Holaster trecensis Zone

This zone is only currently used in northern England (Whitham, 1991), and in some areas has been replaced by the standard ammonite zonal equivalent (= C. guerangeri Zone) used for this part of the Cenomanian (Gaunt et al., 1992).

Base: The base of the zone is the top of the Nettleton Stone (Whitham, 1991; Gaunt et al., 1992)

Top: The top of the zone is the sub-Black Band (s.l.) erosion surface (Whitham, 1991; Gaunt et al., 1992).

Range of index species: The index ranges from the middle of the nominate zone into the overlying Sciponoceras gracile Zone (Whitham, 1991).

Key fauna:

Annelida:	Rotularia umbonata
Brachiopoda:	Gibbithyris spp.
	Ornatothyris sulcifera
Bivalvia:	Inoceramus pictus
Echinoidea:	Camerogalerus cylindricus
	Echinocorys sphaerica
	Holaster trecensis
Nautiloidea:	nautiloids

Faunal abundance & preservation: The zone is rather poorly fossiliferous compared to the underlying H. subglobosus Zone, although there are some local faunal acmes. Crushed specimens are not infrequent.

Bio-markers: In the lower part of the zone, Ornatothyris sulcifera, Gibbithyris spp. and Rotularia umbonata co-occur (Whitham, 1991). There is an acme of Holaster trecensis in the top of the zone, associated with Camerogalerus cylindricus and Ornatothyris (Whitham, 1991).

Age: Late Cenomanian