Gortalughany

Also within

Fermanagh County

Climate exposure

This is about exposure to a nationwide pressure this habitat type carries — not a verdict on this site's own management.

Habitats

Fast flowing river and stream

Geology & landscape

Geological Feature: Cave / Cavern, Karst · Geological Period: Carboniferous · Rock Type: Chert, Limestone

Landscape processes: Glacial, Karst, Peatland / Mire, Periglacial

Birds & fish recorded

Birds

Description

Gortalughany Cave, Karst, Carboniferous stratigraphy Gortalughany is of special scientific interest because of its important geological and physiographical features. It contains excellent exposures of the areas Carboniferous geology together with a range of characteristic karst landforms including cave systems which are distinctively different to those found on the nearby Marlbank. The geology of the area consists of a series of Carboniferous age rocks, mainly limestones, which are around 337 million years old. At that time these rocks formed in warm; shallow and biologically productive equatorial waters. A series of disused quarries around Gortalughany offer a superb section through the Dartry Limestone Formation. While the type location for this Formation is in the Republic of Ireland, the current area is considered to be of outstanding geological interest with regard to the exposure offered through the Dartry Limestone. The thickness of the Dartry Limestone Formation is extremely variable and in the Gortalughany area, where the Knockmore Limestone Member is absent, the Formation is about 130m thick contrasting with areas to the west and north where the Formation is some 280-300m thick. The Asbian age of the Dartry Formation is confirmed, not so much by its contained fauna but by the occurrence of Asbian ammonoids in both the overlying Meenymore and Bellavally Formations. The Formation contains an abundant macrofauna dominated by corals and brachiopods. The top bed especially of these limestones are coral-rich, being packed with in situ colonies of Siphonodendron irregulare and is up to 1m thick. This distinctive bed is particularly well exposed in the Gortalughany area. Forming part of the Dartry Limestone Formation, the Cloghany Limestone Member is confined to the north and east sides of Cuilcagh Mountain. The rock unit occurs at or near the top of the Dartry Limestone Formation. It differs from the latter, which is typically cherty, in lacking chert and consisting of fine foraminiferal grainstone. The Cloghany Limestone Member is best seen where it forms the sides of a pot hole at Cloghany in Beighy Townland. Here it attains a maximum thickness of 1.3m. The dominant and most distinctive part of the member is a limestone bed between 0.66 and lm thick, which succeeds the basal shales and consists of pale to medium grey, coarsely crinoidal, fine-grained, foraminiferal packstone-grainstone. This limestone contains abundant fossil foraminifera and algae. The distribution of the Cloghany Limestone Member around Cuilcagh Mountain has proved to be crucial in defining the top of the Dartry Limestone Formation in this area. The Gortalughany area forms part of the larger upland limestone block occurring in west and south-west Fermanagh. This area hosts a series of distinctive landforms resulting from karstification, the interaction of rainwater and streams and the limestone. The action of water in dissolving the limestone has produced underground caves while the surface is pockmarked by an extensive series of distinctive hollows known as dolines. A number of streams can be seen flowing underground via swallow holes. The major potholes and cave systems developed on east Cuilcagh represent a unique style ofcave development in Northern Ireland. The cave systems are excellent examples of rift caves with poor horizontal development and have a stepped profile typical of joint controlled caves developed in well bedded limestones. While nearby caves such as those at Marble Arch are better known, caves at Gortalughany have formed in a different manner, generally controlled to a high degree by the local geology. The caves of the Marlbank area have extensive horizontal networks ofpassages and chambers that have developed within the more homogenous Knockmore Limestones. The latter limestone is absent from the Gortalughany area. Surface water here eventually flows onto a series of less uniform limestones, notably the Dartry Limestone which are typically strongly bedded and containing frequent bands of insoluble chert. These circumstances tend to create potholes with narrow entrance shafts in the Cam and Cloghany Limestones, widening with depth into the Dartry Limestone. There is a strong tendency for vertical shafts to develop along major vertical joints with horizontal passages being very limited. The main caves are in the Pollnatagha and Black Pot area and have developed along a single structural trend major joints or small faults oriented at 245°. The pots are frequently open to the surface and consist of deep vertical rift shafts separated by short horizontal passages. The main caves within the area include Peter Bryant's Hole 25m deep with 150m of horizontal development, Pollnaclanawley 70m deep with six shafts and with 150m of horizontal passage, Black Pot a complex series of fracture controlled rifts totalling some 75m in depth with about 500m ofhorizontal development and Peter Bryant's Bullock Hole a joint controlled 48m deep pot with a blocked chamber at the bottom. Along the border the Polliniska, Pollnatagha and Pollprughlisk group of pots and caves can be found. These are a series of interconnected fracture controlled rift passages entered via a number of deep vertical pots, of which only one, Polliniska, is currently an active sink. Pollprughlisk is the oldest sink, now completely abandoned and lying inside County Cavan. Polliniska is 10m deep, Pollnatagha, 52m and Pollprughlisk 67m. Total horizontal passage development is estimated at over 600m. The area hosts an extensive doline field which forms part of the adjoining Legacurragh doline complex to the north. Presumed to be formed by solution action, collectively this doline field is one of the best developed and preserved fields in Northern Ireland. The shakeholes, or dolines, in the Gortalughany area are notably smaller in scale than those in the Legacurragh area and some may represent peat pseudo-karst features resulting from peat pipe development and collapse processes. The majority appear to be a result of karstification of the underlying limestone. A number of other surface features within the site owe their origins to a period at the end of the last Ice Age. At that time frozen ground prevented surface water, originating as glacial meltwater, from sinking as it currently does. Instead, large volumes of water eroded the now dry valleys at The Pound and along the border south of Greenan Rock with the steepend walls representing abandoned waterfalls. The lack of breakdown debris on the floors of these dry valleys indicates that these features are not a result of collapsed cave passage. Greenan Arch is a natural bridge and is interpreted as another late glacial feature, formed during permafrost conditions, and is thought possibly to be the result of stream capture. https://www.daera-ni.gov.uk/publications/gortalughany-assi

Species mentioned

Plant communities