsin lithostratigraphic Unit II (see "Lithostratigraphy" section, thischapter). The zone between 495 and 606.6 mbsf represents a zone ofsulfate reduction, probably due to sulfate-reducing bacteria. Thepresence of sulfate below 500 mbsf leads to a reduction in bacterio-
374
SITE 978
cm6
cm
1 0 -
1 5 -
2 0 -
2 5 -
Figure 37. Steep fault in bioturbated semiconsolidated Pliocene? clay withabout 1 cm normal displacement. Section 978A-17R-5, 6-28 cm. Note trans-fer zone at upper right (interval 10-12 cm).
110-
1 1 5 —
120-
Figure 38. Dilational fractures in well-consolidated late Miocene mudstone.In the fracture at bottom left, note the matching walls of the fracture, theupward increase in the amount of dilation, and the component of displace-ment down to the left. At the bottom, the displacement is apparently trans-ferred along a bedding-parallel slip surface to another dilational fracture tothe right. The fractures are filled with clay and fragments of the surroundingmudstone. Section 978A-50R-1, 108-121 cm.
genie methane production, as shown by the drop in headspace meth-ane concentrations below 470 mbsf (see "Organic Geochemistry"section, this chapter).
Carbonate Diagenesis
Alkalinity was measured on only one sample below 492.2 mbsfbecause of the low amounts of interstitial water recovered. The alka-linity profile shows a maximum of 3.5 mM at 269.5 mbsf that corre-sponds with the highest ammonia concentrations and then decreasesdowncore to concentrations well below average seawater values (Fig.43B). This may indicate that the rate of organic matter decompositionis highest at that depth and that alkalinity is consumed at depth bycarbonate precipitation and/or clay or zeolite formation. The calcium
SITE 978
cm100-
105-
110-
Figure 39. Dilational fractures and brecciation in late Miocene mudstone.Note that most of the fractures have matching walls and that the larger frag-ments can be fitted back together. The fracture fill appears to be clay derivedfrom the underlying layer, but the relationship is disturbed by a drilling-induced biscuit structure. Section 978A-48R-5, 100-114 cm.
profile is dominated by the evaporite source at depth, whereas mag-nesium concentrations appear to be more influenced by carbonate di-agenesis. Magnesium concentrations are consistently below seawaterconcentrations, indicating that precipitation of high magnesium cal-cite or dolomite has occurred in the sediments. The dramatic magne-sium increase below 600 mbsf (Fig. 43) suggests that part of themagnesium may be derived from a brine.
The strontium concentration profile, which shows a maximum at492.20 mbsf, can be explained by carbonate recrystallization. Al-though biogenic carbonate is not very rich in strontium, its dissolu-tion and inorganic reprecipitation releases strontium to interstitialwaters (Manheim and Sayles, 1974). The strontium minimum at606.05 mbsf suggests the precipitation of a strontium-bearing miner-al.
In conclusion, the interstitial water profiles at Site 978 appear tobe strongly influenced by the presence of a saline brine, possibly apaleo-fluid trapped below the Pliocene-Pleistocene sediments or de-rived from large-scale fluid circulation, coupled with the in situ dis-solution of gypsum within lithostratigraphic Unit II.
PHYSICAL PROPERTIES
Physical property measurements were made on whole-core sec-tions (for MST and thermal conductivity measurements), split cores(for sonic velocity measurements), and discrete samples (for indexproperties) for Site 978. Natural gamma ray was measured at 10-cmintervals on cores as part of the MST. MST and thermal conductivitymeasurements were made on every section. Index properties weremeasured once per section until Core 978A-32X and every other sec-tion from Core 978A-33X onwards. The MST velocity was measuredfor only the RCB cores. Velocity measurements using DSV andHamilton frame transducers were made on every section. Results areshown in Figures 48-51.
