Earth Science Conservation Review
| Faughan and Dungiven Basins - Tamnagh | Londonderry |
| Site Type: | Inland exposure |
| Site Status: | TBC |
| Grid Reference: | C591025,C6000 |
| Google maps: | 54.86719,-7.07951 |
| Rocks | |
|---|---|
| Rock Age: | Quaternary |
| Rock Type: | Gravel, Sand |
| Interest | |
| Other interest: | Glacial deposit, Glacio-fluvial sediment, cross-valley moraine, deltas, esker |
Summary of site:
The Sluggada Burn drains the eastern slopes of Learmount Mountain, the northern slopes of Dart Mountain and the western slopes of Sawel Mountain. It flows north and then north west, reaching the village of Park after about 4.5km. A feature of the burn is a series of cross-valley ridges with associated sediments. The first group is 1.25km south east of the village and although they are now much dissected and poorly exposed, they can be seen to associate with the valley-side terraces.
About 2km south, the valley is spanned by two further ridges, about 7m high, that pass laterally and vertically into glacial drift. Immediately south of them there is a steep sided, linear mound consisting of cross-bedded sand and gravels and, on the valley side, a wedge-shaped remnant of a more extensive stack of sediments. Five units are recognised, three in continuity and, over 40m upstream, a further two. At the base, unit 1 commences with 1m of coarse pebble and cobble gravels, silty laminations and boulders. Unit 2 consists of over 2m of deformed fine sand and medium grained sands, followed in unit 3 by massive cobble beds of unknown thickness (because its top is missing). Unit 4 is composed of cross-bedded sands and cobble gravels followed, across an eroded contact, by a massive stack of cobble gravels. This southernmost part of the deposit is marked by a 35º slope, 15m high.
Half a kilometre upstream and 30m higher are three steep-sided ridges, about 20m across and 15m high, extending for 200m across the valley. They are beaded (expanded at intervals, rather like a string of beads) and originate in a mound 40m above their top level. They consist of troughs of gravels and cross-bedded sands. The internal sedimentary structures are inclined at 15º, aligned with the ridge axes.
This association of structures and associated sediments is a complex of moraines, delta lake fills and eskers. The topmost lake level appears to have been at 256m above modern sea level. The 35º slope could have been a contact face with the glacial ice. The beaded structures appear to be modified eskers.
About 2km south, the valley is spanned by two further ridges, about 7m high, that pass laterally and vertically into glacial drift. Immediately south of them there is a steep sided, linear mound consisting of cross-bedded sand and gravels and, on the valley side, a wedge-shaped remnant of a more extensive stack of sediments. Five units are recognised, three in continuity and, over 40m upstream, a further two. At the base, unit 1 commences with 1m of coarse pebble and cobble gravels, silty laminations and boulders. Unit 2 consists of over 2m of deformed fine sand and medium grained sands, followed in unit 3 by massive cobble beds of unknown thickness (because its top is missing). Unit 4 is composed of cross-bedded sands and cobble gravels followed, across an eroded contact, by a massive stack of cobble gravels. This southernmost part of the deposit is marked by a 35º slope, 15m high.
Half a kilometre upstream and 30m higher are three steep-sided ridges, about 20m across and 15m high, extending for 200m across the valley. They are beaded (expanded at intervals, rather like a string of beads) and originate in a mound 40m above their top level. They consist of troughs of gravels and cross-bedded sands. The internal sedimentary structures are inclined at 15º, aligned with the ridge axes.
This association of structures and associated sediments is a complex of moraines, delta lake fills and eskers. The topmost lake level appears to have been at 256m above modern sea level. The 35º slope could have been a contact face with the glacial ice. The beaded structures appear to be modified eskers.
| Enlander, I., Dempster, M. & Doughty, P., 2024. Faughan and Dungiven Basins - Tamnagh, County Londonderry, site summary. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/summary.php?item=503. Accessed on 2024-12-26 |
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