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AbstractDuring the early Pliocene a dynamic marine-based ice sheet retreated from the Wilkes Land margin with periodic ice advances beyond Last Glacial Maximum position. A change in sand provenance is indicative of a more stable Mertz Glacier system during the Late Pleistocene. East Antarctic Ice Sheet (EAIS) dynamics were evaluated through the analysis of marine diamictons from Integrated Ocean Drilling Program (IODP) site U1358 on the Adélie Land continental shelf. The warmer than present conditions of the early Pliocene coupled with the site's proximity to the landward sloping Wilkes Subglacial Basin provided the rationale for the investigations at this site. Based on visual core descriptions, particle size distributions, and major and trace element ratios, we interpret the origin of lower Pliocene strata by intermittent glaciomarine sedimentation with open-marine conditions and extensive glacial advances to the outer shelf. Heavy mineral analyses show that sand-sized detritus in the lower Pliocene strata was sourced from local intermediate to high-grade metamorphic rocks near Mertz Glacier. In contrast, Pleistocene diamictons exhibit a larger contribution from a prehnite-pumpellyite greenschist facies suggesting supply via iceberg rafting from northern Victoria Land. From this sedimentological evidence, we postulate a shift from a dynamic EAIS margin in the early Pliocene to possible stabilization in the Pleistocene.

Sequence boundary ages determined in shallow-water sediments obtained from ODP (Ocean Drilling Program) Leg 189 Site 1171 (South Tasman Rise) compare well with other stratigraphic records (New Jersey, United States, and northwestern Europe) and [[delta].sup.18]O increases from deep-sea records, indicating that significant (>10 m) eustatic changes occurred during the early to middle Eocene (51-42Ma). Sequence boundaries were identified and dated using lithology, bio- and magnetostratigraphy, water-depth changes, CaC[O.sub.3] content, and physical properties (e.g., photospectrometry). They are characterized by a sharp bioturbated surface, low CaC[O.sub.3] content, and an abrupt increase in glauconite above the surface. Foraminiferal biofacies and planktonic/benthic foraminiferal ratios were used to estimate water-depth changes. Ages of six sequence boundaries (50.9, 49.2, 48.5-47.8, 47.1, 44.5, and 42.6 Ma) from Site 1171 correlate well to the timings of [[delta].sup.18]O increases and sequence boundaries identified from other Eocene studies. The synchronous nature of sequence boundary development from globally distal sites and [[delta].sup.18]O increases indicates a global control and that glacioeustasy was operating in this supposedly ice-free world. This is supported by previous modeling studies and atmospheric [rho]C[O.sup.2] estimates showing that the first time [rho]C[O.sup.2] levels decreased below a threshold that would support the development of an Antarctic ice sheet occurred at ca. 51 Ma. Estimates of sea-level amplitudes range from ~20 m for the early Eocene (51-49 Ma) and ~25 m to ~45 m for the middle Eocene (48-42 Ma) using constraints established for Oligocene [[delta].sup.18]O records. Keywords: Eocene, eustasy, Ocean Drilling Program, Leg 189, stratigraphy, foraminifer, sea level, Australia, Site 1171.

Sequence boundary ages determined in shallow-water sediments obtained from ODP (Ocean Drilling Program) Leg 189 Site 1171 (South Tasman Rise) compare well with other stratigraphic records (New Jersey, United States, and northwestern Europe) and [[delta].sup.18] O increases from deep-sea records, indicating that significant (>10 m) eustatic changes occurred during the early to middle Eocene (51-42 Ma). Sequence boundaries were identified and dated using lithology, bio- and magnetostratigraphy, water-depth changes, CaC[O.sub.3] content, and physical properties (e.g., photospectrometry). They are characterized by a sharp bioturbated surface, low CaC[O.sub.3] content, and an abrupt increase in glauconite above the surface. Foraminiferal biofacies and planktonic/benthic foraminiferal ratios were used to estimate water-depth changes. Ages of six sequence boundaries (50.9, 49.2, 48.5-47.8, 47.1, 44.5, and 42.6 Ma) from Site 1171 correlate well to the timings of [[delta].sup.18] O increases and sequence boundaries identified from other Eocene studies. The synchronous nature of sequence boundary development from glob ally distal sites and [[delta].sup.18] O increases indicates a global control and that glacioeustasy was operating in this supposedly ice-free world. This is supported by previous modeling studies and atmospheric [rho]C[O.sub.2] estimates showing that the first time [rho]C[O.sub.2] levels decreased below a threshold that would support the development of an Antarctic ice sheet occurred at ca. 51 Ma. Estimates of sea-level amplitudes range from ~20 m for the early Eocene (51-49 Ma) and ~25 m to ~45 m for the middle Eocene (48-42 Ma) using constraints established for Oligocene [[delta].sup.18]O records. Keywords: Eocene, eustasy, Ocean Drilling Program, Leg 189, stratigraphy, foraminifer, sea level, Australia, Site 1171.

