Chalk Group Lithostratigraphy: Northern Ireland - Galboly Chalk Member

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The Galboly Chalk Member (stratotype: roadside 'pillar', south of Garron Point [D 301 245], with a maximum thickness of 5.85 m, comprises a creamy limestone with many dark, irregular marly partings at the base associated with glauconite grains (Fletcher, 1977). The latter is overlain by flinty, locally 'wavy' bedded chalk, capped by an erosion surface with scattered small flints (Fletcher, 1977). Wilson and Manning (1978) considered that there was little to distinguish the Galboly and overlying Cloghastucan Chalk, describing both as comprising gritty greyish-cream sediment with comminuted inoceramid bivalve shell. The glauconite content of the Galboly Chalk has been attributed to the reworking of underlying Lower Cretaceous strata (Hibernian Greensands) (Wilson & Manning, 1978). Apart from inoceramid shell, the only other common fossils are calyx plates of the crinoid U. socialis, and distinctive morphotypes of the echinoid Echinocorys (Fletcher, 1977; Wilson & manning, 1978).

Macrofossil Biozonation: U. socialis 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.