Chalk Group Lithostratigraphy: Northern Ireland - Cloghastucan Chalk Member

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The Cloghastucan Chalk Member (stratotype: Galboly-Cloghastucan foreshore [D 301 245]), c. 2.23 m thick at the stratotype locality, is a thin, flinty limestone unit characterised by the occurrence of the crinoid Marsupites testudinarius and comminuted inoceramid bivalve shell (Fletcher, 1977). A conspicuous c. 0.17 m thick coalescing nodular flint near the top of the succession is named the Oweynamuck Flint Band (Fletcher, 1977). The base of the member is marked by a thin zone of 'wavy' bedding with green (? =glauconitised) pebbles and poorly formed white flints (Wilson & Manning, 1978), and the top of the unit according to Fletcher (1977) is the top of a 0.15 m thick 'wavy' bedded unit, although Wilson & Manning (1978) stated that it was the base of a 0.1 m thick belt of 'wavy' bedding, within which there was a sudden increase in comminuted inoceramid shell. The absence of M. testudinarius from the Cloghastucan Chalk above the Oweynamuck Flint might indicate assignment of this part of the succession to the U. anglicus Zone (Wilson & Manning, 1978).

Macrofossil Biozonation: M. testudinarius Zone & ?U. anglicus Zone

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.