Sedimentology, mineral magnetism, andoxygen isotope stratigraphy of ODP Hole 133-819A

To investigate late Quaternary paleoclimatic and paleoceanographic change in the sedimentary record, preserved on the Australian Continental Margin during the late Quaternary, core material was collected from Ocean Drilling Program, Leg 133, Site 819. An expanded sequence of late Quaternary, rhythmically bedded, predominantly hemipelagic sediments were recovered from Hole 819A. The foraminiferal d18O record preserved at Hole 819A suggests that the late Quaternary section is incomplete. Both benthic and planktonic d18O stratigraphies can be traced tentatively downcore to stage 6 at about 32.5 mbsf, where a major hiatus occurs. At this level, a slump detachment surface has been identified (Shipboard Scientific Party, 1991). This slump has removed marine oxygen isotope stages 7 to 13. Below 32.5 mbsf, continuous correlation can be achieved in the planktonic d18O curve, with existing deep-sea foraminiferal oxygen isotope stratigraphies from stage 14 through stage 28. The major hiatus at 32.5 mbsf marks the position of a significant change in the character of the sedimentation at Site 819. Sediments below 32.5 mbsf, relative to those above 32.5 mbsf, are characterized by less variation in mean particle size; lower percentages of carbonate content in the coarse fraction (>63 µm); a stronger relationship between the percentage of fine fraction and magnetic mineral concentration, and lower foraminiferal abundances. Above the hiatus, large fluctuations in mean particle size occurred, which have been interpreted to be the result of high foraminiferal abundances. Early highstands show high terrigenous influx in the fine fraction above the hiatus. This is the opposite of the general idea of high terrigenous influx during lowstands of sea level on siliciclastic dominated continental margins. We are far from understanding the origin of this material and further investigation will be required (see also Glenn et al., this volume). All our records, except the planktonic foraminiferal oxygen isotope record, indicate that the major hiatus marks the position of a significant change in the environment at Site 819. The planktonic foraminiferal d18O record suggests that environmental change occurred prior to the formation of the hiatus (i.e., near the Brunhes/Matuyama [B/M] boundary). The interval between the B/M boundary and the hiatus represents a transitional period between two different patterns of ocean circulation. Throughout most of the lower part of the sequence, Site 819 was at a shallow-water depth and local oceanographic conditions were dominated by sluggish Subtropical Central Water (SCW) flow. However, near the B/M boundary, ocean circulation patterns intensified, reflecting a worldwide change in paleoenvironment. Enhanced ocean circulation patterns were possibly aided by tectonic subsidence. During this period Site 819 became progressively more under the influence of Antarctic Intermediate Water (AAIW), than SCW. In the upper part of the sequence at Hole 819 A, we see a continuation of the pattern of oceanographic reorganization suggested during stages 21 through 14. Intensification of the subsurface oceanographic circulation was also accompanied by the progressive wedging southward of surface waters associated with the East Australian Current (EAC). The change in the nature of the records in the lower and upper parts of the sequence at Site 819 are thought to reflect perturbations by the orbital eccentricity cycle.

Calcareous nannofossil stratigraphy and datum levels of ODP Site 182-1127, Great Australian Bight

Ocean Drilling Program (ODP) Leg 182 drilled at nine sites on the Great Australian Bight, which is located directly south of the Australian continent. Leg 182 proposed to examine the paleoceanographic evolution of a midlatitude, cool-water carbonate platform. During drilling on the Great Australian Bight, three sites (1127, 1129, and 1131) recovered highly expanded Pleistocene sections. This paper presents the detailed calcareous nannofossil biostratigraphy of the most distal site. This report should provide a useful Pleistocene biostratigraphic reference for this previously unknown area.

