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

Name

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

Type section

Ballymagarry Quarry [C 889 407].

Primary Reference Section

The western side of Port More [D 073 439] and Downhill in north Derry.

Found throughout the Londonderry Shelf, North Antrim Basin and Southern Uplands High. Absent from the Midland Valley (East Antrim) Basin and Highland Border High.

Formal subdivisions

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

Lithology

Limestone (chalk) with extremely large flat lying and near-continuous flint bands. Divided into three ‘Beds’ (A to C) separated by well-marked bedding planes.

Definition of upper boundary

Marked by the base of the prominent continuous flint band termed the Long Gilbert Flint Band within the Tanderagee Chalk Formation.

Definition of lower boundary

Conformably overlies the Portrush Chalk Formation at a level of a well-marked bedding plane immediately below the inception of large flat lying and near continuous flint nodules.

Thickness

10.95m at its type-site.

Distribution

Absent from the Highland Border High and East Antrim Basin presumably by pre-Palaeogene erosion.

Previous names

Ballymagarry Chalk Member.

Parent

Ulster White Limestone Group.

Age and biostratigraphy

Upper Cretaceous, Campanian. Belemnitella mucronata Zone sensu lato.

References

Fletcher (1977).