Archaeocyathid-bearing Erratics from Dwyka Subgroup (Permo Carboniferous) of South Africa, and their Importance to Continental Drift

Abstract

THE Dwyka Subgroup, forming the basal division of the Karroo Group, comprises a thick sequence of glacial morainic debris and boulder shales, together with subordinate shales, varvites, and lenticular sandstones. In the southern Cape, tillitic rocks are overlain by the so-called “Upper Dwyka shales”, an argillaceous sequence at the top of which are white-weathering carbonaceous shales, the “White Band”. The latter is overlain by a thin but persistent chert band which forms the arbitrary boundary with the overlying Ecca Subgroup. The Upper Dwyka shales have yielded all the animal fossils of this subgroup in the southern Cape. McLachlan and Anderson¹ have recorded orthocerid nautiloids, the brachiopod Attenuatella, the bivalves Phestia and (?)Nuculopsis, palaeoniscoid fish, radiolarians, spiral coprolites suggestive of the presence of sharks, fossil wood, foraminifers, and miospores from the base of the succession near Kimberley. They² favoured a Sakmarian age for this marine incursion. The non-marine² White Band has yielded the aquatic reptile Mesosaurus and the crustaceans Notocaris, “Pygaspis”, and Anthrapalaemon.