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Earth Science Conservation Review
| Aghatirourke Townland caves, east Cuilcagh | Fermanagh |
| Site number: | 194 | File Number: | H13 |
| ESCC: | EO | ||
| Locality Type: | Cave | Status: | ASSI |
| Grid Reference: | H15613098,H15553067 Centroid, Not Entered | ||
| Google maps: | 54.22725,-7.76079 | ||
| County: | Fermanagh | Council area: | Fermanagh & Omagh District Council |
| Period: | Carboniferous | ||
| Stages: | Visean | ||
| Lithostrat: | Carn Limestone Member, Dartry Limestone Formation | ||
| Site Description | |
|---|---|
| Highlights: | |
The highest strata of the Dartry Limestone Formation in Subarea-1 consist of alternating limestones and shales that are assigned to the Carn Limestone Member. The complete sequence including the lower and upper contacts are exposed in these caves on the east side of Cuilcagh Mountain. | |
| Description: | |
The occurrence of these interbedded, fossiliferous limestones and shales was recognised first by Brunton and Mason (1979) in the Carn area of Co. Fermanagh (H12 44). In the belief that they represented the start of a major marine regression near the end of the Asbian the rocks were consequently assigned to the base of the Meenymore Formation. Since then the GSNI have determined the full extent of their outcrop and recognised the same lithologies on the south side of Belmore Mountain and on the east flank of Cuilcagh Mountain. At Carn the thickness of the member is estimated at 60m, but on Cuilcagh Mountain it never exceeds 7.87m. The absence of the Carn Member in many parts of Co. Fermanagh may be due to non-exposure or to non-deposition during Asbian times but on east Cuilcagh there is strong evidence that the sequence suffered erosion prior to deposition of the hypersaline and supratidal sediments of the Meenymore Formation. The contact between the Meenymore Formation and the Dartry Limestone Formation is thus disconformable and the presence or absence of the Carn Member is likely to be a factor related more to the amount of erosion that preceeded deposition of sediments of the former formation than to non-deposition of these limestones and shales. It is now believed that these truly marine limestones and shales, of the Carn Limestone Member, are the highest beds of the Dartry Formation and do not form part of the Meenymore Formation, the basal unit of the Leitrim Group. Although Brunton and Mason (op. cit., p.99) introduced the lithostratigraphical name "Carn Limestone" they did not select a stratotype section and may have believed that the outcrop in the Boho area was the only place where these rocks occurred since its thickness thins rapidly away from Carn. Since neither the upper nor lower contacts are exposed in the outcrop at Boho-Carn, but are well-defined on east Cuilcagh it was decided to select sections in the latter area for ASSI status. Two sections on the east side of Cuilcagh Mountain are selected which contain strata that are representative of the Carn Limestone Member. Both are located on the gently undulating peat and till-covered ground located west of Legacurragh Gap. The rocks are exposed in caves; the northern example (H1561 3098) is located 250m northwest of Legacurragh Gap and exposes the basal 0.55m of the Meenymore Formation and 5.5m of the underlying Carn Member. The southerly 'cave' or collapsed pothole (H1555 3067) is located 320m south of the northern cave, 250m west-southwest of Legacurragh Gap, exposes 4.25m of the Cara Member overlying the Cloghany Member, which is 0.77m thick, and 1.7m of cherty bedded limestone of the Dartry Formation. Correlation between the respective parts of the Carn Member is by means of a 0.2m thick bed of highly distinctive nodular shaley limestone which occurs in both sections. The Carn Limestone Member consists of alternating limestones and shales with the carbonate beds tending to be thicker than the shales. The limestones are medium to dark grey fine-grained pyritous packstones and micritic wackestones containing a sparse fauna of crinoid debris, brachiopods and bryozoa. Blue-black chert is found both as small discrete nodules in the limestones and as thin beds. Bioturbation is prevalent in the limestones, in some to such an extent as to produce a pseudobrecciated appearance. The shales are consistently blue-grey or dark grey when fresh and weather brown, calcareous with a sparse fauna of small solitary corals, crinoid ossicles, brachiopods and bryozoa and small scattered carbonate nodules. | |
| Interpretation: | |
The lithologies of the Carn Limestone Member were deposited in a marine environment. The periodic introduction of copious amounts of mud detritus clearly hindered the development of a diverse marine benthos. It is also apparent that land areas, though still distant were being subjected to enhanced erosion and the finer products of this weathering cycle were now reaching all parts of the basin. In view of the fact that thick red-bed sequences, of the Kilskeery Group, were accumulating in new, non-marine basins in the Fintona Block, 25km to the northeast, at the same time, it is hardly surprising that these changes in lithology were taking place in adjacent marine basins. It is now believed that local thickness variations and the total absence of the Carn Member in many parts of Subarea-1, were caused by a transitory episode of uplift and erosion of the Dartry Limestone surface, prior to the deposition of the Meenymore Formation. | |
| Conclusions: | |
The distribution of the Carn Limestone Member of the Dartry Limestone Formation is severely restricted in Co. Fermanagh. Nevertheless its presence at the top of this formation offers clues as to the timing of tectonic activity in this area and its effects on the sedimentary record of Lower Carboniferous rocks. | |
| Notes: | |
For information on other sites in Subarea-1 see; Key Site 1174 - Subarea-1; Derrygonnelly-Marble Arch-Cuilcagh. | |
| Keywords | |
|---|---|
| Rocks: | Limestone, Shale |
| Fossil Groups: | Brachiopod, Coral, Crinoid, Polyzoan |
| Relations: | Marine sediments |
| References (1) | |||
|---|---|---|---|
| Brunton, C.H.C. & Mason, T.R., 1979. Palaeoenvironments and correlations of the Carboniferous rocks in west Fermanagh, Ireland. Bulletin of the British Museum (Natural History), Geology, vol. 32, pp.91-108. | |||
| Map(s): | See 1:50,000 O.S. Sheet 26 (Lough Allen); GSNI (1991) 1:50,000 Sheet 44, 56 and 43 (Derrygonnelly & Marble Arch). | ||
| Record type: | ESCR report | ||
| Entered by: | Doughty, P.J. | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Aghatirourke Townland caves, east Cuilcagh, County Fermanagh, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=194. Accessed on 2026-11-03. |
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