Paper No. 6
Presentation Time: 2:45 PM
NEW INSIGHTS ON THE PERMIAN-TRIASSIC BOUNDARY FROM BEARDMORE GLACIER AREA, CENTRAL TRANSANTARCTIC MOUNTAINS, ANTARCTICA: IMPLICATIONS FROM THE INTEGRATED ICHNOLOGY, SEDIMENTOLOGY, PALEONTOLOGY, AND PALEOSOLS OF THE UPPERMOST BUCKLEY FORMATION AND LOWERMOST FREMOUW FORMATION
Permian-Triassic boundary successions were studied for their ichnologic, sedimentologic, and paleopedologic characteristics in the Upper Permian Buckley (BF) and Lower Triassic Fremouw Formation (FF) in the Beardmore Glacier region, Central Transantarctic Mountains, Antarctica. Changes in trace fossil composition, occurrence, and sedimentary facies at Lamping Peak, Coalsack Bluff, Wahl Glacier, and Graphite Peak suggest decreasing ichnodiversity from the BF to the FF, reflecting a shift from high to low soil moisture and water tables and improving drainage. The upper BF contains interbedded braided river, paludal, lacustrine, and organic-rich floodplain deposits emplaced at paleopolar latitudes under a humid, cool temperate climate. The lower FF contains alternating braided river and relatively inorganic floodplain deposits also emplaced at paleopolar latitudes but under a warmer and seasonally drier climate. Traces in the BF were found mostly in paludal and lacustrine deposits, with few found in fluvial deposits and none in coal. The few small-diameter vertical and horizontal burrows found in fluvial deposits represent shallow burrowing in aquatic and semiterrestrial settings. Burrow networks, trails, and resting traces in paludal and lacustrine deposits are mostly horizontal, representing shallow tiering in aquatic settings. Paludal deposits typically contain tree stumps and logs in a variety of preservational states, commonly exhibiting evidence of burning or charring. In contrast, traces in the FF record better-drained conditions, lower soil moisture, and lower water tables. Overbank deposits contain small-diameter (~2-5 cm), large-diameter (~10-15 cm), and mega-diameter (~50 cm) vertebrate burrows that penetrate to 15-100 cm below the paleosurface. Also present are simple to complex, shallow (< 5 cm) to deep (20-50 cm) branching rhizoliths in a variety of preservation states that reflect high to low soil moisture conditions. Burrows on channel bar-forms and in abandoned channels record fluctuating flow. Some bar-forms have high concentrations of small-diameter (0.5-1 cm) vertical (10-30 cm) burrows suggesting lower water levels and diminished flow, while slack water deposits and abandoned channels contain annelid, horseshoe crab, millipede, and probable centipede trails.