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doi:10.2204/iodp.pr.318.2010

Site summaries

Site U1355

The primary objective at Site U1355 (proposed Site WLRIS-06A) was to core across Unconformity WL-U3 to obtain the timing and nature of the first arrival of the ice sheet to the Wilkes Land Continental Margin in a distal setting. Site U1355 is at the transition between the continental rise and the abyssal plain in a water depth of 3729 mbsl (Fig. F14).

MCS reflection profiles crossing Site U1355 (Fig. F15) image three of the Wilkes Land margin regional unconformities (WL-U3, WL-U4, and WL-U5). Unconformity WL-U3 is observed at ~782 mbsf (5.95 ms two-way traveltime [TWT]) and was interpreted to separate preglacial strata below from glacial strata above. Thus, coring across Unconformity WL-U3 was intended to document the first arrival of the ice sheet to the Wilkes Land Continental Margin. This "onset" of glaciation is presently inferred to have occurred during the earliest Oligocene.

Site U1355 was also designed to provide a distal record of Oligocene–Pliocene (?) glacial–interglacial (i.e., colder versus warmer) and ice sheet variability. Regional Unconformity WL-U5 is imaged in the seismic data at ~709 mbsf (5.6 s TWT) (Fig. F15). Unconformity WL-U5 represents a major shift in continental rise sedimentation with the onset of thick levee deposits above the unconformity. Coring across Unconformity WL-U5 aimed to document the timing, nature, and cause of this shift in sedimentation.

Guided by the regional seismic interpretations, Site U1355 is where the uppermost sedimentary section is relatively thin, or has been eroded, so that Unconformity WL-U3 could be reached at a shallower depth in contrast to other locations offshore the Wilkes Land margin.

Based on the seismic facies at Site U1355, the lithologies expected were fine-grained distal turbidites, contourites, and hemipelagites (Escutia et al., 1997, 2000, 2002; De Santis et al., 2003; Donda et al., 2003). This interpretation was supported by the sediments recovered from Site 269 (Hayes, Frakes, et al., 1975) located on the abyssal plain ~280 km seaward from Site U1355.

Four cores from one hole were obtained at Site U1355. Cores 318-U1355A-1R through 4R penetrated from 0 to 31.7 mbsf and recovered 14.95 m (47%). The stratigraphic integrity of most of the core was highly compromised by drilling disturbance. The sediments are composed of angular igneous and metamorphic fragments. These fragments are unconsolidated, clast-supported, moderately to well-sorted sandy granule–pebble conglomerates grading upward into well-sorted, fine, crudely stratified sands. One 3 cm thick interbed of dark greenish gray diatom-bearing silty clay was preserved between two upward-fining units. The mechanism for the formation of the upward-fining beds is through gravity flow, most likely a high-density turbidity current.

Samples from Hole U1355A were analyzed for siliceous microfossils, foraminifers, and palynomorphs. Core catcher samples from Cores 318-U1355A-1R through 4R and additional samples from clay-rich clasts within the cores were analyzed for diatoms. The core material yielded an abundant Antarctic flora dominated by Fragilariopsis kerguelensis and Thalassiosira lentiginosa. The association of these typical Pleistocene–Holocene Antarctic diatoms along with common Actinocyclus ingens and Actinocyclus ingens var. ovalis indicates an age no older than late Pleistocene. Reworking from Miocene and Eocene material was recorded. A sample from the top of the hole yielded a rich and diverse modern (Holocene) Antarctic diatom assemblage. Radiolarians typical of late Pleistocene–Holocene Antarctic waters were also found in the core catchers and seafloor samples with an overall low abundance. The seafloor sample yielded a low diversity planktonic foraminifer assemblage dominated by Neogloboquadrina pachyderma, indicating an age <9.2 Ma. Palynomorphs were recorded in the seafloor sample and Samples 318-U1355A-1R-CC and 4R-CC. Notable finds included Holocene organic-walled dinoflagellate cysts (dinocysts), foraminifer linings, copepod eggs, reworked late Eocene dinocysts, and reworked Paleogene and/or Cretaceous spores and pollen.

The physical property program for Hole U1355A cores included nondestructive measurements of gamma ray attenuation (GRA) densitometer bulk density, magnetic susceptibility, natural gamma ray (NGR) emission, and P-wave velocity on whole-round core sections. Whole-round and section-half core logging measurements are significantly affected by poor core quality, and the data are therefore compromised. Magnetic susceptibility values are relatively high, reflecting the lithologic composition of the individual clasts in the gravels and sands. The silty diatom-bearing clay clasts are characterized by pronounced lower magnetic susceptibility, bulk density, and sonic velocity values but higher NGR counts. P-wave velocities increase from 1800 m/s at the seafloor to >1920 m/s at the base of Core 318-U1355A-2R.

In summary, operations at Site U1355 revealed that the nature of the seafloor was not the expected fine-grained sediments. After failing to core into the seafloor with the advanced piston corer (APC), the rotary core barrel (RCB) system was tried (see "Operations") and yielded 31.7 m of Pleistocene–Holocene unconsolidated coarse gravels and sands. The nature of the sediment prevented any further advance. We decided to abandon Hole U1355A and move to Site U1356, where we could achieve the same scientific objectives.

Site U1356

Site U1356 (proposed Site WLRIS-07A) is at the transition between the continental rise and the abyssal plain at 4003 mbsl (Fig. F16). The main objective at Site U1356 was to core across regional Unconformity WL-U3 to obtain the timing and nature of the first arrival of the ice sheet to the Wilkes Land Continental Margin in a distal setting.

Similar to Site U1355, three regional unconformities reported from the Wilkes Land margin (Unconformities WL-U3, WL-U4, and WL-U5) are imaged at Site U1356 (Fig. F17). Unconformity WL-U3, interpreted to separate preglacial strata below from glacial strata above and presently inferred to have formed during the earliest Oligocene, occurs at ~867 mbsf (6.33 s TWT). Unconformities WL-U4 and WL-U5 are imaged at ~708 and 534 mbsf (6.15 and 5.95 s TWT), respectively, based on assumed velocities (Fig. F17). Coring across Unconformities WL-U4 and WL-U5 was to provide a distal early Oligocene–(?)Pliocene record of glacial–interglacial (i.e., colder versus warmer) and ice sheet and sea ice variability. MCS reflection profiles crossing Site U1356 showed the site was to penetrate a thick sequence of stacked levee deposits developed between two deep-sea channels and above Unconformity WL-U4 (Fig. F17). Based on their geometry and seismic facies associations, these levee deposits are interpreted to form when high volumes of sediment were delivered to the continental shelf edge by a wet-based EAIS (Escutia et al., 2000). Reworking of turbidite deposits by bottom water currents was also suspected based on the presence of wavy reflectors (Escutia et al., 2000, 2002; Donda et al., 2003). Drilling at Site U1356 was thus to examine the earlier stages of development of large sediment levees denoted by Unconformity WL-U5 in addition to the drivers for this change. Below the levee deposits and closely coinciding with Unconformity WL-U4, strata are characterized by horizontal and continuous reflectors of varied amplitude, which are interpreted to represent hemipelagic and distal turbidite and contourite sedimentation based on comparisons with sediments recovered at Site 269 (Hayes, Frakes, et al., 1975).

Hole U1356A was cored to 1006.4 mbsf. The dominant lithofacies are moderately to strongly bioturbated claystone and calcareous claystone with a Zoophycos or Nereites ichnofacies. Subordinate lithofacies include laminated silty claystones, diamictites, mudstones and sandstones with dispersed to common clasts, and graded or cross-laminated siltstones and sandstones. These facies associations are interpreted to result from hemipelagic sedimentation with variable bottom current and gravity flow influence. Wavy submilimeter-thick black concretions observed below ~373 mbsf are interpreted as a form of silica diagenesis. Carbonate-cemented sandstones and conglomerates are also present below this depth.

The sedimentary section is divided into 11 lithostratigraphic units.

Units I and II (0–278.4 mbsf) are composed of diatom oozes and diatom-rich silty clays with dispersed gravel indicating hemipelagic sedimentation with ice rafting.

Units III (278.40–459.4 mbsf), V (593.8–694.4 mbsf), and VII (723.5–782.7 mbsf) are characterized as repetitively interbedded light greenish gray bioturbated claystones and brown laminated claystones with cross-laminated siltstone and sandstone interbeds. These units are interpreted to indicate cyclical changes in bottom oxygenation, current strength, and fine-grained terrigenous sediment supply. Gravel-sized clasts are rare in these units, and only minimal evidence for ice rafting from rare dispersed sand grains is present.

Units IV (459.4–593.8 mbsf) and VI (694.4–723.5 mbsf) are characterized by extensive interbeds of contorted diamictites and other gravel-bearing lithologies, indicating a strong gravity flow influence.

Units VIII (782.7–879.7 mbsf) and IX (879.7–895.5 mbsf) are composed of mudstones with extensive contorted and convolute bedding.

Unit X (895.5–948.8 mbsf) is composed of crudely stratified and graded sandstones. These units are affected by several types of mass transport, including submarine slides and slumps.

Unit XI (948.8–1006.4 mbsf) is characterized by bioturbated claystones with subordinate stratified siltstone and sandstone, indicating hemipelagic sedimentation with minor bottom current and gravity flow influence.

Units IX, X, and XI (below ~880 mbsf) have a clay mineral assemblage dominated by smectite and kaolinite, indicating chemical weathering under relatively warm and humid conditions. This clay mineral assemblage is distinctly different from that of the overlying units (above ~880 mbsf), where the dominant clay minerals are illite and chlorite, indicative of physical weathering in a glacially influenced environment.

Siliceous microfossils (diatoms and radiolarians), calcareous nannofossils, and organic-walled dinoflagellates (dinocysts) are the primary source of microfossil-based age control for Hole U1356A. The different microfossil groups resolve the stratigraphy nearly exclusive of one another by depth. Diatoms provide a high-resolution stratigraphy for the uppermost lower Miocene to the lowermost Pliocene drape (the upper 387 mbsf). Calcareous nannofossils and, to a lesser extent, dinocysts resolve the lower Miocene and Oligocene interval between ~434.5 and ~875.12 mbsf). Dinocysts provide the only microfossil age control for the lowermost Oligocene and the Eocene (~895.5 and ~995.32 mbsf). Radiolarians and planktonic foraminifers provide secondary age control, which is in agreement with the other fossil groups.

Diatoms and radiolarians suggest that the Pleistocene and all but the lowermost Pliocene (i.e., 0 to ~4.2 Ma) are missing from Hole U1356A and that at least two other major hiatuses are centered around 4.6 and 28.38 mbsf. This indicates that much of the upper upper Miocene is also missing. A break in sedimentation in the lower Miocene is suggested by foraminifers and nannofossils. The duration of this hiatus is at present uncertain because of major reworking (foraminifers and pyritized siliceous microfossils) and scant biostratigraphic data through this interval, but available evidence constrains this hiatus to the earliest Miocene. A relatively thick (~375 m) Oligocene sequence is constrained by magnetostratigraphy and partially by dinocyst and provisional nannofossil data. The lowermost Oligocene, the upper Eocene, and most of the middle Eocene are missing in a long hiatus from 47.9 to 33.6 Ma based on dinocyst evidence. The oldest break in sedimentation occurs in lower Eocene strata between Sample 318-U1356A-100R-CC and 101R-CC (939.86–951.87 mbsf). Dinocyst stratigraphy indicates this hiatus spans from 52.2 to 50.8 Ma.

Three intervals with continuous enough recovery and sufficient biostratigraphic data establish a correlation to the geomagnetic polarity timescale (GPTS). Cores 318-U1356A-14R through 51R appear to correlate to polarity Chrons C5AAn to C5Cn.3n. A mid-Miocene hiatus could be placed just above Core 318-U1356A-46R because the polarity stratigraphy from Cores 318-U1356A-46R through 51R does not have a straightforward fit to Chrons 5Dn and below. Cores 318-U1356A-68R through 92R correlate to polarity Chrons C7An–C12R. The lowermost normal polarity interval in Core 318-U1356A-105R and the top part of 106R corresponds to Chron C24n.3n based on biostratigraphic evidence. Core 318-U1356A-104R is dominantly reversed polarity with a short normal polarity interval correlating to Chron C24n.2n, also based on biostratigraphic data. The top of Core 318-U1356A-104R and all of 103R record Chron C24n.1n. Whereas Core 318-U1356A-102R has reversed polarity and fits within Chron C23r, Core 318-U1356A-101R could record the base of Chron 23n.2n. The correlation of Cores 318-U1356A-100R and 99R is not straightforward because they mostly have reversed polarity, whereas Chron C23n.2n is of normal polarity. Since the transition recorded in Core 318-U1356A-101R and correlation to Chron C23n.2n fits with a constant sediment accumulation–rate model extrapolating upward from the Chron C24n tie points, the hiatus is most likely positioned between Cores 318-U1356A-101R and 100R. The smallest gap would place the transition recorded in Core 318-U1356A-99R at the base of Chron C22n with Core 318-U1356A-100R being Chron C22r in age. This magnetostratigraphic interpretation matches the dinocyst stratigraphy.

Carbonate contents for most of the section are below 2 wt%, and levels of organic carbon, sulfur, and nitrogen are below detection limits. Major and trace elements (SiO₂, Al₂O₃, TiO₂, K₂O, Na₂O, MgO, Fe₂O₃, P₂O₅, Sr, Ba, Sc, Co, and V) show pronounced downcore variations, which can be summarized in three geochemical intervals: (1) an upper interval from 0 to 878 mbsf where all elements show minor fluctuations, reflecting elemental association with biogenic and physically weathered terrigenous phases; (2) a transitional interval from 878 to 920 mbsf where all elemental concentrations show significant changes in their absolute values; and (3) a lower interval from 920 to 1000 mbsf where most elements show characteristics of highly weathered terrigenous material.

