From the inner shelf to the deep sea: depositional environments on the West Antartic Peninsula margin: a sedimentological and seismostratigraphic study (ODP LEG 178)
Aim of this study was to describe and characterize three typical West Antarctic Peninsula continental margin depositional environments. Seismic, downhole and laboratory tools and techniques were applied to record physical and chemical proxies for a mulifacetted and differenciated understanding of the particular environments. 1) A detailed seismostratigraphic characterisation of the unique Antarctic inner and outer shelf along the passive margin of the West Antarctic Peninsula has been complemented by logging informations that are tied to the seismic profiles via a new continuous depth vs. velocity profile. Sealevel fall overcompensated by increased isostatic subsidence due to ice build-up that affected the continent and the adjacent shelfs is the most likely explanation for time synchronous start of topset preservation at ~2.8 Ma observed in Antarctic Peninsula and East Antarctic shelf records in conjunction with Nothern Hemnisphere Glaciation. 2) Seismostratigraphic Model of Palmer Deep based on seismic Deep Tow Boomer records. 3) Large mounts on the continental rise along the Antarctic Peninsula margin between 63°S and 69°S and within 200 km of the shelf break are interpreted as sediment drifts, separated by turbidity current channels. Using a special standardized moving window counting routine the spatial facies information data has been transformed into a regional Antarctic Peninsula ice volume indicator curve that is in good agreement with the Lear et al., 2000 data over the past 10 Ma. This regional ice volume curve for the Antarctic Peninsula is the most significant finding of this thesis. All evaluated proxy data prove that the early Pliocene was a time of reduced global- and Antarctic ice volume (-70%) and sea ice extent. Never before and after during the last 10 Ma was palaeo productivity higher at the rise than during this time. During the late Miocene the ice sheet was highly dynamic with frequent advances and retreats. Starting at 3.2 Ma in concert with the Northern Hemisphere Glaciation the ice sheet became a permanent feature occupying the shelf during most of the glacial half cycles.
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