Late Pliocene margin development and mega debris flow deposits on the Antarctic continental margins: Evidence of the onset of the modern Antarctic Ice Sheet?

Abstract

Major global climatic changes in the Cenozoic coincided with major changes in volume of polar ice sheets, which are reflected in the sedimentary regime of polar continental margins. We compile and review the most recent evidences of the Neogene architectural change in the sedimentary units of the Antarctic continental margins to provide a comprehensive interpretation of timing and circumstances of the last of these changes.We review and interpret the seismic stratigraphy and the borehole data (where available) from 6 key sectors of East and West Antarctica: the continental margins of the Antarctic Peninsula, Prydz Bay, Wilkes Land, Weddell Sea, Eastern and Western Ross Sea. In these margins we identify the following change in the geometry of the sedimentary deposits: margin-wide erosion and subsequent progradation on the continental shelf; stratal downlap on the continental slope; major mass wasting deposits on the continental rise. The change is apparently synchronous and dated about 3 Ma in the Antarctic Peninsula and Prydz Bay margins and broadly concomitant in the others sectors. This suggests a common driving force, which we suggest to be the late Pliocene climatic change that induced the transition of the Antarctic ice sheet regime from polythermal to present polar cold, dry-based conditions. We infer that in consequence of the late Pliocene global cooling, meltwater decreased in quantity and focussed within the main ice-troughs where large ice streams began to flow. The regional erosion was followed by focussing of the sedimentary transport at the base of the large ice streams and faster progradation of sedimentary wedges at the mouth of the ice-troughs. This induced large failures of the continental slope, while the continental rise was progressively deprived of terrigenous sediments.