Paper No. 22
Presentation Time: 9:00 AM-6:30 PM
A DIVERSE HIGH-LATITUDE ICHNOFAUNA FROM THE PERMIAN PAGODA AND MACKELLAR FORMATIONS (BEACON SUPERGROUP), SHACKLETON GLACIER AREA, CENTRAL TRANSANTARCTIC MOUNTAINS, ANTARCTICA
A diverse high-latitude ichnofauna is described from the Beacon Supergroup in the Shackleton Glacier area of the Central Transantarctic Mountains, Antarctica. Trace fossils are from the Permian Pagoda and Mackellar formations that represent glacial, glacial-lacustrine, and post-glacial shallow marine paleoenvironments during the transition from icehouse to temperate climatic conditions. Traces from the Pagoda Formation are in rippled sandstone and siltstone beds, whereas traces from the Mackellar Formation are preserved almost entirely in black shale. Trace fossil preservation ranges from poor to moderate due to recrystallization from dolerite intrusions. Trace fossil assemblages from both formations are similar, as examples consist largely of two dominant morphologies: (1) horizontal, straight to slightly curved, overlapping trails and/or burrows of varying length and width, and (2) oblong, circular, or bilobate, convex hyporelief traces on bedding planes. Traces from the Pagoda Formation are assigned to Arenicolites, Aulichnites, Cochlichnus, Conichnus, Cruziana, Fucusopsis, Gyrochorte, Halopoa, Margaritichnus, Palaeophycus, Phycodes, Planolites, Rusophycus, Sagittichnus, Scolicia, and Treptichnus. Traces from the Mackellar Formation are assigned to Arenicolites, Aulichnites, Lockeia, Palaeophycus, Planolites, Sagittichnus, Scolicia, Selenichnites, and escape traces. The majority of traces are diminutive in size compared with typical examples. These morphotypes suggest feeding, grazing, and resting behaviors in stressed marine environments (e.g., low salinity and high sedimentation rate?) rather than freshwater lakes, and are commonplace in the Cruziana ichnofacies. A few intervals in the Pagoda Formation, however, do contain conchostracans and rare euthycarcinoids, suggesting lacustrine conditions. Potential tracemakers include, but are not limited to aquatic annelids, anemones, gastropods, trilobites or other arthropods with similar appendages, horseshoe crabs, and various other epi- and infaunal suspension- or deposit-feeding organisms. This study is the first to detail the traces in the Shackleton Glacier area that further provide clues to the paleoenvironmental conditions in a unique late Paleozoic polar ecosystem with no modern analog.