DECIPHERING THE EARLY TRIASSIC RECOVERY ENVIRONMENT: THE SEARCH FOR MUD AGGREGATES IN THE KAROO BASIN, SOUTH AFRICA
This study tests the hypothesis that Early Triassic arid soils once existed in the Karoo Basin based on the presence or absence of pedogenic mud aggregates in the Katberg Sandstone, Carlton Heights. Other modern and ancient studies have used the presence of aggregates in fluvial deposits as an indicator of an arid and highly seasonal climate in which Vertisols were alternately wetted and dried. When eroded, sand-sized mud clasts were transported as bedload in anabranching systems recording the presence of these soil types that may no longer be in the stratigraphic record.
Criteria used in the present study to identify an “aggregate” clast include an unique shape, the inclusion of individual silt clasts within the grain boundary, and pore space surrounding an uncompressed clast. A surrounding network of quartz grains protected aggregate texture during compaction. Results, to date, indicate that aggregates are present in anabranching channel deposits at Carlton Heights. Quartz grains are very fine sand (X=98 µm) whereas aggregates are fine sand (131 µm) size. There is no evidence for Vertisols in the Katberg Formation; rather, evidence exists for Calcisols in the sequence. Hence, these may be the first evidence for pedogenic mudclast aggregates that did not originate in Vertisols.