The BGS Lexicon of Named Rock Units — Result Details

Creggan Chalk Formation

Computer Code: CGCK Preferred Map Code: notEntered
Status Code: Full
Age range: Campanian Age (KC) — Campanian Age (KC)
Lithological Description: Limestone (chalk), with common Inoceramus fragments (up to 20%) and many small burrow-fill flints scattered throughout. The upper part contains several horizons of green-coated pebbles that coalesce towards the basin margins to form a single conspicuous hardground with rolled and mineralized fossils, most notably belemnites and echinoid steinkerns. Glauconitic in its marginal overlap facies, where the uppermost beds/surfaces are attenuated, gritty, glauconitic and algal-topped (stromatolitic).
Definition of Lower Boundary: The lower boundary is taken at the point in the succession where there is a sudden increase in Inoceramus fragments. At Creggan this occurs 0.23m above the Oweynamuck Flint Band within the top of the Cloghastucan Chalk Formation. The formation oversteps older beds and is itself overstepped by younger beds over structural highs.
Definition of Upper Boundary: The upper boundary is taken at the highest of several green-coated chalk pebble beds within the Inoceramus-rich limestone. This unit is termed the Bendoo Pebble Bed (of ?member status) in the North Antrim Basin. Overlain by the Boheeshane Chalk Formation.
Thickness: 3.45m at the type locality.
Geographical Limits: Northern Ireland in the North Antrim and East Antrim basins and the Southern Upland area. Oversteps onto the Highland border area and a limited northern part of the Londonderry Shelf.
Parent Unit: Ulster White Limestone Group (UWLF)
Previous Name(s): Creggan Chalk Member (-2688)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  The type section of the Ballykeel Chalk (the original name for this unit) in Fletcher (1967) is on the southeast coast of Island Magee at [J 9710 4860]. See Fletcher (1967, p.70, Figure 15) 
Type Section  Gortin Quarry, Creggan. The full succession is visible where the basal contact is with the Cloghastucan Chalk and there is a disconformity with the overlying Boheeshane Chalk. 
Reference(s):
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. 
Fletcher, T P. 1967. Correlation of the Cretaceous exposures of east Antrim. Unpublished MSc Thesis, Queens University, Belfast. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable