ESCR - Mourne Plain Complex

Earth Science Conservation Review

Summary Full report
Mourne Plain Complex - Overview	Down

Site number:	440
ESCC:	IS
Locality Type:	Coastal section, Inland exposure, Pit
Grid Reference:	J31923166,J33443167,J32703098 Corners of site, Not Entered
Google maps:	54.2168,-5.97798
County:	Down	Council area:	Newry, Mourne & Down District Council
Period:	Quaternary
Stages:	Late Midlandian

Site Description
Highlights:
The Mourne Plain Complex is located on the coastal belt between Killowen (319200 316600), Ballymartin (334400 316700) and Cranfield Point (327000 309800), immediately south of the Mourne Mountains massif, Co. Down. The nature, pattern and size of the curvilinear, subparallel moraine ridges located between the Mourne mountains and the lateglacial shorelines of Co. Down, are visually striking features and facilitate the modelling of ice retreat patterns across this region during the early part of the deglacial period. The moraines record the phased retreat of the main Late Midlandian ice westwards into Carlingford Lough. Withdrawal of ice from the Plain was followed by an extensive readvance of ice from Carlingford as far east as the moraine ridge at Cranfield Point. The complex shows cross-cutting moraine ridges dating from the initial and subsequent readvance retreat phases. The volume of these ice marginal moraines, together with the sedimentological characteristics of the associated proglacial outwash, documents a considerable sediment flux to the ice margin (Dardis & McCabe, 1983). Numerous exposures in commercial sand and gravel pits record highly variable sediment inputs and facies sequences. The description and interpretation of these facies is critical for modelling changes in late Midlandian relative sea levels, as facies characteristics indicate temporal and spatial variations between glacioterrestrial and glaciomarine sedimentation. The extent of aggregate extraction indicates the high importance of the deposits as an economically valuable source of mineral aggregate.
Description:
The low-lying Mourne Plain is underlain by Silurian greywacke sandstones and mudstones, with the exception of a small area of Carboniferous limestone at the entrance to Carlingford Lough (Wilson, 1972). The bedrock geology is rarely exposed, except at a few coastal locations, as it is almost completely covered by thick glacigenic deposits e.g. the morainic ridge at Ballymartin (334500 317000) attains a local topographic height of 60m within 300m of the coast, while the Cranfield moraine at Tullyframe (326300 316800) rises to 70m above the general level of the lowland to the southwest. These may be regarded as minimal depths of material within the more prominent moraines. This contrasts with the steeply rising, largely drift-free bedrock slopes of the Mourne Mountains granite massif to the north, which dominates the local topography. Together the two areas supply the majority of clasts found within the glacigenic deposits. The morphology of the area contains three principal glacigenic topographic elements: 1) Curvilinear recessional moraines tending generally from northwest to southeast are related to late Midlandian ice retreat from the Plain westward into Carlingford Lough. The ridges in the east of the Plain are widely spaced and discontinuous whereas further west they occur as tightly spaced occasionally intersecting or crosscutting ridges and segments. 2) Spreads of proglacial outwash, which occur at lower altitudes in the more extensive inter-morainal lows contain enclosed depressions. 3) A series of shoreline notches and benches are cut into the outwash and moraine ridges by both lateglacial and postglacial marine highstands. A number of exposures have been chosen to illustrate the range of sedimentological processes, which together have resulted in the morphological diversity of the Mourne Plain. Sections have been selected which display the sedimentological complexity and variability typical of the Plain's three major morphological elements. The landforms are subdivided, classified and described firstly by morphological type, from west to east. MOURNE PLAIN MORAINES For site specific information on the Mourne Plain Moraines 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 MOURNE PLAIN OUTWASH The most extensive area of outwash on the Mourne Plain lies between 12 and 18m O.D. and measures approximately 1.6km2 in area. The outwash is triangular in plan view, is bounded to the west and north by the ridge of the Cranfield moraine and to the east by a moraine ridge at Ballynahattan (328400 312200). To the south the outwash is notched by a lateglacial strandline at 19m a.s.l. Large areas of the original surface of the outwash plain have been removed as a result of aggregate extraction. For site specific information on the Mourne Plain Outwash see the following site: Key Site 445 - Sandpiper Pit KETTLEHOLES A large number of up to 1km2 interconnected depressions (kettleholes) occur 1km to the west of Ballykeel (323300 316800), within a wide undulating spread which forms the eastern side of the Kilkeel River valley. The largest of these kettleholes contained a lake, which eventually drained to the south along a well-marked channel. A depression at Nace (333000 315800) in a low relief spread contains a poorly exposed section consisting of crossbedded sand with occasional fine gravel stringers. The palaeoflow, measured from cross-bedding, was towards 260deg. The top of the exposure is at ca. 30m O.D., the altitude of a late-glacial marine notch, and is in a depression at the landward end of a channel which dissects the marine notch. Isolated enclosed depressions are also found throughout the Plain (e.g. 329600 313200). RAISED BEACHES In the area between the Cranfield Point and Ballymartin moraine ridges, the seaward margins of the moraine ridges on the Mourne Plain are cut by up to four late-glacial and postglacial beach notches. Spreads and ridges of sand and gravel are eroded to produce a series of steps subparallel to the current coastline. The most continuous of these notches occurs at 20m O.D. at Dunnaval (2.1km long) and 30m O.D. east of Kilkeel (1.5km long). It is noted that notches at these elevations are absent from inside the area bounded by the Cranfield moraine. Between Cranfield Point and Slatemill Road (329300 312500) the undulating terrain is notched at 10m a.s.l., up to 300m inland. This is at a similar height to a raised beach found within the Cranfield moraine, and thus clearly post-dates the moraine. This shoreline is more irregular than the late-glacial notches, and is not as well-marked, probably the result of rapid postglacial isostatic adjustment. A lower notch at 6m a.s.l. is less continuous, and formed an embayed strandline. An almost continuous low ridge (<10m O.D.) trends northeast from Cranfield point for approximately 1km, parallel to the current coastline. Similar landforms occur within the Cranfield moraine in the Soldiers Point and Greencastle areas. For site specific information on the Mourne Plain Raised Beaches see the following site: Key Site 446 - Kilkeel Cliff OVERVIEW The moraines and associated outwash couplets on the Mourne Plain record stages in the decay of the late Midlandian ice sheet, which had its ultimate source in the Lough Neagh-Irish Midlands axis. As the level of the ice sheet fell below the level of the eastern Mourne, topographic control increased in importance, and it is likely that the Mournes were completely encircled by ice during initial downwastage. Moraines