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Earth Science Conservation Review
| Bloody Bridge River Outwash | Down |
| Site number: | 452 | ||
| ESCC: | IS | ||
| Locality Type: | Inland exposure | Status: | TBC |
| Grid Reference: | J378269,J376269 Centroid, Not Entered | ||
| Google maps: | 54.17305,-5.88976 | ||
| County: | Down | Council area: | Newry, Mourne & Down District Council |
| Period: | Quaternary | ||
| Stages: | Late Midlandian | ||
| Site Description | |
|---|---|
| Description: | |
Downcutting into the unconsolidated glacigenic fill of the Bloody River gorge, has produced two exposures 200m apart (J378269, J376269) at 230m a.s.l. The exposures are considered to be contemporaneous, since they are at the same altitude, although they occur at different relative positions along the gorge. The western exposure is overlain by up to 10m of glacigenic deposits forming a valley-side bench. Exposures overlooking the Bloody Bridge River are inaccessible and cannot be investigated in detail. EAST EXPOSURE The upper surface of the exposure is strongly undulating. Three channels trending north to south across the surface are cut up to 4m into the underlying diamict. The exposure is ca. 40m long by up to 8m high. Lithofacies units present are stratified sandy diamict and gravel, overlain by massive diamict and a lens of stratified gravel. Facies description Stacked beds (<7.5m thick) of stratified horizontal- and cross-bedded sandy diamict is matrix-rich, and contains occasional gravel lenses. Contacts are erosional and non-erosional and are planar to undulatory. Beds dip downslope eastward, at ca. 10° near the bedrock contact, becoming subhorizontal (2-3° towards the top of the section). Isolated boulders are frequently glacially bevelled and have a variable a-axis orientation, and there are occasional boulder-cobble clusters. A boulder (<1m) penetrates underlying sandy beds by ca. 30cm. A channel (11m x 3m) towards the base of the exposure contains crudely stratified gravel with numerous irregularly shaped cobble-boulder clusters. The contact between stratified and overlying massive diamict is erosional and undulating. The massive diamict is matrix-supported and forms a discontinuous carapace over the stratified diamict. The unit is <30cm thick, except for two channels cut into the stratified diamict. The larger channel is 2m wide and 1m deep. The stratified gravel lens (4m x 1m) occurs at the lowest point of the deepest surface channel, and has an erosional contact with underlying stratified diamict. The base of the lens consists of clast-supported cobbles and boulders (<0.5m), overlain by pebble and cobble beds. WEST EXPOSURE The exposure is 10m long and 8m thick. Lithofacies units present are stratified sandy diamict and gravel. Facies description The exposure consists of stacked planar and lenticular beds of sandy diamict and interbedded gravel. The lowest 3m consist of granule-rich coarse sandy diamict with occasional silty lenses. Variably oriented cobbles and boulders (<1.5m) occasionally penetrate bed boundaries and deform underlying beds. Sandy diamict is overlain by ca. 1.5m of stratified cobble and pebble. Beds (<20cm thick) are planar to lenticular, with erosional contacts. Gravel is openwork to matrix-supported. A silt-rich lens (ca. 8m x 0.5m) is interbedded with the gravel. Gravel beds grade into the overlying 2m of stratified sandy diamict. Diamict beds are tabular, with conformable contacts. Isolated boulders and cobbles are frequent. A cluster of four boulders (<1m) deforms underlying beds. | |
| Interpretation: | |
The location and geometry of the deposits suggest that the major source of sediment was a glacier which retreated westward along the valley. The cross-valley moraine bench, which overlies the deposits, indicates that sedimentation occurred prior to cross-valley moraine formation. Deposits probably relate to an efflux from a glacier which retreated into the mountains during the main Late Midlandian retreat phase. The eastern exposure consists predominantly of stratified sandy matrix, while the more westerly (upstream) exposure contains coarser deposits, and shows greater variability of texture and bedding. This pattern suggests that the western deposits are ice proximal, grading downslope into a sandier, more distal, facies. The angle of dip of beds declines up-section as a result of sediment aggradation. Coarse gravel which infills a channel and contains clusters which resemble log jams records energetic flow within relatively distal deposits and is typical of terrestrial ice contact fans (Boulton, 1986). Stratified sandy diamict probably originated as debris flows, which typically have non-erosional lower contacts (Middleton & Hampton, 1976). Erosional bed surfaces record sheet flow of saturated sediment (Harvey, 1984). The geometry and clast size distribution of the more ice-proximal exposure record episodic high-energy flows, with erosion of underlying beds. Periods of quiet flow are indicated by the silty lens. Outsize bevelled clasts in the sandy diamict probably record falls from unstable adjacent slopes. Massive diamict overlying stratified diamict is interpreted as debris flows, which are typically matrix-supported. The stratified gravel lens in the surface channel, is interpreted as a channel deposit. The boulder base of the channel deposit is probably a lag. Textural variation records conditions of variable flow and sediment supply. | |
| Notes: | |
For site specific information on other sand and gravel sites within the Bloody Bridge River Valley Complex see the following sites: Key Site 453 - Bloody Bridge River Valley Ridges Key Site 454 - Bloody Bridge River Fan For overview information and references on the Bloody Bridge River Valley Complex see the following site: Key Site 448 - Bloody Bridge River Valley Complex - Overview For overview and site specific information on other sand and gravel sites within the Mourne Mountains area see the following sites: Key Site 440 - Mourne Plain Complex - Overview Key Site 447 - Attical Complex, Mourne Mountains - Overview Key Site 449 - Northeast Mournes Complex - Overview Key Site 450 - Western Mournes - Overview Key Site 451 - Annalong Valley For general information and references on the sand and gravel landscapes of N. Ireland, and for directions to sand and gravel sites other than those within the Mourne Mountains area, see the following site: Key Site 439 - Introduction to the Sand and Gravel Landscapes of N. Ireland | |
| Keywords | |
|---|---|
| Geomorph: | cross-valley moraine, outwash |
| Record type: | ESCR report | ||
| Entered by: | E M Porter | ||
| Last updated: | 8 Jan 2005 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Bloody Bridge River Outwash, County Down, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=452. Accessed on 2026-11-05. |
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