The BGS Lexicon of Named Rock Units — Result Details
Cloghastucan Chalk Formation
| Computer Code: | CLC | Preferred Map Code: | notEntered |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Santonian Age (KS) — Santonian Age (KS) | ||
| Lithological Description: | Limestone (chalk), with an overall "gritty" texture and with some flint bands (mainly small and "spindle-shaped") most notably the coalescing nodular flint course termed the Oweynamuck Flint Band (of bed status defined at the eastern bluff in White Park Bay [D 029 448]). Beds of green-coated chalk pebbles at some levels. Common brachials and calyx plates of Marsupites. | ||
| Definition of Lower Boundary: | At the type site the lower boundary is at a prominent bedding plane immediately above a wavy bedded unit at the top of the underlying Galboly Chalk Formation. Outside the type area the basal contact is disconformable and the junction is marked by an erosion surface with glauconitised chalk pebbles, which includes rolled sponge pseudomorphs. | ||
| Definition of Upper Boundary: | The upper boundary is taken at the top of a thin (0.15m) wavy bedded unit underlying Creggan Chalk Formation chalks rich in Inoceramus debris. The wavy bedded unit contains a marked increase in Inoceramus compared to the rest of the Cloghastucan Chalk Formation. | ||
| Thickness: | Thin succession of 2.33m thickness at its type-site. Absent over structural highs and overlapped by the succeeding member. | ||
| Geographical Limits: | Northern Ireland. Present in the North Antrim and East Antrim basins and parts of the Highland Border and Southern Uplands areas. Absent over the Londonderry shelf. Restricted to the North Antrim and East Antrim (Midland Valley) basins, and overlaps, and is itself overlapped (at the Benvan track [D 2000 413]) onto the Highland Border Ridge (Massif). In the North Antrim Basin the formation is continuous from Murlough Bay to the Portrush-Downhill area but diminishes between Oweynamuck and Portbraddan with a concomitant loss of flints. South of the Highland Border Ridge the formation is first seen at Altmore Burn [D 237 228], is absent around Dooray Bridge but attains its maximum thickness on the south side of Red Bay. It overlaps in the south against the Southern Uplands and is absent south of Castle Dobbs. | ||
| Parent Unit: | Ulster White Limestone Group (UWLF) | ||
| Previous Name(s): | Cloghastucan Chalk Member [Obsolete Name and Code: Use CLC]
(-3306)
Marsupites White Limestone [Obsolete Name and Code: Use CLC] (-1439) |
||
| Alternative Name(s): | none recorded or not applicable | ||
| Stratotypes: | |||
| Reference Section | South of the Highland Border Ridge the Formation is first seen at Altmore Burn [D 237 228]. See Fletcher (1977). | ||
| Type Section | 2.23m of chalk in fallen blocks on the foreshore north of Garron Point. The formation "is most fully developed in the Red Bay and Murlough Bay areas, on either side of the Highland Border Ridge, and the succession exposed in fallen blocks, .... is selected as the type-section". See Fletcher, 1977. | ||
| Reference Section | Benvan track. See Fletcher (1977). | ||
| Reference(s): | |||
| Fletcher, T P. 1967. Correlation of the Cretaceous exposures of east Antrim. Unpublished MSc Thesis, Queens University, Belfast. | |||
| Reid, R E H. 1964. The lower (pre-Belemnitella mucronata) White Limestone of the east and northeast of County Antrim. Irish Nauralists' Journal, Vol.14, 262-269, 296-303. | |||
| Fletcher, T P. 1977. Lithostratigraphy of the Chalk (Ulster White Limestone Formation) in Northern Ireland. Report of the Institute of Geological Sciences, No. 77/24. | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| none recorded or not applicable | |||