Gaster (1924, 1927, 1929, 1932, 1937, 1941, 1944) - Micraster coranguinum Zone
Biostratigraphical correlation: Equates with a variable interval from between the top of the M. cortestudinarium Zone or basal M. coranguinum Zone, to the top of the M. coranguinum Zone of current usage.
Lithostratigraphical correlation: Largely equates with the Seaford Chalk Formation, but might locally include the top of the underlying Lewes Nodular Chalk Formation of southern England. The Trochiliopora Bed of Gaster (1920) is a bryozoan-rich unit near the base of the zone, characterised by an abundance of Trochiliopora gasteri and perhaps correlative with the Warren Sponge Bed near the base of the Seaford Chalk Formation (Wood, WH/95/31R).
Age: Coniacian & Santonian