Cunningtoniceras inerme Zone
Base: The base of the zone is placed immediately below the first appearance of the index species, which in expanded successions occurs within couplet B38 of Gale's (1995) cyclostratigraphical scheme for the Cenomanian.
Top: The top of the zone is placed immediately below the first appearance of the ammonite Acanthoceras rhotomagense (Gale, 1995).
Range of index species: The index species ranges right through the nominate zone, and into the lower part of the overlying A. rhotomagense Zone (Robaszynski et al., 1998).
|Lyropecten (Aequipecten) arlesiensis|
Faunal abundance & preservation: There are local faunal acmes restricted to particular lithological horizons (see Bio-markers). Over basin margins the zone is mostly absent (see: standard macrofossil zonation and correlation of the UK Chalk Group) due to erosion at the base of the overlying A. rhotomagense Zone, however, some of the fauna may survive as reworked and phosphatised specimens.
Bio-markers: In the lower part of the zone, Orbirhynchia mantelliana is abundant, representing the second of three widely developed acmes of this brachiopod in the Cenomanian (Robaszynski et al., 1998). Lyropecten (Aequipecten) arlesiensis and Oxytoma seminudum are abundant in, and partly restricted to, a dark, silty marl coincident with the top of the acme of O. mantelliana (Gale, 1989). This marl was identified as the lower part of couplet B41 in Gale's (1995) cyclostratigraphical scheme for the Cenomanian.
Age: Early to Mid Cenomanian.