Glacial geomorphology of Bonney drift, Taylor Valley, Antarctica

Taylor Dome is a small dome located at the edge of the East Antarctic Ice S heet (EAIS) just inland of the Transantarctic Mountains (TAM) in the McMurd o Sound region of Antarctica. Taylor Dome reaches 2400 m elevation and is c onnected to inland Dome C by a bread ice divide that extends into the inter ior EAIS. Taylor Glacier originates on Taylor Dome and flows eastward for 9 0 km into Taylor Valley in the TAM, to terminate at about 57 m elevation in the west lobe of Lake Bonney. Taylor Glacier was less extensive than now during the last glacial maximum and has since expanded so that it now occupies its most extensive Holocene position. Bonney drift in central and lower Taylor Valley represents the pe nultimate advance of Taylor Glacier. Geomorphological analysis of Bonney dr ift reveals extensive lateral moraines and drift remnants on valley walls u p to 300 m elevation that document an expanded Taylor Glacier which flowed through the central into the lower portion of the valley. In addition, late ral moraines of valley-wall alpine glaciers merge into the Bonney laterals, affording evidence for concurrent advance alpine glaciers. The most striki ng geomorphologic features of Bonney drift are hummocky moraines deposited on the floor of central Taylor Valley. Widespread lacustrine sediments, inc luding bt situ and reworked carbonate plates with the delta (18) O signatur e of Taylor Glacier, are associated with these hummocky moraines. Similar h ummocky moraines are now being formed at the Taylor Glacier snout as it adv ances into the western lobe of Lake Bonney. Glaciological modeling shows th at Taylor Glacier is frozen at its base except near its snout, both now and during the time of the last global glaciation. The observed basal debris i n the easternmost 1.5-2.0 km of the glacier is the sediment source for the frontal hummocky thrust moraines. This basal sediment is frozen onto the gl acier base in a lacustrine environment, rather than resulting from wet-base d conditions. The implication is that the nearly identical Bonney hummocky moraines in central Taylor Valley likewise result from downvalley expansion of a frozen-based Taylor Glacier into its proglacial lakes. This model for the formation of hummocky moraine forms the basis for interpreting the num erous uranium/thorium dates of lacustrine carbonates associated with Bonney drift.