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 diamictons. On the outer shelf, banks that are shallower than 400 m are separated by broad outer-shelf troughs that deepen landward. The prograded sequences 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 times of ice expansion onto the continental shelf. Such deforming till-layer transport has recently been proposed to explain seismic observations beneath ice stream B of the Ross Embayment. Two prominent erosional unconformities with stratal truncations of more than 500 m indicate erosional events that overdeepened the shelf and provided the accommodation space to allow the deposition of these prograding sequences in front of advancing ice streams at times of past glacial maxima. The erosional events that produced these extraordinary downcuts were caused by erosion by ice that expanded onto a shelf with water depths far too shallow for flotation. These two particular erosional surfaces developed either on an initially shallow shelf, or from an extraordinarily high flux of ice, or both.