An interval of stratigraphic condensation extending for 300 km from the fluvially dominated Hudson River estuary to the adjacent continental shelf reveals stratal relationships within an unconformity-related depositional sequence that are commonly difficult to resolve in seismic reflection profiles and outcrop. High-resolution side-scan sonar and bathymetry, more than 100 sediment cores ~2 m long, and radioisotope ([sup.14]C, [sup.137]Cs) age control show that much of the valley was filled by ca. 3 to 1 ka. The present rate of sediment accumulation averages 1 mm/yr, corresponding with a sea-level rise of ~1.2 mm/ yr relative to local bedrock. Condensation is manifested today by sedimentary bypass in most parts of the estuary and by the trapping of available sediment (1.2-5.6 x [10.sup.5] t/yr [metric tons]) along narrow reaches and primarily in the vicinity of the estuarine turbidity maximum, a part of the estuary located upstream of the salinity intrusion ~25 km from the mouth (3.0 x [l0.sup.5] t/yr). Shelf condensation is due to sediment starvation. The condensed interval merges updip with a nascent sequence boundary as the estuary reaches its final filling phase and downdip with the sequence boundary that developed at the Last Glacial Maximum. Delta progradation may take place as available shelf accommodation is filled, but such sediments are expected to be removed once sea level begins to fall. This sedimentation pattern, in which a condensed interval merges with different sequence boundaries, is consistent with the stratigraphic record of the Atlantic margin back to the Paleogene and may be typical of sediment-starved margins. Keywords: estuarine sedimentation, stratigraphic condensation. Hudson River estuary.

Eustatic estimates from the backstripping of Oligocene sections are compared quantitatively with [[delta].sup.18]O data. Each of the nine Oligocene [[delta].sup.18]O events (maxima) identified in previous studies correlates with a stratigraphically determined sea-level lowstand. Oxygen isotopic records from planktonic foraminifers from western equatorial Atlantic Ocean Drilling Program (ODP) Site 929 indicate an isotopic increase of 0.16 [per thousand] per 10 m decrease in the depth of the ocean (apparent sea level, ASL). Amplitudes of ASL change also correlate with moderate- and high-resolution benthic foraminiferal [[delta].sup.18.]O records from ODP Sites 803 (western tropical Pacific) and 929 and from Deep Sea Drilling Project (DSDP) Site 522 (South Atlantic Ocean), with an isotopic change of 0.22 [per thousand] per 10 m of ASL change ([r.sup.2] = 0.807 and 0.960, respectively), and with records from ODP Site 689 (Southern Ocean; 0.13 [per thousand] per 10 m of ASL change; [r.sup.2] = 0.704). This correlation suggests that Southern Ocean deep-water temperature changes were smaller than tropical sea-surface temperature changes between million year-scale glacials and interglacials. It also suggests that the deep-sea Southern Ocean records may provide the best means to calibrate sea level to oxygen isotopes. Keywords: eustasy, apparent sea level, oxygen isotopes, Oligocene, New Jersey, calibration.

