Provenance evolution and chemostratigraphy of a palaeozoic submarine fan-complex: Tanqua Karoo Basin, South Africa

Geochemical studies of mudstones from boreholes in the deep water Permian Skoorsteenberg Formation in the Karoo Basin of South Africa were undertaken to assess stratigraphic and provenance evolution and the feasibility of chemostratigraphic correlation in this sedimentary setting. Data for 38 major and trace elements including rare earth elements were obtained from four boreholes from 304 samples covering proximal to distal parts of the turbidite complex. There are geochemical signals displaying systematic stratigraphic trends across the basin that imply a continuous evolution of one pre-eminent source terrain that supplied the sediment. Changes in ratios of TiO2/Al2O3, La/(La + Lu) and Th/(Th + Y) suggest an increasingly mafic contribution to the depositional system with time. Perversely, however, increasing Zr and Hf abundance up the stratigraphic succession suggest that there was also an increase in the felsic content with time. These apparently conflicting interpretations may be explained by a single source terrain that became increasingly igneous (e.g. less sedimentary rocks being weathered and supplying new sediment) with time although the progressively denuded rocks must have been predominantly mafic. The chemical index of alteration decreased with time possibly suggesting that a less intense weathering regime in the hinterland developed with time. The geochemical data set from the Skoorsteenberg Formation in the Karoo Basin have demonstrated that chemostratigraphy is not an ideal approach to correlation since the geochemical signals have substantial statistical noise that is not easily related to lithology. (C) 2004 Elsevier Ltd. All rights reserved.