Planktonic foraminiferal stratigraphy and datum levels of ODP Leg 182 sites

Planktonic foraminifers from Ocean Drilling Program Leg 182, Holes 1126B and 1126C, 1128B and 1128C, 1130A and 1130B, 1132B, and 1134A and 1134B confirm the neritic record that during the early Miocene the Great Australian Bight region was in a cool-temperate regime with abundant Globoturborotalita woodi. Warm marine environments started to develop in the later part of the early Miocene, and the region became warm temperate to subtropical in the early middle Miocene with abundant Globigerinoides, Orbulina, and Globorotalia, corresponding to global warming at the Miocene climatic optimum. Fluctuations between cool- and warm-temperate conditions prevailed during the late Miocene, as indicated by abundant Globoconella conoidea and Menardella spp. A major change in planktonic foraminiferal assemblages close to the Miocene/Pliocene boundary not only drove many Miocene species into extinction but also brought about such new species as Globorotalia crassaformis and Globoconella puncticulata. Warm-temperate environments continued into the early and mid-Pliocene before being replaced by cooler conditions, supporting numerous Globoconella inflata and Globigerina quinqueloba. Based on data from this study and published results from the Australia-New Zealand region, we established a local planktonic foraminifer zonation scheme for separating the southern Australian Neogene (SAN) into Zones SAN1 to SAN19 characterizing the Miocene and Zones SAN20 to SAN25 characterizing the Pliocene. The Neogene sections from the Great Australian Bight are bounded by hiatuses of ~0.5 to >3 m.y. in duration, although poor core recovery in some holes obscured a proper biostratigraphic resolution. A total of 15 hiatuses, numbered 1 to 15, were identified as synchronous events from the base of the Miocene to the lower part of the Pleistocene. We believe that these are local manifestations of major third-order boundaries at about (1) 23.8, (2) 22.3, (3) 20.5, (4) 18.7, (5) 16.4, (6) 14.8, (7) 13.5, (8) 11.5, (9) 9.3, (10) 7.0, (11) 6.0, (12) 4.5, (13) 3.5, (14) 2.5, and (15) 1.5 Ma, respectively. This hiatus-bounded Neogene succession samples regional transgressions and stages of southern Australia and reveals its stepwise evolutionary history.

Planktonic foraminifera stratigraphy and datums of ODP Site 184-1143 and Hole 184-1146A, South China Sea

The biostratigraphy of Miocene-age sediment samples recovered from Ocean Drilling Program Sites 1143 and 1146, South China Sea, is presented. The preservation of the planktonic foraminifers recovered from both sites varies widely, from poor to very good. The volume of biogenic sediment in the >63-µm size fraction also varies considerably, with many samples being dominated by mud. In comparison to shipboard biostratigraphy, based on core catcher analyses with a depth resolution of ~10 m, we analyzed samples from the two stratigraphic columns every 2-3 m (~45- to 93-k.y. resolution). The placement of planktonic foraminifer zonal boundaries was made at a resolution of ~1.5 m at Site 1146 and ~3.0 m at Site 1143. The higher resolution has resulted in significant changes in biostratigraphic zonal boundary locations compared to shipboard results. For the time interval of 5.54-10.49 Ma, the changes in zonation reveal similar age-depth models at both sites, with three segments of changing sedimentation rate through the upper Miocene, though the differences in sedimentation rates at Site 1146 are subtler than those at Site 1143. The boundary between lithologic Units II and III at Site 1146 corresponds to a sharp change in sedimentation rate (58 to 21 m/m.y.) at 15.1 Ma (the first occurrence of Orbulina suturalis). At this site, the interval from 16.4 to 15.1 Ma is characterized by very high mass accumulation rates in the noncarbonate fraction. Above this interval the carbonate fraction becomes increasingly important in the sediment flux to the South China Sea. At Site 1143, sedimentation rates increase from 8 to 99 m/m.y. at 8.6 Ma. This corresponds to a dramatic increase in both carbonate and noncarbonate mass accumulation rates at the site, but no change in lithology.

Calcareous nannofossil stratigraphy of sediments from ODP Holes 186-1150A and 186-1151C, Japan Trench

To assess the paleoceanographic potential of Leg 186 sediments, we investigated Quaternary calcareous nannofossil flora at Sites 1150 and 1151 in the Japan Trench. Because of the frequent occurrence of barren intervals and the lack of oxygen isotope data, a detailed paleoceanography is not feasible for these cores. We limited our study to the upper 26.07 m of the section from Hole 1150A and the upper 21.01 m of the section from Hole 1151C. The studied samples from Cores 186-1150A-1H through 3H are younger than 0.085 Ma. Core 186-1151C-1H (upper 1.92 meters below seafloor [mbsf]) is younger than 0.085 Ma, and samples between 2H-7, 5-7 cm, and 3H-CC, 5-7 cm, (9.99-21.01 mbsf) are older than 0.245 Ma and younger than 0.408 Ma.

Element stratigraphy across the Cretaceous-Tertiary boundary in ODP Hole 119-738C