Estimates of the magnitudes of changes in third-order (0.5-2 m.y.) eustasy were obtained for Oligocene sequences defined by a suite of largely onshore boreholes of the New Jersey coastal plain. Benthic foraminiferal biofacies and multiple age constraints in a sequence stratigraphic framework formed the database for this study. The geometry of the margin through time was determined using two-dimensional backstripping. The depth ranges of benthic foraminiferal biofacies were determined from a combination of standard factor analysis techniques and the backstripped geometries. Benthic foraminiferal biofacies were then used to determine the depths of the Oligocene margin profiles obtained from backstripping. The water depths of 16 of these horizons were confirmed by independent benthic biofacies determinations from at least two wells. This internal consistency indicates that the data and the two-dimensional backstripping approach were robust. Where benthic biofacies require a vertical shift of the horizons generated by two-dimensional backstripping, eustatic changes were required and were readily calculated. Results indicate a major eustatic fall from the end of the Eocene to the first record of Oligocene deposition. Subsequent long-term shoaling of sea level through the Oligocene was ~30 m in 10 m.y. Superimposed on this long-term trend were higher frequency (third-order) variations in eustasy with amplitudes of ~40 m or less. Keywords: basin analysis, eustasy, New Jersey, Oligocene, sequence stratigraphy.

Previously published Oligocene eustatic records are compared with observed stratigraphic architecture at the New Jersey continental margin in order to evaluate the stratigraphic response to eustatic change. Lower to mid-Oligocene sequence boundaries (33.8-28.0 Ma) are associated with relatively long hiatuses (0.3-0.6 m.y.), in which sedimentation in many places terminated during eustatic falls and resumed early during eustatic rises. Upper Oligocene sequence boundaries are associated with relatively short hiatuses ([is less than] 0.3 m.y.), and provide the best constraints on phase relations between sea-level forcing and margin response. The interval represented by each upper Oligocene sequence varies in dip profile. At updip locations, landward of the clinoform rollover in the underlying sequence boundary, sedimentation commenced after the eustatic low and terminated before the eustatic high (with partial erosion of any younger record). At downdip locations, sedimentation within each sequence was progressively delayed in a seaward direction, beginning during the eustatic rise and terminating near the eustatic low. Combining data from all available boreholes, ages of sequence boundaries (correlative surfaces) correspond closely with the timing of eustatic lows, and ages of condensed sections (intervals of sediment starvation) correspond with eustatic highs. Keywords: New Jersey, Oligocene, eustasy, stratigraphic response, phase lag, sea level.

As atmospheric carbon dioxide is predicted to rise to concentrations not seen in perhaps 25 million years (Myr) (1), scientists are working to understand the impact on Earth's climate and [...]

Abstract: An apparent mismatch between published oxygen isotopic data and other paleoclimate proxies for the span from 26–16 Ma is resolved by calibration against global sea-level estimates obtained from backstripping continental margin stratigraphy. Ice-volume estimates from calibrated oxygen isotope data compare favorably with stratigraphic and palynological data from Antarctica, and with estimates of atmospheric pCO2 throughout the Oligocene to early Miocene (34–16 Ma). Isotopic evidence for an East Antarctic Ice Sheet (EAIS) as much as 30% larger than its present-day volume at glacial maxima during that span is consistent with seismic reflection and stratigraphic evidence for an ice sheet covering much of the Antarctic continental shelf at the same glacial maxima. Palynological data suggest long-term cooling during the Oligocene, with cold near-tundra environments developing along the coast at glacial minima no later than the late Oligocene. A possible mechanism for this long-term cooling is a decrease in atmospheric pCO2 from the middle Eocene to Oligocene, reaching near pre-industrial levels by the latest Oligocene, and remaining at those depressed levels throughout the Miocene. [Copyright &y& Elsevier]

The circum-Antarctic Southern Ocean is an important region for global marine food webs and carbon cycling because of sea-ice formation and its unique plankton ecosystem. However, the mechanisms underlying the installation of this distinct ecosystem and the geological timing of its development remain unknown. Here, we show, on the basis of fossil marine dinoflagellate cyst records, that a major restructuring of the Southern Ocean plankton ecosystem occurred abruptly and concomitant with the first major Antarctic glaciation in the earliest Oligocene (~33.6 million years ago). This turnover marks a regime shift in zooplankton-phytoplankton interactions and community structure, which indicates the appearance of eutrophic and seasonally productive environments on the Antarctic margin. We conclude that earliest Oligocene cooling, ice-sheet expansion, and subsequent sea-ice formation were important drivers of biotic evolution in the Southern Ocean.