Mantelliceras dixoni Zone

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Base: The base of the M. dixoni Zone is immediately below the first occurrence of the index species (Gale, 1995).

Top: The top of the M. dixoni Zone is immediately below the first occurrence of the ammonite Cunningtoniceras inerme (Gale, 1995).

Range of index species: The index species is restricted to the lower part of the M. dixoni Zone (Robaszynski et al., 1998).

Key Fauna:

Brachiopoda: Orbirhynchia mantelliana
Bivalvia: Inoceramus virgatus
Ammonoidea: Acompsoceras spp.
Hyphoplites spp.
Mantelliceras dixoni
M. saxbii
M. spp.
Mesoturrilites spp.

Faunal abundance & preservation: Some fauna present as acmes (O. mantelliana, I. virgatus), and M. dixoni is locally abundant in a hard limestone bed (see: Bio-markers).

Bio-markers: An acme of Inoceramus virgatus occurs slightly below the middle of the Zone, immediately overlain by an acme of M. dixoni in a hard limestone band ('M3' of Gale, 1989, also known as the Dixoni Limestone). Locally (eg. Leighton Buzzard district) the Dixoni Limestone is also characterised by common I. virgatus. Just above the Dixoni Limestone, at about the middle of the M. dixoni Zone, there is an acme of Orbirhynchia mantelliana, representing the lowest of three widely occurring acmes of this brachiopod in the Cenomanian (Gale, 1989, 1995; Robaszynski et al., 1998).

Subzones: None formally recognised in the UK. Gale (1995) recognised three faunal assemblages, successively comprising: (a) common M. dixoni and M. saxbii, with acme of Inoceramus virgatus; (b) diverse turrilitids, including Mesoturrilites spp.; (c) diverse Mantelliceras and rarer Acompsoceras and Hyphoplites.

Age: Early Cenomanian