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Earth Science Conservation Review
| Iniscarn Townland, near Desertmartin | Londonderry |
| Site number: | 298 | File Number: | H89 |
| ESCC: | EO | ||
| Locality Type: | Stream section | Status: | ESCR |
| Grid Reference: | H8290 1 km square | ||
| Google maps: | 54.7517,-6.72647 | ||
| County: | Londonderry | Council area: | Mid Ulster District Council |
| Period: | Carboniferous | ||
| Stages: | Tournasian | ||
| Lithostrat: | Iniscarn Sandstone Formation, Tyrone Group | ||
| Site Description | |
|---|---|
| Highlights: | |
The best exposures of the Iniscarn Sandstone Formation occur in the Iniscarn Water and its principal tributaries in Iniscarn Townland, about 3km SW of Desertmartin. | |
| Description: | |
Iniscarn Townland is located on the NE side of Slieve Gallion. Exposures of the Iniscarn Formation are largely confined to deeply incised northeasterly draining streams, in particular the Iniscarn Water (H83 90) and its NE-flowing tributary (H82 90) located north of Iniscarn House. The Iniscarn Formation in the Iniscarn area forms a fault-bounded outcrop within which the red-beds dip uniformly northwards at between 10-40 deg. The NW limit of the outcrop is the Boveagh Fault that juxtaposes the Iniscarn Formation with the Altagoan Formation and late Vis‚an rocks near Cullion. The outcrop is thought to be faulted on its NE side against the Asbian Desertmartin Limestone Formation. The best exposures of the formation occur in the Iniscarn Water and the stream located 800m to the NW. In the Iniscarn Water, SW of Iniscarn Bridge (H8336 9050) there are numerous exposures of red-beds, the furthest upstream occurring about 1.6km SW of the bridge. The rocks consist primarily of red, coarse-grained arkose, pebbly sandstones and sandy conglomerates. Conglomerates tend to be friable and arranged in beds up to 0.5m thick interbedded with softer mottled red and grey-white sandstones and muddy sandstones. | |
| Interpretation: | |
The sedimentary rocks of the Iniscarn Sandstone Formation largely comprise an upward fining interbedded sequence of conglomerates, pebbly sandstones, sandstones and argillaceous sandstones. The latter lithology occurs primarily at the top of the formation and is transitional upwards to fine-grained red-beds, with pedogenic horizons, of the succeeding Drumard Member of the Altagoan Formation. All the red-beds of the Iniscarn Formation are non-marine, terrestrial deposits. Much of the coarse debris was derived by the erosion of exposed Dalradian metamorphic rocks and was deposited, from flash floods, on alluvial fans adjacent to higher ground. Transport of finer fractions of the eroded debris to more distant parts of the 'basin' led to the accumulation of cross- laminated sandstones and pebbly sandstones. Mud and silt grade material would clearly be transported the greatest distance from the source area by surface water and would eventually form deposits much thinner than the conglomerates and sandstones, but contemporaneous with them. These finer sedimentary rocks are typical of the Drumard Member of the succeeding Altagoan Formation and whilst they undoubtedly succeed the Iniscarn Formation gradationally, elsewhere in the outcrop in Subarea-12 they are also partly contemporaneous with the latter formation. | |
| Conclusions: | |
Exposures of the Iniscarn Formation in Iniscarn Townland are best represented in the stratotype section in Iniscarn Water and in the river located 800m to the NW. | |
| Notes: | |
For information on other sites in Subarea-12 see Key Site 1185 - Subarea-12; Draperstown-Glenshane Pass-Limavady. | |
| Keywords | |
|---|---|
| Rocks: | Arkose, Conglomerate, Sand, Sandstone |
| Structures: | cross-bedding |
| Paleoenv: | alluvial fan |
| Access | |
|---|---|
| Approach: | 3km SW of Desertmartin. |
| Map(s): | GSNI (1995) 1:50,000 Solid Geology of Sheet 26 (Draperstown). | ||
| Record type: | ESCR report | ||
| Entered by: | Doughty, P.J. | ||
| Last updated: | 6 Jun 2005 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Iniscarn Townland, near Desertmartin, County Londonderry, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=298. Accessed on 2026-11-06. |
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