The BGS Lexicon of Named Rock Units — Result Details

Glenarm Chalk Formation

Computer Code: GAC Preferred Map Code: notEntered
Status Code: Full
Age range: Campanian Age (KC) — Campanian Age (KC)
Lithological Description: Limestone (chalk), with flints ranging from small nodular at the base through nodular to tabular flints in the middle part of the sequence to massive nodular at the top. The Formation can be divided into four "Beds" (A to D) by subdivision on bedding planes. In the North Antrim Basin the Formation includes two well-developed hardgrounds, the North Antrim Hardgrounds (of member? status) and the sequence is therefore incomplete. In the Midland Valley (East Antrim) Basin only limited wavy bedding and scattered green glauconitised pebbles indicate interrupted sedimentation. This area is regarded as the "standard".
Definition of Lower Boundary: The base is delimited by a prominent weathered-out bedding plane immediately above the Altachuile Breccia (Bed) of the Ballintoy Chalk Formation. Brecciated chalk overlain by a thick limestone unit forming the base of the Glenarm Chalk Formation.
Definition of Upper Boundary: The upper boundary is the weathered-out bedding plane that separates chalk with small tabular flints below from conspicuously shelly wavy-bedded chalk at the base of the conformable Garron Chalk Formation, above.
Thickness: 8.10m at the type area.
Geographical Limits: In Northern Ireland the maximum development is in the East Antrim (Midland Valley) Basin and the formation is also found over the Highland Border high and well developed in the North Antrim Basin. Becomes attenuated including several non-sequences and overstepped by younger formations across the Londonderry Shelf and in the Southern Uplands Belfast district. Cliff sections at White Rocks near Portrush and in the quarry at Larry Bane Head in the northern depositional basin. The sections around Glenarm in the Midland Valley Basin.
Parent Unit: Ulster White Limestone Group (UWLF)
Previous Name(s): Glenarm Chalk Member (-3413)
Glenarm Chalk (-920)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Partial Type Section  Ballycarry. Several hardgrounds are developed in the formation. 
Type Section  Old quarry at Parishagh, half a mile northwest of Glenarm in the Midland Valley (East Antrim) Basin. A distinct threefold division of the formation can be recognized between four prominent bedding planes. 
Reference Section  At Kilwaughter. Several hradgrounds are developed in the formation. 
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. 
Hopson, P M. 2005. A stratigraphical framework for the Upper Cretaceous Chalk of England and Scotland, with statements on the Chalk of Northern Ireland and the UK Offshore Sector. British Geological Survey Research Report RR/05/01 102pp. ISBN 0 852725175 
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