Occurrence of hiatuses PH and NH 1 through NH 7 in DSDP holes

Miocene paleoceanographic evolution exhibits major changes resulting from the opening and closing of passages, the subsequent changes in oceanic circulation, and development of major Antarctic glaciation. The consequences and timing of these events can be observed in variations in the distribution of deep-sea hiatuses, sedimentation patterns, and biogeographic distribution of planktic organisms. The opening of the Drake Passage in the latest Oligocene to early Miocene (25-20 Ma) resulted in the establishment of the deep circumpolar current, which led to thermal isolation of Antarctica and increased global cooling. This development was associated with a major turnover in planktic organisms, resulting in the evolution of Neogene assemblages and the eventual extinction of Paleogene assemblages. The erosive patterns of two widespread hiatuses (PH, 23.0-22.5 Ma; and NH 1, 20-18 Ma) indicate that a deep circumequatorial circulation existed at this time, characterized by a broad band of carbonate-ooze deposition. Siliceous sedimentation was restricted to the North Atlantic and a narrow band around Antarctica. A major reorganization in deep-sea sedimentation and hiatus distribution patterns occurred near the early/middle Miocene boundary, apparently resulting from changes in oceanic circulation. Beginning at this time, deep-sea erosion occurred throughout the Caribbean (hiatus NH 2, 16-15 Ma), suggesting disruption of the deep circumequatorial circulation and northward deflection of deep currents, and/or intensification of the Gulf Stream. Sediment distribution patterns changed dramatically with the sudden appearance of siliceous-ooze deposition in the marginal and east equatorial North Pacific by 16.0 to 15.5 Ma, coincident with the decline of siliceous sedimentation in the North Atlantic. This silica switch may have been caused by the introduction of Norwegian Overflow Water into the North Atlantic acting as a barrier to outcropping of silica-rich Antarctic Bottom Water. The main aspects of the present oceanic circulation system and sediment distribution pattern were established by 13.5 to 12.5 Ma (hiatus NH 3), coincident with the establishment of a major East Antarctic ice cap. Antarctic glaciation resulted in a broadening belt of siliceous-ooze deposition around Antarctica, increased siliceous sedimentation in the marginal and east equatorial North Pacific and Indian Oceans, and further northward restriction of siliceous sediments in the North Atlantic. Periodic cool climatic events were accompanied by lower eustatic sea levels and widespread deep-sea erosion at 12 to 11 Ma (NH 4), 10 to 9 Ma (NH 5), 7.5 to 6.2 Ma (NH 6), and 5.2 to 4.7 Ma (NH 7).

Chemical composition of bottom sediments and rocks from DSDP Holes 3-14 through 64-477

Data on analyses of chemical composition of DSDP samples of bottom sediments and rocks carried out in P.P. Shirshov Institute of Oceanology are reported. Basal sediments and sedimentary rocks prevail in the sample set.

Stable isotope ratios of foraminifera from various DSDP/ODP sites

The equator to high southern latitude sea surface and vertical temperature gradients are reconstructed from oxygen isotope values of planktonic and benthic foraminifers for the following five time intervals: late Paleocene, early Eocene, early middle Eocene, late Eocene, and early Oligocene. Paleotemperatures are calculated using standard oxygen isotope/temperature equations with adjustments to account for (1) variations in sea water delta18O related to changes in global ice volume over time and (2) latitudinal gradients in surface water delta18O. These reconstructions indicate that sea-surface temperatures (SST) of the Southern Oceans in the early Eocene were as high as 15°C, whereas temperatures during the late Paleocene and early middle Eocene reached maximum levels of 10°-12°C. By the late Eocene and early Oligocene high latitude SST had declined to 6 and 4°C, respectively. For most of the early Paleogene, low latitude sub-tropical temperatures remained constant and well within the range of Holocene temperatures (24°-25°C) but by the late Eocene and early Oligocene declined to values in the range of 18° to 22°C. The late Paleogene apparent decline in tropical temperatures, however, might be artificial because of dissolution of near-surface foraminifera tests which biased sediment assemblages toward deeper-dwelling foraminifera. Moreover, according to recent plate reconstructions, it appears that the majority of sites upon which the late Eocene and early Oligocene tropical temperatures were previously established were located either in or near regions likely to have been influenced by upwelling. Global deepwater temperature on average paralleled southern ocean SST for most of the Paleogene. We speculate based on the overall timing and character of marine sea surface temperature variation during the Paleogene that some combination of both higher levels of greenhouse gases and increased heat transport was responsible for the exceptional high-latitude warmth of the early Eocene.

