Chalk Biozone 1 - Ovoidinium verrucosum subsp. verrucosum

Age: Earliest Cenomanian.

Macrofaunal correlation: The M. mantelli Zone.

Definition: The interval between the LAD of Ovoidinium scabrosum to the LAD of Ovoidinium verrucosum subsp. verrucosum.

Comments: The LAD of Ovoidinium verrucosum subsp. verrucosum may occur within the M. mantelli Zone (Foucher, 1979; Foucher & Monteil, 1998), however the top of this Biozone is delienated at the M. mantelli Zone-M. dixoni Zone boundary. The LAD of Ovoidinium scabrosum, which marks the base of the Biozone, is a well established marker for the Albian-Cenomanian boundary (Davey & Verdier, 1973). Alternative markers for the base of this Biozone are the FADs of Microdinium? reticulatum and Exochosphaeridium spp. (Foucher, 1981). Ovoidinium verrucosum subsp. verrucosum is a short-ranging species, its FAD is in the latest Albian (S. dispar Zone) (Costa & Davey, 1992). The LADs of Apteodinium maculatum subsp grande and Canningia torulosa also occur within the M. mantelli Zone (Foucher, 1981).

Lithostratigraphical correlation: The West Melbury Marly Chalk Formation (Southern Province), the Ferriby Chalk Formation (Northern Province) and the Hidra Formation (North Sea).