| Previous Site | Next Site |
Earth Science Conservation Review
| Moyola Valley Complex | Londonderry |
| Site number: | 476 | ||
| ESCC: | IS | ||
| Locality Type: | Inland exposure, Pit | Status: | TBC |
| Grid Reference: | H752972,H832968,H854922 Corners of site, Not Entered | ||
| Google maps: | 54.81743,-6.83018 | ||
| County: | Londonderry | Council area: | Mid Ulster District Council |
| Period: | Quaternary | ||
| Site Description | |
|---|---|
| Highlights: | |
The deposits of the Moyola valley provide a record of the complex development of proglacial landform deposition during deglaciation. The primary controls on ridge morphology were: 1) the wedge-shaped bedrock depression which narrows westward towards the eastern flanks of the Sperrins, 2) ice-margin retreat-rate variation and the location of successive ice-margin positions, 3) proglacial lake formation in the depression of the Moyola Valley. The spatial and temporal pattern of glaciofluvial deposition is demonstrated by the association of subglacial feeder channels with ice-marginal glaciolacustrine sedimentation. Exposures provide examples of depositional sequences in subaqueous environments. Variability in ridge morphology has been linked to palaeoenvironments (cf. Dardis, 1985) and post-depositional meltwater erosion along ridge flanks. | |
| Description: | |
The Moyola Valley complex consists of five distinct glaciofluvial subunits located in the valley of the Moyola river, Co. Londonderry between Moneyneany (275200 497200), Tobermore (283200 496800) and Desertmartin (285400 392200). The deposits occupy a total surface area of approximately 15km2 within the survey area of 47km2. They are categorised and described in four principal morphological forms: A. DISSECTED FLAT-TOPPED RIDGES 1. Nutgrove The Nutgrove ridge, a 10km2 spread of sand and gravel is located at the southeast edge of the Moyola valley, is centred on 281200 493300 between the townlands of Belmont Hill (282300 494300) and Gortahurk (281500 491800), Mormeal (280300 494300) and Nutgrove Wood (282300 493300). The deposit is bordered to the southwest by the rising ground of Slieve Gallion (496m) and to the east by the lowlands of the Moyola/Bann floodplain. The maximum elevation of the subunit decreases northwards from 150 to 90m. Small-scale (<0.25km2) topographic flats occur within the deposit near Boveagh, located at 150m O.D. Elsewhere the deposit's topography is largely dominated by over thirty 10-20m deep, steep-sided, generally flat-bottomed south/north and southwest/northeast trending channels. Steep-sided (<10m deep) southward facing slopes are present e.g. at 282100 492400 and a cluster of three enclosed, small-scale (<0.005km2, <5m deep) depressions at 282200 292900. A 1km long, SW/NE trending, dissected smooth-crested linear ridge adjoins the southwest corner of the deposit at Carncose (284000 488800). The ridge occurs at an elevation of 140-150m O.D. and is bordered by small-scale hummocks and low-lying flats. Nutgrove Exposure An exposure in a commercial pit at Iniscarn Road (282600 492700) in the deeply channelled topography consists of two lithofacies associations (LFAs). The pit face exposes a 200m long by 30m deep section comprised of two faces oriented north/south and southwest/northeast. LFA1 The lowest beds exposed consist of 0.5m of planar stratified, clast supported edge-rounded cobble gravels, showing well-developed a-axis imbrication to 50§N. These gravels grade up into 0.7m of deformed small-scale planar cross-bedded cobble to pebble gravels in a coarse sand matrix and granule-rich sands. Beds thicknesses are variable (10-70cm), showing a general decrease upward to <2cm. Palaeoflow directions, based on cross-bedding and clast orientations were generally to 010-015§N, with a high (20-30§) variance. Clasts consist of high percentages of granite lithotypes (>40%) with smaller amounts (<5%) of conglomerate, sandstone, quartzite, flint and chalk (1%). LFA2 Above a sharp contact with LFA1 a 20-25m deep sequence of planar-cross bedded sand/silt couplets occurs within stacked channels (>20m broad by 6m deep). Individual couplets consist of well-sorted medium sands showing both a- and b-type ripples grading up into very finely laminated (<1mm) silts. Sand beds range from 30cm to 1m thick with silt beds generally <50cm thick. Contacts between the silt beds with overlying sands are predominately sharp. The sand beds are generally massive. The beds dip at low angles (<5§) to 060§N. 2. Belmont Hill (282400 494300) An almost completely grassed exposure shows <1m of small-scale cross-bedded sands, dipping at <10§ to 050§N. Cobble to boulder clasts, are predominately granites (>40%). 