Northern Ireland Chalk nomenclature (Ulster Cretaceous Province) - Ulster White Limestone Group: Pre-Larry Bane Chalk Subgroup: Boheeshane Chalk Formation

Name

The Boheeshane Chalk Member was first proposed in Fletcher (1967, 1977) and adopted in BGS publications subsequently. It is regarded as a formation herein.

Type section

Boheeshane Bay [D045 450] in North Antrim Basin.

Primary Reference Section

Best developed in the North Antrim and East Antrim (Midland Valley) basins. It is overlapped by younger chalk members towards the structural highs. The Whitehead Flint Band is displayed at the reference section at the old quarry (a landfill site) at Whitehead [J474 913].

Formal subdivisions

Includes the Whitehead Flint Band and is informally divided into units A, B and C.

Lithology

Limestone (chalk), with common massive flint bands and tabular flints. Some green-coated chalk pebble beds near the base and as a prominent bed associated with sponges in the middle of the sequence. Hard pellet chalk in softer matrix is common at some levels Divided into three main ‘Beds’ (A, B and C) each further divided into numbered ‘units’. Each ‘Bed’ separated by marked bedding planes that are locally emphasised by weathering. A number of notable fossil acmes throughout. Considered to be much finer-grained than older gritty members and termed ‘White Chalk’ by Wolfe (1968). A distinctive massive flint band, which marks the upper limit of Gonioteuthis, is termed the Whitehead Flint Band (of bed status) whose type reference section is the old quarry at Whitehead [J 474 913].

Definition of upper boundary

Taken at the well-developed erosional surface at the base of the Larry Bane Chalk Formation.

Definition of lower boundary

Base defined by reference to the terminal pebble bed of the Creggan Chalk Formation and the stromatolitic ‘mulatto’ surface in marginal areas.

Thickness

Combined thickness at the type-site of 24.19m. Bed A 8.33m, Bed B 8.69m and Bed C 7.17m.

Distribution

North Antrim and East Antrim basins part of the Southern Uplands area and over parts of the Highland Border and Londonderry Shelf areas.

Previous names

Boheeshane Chalk Member.

Parent

Ulster White Limestone Group.

Age and biostratigraphy

Upper Cretaceous, Campanian. Gonioteuthis quadrata and basal Belemnitella mucronata zones. From Applinocrinus [Saccocoma] cretaceus Subzone (quadrata Zone).

References

Fletcher (1967, 1977).