Biostratigraphy, magnetostratigraphy, granulometry, isotopes and clay mineral composition of ODP Site 188-1165

During Ocean Drilling Program Leg 188 to Prydz Bay, East Antarctica, several of the shipboard scientists formed the High-Resolution Integrated Stratigraphy Committee (HiRISC). The committee was established in order to furnish an integrated data set from the Pliocene portion of Site 1165 as a contribution to the ongoing debate about Pliocene climate and climate evolution in Antarctica. The proxies determined in our various laboratories were the following: magnetostratigraphy and magnetic properties, grain-size distributions (granulometry), near-ultraviolet, visible, and near-infrared spectrophotometry, calcium carbonate content, characteristics of foraminifer, diatom, and radiolarian content, clay mineral composition, and stable isotopes. In addition to the HiRISC samples, other data sets contained in this report are subsets of much larger data sets. We included these subsets in order to provide the reader with a convenient integrated data set of Pliocene-Pleistocene strata from the East Antarctic continental margin. The data are presented in the form of 14 graphs (in addition to the site map). Text and figure captions guide the reader to the original data sets. Some preliminary interpretations are given at the end of the manuscript.

Palynology, source vegetation, environment and age of ODP Site 188-1166 sediments

Twenty-three core catcher samples from Site 1166 (Hole 1166A) in Prydz Bay were analyzed for their palynomorph content, with the aims of determining the ages of the sequence penetrated, providing information on the vegetation of the Antarctic continent at this time, and determining the environments under which deposition occurred. Dinocysts, pollen and spores, and foraminiferal test linings were recovered from most samples in the interval from 142.5 to 362.03 meters below seafloor (mbsf). The interval from 142.5 to 258.72 mbsf yielded palynomorphs indicative of a middle-late Eocene age, equivalent to the lower-middle Nothofagidites asperus Zone of the Gippsland Basin of southeastern Australia. The Prydz Bay sequence represents the first well-dated section of this age from East Antarctica. Dinocysts belonging to the widespread "Transantarctic Flora" give a more confident late Eocene age for the interval 142.5-220.5 mbsf. The uppermost two cores within this interval, namely, those from 142.5 and 148.36 mbsf, show significantly higher frequencies of dinocysts than the cores below and suggest that an open marine environment prevailed at the time of deposition. The spore and pollen component may reflect a vegetation akin to the modern rainforest scrubs of Tasmania and New Zealand. Below 267 mbsf, sparse microfloras, mainly of spores and pollen, are equated with the Phyllocladidites mawsonii Zone of southeastern Australia, which is of Turonian to possibly Santonian age. Fluvial to marginal marine environments of deposition are suggested. The parent vegetation from this interval is here described as "Austral Conifer Woodland." The same Late Cretaceous microflora occurs in two of the cores above the postulated unconformity at 267 mbsf. In the core at 249.42 mbsf, the Late Cretaceous spores and pollen are uncontaminated by any Tertiary forms, suggesting that a clast of this older material has been sampled; such a clast may reflect transport by ice during the Eocene. At 258.72 mbsf, Late Cretaceous spores and pollen appear to have been recycled into the Eocene sediments.

P-wave velocities and applied bed thickness and velocity changes for synthetic seismograms, ODP Leg 188 and Leg 119 sites

Synthetic seismograms provide a crucial link between lithologic variations within a drill hole and reflectors on seismic profiles crossing the site. In essence, they provide a ground-truth for the interpretation of seismic data. Using a combination of core and logging data, we created synthetic seismograms for Ocean Drilling Program Sites 1165 and 1166, drilled during Leg 188, and Site 742, drilled during Leg 119, all in Prydz Bay, Antarctica. Results from Site 1165 suggest that coring penetrated a target reflector initially thought to represent the onset of drift sedimentation, but the lithologic change across the boundary does not show a change from predrift to drift sediments. The origin of a shallow reflector packet in the seismic line across Site 1166 and a line connecting Sites 1166 and 742 was resolved into its constituent sources, as this reflector occurs in a region of large-scale, narrowly spaced impedance changes. Furthermore, Site 1166 was situated in a fluvio-deltaic system with widely variable geology, and bed thickness changes were estimated between the site and both seismic lines.