3. Spring Grove (281900 494800) A small (15m long by 2m deep) exposure of planar cross-bedded medium sands and cobble gravels is located at the northern end of the Nutgrove subunit. Beds dip at <15§ to 300§N. Clasts, up to 80cm in a-axis length, are edge rounded and consist predominately of limestone (30%) and granite (30%) B. FLAT-TOPPED RIDGES 1. Wood Hill (TMD02) A steep-sided spread with an extensive, intact, flat-top occurs in the area immediately north of the Nutgrove subunit described above and extends as far north as Tobermore (283200 496800). The flat-top occupies 1.5km2 and is located at 80m O.D. All lateral, especially northward-facing slopes are steep. The eastern slope forms one side of a large WSW/ENE oriented channel occupied by a misfit stream, while the northern slopes form part of the southern edge of the Moyola river floodplain. Two small (<5m deep) enclosed depressions are present near the southern end of the flat-top at 281700 495200. An exposure in the ridge's eastern flank occurs at Tamnyaskey (282400 495700). Wood Hill Exposure The exposed sequence consists of >35m of generally coarsening upwards low-angle (5-10§) trough cross-bedded sands and cobble to pebble gravels contained within stacked, cross-cutting channels. The sequence can be divided up into three principal LFAs. LFA1 Medium sand bottomsets The lower 6m of the sequence is composed of channels (>20m broad by <4m deep) infilled with well-sorted, rippled fine sands and silty sands. The large-scale trough cross-bedded sands consist of >1m thick b- to a-type ripple sequences and beds solely of a- or b-type ripple sets separated by sharp contacts, with interbedded, laterally discontinuous silt beds (<1cm thick). B-type ripples have a mean length of 30cm. Palaeoflows, based on channel axes orientations and ripple cross-bedding, generally trend to 060§N with a variance of approximately 25§. The sands grade upward into a 6m deep sequence of parallel-bedded rippled sand and silt couplets, of variable thicknesses. The sands are of variable texture (from medium sands to granules), with bed thicknesses varying from 2.5cm to 43.5cm. The finely laminated, rippled silts (approximate wavelength 23cm) range from 0.4cm to 14cm thick. As an example of the couplet textures, a typical unit begins with a sharp lower contact, consists of a 14cm thick silt bed, a 1.7m thick sequence of inversely graded b- to a-type rippled sand beds and a lens of poorly-sorted cobble gravel. This forms a sharp contact with, usually, a horizontally bedded, inversely graded sand or silty sand bed. LFA2 Cross-bedded sands and silt foresets Above a sharp contact marked by a thin (<1cm thick) laterally discontinuous silty bed, 2.3m of a generally coarsening upward sequence of trough cross-bedded granules and pebble gravel occurs. The general palaeoflow, from cross-bedding orientations, was to 100§N. The granular sands coarsen upwards into 3m of poorly-sorted cobble, planar bedded gravel which fine upwards into medium sands. The medium sands are cross-cut by a 20-25m deep sequence of large-scale, planar cross-bedded sand (dipping at 20§ to 060§N) interbedded with pebble gravels. These fine laterally, northwards, into laminated silts (20-25m wide). LFA3 Deformed topsets The sands and silts are overlain by a 1m deep sequence of crudely horizontally-bedded cobble gravels imbricated (to 30§N). These are overlain by 2m of massive and highly irregularly, undulating to sub-vertically bedded sands. C. CROSS-VALLEY RIDGES 1. The Black Hill (TMR01) A 0.25km wide steep-sided linear ridge occurs cross-valley for 2.5km between Spring Grove (281000 494800) and Moneyguiggy (279800 479400). The NW/SE trend, is approximately at right angles to the valley axis. The ridge is dominated by a flat-topped central portion which is locally 35m above the valley floor and rises to 90m O.D. There are several sharper crested lateral extensions of lower relief. Crestlines run parallel to the main ridge orientation. No large-scale exposure exists in the Black Hill ridge although a small-scale almost grassed pit at 280300 496400 exposes interbedded sand and pebble gravel. The ridge is