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Earth Science Conservation Review
| Inisway Quarry | Fermanagh |
| Site number: | 176 | File Number: | H15 |
| ESCC: | ED | ||
| Locality Type: | Quarry (disused) | Status: | local interest |
| Grid Reference: | H161523 Centroid | ||
| Google maps: | 54.41948,-7.75197 | ||
| County: | Fermanagh | Council area: | Fermanagh & Omagh District Council |
| Period: | Carboniferous | ||
| Stages: | Arundian, Visean | ||
| Lithostrat: | Ballyshannon Limestone Formation | ||
| Site Description | |
|---|---|
| Highlights: | |
The Carboniferous rocks exposed in Inisway Quarry are the youngest limestones of the Ballyshannon Formation exposed in Subarea-1. | |
| Description: | |
About 6m of the upper informal 'member' of the Ballyshannon Limestone is exposed in this disused quarry and consists of very thick beds of fine-grained, dark grey bioclastic packstone and medium-thick beds of dark grey shaley limestone. Colonies of Syringopora and abundant Zoophycos traces occur in the shaley limestones. The upper 'member' contains a prolific microfauna in particular including the foraminifera listed below: Globoendothyra delmeri Glomodiscus miloni Glomodiscus oblongus Paraarchaediscus stage involutus P. reditus Uralodiscus sp. Viseidiscus sp. This rich and varied assemblage of archaediscids is indicative of a late Arundian age for the upper part of the formation, the precise position of the Chadian-Arundian boundary has not yet been recognised in Subarea-1. Although the strata exposed in Inisway Quarry belong to the upper informal 'member' of the Ballyshannon Limestone they occur some 40-50m stratigraphically below the top of the formation but are regarded as being typical of the dominant lithology in this part of the sequence. The highest beds in the formation are exposed some 200m to the southwest of the quarry and form low, continuous rock-cored ridges in the fields bordering the southwest side of the C-class road running through Claragh and Inisway townlands. Over a few metres of strata there is a progressive change from the typical dark grey silty packstones, as seen in Inisway Quarry, to dark grey-blue, very crinoidal grainstones. These are sporadically exposed in ditch sections and in small streams at the downslope side of the aforementioned fields and the top bed of the Ballyshannon Limestone is found in the stream on the boundary between Inisway and Magherahar townlands (H1628 5184) 540m south-southeast of the quarry. This bed contains the late Arundian foraminifera Kasachstanodiscus settlensis and Paraarchaediscus stage involutus. | |
| Interpretation: | |
Within the Tyrone Group in Co. Fermanagh and Subarea-1 the Ballyshannon Limestone Formation is the lowest part of the sequence exposed. Because the formation consists primarily of massive limestone beds much of its outcrop, on the southwest shore of Upper Lough Erne, is drift-free and abundant exposures and quarry sections occur in the outcrop between Blaney and Enniskillen. The limestones were all deposited in a marine environment and represent the first major marine transgression that submerged the northern part of Ireland during early Dinantian times. During the early stages of deposition mud and silt detritus derived from the northern land area were still reaching the basin and produced the shaley mudstones that are interbedded with the massive dark coloured limestones. Above these beds, which are typical of the lower 'member' the pale-coloured grainstones and crinoidal, coarse-grained packstones are indicative of a relatively mud-free depositional environment and one which reflects relatively shallow water turbulent conditions. The lithologies of the upper 'member' indicate a return to deeper water, outer shelf conditions of deposition but once again rapid but sustained shallowing led to the formation of a thin grainstone interval, marking the top of the formation. The effects of this bathymetric shallowing are particularly evident in more near-shore sequences, for examples in the Kesh-Omagh and Newtownbutler-Lisnaskea areas and appear to represent a eustatic sea-level fall. Since the Derrygonnelly area was in a location more distant from the land and in a deeper water shelf environment the effects of this shallowing in this area were much less dramatic and clastic sediments are not found at the base of the overlying Bundoran Shale nor is the top limestone bed of the Ballyshannon Formation either micritised or eroded. | |
| Conclusions: | |
Whilst it is possible to nominate other quarries in the formation outcrop between Blaney and Enniskillen that expose a much greater thickness of limestone, several factors favoured the selection of these particular sites as ASSI. All three quarries at Blaney, Carrickreagh and Inisway occur in close proximity to one another and in a part of the outcrop where there is particularly good exposure and the division of the formation into 3 informal 'members' is possible. The position of the Ballyshannon Limestone - Bundoran Shale contact is well defined in the area of Inisway - Blaney West - Claragh townlands and it is one of the few places in Subarea-1 where the upper contact is recognisable. | |
| Notes: | |
For information on other sites in Subarea-1 see; Key Site 1174 - Subarea-1; Derrygonnelly-Marble Arch-Cuilcagh. | |
| Keywords | |
|---|---|
| Rocks: | Limestone |
| Fossil Groups: | Foraminifera, Trace fossil, Trace fossils |
| Fossil List: | Kasachstanodiscus settlensis |
| Relations: | Marine sediments |
| Access | |
|---|---|
| Approach: | 4km E of Derrygonnelly. |
| Map(s): | See 1:50,000 O.S. Sheet 17 (Lower Lough Erne). | ||
| Record type: | ESCR report | ||
| Entered by: | Doughty, P.J. | ||
| Last updated: | 6 Jun 2005 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Inisway Quarry, County Fermanagh, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=176. Accessed on 2026-11-06. |
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