ICHNOFOSSILS AS PROXIES FOR POLAR ECOSYSTEMS AND CLIMATES: AN EXAMPLE OF A HYDROCLIMATE SHIFT IN PERMIAN-TRIASSIC CONTINENTAL DEPOSITS OF THE BEARDMORE GLACIER REGION OF ANTARCTICA

Continental ichnofossils are excellent proxies for ecosystem structure and paleoclimate, as they represent hidden biodiversity typically not represented by body fossils. Ichnofossils produced at high paleolatitude are useful in providing empirical data for deep-time modeling of polar continental ecosystems and climates. The Upper Permian Buckley and Lower Triassic Fremouw formations of the Beacon Supergroup in the Beardmore Glacier region contain a wealth of microbial, plant, invertebrate, and vertebrate ichnofossils in association with body fossil, sedimentological, stratigraphical, and pedological evidence that indicate a hydroclimate shift from poorly drained, high water-table conditions to well-drained, lower water table conditions across the Permian-Triassic boundary (PTB). During this transition, sediments were deposited in a foreland basin along the Panthalassan margin of Antarctica from 75–80° to 65–70° S latitude. The Buckley Formation is characterized by high water-table conditions and dominated by mostly freshwater ichnofossils in lacustrine and fluvial deposits that experienced short-term, intermittent pedogenesis represented by massive units and shallow rhizoliths. The most developed paleosols are preserved as coals; paleosols are poorly developed if present in sandstones, siltstones, and mudstones, but do contain carbonaceous and silicified roots and in situ stumps. The Fremouw Formation is characterized by lower water-table conditions. Freshwater ichnofossils, shallow rhizoliths, invertebrate trails, and vertebrate tracks dominate bars and abandoned channel deposits. Proximal and distal levee, crevasse-splay, and floodplain deposits are dominated by penetrative rhizoliths and rhizohaloes associated with simple burrows in weakly to moderately developed paleosols in poorly to moderately sorted sandstone and muddy siltstone. Small- to mega-diameter, vertebrate burrows are typical in mostly proximal floodplain deposits with weak to moderate pedogenesis. Many of the aquatic ichnofossils cross the PTB without loss in diversity; however, ichnofossils are penetrative in Triassic deposits. Ichnofossils likely reflect activity in warm summer months, similar to present-day life cycles of terrestrial and aquatic organisms in central and northern Alaska.