Thermal Anomalies, Updoming And Non-Marine Sequence Stratigraphy: A Case History From The Karoo Basin, South Africa

Abstract

The Karoo Basin is one of the most extensively exposed and well studied of all the major Gondwana basins along the southern margin of Gondwana. It has been modelled as a retroarc foreland basin in which the basin-fill has been divided into 1st, 2nd and 3rd order depositional sequences, bounded by unconformities and/or abrupt facies changes (Catuneanu et al., 1999), and linked to specific tectonic events in the adjacent orogen to the south. In contrast, Johnson et al. (1997) state that ?no significant unconformities are known to exist within the [Karoo] basin, with the possible exception of the one at the base of the Upper Triassic Molteno Formation?. The foreland basin model further suggests that foreland basin tectonics influenced Karoo stratigraphic relations right up to the base of the Drakensberg Lavas, which are inferred to represent continental rifting, prior to Late Jurassic-Early Cretaceous separation of east and west Gondwana. This paper presents an alternative model for stratigraphic evolution of the non-marine Upper Karoo Basin in which changes in stratal geometries, stacking patterns and accommodation space are explained in terms of thermally-induced pulsed crustal uplift and continental rifting prior to basalt eruption and the separation of east and west Gondwana.