bordered to the west by a small-scale area (<0.25km2) of low relief hummocky ground. The remainder of the valley floor consists of gently rolling topography, interspersed with topographic flats. The northern end of the ridge deflects and is truncated by the course of the present day Moyola river with the lower slopes at the southern end overlapped by the northwest facing lateral slopes of the flat-topped ridge centred at Wood Hill. 2. Moneyneany Ridges Three small-scale (0.5km long, 0.1km wide, 20m high) flat-topped, dissected ridge remnants occur 0.5km west of Moneyneany (275200 497200) on the rising slopes of Crockmore mountain (elevation: 478m O.D.) in the valley of the Douglas river. The ridge crests occur between 140 and 180m O.D. trending approximately NE/SW, at right angles to the long axis of the valley. A small (<0.125km2) topographic flat area occurs at the confluence of the steep-sided inter-ridge depressions, now occupied by misfit tributaries. Three small exposures of stratified sand and cobble gravel occur in one of the ridges. Moneyneany Exposure A 25m long by 5m deep section trending NW/SE (320/140§N) shows three LFAs separated by sharp contacts. LFA 1 Medium Sand The lowest stratigraphic beds are composed of parallel bedded and small-scale trough cross-bedded medium sands with occasional clusters of well-rounded pebble-sized clasts along bed contacts. Palaeoflow, measured from trough cross-bedding orientation, was to 270§. The beds of LFA1 are truncated on their extreme southern edge by trough cross-bedded pebble gravels, dipping to 40§N. LFA2 Cobble Gravel Above a sharp, irregular contact is a 4m thick sequence of generally fining-upwards, planar and small-scale trough cross-bedded pebble to cobble gravels in a sandy matrix. Sand units tend to grade upwards from silty to coarse and granular sands, with both sharp and gradational contacts between adjacent beds. Occasional sand lenses are massive. Beds dip at a low angle (<10§), indicating a palaeoflow to approximately 080§N. LFA3 Muddy Diamict Above a sharp, irregular contact up to 2.5m of convoluted muddy diamict consists of cobbles set in a highly variable muddy to pebbly sand matrix. D. STREAMLINED HILLS ON LOWLAND FLATS 1. Drumsamney Outwash The area centred on The Island (286000 496000) occurs to the east of the Wood Hill deposit and is one of generally low-lying, well-drained, extensive topographic flats punctuated by occasional elongated, isolated hills approximately 15m in local relief. Apparent streamlining occurs in two principal directions, north/south (020§) and northeast/southwest (050§). A small exposure in one hill flank shows a sequence of highly convoluted pebble sands, silt drapes (<1cm thick) and very low-angle (<5§) parallel-bedded medium sands containing small-scale, high-angle normal faults. | |
| Importance: | |
The Moyola valley complex is classed as having a good scientific importance. The valley's deposits provide evidence which can be used in producing a relative chronology of regional deglacial events. The evidence shows: A. The deglaciation of the Moyola valley floor proceeded from west to east, after separation from an ice mass which retreated generally southwards across the Lough Fea platform, B. The rising ground of the Sperrin mountains confined glacial meltwater in both ice-marginal and proglacial locations, allowing the ponding of a series of waterbodies at 80, 90, 150 and 180m O.D., C. The nature of ice margin retreat was both active and the retreat rate temporally variable so that during the area's deglaciation, the ice-margin experienced at least two major reductions in retreat rate allowing the deposition of the Black Hill and Nutgrove deposits, D. Large-scale meltwater flows occurred during the deglacial period along the Bann valley lowlands resulting in dissection and apparent streamlining of fluvioglacial fills. The regional importance of the deposits is they demonstrate that: E. Bann Valley ice retreated in a generally north to south direction (towards the Lough Neagh lowlands) after the lobe occupying the Moyola valley had ablated. | |
| Interpretation: | |