Some of the physical properties, such as susceptibility (Fig. 48A),bulk density, porosity, and void ratio (Fig. 50; Table 9 on CD-ROM)show a distinctive jump in their values at 460 mbsf. This boundaryseen in the physical properties does not correspond to any lithologicalboundary. Differential lithification could be a possible cause for theformation of this boundary.
In comparing Sites 977 and 978, the thermal conductivity data forSite 977 (Fig. 49) and for Site 978 (Fig. 49 and Table 9 on CD-ROM,back pocket, this volume) lie within same range of values. Also, thevelocity values from Site 977 (Fig. 51; Table 9 on CD-ROM) and Site978 (Fig. 51) show similar trends.
The susceptibility data (Fig. 48) show two maxima, at 460 to 600mbsf and from 640 mbsf to the bottom of the hole. The first maximalies in the Pliocene, formation, which contains disseminated pyrite(see "Lithostratigraphy" section, this chapter). The second maximalies in the Miocene.
The grain densities are almost constant with depth (Fig. 50; Table10 on CD-ROM, back pocket, this volume), reflecting little change inthe composition of sediment input.
A gap in the velocity data between 310-330 mbsf was caused byan instrumentation breakdown (Fig. 51; Table 11 on CD-ROM, backpocket, this volume). Two gradients are observed in the data from200 mbsf to 540 mbsf and from 540 mbsf to 600 mbsf. A high veloc-ity value of 2.2 km/s occurs at around 320 mbsf in a semi-lithifiedsand. The data are widely scattered from 630 mbsf to the bottom ofthe hole. This corresponds to the Miocene Lithostratigraphic Unit III(see "Lithostratigraphy" section, this chapter). This unit consists ofcalcareous siltstone, calcareous silty claystone, and calcareous siltysandstone.
REFERENCES
Alonso, B., and Maldonado, A., 1992. Plio-Quaternary margin growth pat-terns in a complex tectonic setting: northeastern Alboran Sea. Geo-Mar.Lett, 12:137-143.
Cande, S.C., and Kent, D.V., 1995. Revised calibration of the geomagneticpolarity timescale for the Late Cretaceous and Cenozoic. J. Geophys.Res., 100:6093-6095.
Claypool, G.E., and Kvenvolden, K.A., 1983. Methane and other hydrocar-bon gases in marine sediment. Annu. Rev. Earth Planet. ScL, 11:299—327.
Colalongo, M.L., Di Grande, A., D'Onofris, S., Giannelli, L., Iaccarino, S.,Mazzei, R., Romeo, M., and Salvatorini, G., 1979. Stratigraphy of LateMiocene Italian sections straddling the Tortonian/Messinian boundary.Boll. Soc. Paleontol. Ital, 18:258-302.
Emerson, S., and Hedges, J.I., 1988. Processes controlling the organic carboncontent of open ocean sediments. Paleoceanography, 3:621-634.
381
SITE 978
Espitalié, J., Laporte, J.L., Leplat, P., Madec, M., Marquis, F., Paulet, J., andBoutefeu, A., 1977. Méthode rapide de caractérisation des roches mères,de leur potentiel pétrolier et de leur degré devolution. Rev. Inst. Fr. Pet,32:23-42.
Manheim, F.T., and Sayles, F.L., 1974. Composition and origin of interstitialwaters of marine sediments, based on deep sea drill cores. In Goldberg,E.D. (Ed.), The Sea (Vol. 5): Marine Chemistry: The Sedimentary Cycle:New York (Wiley), 527-568.
Mauffret, A., Maldonado, A., and Campillo, A.C., 1992. Tectonic frame-work of the Eastern Alboran and Western Algerian Basins, WesternMediterranean. Geo-Mar. Lett., 12:104-110.
Mclver, R.D., 1975. Hydrocarbon occurrences from JOIDES Deep Sea Drill-ing Project. Proc. Ninth Petrol. Congr., 269-280.
Meyers, P.A., 1994. Preservation of elemental and isotopic source identifica-tion of sedimentary organic matter. Chem. GeoL, 144:289-302.
