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Earth Science Conservation Review
| Mourne Plain Complex - Sandpiper Pit | Down |
| Site number: | 445 | ||
| ESCC: | IS | ||
| Locality Type: | Pit | Status: | TBC |
| Grid Reference: | J32823121 Centroid | ||
| Google maps: | 54.21298,-5.96437 | ||
| County: | Down | Council area: | Newry, Mourne & Down District Council |
| Period: | Quaternary | ||
| Stages: | Late Midlandian | ||
| Site Description | |
|---|---|
| Description: | |
The Sandpiper pit (328200 312100) contains three major facies. F1 Stratified sand and gravel This facies consists of 4m of interbedded sand, silt and clay with occasional pebbly gravel lenses and more continuous stratified gravel. Rhythmically bedded sand (5-40cm thick), silt and clay (<5cm thick) are continuous laterally (up to 50m) and subhorizontal. Gravel beds (<10cm thick) are frequently poorly sorted, matrix supported, and show rapid lateral transitions into pebbly sand. Sand beds are horizontally laminated or low angle cross-stratified, containing many ripples overlain by clay drapes (<2cm thick). Pillars and dish structures up to 1.8m across are common. A boulder (1.2m) penetrates the junction between pebbly sand and laminated sand, deforming the underlying laminae. Pebbly sand forms a drape over the boulder, with almost vertical beds against the western side of the boulder, becoming subhorizontal to the east. Underlying sand beds are truncated to the east of the boulder, and are replaced by a wedge of massive sand. Pods of chaotic gravels and boulders located at the eastern end of the exposure deform underlying laminated sand. The largest pod (2m deep by 6m wide by 12m long) has a discus shape, shallowing in all directions. Underlying sand is distorted, with many low to high angle normal and reverse faults, some of which extend up to 30cm into the underlying gravels. Discontinuous, distorted laminated sand occurs within the gravel pod. F2 Stratified diamict Interbedded sand and gravel has a planar contact over 500m with up to 4m of crudely stratified matrix supported diamict (F2). Beds (<10cm thick) are frequently laminated and horizontal. The matrix consists of coarse sand and clasts are predominantly pebbles, with dispersed cobbles and a few small boulders (<0.5m). Larger clasts frequently have a vertical a-axis orientation, penetrating and deforming underlying beds. The bulk of the smaller pebbles have horizontal a-axis fabrics. Crosscutting channels (>10m wide and up to 3m deep) are infilled by stratified sand and gravel and massive sand. Occasionally they are bordered by lines of single cobbles. F3 Massive diamict The stratified diamict has a transitional to erosional contact with overlying massive, clast-deficient diamict (1-4m thick) (F3). The diamict forms a tabular unit across the top of the pit for about 250m. Dispersed clusters and lenses of pebbly gravel contain frequent cobbles and small boulders. A distinct, cobble lined channel which penetrates F1 and F2 is enclosed by a bed of laminated mud (300mm thick) which is conformable with F3. The upper mud boundary is marked by a discontinuous line of cobbles. INTERPRETATION The sediment sequence at Sandpiper pit records the deposit of subaqueous outwash from the Cranfield Point moraine. The western end of the pit occupies an ice proximal position with the sediments becoming progressively more distal to the east. Interbedded sand, silt and gravel record pulses of flow of variable strength. Their marked lateral continuity suggests deposition from density underflows spreading from a glacial efflux. Dish and pillar structures record water escape from saturated sediment. Mud drapes record deposition from suspension between higher energy flows. Random clasts within the sand and outsize clasts within the gravel are probably of ice-rafted origin. The boulder penetrating the laminated sand, and covered by draped pebbly sand, is unequivocal evidence of ice-rafting, since there are no adjacent slopes which could act as a source, and the beds are not glaciotectonized. Massive sand in channels results from grain flow and deposition from suspension and is characteristic of subaqueous outwash (Rust & Romanelli, 1976). Gravel pods distorting laminated sands are interpreted as records of berg grounding events. Laminated sand inclusions within the pods suggest that deposition of fines continued after each grounding. Faulting is the result of the loading of relatively poorly consolidated sediments and the removal of support as entrained ice melted. The stratified diamict (F2) is interpreted as resulting from high density gravity sheet flows. Lateral continuity and thinness of beds suggest a sheet flow which readily incorporated and oriented small clasts ejected in sediment plumes from the ice front. Mass flow on low angle slopes frequently results in poorly laminated diamicts (Gravenor et al., 1984). Channels may have resulted from amalgamation of flows on shallow gradients. Outsized vertical clasts are likely to be ice-rafted debris (Domack & Lawson, 1985). Smaller pebble-sized clasts are aligned along bedding planes. Laminated mud between F1 and F2 records deposition of suspended sediment between scouring events, which remobilized the unconsolidated mud. In one location ice-rafted detritus protected the mud from scouring. Matrix rich massive diamict results from sedimentation from turbid plumes. Some clast clusters are the result of berg overturn or grounding (Eyles & Miall, 1984). The palaeoflow measured in the kettle hole exposure is incompatible with an ice front sediment source located to the west. The deposit is interpreted as the redeposited, winnowed fine fraction from previously emplaced proglacial material. The crossbeds are interpreted as deltaic deposition in an inlet of the late glacial sea, which had exploited a low-lying kettle hole and interconnected meltwater channels. | |
| Interpretation: | |
The sediment sequence at Sandpiper pit records the deposit of subaqueous outwash from the Cranfield Point moraine. The western end of the pit occupies an ice proximal position with the sediments becoming progressively more distal to the east. Interbedded sand, silt and gravel record pulses of flow of variable strength. Their marked lateral continuity suggests deposition from density underflows spreading from a glacial efflux. Dish and pillar structures record water escape from saturated sediment. Mud drapes record deposition from suspension between higher energy flows. Random clasts within the sand and outsize clasts within the gravel are probably of ice-rafted origin. The boulder penetrating the laminated sand, and covered by draped pebbly sand, is unequivocal evidence of ice-rafting, since there are no adjacent slopes which could act as a source, and the beds are not glaciotectonized. Massive sand in channels results from grain flow and deposition from suspension and is characteristic of subaqueous outwash (Rust & Romanelli, 1976). Gravel pods distorting laminated sands are interpreted as records of berg grounding events. Laminated sand inclusions within the pods suggest that deposition of fines continued after each grounding. Faulting is the result of the loading of relatively poorly consolidated sediments and the removal of support as entrained ice melted. The stratified diamict (F2) is interpreted as resulting from high density gravity sheet flows. Lateral continuity and thinness of beds suggest a sheet flow which readily incorporated and oriented small clasts ejected in sediment plumes from the ice front. Mass flow on low angle slopes frequently results in poorly laminated diamicts (Gravenor et al., 1984). Channels may have resulted from amalgamation of flows on shallow gradients. Outsized vertical clasts are likely to be ice-rafted debris (Domack & Lawson, 1985). Smaller pebble-sized clasts are aligned along bedding planes. Laminated mud between F1 and F2 records deposition of suspended sediment between scouring events, which remobilized the unconsolidated mud. In one location ice-rafted detritus protected the mud from scouring. Matrix rich massive diamict results from sedimentation from turbid plumes. Some clast clusters are the result of berg overturn or grounding (Eyles & Miall, 1984). The palaeoflow measured in the kettle hole exposure is incompatible with an ice front sediment source located to the west. The deposit is interpreted as the redeposited, winnowed fine fraction from previously emplaced proglacial material. The crossbeds are interpreted as deltaic deposition in an inlet of the late glacial sea, which had exploited a low-lying kettle hole and interconnected meltwater channels. | |
| Notes: | |
For site specific information on other sand and gravel sites within the Mourne Plain Complex see the following sites: Key Site 441 - Cranfield Moraine Key Site 442 - Glenloughan Pit Key Site 443 - Tullyframe Pit Key Site 444 - Moore Lodge Moraine Key Site 446 - Kilkeel Cliff For overview information and references on the Mourne Plain Complex see the following site: Key Site 440 - Mourne Plain 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 447 - Attical Complex, Mourne Mountains - Overview Key Site 448 - Bloody Bridge River Valley 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 | |
|---|---|
| Relations: | Glacial deposit, Glaciomarine deposit, Glaciotectonic |
| Geomorph: | ice lobe, moraine ridge, outwash |
| Record type: | ESCR report | ||
| Entered by: | E M Porter | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Mourne Plain Complex - Sandpiper Pit, County Down, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=445. Accessed on 2026-11-06. |
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