The Beaufort-Stormberg Group contact – Implications for Karoo Basin development in the Triassic

Abstract

The subaerial unconformity that separates the Beaufort Group (Burgersdorp Formation) from the Stormberg Group (Molteno Formation) is currently the least documented and understood major stratigraphic contact within the fill of the main Karoo Basin of South Africa. The contact represents a major re-organisation of fluvial style, which is accompanied by a complete change in palaeontological representation as well. This work re-defines this contact and demonstrates that the aerial extent of the main Karoo Basin decreases from the Early to Middle Triassic, and that the stratigraphic gap represented by the Beaufort-Stormberg contact merges cratonwards and represents at least the upper Anisian and Ladinian in the south of the basin, and the entire Middle Triassic in the north. This unconformity is preserved in every South-Central African Karoo aged basin and must represent a major change in Triassic basinal tectonics.