Distribution and Association of Sediment Gravity Flow Deposits and Glacial/Glacial-Marine Sediments Around the Continental Margin of Antarctica

Abstract

Marine resedimentation processes, in particular processes involving sediment mass movement, play a key role in determining the ultimate facies associations found in the glacialmarine environment of the Antarctic. This paper discusses the known distribution of sediment gravity flow deposits (as recognized from DSDP data, piston or Phleger core coverage, and from echo-sounding techniques) around the Antarctic continental margin, with particular emphasis upon the association of these mass transport deposits with glacial and glacial-marine sediments. Variations in glacial, bathymetric, and oceanographic conditions appear to most significantly influence the final distribution of slump deposits, debris flow deposits, and turbidites in the Weddell, Ross, and Bellingshausen Seas, and along the Wilkes Land Coast. Because much of the deep Antarctic continental margin is isolated from marine reworking by wind-generated currents, and because local gradients (up to 15°) on the glacially scoured continental shelf may easily exceed those on the continental slope, sediment gravity flow processses locally become the most effective agents of sediment transport and sorting. Due to their widespread depth distribution on the Antarctic margin, sediment gravity flow deposits are intimately interbedded with glacial and glacial-marine sediments. The association of clean turbidite sands with glacial or glacial-marine sediments of the continental shelf highlights the potential danger of assigning either depth significance or a non-glacial origin to ancient turbidite/mixtite associations. Although continental shelf topography in several areas restricts transport of sediment across the shelf and onto the continental slope, sediment has been delivered to the abyssal plain both via submarine canyons and via the intercanyon continental slope. The transport of sand to the abyssal plain via the intercanyon slope is volumetrically of lesser significance; however, this process involves the transition from slumped lithic glacial sediment to well sorted, clean turbidite sand over distances of <10 km. Transport of sand within submarine canyon systems has been active since earliest Miocene time, and has probably been the largest contributor to the total volume (up to 662,000 km2 in Weddell Sea alone) of abyssal plain sands. The activation of canyon systems by the commonly-accepted eustatic model is problematic for the isostatically depressed (average shelf depth = 450 m) Antarctic continental margin. It is possible, however, that (1) scouring at or near the canyon heads by Locally impinging contour currents or (2) an advanced ice margin, have supplied sediment to the deep canyons.