Neutron activation analyses of iridium and other chemical elements were performed across a 1-m-thick, partly nonbioturbated, clay-rich interval at the Cretaceous/Tertiary boundary in ODP Hole 738C. The results show that the boundary interval holds one of the highest Ir enrichments (320 ng Ir/cm2) of all known Cretaceous/Tertiary boundary layers. Iridium concentrations are highest (18 ppb Ir, whole-rock samples) a few centimeters above the base of the clayrich interval and gradually tail off upsection. Compared with background levels the most Ir-rich interval also shows strongly enhanced concentrations of Cr (215 ppm) and slightly elevated Co concentrations (13 ppm). The Ir-rich interval shows low As (< 15 ppm) and Sb (<0.8 ppm) concentrations, a fact that is congruent with absence of abundant authigenic sulfides in the sediment. Irregularly distributed Fe enrichments and a greenish gray color of the Fe-rich intervals may indicate the presence of glauconitic clay minerals and suboxic, slightly reducing conditions during deposition. Rare earth element (REE) abundance patterns change considerably across the Cretaceous/Tertiary boundary interval, reflecting either a change in Cretaceous/Tertiary boundary seawater REE composition or the occurrence of different REE fractionation processes due to changing depositional environment. Element-vs.-element ratios of Hf, Ta, Th, U, Cs, and Sc are similar between the most Ir-rich layers of the boundary section and other levels with lower Ir concentrations. This may imply that the clay fraction of the Ir-rich layers of the Cretaceous/Tertiary boundary interval is made up predominantly of locally derived material. Calculated calcite-free abundances of Hf, Ta, Th, U, Cs, and Sc, on the other hand, are reconcilable with an extraneous origin of the bulk of the clay in the most Ir-rich layers. The Ir in the Cretaceous/Tertiary boundary clay-rich zone in Hole 738C is most likely derived from an earth-impacting asteroid; however, the origin of the clay-rich zone remains enigmatic.

Middle to late Miocene oxygen isotope stratigraphy of ODP site 1085 (SE Atlantic): new constrains on Miocene climate variability and sea-level fluctuations

The middle Miocene delta18O increase represents a fundamental change in earth's climate system due to a major expansion and permanent establishment of the East Antarctic Ice Sheet accompanied by some effect of deepwater cooling. The long-term cooling trend in the middle to late Miocene was superimposed by several punctuated periods of glaciations (Mi-Events) characterized by oxygen isotopic shifts that have been related to the waxing and waning of the Antarctic ice-sheet and bottom water cooling. Here, we present a high-resolution benthic stable oxygen isotope record from ODP Site 1085 located at the southwestern African continental margin that provides a detailed chronology for the middle to late Miocene (13.9-7.3 Ma) climate transition in the eastern South Atlantic. A composite Fe intensity record obtained by XRF core scanning ODP Sites 1085 and 1087 was used to construct an astronomically calibrated chronology based on orbital tuning. The oxygen isotope data exhibit four distinct delta18O excursions, which have astronomical ages of 13.8, 13.2, 11.7, and 10.4 Ma and correspond to the Mi3, Mi4, Mi5, and Mi6 events. A global climate record was extracted from the oxygen isotopic composition. Both long- and short-term variabilities in the climate record are discussed in terms of sea-level and deep-water temperature changes. The oxygen isotope data support a causal link between sequence boundaries traced from the shelf and glacioeustatic changes due to ice-sheet growth. Spectral analysis of the benthic delta18O record shows strong power in the 400-kyr and 100-kyr bands documenting a paleoceanographic response to eccentricity-modulated variations in precession. A spectral peak around 180-kyr might be related to the asymmetry of the obliquity cycle indicating that the response of the dominantly unipolar Antarctic ice-sheet to obliquityinduced variations probably controlled the middle to late Miocene climate system. Maxima in the delta18O record, interpreted as glacial periods, correspond to minima in 100-kyr eccentricity cycle and minima in the 174-kyr obliquity modulation. Strong middle to late Miocene glacial events are associated with 400-kyr eccentricity minima and obliquity modulation minima. Thus, fluctuations in the amplitude of obliquity and eccentricity seem to be the driving force for the middle to late Miocene climate variability.

Stable isotope record and age model for sapropel stratigraphy of ODP Site 160-967

Stable oxygen isotope data from four holes drilled at the Ocean Drilling Program Site 967, which is located on the lower northern slope of the Eratosthenes Seamount, provide a continuous record of Eastern Mediterranean surface-water conditions during the last 3.2 Ma. A high-resolution stratigraphy for the Pliocene-Pleistocene sequence was established by using a combination of astronomical calibration of sedimentary cycles, nannofossil stratigraphy, and stable oxygen isotope fluctuations. Sapropels and color cycles are present throughout the last 3.2 Ma at Site 967, and their ages, as determined by calibration against the precessional component of the astronomical record, are consistent with those estimated for the sapropels of the classical land-based marine sequences of the Punta Piccola, San Nicola, Singa, and Vrica sections (southern Italy). The Site 967 oxygen isotope record shows large amplitude fluctuations mainly caused by variations in surface water salinity throughout the entire period. Spectral analysis shows that fluctuations in the d18O record were predominantly influenced by orbital obliquity and precessional forcing from 3.2 to 1 Ma, and all main orbital frequencies characterize the d18O record for the last million years. The start of sapropel formation at 3.2 Ma indicates a possible link between sapropel formation and the build up of northern hemisphere ice sheets. The dominance of the obliquity cycle in the interval from 3.2-1 Ma further points to the sensitivity of Eastern Mediterranean climate to the fluctuations in the volume of Arctic ice sheets. An intensification of negative isotope anomalies at Site 967, relative to the open ocean, supports a link between high run-off (during warm periods) and sapropel formation. freshwater input would have inhibited deep-water formation, which led to stagnation of deeper waters. Comparison with the land sections also confirms that differential preservation and diagenesis play a key role in sapropel occurrence.

