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Earth Science Conservation Review
| Faughan and Dungiven Basins - Tamnagh | Londonderry |
| Site number: | 503 | ||
| ESCC: | IS | ||
| Locality Type: | Inland exposure | Status: | TBC |
| Grid Reference: | C591025,C6000 End(s) of linear site, Not Entered | ||
| Google maps: | 54.86719,-7.07951 | ||
| County: | Londonderry | Council area: | Derry City & Strabane District Council |
| Period: | Quaternary | ||
| Site Description | |
|---|---|
| Description: | |
A 5km valley drained by the Sluggada Burn located between the slopes of Learmount (258050, 398300) and Sawel (261800, 397300) mountains in the northern footslopes of the Sperrin mountains. In the lower section of the valley, 1.25km southeast of Park (259100, 402500) poorly-exposed dissected cross-valley streamlined ridges form several topographic highs bordered by flat-topped alluvial terraces. Further up-valley at (260000, 400000), two cross-valley 7m high ridges pass laterally and vertically into peat covered diamict. Bordering the ridges to the south, is a steep sided ridge of well-sorted planar cross-bedded sand and cobble gravel. Beds dip at 25§, 120§N. Directly across valley at a lower altitude 9m of stratified sediments are exposed in a valley-side wedge shaped remnant. The complete (composite) exposure consists of five main units. Unit one consists of 1m of shallow dipping (at 10§, 100§N) planar cobble to pebble gravels, overlain by 5m of stacked silty sand beds interbedded with (<15cm thick) discontinuous cobble gravel beds, boulders and contains silt stringers. Unit two consists of 0.8m of deformed massive fine sands and 1.6m of planar-bedded (<10cm) medium sands. Unit three consists of an unknown thickness of stacked, massive, cobble gravel beds. The next unit is exposed a further 43m higher. Unit four consists of the cross-bedded sands and cobble-gravels detailed above. An erosive contact marks the end of the section with Unit five, stacked massive cobble gravels. All other inter-unit contacts are conformable. A steep (35§) 15m high slope marks the southern extent of the feature. 0.5km further up-valley, at 30m higher elevation, three distinct, steep-sided sub-parallel beaded ridges approximately 20m across by 15m high, run 200m cross-valley from a mound 30m in diameter 40m above the ridge tops. A small-scale (10m x 2.5m) exposure in one ridge shows stacked, conformably bedded trough and planar cross-bedded sets of sands and poorly-sorted cobble gravels. Sharp vertical erosional contacts separate geometrically but not texturally similar sets. The small-scale foresets with 2-3cm bed thicknesses and 30cm thick cross-bedding units dip at 15§, 040§N, subparallel to ridge orientation. | |
| Interpretation: | |
The Tamnagh valley is interpreted as containing a complex of cross-valley moraines, deltaic valley fill and eskers. The section detailed is interpreted as representing part of a glaciolacustrine valley fill. Unit four represents the foresets of a glaciolacustrine delta prograding at 120§ N into a waterbody ponded at 256m O.D. The steep slope was possibly formed in ice-contact and represents the ice-front position at the time of the deltas progradation. The poor exposure of the features in the upper-valley leaves interpretation based largely upon morphology. The small scale bedding structures and sharp vertical erosional contacts (interpreted as representing rapid, channelised, cross-cutting avulsion) leads to the interpretation of the slopes as primarily depositional in character and the features as eskers. | |
| Notes: | |
For site specific information on other sites within the Faughan and Dungiven Basins see the following sites: Key Site 499 - Faughan and Dungiven Basins - The Murnies Key Site 500 - Faughan and Dungiven Basins - Derrynaflaw Key Site 501 - Faughan and Dungiven Basins - Banagher Key Site 502 - Faughan and Dungiven Basins - Templemoyle Key Site 504 - Faughan and Dungiven Basins - Cumber Key Site 505 - Faughan and Dungiven Basins - Gosheden Key Site 506 - Faughan and Dungiven Basins - Fawney Key Site 507 - Faughan and Dungiven Basins - Enagh For overview information and references on the Faughan and Dungiven Basins see the following site: Key Site 470 - Faughan and Dungiven Basins - Overview For general information and references on the sand and gravel landscapes of N. Ireland, and for directions to other regional sand and gravel sites, see the following site: Key Site 439 - Introduction to the Sand and Gravel Landscapes of N. Ireland This site is also a Site of Local Nature Conservation Importance. See Key Site 752 - Tamnagh. | |
| Keywords | |
|---|---|
| Rocks: | Gravel, Sand |
| Relations: | Glacial deposit, Glacio-fluvial sediment |
| Geomorph: | cross-valley moraine, deltas, esker |
| Record type: | ESCR report | ||
| Entered by: | E M Porter | ||
| Last updated: | 6 Jun 2005 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Faughan and Dungiven Basins - Tamnagh, County Londonderry, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=503. Accessed on 2026-11-06. |
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