Distribution of foraminifera and other components in ODP Leg 188 sites

During Leg 188 of the Ocean Drilling Program (ODP), employing JOIDES Resolution, we drilled holes at three sites in the southern Indian Ocean in and near Prydz Bay, East Antarctica, between 28 January and 29 February 2000. The objectives of the voyage were to: - Core through sediments deposited when Antarctica underwent the transition from "greenhouse" to the modern "icehouse" state late in the Eocene or early in the Oligocene, at sites obtaining their sediment from the currently subglacial Gamburtsev Mountains that probably were the site of nucleation of the ice sheet (principally Site 1166); - Obtain a sediment record from times at which major changes in the ice sheet volume and characteristics took place as judged from oxygen isotope records, especially at ~23.7 Ma (Oligocene/Miocene boundary), 12-16 Ma (middle Miocene), and 2.7 Ma (late Pliocene) (mainly Site 1165); and - Sample through the upper Pliocene and Quaternary in an attempt to document fluctuations in the extent of the ice sheet over the continental shelf during the Quaternary (especially Site 1167). Paleogene foraminifer-bearing marine sections were not intersected, and thus discussion of marine sections is restricted to the Neogene. Foraminifers are not major contributors to Leg 188 chronostratigraphy but contribute to paleoenvironmental interpretation, to issues such as carbonate compensation depth (CCD) effects and source and history of sediment, and provide a basis for Sr and d18O studies. Chronostratigraphy for the various sections was compiled from diatoms, radiolarians, and paleomagnetism (Shipboard Scientific Party, 2001, doi:10.2973/odp.proc.ir.188.101.2001). Foraminifers were sporadic rather than continuous except in short intervals; however, the Neogene foraminifers from the region are very poorly known and the new records proved to be of significant value in paleoenvironmental interpretation. Only at Site 1167 did drilling intersect a section that yielded foraminifers virtually throughout. Other than for the very young section at each site, there is virtually no continuity of assemblages between sites and thus each section is treated here as separate and unrelated.

Diatom datums and abundance in ODP Hole 188-1165B and 188-1166A sediments

The biostratigraphic distribution and qualitative relative abundance of Quaternary-Pliocene diatoms from Ocean Drilling Program Leg 188, Sites 1165 (64.380°S, 67.219°E) and 1166 (67.696°S, 74.787°E) offshore from East Antarctica, are documented in this report. The upper ~50 meters below seafloor (mbsf) of Hole 1165B consists of brown diatom-bearing silty clay spanning the upper Pleistocene to lower Pliocene. The diatom stratigraphy indicates a disconformity at ~17.1 mbsf of 0.5- to 0.6-m.y. duration. The integration of biostratigraphic and magnetostratigraphic data identified other disconformities at ~6.0, 14.4, 15.6, and 16.0 mbsf, but the duration of these hiatuses cannot be resolved through diatom biostratigraphy. In Hole 1166A, a narrow interval of diatomaceous Quaternary sediment is identified in the upper 2.92 mbsf and dated biostratigraphically at <0.38 Ma. The remaining Quaternary-Pliocene section is dominated by diamicton, except at ~114 mbsf, where two thin diatomaceous beds are present. The lower bed is ~65 cm thick, 2.5-2.7 to 2.7-3.2 Ma in age, and possibly disconformably overlain by the upper bed, which is ~15 cm thick and 1.8-2.0 to 2.1-2.5 Ma in age. The Pliocene assemblages in Hole 1166A contain components of both Southern Ocean and Antarctic continental shelf (Ross Sea) diatom floras.

Sulphate and d34S in pore waters and d13C, d18O and mineral composition of carbonate nodules from ODP Leg 188 sites

Carbon and oxygen isotopic compositions of authigenic carbonate nodules or layers reflect the diagenetic conditions at the time of nodule growth. The shallowest samples of carbonate nodules and dissolved inorganic carbon of pore water samples beneath the sulfate reduction zone (0-160 meters below seafloor [mbsf]) at Site 1165 have extremely negative d13C values (-50 per mil and -62 per mil, respectively). These negative d13C values indicate nodule formation in association with anaerobic methane oxidation coupled with sulfate reduction. The 34S of residual sulfate at Site 1165 shows only minor 34S enrichment (+6 per mil), even with complete sulfate reduction. This small degree of apparent 34S enrichment is due to extreme "open-system" sulfate reduction, with sulfate abundantly resupplied by diffusion from overlying seawater. Ten calcite nodules from Site 1165 contain minor quartz and feldspar and have d13C values ranging from -49.7 per mil to -8.2 per mil. The nodules with the most negative d13C values currently are at depths of 273 to 350 mbsf and must have precipitated from carbonate largely derived from subsurface anaerobic methane oxidation. The processes of sulfate reduction coupled with methane oxidation in sediments of Hole 1165B are indicated by characteristic concentration and isotopic (d34S and d13C) profiles of dissolved sulfate and bicarbonate. Three siderite nodules from Site 1166 contain feldspar and mica and one has significant carbonate-apatite. The siderite has d13C values ranging from -15.3 per mil to -7.6 per mil. These siderite nodules probably represent early diagenetic carbonate precipitation during microbial methanogenesis.