249 Stratigraphy (Posters)

Wednesday, 12 October 2011
9:00 AM - 6:00 PM
Hall C

TECTONICALLY DRIVEN FACIES AND ARCHITECTURAL CHANGE ACROSS THE PERMIAN-TRIASSIC BOUNDARY: BEARDMORE GLACIER REGION, CENTRAL TRANSANTARCTIC MOUNTAINS, ANTARCTICA

Paper number: 249-14
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Abstract

Strata exposed in the Beardmore Glacier Region (BGR) of the Central Transantarctic Mountains preserve one of the rare, terrestrial, paleopolar Permian-Triassic (P-T) successions on Earth. A dramatic change in facies and stacking pattern across the P-T boundary is evident in all outcrops. Isolated, volcaniclastic sandy braided channels encased in organic floodplain facies of the Upper Permian Buckley Formation (BF) transition across a regional unconformity into highly interconnected, quartz-dominated sandy braided channels and relatively inorganic floodplains of the Lower Triassic Fremouw Formation (FF). BF facies include fine-grained sandstone, laminated siltstone, organic mudstone, carbonaceous shale, and coal. BF paleoenvironments included sandy braided channels, levees, splays, abundant lakes, swamps, and flora-rich soil-covered floodplains. Ichnodiversity (trace fossil variance) in the BF is high. In contrast the FF is dominated by coarser-grained sandstone and inorganic mudstone. FF paleoenvironments included flashy braided streams, abandoned channels, splays, and flora-poor floodplains. Ichnodiversity in the FF is low.

Four P-T transitional successions at Wahl Glacier, Lamping Peak, Coalsack Bluff, and Graphite Peak are compared. The P-T transition at Wahl Glacier, Lamping Peak, and Coalsack bluff is abrupt with white-black speckled volcaniclastic BF sandbodies and coal/carbonaceous shale erosionally truncated by tan-colored, coarse-grained conglomeratic sands of the FF. Rarely, greenish-gray “transitional” sandstones are found below the first distinct tan-colored FF sandbody. The P-T transition at Graphite Peak is more complex and includes a 10m-thick interval of greenish-gray “transitional” sand below the first distinct erosionally based FF sandbody.

Facies, ichnofacies, architectural, and provenance changes across the P-T boundary suggest that high accommodation, likely related to lithospheric loading, dominated during BF deposition. A transitional period reflecting a change from volcaniclastic sedimentation to quartz-dominated clastics is preserved in select areas of the basin. Sedimentation off the craton and reduced accommodation became the norm during FF deposition, with the advance of FF clastic wedges likely being time transgressive across the basin.