New evidence for diachroneity of the Ecca–Beaufort contact

Abstract

The rocks of the Karoo Supergroup were deposited in a retro-arc foreland basin over an extended period from the late Carboniferous to the Middle Jurassic.1,2 They are internationally renowned for their wealth of fossils, particularly therapsids, which have enabled biostratigraphic subdivision of the rocks of the Beaufort Group3–5 and Elliot and Clarens Formations.6 Although a great deal of lithological amd palaeontological research has been done in the basin, the exact position of the Ecca–Beaufort contact remains a subject of debate. Various authors3,7,8 have hinted at the diachroneity of this contact in the main Karoo Basin, but these ideas have lacked direct evidence. This paper addresses this issue and reports on the presence of rocks of the Pristerognathus Assemblage9 (previously uppermost Tapinocephalus Zone4,10) immediately overlying the Ecca Group in the southern Free State. This discovery greatly extends the geographic occurrence of the Zone and has important implications for basin development models.

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