The BGS Lexicon of Named Rock Units — Result Details

Garron Chalk Formation

Computer Code: GRCK Preferred Map Code: notEntered
Status Code: Full
Age range: Campanian Age (KC) — Campanian Age (KC)
Lithological Description: Limestone (chalk) with characteristic giant flints ("massive flint rolls") and significant quantities of Inoceramus fragments. I divided into three informal "Beds" (A to C).
Definition of Lower Boundary: The lower boundary, which is conformable on the Glenarm Chalk Formation, is taken at a bedding plane above which wavy-bedded, conspicuously shelly chalk with corals and bryozoa occurs.
Definition of Upper Boundary: The upper boundary is conformable with the overlying Portrush Chalk Formation and is taken at a bedding plane above wavy-bedded sediment with small nodular flints.
Thickness: 9.65m in the type section.
Geographical Limits: Northern Ireland: North Antrim Basin, East Antrim (Midland Valley) Basin and across structural highs with the exception of the southern and westeren Londonderry Shelf. The formation oversteps older beds over structural highs and is itself overstepped by younger beds in the Londonderry Shelf area.
Parent Unit: Ulster White Limestone Group (UWLF)
Previous Name(s): Garron Chalk Member (-2830)
Garron Chalk (-293)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Portaneevy on the north coast, Portantonnish on Rathlin Island shows the characteristic giant "flint-circles". Exposure within the foreshore platform. 
Reference Section  Ballysillan Quarry shows the characteristic giant "flint-circles". Exposure on the west wall of the quarry. 
Type Section  Cliff section just north of the Post Office at Garron Point. Overlies the Glenarm Chalk at a distinct bedding plane above which wavy-bedded very shelly chalk occurs. The formation is divided at well-defined bedding planes into three units. The unit is characterised by giant flints, some arranged in circles on bedding planes and its high content of Inoceramus fragments. See Fletcher (1967, p.103). 
Reference(s):
Fletcher, T P. 1967. Correlation of the Cretaceous exposures of east Antrim. Unpublished MSc Thesis, Queens University, Belfast. 
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 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable