Northern Province Chalk nomenclature - Hunstanton Formation

Name

The term Hunstanton Formation is defined herein. It is a modification of a number of previous names given to the beds with a distinctive red colour (in part), below a strongly developed erosion surface and of Albian age (known to be of Lower Cenomanian age as defined by Mitchell, 1995 in the ‘Cleveland Basin’) found below a strongly developed erosion surface beneath the Chalk Group (and from which it is now specifically excluded).

Type section

Hunstanton Cliff [TF 6725 4130 to TF 6786 4238], north Norfolk (Owen, 1995; Gallois, 1994).

Primary Reference Section

South Ferriby Quarry [SE 9915 2045], Lincolnshire (Gaunt et al., 1992).

Formal subdivision

None herein. The Hunstanton Formation as defined by Mitchell (1995a) describing the thick succession at Speeton in the Cleveland Basin is divided into five members. These are in ascending order the Queens Rocks Member, Speeton Beck Member, Dulcey Dock Member, Weather Castle Member and the Red Cliff Hole Member.

Lithology

Rubbly to massive chalks with marl bands; typically pink to brick-red in colour (due to disseminated hematite), but locally upper part grey due to secondary alteration of the iron minerals. The lower part of the formation is commonly weakly sandy.

Definition of upper boundary

Erosion surface, locally developed as a hardground, overlain by nodular chalk (lowest Cenomanian) of Paradoxica (or Sponge) Bed or (in Cleveland Basin) Crowe’s Shoot Member (Mitchell, 1995a); this horizon (the base of the Lower Chalk in Norfolk, or elsewhere of the Ferriby Formation) may or may not correspond with the upper limit of red chalks.

Definition of lower boundary

Sharp or (apparently) gradational boundary of marly chalks with ferruginous sandstones of Carstone Formation or (in Cleveland Basin) with mudstone of Speeton Clay Formation; commonly marked by a line of phosphatic nodules (burrow-fills).

Thickness

c. 1 m at type section in Norfolk, typically 3 m in Lincolnshire and south Yorkshire, thinning over Market Weighton High but expanding up to an estimated c. 30 m in Cleveland Basin with c. 24 m exposed in the cliffs at Speeton.

Distribution

Present throughout Yorkshire (including the Cleveland Basin where it attains its maximum development) and Lincolnshire and extends southwards to its type locality of Hunstanton on the north Norfolk coast.

Previous names

Red Chalk (see definition in Southern Province section)

Hunstanton Limestone

Hunstanton Red Rock

Hunstanton Chalk Formation

Hunstanton Red Chalk Formation (Owen, 1995 and Mortimore et al., 2001)

Hunstanton Chalk Member (Wood and Smith, 1978).

Parent

Stand alone formation beneath and excluded from the definition of the Chalk Group.

Age and biostratigraphy

Lower Cretaceous, middle to upper Albian.

References

Owen (1995); Mitchell (1995a).