Meyers, P.A., and Brassell, S.C., 1985. Biogenic gases in sediments depos-ited since Miocene times on the Walvis Ridge, South Atlantic Ocean. InCaldwell, D.E, Brierley, J.A., and Brierley, C.L. (Eds.), Planetary Ecol-ogy: New York (Van Nostrand Reinhold), 69-80.
Meyers, P.A., and Shaw, T.J., 1996. Organic matter accumulation, sulfatereduction, and methanogenesis in Pliocene-Pleistocene turbidites on the
Iberia Abyssal Plain. In Whitmarsh, R.B., Sawyer, D.S., Klaus, A., andMasson, D.G. (Eds.), Proc. ODP, Sci. Results, 149: College Station, TX(Ocean Drilling Program), 705-712.
Meyers, P.A., and Snowdon, L.R., 1993. Sources and migration of methane-rich gas in sedimentary rocks on the Exmouth Plateau: northwest Austra-lian continental margin. In Oremland, R.S. (Ed.), Biogeochemistry ofGlobal Change: New York (Chapman and Hall), 434-446.
Pickering, K.T., Hiscott, R., and Hein, F.J., 1989. Deep-Marine Environ-ments: Clastic Sedimentation and Tectonics: London (Unwin Hyman).
Raymo, M.E., Hodell, D., and Jansen, E., 1992. Response of deep ocean cir-culation to initiation of Northern Hemisphere glaciation (3-2 Ma). Pale-oceanography, 7:645-672.
Shipboard Scientific Party, 1990. Site 767. In Rangin, C, Silver, E.A., vonBreymann, M.T., et al., Proc. ODP, Init. Repts., 124: College Station, TX(Ocean Drilling Program), 121-193.
Wright, R., 1978. Neogene paleobathymetry of the Mediterranean based onbenthic foraminifers from DSDP Leg 42. In Hsü, K.J., Montadert, L., etal., Init. Repts. DSDP, 42 (Pt. 1): Washington (U.S. Govt. PrintingOffice), 837-846.
Ms 161IR-108
NOTE: For all sites drilled, core-description forms ("barrel sheets") and core photographs canbe found in Section 3, beginning on page 429. Smear-slide data can be found in Section 4, be-ginning on page 949. Thin-section data can be found in Section 5, beginning on page 991. SeeTable of Contents for material contained on CD-ROM.
Table 5. Results of inorganic and total carbon (TC) analyses of Pliocene-Pleistocene sediment samples from lithostratigraphic Unit I at Site 978.
Core, section,interval (cm)
161-978A-3R-1, 8-93R-1, 29-304R-1, 122-1234R-1, 132-1334R-1, 142-1444R-2, 2-34R-2, 133-1344R-5, 10-115R-1, 14-155R-1, 118-1195R-2, 42-436R-1,40-416R-2, 15-166R-4, 90-916R-5, 73-747R-1, 102-1037R-5, 92-937R-5, 116-1177R-6, 84-858R-1,37-388R-1, 86-878R-3, 23-248R-3, 114-1159R-1,95-969R-5, 10-119R-6, 18-19
10R-1, 108-10910R-2, 53-5410R-3, 42-4311R-1, 145-14611R-2, 48-4911R-3, 120-121HR-5,5-612R-1,63-6412R-3, 55-5612R-4, 95-9612R-5, 105-10613R-3, 33-3413R-6, 40-4214R-3, 33-3414R-5, 13-1414R-6, 40-4114R-7, 10-1115R-1, 32-3315R-3, 87-8815R-4, 50-5115R-5, 100-10116R-1, 16-1716R-4, 75-7616R-4, 137-13816R-5, 84-85
Depth(mbsf)
213.08213.29223.92224.02224.12224.22225.53228.30232.44233.48234.22236.60237.35241.10242.43246.92252.82253.06254.24255.87256.36258.73259.64266.05271.20272.78275.88276.83278.22285.75286.28288.50290.35294.53297.45299.35300.95306.93311.50316.43319.23321.00322.20323.12326.67327.80329.80332.66337.75338.37339.34