Based on the available morphological and sedimentological evidence, the majority of the deposits are inferred to be the products of ice-marginal and glaciolacustrine sedimentation. The following general models are proposed for the processes of formation. There is however a lack of exposures with which to fully constrain the modelling: A. DISSECTED FLAT-TOPPED RIDGES The Nutgrove deposit is inferred to be an ice-marginal subaqueous spread which was deeply dissected by later fluvioglacial erosion after lake levels fell. The exposed sediments show a sequence of sand and silt rhythmites, representing deposition from subaqueous density currents in an extensive proglacial waterbody. The small remnant areas of flat-tops indicates that deposition continued to at least the height of a waterbody surface ponded to 150m O.D. Sediment supply is inferred to have been from subglacial meltwater efflux located in an ice margin lying 1-2.5km due south of Nutgrove. The feeder channel is possibly marked by the linear ridge segments located at Carncose (283500 488600) and the basal gravels of the exposure at Nutgrove which show an a-axis imbrication to 050§N, inferred to have been parallel to flow. The presence of the retreating ice-margin is also recorded by the steep (ice-contact) slopes in the southern portion of the deposit and the rapid aggradation of the fan by the burial of ice blocks by sediments which results in a kettled or hummocky topography. B. FLAT-TOPPED RIDGES After a partial drainage of the lake and a reduction of lake levels, glaciofluvial erosion of the topography by meltwaters issuing from a southerly source formed generally north/south oriented proglacial meltwater channels. Sediment, entrained in the meltwater, flowed northward principally via the meltwater channel at Spring Grove, aggrading a Gilbert-type delta at Wood Hill consisting of well-sorted sand deposited as subaqueous density flows in a ponded waterbody with a surface at 80m O.D. The section at Tamnyaskey in the ridge flank shows a transverse section in sandy bottomsets, with a high degree of sorting resulting from resedimentation, planar cross-bedded foresets and coarse grained, poorly-sorted, fluviatile topsets, which have been subject to post-depositional remobilisation. Palaeoflows of the bottomset channels vary around a general trend to the northeast, in agreement with the model of their resedimentation from the erosion of the Nutgrove ridge. Ice blocks, transported with the meltwater and buried in the aggrading sediments later melted out to leave the kettle-hole depressions in the otherwise flat delta surface. C. CROSS-VALLEY RIDGES The location, elevation and sedimentology of the cross-valley ridges depict the general, phased retreat of Bann Valley ice from the upper reaches of the Moyola Valley depression easterly towards the Lough Neagh lowlands, the location of two major ice-marginal stages and the height of proglacial waterbodies which existed during ice wastage. Poor exposure limits detailed sedimentological examination of the cross-valley ridge forming Black Hill. However morphological and regional evidence suggest that the deposit aggraded in a waterbody ponded at 90m O.D. with sediment laden glacial meltwater flowing generally from an ice-margin located to the east of the ridge. Hummocky ground to the west of the ridge is inferred to represent localised deposition of sediment as ice marginal retreat rates slowed to the halt stage which allowed the aggradation of the cross-valley ridge. The gentle, rolling topography of Moyola valley floor is inferred to represent subglacial diamict ridges and glaciolacustrine rain-out deposition, interspersed with flat areas of post-depositional fluvial erosion and flood-plain alluvium deposition. The steep-sided morphology of the ridges at Moneyneany is interpreted to be erosional rather than ice-contact in origin. Fluvially eroded sediment deposited as a small, probably subaqueous fan downslope (274300 497000) associated with ice-marginally ponded water at 180m O.D. in the valley. D. STREAMLINED HILLS The streamlined hills occupying the lowlands of the present day Moyola river flood plain are interpreted to represent remnant, glaciofluvially eroded outwash deposits. The streamlining is attributed to erosion by large scale, catastrophic meltwater floods by meltwater flowing generally northwards along the Bann valley lowlands, following the drainage of ponded proglacial waterbodies. The following tentative deglacial model is proposed for late glacial events in the Moyola valley and is based on available sediment exposures and landform morphology. 1. During the last glaciation, an ice lobe related to ice in the Bann valley, occupied the present Moyola valley. 