WHEN DID GONDWANA GLACIATION OCCUR IN ANTARCTICA, AND HOW LARGE WERE THE GLACIERS? THE STRATIGRAPHIC AND PALEOGEOGRAPHIC IMPLICATIONS OF GLACIOTECTONIC DEFORMATION WITHIN PERMIAN STRATA, SOUTHERN VICTORIA LAND AND DARWIN GLACIER REGIONS, ANTARCTICA

Glaciogenic rocks of the Permian Metschel Tillite and Darwin formations in southern Victoria Land and the Darwin Glacier region contain glaciotectonic and soft-sediment deformational structures that include: (1) folded, faulted, and sheared diamictites and pre-glacial (Devonian) strata; (2) thrust faults, sheets and nappes of Permian glacial and Devonian strata; and (3) massive Devonian sandstone with dewatering pipes/sheets, and sand volcanoes that protrude above the pre-glacial erosion surface cut on top of the Devonian Hatherton Sandstone. These structures formed as subglacial deforming beds, thrust moraines at glacial termini, and as proglacial water expulsion features. The orientations of these features indicate that glaciotectonic transport, and associated glacial flow, was convergent within southern Victoria Land with flow off the East Antarctic Craton from the west, and off an area located in the direction of the present Ross Sea to the east. The occurrence of glaciotectonic structures and associated paleoflow indicators imply that Victoria Land was located along the ice margin during Gondwana glaciation rather than located beneath a major ice spreading center as previously hypothesized, thus dramatically limiting the size of the Gondwana glaciers in Antarctica, and hence Gondwanaland. The contact separating glaciogenic strata from underlying Devonian rocks was deformed by soft sediment shearing and liquefaction. The occurrence of unconsolidated Devonian sands at the time of Permian glaciation suggests that this area was not previously glaciated, otherwise the land surface would have been stripped down to bedrock. Such features limit the timing of late Paleozoic glaciation in this part of Antarctica to the Permian, and severely restrict the theoretical size of Gondwanide ice sheets during the Carboniferous (if present) and Permian.