Chalk Biozone 12 - Callaiosphaeridium asymmetricum
Age: Early Campanian.
Macrofaunal correlation: The lowermost O. pilula Zone to the middle G. quadrata Zone.
Definition: The interval between the LAD of Cassiculosphaeridia reticulata to the LAD of Callaiosphaeridium asymmetricum.
Comments: The index for the top of this biozone, Callaiosphaeridium asymmetricum, has a well established LAD within the Q. quadrata Zone (Haq et al., 1987; Costa & Davey, 1992).
Lithostratigraphical correlation: The Newhaven Chalk and Culver Chalk formations (Southern Province), the Flamborough Chalk Formation (Northern Province) and the Mackerel Formation (North Sea).