Implications of isotopic and other geochemical data from a Cretaceous-Tertiary transition in southern Africa

Isotopic, palaeontological and geochemical details of a drill-core section at Richard's Bay, South Africa, are reported. Foraminiferal evidence shows that the section encompasses a transition from the Maastrichtian to the Danian, one of the very few sites in the Southern Hemisphere on land. The carbon isotope profile of the carbonate fraction shows a large negative excursion at the transition. The corresponding oxygen isotope excursion is largely parallel but less pronounced. It is argued that this Cretaceous-Tertiary (K/T) boundary is characterised by strong and well-identified local influences, seen in the mineralogy, in trace-element data, and in partially parallel carbon and oxygen isotopic signals. A possible scenario is presented in which marine regression is accompanied by increased influence of terrestrial material in this lagoonal environment. This could point towards similar, if often less pronounced, influences in some other well-documented K/T sites.