record periods of stillstand during this retreat, and exposures such as that at Moore Lodge indicate that a number of oscillations of the ice front were superimposed on this general pattern. Charlesworth (1955) identified the Cranfield moraine as a limit of the major readvance which fronts the drumlin swarms of County Down. Alternative limits for the readvance have been presented by Stephens and McCabe (1977) based on the existence of lateglacial shorelines between certain moraine ridges. These lateglacial shoreline notches are the result of the interplay of glacioeustatic and glacioisostatic processes (Stephens & McCabe, 1977). The moraines at Cranfield and Ballykeel were felt to be the most likely candidates for the terminus of readvance ice, which entered Carlingford Lough from the northwest. However, the pinching out of the high lateglacial shoreline at Ballykeel may simply be the result of coastal erosion removing evidence of its continuation to the east or due to the presence of bedrock at the surface. The truncation of moraine ridges at ca. 30m O.D. at Kilkeel, and at ca. 20m O.D. at Dunnaval confirms this conclusion. It is suggested that the Cranfield moraine marks the terminus of the Carlingford ice lobe. The topography of the Cranfield moraine records a distinctly lobate form in the ice margin, and sediments at Tullyframe and Glenloughan record outwash processes at the ice front. A similar lobate form has been described for a similar ice lobe centred in Dundalk Bay (McCabe et al., 1987). The processes recorded in the sediment pile at the Sandpiper pit are related to the ice front position in a glacioisostatically depressed basin, where it is likely that the ice mass would terminate in a marine environment (Eyles & McCabe, 1989). This interpretation is supported by the presence of Late-glacial raised beaches immediately outside the Cranfield moraine limit. This confirms that readvance ice entered the late glacial sea. Rapid ice flow into Carlingford Lough is inferred from valley and coastal drumlins in the Warrenpoint area. Massive diamict overlying marine mud on the coast at Cranfield Point records readvance over ice distal muds and provides critical stratigraphic evidence of a major readvance. The raised beach deposits assist in the definition of the sequence of events during the later stages of deglaciation. Higher beaches are evidence of the lateglacial marine transgression, which accompanied the retreat of the ice sheet from the Plain, as an isostatically depressed lowland area, became available for erosion and inundation. The sediments exposed along the coastline record an emergent sequence of shallow marine and beach environments. The cobble and boulder line at the base of the succession is a boulder pavement containing reworked clasts (Eyles, 1987). Cross-cutting striations on a glacially bevelled upper surface suggests later overriding by pack ice. Relatively thick low-angle cross stratified sand is typical of the transition between offshore and shoreface zones (Bourgeois & Leithold, 1984). Cross stratification records rapid deposition of sediment eroded from shoreface bars, and hummocky cross- stratification is consistent with rapid deposition from oscillatory flows below fair weather base (Bourgeois, 1980). Small channels are scours which are frequent in this zone of wave build up and rapid changes in flow regime. Interstratification of sand and gravel is typical of lower shoreface (Bourgeois & Leithold, 1984). Stacked sheets of gravel and coarse sand are characteristic of the upper shoreface zone, and are the product of reworking by waves and marine currents (Nemec & Steel, 1984). Overall coarsening upward of gravel culminates in beachface deposits of shape and size sorted gravels. Textural uniformity and lateral persistence of individual beds are typical of this zone (Clifton, 1973). The coarseness of many of the beds is the result of storm events, which winnow finer sediments to produce overbeach deposits. Emergent beach facies exposed in the Kilkeel cliff are evidence for a gradual lowering of relative sea level as isostatic rebound outstripped the input from retreating ice sheets. Truncation of the Cranfield moraine by lateglacial beaches indicates that glacier ice was still present at this site while rebound was under way. Postglacial raised beaches found both within and without the Cranfield moraine indicate that relative lowering of sea level continued after the final deglaciation of the area. IMPORTANCE The complex of morainic ridges and outwash sequences of the Mourne Plain demonstrates important geomorphological and glaciological concepts linked to the decay of tidewater ice margins in the Irish Sea. It forms the only well-described terrestrial topographic record of a marine based ice lobe (McCabe et al., 1984). The spatial sequence, sedimentological content and spacing of the morainic, ice marginal sediment piles demonstrate aspects of the ice mass condition and phased nature of generally rapid retreat. The Cranfield moraine contains a stratigraphy indicating a readvance of ice from Carlingford Lough onto the plain. The dating of glaciomarine muds in the sequence using biostratigraphic data will hopefully verify that the readvance was related to a significant readvance of the Irish ice sheet around 15kyr B.P. recorded from other sites around the Irish coastline (McCabe, 1996). The raised beach notches cut into the deposits indicate the influence of a marine highstand in the area synchronous with the readvance event. The Cranfield area represents a critical location for; 1) examining the relation of marine influences upon a terrestrial ice mass, 2) demonstrating the importance of stratigraphy in reconstructing ice mass dynamics, and 3) the relation of the Carlingford readvance to millennial time-scale events in the circum-North Atlantic (cf. McCabe, 1996) which will attach an international importance to the coastal glaciomarine site network in Northern Ireland.
Importance:
The complex of morainic ridges and outwash sequences of the Mourne Plain demonstrates important geomorphological and glaciological concepts linked to the decay of tidewater ice margins in the Irish Sea. It forms the only well-described terrestrial topographic record of a marine based ice lobe (McCabe et al., 1984). The spatial sequence, sedimentological content and spacing of the morainic, ice marginal sediment piles demonstrate aspects of the ice mass condition and phased nature of generally rapid retreat. The Cranfield moraine contains a stratigraphy indicating a readvance of ice from Carlingford Lough onto the plain. The dating of glaciomarine muds in the sequence using biostratigraphic data will hopefully verify that the readvance was related to a significant readvance of the Irish ice sheet around 15kyr B.P. recorded from other sites around the Irish coastline (McCabe, 1996). The raised beach notches cut into the deposits indicate the influence of a marine highstand in the area synchronous with the readvance event. The Cranfield area represents a critical location for; 1) examining the relation of marine influences upon a terrestrial ice mass, 2) demonstrating the importance of stratigraphy in reconstructing ice mass dynamics, and 3) the relation of the Carlingford readvance to millennial time-scale events in the circum-North Atlantic (cf. McCabe, 1996) which will attach an international importance to the coastal glaciomarine site network in Northern Ireland.
Notes:
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, raised beach