2. During deglaciation, Bann valley ice retreated southward from its maximum northerly extent. Contemporaneously the ice lobe occupying the Moyola Valley receded from its most westerly extent, a margin at least as far west as Labby (275500 492100) and Moneyneany (275300 497200). During its recession, meltwater was ponded against the rising ground of the surrounding valley sides and the ice-mass occupying the Lough Fea platform, forming an ice marginal lake in the upper valley reaches at Moneyneany with a maximum elevation of 180m O.D. 3. Sediment issuing from the retreating ice margins to the east was deposited as subaqueous outwash in the waterbody ponded in the proglacial area, forming the ridges at Moneyneany. Ice marginal ponding of water is recorded from other locations around the valley rim, with small-scale subaqueous deposition occurring at 225m O.D. on the southern Moyola valley slopes of Slieve Gallion at Gortahurk (281100 491900). 4. The lack of a suite of distinct recessional moraine ridges on the valley floor indicates that ice retreat rates must have been fairly constant and rapid, up to a still stand of the ice margin during the formation of the cross-valley ridge at Black Hill which marks the location of ice-marginal effluxes. The flat-top indicates deposition into a ponded water body located at 90m O.D. 5. Ice retreat continued until the ice margin was situated near Boveagh (282800 491100). During this time the valley lake level had continued to rise to a minimum elevation of 150m O.D. During a temporary deceleration of ice retreat rates and the stabilising of the ice-margin position, an extensive flat-topped glaciolacustrine delta was deposited from subglacial effluxes draining generally northwards from ice located in the Bann Valley. At the western end of the Moyola valley, generally southwards ice backwastage across the col of the Lough Fea platform (275500 487000), resulted in ice lobes occupying the upper reaches of the White water and Black water valleys. Meltwater issued northeastwards during the ponding of water at 150m O.D. in the Moyola valley resulting in the formation of a flat-topped glaciolacustrine delta at Disert (276200 492700) (see Key Site 477 - Lough Fea). 6. A rapid lowering of the waterbody surface resulted in dissection of the delta top by subaerial meltwater erosion, transport of the sediment and the aggradation of a delta up to this lower elevation (80m O.D.) at Wood Hill. 7. Further dissection of subaqueous outwash at Drumsamney, deposited in the lowlands of the Moyola drainage basin during and after the drainage of the proglacial lake resulted in the formation of elongated, stratified subaqueous outwash remnants. | |
| Notes: | |
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 | |
| Keywords | |
|---|---|
| Rocks: | Gravel, Sand |
| Relations: | Glacio-fluvial sediment |
| Geomorph: | cross-valley moraine, deltas, ice-dammed lake, moraine ridge, proglacial lake |
| Measurements | |||||
|---|---|---|---|---|---|
| Length: | Width: | Height: | |||
| Depth: | Area: | 47km2 | |||
| Access | |
|---|---|
| Management: | |
The Moyola valley complex is classed as having a good conservation worthiness. This is due to: A. Its predominately rural location, at the margin of the highly scenic Sperrin mountains range, B. the large-scale, flat-topped and dissected landforms occurring in skyline locations providing topographic diversity to otherwise monotonously gently rising ground, C. construction and excavation of the deposits is relatively limited, D. a pit at Belmont Hill, which has been restructured to provide recreational facilities, forms a good example of the benefits that investment in the rehabilitation of disused pits can achieve. | |
| Uses | |
| Uses: | Some commercial quarrying; recreation |
| References (3) | |||
|---|---|---|---|
| Dardis, G.F., 1985. Genesis of Late Pleistocene Cross-Valley Moraine ridges, South-Central Ulster, Northern Ireland Earth Surface Processes and Landforms, vol. 10, pp.483-495. | |||
| Hartley, J.J., 1933. The geology of north-eastern Tyrone and the adjacent parts of County Londonderry Proceedings of the Royal Irish Academy, vol. 41 pt. B. | |||
| 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. Moyola Valley Complex, County Londonderry, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=476. Accessed on 2026-11-06. |
| Previous Site | Next Site |