Chalk Group Lithostratigraphy: Northern Ireland - Ballintoy Chalk Member

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The Ballintoy Chalk (stratotype: Ballintoy Harbour [D 049 451]), c. 12.65 m thick at the type locality, is delimited by an erosion surface (at the top of the underlying Larry Bane Chalk) at the base, and a zone of 'wavy' bedding at the top (Fletcher, 1979). The upper boundary of the member comprises a unit with pellet-like lumps of indurated chalk in a matrix of hard, wavy bedded limestone, and small, angular chips of flint, named the Altachuile Breccia, which Fletcher (1977) attributed to storm activity. Numerous, closely spaced, small nodular flints occur in the lower part of the member, passing up into a unit with discontinuous tabular flints; these features plus faunal contrasts being the basis for further (probably over-elaborated) subdivision (Fletcher, 1977). The fauna includes locally common specimens of the belemnite Belemnitella, the echinoids Echinocorys ex gr. conica and Galeola and ammonites; the brachiopod Cretirhynchia lentiformis is particularly characteristic of the interval (Fletcher, 1977; Wilson & Manning, 1978).

Macrofossil Biozonation: B. mucronata Zone s.l. (pars)

Correlation: see Correlation with other UK Chalk Group successions

References[edit]

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.