Access
Management:
Sections in outwash and morainic ridges are principally in used and disused pits. Raised beach deposits terminate at the coast in an unstable cliffline up to 15m high. Sediments in these coastal exposures, which predate the beach deposits, are of importance in assessing glacigenic environments during deglaciation. The major moraine ridges are largely intact, with little skyline excavation or development. It is unfortunate that the most prominent excavation on the Cranfield moraine is at Dunnaval, one of the highest points on the moraine and the site of a conspicuous rath. Major pits at Ballynahattan, such as the Sandpiper complex, are readily visible from the coast road, and detract from a predominantly rural landscape. The outwash plain and raised beach topography in which extraction has generally taken place has resulted in a rectilinear 'hole in the ground' landscape, with pit boundaries following former field boundaries. This condition provides limited scope for aesthetically pleasing reinstatement. Restoration of pits, especially along the coastal fringe is usually only the minimum compatible with planning approval, taking the form of grading of pit faces and levelling of pit floors. In the absence of a regional approach to the restoration and use of pits at the end of their working lives, it is inevitable that reinstatement will be piecemeal and of a variable standard as has the reinstatement of disused pits to date. The most common form of landscaping involves grading of the quarry boundaries, levelling of the floor, and reseeding of the resultant surface with grass. As pits have frequently been left untouched they have used as ad hoc dumps and repositories of defunct machinery. Low water tables mean that abandoned pits do not readily flood, reducing the possibilities for amenity-based reinstatement. However some of the pits in low lying outwash at Ballynahattan are apparently prone to relatively shallow flooding when pumping ceases, which may permit amenity landscaping in a few locations. Ridge top pits present a more intractable problem, since the 'gap tooth' effect is not susceptible to cosmetic restoration. Control of future development depends on perceived economic and aesthetic priorities within a regional planning policy.

