Southern Province Chalk nomenclature - Grey Chalk Subgroup:Beer Head Limestone Formation

3.1.1.1 Beer Head Limestone Formation

Name

First proposed by Jarvis and Woodroof (1984) to replace the Cenomanian Limestone of Smith (1957, 1965) [Fig.5b/5] but is redefined herein to exclude their Pinnacles Member which is equivalent to the Plenus Marls Member elsewhere. It was not mapped separately in south Devon but is traceable on coastal sections

Type section

Hooken Cliffs, [SY 210 881 to 227 878], Devon.

Primary Reference Section

Beer Head [SY 227 879], and Wilmington Quarry [SY 209 997], Devon.

Formal subdivision

None herein but defined as comprising the Pounds Pool Sandy Limestone, Hooken Nodular Limestone and Little Beach Bioclastic Limestone members of the Beer Head Limestone Formation of Jarvis and Woodroof (1984).

Lithology

Complex thin sequence of bedded coarse calcareous sandstone, bioclastic limestone, calcarenite and shell-detrital limestone, with a distinct nodularity and well-developed hardgrounds. Glauconitic and phosphatic. Includes the Wilmington Sand Member in calcarenite facies.

Definition of upper boundary

Disconformable at the surface of the Humble Point Hardground with the Pinnacles Member (of Jarvis and Woodroof, 1984), which is the sub-Plenus Marls Member erosion surface.

Definition of lower boundary

Disconformable on the burrowed Small Cove Hardground of the Upper Greensand Formation.

Thickness

Up to 10.4m at Hooken Cliffs.

Distribution

Confined to the area south of the mid-Dorset Swell in Dorset

Previous names

Directly equivalent to the Chloritic Marl of Meyer (1874), the Chalk Marl of Jukes-Browne and Hill (1896) and the Cenomanian Limestone of Smith (1965). Correlates with the Pounds Pool Sandy Limestone, Hooken Nodular Limestone and Little Beach Bioclastic Limestone members of the Beer Head Limestone Formation of Jarvis and Woodroof (1984).

Parent

Grey Chalk Subgroup.

Age and biostratigraphy

Upper Cretaceous, Cenomanian. Mantelliceras mantelli to Calycoceras geurangeri Zones.

References

Mortimore, Wood and Gallois (2001).