| Previous Site | Next Site |
Earth Science Conservation Review
| Newtownbutler Stream | Fermanagh |
| Site number: | 204 | File Number: | H42 |
| ESCC: | EO | ||
| Locality Type: | Stream section | Status: | ESCR |
| Grid Reference: | H4226 1 km square | ||
| Google maps: | 54.18174,-7.35671 | ||
| County: | Fermanagh | Council area: | Fermanagh & Omagh District Council |
| Period: | Carboniferous | ||
| Stages: | Visean | ||
| Lithostrat: | Ballyshannon Limestone Formation, Bundoran Shale Formation, Tyrone Group | ||
| Site Description | |
|---|---|
| Highlights: | |
The top of the Ballyshannon Limestone, the contact with the base of the overlying Bundoran Shale Formation and fossiliferous beds in the lower part of that formation are exposed in the south- flowing stream that forms the boundary between Mockbeggar and Mullynagowan townlands, northeast of Newtownbutler. The complete section is some 350m long. The top beds of the Ballyshannon Limestone Formation consist of pale grainstones that are referred to as the Newtownbutler Limestone Member, a new lithostratigraphical unit that is succeeded abruptly by the Mullynagowan Sandstone Member, a new member at the base of the Bundoran Shale Formation. The section described is the stratotype for both new members. | |
| Description: | |
The Newtownbutler Stream section is located in the boundary between Mockbeggar and Mullynagowan townlands about 1km east- northeast of Newtownbutler crossroads. The southern end of the section is located some 40m south of the farm lane bridge at H4260 2642 and the north end of the stratotype outcrop is 40m north of the bridge at the first sharp bend in the stream. North of this bend in the river, the remaining 250m, or so, of river exposes lithologies typical of the Bundoran Shale Formation but which, unusually, contain a very rich development of colonial corals. The formation contact is located about 25m north of the bridge. I - Ballyshannon Limestone Formation Exposures of alternating blue-grey and dark grey crinoidal packstones and dark grey bioturbated and bituminous shaley siltstones, mudstones and argillaceous limestones occur in the Newtownbutler Stream between the farm lane bridge and Lurganboy Bridge 600m to the southwest. They contain a relatively abundant coral-brachiopod fauna and foraminifera including Paraarchaediscus stage involutus indicating a mid- to late Arundian age. The contact between these strata and grainstones of the Newtownbutler Member is not exposed. Newtownbutler Limestone Member The type section of this new unit is located upstream and downstream of the aforementioned farm lane bridge at H4258 2647, 880m east-northeast of the crossroads in Newtownbutler. Although the upper contact is exposed here, the base is concealed and the full thickness of the member is not known. There is however an estimated 8m of limestone between the base of the succeeding Bundoran Shale, north of the bridge, and the base of the river section some 40m to the south of the bridge. The member consists exclusively of pale and medium grey-fawn grainstones arranged in thick beds without shales. Detrital quartz and feldspar is confined to the lowest beds and in the 0.52m thick basal bed comprises about 50% of the rock and imparts a crude undulose lamination, with thin cross laminated units. The quartz content decreases upwards in the basal bed as does overall grainsize of carbonate and clastic particles. Large bioclasts and bioclast fragments are uncommon with the one exception being the smooth terebratulid brachiopod Composita ambigua which most commonly occurs as conjoined valves and appears to have been sufficiently robust to withstand turbulence in the depositional environment. Higher beds are quartz-free and consist of unlaminated, medium to dark grey grainstones with variably micritised ooids, peloids and carbonate clasts. A sparse microbiota includes the alga Koninckopora and the archaediscids Nodosarchaediscus sp. and involutus stage Paraarchaediscus. II - Bundoran Shale Formation The lithologies that comprise this formation in Subarea-2 are identical to those recorded throughout the remainder of the outcrop in Northern Ireland and consist of dark grey, very fossiliferous, calcareous and micaceous, blocky mudstones and silty mudstones with thin to very thick beds of dark blue-grey bioclastic limestone. The most extensive outcrop of the Bundoran Shale is in the Newtownbutler Stream in the part of the section overlying the basal sandstone member and north of H4256 2660. The strata consist largely of interbedded dark grey calcareous shales with numerous squashed colonies of Siphonodendron martini and S. sociale, and thin to very thick blue-grey limestones with large upright coral colonies, particularly of Diphyphyllum. The river bed downstream of such shales and to a lesser extent, limestones is