(Table T1) Mineral composition of oriented clay aggregates from ODP Leg 190 sites

Three sites were cored on the landward slope of the Nankai margin of southwest Japan during Leg 190 of the Ocean Drilling Program. Sites 1175 and 1176 are located in a trench-slope basin that was constructed during the early Pleistocene (~1 Ma) by frontal offscraping of coarse-grained trench-wedge deposits. Rapid uplift elevated the substrate above the calcite compensation depth and rerouted a transverse canyon-channel system that had delivered most of the trench sediment during the late Pliocene (1.06-1.95 Ma). The basin's depth is now ~3000 to 3020 m below sea level. Clay-sized detritus (<2 µm) did not change significantly in composition during the transition from trench-floor to slope-basin environment. Relative mineral abundances for the two slope-basin sites average 36-37 wt% illite, 25 wt% smectite, 22-24 wt% chlorite, and 15-16 wt% quartz. Site 1178 is located higher up the landward slope at a water depth of 1741 m, ~70 km from the present-day deformation front. There is a pronounced discontinuity ~200 m below seafloor between muddy slope-apron deposits (Quaternary-late Miocene) and sandier trench-wedge deposits (late Miocene; 6.8-9.63 Ma). Clay minerals change downsection from an illite-chlorite assemblage (similar to Sites 1175 and 1176) to one that contains substantial amounts of smectite (average = 45 wt% of the clay-sized fraction; maximum = 76 wt%). Mixing in the water column homogenizes fine-grained suspended sediment eroded from the Izu-Bonin volcanic arc, the Izu-Honshu collision zone, and the Outer Zone of Kyushu and Shikoku, but the spatial balance among those contributors has shifted through time. Closure of the Central America Seaway at ~3 Ma was particularly important because it triggered intensification of the Kuroshio Current. With stronger and deeper flow of surface water toward the northeast, the flux of smectite from the Izu-Bonin volcanic arc was dampened and more detrital illite and chlorite were transported into the Shikoku-Nankai system from the Outer Zone of Japan.

Isotope record of Nd-Sr-Pb in deep sea sediments from the Pacific (Table 2)

Pelagic clay of the east-central Pacific province is shown to be a mixture of three primary detrital components, reflecting continental source areas in Asia, North America, and Central and South America. Relative contributions from each source area are a function of geography, and this distribution appears to have remained constant over the past five million years, despite changing flux rates. A Q-mode factor analysis of downcore records for Pb, Sr, and Nd isotopes identified three factors that account for 98% of the total variance. These factors represent the radiogenic isotopic signatures of 1) late Cenozoic Asian dust, which dominates in the central North Pacific; 2) North American continental hemipelagic/eolian sources, restricted mainly to the easternmost North Pacific at ~30 °N latitude; and 3) Central and South American sources, restricted to areas east of ~100 °W longitude. South of the Intertropical Convergence Zone (~6 °N), the Asian dust signature diminishes abruptly. We conclude that late Cenozoic Asian dust sources can be isotopically differentiated downcore from both North American and South and Central American sources in the eastcentral Pacific. This approach has a utility for identifying changes in long-term Cenozoic atmospheric circulation patterns.

Nd-Sr isotopes, diatom and biogenic opal content of Pliocene sediments from IODP Site 318-U1361

Warm intervals within the Pliocene epoch (5.33-2.58 million years ago) were characterized by global temperatures comparable to those predicted for the end of this century (Haywood and Valdes, doi:10.1016/S0012-821X(03)00685-X) and atmospheric CO2 concentrations similar to today (Seki et al., 2010, doi:10.1016/j.epsl.2010.01.037; Bartoli et al., 2011, doi:10.1029/2010PA002055; Pagani et al., 2010, doi:10.1038/ngeo724). Estimates for global sea level highstands during these times (Miller et al., 2012, doi:10.1130/G32869.1) imply possible retreat of the East Antarctic ice sheet, but ice-proximal evidence from the Antarctic margin is scarce. Here we present new data from Pliocene marine sediments recovered offshore of Adélie Land, East Antarctica, that reveal dynamic behaviour of the East Antarctic ice sheet in the vicinity of the low-lying Wilkes Subglacial Basin during times of past climatic warmth. Sedimentary sequences deposited between 5.3 and 3.3 million years ago indicate increases in Southern Ocean surface water productivity, associated with elevated circum-Antarctic temperatures. The geochemical provenance of detrital material deposited during these warm intervals suggests active erosion of continental bedrock from within the Wilkes Subglacial Basin, an area today buried beneath the East Antarctic ice sheet. We interpret this erosion to be associated with retreat of the ice sheet margin several hundreds of kilometres inland and conclude that the East Antarctic ice sheet was sensitive to climatic warmth during the Pliocene.

Geochemical analysis at ODP Site 207-1259 from the Demerara Rise in the western equatorial Atlantic

Organic carbon-rich shales deposited during the Coniacian-Santonian Oceanic Anoxic Event 3 were drilled during ODP Leg 207 at Demerara Rise. We present integrated high-resolution geochemical records of core intervals from ODP Sites 1259 and 1261 both from nannofossil biozone CC14. Our results reveal systematic variations in marine and detrital sediment contribution, depositional processes, and bottom water redox conditions during black shale formation at two locations on Demerara Rise in different paleo-water depths. A combination of redox proxies (Fe/S, P/Al, C/P, redox-sensitive/sulfide-forming trace metals Mn, Cd, Mo, Ni, V, Zn) and other analytical approaches (bulk sediment composition, P speciation, electron microscopy, X-ray diffraction) evidence anoxic to sulfidic bottom water and sediment conditions throughout the deposition of black shale. These extreme redox conditions persisted and were periodically punctuated by short-termed periods with less reducing bottom waters irrespective of paleo-water depth. Sediment supply at both sites was generally dominated by marine material (carbonate, organic matter, opal) although relationships of detrital proxies as well as glauconitic horizons support some influence of turbidites, winnowing bottom currents and/or variable detritus sources, along with less reducing bottom water at the proposed shallower location (ODP Site 1259). At Site 1261, located at greater paleo-depth, redox fluctuations were more regular, and steady hemipelagic sedimentation sustained the development of mostly undisturbed lamination in the sedimentary record. Strong similarities of the studied deposits exist with the stratigraphic older Cenomanian-Turonian OAE2 black shale sections at Demerara Rise, suggesting that the primary mechanisms controlling continental supply and ocean redox state were time-invariant and kept the western equatorial Atlantic margin widely anoxic over millions of years.