Consolidation tests, elastic properties and grain size measurements at the consolidations samples from different Holes of IODP Expedition 302

The Integrated OceanDrilling Program's Expedition 302, the Arctic Coring Expedition (ACEX), recovered the first Cenozoic sedimentary sequence from the central Arctic Ocean. ACEX provided ground truth for basin scale geophysical interpretations and for guiding future exploration targets in this largely unexplored ocean basin. Here, we present results from a series of consolidation tests used to characterize sediment compressibility and permeability and integrate these with high-resolution measurements of bulk density, porosity and shear strength to investigate the stress history and the nature of prominent lithostratigraphic and seismostratigraphic boundaries in the ACEX record. Despite moderate sedimentation rates (10-30 m/Myr) and high permeability values (10**-15 -10**-18 m**2), consolidation and shear strength measurements both suggest an overall state of underconsolidation or overpressure. One-dimensional compaction modelling shows that to maintain such excess pore pressures, an in situ fluid source is required that exceeds the rate of fluid expulsion generated by mechanical compaction alone. Geochemical and sedimentological evidence is presented that identifes the Opal A-C/T transformation of biosiliceous rich sediments as a potential additional in situ fluid source.However, the combined rat of chemical and mechanical compaction remain too low to fully account for the observed pore pressure gradients, implying an additional diagenetic fluid source from within or below the recovered Cenozoic sediments from ACEX. Recognition of the Opal A-C/T reaction front in the ACEX record has broad reaching regional implications on slope stability and subsurface pressure evolution, and provides an important consideration for interpreting and correlating the spatially limited seismic data from the Arctic Ocean.

Cenozoic record of continental mineral deposit on Broken and Ninetyeast Ridges, Indian Ocean

The mineral component of pelagic sediments recovered from the Indian Ocean provides both a history of eolian deposition related to climatic changes in southern Africa and a record of terrigenous input related to sediment delivery from the Himalayas. A composite Cenozoic dust flux record from four sites in the central Indian Ocean is used to define the evolution of the Kalahari and Namib desert source regions. The overall record of dust input is one of very low flux for much of the Cenozoic indicating a long history of climate stability and regional hyperaridity. The most significant reduction in dust flux occurred near the Paleocene/Eocene boundary and is interpreted as a shift from semiarid climates during the Paleocene to more arid conditions in the early Eocene. Further aridification is recorded as stepwise reductions in the input of dust material which occur from about 35 to 40 Ma, 27 to 32 Ma, and 13 to 15 Ma and correlate to significant enrichments in benthic foraminifer delta18O values. The mineral flux in sediments from the northern Indian Ocean, site 758, records changes in the terrigenous input apparently related to the erosion of the Himalayas and indicates a rapid late Cenozoic uplift history. Three major pulses of increased terrigeneous sediment flux are inferred from the depositional record. The initial increase began at about 9.5 Ma and continued for roughly 1.0 million years. A second pulse with approximately the same magnitude occurred from about 7.0 to 5.6 Ma. The largest pulse of enhanced terrigenous influx occurred during the Pliocene from about 3.9 to 2.0 Ma when average flux values were severalfold greater than at any other time in the Cenozoic.

Calcium carbonate global LGM Burial rate data

Global databases of calcium carbonate concentrations and mass accumulation rates in Holocene and last glacial maximum sediments were used to estimate the deep-sea sedimentary calcium carbonate burial rate during these two time intervals. Sparse calcite mass accumulation rate data were extrapolated across regions of varying calcium carbonate concentration using a gridded map of calcium carbonate concentrations and the assumption that accumulation of noncarbonate material is uncorrelated with calcite concentration within some geographical region. Mean noncarbonate accumulation rates were estimated within each of nine regions, determined by the distribution and nature of the accumulation rate data. For core-top sediments the regions of reasonable data coverage encompass 67% of the high-calcite (>75%) sediments globally, and within these regions we estimate an accumulation rate of 55.9 ± 3.6 x 10**11 mol/yr. The same regions cover 48% of glacial high-CaCO3 sediments (the smaller fraction is due to a shift of calcite deposition to the poorly sampled South Pacific) and total 44.1 ± 6.0 x 10**11 mol/yr. Projecting both estimates to 100 % coverage yields accumulation estimates of 8.3 x 10**12 mol/yr today and 9.2 x 10**12 mol/yr during glacial time. This is little better than a guess given the incomplete data coverage, but it suggests that glacial deep sea calcite burial rate was probably not considerably faster than today in spite of a presumed decrease in shallow water burial during glacial time.