The Cenomanian–Turonian extinction and oceanic anoxic event: evidence from southern Tibet

Abstract

Deep shelf locations on the Perigondwanan margin of southern Tibet record a major extinction of foraminifera and calcareous nannoplankton in the latest Cenomanian (top of the Rotalipora cushmani Zone). This is followed by a low diversity survival interval that straddles the Cenomanian–Turonian boundary ( Whiteinella archaeocretacea Zone) during which only low diversity, surface water-dwelling foraminifera and nannoplankton and ‘microfilaments’ are present. Rapid recovery in the early Turonian saw the appearance of new species, the reappearance of many Lazarus species and the reestablishment of a diverse community of planktonic foraminifera that included a range of shallow to deep-water column dwellers. The extinction and survival intervals coincide with the development of dysaerobic facies characterised by small-sized burrows and moderately large-sized framboid pyrite populations. At no time does the water column appear to have become sulfidic. This study indicates that the end-Cenomanian oceanic anoxic and extinction events were also manifested in moderately high southerly palaeolatitudes on the southern margin of the Tethyan Ocean, thereby increasing the known extent of this global event, albeit with the proviso that the ‘anoxic event’ was a dysoxic one.