THE DIASTEMIC RECORD OF EARLY TRIASSIC RECOVERY ENVIRONMENTS IN THE KAROO BASIN, SOUTH AFRICA

The Lower Triassic Katberg Formation (Beaufort Group, Karoo Supergroup), South Africa, is a fine-grained, arenaceous unit deposited under ephemeral bedload-dominated fluvial conditions and previously interpreted as representing a continuous stratigraphic record. Its genesis was linked directly to the end-Permian extinction event and considered to exhibit the results of a trend towards aridification. The present study documents the lowermost Katberg Formation exposed at Carlton Heights, Northern Cape Province, to test the aridification hypothesis.

Four lithofacies vary in both vertical and lateral relationships, with feldspathic sandstone dominating the stratigraphy. Pisolith-size nodular conglomerate consists of pedogenically derived carbonate nodules originally precipitated within aridisols, none of which are either exposed or reported from the formation. Rather, the only evidence of extreme aridification is found within channel lag, barform, and overbank deposits marking landscape degradation. Landscape aggradation characterizes the entire stratigraphy in which two feldspathic sandstone geometries, interpreted as ephemeral sheetflood deposits and deeper, sand-bed anabranching systems, dominate. Intercalated with these sandstone bodies are overbank fines that consist of polyphase siltstone paleosols. These consist of bioturbated inceptisols overprinted by gleysols wherein large pedogenic carbonate nodules formed under a high regional water table. Evidence exists for periodic drying in these wet regimes, but no evidence exists for extreme aridity. Hence, the lowermost Katberg Formation superficially exhibits a continuous sedimentological record, but significant diastems exist as evidenced by the concentration of aridisol precipitates at the base of each degradational cycle. A wet-humid model for the Early Triassic in this part of the Karoo Basin is presented wherein this record is interpreted as a function of climate oscillations rather than either episodic uplift in the Cape Fold Belt or any ecosystem response to the end-Permian extinction.