Complex exposure history of pre-LGM glacial drifts in Terra Nova Bay (Victoria Land), using a multiple cosmogenic nuclide approach.

Glacially scoured morphology characterizes coastal piedmonts in the Terra Nova Bay area. Rounded mountain tops occur below the highest erosional trimlines on the flanks of glacial troughs draining the East Antarctic Ice Sheet (EAIS) and in intervening reliefs. Complex older drifts rest on deglaciated areas above the younger late Pleistocene glacial drift. The authors use geomorphological and glacial geological surveys and surface exposure dating to reconstruct a local chronology of pre-Last Glacial Maximum (LGM) variations of the EAIS and related outlet glaciers. Glacially transported erratics, as well as bedrock surfaces were sampled for cosmogenic-nuclide analysis (10Be and 21Ne). Bedrock samples show consistent 10Be and 21Ne exposure ages indicating exposure since at least 4 Ma with an erosion rate of about 17 cm/Ma; contrary to this, exposure ages of the older drift(s) range from 87 ka to 1352 ka. Furthermore, differences between 21Ne and 10Be exposure ages of the erratics indicate complex exposure histories with substantial periods of burial by cold-based ice. Rounded mountain tops represent relict landscape features eroded by the EAIS and its related inter-connected glacier system which overrode the whole coastal area; afterwards, the coastal piedmonts were repeatedly exposed and buried by ice from local and outlet glaciers which did not modify the pre- existing landscape.