The most common sediment type cored on the continental shelf is relict diamicton. Sediments were deposited by grounded ice (basal tills) through lodgement processes or from floating ice. The seaward limit of basal tills is the shelf edge. Glacial marine sediments derived from floating ice are probably deposited near the grounding line of ice shelves. Several criteria distinguish basal tills from glacial marine sediments.
Sedimentation on exposed Antarctic continental shelf is predominantly marine rather than glacial. Antarctica generally lacks a wave dominated coastal zone and the continental shelf is unusually deep (average 500 m). Therefore, waves and wind-generated currents have little influence on bottom sediments. Tidal and thermohaline currents are apparently too weak to erode the cohesive basal tills and glacial marine sediments. Mass-flow processes are the important factors in shelf sedimentation today. Turbidites, consisting of well sorted quartz sands, are widespread on the continental margin and abyssal floor. These sands are commonly interbedded with poorly sorted glacial marine sediments. Calcareous turbidites have also been cored in the Ross Sea. Laminated siliceous oozes, which are almost devoid of ice-rafted debris, fill many shelf depressions.
At the shelf edge and upper slope, geostrophic currents erode the bottom and transport sands by traction, while silts and clays are suspended and transported parallel to the slope. These currents are disrupted only in areas where shelf waters are sufficiently dense to displace and mix with circumpolar waters (thermohaline mixing). This mixed bottom water flows downslope at velocities of only a few centimeters per second, depositing laminated silts along the flow path. Ice-rafting diminishes sharply seaward of the present ice front, and ice-rafted debris comprises a minor component of slope and rise deposits.