REEVALUATION OF THE LATE PALEOZOIC GLACIGENIC DEPOSITS OF THE PAGODA FORMATION AT TILLITE GLACIER, CENTRAL TRANSANTARCTIC MOUNTAINS, ANTARCTICA

Antarctica has long been hypothesized to have been covered by an extensive terrestrial ice sheet during the late Paleozoic Gondwanan Ice age. Reexamination of the glacigenic units in the central Transantarctic Mountains (CTM) are challenging this conclusion and are suggesting that deposition occurred primarily in a glacimarine setting with sediment derived from ice flowing out of multiple glacial centers. In particular, study of the strata in a 190-m-thick section of the Pagoda Formation at Tillite Glacier has identified the occurrence of massive and stratified diamictites, sandstones and dropstone-bearing mudrocks. Synsedimentary deformational structures in these strata are abundant and include load (small and large-scale), dewatering, and slide and slump structures. All of these features indicate subaqueous deposition in a glacimarine environment from meltwater plumes, iceberg rafting, debris flows and other mass flow processes. At the Tillite Glacier site, a single sheared diamictite suggests subglacial deposition near the grounding line of a wet-based glacier.

Regional studies in CTM indicate that subglacial diamictites and proximal glacimarine sediments were deposited primarily along basin margins; whereas glacimarine sediments predominate within the basin. The findings of these studies contrast with earlier reports from CTM that identified these strata as the deposits of a terrestrial glacial system. Previous reports identified many of the diamictites as “tillites” and concluded that each “tillite” marked a separate glacial advance and retreat episode. A sequence stratigraphy and re-evaluation of glacial advance and retreat cycles for these deposits are currently being determined.

Re-correlation of fossil spores and pollen with Australian palynomorph zones indicate that the Antarctic glacigenic strata are restricted to the Lower Permian. The findings reported here suggest that glaciation was less widespread (temporally and spatially) in Antarctica than was previously hypothesized, and that it was unlikely that a single ice sheet covered Antarctica during the late Paleozoic.