Inorg. C(wt%)
4.535.233.053.513.764.003.485.113.943.903.483.955.194.813.993.554.885.463.863.264.693.845.225.083.684.285.525.924.303.534.613.626.085.145.995.124.695.615.314.795.335.184.984.074.914.705.284.995.373.334.05
CaCO,(wt%)
37.743.625.429.231.333.329.042.632.832.529.032.943.240.133.229.640.745.532.227.239.132.043.542.330.735.746.049.335.829.438.430.250.642.849.942.639.146.744.239.944.443.141.533.940.939.244.041.644.727.733.7
TC(wt%)
4.885.533.363.744.104.233.695.604.364.173.914.425.705.214.554.185.475.614.263.714.914.224.965.534.025.155.926.184.654.034.914.246.355.566.475.485.086.055.745.225.745.615.474.485.395.025.905.425.733.924.39
TOC(wt%)
0.350.300.310.230.340.230.210.490.420.270.430.470.510.400.560.630.590.150.400.450.220.380.000.450.340.870.400.260.350.500.300.620.270.420.480.360.390.440.430.430.410.430.490.410.480.320.620.430.360.590.34
TN(wt%)
0.090.070.140.040.090.120.080.110.090.090.090.110.100.110.090.120.110.080.080.090.120.090.090.090.080.100.070.090.090.060.090.130.070.060.100.110.110.100.090.130.090.090.110.120.120.010.140.110.060.140.12
TS(wt%)
0.020.510.780.701.630.000.020.801.010.000.840.890.340.310.831.030.000.760.941.150.001.010.560.800.430.880.190.711.220.000.001.450.000.000.380.650.620.000.710.640.340.000.770.450.090.341.320.420.290.690.00
C/N
4.545.002.586.714.412.243.065.205.443.505.574.985.954.247.266.136.262.195.835.832.144.930.005.834.96
10.156.673.374.549.723.895.564.508.175.603.824.145.135.573.865.315.575.203.994.67
37.335.174.567.004.923.31
:
SITE 978
Table 5 (continued).
Core, section,interval (cm)
17R-1, 115-11617R-3, 16-1719R-5, 117-11919R-6, 106-10820R-1, 128-12920R-4, 62-6321R-4, 116-11722R-1,93-9422R-2, 14-1522R-5, 108-10923R-1, 123-12423R-3, 29-3023R-6, 29-3024R-1,90-9124R-3, 66-6724R-3, 91-9225R-1,82-8325R-2, 140-14125R-5, 90-9125R-6, 23-2426R-1, 15-1626R-2, 60-6126R-4, 70-7126R-5, 58-5927R-1,89-9027R-4, 76-7727R-7, 51-5228R-3, 84-8528R-4, 112-11428R-5, 60-6228R-6, 57-5929R-1,44-4529R-3, 91-9229R-4, 76-7729R-7, 11-1230R-1, 119-12030R-4, 46-4731R-2.61-6231R-2, 102-10331R-4.75-7632R-2, 60-6232R-3, 52-5332R-CC, 10-1233R-2, 65-6633R-3, 60-6134R-1,38-3934R-3, 127-12835R-3, 84-8535R-4, 104-10535R-6, 90-9136R-2, 19-2036R-3, 55-5637R-4, 37-3837R-5, 59-6038R-2, 93-9438R-5, 24-2539R-3, 76-7739R-5, 42-4340R-3, 10-1140R-3, 131-13340R-5, 135-13740R-7, 6-841R-1, 100-10141R-3, 45-4641R-6, 24-2542R-3, 46-4742R-4, 41-4242R-5, 108-11043R-1, 63-6543R-2, 10-1243R-3, 39-4143R-4, 24-2543R-6, 62-6444R-1,60-6144R-3, 50-5144R-3, 97-9844R-CC, 12-1347R-1, 15-1647R-1,47-4847R-1,59-6047R-2, 66-6747R-2, 140-14147R-3, 131-13247R-CC, 10-1148R-1, 115-116
Depth(mbsf)
