HR: 0800h
AN: PP41B-0651    [Abstracts]
TI: Pliocene Glacial Cyclicity and Diagenetic Effects in a Deep-Sea Sediment Drift on the Pacific Margin of the Antarctic Peninsula (ODP Leg 178, Site 1095)
AU: * Hepp, D A
EM: dhepp@uni-bremen.de
AF: Department of Geosciences, Bremen University, P.O. Box 330440, Bremen, 28334 Germany
AU: * Hepp, D A
EM: dhepp@uni-bremen.de
AF: Research Center Ocean Margins (RCOM), Bremen University, P.O. Box 330440, Bremen, 28334 Germany
AU: Moerz, T
EM: tmoerz@uni-bremen.de
AF: Research Center Ocean Margins (RCOM), Bremen University, P.O. Box 330440, Bremen, 28334 Germany
AU: Thiede, J
EM: jthiede@awi-bremerhaven.de
AF: Alfred Wegener Institute for Polar and Marine Research (AWI), Am Handelshafen 12, Bremerhaven, 27570 Germany
AU: Dullo, W
EM: cdullo@ifm-geomar.de
AF: Leibniz-Institute of Marine Science (IFM-GEOMAR), Wischhofstr. 1-3, Kiel, 24148 Germany
AB: Giant deep-sea sediment drifts are widespread features along the continental rise of the West Antarctic Peninsula, representing the most proximal continuous sedimentary recorders for West Antarctic ice events and glacial-interglacial cyclicity. Sediment physical, geochemical records and x-ray images derived from ODP Leg 178 Site 1095 (Sediment Drift 7) show characteristics in glacial-interglacial cyclicity and associated sedimentary processes during Pliocene. Two boundary types dividing half-cycles have been recognized: (1) interglacial-to-glacial transitions that are distinct and characterized by a sharp boundary and abrupt change in lithology, (2) glacial-to-interglacial transitions that are diffuse and characterized by a gradual decline of sediment physical and geochemical values with a marked reduction in sedimentation rates. The last-mentioned transition is accompanied by a minima zone in magnetic susceptibility, which comprises the upper portion of glacials and lower portions of interglacials. This minima zone is linked to diagenetic processes that transform magnetic iron minerals to paramagnetic minerals. We assume anaerobic oxidation of methane at the sulfate/methane transition with a release of hydrogen sulfide that in turn reduces ferrimagnetic magnetite to paramagnetic sulfides. This process gets especially prominent in sections with low sedimentation rates and high organic fluxes. The glacial/interglacial boundaries defined in conjunction with magneto- and biostratigraphic tie-points form the framework for the calculation of relative sedimentation and accumulation rates used for reconstructing early Pliocene paleoproductivity and terrigenous flux to the drift. Warm early Pliocene climate conditions for West Antarctic Peninsula region are indicated by open ocean conditions in glacials, short residence times of the grounded ice sheet at the shelf edge with sporadic fluctuations as well as periodic collapses of the ice-sheet front. We propose a 5-phase drift sedimentation model for the early Pliocene and postulate a highly dynamic ice sheet, sensitive to Milankovich eccentricity forcing and regional climate conditions. The ice sheet lay closer to the shelf edge than it was the case during the late Quaternary.
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 4558 Sediment transport (1862)
DE: 4926 Glacial
DE: 4936 Interglacial
DE: 9310 Antarctica (4207)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005