Northern Ireland Chalk nomenclature (Ulster Cretaceous Province) - Ulster White Limestone Group: Post-Larry Bane Chalk Subgroup: Ballintoy Chalk Formation
Name
The Ballintoy Chalk Member was first proposed in Fletcher (1967, 1977) and adopted in BGS publications subsequently. It is regarded as a formation herein.
Type section
The type section is taken on gently dipping rock platforms in Ballintoy Harbour [D 040 456] in the North Antrim Basin. More accurate measurements are achieved from Larry Bane Head and Quarry to the east. The maximum development of the Member was formerly visible in air-weathered cliffs in White Bay. The type section defined by Fletcher in his 1967 thesis is at White Bay [D 3280 1510]
Primary Reference Section
North Antrim and Midland (East Antrim) Basins and on the eastern Londonderry Shelf. The member is continuous around the outcrop from Portrush to north Belfast.
Formal subdivisions
The highest unit within the Formation is named the Altachuile Breccia (presumably of bed status). The whole formation is divided informally from the base into A and B units.
Lithology
Limestone (chalk) with small flints scattered in the lower part and small discontinuous tabular flints in the upper part. The formation can be divided two ‘Beds’ (A and B) separated by conspicuous separation planes. The formation is terminated by the ‘wavy-bedded’ Altachuile Breccia (of member? status).
Definition of upper boundary
Conformably succeeded by the Glenarm Chalk Formation above the Altachuile Breccia (Member?).
Definition of lower boundary
Conformably overlies ‘Bed’ B of the Larry Bane Chalk Formation. Oldest of the post-Larry Bane Chalk ‘Subgroup’.
Thickness
12.65m at its type site with Bed A 9.65m and Bed B 3.00m.
Distribution
Principal outcrop is within the North Antrim and East Antrim (Midland Valley) basins. Oversteps the Larry Bane Formation onto the Southern Uplands, Highland Border and the northernmost part of the Londonderry Shelf.
Previous names
White Bay Chalk of Fletcher (1967)
Ballintoy Chalk Member.
Parent
Ulster White Limestone Group.
Age and biostratigraphy
Upper Cretaceous, Campanian. Belemnitella mucronata Zone sensu lato.
References
Fletcher (1967, 1977).