343.35345.36368.57369.96372.28376.12386.26391.13391.84397.28401.03403.09407.59410.20412.96413.21419.72421.80425.80426.63428.65430.60433.70435.08438.99443.36447.61451.64453.42454.40455.87457.94461.41462.76466.41468.29472.06478.81479.22481.71488.40489.92496.06498.05499.50505.88509.77519.04520.74523.60526.59528.45539.37541.09546.53550.34557.46560.12566.40567.61570.65572.36573.80576.25580.54585.96587.41589.58592.73593.70595.49596.84600.22602.30605.20605.67607.40630.75631.07631.19632.76633.50634.91635.03641.45
Inorg. C(wt%)
4.934.584.885.235.014.335.574.894.315.534.905.695.614.765.595.924.504.826.555.024.404.744.116.335.096.574.894.916.594.987.134.735.056.565.536.054.625.036.796.236.694.654.495.905.115.066.644.836.694.224.496.706.614.694.827.326.705.126.944.244.397.046.983.224.635.087.132.974.543.127.270.586.887.197.654.427.982.372.192.483.332.312.982.143.34
CaCO3
(wt%)
41.138.240.743.641.736.146.440.735.946.140.847.446.739.746.649.337.540.254.641.836.739.534.252.742.454.740.740.954.941.559.439.442.154.646.150.438.541.956.651.955.738.737.449.142.642.155.340.255.735.237.455.855.139.140.261.055.842.657.835.336.658.658.126.838.642.359.424.737.826.060.64.8
57.359.963.736.866.519.718.220.727.719.224.817.827.8
TC(wt%)
5.324.785.255.705.524.666.025.284.84
5.416.075.925.205.166.144.925.216.865.504.835.224.756.875.586.945.275.366.775.397.445.025.38
5.906.294.945.376.866.466.945.044.786.085.405.42
5.146.864.635.086.926.765.125.147.456.865.507.114.714.747.377.133.565.165.477.283.424.903.177.430.737.117.398.014.838.232.462.252.633.502.393.132.23
TOC(wt%)
0.390.200.370.470.510.330.450.390.530.350.510.380.310.440.000.220.420.390.310.480.430.480.640.540.490.370.380.450.180.410.310.290.33
0.370.240.320.340.070.230.250.390.290.180.290.360.240.310.170.410.590.220.150.430.320.130.160.380.170.470.350.330.150.340.530.390.150.450.360.050.160.150.230.200.360.410.250.090.060.150.170.080.150.09
TN(wt%)
0.010.120.120.060.060.110.060.060.070.110.110.050.050.070.120.050.070.070.050.120.070.070.080.050.070.050.120.060.040.060.040.050.06
0.060.050.070.060.050.050.040.070.070.050.070.074.670.070.040.130.070.040.050.080.070.040.050.070.030.080.080.050.040.080.080.070.040.080.070.040.030.020.040.040.040.070.040.030.040.040.040.040.060.06
TS(wt%)
0.020.170.040.160.840.370.470.050.450.000.100.050.921.280.020.100.000.060.000.090.050.500.610.090.180.060.070.000.130.000.000.000.04
0.582.331.021.190.000.000.060.810.550.000.001.030.001.040.651.191.740.180.160.390.510.090.030.450.060.710.340.060.100.590.390.830.090.870.640.000.050.100.030.050.000.820.080.000.001.600.000.000.000.00
C/N
45.501.943.609.149.923.508.757.588.833.715.418.877.237.330.005.137.006.507.234.677.178.009.33
12.608.178.633.698.755.257.979.046.776.42
7.195.605.336.611.635.377.296.504.834.204.836.000.065.174.963.689.836.423.506.275.333.793.736.336.616.855.107.704.374.967.736.504.386.566.001.466.228.756.715.83
10.506.837.293.501.754.384.962.332.921.75
3.S3
SITE 978
Table 5 (continued).