typically covered with coral debris washed from the rocks. Mullynagowan Sandstone Member At the base of the Bundoran Shale Formation in the Newtownbutler area of Subarea-2 is a new sandstone unit which is not completely exposed at its stratotype section but which is about 2m thick. At its base the sandstone rests directly on grainstones of the Newtownbutler Member and although there is no evidence of the contact being erosional, it is likely that the relationship between the members is disconformable. The base of the member is located about 25m north of the farm lane bridge, in the bed of the river. The lowest bed of the Mullynagowan Member consists of 0.12m of pale grey, fine-grained, parallel laminated, highly bioturbated, calcareous, micaceous subarkose to quartz arenite. Succeeding medium and dark grey sandstones are very silty and bioturbation structures are dominated by burrows of Chondrites and less commonly of either Rhizocorallium or Teichichnus. Increasing carbonate content in higher beds is accompanied by the appearance of parallel and undulose laminations and bioclasts, in particular individual crinoid ossicles and brachiopod fragments. This is particularly evident from the pitted, weathered surface of the calcareous sandstone exposed below the farm building 20m east of the stratotype river section. Only about 0.7m of sandstone is exposed in this part of the stratotype but other exposures some 30m to the northeast, at the sharp bed in the river show the gradational change from very calcareous bioclastic sandstones, at the top of the member, to succeeding medium and dark grey sandy limestones. | |
| Interpretation: | |
The occurrence of two sandstone members in the lower part of the Bundoran Shale Formation in northwest Ireland is reviewed by Philcox et al. (1992). Of these the most widespread is the Dowra Sandstone which occurs in four deep boreholes, but in only one of them, at Dowra, Co. Cavan, is the sandstone located at the base of the formation. The other member, the Drumkeeran Sandstone, is only recorded in the deep borehole at Drumkeeran, Co. Leitrim, at the base of the formation. Whilst it seems likely that the former sandstone was derived from the north, the latter is tentatively interpreted as southerly derived sediment. Both members are restricted to central parts of the depositional basin and are thought by Philcox et al. to reflect uplift around the margin. The occurrence of new limestone and new sandstone members at the top and base respectively of the Ballyshannon and Bundoran formations is also a feature of the succession in the Kesh-Omagh area of the Northwest Basin, some 50km north of Newtownbutler. In that area they reflect an episode of bathymetric shallowing and micritisation at the top of the Ballyshannon Limestone and further marine regression, exposure and proximal erosion, of the altered limestones, and metamorphic basement, in early Bundoran Shale times. In the Kesh-Omagh area the basal beds of the Bundoran Shale are sandstones and conglomerates, the Skea Sandstone Member, that thin southwards and become finer in that direction and were clearly derived from a northern source area located on the Dalradian rocks in the western part of the Sperrin Mountains. This source did not provide clastic debris for the Mullynagowan Sandstone Member and a more likely source lies to the south on the Down-Longford Lower Palaeozoic rocks. The grainstones of the Newtownbutler Member are indicative of shallow water conditions and reflect an identical sequence of events in south Fermanagh as in the Kesh-Omagh area. | |
| Conclusions: | |
The Newtownbutler stream between Mockbeggar and Mullynagowan townlands in Subarea-2, offers a unique section completely exposing the contact between the Ballyshannon and Bundoran formations and is the stratotype for new lithostratigraphical members at their top and base respectively. | |
| Notes: | |
For information on other sites in Subarea-2 see; Key Site 1175 - Subarea-2; Lisnaskea-Fivemiletown. | |
| Keywords | |
|---|---|
| Rocks: | Limestone, Shale |
| Fossil Groups: | Brachiopod, Coral, Foraminifera, Microfossil, Microfossils, Trace fossil, Trace fossils |
| Fossil List: | Koninckopora sp. (monolaminar) , Paraarchaediscus stage involutus |
| Relations: | Marine sediments |
| Access | |
|---|---|
| Approach: | The Newtownbutler Stream section is located in the boundary between Mockbeggar and Mullynagowan townlands about 1km ENE of Newtownbutler crossroads. |
| References (1) | |||
|---|---|---|---|
| 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. | |||
| Record type: | ESCR report | ||
| Entered by: | Doughty, P.J. | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Newtownbutler Stream, County Fermanagh, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=204. Accessed on 2026-11-07. |
| Previous Site | Next Site |