ESCR - Kilrea

Earth Science Conservation Review

Summary Full report
Kilrea	Antrim, Londonderry

Site number:	467
ESCC:	IS
Locality Type:	Inland exposure, Pit	Status:	TBC
Grid Reference:	C949259,C948037 End(s) of linear site, Not Entered
Google maps:	55.0718,-6.51436
County:	Antrim, Londonderry	Council area:	Causeway Coast & Glens Borough Council
Period:	Quaternary

Site Description
Highlights:
The complex of deposits of the central Bann valley demonstrate a close topographic association between subaqueous outwash, deltaic and esker depositional environments. Successive ice-marginal fronts ended in ponded water as the ice mass contracted southwards. North of Kilrea, Co. Londonderry (292700 412600), poorly-exposed subaqueous outwash, which formed in front of a relatively rapidly retreating ice margin, occurs in a 2km wide zone of relatively low relief (<15m high) ridges oriented approximately NNW/SSE. The pristine flat-topped, steep-sided deposits at Tully Hill (292300 414900) were formed by inputs from a high energy subglacial conduit (jet) into a glaciolacustrine setting. The branched ridges of stratified sand and gravel forming the deposits immediately south of Kilrea represent a pristine example of predominately subglacial glaciofluvial deposition. Sedimentation from meltwater flowing generally northwards during the deglacial phase probably occurred in R-type subglacial channels located in a topographic low. Deposition of all the sediments post-dates the streamlining event which resulted in the drumlin landforms flanking the deposits. The deposits provide evidence for north to south ice marginal retreat towards Central Ulster and the Lough Neagh lowlands during the deglacial phase. They also indicate variation in relative glacial retreat velocities and demonstrate pristine ice-contact morphology. Poor exposure limits detailed sedimentological examination of all ridges. Conclusions are based therefore on the interpretation of four exposures together with extensive geomorphological evidence.
Description:
The complex is located in a structural low in the Antrim basalts, located 15km to the north of Lough Neagh and bordered 15km to the west by the Sperrin Mountains and 5km to the east by Long Mountain. As a whole the system is oriented approximately NNW/SSE (330§N), subparallel to the axis of the lower River Bann. The complex is approximately 16km long and at maximum is a 2km wide zone of ridge segments characterised in places by steep ice-contact slopes, interspersed with topographic flats and areas of hummocky topography. The deposit's margins feather onto and overlie the streamlined rock ridges and drumlins of the Bann valley. The orientation of the ridge crests within the complex varies (<90§) relative to the direction of streamlining and bedrock glacial striae (15-25§N) observed at Movanagher. The majority of the complex (70%) is located to the west of the river, crossing the present course near Movanagher (292800, 415900). At Kilrea (292800, 412800) and Artnagross (292800, 416200) the sediments are dissected by glacial meltwater channels. Immediately south of Kilrea, several relatively large (ranging from 0.06km2 to 0.02km2) and many small (<0.01km2) enclosed depressions are filled with ponded water. The complex is subdivided into four principal morphological units and will be described from north to south: 1) Centred on Vow (291800 417700), 4.5km north of Kilrea, and east of the River Bann, is a 2km wide zone of ENE/WSW trending flat-topped ridges of relatively low relief (<10m) and NNE/SSW trending beaded ridges (15-20m high). 2) To the west of the river from Movanagher to Kilrea is a 3.5km long, 0.5km wide at maximum zone of sharp-crested and flat-topped ridges. This zone contains Tully Hill and the site of Kilrea town, which consist of flat-topped, steep-sided ridges located at approximately 40m a.s.l. 3) Immediately south of Kilrea is an area (<2km2) of hummocky ground with interspersed lakes within enclosed depressions in stratified drift. 4) An approximately 7km long zone of discontinuous steep-sided ridges and mounds of medium relief (20-40m) oriented generally NNE/SSW occur between Drumimerick Hill (293200 410300) and Inishrush (294800 403700). Exposures of the sediments are rare. Two pits exist in the area around Vow (291800 417700). PIT 1 : Vow Exposure (KLS0101A) The most northerly exposure in the complex occurs in a pit which exposes a 100m long by 16m high section through a sequence of three principal lithofacies associations (LFA). The stratigraphy can be subdivided into three LFAs which show a general fining upward sequence: LFA 1 : Boulder Gravel The stratigraphically lowest unit exposed consists of stacked, shallow-dipping (<10§), amalgamated beds of very poorly-sorted cobble to boulder gravels. The gravels are mainly clast-supported with a variable matrix in occasional beds of granules. Clasts consist principally (>90%) of local basalts, with erratics of schist (<5%), granite (<5%) and chert (<2%) of more distant, southerly