Reconstruction of Pre-Glacial Topography using a Post-Glacial Flooding Surface: Upper Paleozoic Glacial Deposits, Central Transantarctic Mountains, Antarctica

John L. Isbell, Greg A. Gelhar, and Gina M. Seegers

Because flooding surfaces are essentially horizontal surfaces that result from an abrupt increase in water depth, they can be used as datums for reconstructing paleotopography. A flooding surface that separates upper Paleozoic glacial deposits from overlying post-glacial black shales in the central Transantarctic Mountains of Antarctica is used as a datum for reconstructing the pre-glacial topography in this region. The post-glacial flooding surface resulted from flooding of the depositional basin following the collapse of the Gondwanide Ice Sheet. Results using this approach aided us in re-evaluating the factors that controlled the formation of the depositional basin in Antarctica and in determining the tectonic setting of the paleo-Pacific margin of Antarctica during th late Paleozoic. This technique maybe useful for reconstructing paleotopography in other similar settings.

Upper Paleozoic glacial deposits in the central Transantarctic Mountains are the basal deposits within a late Paleozoic basin that formed along the margin of the East Antarctic Craton. This basin was a foreland basin throughout much of its history, and was part of a larger-scale basin that stretched across the paleo-Pacific margin of Gondwanaland. Our reconstruction of the pre-glacial topography in the central Transantarctic Mountains indicates that deposition began within two topographic depressions located on top of eroded rocks of a lower Paleozoic orogenic belt. Isopach, paleocurrent, and lithofacies data support such a reconstruction. This finding suggests that tectonic activity was not a factor in the formation a of the depositional basin, and that little or no tectonic activity was occurring along the adjacent continental margin during glacial deposition.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California