AAPG Annual Convention and Exhibition

Datapages, Inc.Print this page

Ichnocoenoses and Ichnofacies of Marine and Continental Deposits in Permian–Triassic Strata of the Beacon Supergroup, Beardmore Glacier Area, Central Transantarctic Mountains, Antarctica

Abstract

Ichnological investigations of Permian–Triassic strata in the Beacon Supergroup (BS), Beardmore Glacier region (BGR), have identified unique trace fossil-lithofacies and trace fossil-pedofacies associations that define ichnocoenoses and ichnofacies in marine deposits and ichnocoenoses in continental deposits. The study intervals include the: 1) Lower Permian Pagoda, Mackellar (MF), and Fairchild (FF) formations; 2) Lower–Upper Permian Buckley Formation (BF); and 3) Lower–Middle Triassic Fremouw Formation (TFF). These units were deposited at ∼65–85°S paleolatitude during the Permian–Triassic. The oldest formations studied were the MF and FF at Turnabout Ridge and Buckley Island. Strata were deposited in marine submarine fan-channel complexes (lower MF), on the prodelta and delta-front (upper MF), and on the fluvial-delta plain (FF). Trace fossil and lithofacies associations in the MF represent communities of shallow tiered and low diversity, sometimes monospecific, organism behaviors influenced strongly by an influx of sediment-laden freshwater into a marine setting: Arenicolites, Cruziana, Gordia, Lingulichnus, Lockeia, Palaeophycus, Phycodes, and Skolithos ichnocoenoses. These ichnocoenoses form the basis for depauperate and diminutive Skolithos and Cruziana ichnofacies. Trace fossil and lithofacies associations in the FF represent depauperate communities due to rapid sedimentation on the delta and delta plain. The BF at Lamping Peak (LP), Wahl Glacier (WG), and Graphite Peak (GP) records sandy braided rivers and organic-rich floodplains containing abundant shallow lakes, lake-margin forests, and gleyed weakly developed paleosols. Trace fossil and lithofacies associations represent mostly aquatic communities in rivers and lakes of shallow tiered and low diversity, sometimes monospecific, organism behaviors that record microbial mats, insects, crustaceans, and fish: Kouphichnium, Undichna, Planolites, and Cochlichnus ichnocoenoses. The TFF at WG, Wyckoff Glacier, LP, Coalsack Bluff, and GP preserve sandy braided rivers and organic-poor floodplains containing shallow ponds and abandoned channels. Weakly to more strongly modified paleosols are evident. Trace fossil and lithofacies associations represent shallow tiered aquatic and shallow to deep-tiered terrestrial communities recorded by Arenicolites, Fuersichnus, Haplotichnus, Planolites, primitive and derived archosaurs tracks, and therapsid tracks and burrows.