Core, section,interval (cm)
48R-3, 78-7948R-4, 90-9148R-4, 94-9548R-4, 139-14049R-1, 118-11949R-3, 29-3049R-3, 38-3949R-4, 69-7049R-6, 35-3650R-2, 24-2550R-3, 76-7750R-5, 16-1850R-5, 27-2851R-1, 113-11451R-2, 51-5252R-1,76-7752R-2, 27-2852R-2, 99-10053R-1, 58-5953R-2, 76-7753R-2, 133-13453R-2, 135-13653R-3, 9-1053R-4, 49-5053R-CC, 8-9
Depth(mbsf)
644.08645.70645.74646.19651.08653.19653.28655.09657.75661.34663.36665.76665.87670.33671.21679.56680.57681.29688.99690.66691.23691.25691.49693.39694.25
Inorg. C(wt%)
3.413.372.982 . 1 82.943 .152.892.184.581.892.891.823.711.693.051.912.182.391.823.243.802.543.592.202.34
CaCO3
(wt%)
28.428.124.818.224.526.224.118.238.215.724.115.230.914.125.415.918.219.915.227.031.721.229.918.319.5
TC(wt%)
4.683.533.362.593.223.283.172.454.772.063.262.143.791.913.162.132.382.792.123.413.892.81
2.362.52
TOC(wt%)
1.270.160.380.410.280.130.280.270.190.170.370.320.080.220.110.220.200.400.300.170.090.27
0.160.18
TN(wt%)
0.050.060.050.060.070.030.070.050.050.070.060.070.020.060.030.060.040.060.060.040.030.05
0.050.04
TS(wt%)
0.000.000.000.000.000.001.100.000.000.000.033.480.013.140.000.000.000.113.230.000.002.57
0.000.00
C/N
29.633.118.877.974.675.064.676.304.432.837.195.334.674.284.284.285.837.785.834.963.506.30
3.735.25
Notes: Total organic carbon (TOC) concentrations are calculated from the difference between inorganic carbon and TC concentrations. C/N ratios are calculated from TOC and totalnitrogen (TN) concentrations and are given as atom/atom ratios. TS = total sulfur concentration. This table is also on the CD-ROM, back pocket, this volume.
CaCO TOC (%)0.4 0.8
700
Figure 40. Organic carbon and CaCO3 concentrations in sediment samplesfrom Hole 978A.
384
SITE 978
Table 6. Results of Rock-Eval pyrolysis analyses of organic-rich samples selected from Hole 978A.
Core, section,interval (cm)
161-978A-6R-5, 73-747R-1, 102-1039R-6, 18-1911R-3, 120-12115R-5, 100-10120R-1, 128-12926R-4, 70-7136R-2, 19-2041R-6, 24-2548R-3, 78-7950R-2, 24-2553R-2, 133-134
Depth(mbsf)
242.43246.92272.78288.50329.80372.28433.70526.59580.24644.08661.34691.23
TOC(%)
0.400.560.360.540.640.460.460.680.670.130.270.10
Tmax
(°C)
487442
s,
0.000.130.020.020.170.010.000.060.010.030.100.04
s2
0.640.880.470.921.460.680.730.600.520.390.830.57
s3
1.451.411.451.491.361.511.561.211.070.780.830.70
PI
0.000.130.040.020.100.010.000.090.020.070.110.07
S2 /S3
0.440.620.320.611.070.450.460.490.480.501.000.81
PC
0.050.080.040.070.130.050.060.050.040.030.070.05
HI
160157130170
1471588877
300307570
OI
362251402275212328339177159600307700
Notes: Total organic carbon (TOC) concentrations are derived from the Rock-Eval parameters and therefore differ somewhat from the TOC values of the same samples in Table 5.Tmax values could not be measured accurately for samples with low (<0.5%) TOC contents. Units of the various Rock-Eval parameters are given in the "Explanatory Notes" chap-ter (this volume).
