Palaeoceanographic events in the Middle Cenomanian of Northwest Europe

Abstract

Six rhythmic (chalk/marl) mid-Cenomanian sections have been studied: Culver Cliff, Southerham, Folkestone and Cap Blanc Nez (Anglo-Pads Basin); Speeton, South Ferriby (Cleveland Basin, UK). Individual beds can be correlated on lithology, macrofauna and trace fossils. Sections span rhythms B33-C14 of Gale (1989). Planktonic foraminiferan percentage increases above rhythm C10. Lyropecten (Aequipecten) arlesiensis and Actinocamax primus only occur in marls B41 and C1, respectively. Together with Syncyclonema membranacea and Oxytoma seminudum, they accompany a double-peaked δ 13C excursion. The first, weaker peak occurs in chalk B41; the second at the C1-C2 boundary. The excursion is not diagenetic in origin and peaks result from burial of organic carbon during transgressions following sea level falls. Total organic carbon content is always <0.6%, with weak peaks coincident with the δ 13C peaks at Folkestone, but not at Southerham. Microbiotic responses across the excursion include: temporary absence of Tritaxia macfadyeni and brief appearance of Favusella washitensis; reduction in maximum size of planktonic foraminifera; and decline in dinoflagellate cyst abundance but little change in their diversity. The mid-Cenomanian carbon excursion is weaker (maximum shift 1%) than the late Cenomanian excursion and not associated with any extinctions.