STRATIGRAPHIC AND CLAY MINERAL ANALYSES OF PERMIAN-TRIASSIC BOUNDARY SECTIONS FROM THE CENTRAL TRANSANTARCTIC MOUNTAINS, ANTARCTICA

The terrestrial expression of the Permian-Triassic boundary (PTB) in the central Transantarctic Mountains, Antarctica includes fossil soils, or paleosols, that may provide insights into the environmental context of the proposed mass extinction event at approximately 252 Ma. Stratigraphic field observations and sedimentary rock samples were collected from three different localities: Graphite Peak, McIntyre Promontory, and McIntosh Ridge (in the Cumulus Hills) in order to correlate the stratigraphy between the Beardmore and Shackleton Glacier regions (~90 km transect) and to analyze the bulk clay mineralogy of these strata to better understand their high-latitude environment of formation. These stratigraphic sections all preserve coal beds, fossilized flora (e.g., silicified wood, Glossopteris floral elements), and thin bifurcating roots found in grey wackestones identified as paleosols, or more specifically Protosols, that characterize upper Permian strata (Buckley-Fremouw Fm boundary). Lowermost Triassic sections contain vertebrate fossils (i.e. Lystrosaurus), and plant fossils such as Dicroidium (lower-middle Fremouw Fm) in strata with fine-medium grain fluvial ribbon sandstones alternating with grey unaltered wackestones. The Permian-Triassic boundary has been constrained to a narrow stratigraphic thickness of <3 m amongst the study sites. Preliminary clay mineralogy indicates that paleosols from this time and high-latitude location lack substantial pedogenic development. Furthermore, these new results are unlike previous Antarctic paleosol studies that identify berthierine as a dominant phyllosilicate mineral in earliest Triassic strata. Nevertheless, there appears to be an important ecological transition from landscapes characterized by peat-forming wetlands and localized patches of large-statured trees in the latest Permian to more “open” parklands with small-statured herbaceous plants and better drainage in the earliest Triassic. Although some results conflict with previous research, continued studies of Antarctic paleosols will enhance our knowledge of the Gondwanan PTB paleoenvironment and may give insight into changes that led to or followed the suggested mass extinction event.