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

Name

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

Type section

Cliff section just north of the Post Office at Garron Point [D 301 239].

Primary Reference Section

Whiterocks and Larry Bane Head in the North Antrim Basin. Portaneevy [D 063 444] on the north coast, Portantonnish on Rathlin Island and Ballysillan Quarry [J 305 778] show the characteristic giant ‘flint-circles’.

Formal subdivisions

None but divided informally into units A to C from the base.

Lithology

Limestone (chalk) with characteristic giant flints (‘massive flint rolls’) and significant Inoceramus fragments. Is divided into three ‘Beds’ (A to C).

Definition of upper boundary

Conformable with Portrush Chalk Formation at a bedding plane above wavy-bedded sediment with small nodular flints.

Definition of lower boundary

Conformable on the Glenarm Chalk Formation at a bedding plane, above which wavy-bedded conspicuously shelly chalk with corals and bryozoa occurs.

Thickness

9.65m in type section.

Distribution

North Antrim Basin, East Antrim (Midland Valley) Basin and over structural highs with the exception of the southern and western Londonderry Shelf. Oversteps younger beds over structural highs.

Previous names

Garron Chalk of Fletcher (1967).

Garron Chalk Member.

Parent

Ulster White Limestone Group.

Age and biostratigraphy

Upper Cretaceous, Campanian. Belemnitella mucronata Zone sensu lato.

References

Fletcher (1967, 1977).