Holaster subglobosus Zone

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This zone is only currently used in northern England (Whitham, 1991), and in some areas has been replaced by the standard ammonite zonation used in the Cenomanian (Gaunt et al., 1992).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).

Key fauna:

Brachiopoda: Concinnithyris subundata
Grasirhynchia martini
Monticlarella rectifrons
Orbirhynchia mantelliana
Bivalvia: Aucellina
Entolium orbiculare
Inoceramus crippsi
I. schoendorfi
Lyropecten (Aequipecten) arlesiensis
Oxytoma sp.
Pycnodonte vesiculare
Belemnoidea: Actinocamax primus
Belemnocamax boweri
Ammonoidea: Acanthoceras jukesbrownei
A. rhotomagense
Hypoturrilites sp.
Parapuzosia (Austiniceras) austeni
Schloenbachia sp.
Turrilites sp.
Echinoidea: Echinocorys sphaerica
Holaster subglobosus

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