Access

Management:

Sections in outwash and morainic ridges are principally in used and disused pits. Raised beach deposits terminate at the coast in an unstable cliffline up to 15m high. Sediments in these coastal exposures, which predate the beach deposits, are of importance in assessing glacigenic environments during deglaciation. The major moraine ridges are largely intact, with little skyline excavation or development. It is unfortunate that the most prominent excavation on the Cranfield moraine is at Dunnaval, one of the highest points on the moraine and the site of a conspicuous rath. Major pits at Ballynahattan, such as the Sandpiper complex, are readily visible from the coast road, and detract from a predominantly rural landscape. The outwash plain and raised beach topography in which extraction has generally taken place has resulted in a rectilinear 'hole in the ground' landscape, with pit boundaries following former field boundaries. This condition provides limited scope for aesthetically pleasing reinstatement. Restoration of pits, especially along the coastal fringe is usually only the minimum compatible with planning approval, taking the form of grading of pit faces and levelling of pit floors. In the absence of a regional approach to the restoration and use of pits at the end of their working lives, it is inevitable that reinstatement will be piecemeal and of a variable standard as has the reinstatement of disused pits to date. The most common form of landscaping involves grading of the quarry boundaries, levelling of the floor, and reseeding of the resultant surface with grass. As pits have frequently been left untouched they have used as ad hoc dumps and repositories of defunct machinery. Low water tables mean that abandoned pits do not readily flood, reducing the possibilities for amenity-based reinstatement. However some of the pits in low lying outwash at Ballynahattan are apparently prone to relatively shallow flooding when pumping ceases, which may permit amenity landscaping in a few locations. Ridge top pits present a more intractable problem, since the 'gap tooth' effect is not susceptible to cosmetic restoration. Control of future development depends on perceived economic and aesthetic priorities within a regional planning policy.

