The Cushendall Formation is a geologic formation of Early Devonian age in Northern Ireland where it outcrops at Cushendall, County Antrim.
History Surveys of Cushendall were undertaken in 1886 and it was concluded that the rocks were metamorphic in origin.Cushendall, Sheet 14 Geological Survey of Ireland, 1886 The first geological maps of the area were produced by Bailey & McCallien (1934),Bailey, E.B. and McCallien, W.J. (1934): The metamorphic rocks of North-east Antrim. Transactions of the Royal Society of Edinburgh: Earth Sciences, vol. 58, pp.163-177 and Wilson (1953) was the first to conclude the rocks were Early Devonian in age and he placed them into the Old Red Sandstone as a new, unnamed member.Wilson, H. E. (1953): The petrography of the Old Red Sandstone rocks of the north of Ireland. Proceedings of the Royal Irish Academy, vol. 55, pp.283-320
Simon (1984b) defined the Cushendall Formation as a separate geological formation when he defined the Cross Sieve Group.Simon, J B. (1984b). Provenance and depositional history of the Lower Old Red Sandstone of northeast Antrim. Irish Journal of Earth Sciences 6, 213-228.
Geology and location
The Cushendall Formation is formed of rhyolite and basalt clasts overlain by conglomerate. The age of the formation can not be dated any more precisely than the Early Devonian due to the lack of fossils preserved, and it was part of the Cross Slieve Group in the Old Red Sandstone; it is believed it is the youngest of the three formations of the Cross Slieve Group. It is underlain by intrusive igneous porphyry and the formation is up to thick in places.
The Cushendun Formation outcrops only at Port Obe, Cushendall on the northeastern section of Cross Slieve; the northeastern section is dominated by the Cushendun Formation.
Paleogeography It is believed that the Cushendall Formation represented an alluvial environment which at some point experienced volcanic activity.
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