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Earth Science Conservation Review
| Rockfield (Mitton's) Quarry | Fermanagh |
| Site number: | 209 | File Number: | H43 |
| ESCC: | ED | ||
| Locality Type: | Quarry (working) | Status: | ESCR |
| Grid Reference: | H405310 Centroid | ||
| Google maps: | 54.22678,-7.37901 | ||
| County: | Fermanagh | Council area: | Fermanagh & Omagh District Council |
| Period: | Carboniferous | ||
| Stages: | Visean | ||
| Lithostrat: | Dartry Limestone Formation, Leitrim Group, Meenymore Formation, Tyrone Group | ||
| Site Description | |
|---|---|
| Highlights: | |
Rockfield Quarry is the only locality in Subarea-2 where the contact between the Dartry Limestone and Meenymore formations is exposed. The quarry also provides an excellent, if largely inaccessible, section of the top 90-100m of the Dartry Limestone Formation. | |
| Description: | |
Rockfield Quarry is located some 4.5km southeast of the centre of Lisnaskea and about 800m north of the B36 between Donagh and Rosslea. It is located in a narrow valley between drumlinoid till hills in Rockfield and Mullaghcapple Glebe townlands to the west and east respectively. Some 8m of till overlies bedrock head on the west side of the quarry. The quarry is just over 300m long and about 80m wide and has a N-S orientation. Some 90-100m of bedded cherty limestones of the Dartry Formation are exposed in the quarry and, at its extreme north end is exposed the contact between the formations and the basal 2m of the Meenymore Formation. The strata are inclined northwards at between 6-12 deg. The formation contact is not erosional but because of its abrupt nature and the fact that it separates sedimentary rocks that were deposited in such contrasting environments, it is probably disconformable. I - DARTRY LIMESTONE FORMATION At the top of the north face of Rockfield Quarry it is possible to prepare a lithological log of the top 4.5m of the Dartry Limestone Formation. It is also evident that distinctive lithological units occur in the 17-20m of strata that are located stratigraphically below the base of this section; these strata include a unit, some 5-6m thick which is probably the Ballagh Limestone Member and which here occurs between 13 and 20m below the top of the Dartry Formation. The black ferruginous shales that occur in the measured section, and some 10m lower, in the north face of the quarry are not recognised elsewhere in the formation outcrop. The 5-6m of pale weathering limestones, probably equivalent to the Ballagh Member are particularly distinctive and, in being relatively unbedded and lacking shale horizons, would fit precisely with the definition of this member, and other grainstones in this and older formations in the Northwest Basin. The 0.6m limestone that occurs just below the top of the Dartry Formation is a particularly distinctive chert- free, mottled and laminated, bioturbated, dark grey, very fine- grained spicular packstone that contains stunted foraminifera including Archaediscus sp. and A. stage concavus. No macrofauna was recovered from these strata. II - MEENYMORE FORMATION About 2m of strata representing the base of the Meenymore Formation succeed the top of the Dartry Limestone and are exposed at the base of the excavated, steep, till slope in the northwest corner of the quarry. With the exception of rare crinoid ossicles in the lowest shales and in the 0.24m thick peritidal micrite, all other lithologies are unfossiliferous. Exposed in the west wall of the quarry site, 60-80m north of the north rim of the quarry are pale grey to fawn, very calcareous blocky silty mudstones and, slightly higher in the wall, and at a slightly higher stratigraphical level, are dark grey blocky mudstones. Both lithologies are fossiliferous, the former in particular containing an assemblage of marine fossils including gastropods, orthocone nautiloids, small solitary corals, large crinoid ossicles, brachiopods, bivalves, very scarce trilobites and specifically indeterminate, micrite-coated specimens, of the goniatite Nomismoceras. The dark grey mudstones are much less prolific but contain occasional specimens of the B2 goniatite Bollandoceras cf. micronotum. Laminated stromatolitic (cyanobacteria) supratidal carbonates do not occur in the 2m of strata of this formation exposed at the north end of Rockfield Quarry but they are recorded at many other localities in the formation outcrop and are thus still typical of the formation definition in the Northwest Basin. | |
| Interpretation: | |
The facies change between the Dartry Limestone and Meenymore formations is between relatively deep and extremely shallow water environments. The occurrence of grainstones, the Ballagh Member, in the top part of the Dartry Formation could be an indication of an episode of shallow water turbulent conditions. This is particularly hard to envisage in terms of sudden bathymetric shallowing and deposition of the grainstones, followed equally rapidly by a return to deep water, anoxic conditions as evidenced by the 0.9m thick black, ferruginous shale resting directly on top of the Ballagh Member in the quarry. Given the considerable variation in the thickness of the Ballagh Member it is possible that the grainstone accumulated in shallow water, elsewhere in the basin, and was transported downslope into the deeper water, mud and fine, spicular carbonate environment that is so typical of the rest of the Dartry Formation. The highly bioturbated nature of the top limestone bed (0.6m thick) in the Dartry Formation is perhaps indicative of a virtual pause in the influx of detritus thereby allowing time for a soft-bodied, burrowing fauna to colonise the seabed and substrate. Such an event may have been caused by major tectonism in the basin, and at its margins causing the formation of major, non- marine basins and the uplift of the top surface of the Dartry Limestone and formation of the huge area of intertidal and supra- tidal flats on which the sediments of the Meenymore Formation accumulated. None of the sedimentary rocks that occur in this formation in Rockfield Quarry or elsewhere in the outcrop contradict this environmental interpretation. Indeed based on the unusual frequency with which red-beds occur in the Meenymore Formation in Subarea-2, it seems likely that subaerial exposure of the intertidal, supratidal and evaporitic sediments was a regular occurrence in this part of County Fermanagh and in all of the Slieve Beagh area. | |
| Conclusions: | |
Rockfield Quarry offers a unique exposure of the contact between the Dartry Limestone and Meenymore formations in Subarea-2. | |
| Notes: | |
For information on other sites in Subarea-2 see; Key Site 1175 - Subarea-2; Lisnaskea-Fivemiletown. | |
| Keywords | |
|---|---|
| Rocks: | Limestone, Shale |
| Fossil Groups: | Bivalve, Brachiopod, Coral, Crinoid, Foraminifera, Gastropod, Goniatite, Nautiloid, Trilobite |
| Fossil List: | Bollandoceras cf. micronotum, Nomismoceras sp. |
| Relations: | Marine sediments |
| Access | |
|---|---|
| Approach: | Rockfield Quarry is located some 4.5km southeast of the centre of Lisnaskea and about 800m north of the B36 between Donagh and Rosslea. |
| Record type: | ESCR report | ||
| Entered by: | Doughty, P.J. | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Rockfield (Mitton's) Quarry, County Fermanagh, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=209. Accessed on 2026-11-08. |
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