Chronostratigraphy of the Chalk Group - Cenomanian Stage
The Cenomanian stage was originally proposed by d'Orbigny (1847) for the succession at Le Mans in the Paris Basin (Tröger & Kennedy, 1996).
Definition of base of stage
The internationally agreed citerion for the recognition of the base of the Cenomanian stage is the first appearance of the planktonic foraminifera Rotalipora globotruncanoides (Tröger & Kennedy, 1996).
In the UK, the base of the Cenomanian is coincident with the base of the M. mantelli Zone, which is also the horizon of an unconformity between the Chalk Group and older Cretaceous deposits.
Constituent Chalk Group lithostratigraphical units in the UK
Integrated Southern England Lithostratigraphy (except SE Devon): West Melbury Marly Chalk Formation, Zig Zag Chalk Formation, basal Holywell Nodular Chalk Formation.
S E Devon: Beer Head Limestone Formation (sensu Mortimore et al., 2001), basal Holywell Nodular Chalk Formation (Pinnacles Member).
Northern England: Ferriby Chalk Formation & basal Welton Chalk Formation
East Anglia: Lower Chalk (including Cambridge Greensand) & basal Middle Chalk
N. Ireland: Cenomanian strata do not form part of the Chalk Group
North Sea: Hidra Formation
|UK (except northern England)||Northern England|