IMPLICATIONS FOR PALEOENVIRONMENTAL CONDITIONS AT THE P/TR EXTINCTION EVENT BASED ON TRACE FOSSILS FROM THE LATE PERMIAN AND EARLY TRIASSIC OF THE KAROO BASIN

An ichnotaxon, previously reported as Macanopsis, is described as a new ichnospecies for burrows in the Late Permian and Early Triassic rocks of the Karoo Basin, South Africa. The new taxon is based on large collections from pedogenically modified overbank deposits that are interpreted as gleysols. The unlined burrows consist of a long (≥0.5 m) cylindrical tube, ranging from 1-2 cm in diameter, terminating in a slightly larger living chamber. They are passively filled and preserve a hierarchy of scratch patterns on the burrow walls that include longitudinal, transverse, and crescent shaped markings. Calcareous concretions are associated with burrowed siltstone intervals and generally restricted to the lowermost decimeter. In some instances, nodules nucleated around burrows. Stable δ¹³C and δ¹⁸O isotope data of calcite cement in the burrow fill, entombing siltstone, and associated calcareous nodules all cluster together when plotted, indicating that nodule formation occurred following burrow horizon abandonment and a rise in regional water table. Isotopic data reflect calcite precipitation under a semi-closed system under saturated conditions. A model for burrow emplacement, abandonment and infill, and subsequent cementation by calcite is presented demonstrating that previous interpretations of Late Permian and Early Triassic paleosol types associated with the P/Tr extinction event must be re-evaluated.