Upper Cretaceous-Paleogene stratigraphy of ODP Sites 113-689 and 113-690

This contribution summarizes the biostratigraphy of planktonic foraminifers, calcareous nannofossils, and benthic foraminifers, in combination with the magnetostratigraphy, carbon and oxygen isotope stratigraphy of benthic foraminifers, and CaCO3 stratigraphy for the Maestrichtian through Paleogene calcareous sequences recovered at Sites 689 and 690 on Maud Rise (at about 65°S, eastern Weddell Sea, Antarctica). These data represent the southernmost calciumcarbonate record available for that interval, and thus extend the biostratigraphic and isotopic database to higher latitudes. Sites 689 and 690 form the southernmost anchor of a north-south transect through the Atlantic Ocean for Paleogene biostratigraphy and chemostratigraphy.

Calcareous nannofossil stratigraphy, mass accumulation rates and bulk density of sediments from ODP Leg 173 sites

Drilling on the Iberia Abyssal Plain during Ocean Drilling Program Leg 173 allowed us to recover Upper Cretaceous through Paleocene sediments at Sites 1068 and 1069 and only upper Paleocene sediments at Site 1067, which expands considerably the Upper Cretaceous to Paleocene record for this region. Of these three sites, Site 1068 recovered uppermost Cretaceous sediments as well as the most complete Paleocene record, whereas Site 1067 yielded only uppermost Paleocene sediments (Zone CP8). Site 1069 provided a rather complete upper Campanian through Maastrichtian section but a discontinuous Paleocene record. After a detailed calcareous nannofossil biostratigraphy was documented in distribution charts, we calculated mass accumulation rates for Holes 1068A and 1069A. Sediments in Hole 1068A apparently record the final stages of burial of a high basement block by turbidity flows. Accumulation rates through the Upper Cretaceous indicate relatively high rates, 0.95 g/cm**2/k.y., but may be unreliable because of the lack of datum points and/or possible hiatuses. Accumulation rates in the Paleocene section of Hole 1068A fluctuated every few million years from lower (~0.35 g/cm**2/k.y.) to higher rates (~0.85 g/cm**2/k.y.) until the latest Paleocene, when rates increased to an average of ~2.0 g/cm**2/k.y. Mass accumulation rates for the Upper Cretaceous in Hole 1069A indicate a steady rate of ~0.60 g/cm**2/k.y. from 75 to 72 Ma. There may have been one or more hiatuses between 72 and 68 Ma (combined Zone CC24 through Subzone CC25b), as indicated by the very low accumulation rate of 0.15 g/cm**2/k.y. The Paleocene section of Hole 1069A does not show the same continuous record, which may result from fluctuations in the carbonate compensation depth and poor recovery (average = 40%). Zones CP4 and CP5 are missing within a barren interval; this and numerous other barren intervals affect the precision of the nannofossil zonation and calculation of mass accumulation rates. However, in spite of these missing zones, mass accumulation rates do not seem to indicate the presence of hiatuses as the rates for this barren interval average ~1.0 g/cm**2/k.y. This study set out to test the hypothesis that a reliable biostratigraphic record could be constructed from sediments derived from turbidity flows deposited below the carbonate compensation depth. As illustrated here, not only could a reliable biostratigraphic record be determined from these sediments, but sedimentation and mass accumulation rates could also be determined, allowing inferences to be drawn concerning the sedimentary history of this passive margin. The reliability of this record is confirmed by independent verification by the establishment of a magnetostratigraphy for the same cores.

Planktonic foraminifera stratigraphy and datum events of ODP Leg 198 sites

During Leg 198 of the Ocean Drilling Program (ODP), Paleogene sediments were recovered form 10 holes at four sites along a bathymetric transect from the Southern High of Shatsky Rise. In terms of age, the Paleogene successions span from the Cretaceous/Paleocene boundary to the early Oligocene. Sediments are mainly composed of tan nannofossil ooze with scattered darker layers richer in clay. This data report concerns planktonic foraminiferal biostratigraphy from three holes, specifically Hole 1209A (water depth = 2387 m), Hole 1210A (water depth = 2573 m), and Hole 1211A (water depth = 2907 m). The thickness of Paleogene sediments is 105.90 m in Hole 1209A, 95.05 m in Hole 1210A, and 56.11 m in the deepest Hole 1211A. Preliminary investigations conducted on board revealed that at Site 1209 the succession was mostly complete, whereas the succession was more condensed at Site 1211.