Reconstruction of preglacial topography using a postglacial flooding surface: Upper Paleozoic deposits, central Transantarctic Mountains, Antarctica

Upper Paleozoic glacial deposits in the central Transantarctic Mountains are the basal deposits within a late Paleozoic to early Mesozoic basin that formed along the margin of the East Antarctic Craton. This basin was a foreland basin throughout much of its his tory, and was part of a larger-scale basin that stretched across the paleo-Pacific margin of Gondwanaland. Our reconstruction of the preglacial topography in the central Transantarctic Mountains suggests that deposition began within two topographic depressions located on top of eroded rocks of the lower Paleozoic Ross Orogenic Belt. Isopach, paleocurrent, and lithofacies data support such a hypothesis, This interpretation implies that tectonic activity was not a factor in the formation of the depositional basin, and that little or no tectonic activity was occurring along the adjacent continental margin during glacial deposition. Although glacial deposits are present all along the paleo-Pacific continental margin of Antarctica and Gondwanaland, our findings suggest that initial sedimentation began within a series of discontinuous depocenters. A flooding surface that separates upper Paleozoic glacial deposits from overlying postglacial black shales in the central Transantarctic Mountains is used as a datum for reconstructing the preglacial topography. The postglacial flooding surface resulted from flooding of the depositional basin following collapse of the Gondwanide ice sheet. Results using this approach aided us in reevaluating 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 deposition of the upper Paleozoic glacial rocks. The use of a flooding surface as a datum is a technique that may be useful for reconstructing paleotopography in other settings.