REEXAMINATION OF CHANGES IN FLUVIAL STACKING PATTERN ACROSS THE PERMIAN-TRIASSIC BOUNDARY IN THE CENTRAL TRANSANTARCTIC MOUNTAINS, ANTARCTICA

Changes in fluvial stacking patterns of channel deposits are often associated with changes in fluvial style (e.g., change from meandering to braided streams), changes in the rate of the creation of accommodation (e.g., subsidence, eustatic changes in sea level), and changes in sediment influx rates (e.g., climate change, loss of vegetation). For Upper Permian and Lower Triassic strata, a number of studies have identified this change as the result of the loss of plants and increased erosion associated with the end-Permian Mass extinction. Such relationships have been identified in South Africa, Spain, eastern Australia, Russia, and Antarctica. This study re-examines the fluvial deposits in the central Transantarctic Mountains (CTM), Antarctica to better understand the controls on sedimentation during the Late Permian and Early Triassic.

Fluvial stacking patterns change across the Permian-Triassic (P/T) boundary in CTM from sparse channels contained within thick floodplain deposits in the Permian Buckley Formation to stacked channels with sparse floodplain deposits in the Lower Triassic Fremouw Formation. The Permian channels consist of fine- to medium-grained sandstone bodies with abundant cross-bedding, cross-laminations, and horizontal laminations. These deposits were previously identified as meandering rivers. However, reevaluations of the sand bodies suggest they were deposited as braided rivers. Thick successions of laminated siltstones with intermittent interbedded intervals of siltstone, fine-grained sandstone, and thin coal beds in the Buckley Formation are interpreted as strata deposited in lacustrine and mire environments. The stacked medium- to coarse-sandstone bodies of the Fremouw Formation are interpreted as braided rivers. The high abundance of lakes, floodplains, and low channel stacking suggest high accommodation in the Permian, whereas, stacked channel sandstone bodies in the Triassic suggest a low accommodation setting. We hypothesize that the change in accommodation across the P/T boundary was the result of tectonism and differential subsidence in an under-filled Permian foreland basin changing to an over-filled basin during the Triassic.