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Earth Science Conservation Review
| Greenan Mountain - Carboniferous | Tyrone |
| Site number: | 247 | File Number: | H36 |
| ESCC: | EO | ||
| Locality Type: | Stream section | Status: | ESCR |
| Grid Reference: | H316668 Centroid | ||
| Google maps: | 54.549,-7.51166 | ||
| County: | Tyrone | Council area: | Fermanagh & Omagh District Council |
| Period: | Carboniferous | ||
| Stages: | Namurian, Visean | ||
| Lithostrat: | Greenan Sandstone Formation | ||
| Site Description | |
|---|---|
| Highlights: | |
The stratotype section reveals the basal breccia and lowest sandstones of the Greenan Sandstone Formation. Miospore assemblages recovered in this section are of late Vis‚an-early Namurian age. | |
| Description: | |
The stratotype stream section is located on the south side of Greenan Mountain, 4.1km east of the village of Lack. Two streams drain this sector of the mountain and merge at the base of the steep slope which fringes the base of the mountain and marks the main outcrop, and reflects the soft nature, of sandstones of the Greenan Formation. The westerly stream is the stratotype section. Strata in the stream are inclined at between 70-85 deg. northwestwards and, based on cross-lamination structures are inverted. East of the stratotype metamorphic rocks and sandstones of the Greenan Formation are separated by a fault. The unconformity at the base of the formation occurs in the stream, at the north end of the section (H3152 6679) and may be traced southwestwards across the face of the mountain. The basal epiclastic breccia is about 30m thick and is exposed at the north end of the stratotype. The matrix, in the lowest few metres of the breccia, is an unsorted aggregate of fine debris of metamorphic rocks with angular boulders of phyllitic and psammitic schist, vein quartz and pegmatitic quartz up to 0.25m in diameter. Higher in the breccia, clast size decreases and the proportion of coarse sand matrix increases. The breccia is overlain, in the stratotype by 5m of red mudstones and siltstones with nodular pedogenic carbonate. The remainder of the stratotype, and of the formation in general, comprises medium- to coarse-grained, purple-grey feldspathic sandstones, which weather to a distinctive orange-purple colour, and laminae of purple-red and green mudstone. Parallel laminations and trough cross-bedding are common, and clasts, up to 0.06m, in diameter, of schist and pegmatitic quartz are scattered in the sandstones. Mudstones suitable for palynological analysis occur at four levels in the lower 100m of the formation and three of these occur in the stratotype section. The lowest sample consists of green mudstone clasts in sandstone, 1.5m above the basal breccia and the other two samples are of laminae of green mudstone in the lower 50m of sandstone in this section. These samples yielded a sparse miospore assemblage including the following forms: Calamospora parva Densosporites brevispinosus Dictyotriletes mediareticulatus Knoxisporites cinctus Lycospora pusilla Microreticulatisporites microreticulatus M. cf. punctatus Punctatisporites punctatus P. solidus Schulzospora campyloptera Stenozonotriletes sp. Tripartites vetustus Verrucosisporites morulatus V. nitidus A similar, but more diverse miospore assemblage was recovered from 0.08m of blue-grey mudstone that occurs at least 70m above the formation base and is exposed in the stream section at H3145 6660, 200m SW of the stratotype. This includes additional miospores including: Acanthotriletes sp. Apiculatisporites sp. Aurorospora cf. solisorta Calamospora pallida Cingulizonates bialatus Convolutispora venusta Densosporites anulatus Granulatisporites microgranifer Punctatisporites nitidus Radiizonates striatus Reticulatisporites sp. Retusotriletes sp. Rotaspora knoxi Verrucosisporites cerosus Waltzispora polita The occurrence of the species M. microreticulatus, S. campyloptera, T. vetusta and V. morulatus indicates an assignment to either the VF or NC Miospore Zones (Brigantian - Pendleian stages). The additional occurrence of Rotaspora knoxi is particularly significant as this form first appears at the base of the VF Zone equivalent to the base of the Brigantian Stage. | |
| Interpretation: | |
The sedimentary rocks of the Greenan Sandstone Formation were deposited in a non-marine basin that was quite separate from the southerly-located basin in which the partly coeval Kilskeery Group accumulated. The relatively thin basal breccia of the Greenan Sandstone Formation developed more or less in situ by direct weathering of basement metamorphic rocks. The occurrence of calcrete nodules in the mudstones and thin sandstones directly overlying the basal breccia are indicative of subaerial exposure and formation of soil profiles. The structure of the cross- laminated sandstones that dominate the remainder of the alluvial fill of this northern basin is interpreted as indicating a high flux of sediment entering the basin, thus maintaining a low topographic contrast between the metamorphic source rocks and the basin. The occurrence of the alga Botryococcus in green mudstones reflects the presence of temporary fresh or brackish water lakes. It appears that this basin lay to the north of the southwesterly extension of the Tyrone Igneous Complex and received detritus from a source area of Dalradian rocks with granitic intrusions and a Lower Palaeozoic ophiolite. | |
| Conclusions: | |
The stratotype section is unique in exposing both the basal breccia and lower part of the sandstone dominated sequence of the Greenan Sandstone Formation and in containing miospore assemblages by which the rocks are dated. | |
| Notes: | |
For information on other sites in Subarea-4 see; Key Site 1177 - Subarea-4; Fintona Block. This area is also important for Mineralogy and Metallogenesis. See Key Site 559 - Greenan Mountain, near Lack. | |
| Keywords | |
|---|---|
| Rocks: | Breccia, Mudstone, Sand, Sandstone |
| Fossil Groups: | Miospore |
| Fossil List: | Microreticulatisporites microreticulatus |
| Access | |
|---|---|
| Approach: | The stratotype section is located on the south side of Greenan Mountain, 4.1km east of the village of Lack. |
| Record type: | ESCR report | ||
| Entered by: | Doughty, P.J. | ||
| Last updated: | 6 Jun 2005 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Greenan Mountain - Carboniferous, County Tyrone, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=247. Accessed on 2026-11-06. |
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