Sandstone petrography, provenance and plate tectonic setting in Gondwana context of the southeastern Cape-Karoo Basin

Abstract

Mineralogical and grain-size data obtained from a thin-section petrographic study of approximately 300 sandstone and diamictite samples from the Cape Supergroup and Karoo Sequence in the southeastern part of the Cape-Karoo Basin are presented. Sandstones in the Cape Supergroup fall in the ultraquartzose, quartzose, subfeldspathic, and feldspathic fields on a QFL diagram. In the Ecca Group and Adelaide Subgroup (Beaufort Group) the sandstones are ultralithofeldspathic, but in the upper units of the Karoo Sequence they range from lithic to sublithic. Deductions made by previous workers concerning the nature of the source areas that supplied sediment to the Cape-Karoo Basin are reviewed. The present study indicates that the Cape Supergroup was derived from a non-orogenic continental block