Physical properties generally change at the identified lithostratigraphic boundaries at Site U1356. Velocity, density, and porosity data clearly reflect the positions of features such as Unconformities WL-U5 and WL-U3. The grain density increases from ~2.6 g/cm³ at the seafloor to ~2.8 g/cm³ at 1000 mbsf. Magnetic susceptibility data exhibit rhythmic changes, which are especially visible in the cores with improved recovery starting at Core 318-U1356A-47R and more so from Core 318-1356A-68R downward.

Site U1357

The primary objective at Site U1357 (proposed Site ADEL-01B) was to recover a continuous ~200 m Holocene sedimentary section from the Adélie Basin located on the Antarctic continental shelf off the Wilkes Land margin. The Adélie Basin is a 1000 m deep glacially scoured trough separated from the Adélie Depression (70 km eastward) by the 200 m deep Adélie Bank (Figs. F10, F11). Previous piston and kasten coring of the upper sediment column shows that sediments in the Adélie Basin are deposited as annual to near-annual layers averaging 2 cm in thickness. The thickness of the Holocene sedimentary section above the last glacial diamict (190 m; Fig. F12) is consistent with this high rate of sedimentation being maintained for the past 10,000 y.

The ultrahigh resolution Adélie Basin Holocene section will be used to produce the first annually resolved time series of oceanographic and climatic variability derived from a Southern Ocean marine sediment core. These data can be directly compared to annual ice-core records from Antarctica's coastal ice domes as well as other marine sediment cores from the Antarctic Peninsula and other parts of the East Antarctic margin. The site is sensitive to drainage winds from Antarctica as well as the polar easterly winds, sea ice extent, the SAM, and the position of the southern boundary of the Antarctic Polar Frontal Zone in the Indian and Pacific oceans. Little is known about past variability in these systems from marine records, and none have annual or near-annual resolution. The Adélie Basin site lies directly downwind and downcurrent from the Mertz Glacier polynya (Massom et al., 2001, 2003) and therefore collects biogenic materials produced in one of Antarctica's major coastal polynyas. The Mertz Glacier polynya and underlying Adélie Depression may produce as much as 25% of all ABW (Rintoul, 1998; Marsland et al., 2004; Williams et al., 2008). Given the known presence of benthic foraminifers in the Adélie Basin and the substantial bottom water temperature anomaly associated with local high-salinity shelf water, Site U1357 has the potential to yield information on ABW production through time. Understanding Holocene climate variability at this East Antarctic site will aid in determining the range and characteristics of natural climate variability during a period of relatively constant atmospheric carbon dioxide levels. This record will also aid in the assessment of different forcing factors (solar, ocean-atmosphere interaction, and volcanic) responsible for climate change over the past 10,000 y.

Sediments accumulate in the 1000 m deep Adélie Basin (Figs. F10, F11) as a thick drape overlying a high-amplitude reflector with no underlying penetration (Fig. F12). The strong reflector is interpreted as a glacial diamict from the Last Glacial Maximum. The EAIS expanded to the shelf edge during the Last Glacial Maximum (Domack, 1982; Barnes, 1987; Eittreim et al., 1995), and the Adélie Basin was filled with ice. Ice lift-off and southward retreat from other deep shelf basins of East Antarctica occurred between 10,000 and 11,000 y ago (Siegert et al., 2008; Leventer et al., 2006). This is the expected age range of the lowermost sediments recovered from Site U1357. The seismic line shows 190 m of continuous, horizontal, parallel reflectors at the site, consistent with a drape of Holocene sediment undisturbed by sea level change or glacial erosion.

Three holes were cored at Site U1357. In Hole U1357A, Cores 318-U1357A-1H through 21X penetrated to 186.6 mbsf, recovered 183.87 m of diatomaceous ooze, and penetrated the underlying last glacial diamict. After offsetting the ship 50 m east of Hole U1357A, we cored Hole U1357B. Cores 318-U1357B-1H through 19H penetrated to 170.7 mbsf and recovered 172.44 m (101%) of sediment. Hole U1357C, offset 25 m west of Hole U1357A, produced Cores 318-U1357C-1H through 11H, penetrated to 103.8 mbsf, and recovered 110.7 m (107%) of sediment. Cores from Hole U1357A were split and described during the expedition. Cores from Holes U1357B and U1357C were preserved as whole-round sections for postcruise splitting, describing, and sampling. All cores from this site contained sediments that vigorously degassed methane and hydrogen sulfide upon decompression to 1 atmosphere. Gas pressure caused expansion of the sediment section, which resulted in the loss of some sediment from core breaks as well as section breaks, particularly above 40 mbsf. This was minimized by drilling small holes in the core liners at regular intervals.

The sediments from Site U1357A consist of three lithologic units. The uppermost Unit I is 170 m of laminated Holocene diatom ooze. Unit I overlies a 15 m transitional unit of sand and silt-bearing diatom ooze (Unit II), which in turn sits on a hard, carbonate-cemented, and poorly sorted gravelly siltstone (Unit III, a diamict). Units I and II exhibit regular laminations defined by color (alternating dark olive brown to light greenish brown layers) and textural variability. Individual laminae range in thickness from 1 to 3 cm and extend throughout the entire 186 m thick section lying on top of the diamict.

Based on analysis of multiple samples from core breaks and section breaks, Site U1357 sediments contain a well-preserved Holocene Southern Ocean diatom flora with varying contributions from cool open-ocean and sea ice–associated taxa (Armand et al., 2005; Crosta et al., 2005). Radiolarians, silicoflagellates, and sponge spicules are common and well preserved. Organic-walled dinoflagellate cysts are present as well as motile stages, abundant tintinnid loricae, and copepod remains.

Light and dark laminae were sampled throughout the Holocene section. Based on trends in diatom assemblage succession within paired laminae as well as previous work from the Adélie Basin region (Denis et al., 2006) and other laminated diatom sections from the east Antarctic margin (e.g., Stickley et al., 2005; Maddison et al., 2006), each light–dark laminae couplet is provisionally interpreted as a single season of biogenic production and accumulation. It is assumed that diatomaceous sediments begin to accumulate during spring sea ice retreat following the development of early season phytoplankton blooms in the Mertz Glacier polynya. Blooms persist through summer open-water conditions and conclude with the autumn regrowth of sea ice and destabilization of the water column. The unusually high accumulation rates (averaging 2 cm/y) are likely the result of syndepositional focusing processes that sweep biogenic debris from the shallow Adélie and Mertz banks into the deep shelf troughs of the Adélie Basin and Adélie Depression.

A low-diversity assemblage of calcareous planktonic (Neogloboquadrina pachyderma and Globigerina bulliodes) and benthic foraminifers (Globocassidulina subglobosa and Triloculina frigida) occurs in Site U1357 Holocene sediments. Planktonic foraminifers were observed throughout the sedimentary section, and benthic foraminifers were observed in several core-break samples that were sieved. The occurrence of well-preserved calcareous foraminifers is unusual in Antarctic shelf basins, as shelf bottom waters are highly undersaturated with respect to calcite. High sedimentation rates likely contribute to foraminifer preservation in the Adélie Basin sediments.

