Northern Ireland Chalk nomenclature (Ulster Cretaceous Province) - Ulster White Limestone Group: Post-Larry Bane Chalk Subgroup: Ballymagarry Chalk Formation
Name
The Ballymagarry Chalk Member was first proposed in Fletcher (1977) and adopted in BGS publications subsequently. It is regarded as a formation herein.
Type section
Ballymagarry Quarry [C 889 407].
Primary Reference Section
The western side of Port More [D 073 439] and Downhill in north Derry.
Found throughout the Londonderry Shelf, North Antrim Basin and Southern Uplands High. Absent from the Midland Valley (East Antrim) Basin and Highland Border High.
Formal subdivisions
None but informally divided into units A to C from the base.
Lithology
Limestone (chalk) with extremely large flat lying and near-continuous flint bands. Divided into three ‘Beds’ (A to C) separated by well-marked bedding planes.
Definition of upper boundary
Marked by the base of the prominent continuous flint band termed the Long Gilbert Flint Band within the Tanderagee Chalk Formation.
Definition of lower boundary
Conformably overlies the Portrush Chalk Formation at a level of a well-marked bedding plane immediately below the inception of large flat lying and near continuous flint nodules.
Thickness
10.95m at its type-site.
Distribution
Absent from the Highland Border High and East Antrim Basin presumably by pre-Palaeogene erosion.
Previous names
Ballymagarry Chalk Member.
Parent
Ulster White Limestone Group.
Age and biostratigraphy
Upper Cretaceous, Campanian. Belemnitella mucronata Zone sensu lato.
References
Fletcher (1977).
6.2.3.6 Tanderagee Chalk Formation
Name
The Tanderagee Chalk Member was first proposed in Fletcher (1977) and adopted in BGS publications subsequently. It is regarded as a formation herein.
Type section
Long Gilbert Quarry, Ballymagarry [C 889 407], south wall of western part of quarry.
Primary Reference Section
Numerous in the North Antrim Basin, the southern Londonderry Shelf and in the Southern Uplands. It is seen in sections between Magheralin and Trummery, Groganstown and the ‘Hairpin Bend’ region of Ballysillan, Ballycastle to Ballintoy, Portbraddan to Downhill and between Carmean and Stewartstown.
Formal subdivision
Includes the Long Gilbert Flint Band (of bed status) and informally divided into units A to E from the base.
Lithology
Limestone (chalk) with flint bands. Divided into five ‘Beds’ (A to E). Abundant belemnites in lower ‘Bed’ A and by an acme of crinoid debris in ‘Bed’ C. Elsewhere asteroid and crinoid debris common.
Definition of lower boundary
Conformable, on the Ballymagarry Chalk Formation, at a bedding plane immediately below the thick continuous tabulate Long Gilbert Flint Band where this exists. Or at the same bedding plane marking the faunal change from the Ballymagarry Chalk Formation fauna.
Definition of upper boundary
Conformable, with the overlying Port Calliagh Chalk Formation, at a bedding plane below a ‘belt of complex flints’.
Thickness
7.63m at type-site.
Distribution
Outcrops in the Southern Uplands area, the North Antrim Basin and in the southern part of the Londonderry Shelf. Absent in the East Antrim Basin, the Highland Border High and northern Londonderry shelf due to pre-Palaeogene erosion.
Previous names
Tanderagee Chalk Member.
Parent
Ulster White Limestone Group.
Age and biostratigraphy
Upper Cretaceous, Maastrichtian. Belemnella lanceolata Zone?
References
Fletcher (1977).