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Earth Science Conservation Review
| Tircar Stream, Fivemiletown | Tyrone |
| Site number: | 215 | File Number: | H44 |
| ESCC: | EO | ||
| Locality Type: | Stream section | Status: | ESCR |
| Grid Reference: | H48804677,H48564728 End(s) of linear site, Not Entered | ||
| Google maps: | 54.36709,-7.2492 | ||
| County: | Tyrone | Council area: | Mid Ulster District Council |
| Period: | Carboniferous | ||
| Stages: | Asbian, Visean | ||
| Lithostrat: | Alderwood Mudstone Member, Leitrim Group, Meenymore Formation | ||
| Site Description | |
|---|---|
| Highlights: | |
The Tircar stream section exposes the probable base of the Alderwood Mudstone Member and the greatest variety of lithologies and thickness of strata in the outcrop. | |
| Description: | |
The Tircar stream is one of the major tributaries of the Colebrook River that rises on Slieve Beagh and flows west and northwards to join the main river. Exposures of the Alderwood Member occur over a 500m length of the stream and form discontinuous outcrops. At the southern end of the section (H4880 4677) strata crop out in the river bed as a series of small falls and are inclined northwestwards at about 40 deg. The top bed of the Meenymore Formation here is a bed of very coarse-grained and gritty brown sandstone which is overlain by about 1.5m of grey mudstones with a bed, 0.3m thick near the base, that consists of a sedimentary breccia incorporating angular lumps of pale-coloured micrite and fossil debris in a hash of crinoidal-rich mudstone and siltstone. There is a suggestion that the contact between the sandstone and the grey mudstones is a fault with an E-W orientation. A few metres north of this locality, low exposures of fine- grained, medium grey, peritidal limestones crop out on the SW bank of the stream at H4869 4693. These contain a fauna of brachiopods and small solitary corals and rare, solid specimens of goniatites. The microbiota of these limestones is somewhat impoverished but does indicate an Asbian and younger age. Intraclasts, up to 0.03m diameter occur in these limestones and consist of pale fawn-grey, very coarse-grained, serpulid- ostracod-nautiloid rich carbonate in a silty, very shaley matrix. Small nodules of black chert, and pyrite, are also common. Strata at the north end of the Tircar stream section consist of dolomitised and silicified microsparites, laminated (? stromatolitic) carbonates, grey mudstones and bioclastic mudstones. Because of their proximity to the Clogher Valley Fault zone the dip and strike of being is extremely variable and minor shearing and calcite veining is prevalent. | |
| Interpretation: | |
During late Asbian times the Meenymore Formation was deposited on a vast area of intertidal, supratidal and subaerial flats that border a northern land area and extended from Co. Sligo to east Co. Tyrone, and probably beyond. The Alderwood Mudstone Member consists of sedimentary rocks deposited entirely in a shallow water marine environment. Water depths and salinities varied considerably and supratidal, peritidal and open shelf marine conditions existed at various times in the area. There is however no obvious depositional cyclicity recognisable in the rocks and they do not correlate with the Bellavally Formation of northwest Ireland. In the section at Ashfield Mountain Bar (Key Site 260) chosen to represent the Meenymore Formation on Slieve Beagh (Subarea-5) are large (over 1m long) allochthonous limestone blocks which are virtually identical to limestones exposed in the Tircar stream at H4869 4693. These blocks occur in grey unfossiliferous mudstones and are thought to have moved downslope from shallow water. They also contain a conodont fauna that includes the Asbian index species Gnathodus bilineatus. On this basis it seems clear that the Alderwood Mudstone Member was deposited in a shallow water marine environment but is not the highest part of the Meenymore Formation in Subarea-2 and on Slieve Beagh. One explanation for its geographical location at the northern edge of the outcrop of the northward younging Meenymore Formation is dependant on the presence of strike faults which are as yet unrecognised in the field. | |
| Conclusions: | |
The Alderwood Mudstone Member consists exclusively of over 200m (GSNI, 1982) of marine sediments of late Asbian age. The Tircar stream section exposes a wide variety of lithologies attributable to this member, which occurs within the Meenymore Formation. | |
| Notes: | |
For information on other sites in Subarea-2 see; Key Site 1175 - Subarea-2; Lisnaskea and Fivemiletown. | |
| Keywords | |
|---|---|
| Rocks: | Limestone, Mudstone, Sand, Sandstone |
| Fossil Groups: | Arthropod, Brachiopod, Conodont, Coral, Crinoid, Goniatite, Nautiloid |
| Fossil List: | Gnathodus bilineatus |
| Relations: | Marine sediments |
| Measurements | |||||
|---|---|---|---|---|---|
| Length: | 500 m | Width: | Height: | ||
| Depth: | Area: | ||||
| Access | |
|---|---|
| Approach: | 4.5km ESE of Fivemiletown. |
| References (1) | |||
|---|---|---|---|
| Padget, P., 1951. The geology of the Clogher-Slieve Beagh area, Co. Tyrone. Scientific Proceedings of the Royal Dublin Society, vol. 26, pp.63-83. | |||
| Map(s): | GSNI (1982) 1:50,000 Solid Geology Sheet 45 (Enniskillen). | ||
| Record type: | ESCR report | ||
| Entered by: | Doughty, P.J. | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Tircar Stream, Fivemiletown, County Tyrone, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=215. Accessed on 2026-11-07. |
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