FLUVIAL SYSTEMS AND CARBONATE NODULES REVEAL LATE PERMIAN CLIMATE CHANGE AT WAPADSBERG PASS, EASTERN CAPE PROVINCE, SOUTH AFRICA

Changes in late Permian climate are crucial to understand the dynamics responsible for the end Paleozoic mass extinction. The Karoo Basin, South Africa, has been the focus for documenting terrestrial ecosystem response because of Permian and Triassic rocks that cross the purported boundary. The present study builds on previously reported stratigraphy at outcrops exposed in Wapadsberg Pass near Graaff Reinet, Eastern Cape province.

The R61 roadcut consists of interfluvial and fluvial deposits of aggradational and degradational landscapes. Floodplain aggradation includes fining-upward sequences of fine sand and silt in m-scale beds. Weakly developed paleosols are identified by vertical to sub-vertical rhizoconcretions and/or horizons of calcite-cemented nodules. Meandering rivers represent initiation of degradational processes and include basal channel deposits of fine-to-medium Qtz-wackes in lenticular geometries. Channels fills consist of either sandstone bar forms and/or siltstone plugs of abandonment. Landscape equilibrium is demonstrated by rooted paleosols and an autochthonous forest litter.

Stable isotope values from carbonate-cemented concretions show a positive δ¹³C excursion to -5.7 PDB in paleosols ~60 m below the P/T boundary without significant deviation in δ¹⁸O SMOW values. Subsequently, δ¹³C values become more negative upsection reaching -14.9 at the P/T boundary. These trends are interpreted to represent a change from increasingly seasonal to more wetland conditions in the latest Permian. There is no significant change in δ¹⁸O SMOW values.

Climate trends based on stable isotope data are augmented by physical stratigraphy. Meandering channel fills are characterized by multiple, stacked paleosols within abandoned channels, indicating the presence of ephemeral conduits and dramatic swings in seasonality. These data may support an overall drying trend in the latest Permian, although wetlands play more of a role in the landscape than previously recognized.