Permian and Triassic Biogenic Structures in the Shackleton Glacier Area,Transantarctic Mountains: Record of Nonmarine Benthic Communities and their Response to Climate Change

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This award supports a project to study trace fossils in the Permian and Triassic portions of the Beacon Supergroup in the central Transantarctic Mountains. The sedimentary sequence in the central Transantarctic Mountains indicates that during the Permian and Triassic this portion of the paleo-Pacific margin of Gondwana was successively covered by a continental glacier (Pagoda Formation), flooded by an inland sea (Mackellar Formation), blanketed with sediment deposited by rivers flowing across a sandy braid plain (Fairchild Formation), and covered with sands and silts deposited in braided river channels and floodplains (Buckley and Fremouw Formations). This sequence of events was induced by amelioration of the climate and changes in tectonic regime. Although the rich floras of the Buckley and Fremouw Formations and well preserved vertebrate fauna of the Fremouw Formation are the subject of continuing extensive studies, little is known about the benthic fauna that inhabited the widespread inland waters throughout the Permian and Triassic and its response to climate change. The animals themselves are not preserved as fossils, but biogenic structures, including both trace fossils (ichnofauna; discrete tracks, trails and burrows) and ichnofabric (general disruption caused by biologic activity), give information about the benthic fauna that produced them. This information includes: 1) the size and general body plan of the producers, giving keys to their identity; 2) an approximation of the faunal diversity; 3) the behavior of the producers; 4) the environmental preferences of the producers; 5) the use of trophic and spatial resources by the producers; and 6) the activity and abundance of the benthic fauna relative to physical and depositional processes, as reflected by ichnofabric. In this study, the trace fossils and ichnofabric in diverse subaqueous facies within the Mackellar, Fairchild, Buckley and lower Fremouw Formations will be described and interpreted t o develop a picture of the Permian and earliest Triassic benthic aquatic fauna and its response to climate change. Trace fossils and their sedimentological context will be described and photographed in the field, representative specimens will be collected for laboratory study, and the extent of sediment disruption by animals will be evaluated. Samples will be cut and polished in the laboratory to elucidate trace morphology and enhance ichnofabric. Very little is known about ancient nonmarine aquatic benthic communities and ichnofaunas, in spite of the fact that these habitats have been occupied since the Paleozoic. Recent work suggest that major changes in these communities occurred during the Permian and earliest Triassic when burrowers became more abundant. This study will provide rare documentation of ichnofaunal (and indirectly faunal) distributions in diverse aquatic environments at a crucial time during evolution of aquatic benthic communities, and will uniquely address the question of how aquatic benthic faunas responded to climate amelioration after glaciation. Equally important, data collected will be used to assess the ichnofaunal similarity in correlative units between Antarctica and other Gondwana continents, particularly South America and Africa, and to test hypotheses regarding differences between ichnofaunas found in equivalent depositional regimes in marine and nonmarine environments.