Northern Province Chalk nomenclature - Ferriby Chalk Formation
Name
The Ferriby Chalk Formation was first proposed by Wood and Smith (1978) as a replacement for the Lower Chalk as applied to the northern Province. This paper included the Hunstanton Chalk Member (Red Chalk) at the base of the formation that is excluded (see Hunstanton Formation above) by later workers (e.g. Mitchell 1991, 1993). Herein the term also excludes the Hunstanton Formation.
Type section
South Ferriby Quarry [SE 9915 2045] (Gaunt et al., 1992).
Reference Section
Speeton Cliffs [TA 162 752 to TA 192 744] (Wright, 1968; Mitchell, 1995a).
Formal subdivision
None herein but the formation includes a number of named (see Wood and Smith, 1978) units that are considered of bed status. Jeans (1980) proposed a scheme of seven members but this has not gained widespread use in the literature.
Lithology
Grey, soft, marly, flint-free chalk, typically weathering buff in exposures; locally includes pinkish bands; some harder, gritty, shell-debris-rich beds, and thin discrete marl seams.
Definition of upper boundary
Uneven erosion surface that may be stained with iron minerals and glauconite, at the top of a succession of marly chalk (Ferriby Formation) and a little way above the so called Upper Pink Band (of bed status). This surface is succeeded by a thin unit of marls and marly chalks (the Plenus Marls Member, Welton Formation), which generally forms a topographical slack at outcrop. This facilitates the mapping of the top of Ferriby Formation, which is also readily recognised from geophysical log signature in boreholes.
Definition of lower boundary
At an erosion surface, locally developed on a hardground, overlain by nodular chalk (lowest Cenomanian) of Paradoxica (or Sponge) Bed or, in the Cleveland Basin, the flaser-bedded white chalks with red or purple marls of the Crowe’s Shoot Member (Gaunt et al., 1992; Mitchell, 1995a).
Thickness
The Formation is typically about 20 to 25 m thick throughout the southern part of the region. It thins to 10 to 15 m over the Market Weighton High (Jeans, 1973) and its extension to Hornsea. It thickens immediately at the margin of the Cleveland Basin to the north, being 33 to 35 m thick on the coast at Speeton (Wright, 1963; Jeans, 1980), and possibly 50 m or more in boreholes inland near Fordon.
Distribution
Throughout Yorkshire and Lincolnshire
Previous names
‘Chalk without Flints’ or ‘Lower Chalk’ of early Geological Survey maps, but excluding Plenus Marls; Ferriby Chalk Formation (in some cases this includes the basal unit now separated as the Hunstanton Formation).
Parent
Chalk Group.
Age and biostratigraphy
Upper Cretaceous, Cenomanian (Mantelliceras mantelli to Calycoceras guerangeri Zone).
References
Wood and Smith (1978); Gaunt et al. (1992); Whitham (1991).