Paper No. 133-0
TEPHRA-FILLED TROUGHS IN PATTERNED GROUND: A PROXY FOR THE DISTRIBUTION OF SUBSURFACE ICE
LEWIS, Adam R., MARCHANT, David R., and MOORE, Eric J., Department of Earth Sciences, Boston Univ, 685 Commonwealth Ave, Boston, MA 02215, alewis@bu.edu

Contraction-crack polygons occur at the surface of unconsolidated debris in the western Dry Valleys region of Antarctica. In plan view, V-shaped troughs circumscribe active polygons. The concentration of subsurface ice is a primary control for the cross-sectional shape of polygon troughs. Deep troughs, in excess of 3 m deep and 5 m wide, form in sediment saturated with ice (for example, stagnant debris-covered glaciers). Shallow troughs, ~1 m deep and of variable width, form in sediment undersaturated with ice (for example, ice-cemented sand-and-gravel deposits). Trough depth is thus a proxy for the concentration of underlying ice. A proxy for paleo-ice concentration in surface deposits comes from examining the configuration of tephra that occupies ancient polygon troughs. Ashfall faithfully represents the cross-sectional shape of troughs, just as the configuration of recent snowfall conforms to the shape of modern polygon troughs. Cryoturbation beyond that associated with thermal contraction is minimal in the hyper-arid, cold desert climate of the western Dry Valleys region. Here, we describe the morphology of dated ashfall that occupies relict polygon troughs in the western Asgard Range and in the Quartermain Mountains. The results suggest that ice-cored drifts were of greater areal extent during mid-to-late Miocene time than they are today.

GSA Annual Meeting, November 5-8, 2001
General Information for this Meeting
Session No. 133--Booth# 78
Quaternary Geology/Geomorphology (Posters) I
Hynes Convention Center: Hall D
1:30 PM-5:30 PM, Wednesday, November 7, 2001
 

Copyright 2001 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.