| Popis: |
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 gley- sol 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 mark- ings found around the circumference of the burrow, but which are less densely concentrated on the burrow floor. Cal- careous concretions are associated with burrowed siltstone intervals, generally restricted to the lowermost decimetre, with nodules nucleating around burrows. Stable d 13 C and d 18 O isotope data on calcite cement in the burrow fill, entombing siltstone, and associated calcareous nodules all cluster together when plotted, indicating that nodule forma- tion occurred following burrow horizon abandonment and a rise in regional water table. Isotopic data reflect calcite pre- cipitation under a semi-closed system in saturated condi- tions. 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. |
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