References (25)
Bourgeois, J., 1980. A transgressive shelf sequence exhibiting hummocky stratification: the Cape Sebastian Sandstone (Upper Cretaceous), southwestern Oregon Journal of Sedimentary Petrology, vol. 50, pp.681-702.
Bourgeois, J. & Leithold, E.L., 1984. Wave-worked conglomerates - Depositional processes and criteria for recognition In CSPG Memoir 10, Sedimentology of Gravels and Conglomerates, pp.331-343.
Charlesworth, J.K., 1939. Some observations on the glaciation of north-east Ireland Proceedings of the Royal Irish Academy, vol. 45 pt. B, pp.255-295.
Charlesworth, J.K., 1955. The Carlingford readvance between Dundalk, Co. Louth and Kingscourt and Lough Ramor, Co. Cavan Irish Naturalists Journal, vol. 11, pp.299-302.
Church, M. & Gilbert, R., 1975. Proglacial fluvial and lacustrine sedimentation Society of Economic Palaeontologists & Mineralogists Special Publication, numb. 23 In Glaciofluvial and glaciolacustrine sedimentation, pp.22-100, Tulsa, Oklahoma.
Clifton, H.E., 1973. Pebble segregation and bed lenticularity in wave-worked versus alluvial gravel Sedimentary Geology, vol. 20, pp.173-187.
Collinson, J.D. & Thompson, D.B., 1982. Sedimentary structures.
Domack, E.W. & Lawson, D.E., 1985. Pebble fabric in an ice-rafted diamicton Journal of Geology, vol. 93, pp.577-591.
Eyles, C.H., 1988. A model for striated boulder pavement formation on glaciated, shallow-marine shelves: an example from the Yakataga Formation, Alaska Journal of Sedimentary Petrology, vol. 58 pt. 1, pp.62-71.
Eyles, N. & McCabe, A.M., 1989. Glaciomarine facies within subglacial tunnel valleys: the sedimentary record of glacioisostatic downwarping in the Irish Sea Basin Sedimentology, vol. 36, pp.431-448.
Eyles, N. & Miall, A.D., 1984. Glacial Facies In Facies Models, 2nd Edition, Reprint Series Geoscience Canada, Ontario.
Gravenor, C.P., von Brunn, V. & Dreimanis, A., 1984. Nature and classification of waterlain glaciogenic sediments, exemplified by Pleistocene, late Paleozoic and late Precambrian deposits Earth Science Reviews, vol. 20, pp.105-166.
Kuenen, P.H. & Migliorini, C., 1950. Turbidity currents as a cause of graded bedding Journal of Geology, vol. 58, pp.91-127.
McCabe, A.M., Dardis, G.F. & Hanvey, P.M., 1987. Sedimentation at the margins of a Late Pleistocene ice-lobe terminating in shallow marine environments, Dundalk Bay, eastern Ireland. Sedimentology, vol. 34.
McCabe, A.M., Dardis, G.F. & Hanvey, P.M., 1984. Sedimentology of a Late-Pleistocene submarine moraine complex, County Down, Northern Ireland. Journal of Sedimentary Petrology, vol. 54, pp.716-730.
McCabe, A.M., 1996. Dating and rhymicity from the last deglacial cycle in the British Isles Journal of the Geological Society of London, vol. 153, pp.499-502.
Middleton, G.V. & Hampton, M.A., 1976. Subaqueous sedimentation transport and deposition by sediment gravity flows In Marine sediment transport and environmental management, pp.197-218 Wiley, New York.
Mulholland, J.W., 1982. Glacial stagnation zone retreat in New England: bedrock control Geology, vol. 10, pp.567-571.
Nemec, W. & Steel, R.J., 1984. Alluvial and coastal conglomerates: their significant features and some comments on gravelly mass-flow deposits In CSPG Memoir 10, Sedimentology of gravels and conglomerates.
Postma, G., 1986. Classification for sediment gravity-flow deposits based on flow conditions during sedimentation Geology, vol. 14, pp.291-294.
Rust, B.R. & Koster, E.H., 1984. Coarse alluvial deposits In Facies Models, 2nd Edition, Reprint Series Geoscience Canada, Ontario.
Rust, B.R. & Romanelli, R., 1975. Late Quaternary subaqueous outwash deposits near Ottawa, Canada Society of Economic Palaeontologists & Mineralogists Special Publication, numb. 23 In Glaciofluvial and glaciolacustrine sedimentation, pp.177-192, Tulsa, OK.
Shaw, J., 1975. Sedimentary successions in Pleistocene ice-marginal lakes Society of Economic Palaeontologists & Mineralogists Special Publication, numb. 23 In Glaciofluvial and glaciolacustrine sedimentation, Tulsa, OK.
Stephens, N. & McCabe, A.M., 1977. Late-Pleistocene ice movements and patterns of Late- and post-glacial shorelines on the coast of Ulster, Ireland. Special Issue of the Geological Journal, numb. 7 In The Quaternary History of the Irish Sea., pp.179-198.
Wilson, H.E., 1972. Regional Geology of Northern Ireland. HMSO, Belfast.

Record type:	ESCR report
Entered by:	E M Porter

Enlander, I., Dempster, M. & Doughty, P., 2026. Mourne Plain Complex - Overview, County Down, site details. [In] Earth Science Conservation Review.
https://www.habitas.org.uk/escr/site.php?item=440. Accessed on 2026-11-06.