Eight belemnite biohorizons in the Cenomanian of northwest Europe and their importance

Eight belemnite biohorizons (BB) are recognized in the Cenomanian of northwest Europe, and can be related to both the ammonite zonal/subzonal and Cenomanian cyclostratigraphic schemes. These biohorizons are: BB I (Neohibolites praeultimus) in the basal Neostlingoceras carcitanense Subzone (Mantelliceras mantelli Zone); BB2 (Neohibolites ultimus) in the upper N. carcitanense Subzone (M. mantelli Zone); BB3 (N. ultimus) in the Sharpeiceras schluteri Subzone (M. mantelli Zone); BB4 (N. ultimus) at the base of the Mantelliceras dixoni Zone; BB5 (N. ultimus) in the Cunningtoniceras inerme Zone; BB6 (Praeactinocamax primus and Belemnocamax boweri) in the lower Acanthoceras rhotomagense Zone; BB7 (B. boweri) in the middle A. jukesbrownei Zone; and BB8 (P. plenus) in the mid Metoicoceras geslinianum Zone. Belemnites are associated with deposits overlying the transgressive surfaces in the early transgressive systems tracts (BB2-4, BB6-8) or, rarely, with higher-frequency transgressive surfaces in lowstand deposits (BB5). Early transgressive systems tracts also commonly have small positive delta C-13 excursions, although there is no one-to-one correspondence between the excursions and the belemnite biohorizons. A review of delta O-18 curves for the Cenomanian Stage suggests little evidence for a temperature control on the distribution of belemnites. Copyright (C) 2005 John Wiley & Sons, Ltd.