Northern Ireland Chalk nomenclature (Ulster Cretaceous Province) - Ulster White Limestone Group: Post-Larry Bane Chalk Subgroup: Garron Chalk Formation: Difference between revisions
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Latest revision as of 13:13, 11 June 2014
Name
The Garron Chalk Member was first proposed in Fletcher (1967, 1977) and adopted in BGS publications subsequently. It is regarded as a formation herein.
Type section
Cliff section just north of the Post Office at Garron Point [D 301 239].
Primary Reference Section
Whiterocks and Larry Bane Head in the North Antrim Basin. Portaneevy [D 063 444] on the north coast, Portantonnish on Rathlin Island and Ballysillan Quarry [J 305 778] show the characteristic giant ‘flint-circles’.
Formal subdivisions
None but divided informally into units A to C from the base.
Lithology
Limestone (chalk) with characteristic giant flints (‘massive flint rolls’) and significant Inoceramus fragments. Is divided into three ‘Beds’ (A to C).
Definition of upper boundary
Conformable with Portrush Chalk Formation at a bedding plane above wavy-bedded sediment with small nodular flints.
Definition of lower boundary
Conformable on the Glenarm Chalk Formation at a bedding plane, above which wavy-bedded conspicuously shelly chalk with corals and bryozoa occurs.
Thickness
9.65m in type section.
Distribution
North Antrim Basin, East Antrim (Midland Valley) Basin and over structural highs with the exception of the southern and western Londonderry Shelf. Oversteps younger beds over structural highs.
Previous names
Garron Chalk of Fletcher (1967).
Garron Chalk Member.
Parent
Ulster White Limestone Group.
Age and biostratigraphy
Upper Cretaceous, Campanian. Belemnitella mucronata Zone sensu lato.
References
Fletcher (1967, 1977).