In addition to abundant diatoms and foraminifers, sediments in Hole U1357A contain large quantities of fish debris, including at least 44 layers of concentrated fish vertebrae. With abundant phosphatic, calcareous, opaline, and organic biogenic detritus, Site U1357 sediments offer an unusually diverse array of assemblage-based and geochemical environmental tracers for shore-based studies.

Site U1357 sediments posed a significant challenge for the analysis of physical properties. The sediments are so diatomaceous that they exhibit extremely low to negative magnetic susceptibility. Whole-round core analysis of all three holes using a Bartington loop sensor and split-core analysis using a point source magnetic susceptibility sensor in Hole U1357A did not yield useful data for hole to hole correlation. The production of millimeter-scale pockmarks from degassing of methane and hydrogen sulfide throughout the sediment column makes bulk density determination difficult using discrete sample analysis (moisture and density) or with the GRA densitometer. NGR levels are minimal because of the low concentration of terrigenous material in lithostratigraphic Unit I. Nevertheless, with sufficient background count correction NGR track scans yielded useful data for the correlation of cores from Holes U1357B and U1357C and a portion of cores from Hole U1357A.

Additional information for attempting hole to hole correlation was provided by magnetic susceptibility determination of >1800 discrete samples that had been taken from Hole U1357A at 10 cm intervals for postcruise foraminifer analysis. Each dried sample was weighed and analyzed with the Kappabridge KLY magnetic susceptibility detector. The Kappabridge has roughly 2 orders of magnitude greater sensitivity than the whole-core loop or split-core point source sensors. The resulting data set suggests that magnetic susceptibility measurements of discrete samples might be of use in developing a robust hole to hole correlation.

Site U1357A is located close to the south magnetic pole, and we observed the expected high inclinations in the paleomagnetic signature of split-core sections. After processing and matching paleomagnetic declinations across core breaks, Hole U1357A yielded a paleomagnetic secular variability profile that appears to match a geomagnetic secular variation model spanning the last 7000 y (CALS7k.2 of Korte and Constable, 2005) for 66°S, 144°E. The age-depth relationship predicted by application of this model to the secular variation signal obtained from Hole U1357A is consistent with that expected for this site based on radiocarbon dating of the upper 50 m of the sediment column (Costa et al., 2007) and the overall sediment sequence thickness.

Geochemical analysis of 96 sediment samples from Hole U1357A yielded CaCO₃ contents ranging from 1 to 3 wt% for most of the hole, with one distinct carbonate-rich layer (CaCO₃ > 9 wt%) at 126.34 mbsf. Organic C content is uniformly high (for Antarctic shelf sediments), between 1 and 2 wt%. C/N ratios between 7 and 12 are consistent with relatively well preserved and labile marine organic matter. SiO₂ concentrations are high (76–91 wt%) and are accompanied by low concentrations of TiO₂ (<0.3 wt%) and Al₂O₃ (<5.6 wt%), as expected for a nearly pure diatom ooze with little terrigenous input. The authigenic phosphate mineral struvite (NH₄MgPO₄·6H₂O), which forms through bacterial biomineralization in anoxic sediments in the presence of ammonium, was observed at several depths.

Headspace methane concentrations varied by more than an order of magnitude downcore, increasing from 5,000 to 43,000 ppm from 0 to 20 mbsf and then declining to highly variable concentrations at greater depths, mostly between 5,000 and 18,000 ppm. Significant concentrations of H₂S were detected as well, consistent with anoxic diagenesis of organic-rich sediments. An extensive microbiology program, focusing on phospholipid analyses and molecular 16S ribosomal ribonucleic acid (rRNA) sequencing, was completed in the upper 20 m of Hole U1357C. Pore water samples collected from adjacent whole-round core samples show no detectable SO₄⁼ except in core top samples suspected of contamination with seawater. Ammonium increases almost linearly from near-surface values of 900 to 4500 µM at 18 mbsf. Total dissolved inorganic carbon and alkalinity increase to 18 mbsf as well, to values of 79.6 and 88 mM, respectively, whereas pH drops to 7.5 at 20 mbsf. These profiles are consistent with bacterially mediated diagenesis within anoxic pore waters. Methane is derived from CO₂ reduction following the removal of SO₄⁼. Pore waters were not analyzed deeper than 20 mbsf in the core, but samples for 16S rRNA sequencing were taken from core ends to the maximum depth of penetration in Hole U1357C (103.8 mbsf).

Site U1358

Site U1358 (proposed Site WLSHE-08A) is on the continental shelf off the Adélie Coast (Fig. F18) at 499 mbsl. The main objective at Site U1358 was to core across regional Unconformity WL-U8. This unconformity marks a distinct change in the geometry of the progradational wedge from low-dipping strata below to steeply dipping foresets above (Eittreim et al., 1995; Escutia et al., 1997; De Santis et al., 2003) (Fig. F19). This is inferred to represent a significant change from intermittent glaciers to persistent oscillating ice sheets, either during the late Miocene (Escutia et al., 2005; Cooper et al., 2008) or during the late Pliocene (~3 Ma) (Rebesco et al., 2006). The steep foresets above Unconformity WL-U8 are thought to likely consist of ice proximal (i.e., till, diamictite, and debris flows) and open-water sediments deposited as grounded ice sheets extended intermittently onto the outer shelf, similar to sediments recovered at ODP Site 1167 on the Prydz Bay Trough fan (O'Brien, Cooper, Richter, et al., 2001; Passchier et al., 2003).

Site U1358 lies at the westernmost edge of the Mertz Bank (Fig. F18) and receives drainage from the EAIS through the Wilkes subglacial basin (Fig. F4). At Site U1358, Unconformity WL-U8 occurs at ~165 mbsf (0.84 s TWT) (Fig. F19). MCS reflection profiles crossing Site U1358 show gently dipping strata on the shelf that are truncated near the seafloor (Fig. F19). This provided a unique opportunity to sample across the unconformity by drilling at very shallow penetration. The record from Site U1358 will also complement the more distal (i.e., glacial–interglacial cycles) record from Site U1359, located on the continental rise.

We drilled two short holes at Site U1358 in a water depth of 499 mbsl. Unfortunately, we were only able to penetrate to 35.6 mbsf before the drill collars failed and we had to abandon the hole.

Hole U1358A was drilled to a total depth of 2.0 m and Hole U1358B was drilled to a total depth of 35.6 mbsf, both using the RCB system. The upper 8.2 m is unconsolidated and moderately to strongly disturbed by drilling. Below 8.2 mbsf, the sediments are consolidated and only slightly disturbed by drilling. Holes U1358A and U1358B penetrated diamictons and diamictites and are placed within a single lithostratigraphic unit. The diamictons in the upper 8.2 mbsf were probably deposited from floating ice. The diamictites below 8.2 mbsf were either deposited from floating ice, where crudely stratified and laminated, or subglacially with possible remobilization by glacigenic debris flow.

Sediments in Holes U1358A and U1358B contain siliceous and organic microfossils. Diatom biostratigraphy provides tentative stratigraphic control throughout the section. Pliocene strata (9.32–28.62 mbsf) are overlain by uppermost Pleistocene to Holocene strata. Dinocysts and radiolarians were encountered in trace amounts only and provide no further age constraints. Foraminifers were not encountered in holes drilled at Site U1358. Diatom assemblages suggest a high-nutrient, open-water environmental setting, similar to that of the modern-day Southern Ocean north of the winter sea ice extent. Palynological associations are a mix of reworked and in situ palynomorphs. In situ protoperidinioid dinocysts confirm a nutrient-rich environment. High abundances of reworked Mesozoic/Paleozoic microfossils indicate a significant input of eroded sediments.

Whole-core magnetic susceptibility was measured at 2.5 cm intervals (2 s measurement time). The raw data values range from 3 to 2834 instrument units (IU). However, the majority of measurements vary between 200 and 400 IU, with some peaks in Core 318-U1358B-4R representing gravel clasts. Variations in GRA density reflect variations in the composition of the Pliocene–Pleistocene diamictite that varies between clast-rich muddy and clast-rich sandy lithologies.

Site U1359

Site U1359 (proposed Site WLRIS-04A) is located on the continental rise at 4003 mbsl (Fig. F20). The main objective at Site U1359 was to obtain an expanded record for the late Neogene to Quaternary to provide a history of climate and paleoceanographic variability and to test the stability of the EAIS during the middle Miocene to Pleistocene extreme warm periods (e.g., Miocene climate optimum, early Pliocene, and Pleistocene marine isotope Stages [MIS] 31 and 11). This record was to also provide the timing and nature of deposition of the upper seismic units (i.e., above Unconformity WL-U6) defined on the Wilkes Land margin (De Santis et al., 2003; Donda et al., 2003) (Fig. F21). These units include a shift in sedimentary depocenters from the continental rise to the outer shelf, possibly corresponding to the transition from a dynamic wet-based EAIS to a more persistent cold-based EAIS (Escutia et al., 2002; De Santis et al., 2003) and inferred to occur during the late Miocene–Pliocene (Escutia et al., 2005; Rebesco et al., 2006). At Site U1359, Unconformities WL-U6, WL-U7, and WL-U8 lie at approximately 4.61, 4.44, and 4.23 s TWT, respectively (approximately 520, 323, and 126 mbsf, respectively) (Fig. F21).

Site U1359 is on the eastern levee of the Jussieau submarine channel (Figs. F20, F21). The Jussieau channel is one of the intricate networks of slope canyons that develop downslope into channels and coalescing deep-sea fans (Escutia et al., 2000). Site U1359 is located in an upper fan environment where the levee relief (measured from the channel thalweg to the top of the levee) is ~400 m (Fig. F21). MCS profiles across the site show that widespread channels with high-relief levees occur on the Wilkes Land margin above Unconformity WL-U5 (Escutia et al., 1997, 2000; Donda et al., 2003) (Fig. F21). The fine-grained components of the turbidity flows traveling through the channel and hemipelagic drape are inferred to be the dominant sedimentary processes building these large sedimentary levees (Escutia et al., 1997, 2000; Donda et al., 2003). Bottom currents can further influence sedimentation in this setting (Escutia et al., 2002; Donda et al., 2003). Similar depositional systems were drilled during Leg 178 in the Antarctic Peninsula (Barker, Camerlenghi, Acton, et al., 1999) and Leg 188 in Prydz Bay (O'Brien, Cooper, Richter, et al., 2001).

At Site U1359, Holes U1359A–U1359D were drilled to total depths of 193.50, 252.00, 168.70, and 602.2 mbsf, respectively. In Holes U1359A and U1359B, the APC system was used to refusal, followed by extended core barrel (XCB) drilling. Only the APC system was used in Hole U1359C. Hole U1359D was drilled using the RCB system and core was only recovered below 152.2 mbsf. Silty clay with dispersed clasts is the dominant lithology observed throughout all holes at Site U1359. There are noticeable variations in the amount of biogenic components, bioturbation, and sedimentary structures, in particular the presence or absence of packages of silt–fine sand laminae and large variations in diatom abundance. Five distinct lithofacies are identified based on variations in the style of laminae, bioturbation, or the relative abundance of the biogenic component. Three lithostratigraphic units are defined on the basis of observed changes in facies associations. Lithostratigraphic Unit I (0–43.5 mbsf) consists of decimeter-scale alternations of yellow-brown and olive-gray diatom-rich silty clays with dispersed clasts with occasional foraminifer-bearing clayey silt and sandy silt. Unit II (43.5–247.1 mbsf) consists of bioturbated diatom-bearing silty clays interbedded with olive-gray diatom-bearing silty clays, which are mostly massive but contain decimeter-scale packages of olive-brown silty clay with silt laminae. Unit III extends from 247.1 mbsf to the bottom of the cored section at 596.32 mbsf and consists of bioturbated diatom-bearing silty clays interbedded with laminated silty clays. The laminated silty clays contain more subtle, but persistent, submilimeter- to millimeter-scale laminae compared to Unit II. Clasts >2 mm in size occur throughout all lithostratigraphic units and are mostly dispersed in nature (i.e., trace to 1% in abundance).

The sedimentology of Units I and II is consistent with levee deposition by low-density turbidity currents, whereas the facies associations in Unit III probably represent deposition in an environment influenced by periodic variations in contour current strength or saline density flows related to bottom water production, with turbidity currents having less influence than the overlying units. The regular nature of the interbedding (i.e., beds 2–5 m thick) of the laminated and bioturbated facies within all three lithostratigraphic units suggests that the sedimentary record recovered from Site U1359 is cyclic in nature. The diatom-bearing and diatom-rich silty clays (Facies 1 and 2) were probably deposited by hemipelagic sedimentation in a higher productivity environment relative to the other facies. The clays and silty clays (Facies 3–5) indicate high terrigenous sedimentation rates and/or lower biogenic productivity, perhaps related to the duration of seasonal sea ice cover regulating light availability in surface water or wind-regulated control of the mixed layer depth, which in turn controls productivity. The opposite scenario may apply tor the diatom-bearing to diatom-rich silty clay facies (Facies 1 and 2). An increase in terrigenous input may result from ice advance across the shelf or increase in sedimentation from bottom currents. The passage of cold saline density flows related to bottom water production at the Wilkes Land margin (e.g., high-salinity shelf water flowing from the shelf into the deep ocean to form ABW) should also be considered as a potentially important sediment transport mechanism. The deposition model for recovered sediments at Site U1359 may represent a continuum of all three processes, in addition to pelagic and ice-rafted components, as indicated by the presence of diatom remains and dispersed clasts throughout.

Combined micropaleontology assigns the recovered successions at Site U1359 to the upper middle Miocene to upper Pleistocene. Integrated diatom, radiolarian, foraminifer, and magnetostratigraphic data highlight a late Pliocene to early Pleistocene hiatus (~2.5–1.5 Ma) and a lower to mid-upper Miocene condensed interval (representing ~9.8–7 Ma).

Miocene diatom assemblages mainly include open-water taxa. In addition, a notable increase in the abundance of stephanopyxid specimens may be interpreted as either an indication of shallowing water depths or an increase in reworking of shallower water sediments. The lack of planktonic and benthic foraminifers suggests that late middle Miocene bottom waters were corrosive to calcareous foraminifers except for brief periods (e.g., ~10 Ma, represented when calcareous benthic foraminifers were preserved). Also during the Pliocene, open-water taxa and variable abundances of benthic, neritic, and sea ice–associated taxa dominated diatom assemblages. The dinocyst assemblages predominantly comprise heterotrophic taxa, indicating that the biosiliceous-rich sediments were deposited in a high-productivity and sea ice–influenced setting. High abundances of sporomorphs reworked from Paleogene, Mesozoic, and Paleozoic strata suggest strong erosion in the hinterland. The general lack of planktonic and calcareous benthic foraminifers suggests that Pliocene bottom waters were corrosive to the thin-shelled tests of planktonic foraminifers. Diatom and radiolarian Pleistocene assemblages at Site U1359 are dominated by typical Neogene Southern Ocean open-water taxa with variable abundances of benthic, neritic, and sea ice–associated diatom taxa. This indicates a pelagic, well-ventilated, nutrient-rich, sea ice–influenced setting, corroborated by the presence of heterotrophic-dominated dinocyst assemblages. The preservation of planktonic foraminifers in the Pleistocene indicates that bottom waters were favorable to the preservation of calcium carbonate. Further, pervasive reworked sporomorphs of Paleogene, Mesozoic, and Paleozoic age again point to continuing strong erosion in the hinterland.

Paleomagnetic investigations at Site U1359 involved analysis of discrete samples from Holes U1359A, U1359B, and U1359D and measurement of archive halves from all four holes. A composite polarity log was correlated to the GPTS of Gradstein et al. (2004), documenting a complete Pliocene section from the top of Chron C2An to the bottom of Chron C3An. A gap including Chron Cn2 and a period of extremely slow (and probably discontinuous) sediment accumulation from Chron C3Ar to the top of Chron C5n aligns with the biostratigraphic assessments.

Routine headspace gas analyses were carried out on samples from Holes U1359A–U1359D, and 71 samples were taken for analyses of percent carbonate, carbon, nitrogen, and sulfur content, as well as major and trace element analyses. Furthermore, 51 interstitial water samples were taken in close collaboration with the microbiology samples from the top ~20 m (0.1–20.1 mbsf) of holes.

CaCO₃ contents for most samples vary between <1 and 3.2 wt%. A distinct carbonate-rich layer, with a CaCO₃ content of 39.7 wt%, was found at 372.45 mbsf and corresponds to a minor lithology of diatom-bearing nannofossil ooze. On the basis of the distribution patterns of the major and trace elements, four broad intervals can be distinguished between 0 and ~200, ~210 and ~310, ~310 and 536, and 547.39 and 594.79 mbsf.

The interstitial water measurements reveal chemical gradients that are consistent with active diagenesis of buried organic matter within the sulfate reduction zone (SRZ). Significant levels of sulfate at the bottom of the observed profile (~23 mM at 20.1 mbsf) imply that the sampled interval did not reach the carbon dioxide (methanic) reduction zone (see "Site U1357" for contrasting behavior).

Microbiological sampling was conducted in Hole U1359B and was supported with pore water sampling. A total of 52 ten-centimeter whole rounds were taken from the top 20 m and frozen at –80°C for onshore phospholipid analyses and molecular 16S rRNA sequencing. Between 20 and 200 mbsf, seventeen 5 cm³ samples were taken and preserved for onshore molecular 16S rRNA sequencing.

The physical property program for Site U1359 includes routine runs on the Whole-Round Multisensor Logger (WRMSL), which includes the GRA bulk density, magnetic susceptibility, and P-wave velocity logger (PWL) sensors, as well as NGR measurements. P-wave velocity was also analyzed, and samples were taken for moisture, density, and porosity measurements from Holes U1359A, U1359B, and U1359D. Thermal conductivity measurements were taken in cores from all holes. Cyclicities at several scales is observed in the intervals where the magnetic susceptibility ranges between 40 and ~100 IU. Furthermore, the NGR data together with the magnetic susceptibility and GRA density data were used to correlate the four holes drilled at Site U1359 and to define a composite record. In addition, pronounced lower density values between 50 and 65 mbsf (50 and 65 m core composite depth below seafloor [CCSF-A]), below the lithostratigraphic Unit I–II transition, suddenly drop at ~99.5 mbsf (~101 m CCSF-A), which coincides with the lithologic change from diatom-bearing to diatom-rich silty clays (lithostratigraphic Subunit IIa–IIb transition), as well as a shift to slightly lower values at ~248 mbsf (~264 m CCSF-A; lithostratigraphic Unit II/III boundary).

Downhole logging measurements in Hole U1359D were made after completion of RCB coring to a total depth of 602.2 mbsf (drilling depth below seafloor [DSF]). Three tool strings were deployed in Hole U1359D, the triple combination (triple combo), Formation MicroScanner (FMS)-sonic, and Versatile Sonic Imager (VSI). Hole U1359D was divided into two logging units (0–260 and 260–606 mbsf) on the basis of the logs. The upper logging unit is characterized by high-amplitude swings in bulk density, NGR, and resistivity values. It is also characterized by a lack of a compaction trend with depth; the mean bulk density value remains constant, whereas the resistivity values decrease with depth. The transition to the unit below is gradual. Logging Unit 2 is characterized by generally lower amplitude bulk density and resistivity variations than the unit above, but the several millimeter-scale alternations are still clearly defined. A normal compaction trend resumes in bulk density and sonic velocity. NGR continues to show high variability, and several large drops in NGR values are observed between 350 and 450 mbsf. Near the base of the hole at 574–580 mbsf, a 6 m interval of higher bulk density and resistivity indicates a cemented bed or series of cemented beds. Heat flow at Site U1359 was estimated at 62.4 mW/m², a typical value for the ocean floor.

Site U1360

Site U1360 (proposed Site WLSHE-09B) is on the continental shelf off the Adélie Coast (Fig. F18) at 495 mbsl. The main objective at Site U1360 was to core across the regional Unconformity WL-U3 to determine the timing and nature of the first arrival of the ice sheet to the Wilkes Land Continental Margin. Site U1360 lies at the eastern edge of the Adélie Bank (Fig. F18) and receives drainage from the EAIS through the Wilkes subglacial basin. Glacier ice and the entrained debris draining through the basin and extending to the continental shelf would provide evidence for a large-scale ice sheet on Antarctica.

Regional Unconformity WL-U3 is interpreted to record the first expansion of the EAIS across the shelf in this sector of the East Antarctic margin and therefore to separate preglacial strata below from glacial strata above (Eittreim et al., 1995; Escutia et al., 1997; De Santis et al., 2003). Drilling in Prydz Bay during Leg 188 (O'Brien, Cooper, Richter, et al., 2001), and results from Site 269 (Hayes, Frakes, et al., 1975), Leg 189 in the Tasman Gateway (Exon, Kennett, Malone, et al., 2001), and ODP Leg 182 Site 1128 in the Great Australian Bight (e.g., Mallinson et al., 2003), among others, led Escutia et al. (2005) to postulate an early Oligocene age (i.e., 33.5–30 Ma) for the development of Unconformity WL-U3.

At Site U1360, Unconformity WL-U3 was predicted to occur at ~165 mbsf (0.81 s TWT) (Fig. F22). MCS reflection profiles crossing Site U1360 show gently dipping strata on the shelf truncated near the seafloor (Fig. F22). This provided a unique opportunity to sample across the unconformity with very shallow penetration. The proximal record from Site U1360 will complement the distal record of the first arrival of the EAIS to the Wilkes Land margin obtained at Site U1356.

Hole U1360A was drilled to a total depth of 70.8 mbsf using the RCB system. Only 60 cm was recovered in the upper 14.3 mbsf, and sediments are unconsolidated and moderately to strongly disturbed by drilling (Core 318-U1360A-1R). Below 14.3 mbsf (Cores 318-U1360A-2R through 6R), the sediments are consolidated and most recovered intervals are only slightly disturbed by drilling. Based on visual core descriptions and smear slide analyses, Hole U1360A constitutes diamictons, mudstones, sandstones, and diamictites, which are placed into two lithostratigraphic units. Unit I consists of unconsolidated clast-rich sandy diamicton. The diamicton is slightly compacted but soft and crudely stratified and includes one lamina of clay-rich diatom ooze with a yellowish color in interval 318-U1360A-1R-1, 18–20 cm. A trace of diatoms is present in the matrix of the diamictite. Rare shell fragments are also present in this unit. Clast percentages are as high as 25%, and clasts are primarily composed of angular, indurated olive-green to olive-brown mudstone fragments, 2–8 mm in size. Crystalline rock clasts, including basalt and gneiss and as large as 7 cm have subrounded and faceted shapes. The unconsolidated diamictons were probably deposited from floating ice and most likely represent deposition from a floating glacier tongue or icebergs releasing debris over the site. The lamina of diatom ooze is indicative of a brief period of open-marine conditions with high productivity and low terrigenous sedimentation rates.

The top of Unit II marks a sharp change in lithology and induration of the cores, from unconsolidated diamicton above to carbonate-cemented claystone below. An early Oligocene age is assigned to the interval below interval 318-U1360A-3R-1, 8 cm, whereas no age assignment is possible for Core 318-U1360A-2R. Five different lithofacies are recognized in a sequence from top to bottom in this unit: (1) olive-green claystone with moderate bioturbation, (2) dark green claystone with dispersed clasts, (3) dark greenish gray sandy mudstone with dispersed clasts, (4) olive-brown sandstone with dispersed clasts, and (5) gray clast-rich sandy diamictite. Overall, Unit II can be characterized as a fining-upward sequence from diamictite at the base to claystone at the top. Bivalve shell fragments, some of which are pyritized, are common in the lower portion of Unit II. The lithofacies distribution is consistent with an ice-proximal to ice-distal glaciomarine depositional environment, similar to that described from the Oligocene and Miocene strata of the Victoria Land Basin, Ross Sea, Antarctica (Naish et al., 2001; Powell and Cooper, 2002). Five samples from Hole U1360A were prepared for X-ray diffraction (XRD) analysis of the clay fraction. A mixture of all the major clay mineral groups characterizes the clay mineral assemblages in these samples. The dominant clay mineral components are smectite, illite, and chlorite, with a lesser contribution of kaolinite and pyrophyllite-talc. The cores assigned to the early Oligocene have clay mineral assemblages similar to those reported from lower Oligocene shelf strata around the Antarctic margin (e.g., Hambrey et al., 1991; Ehrmann et al., 2005). The abundance of illite and chlorite are consistent with a glacial-marine depositional setting for the claystone, mudstone, sandstone, and diamictite facies described within lithostratigraphic Unit II. The relatively large contribution of talc, however, is not typical of Paleogene sediments on the Antarctic shelf and may reflect the weathering of a low-grade metamorphic facies, derived from a basic or ultrabasic igneous protolith, locally on the Wilkes Land margin or within the Wilkes subglacial basin.

Dinoflagellate cysts (dinocysts) and diatoms provide age control for Hole U1360A. They suggest that Core 318-U1360A-1R (0–0.54 mbsf) comprises an uppermost Pleistocene matrix with intraclasts of upper Eocene to lower Oligocene material. An age could not be assigned to the strata between Section 318-U1360A-1R-CC and interval 318-U1360A-3R-1, 8 cm (0.54–23.38 mbsf), because of poor recovery. Samples 318-U1360A-3R-1, 8 cm, to 6R-CC (23.38–53.78 mbsf) are of early Oligocene (< 33.6 Ma) age.

Sediments within Core 318-U1360A-1R (0–0.54 mbsf) comprise an uppermost Pleistocene matrix with intraclasts of late Eocene to early Oligocene age. Diatoms indicate that during the latest Pleistocene, the shelf at Hole U1360A was not subjected to year-round ice cover but was influenced by seasonal sea ice either directly or indirectly. Combined microfossil analyses suggest the sedimentary interval below interval 318-U1360A-3R-1, 8 cm (23.38 mbsf), is early Oligocene (<33.6 Ma) in age. Early Oligocene microfossils indicate a shallow-water shelf environment with low salinities and high nutrient levels, likely driven by seasonal sea ice. Sporomorphs may represent reworking from older strata and/or contemporaneous vegetation in the hinterland.

Two samples from Hole U1360A (Samples 318-U1360A-4R-1, 15 cm, and 4R-2, 72 cm) had reversed polarity, consistent with an age of Chron C12r as predicted by the biostratigraphy.

The fining-upward sequence from diamictites at the base (Core 318-U1360A-6R) to claystones at the top (Cores 318-U1360A-2R through 3R) is also documented in the general decrease in magnetic susceptibility values from the bottom to the top of the hole. Variations in GRA density nicely reflect variations in lithology between clast-rich diamictite, sandy mudstone with dispersed clasts, and claystone. Calculated porosity ranges from 49% to 17% and generally decreases with depth. Grain densities range from 2.62 to 2.7 g/cm³.

Site U1361

Site U1361 (proposed Site WLRIS-05A) is on the continental rise at 3466 mbsl (Fig. F23). Similar to Site U1359, the main objective at Site U1361 was to provide a history of climate and paleoceanographic variability record from the middle Miocene to the Pleistocene and to test the stability of the EAIS during extreme warm periods (e.g., Miocene climate optimum, early Pliocene, and Pleistocene MIS 31 and 11). Drilling at this site targeted the timing and nature of deposition of the upper seismic units (i.e., above Unconformity WL-U6) defined on the Wilkes Land margin (De Santis et al., 2003; Donda et al., 2003) (Fig. F24). Within these units, a shift in sedimentary depocenters from the continental rise to the outer shelf, possibly corresponds to the transition from a dynamic wet-based EAIS to a more persistent cold-based EAIS (Escutia et al., 2002; De Santis et al., 2003), which is inferred to occur during the late Miocene–Pliocene (Escutia et al., 2005; Rebesco et al., 2006). At site U1361, Unconformities WL-U6, WL-U7, and WL-U8 lie at approximately 5.13, 5.03, and 4.78 s TWT), respectively (approximately 385, 300, and 100 mbsf, respectively).

