Chalk Group Lithostratigraphy: Northern Ireland - Ballymagarry Chalk Member

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The Ballymagarry Chalk (stratotype: Ballymagarry Quarry [C 889 407]), 10.95 m thick at the type locality, comprises a succession characterised by extremely large flints, including Paramoudra flints, and is coeval with the Paramoudra Chalk of the East Anglian Chalk Group succession (Fletcher, 1977; Wilson & Manning, 1978). The member is delimited by a conspicuous bedding plane at the base, and by the base of a prominent tabular flint, named the Long Gilbert Flint, at the top (Fletcher, 1977). The fauna includes the echinoids Galerites, Echinocorys pyramidata, and E. belgica and the brachiopod Cretirhynchia magna, elements of which suggest assignment to the Maastrichtian, although the occurrence of the belemnite Belemnitella ex gr. langei favours the latest Campanian (Wilson & Manning, 1978). Echinocorys pyramidata characterises the Overstrand-Pyramidata Hardground at the Campanian / Maastrichtian boundary in the East Anglian Chalk Group succession.

Macrofossil Biozonation: B. mucronata Zone s.l.

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.

WILSON, H E & MANNING, P I. Geology of the Causeway Coast, Vol. 2. Memoir of the British Geological Survey of Northern Ireland.

See: Beeston Chalk