Category:Northern Ireland Chalk nomenclature (Ulster Cretaceous Province) - Ulster White Limestone Group: Post-Larry Bane Chalk Subgroup

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Name

Proposed by Fletcher (1977) as the Post- Larry Bane Chalk White Limestone as an informal term to cover the upper Campanian and Maastrichtian Chalks above the highest of three distinctive and traceable erosion surfaces marking the top of the Larry Bane Chalk Formation.

Type section

Ballycastle area [D 115 420], North Antrim Basin.

Primary Reference Section

Cliff and quarry sections around Ballycastle [D 114 420]; Whiterocks [C 893 409] and Garron Point [D 301 239].

Formal subdivisions

Fletcher (1977) proposed eight members that are regarded as formations herein. They are in ascending order the Ballintoy Chalk formation, Glenarm Chalk Formation, Garron Chalk Formation, Portrush Chalk Formation, Ballymagarry Chalk Formation, Tanderagee Chalk Formation, Port Calliagh Chalk Formation and the Ballycastle Chalk Formation

Lithology

Limestone (chalk) with layers of nodular, tabular and ‘paramoudra’ type flints.

Definition of upper boundary

Placed at the erosion surface at the top of Ulster White Limestone Group sequence beneath Palaeogene Antrim Basalts.

Definition of lower boundary

Placed at base of Ballintoy Chalk Formation at the top of the Larry Bane Chalk Formation where it is marked by the upper of three persistently strong erosion surfaces.

Thickness

89.28m from type sites of constituent members, but the full thickness is very variable due to pre-Palaeogene Basalts erosion.

Distribution

Known throughout Northern Ireland. Its major development is in the North Antrim, East Antrim and Southern Upland basins. Oversteps onto structural highs.

Previous names

None formally but may be considered as the partial equivalent to those defined as ‘Beds of the zone of Belemnitella mucronata’ by Hancock (1961). This group of sediments are usually easily recognised by the presence, in sections, of the characteristic underlying Larry Bane Chalk Formation and is reported by Fletcher (1977) to be recognisable within downhole geophysical logs.

Parent

Ulster White Limestone Group.

Age and biostratigraphy

Upper Cretaceous, Upper Campanian to Maastrichtian. Belemnitella mucronata to Belemnella occidentalis zones.

References

Fletcher (1967, 1977); Griffith and Wilson (1982