CHANGES IN FLUVIAL ARCHITECTURE ACROSS THE PERMIAN-TRIASSIC BOUNDARY IN ANTARCTICA: WAS GEOMORPHIC CHANGE DUE TO THE EXTINCTION OF LAND PLANTS, CLIMATE CHANGE, OR THE RESULT OF TECTONISM?

For the Phanerozoic, the Permian-Triassic (P-T) transition was the single most stressful time for Earth's biota. Despite the environmental impact that occurred during this interval, little is know about how the loss of vegetation modified the terrestrial landscape. Recent studies on strata in South Africa and Spain have hypothesized that changes in fluvial style across the P-T boundary were caused by an increase in sediment yield following the extinction of land plants. However, these studies did not rigorously test alternative hypotheses for the observed changes. The interval encompassed by the late Paleozoic and early Mesozoic was a time of changing climatic and tectonic conditions. Like plant extinction, climate and tectonism also influence sediment yields and result in changing depositional architectures.

Strata of the Permian Buckley and Triassic Fremouw Formations in the Beardmore Glacier region of Antarctica occur as extensive bedding-plane and cliff-face exposures. These strata, which consist of thick sandstones, siltstones, paleosols, and shales, are deposits of sandy braided streams that display a change in depositional architecture across the P-T boundary. Changes in architecture include: 1) an increase in sandstone stacking patterns, 2) an increase in channel interconnectedness, and 3) an increase in coarse- to fine-grained clastic ratios.

This study is a work in progress. We are using lithofacies, architectural analysis, paleocurrent orientations, and sandstone composition to test the legitimacies of the aforementioned hypotheses. Preliminary results suggest that the causes of geomorphic change were more complex than those suggested by previous investigations of P-T strata elsewhere.