Holaster subglobosus Zone
This zone is only currently used in northern England (Whitham, 1991), and in some areas has been replaced by the standard ammonite zonation used in the Cenomanian (Gaunt et al., 1992).
Base: The base of the zone is the top of the Hunstanton Formation ('Red Chalk', Albian), at the base of the Chalk Group (Whitham, 1991, Gaunt et al., 1992).
Top: The top of the zone is the top of the Nettleton Stone (Whitham, 1991; Gaunt et al., 1992).
Range of index species: The index ranges from a short distance above the base of the nominate zone to the lower part of the overlying H. trecensis Zone (Whitham, 1991).
|Lyropecten (Aequipecten) arlesiensis|
|Parapuzosia (Austiniceras) austeni|
Faunal abundance & preservation: The zone is locally very fossiliferous, with the fauna concentrated into acmes at some levels.
Bio-horizons: Aucellina is common in the lower part of the zone, overlain by shell-rich horizons with common Inoceramus crippsi and Inoceramus schoendorfi (Whitham, 1991). Higher in the zone there is an acme of Orbirhynchia mantelliana, overlain by the fossiliferous Totternhoe Stone, with a fauna that includes characteristic elements such as Lyropecten (Aequipecten) arlesiensis, Oxytoma, Entolium orbiculare,Grasirhynchia martini and Actinocamax primus (Whitham, 1991). In the upper part of the zone, Concinnithyris, Echinocorys sphaerica and Acanthoceras are common, and just below the top of the zone is an acme of Pycnodonte vesiculare (Whitham, 1991).
Age: Early to Mid Cenomanian