Category:Northern Ireland Chalk nomenclature (Ulster Cretaceous Province) - Ulster White Limestone Group: Larry Bane Chalk Formation: Difference between revisions

Name

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

Type section

Larry Bane Bay [D058 452]. Specifically in the cliff section [D 0500 4500] 400 metres NNE of Ballintoy in the North Antrim Basin.

Primary Reference Section

North Antrim Basin particularly Carrickarade to Portbraddan and in the East Antrim Basin.

Formal subdivisions

Informally divided into units A and B, which are said to have a characteristic one-third (A) to two-thirds (B) thickness relationship throughout the province.

Lithology

Limestone (chalk) with numerous flint bands. Shell debris abundant with distinct ‘pellet’ or fragmentary limestone clasts evident on weathered surfaces. Three persistent erosion surfaces divide the Larry Bane Chalk Formation into two ‘Beds’ (A and B). These surfaces may be treated as marl seams. Very large Belemnites are a prominent feature of this formation.

Definition of upper boundary

Conformable at an upper prominent erosion surface/marl beneath the Ballintoy Chalk Formation. Overlapped by younger members at margins of structural highs.

Definition of lower boundary

Conformable at lower prominent erosion surface/marl resting on Boheeshane Chalk Formation.

Thickness

7.29m at type-site with Bed A 2.44m and Bed B 4.85m thick. This 1:2 ratio of bed thickness is considered to be characteristic of the whole Larry Bane Chalk Formation outcrop.

Distribution

Known throughout the North Antrim and east Antrim (Midland Valley) basins of Northern Ireland.

Previous names

Larrybane Chalk of Fletcher (1967)

Larry Bane Chalk Member.

Parent

Ulster White Limestone Group.

Age and biostratigraphy

Upper Cretaceous, Campanian. Belemnitella mucronata Zone.

References

Fletcher (1967, 1977).