800
400
Headspace methane (ppm)
10° 101 102 103 104 105
2 0 0 -
Q.CDQ
200Oxygen index
400
Figure 41. Rock-Eval van Krevelen-type diagram of Pleistocene sapropelsfrom Hole 978A. Organic matter appears to be a mixture of Type II algalmaterial that has been variably oxidized and Type III continental or detritalorganic matter. Hydrogen index = mg hydrocarbons/g organic carbon; oxy-gen index = mg CO2/g organic carbon.
4 0 0 -
6 0 0 -
Figure 42. Headspace methane concentrations in sediments from Hole 978A.Interstitial sulfate concentrations begin to increase where methane virtuallydisappears at 500 mbsf.
SITE 978
Table 7. Results of headspace gas analyses of sediments from Hole 978A.
Core, section,interval (cm)
161-978A-1R-CC, 0-53R-1,0-54R-3, 0-55R-2, 0-56R-4, 0-57R-4, 0-58R-4, 0-59R-4, 0-510R-4, 0-511R-4, 0-512R-4, 0-513R-4, 0-514R-4, 0-515R-3, 0-516R-3, 0-517R-4, 0-518R-4, 0-519R-4, 0-520R-4, 0-521R-4, 0-522R-4, 0-523R-4, 0-524R-4, 0-525R-4, 0-526R-4, 0-527R-4, 0-528R-4, 0-529R-2, 0-530R-2, 0-531R-4.0-532R-5, 0-533R-4, 0-534R-4, 0-535R-4, 0-536R-4, 0-537R-4, 0-538R-4, 0-539R-4, 0-540R-4, 0-541R-3.0-542R-3, 0-543R-3, 0-544R-2, 0-547R-4, 0-548R-4, 0-549R-4, 0-55OR-3, 0-551R-2, 0-552R-2. 0-553R-4, 0-5
Depth(mbsf)
109200212221228237247257266276285295305313323334343353353372382391401410420430439446456468479487497507516526536545555563573576590622632641650658667680
c,
8063225271654314489228723123117642171515796199991528183641277722561173878930
20710134871734512407103153083128777560329348184300308038163155673575231565289306233232198123106381896
15796
c2
5447736575341074106965275233334
52733232
c3
132116775991535928725433
32293437119
7
IC4
9695
64
IC5
856
C,/C2
450541363622327330339213619315928573056278831942256248422332071224819272068206315421840151216471606143310271272789
4628341102781166662
Notes: Dominance of methane in sediments above 500 mbsf indicates that most of the gases originate from in situ fermentation of organic matter. The presence of significant amountsof thermogenic C3, C4, and C5 gases below 300 mbsf suggests that heat flows were once higher at Site 978.
Table 8. Interstitial water data from Hole 978A.
Core, section,interval (cm)
161-978 A-4R-2, 140-1509R-3, 140-15014R-3, 140-15017R-3, 140-15020R-3, 140-15023R-3, 140-15026R-3, 140-15029R-1, 140-15032R-4, 140-15035R-3, 140-15038R-3, 135-15041R-2, 135-15044R-3, 135-15048R-3, 135-15053R-3, 135-150
Depth(mbsf)
225.60269.50317.50346.60375.40404.20432.90458.90492.20519.60548.45575.65606.05644.65692.75
PH
7.47.37.27.37.27.37.27.67.6n.d.n.d.7.3n.d.n.d.n.d.
Alkalinity(mM)
2.0913.5092.5471.7091.851.4371.3810.7630.554n.d.n.d.1.04n.d.n.d.n.d.
