Kilcoan
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Geology & landscape
Geological Period: Cretaceous, Jurassic · Rock Type: Conglomerate, Limestone, Sandstone
Description
Kilcoan Cretaceous Stratigraphy Kilcoan is of importance because of its geology. Specifically the site is the type locality for the Island Magee Siltstones Member and the Kilcoan Sands Member of the Hibemian Greensands Formation. In addition exposure includes the Belfast Marls Member. These are among the oldest rocks of Cretaceous age in Ireland. The Belfast Marls Member is about 1.22 m thick and consists of deep green glauconitic marly sands with a faunal assemblage dominated by individuals of Schloenbachia spp. and Acanthoceras. The Island Magee Siltstones Member is a monotonous sequence of green to khaki coloured sandstones, some with silt or clay, totalling about 4.6 m thickness in all. Bed thickness varies from a few centimetres up to a metre. This is also the type locality for the Kilcoan Sands Member. The section consists of a basal conglomerate 0.90 m thick containing small cobbles of sandstone which can be matched with sandstones from the pre-Senonian greensands north of Lame. It is succeeded by glauconitic quartz sand in which rhynconellids and Osfrea are common. The next 1.52 m contains much Inoceramus and Osfrea debris, the flat broken shells being aligned with the bedding and producing a banding effect. Rhynconellids continue into the Inoceramus beds but appear to give way in prominence to the terebratulids of which Gibbithyris and Carneifhyris are particularly common. In the final 3.66m there is initially a general paucity of fossils. In the highest levels fossils again appear to be more abundant, especially the echinoids Conulus and Echinocorys. At the top, this member is overlain by the Cloghfin Sponge Beds Member of the Ulster White Limestone Formation. Fossils have been recovered from this site which date from earlier geological time periods not now represented by rocks anywhere in Ireland. Some of these specimens, especially those of Middle Jurassic age, may have been swept in from the Mesozoic sedimentary basin a little to the north-west and incorporated into the Cretaceous age sediments at Kilcoan. The history of Cretaceous sedimentation in the Hibemian Greensands Formation of the Hillsport Basin is best seen at this site. It allows the relationships between tectonism and sedimentation to be demonstrated. https://www.daera-ni.gov.uk/publications/kilcoan-assi