Site U1361 is located on the right (east) levee of the Jussieau submarine channel downstream from Site U1359 (Figs. F23, F24). The levee relief (measured from the channel thalweg to the top of the levee) at Site U1361 is ~195 m (Fig. F24). The fine-grained components of the turbidity flows traveling through the channel and hemipelagic drape are inferred to be the dominant sedimentary processes building these levees (Escutia et al., 1997; 2000; Donda et al., 2003). Bottom currents can further influence sedimentation in this setting (Escutia et al., 2002; Donda et al., 2003). The record from Site U1361 should be complementary to the record from Site U1359. Similar depositional environments were cored during Leg 178 in the Antarctic Peninsula (Barker, Camerlenghi, Acton, et al., 1999) and Leg 188 in Prydz Bay (O'Brien, Cooper, Richter, et al., 2001).

Two holes were drilled at Site U1361. Hole U1361A reached a total depth of 388.0 mbsf. The APC system was used to refusal at 151.5 mbsf, followed by XCB drilling to the bottom of the hole at 388.0 mbsf. Hole U1361B reached 12.1 mbsf using the APC system. Five lithofacies (designated A–E) were identified at Site U1361, and, based on their distribution in Hole U1361A, two lithostratigraphic units are defined. Facies A and B consist of clays and silty clays with common diatoms and foraminifer and rare decimeter-scale sets of millimeter- to centimeter-scale silt and clay laminae. These facies are restricted to the interval between 0.0 and 34.9 mbsf (lithostratigraphic Unit I). Facies A and B were deposited in hemipelagic depositional environments, with isolated sets of silt and clay laminae indicating occasional sedimentation from low-density turbidity currents or saline density flows in a distal levee setting (Escutia et al., 2008). Facies C and D are strongly bioturbated silty clays and diatom/nannofossil oozes with intervals containing dispersed clasts. Facies E consists of laminated clays. Facies C–E are present between 34.9 and 386.3 mbsf (lithostratigraphic Unit II) and are typical of contourite facies associations, although downslope currents possibly contributed sediment as well.

Samples 318-U1361A-1H-CC through 41X-CC (1.5–386.31 mbsf) were analyzed for microfossils. Diatoms and radiolarians provide good age control for Hole U1361A, resolving an uppermost Pleistocene through uppermost middle Miocene sedimentary succession with no major breaks in sedimentation.

Miocene diatom assemblages at Site U1361 are indicative of productive, seasonally variable, open-marine conditions. Fluctuations in the abundance of marine benthic and tychopelagic taxa such as Cocconeis spp., Diploneis spp., Paralia sulcata, stephanopyxids, and Trinacria excavata may indicate pulses of shelfal material to the drill site. The presence of well-preserved benthic foraminifers in Sample 318-U1361A-34X-CC (321.07 mbsf) suggests that depositional settings were favorable for calcite preservation (i.e., not corrosive) for brief intervals in the Miocene. The persistent presence of reworked Mesozoic/Paleozoic sporomorphs within the palynological associations suggests ongoing erosion in the hinterland.

Late Neogene diatom assemblages from sediments drilled at Site U1361 are typical Southern Ocean open-water taxa with variable abundances of benthic, neritic, and sea ice–associated diatoms, indicating a high-nutrient, high-productivity sea ice–influenced setting throughout the late Neogene. High abundances of reworked sporomorphs within the palynological associations indicate strong erosion in the hinterland. Dinocysts are absent during this interval. The preservation of planktonic foraminifers in the Pleistocene indicates that bottom waters were favorable to the preservation of calcium carbonate.

Paleomagnetic investigations at Site U1361 document a complete section from the top of Chron C2n to the top of Chron C3n. Below Chron C2n, the recovered core was disturbed, and no complete analysis of the discrete samples is obtainable as of yet. The lower portion of Hole U1361A can plausibly be correlated to the bottom of Chron C5n to Chron C5An.

Forty samples from Hole U1361A were taken for analyses of carbonate, carbon, nitrogen, and sulfur content, as well as major and trace elements. As a result of technical problems with the inductively coupled plasma–atomic emission spectrometer, no major and trace element analyses could be obtained. CaCO₃ contents for most samples are well below detection limit (<1 wt%). Between 313.96 and 342.04 mbsf, however, carbonate contents increase to 12.1–24.8 wt%. This matches the recognition of nannofossil-bearing clays constituting one of three major facies below 313.2 mbsf (Subunit IIb). Carbon, nitrogen, and sulfur contents were measured on 15 selected samples covering the full range of CaCO₃ contents (0–24.8 wt%). All concentration levels are very low (i.e., C < 0.5 wt%, N < 0.03 wt%, and S < 0.02 wt%) except for the four samples with high calcium carbonate contents. Taken together with the CaCO₃ measurements, these samples yield total organic carbon concentrations <0.3 wt%, which is within the error for the respective measurements.

The physical property program at Site U1361 included routine runs on the WRMSL, which includes the GRA density, magnetic susceptibility, and PWL sensors, as well as NGR measurements. P-wave velocity measurements were also taken, and samples were taken and analyzed for moisture, density, and porosity. Thermal conductivity measurements were made in one section of all cores. The magnetic susceptibility data exhibit relatively high amplitude variations, and this apparent cyclicity at several scales occurs especially in the upper 165 mbsf and between 305 mbsf and the bottom of the hole. There are two intervals with recurring, relatively lower magnetic susceptibility units between 165 and ~185 mbsf and between 265 and 305 mbsf. The variations in GRA density reflect the regular fluctuations in lithology and porosity. The relative moisture content varies between 63 and 22 wt%, and porosity varies from 82% to 42% with a gradual decrease with increasing depth and overburden pressure. A common feature of density, porosity, and water content records of Site U1361 is a slight change to higher gradients below 330 mbsf that occurs within lithostratigraphic Subunit IIb.

Downhole logging operations started after a successful reentry of Hole U1361A, which had been left temporarily to allow an iceberg to pass. Runs with the triple combo tool string followed by the FMS-sonic tool string in Hole U1361 were successful. The downhole logs in Hole U1361A have high-amplitude 1–5 m scale variability superimposed on a downhole compaction trend. The character of the logs changes gradually downhole, with no major steps in the base levels, so the entire logged interval was assigned to one logging unit. It is likely that Milankovitch band variability at eccentricity and possibly obliquity periods is recorded at Site U1361. The downhole measurements at Site U1361 included four advanced piston corer temperature tool (APCT-3) deployments in Hole U1361A. Thermal resistance was calculated over the intervals overlying the APCT-3 measurements, and the resulting linear fit of the temperature gives a heat flow value of 58.2 mW/m².

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