| Previous Site | Next Site |
Earth Science Conservation Review
| Glendurragh River, Lack | Fermanagh |
| Site number: | 217 | File Number: | H26 |
| ESCC: | EO | ||
| Locality Type: | Stream section | Status: | ESCR |
| Grid Reference: | H275672 Centroid | ||
| Google maps: | 54.55283,-7.57498 | ||
| County: | Fermanagh | Council area: | Fermanagh & Omagh District Council |
| Period: | Carboniferous | ||
| Stages: | Tournasian | ||
| Lithostrat: | Omagh Sandstone Group | ||
| Site Description | |
|---|---|
| Highlights: | |
The Glendurragh River section comprises a very variable sequence of dominantly coarse clastic and argillaceous sedimentary rocks of the Omagh Sandstone Group. The plane of the basal unconformity with metamorphic basement is exposed. Abundant miospores occur in grey mudstones. | |
| Description: | |
The section of the Glendurragh River in which is exposed the Omagh Sandstone Group is located about 600m north of Lack. The basal unconformity is exposed (H2753 6720) in the north bank of the river, some 20m downstream (west) of Lagalumber Bridge and is overlain by almost 3m of conglomerates, pebbly sandstones, sandstones and thin siltstones. All lithologies are coloured in shades of purple-red and brown. Strata in this basal section are inclined westwards at between 25-35 deg. but this declines to about 15 deg. at higher levels to the west. Immediately overlying this section are cross laminated purple-red sandstones and thick beds of vein quartz pebbly, very coarse-grained sandstones. The most westerly exposure in the section occurs about 300m west (H2731 6703) of the basal unconformity. Above the basal clastic section lithologies are extremely varied and are interbedded in a haphazard manner. Red-beds, in particular very coarse-grained pebbly sandstones and sandstones are common and are interbedded with 'unbedded' palaeosols comprising purple-red, gritty, silty and sandy soils with disorganised gravel beds. Some 100m downstream of the base of the section the colour of the sediments changes from purples and reds to grey-green and dark and light grey. Palaeosol horizons do occur sporadically but most lithologies now consist of interbedded sandstones, siltstones and carbonaceous mudstones. Grading is common in the sandstones with the basal layer of individual beds often containing quartz pebbles up to 0.01m diameter and large pieces of grey mudstone, in a very coarse-grained matrix. Grey mudstones sampled at four horizons in the western 200m of the section all contained abundant miospores including the following forms: (list reads left to right) Apiculiretusispora fructicosa Auroraspora corporiga A. macra A. solisortus Baculatisporites fusticulus Bascaudaspora submarginata Calamospora spp. Convolutispora circumvallata C. permixta Crassispora trychera Densosporites spitsbergensis Dictyotriletes cf. flavus Discernisporites micromanifestus D. sullivani Endoculeospora gradzinskii Geminospora spongiata Grandispora echinata Hymenozonotriletes explanatus Knoxisporites triangularis Lophozonotriletes tuberosus Plicatispora scolecophora Prolycospora rugulosa Punctatisporites minutus Rugospora lactucosa R. minuta R. polyptycha Schopfites claviger S. delicatus Spelaeotriletes cf. pretiosus S. resolutus Velamisporites magnus Verrucosisporites gibberosus V. irregularis The occurrence of the CM Biozone index taxa A. macra and S. claviger, combined with the absence of the Pu Biozone index taxon Lycospora pusilla indicate a Tournaisian (CM Zone) age. The most westerly exposure in the stream (H2731 6703) is a bed, 0.21m thick, consisting of medium grey, pyritous, very calcareous sandy siltstone with abundant plant remains. Rare specimens of bivalves, gastropods and fish scales and teeth also occur. | |
| Interpretation: | |
Significant facies changes occur in the outcrop of the Omagh Sandstone Group in Subarea-3. From their northeast extremity at Omagh, to the margins of the Lack Inlier there is a marked decrease in the thickness and overall grainsize of the basal clastic beds. This is accompanied by a significant change in the colour of the sediments which, in the Lack area, are dominantly of greys and greens. Around Omagh there is a thick basal sequence of red-coloured sandstones and conglomerates. The Glendurragh Stream section of the Omagh Sandstone Group illustrates clearly the variable nature of the environments that existed in this part of N. Ireland in late Tournaisian times. Though dominated by fluvial sediments, there are clear indications of temporary lacustrine phases and, at all levels, of subaerial exposure and pedogenesis (soil formation). At no level in the Glendurragh River section is there unequivocal evidence of a marine influence. Elsewhere however, adjacent to the Lack Inlier, in other stream sections exposing the Omagh Sandstone Group, is abundant evidence of supratidal and intertidal hypersaline environments. This is exemplified by the occurrence of laminated algal (cyanobacterial) limestones, evaporite replacement textures and particularly by the profuse growth of serpulid 'reefs' in some limestones. Coarse-grained calcareous laminated sandstones interbedded with the limestones and shales frequently contain abundant crinoid ossicle debris, bivalves and occasional rhynchonellid brachiopods indicating deposition in, or very close to, a truly marine environment. Late Tournaisian marine sediments, such as the Waulsortian mounds, that are developed near Enniskillen (Subarea-1) were only deposited in the southwestern part of N. Ireland and throughout the remainder of Ireland. Much of N. Ireland represents the site of an extensive floodplain across which meandered river systems and on which developed temporary lakes. Localised fault-line scarps encouraged erosion of metamorphic basement and accumulation of coarse debris on small alluvial fans. Localised marine incursions were transitory episodes but the influence of saline waters encouraged the development of sabkha at high levels in the Omagh Sandstone Group. Regional uplift and gentle warping over much of N. Ireland occurred in late Tournaisian and early Vis‚an times resulting in erosion of the top of the Omagh Sandstone Group and the development of an unconformity, before the basal beds of the Tyrone Group, the Claragh Sandstone Formation, were deposited. | |
| Conclusions: | |
This section is one of the few that exposes the basal unconformity of the Omagh Sandstone Group and, in a relatively small exposure, contains most of the lithologies that are typical of this extremely variable lithostratigraphical unit. | |
| Notes: | |
For information on other sites in Subarea-3 see; Key Site 1176 - Subarea-3; Kesh-Omagh. | |
| Keywords | |
|---|---|
| Rocks: | Mudstone, Sand, Sandstone |
| Fossil Groups: | Bivalve, Fish, Gastropod, Miospore |
| Fossil List: | Schopfites claviger |
| Relations: | Fluvial sediments |
| Access | |
|---|---|
| Approach: | About 600m north of Lack. |
| Record type: | ESCR report | ||
| Entered by: | Crowther, P.R. | ||
| Last updated: | 6 Jun 2005 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Glendurragh River, Lack, County Fermanagh, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=217. Accessed on 2026-11-06. |
| Previous Site | Next Site |