PALAEOCEANOGRAPHIC EVENTS IN THE MIDDLE CENOMANIAN OF NORTHWEST EUROPE

Six rhythmic (chalk/marl) mid-Cenomanian sections have been studied: C ulver Cliff, Southerham, Folkestone and Cap Blanc Nez (Anglo-Paris Bas in); Speeton, South Ferriby (Cleveland Basin, UK). Individual beds can be correlated on lithology, macrofauna and trace fossils. Sections sp an 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. Toget her with Syncyclonema membranacea and Oxytoma seminudum, they accompan y a double-peaked deltaC-13 excursion. The first, weaker peak occurs i n chalk B41; the second at the C1-C2 boundary. The excursion is not di agenetic in origin and peaks result from burial of organic carbon duri ng transgressions following sea level falls. Total organic carbon cont ent is always <0.6%, with weak peaks coincident with the deltaC-13 pea ks at Folkestone, but not at Southerham. Microbiotic responses across the excursion include: temporary absence of Tritaxia macfadyeni and br ief 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 excurs ion is weaker (maximum shift 1 parts per thousand) than the late Cenom anian excursion and not associated with any extinctions.