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Earth Science Conservation Review
| Tullyhona - Carboniferous | Fermanagh |
| Site number: | 181 | File Number: | H13 |
| ESCC: | EO | ||
| Locality Type: | Stream section | Status: | local interest |
| Grid Reference: | H153338 Centroid | ||
| Google maps: | 54.25331,-7.76524 | ||
| County: | Fermanagh | Council area: | Fermanagh & Omagh District Council |
| Period: | Carboniferous | ||
| Stages: | Asbian, Visean | ||
| Lithostrat: | Benbulben Shale Formation, Dartry Limestone Formation, Glencar Limestone Formation | ||
| Site Description | |
|---|---|
| Highlights: | |
The stream section located south of the forest track in Tullyhona Townland is one of the most important sections in the Cuilcagh Mountain part of Subarea-1. It exposes the top beds of the Benbulben Shale and their conformable contact with the overlying limestone and thin shales of the Glencar Limestone Formation. At the top (south) end of the section is the abrupt contact between bedded limestones and shales of the Glencar Formation and the base of massive mud mound limestones of the Knockmore Member of the Dartry Limestone Formation. | |
| Description: | |
The contact between the Benbulben Shale and Glencar Limestone formations occurs in the Tullyhona stream section 5m south of the culverted forest road, located 2.3km west-southwest of Florence Court. Strata are inclined southwards at between 10 and 16 deg. and the section covering the Glencar Formation is not apparently faulted and thus exposes some 40m of thick limestones and thin shales. The transition from dark grey shaley mudstones to limestones and thin shales occurs over about 0.3m of strata and involves primarily an increase in the carbonate content of the mudstones, becoming argillaceous limestones at the base of the Glencar Formation. No diagnostic fauna was found in the mudstones. | |
| Interpretation: | |
Uninterrupted uniform subsidence of the Northwest Basin continued through the deposition of the Benbulben Shale Formation with only very small amounts of sand material reaching most parts of the basin as thin turbidity flows. This lack of sand may indicate either the remoteness of the shale basin from land source areas or that the land areas had a very subdued topography and thus produced only fine detritus as a result of denudation. The transition between the Benbulben Shale and Glencar Limestone is concomitant with a further reduction in the amount of mud detritus reaching all parts of the basin and the deposition and accumulation of fine carbonate sediments becomes the dominant process. Philcox et al. (1992) believe that the Glencar Limestone Formation is in fact no more than a diachronous transitional facies between the Benbulben Shale and the Dartry Limestone Formation. The mud mound facies (Knockmore Limestone Member) of the Dartry Limestone Formation is believed to have been deposited (accumulated) in a relatively deep water environment compared to the typical cherty limestones and grainstones that elsewhere dominate the formation outcrop and which are mutually exclusive with the mound limestones. Selective deepening of parts of the Northwest Basin was controlled by contemporaneous basinal faults and the mud mounds thus reflect seismically active areas. | |
| Conclusions: | |
The Tullyhona stream section is unique in Subarea-1 in exposing a complete, uninterrupted, section through the Glencar Limestone Formation and the contact, at the base, with the underlying Benbulben Shale Formation and at the top, with the succeeding Dartry Limestone Formation. | |
| Notes: | |
For information on other sites in Subarea-1 see; Key Site 1174 - Subarea-1; Derrygonnelly-Marble Arch-Cuilcagh. | |
| Keywords | |
|---|---|
| Rocks: | Limestone, Shale |
| Relations: | Marine sediments |
| Access | |
|---|---|
| Approach: | 2.3km WSW of Florence Court. |
| References (2) | |||
|---|---|---|---|
| Oswald, D.H., 1955. The Carboniferous Rocks between the Ox Mountains and Donegal Bay. Journal of the Geological Society of London, vol. 111, pp.167-186. | |||
| Philcox, M.E., Baily, H., Clayton, G. & Sevastopulo, G.D., 1992. Evolution of the Carboniferous Lough Allen Basin, Northwest Ireland. Special Publications of the Geological Society of London, numb. 62 In Basins on the Atlantic Seaboard: Petroleum Geology, Sedimentology and Basin Evolution., pp.203-215. | |||
| Map(s): | See 1:50,000 O.S. Sheet 26 (Lough Allen). | ||
| Record type: | ESCR report | ||
| Entered by: | Doughty, P.J. | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Tullyhona - Carboniferous, County Fermanagh, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=181. Accessed on 2026-11-08. |
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