Katbergia Gen. Nov., a New Trace Fossil from Upper Permian and Lower Triassic Rocks of the Karoo Basin: Implications for Palaeoenvironmental Conditions at the P ⁄tr Extinction Event

A new ichnogenus and ichnospecies of burrow, Katbergia carltonichnus, are described from Upper Permian and Lower Triassic rocks of the Karoo Basin, South Africa, where they are preserved in pedogenically modified overbank deposits that are interpreted as inceptisols subsequently gleysol overprinted. Sigmoidal burrows consist of a long (‡0.5 m) cylindrical tube, ranging from 1–2 cm in diameter, terminating in a slightly larger living chamber. The burrows are unlined and passively filled, preserving a hierarchy of scratch patterns on the burrow walls. Scratch patterns include longitudinal, transverse, and crescent-shaped markings found around the circumference of the burrow, but which are less densely concentrated on the burrow floor. Calcareous concretions are associated with burrowed siltstone intervals, generally restricted to the lowermost decimetre, with nodules nucleating around burrows. Stable dC and dO isotope data on 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 in 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 palaeosol types associated with the P ⁄Tr extinction event must be re-evaluated.