Salinity(‰)
384242454446464851525760646979
Cl(mM)
686726747780
822835
92093310071060111411381364
Ca(mM)
13.015.218.322.225.729.932.837.042.451.161.381.094.399.7132.0
Mg(mM)
35.835.632.333.537.232.634.435.037.341.237.837.230.142.552.5
Mn(µM)
4.53.53.5476.55.55.56.577.584959171
Sr(µM)
4986709141167139216701800195020201725162013959801070365
SO4(mM)
0.010.240.270.000.000.001.400.480.665.828.3711.9218.5619.4519.36
NH4(µM)
313433623466337130343280301229162743224724431665151112651647
H4SiO4
(µM)
307.27247.07221.28238.47206.23195.48130.98103.04103.04184.73113.79137.4387.99107.3421.34
Li(µM)
12614616918120121 1230244261255250246194242306
Na(mM)
574602584607640682643719775815867
9729311118
K(mM)
5.315.234.804.434.944.164.325.804.675.235.056.937.053.964.31
PO4(µM)
<2.5<2.5<2.5<2.5<2.57.515.785.20
<2.5<2.5<2.5<2.5<2.5<2.5<2.5
Note: n.d. = not determined. This table is also on the CD-ROM, back pocket, this volume.
SITE 978
200
PH7.0 7.2 7.4 7.6
Q.CD
Q
400 -
600 -
BAlkalinity (mM)
2 4 200
400
600 -
200
Ca2 + (mM)
100 150
M g 2 + (mM)
30 40 50
200
400 -
CLCDQ
600 -
K+ (mM)
5 10
Na+ (mM)
15 400 800 1200
Figure 43. Concentration profiles of (A) pH, (B) alkalinity, (C) calcium, and(D) magnesium in Hole 978A. The dashed lines indicate standard seawater(International Association for the Physical Sciences of the Ocean [IAPSO])composition.
200
Salinity (‰)40 60 80
B(mM)
4 0 0 -
6 0 0 -
600
I I <
\ S
I
tI |
1000 1401 1 '
i 1 Λ ^
200
Sr2 + (µM)0 1000 2000
Li+ (µM)
0 100 200 300
Figure 44. Concentration profiles of (A) salinity, (B) chloride, (C) strontium,and (D) lithium in Hole 978A. The dashed lines indicate standard seawater(IAPSO) composition.
Figure 45. Concentration profiles of (A) sulfate, (B) manganese, (C) potas-
sium, and (D) sodium in Hole 978A. The dashed lines indicate standard sea-
water (IAPSO) composition.
200
N H 4
+ (mM)2 3
BSilica (µM)
0 100 200 300
4 0 0 -
Q.
ΦQ
6 0 0 -
Figure 46. Concentration profiles of (A) ammonium and (B) silica in Hole
978A.
600 -
600 14001000
Cl (mM)
Figure 47. Cross plot of Cl and Na concentrations in Hole 978A showing
their linear relationship.
387
SITE 978
200
f 400
CD
Q
Susceptibility0 40 80
Density (g/cm3)1.2 1.6 2.0
Counts20 40
600 *
-I-H
J
• ^
pjr 1—
=
' \
— =
•^—* 1
Smoothed Figure 48. MST data (susceptibility, density, and naturaldata(1 m) . . „ , __o . F J
gamma) for Hole 978A.
200
Conductivity(W/[m K])
1 2
Figure 49. Thermal conductivity data for Hole 978A.
200
Velocity (km/s)1.6 2.0 2.4
200
300 -
£400 -
500
600 -
700
Grain density(g/cm3)
2.7 2.9
%
^ * i
— % .. -
if**5* * * *
•*<#
r *.{**• •••
** !••— . •* —
\!
>\
f * *
Bulk density(g/cm3)
1.8 2.2
1-i •
*Λ.*««•#*̂— * —
Porosity(%)
35 45 55
•i•-.;t .
- l;• .
*t
•# *— *. * —
• . .
Void ratio
0.6 1.2
•£•-_ »i _
• •*̂
- 1 -•f.
V •' *
- ,j
/ .ij
t
" i i i
Figure 50. Index property data for Hole 978A.
Figure 51. Seismic velocity data for Hole 978A.
388