HR: 15:25h
AN: NS33A-08    [Abstracts]
TI: Ground-Penetrating Radar Studies of Late Pleistocene-Holocene Lacustrine Deltas in Lower Taylor Valley, Antarctica: Implications for Lake History
AU: * Horsman, J L
EM: jlhorsman@plymouth.edu
AF: Center for the Environment Plymouth State University, MSC #63, Plymouth, NH 03264, United States
AU: Prentice, M L
EM: mlprenti@indiana.edu
AF: Indiana Geological Survey Department of Geological Sciences, Indiana University 611 N. Walnut Grove, Bloomington, IN 47405-2208, United States
AU: Arcone, S A
EM: Steven.A.Arcone@erdc.usace.army.mil
AF: U.S. Army ERDC-Cold Regions Reseach and Engineering Laboratory, 72 Lyme Road, Hanover, NH 03755, United States
AU: Delaney, A J
EM: Allan.J.Delaney@erdc.usace.army.mil
AF: U.S. Army ERDC-Cold Regions Reseach and Engineering Laboratory, 72 Lyme Road, Hanover, NH 03755, United States
AB: We conducted multiple-frequency (100 to 900 MHz) ground-penetrating radar surveys of sandy terraces along streams in lower Taylor Valley, Antarctica, to determine their origin. These terraces are presently identified as relict deltas formed by glacial meltwater streams entering Glacial Lake Washburn which was dammed by a lobe of the Ross Sea component of the West Antarctic Ice Sheet (WAIS) during the Last Glacial Maximum (LGM) and subsequent deglacial period. The maximum elevation of the lake surface during the LGM, 350 m asl, and its subsequent history are controversial. Previous evidence for paleo lake levels comes largely from the deltas. We collected radar profiles on four sandy terraces along two streams in the Lake Fryxell basin, Delta and Crescent Streams, up to 120 m asl. Reflector geometry is interpreted as primarily representing sedimentary bedding. The GPR images show deltaic sediments composed of topset and foreset beds with thicknesses of 2 to 3 m draped over crudely stratified, most likely alluvial sediments. The deltaic sediments are commonly less than about 50 percent of the volume of the morphologic features that exhibit 4 to 6 m of relief. Thus, most terraces are delta- capped alluvial deposits. The deltaic sediments are commonly composed of multiple sets of topset-foreset units separated by erosion surfaces. The architecture of the units as well as the trajectories of topset-foreset contacts within the units indicate that, as the deltas prograded into the lake, lake-levels both fell and rose a few meters. Overall, we infer that the glacial lake was shallower at its margin than previously inferred. Further, meter-scale lake-level fluctuations were superimposed on the long-term, deglacial lake-level fall of at least 100 m.
DE: 9310 Antarctica (4207)
SC: Near-Surface Geophysics [NS]
MN: 2007 Fall Meeting