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

Name

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

Type section

Roadside ‘pillar’ south of Garron Point [Irish Grid Reference [D 301 245] but this site is noted in Fletcher (1977) as being within an unstable residual block near to the main road. An alternative type section can be ‘built-up’ from foreshore blocks or from the indifferently exposed old quarry at Milltown [D 255 243].

Primary Reference Section

Milltown [D 255 243] and in central Murlough Bay [D 200 401].

Formal subdivisions

None

Lithology

Chalk, with some flint bands and ‘incipient flints’. Marl partings common to base with some glauconite.

Definition of lower boundary

The exact relationship with the underlying Cloghfin Sponge Formation is not certain (Fletcher, 1978 p. 8 para 2). It is taken a well-developed separation plane above which the beds contain no appreciable arenaceous ‘contamination’.

Definition of upper boundary

At a prominent bedding plane (an erosion surface in part) immediately above a zone of wavy and disturbed bedding. Overlain by the Cloghastucan Chalk Formation.

Thickness

5.85m at its type section.

Distribution

Known throughout the North Antrim and East Antrim Basins and part of the Southern Upland, Highland Border and northern Londonderry Shelf. Absent elsewhere.

Previous names

Galboly Chalk Member.

Parent=

Ulster White Limestone Group.

Age and biostratigraphy

Upper Cretaceous, Santonian. Uintacrinus socialis Zone (in part).

References

Fletcher (1967, 1977).