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

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Name

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

Type section

West of Ballycastle Pier [D 120 415].

Primary Reference Section

Ballymagarry Quarry, Castle Point Quarry and cliffs and foreshore eastward to Ballycastle.

Formal subdivision

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

Lithology

Limestone (chalk) with nodular flint bands which have a carious habit in the upper part of the formation. Divided into seven ‘Beds’ (A to G).

Definition of upper boundary

Erosional contact with Palaeogene Basalts or Quaternary deposit.

Definition of lower boundary

Conformable on the Port Calliagh Chalk Formation at a prominent weathered-out bedding plane at the top of ‘Bed’ F of that lower formation and characterised by tabulate flints.

Thickness

13.72m at type-site.

Distribution

Limited to the Ballymagarry and Ballycastle areas by pre-Palaeogene erosion

Previous names

Forms the upper part of the Ballycastle White Limestone of Wood (1967).

Ballycastle Chalk Member.

Parent

Ulster White Limestone Group.

Age and biostratigraphy

Upper Cretaceous, Maastrichtian. Belemnella occidentalis Zone.

References

Fletcher (1967, 1977).