Meredith Kelly

Late Cenozoic paleoenvironment in southern Victoria Land, Antarctica, based on a polar glaciolacustrine deposit in western Victoria Valley

Situated in the Transantarctic Mountains, western Victoria Valley is in a key position to test the late Cenozoic stability of the East Antarctic Ice Sheet, as well as that of the surrounding landscape surface. Victoria drift, which covers most of western Victoria Valley, represents a peculiar yet common type of deposit in the region. The sedimentology of Victoria drift is dominated by loose, sorted material, which preserves lacustrine algae, quite unlike tills in the Dry Valleys. Ridges characterize its morphology. Extraordinarily old ridges and mounds as well as fresh features and unweathered and perched boulders occur without apparent order. Accelerator Mass Spectrometry (AMS) radiocarbon dates of algae from within Victoria drift range from 11;th054 ± 95 to >45;th000 14 C yr B.P. and are not arrayed in chronological order across the drift sheet. Resting on a Miocene erosion surface, Victoria drift is the only widespread deposit in western Victoria Valley younger than ca. 14 Ma. One hypothesis is that the drift consists of moraines. The strength of this hypothesis is that it explains the arcuate form of many ridges. However, it does not explain the sedimentology, weathering characteristics, or radiocarbon dates. A second hypothesis is that Victoria drift is a unique polar glaciolacustrine sediment facies deposited by a “lake-ice conveyer.” The morphologic features, sedimentology, weathering characteristics, and radiocarbon dates of the drift are all consistent with deposition in a perennially ice-covered lake. This second hypothesis implies polar glacial conditions during deposition of the drift sheet in order to maintain a permanently ice-covered proglacial lake.