Margin architecture reveals the transition to the modern Antarctic ice sheet ca. 3 Ma

Seismic reflection data collected primarily on the continental slope of the Pacific margin of the Antarctic Peninsula after drilling Ocean Drilling Program (ODP) Leg 178 allow us to date a regional change in the style of margin accretion to ca. 3 Ma. Late Pliocene deep erosion of continental shelf and slope, which likely included the emplacement of a megadebris-flow deposit, was followed by prominent growth of steep, relatively stable continental slope prograding wedges, while the deep distal margin sedimentation rate was significantly reduced. A review of the available stratigraphy from Deep Sell Drilling Project-ODP drilling, and correlation with available seismic stratigraphic information, allowed us to recognize comparable changes in terms of age and trends in continental margin evolution in several places around Antarctica. We argue that this late Pliocene architectural change of the Antarctic margin reflects a change in the texture and water content of the sediment delivered by the Antarctic ice sheet following the transition from wet- to dry-based ice regimes. This circum-Antarctic change coincides with the late Pliocene (ca. 3 Ma) global cooling and is proposed as the marker event of the transition to the modern cold polar dry-based Antarctic ice sheet.