Glacial geomorphology of bonney drift, taylor valley, antarctica

Abstract

Taylor Dome is a small dome located at the edge of the East Antarctic Ice Sheet (EAIS) just inland of the Transantarctic Mountains (TAM) in the McMurdo Sound region of Antarctica. Taylor Dome reaches 2400m elevation and is connected to inland Dome C by a broad ice divide that extends into the interior EAIS. Taylor Glacier originates on Taylor Dome and flows eastward for 90 km into Taylor Valley in the TAM, to terminate at about 57m 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 penultimate advance of Taylor Glacier. Geomorphological analysis of Bonney drift reveals extensive lateral moraines and drift remnants on valleywalls up to 300m elevation that document an expanded Taylor Glacier which flowed through the central into the lower portion of the valley. In addition, lateral moraines of valley‐wall alpine glaciers merge into the Bonney laterals, affording evidence for concurrent advance alpine glaciers. The most striking geomorphologic features of Bonney drift are hummocky moraines deposited on the floor of central Taylor Valley. Widespread lacustrine sediments, including in situ and reworked carbonate plates with the δ18 O signature of Taylor Glacier, are associated with these hummocky moraines. Similar hummocky moraines are now being formed at the Taylor Glacier snout as it advances into the western lobe of Lake Bonney. Glaciological modeling shows that 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 in the easternmost 1.5–2.0km of the glacier is the sediment source for the frontal hummocky thrust moraines. This basal sediment is frozen onto the glacier base in a lacustrine environment, rather than resulting from wet‐based 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 numerous uranium/thorium dates of lacustrine carbonates associated with Bonney drift.