SEISMIC STRATIGRAPHIC EVIDENCE OF ICE-SHEET ADVANCES ON THE WILKES LAND MARGIN OF ANTARCTICA

The Wilkes Land continental shelf, similar to other Antarctic shelves, is underlain by thick sequences of steeply prograded glacial diamicto ns. On the outer shelf, banks that are shallower than 400 m are separa ted by broad outer-shelf troughs that deepen landward. The prograded s equences are found preferentially in these broad outer-shelf troughs. We propose that these outer-shelf prograding wedges were deposited by fallout from deforming till-layer transport beneath ice streams at tim es of ice expansion onto the continental shelf. Such deforming till-la yer transport has recently been proposed to explain seismic observatio ns beneath ice stream B of the Ross Embayment. Two prominent erosional unconformities with stratal truncations of more than 500 m indicate e rosional events that overdeepened the shelf and provided the accommoda tion space to allow the deposition of these prograding sequences in fr ont of advancing ice streams at times of past glacial maxima. The eros ional events that produced these extraordinary downcuts were caused by erosion by ice that expanded onto a shelf with water depths far too s hallow for flotation. These two particular erosional surfaces develope d either on an initially shallow shelf, or from an extraordinarily hig h flux of ice, or both.