origin. LFA 2 : Sand The coarse gravels are overlain abruptly by a complex sequence of broad (20-30m wide, 5-10m deep) sand-infilled channels dipping at 5-10§ to 350§N. Infills consist of sands (dipping at 5-25§, generally to 015§N) interbedded with thin (<5cm) mud drapes, thin (<25cm) lenses of bimodal cobble/sand, sand (<20cm) and occasional rippled and planar laminated silty beds (<2cm). LFA 3 : Rhythmites The stratigraphically highest unit consists of up to 8m of finely-interbedded laminated silts, sands, clays and frequent lonestones (pebble to cobble). Beds are <5cm thick, flat-lying and show frequent alternations in grain size on both millimetre and centimetre scales. Locally (20m along the section) in the southern part of the exposure flat-lying beds are contained within a sag-like structure up to 20m across and 4m in depth. PIT 2: Artiloman (KLS0101B) The rhythmites are also exposed at Artiloman (290900 416800), 0.8km further south, at the top of a beaded, steep-sided ridge segment and drape of planar poorly-sorted, interbedded cobble and pebble gravels. The exposure's southern face (10m long, 4m high) shows amalgamated beds of cobble gravel dipping at <15§ to 060§N and 330§N. The smaller-scale (4m by 2m high) northern face consists of a sequence of horizontally bedded, massive to laminated sands, rhythmically interbedded at variable bed thicknesses by finely laminated silts and muds. The exposure also shows extensional faulting with downthrows ( of <50cm) to the east, towards the side of the ridge. Additional exposures in the complex are almost completely grassed/scree covered or at a small scale. At Movanagher, two exposures in a steep-sided, 13m high linear ridge segment 0.5km apart, display 6m and 3m respectively of very poorly-sorted, clast-supported amalgamated cobble/boulder gravels. Poorly-defined clast imbrication suggests a northward palaeoflow. PIT 3: Moneygran (KLS0201A) At Moneygran (294400 410800), 2.5km south of Kilrea, an exposure (35m long by 3m high) shows a slumped (dipping at 20§ to 270§N) and convoluted sequence of horizontally bedded cobble gravels and pebbly sands. These are overlain by small-scale cross-bedded sands (dipping at 20§ to 270§N) fining upwards to laminated silts. Other small exposures of poorly-exposed stratified sands and gravels occur immediately east of Kilrea town (293400 412900), at Bark Hill (293300 411500), and Scroggy Hill (294400 404100).
Importance:
The Kilrea complex provides a range of sedimentary and geomorphological evidence for constructing an hypothesis which explains the nature of deglaciation in the mid Bann valley. The deposits demonstrate: A) A general north to south pattern of ice-mass retreat; B) During deglaciation the ice-front retreat rate was not constant but rather varied from relatively rapid to periods of temporary halting; C) The carriage by ice and subsequently meltwater, of clasts (including agglomerate black slates chert, quartz porphyry and gabbro) originating from an area further south i.e. the Tyrone Igneous Complex (cf. Hartley, J.J., 1933); D) Pristine morphology of landforms in places e.g. Tully Hill, providing good examples of both geomorphology, the evolution of the proglacial environment and its links with the subglacial environment.
Interpretation:
The deposits occurring at Vow, to the north of Kilrea, are interpreted as a subaqueous outwash complex, formed from a subglacial efflux into ponded water. This interpretation is based on: 1) The fining-up sequence (of gravel, sand, rhythmites) indicates a decline in energy and sediment supply, related to either rapid ice retreat or lateral switching of input source. 2) Amalgamated, coarse-grained and poorly-sorted gravels suggest deposition from a high energy efflux at or near an ice margin (cf. Rust and Romanelli, 1975). 3) Low angle dipping, channelised, cross-cutting sands characterise foreset deposition with channel avulsion. 4) Rhythmites record pulses of sediment supply, with sand and silt beds marking alternation between traction (underflow) and suspension load dominated deposition periods. 5) Bimodal gravels (cobbles within sands) record avalanche-front deposition and turbulent eddying of finer material on a subaqueous palaeoslope (Shaw, 1991). 6) Isolated pebbles within laminated fine sediments may record ice-rafting or represent outrunners from distributary channels feeding the outwash fan. The subaqueous spread did not aggrade into a classic flat-topped, foreset dominated delta type, which suggests that the feature records rapid ice retreat rather than a discrete or prolonged halt in the ice margin. It is suggested that the gravel, sand, rhythmite sequence is a signature for an event of this type. The rapid ice retreat did not allow the aggradation of sediment to the elevation of the water body surface and thus the full development of deltaic morphology. To the south, the elevated topographic flats of Tully Hill and the site of Kilrea (0.06 and 0.1km2 respectively) probably record glaciolacustrine delta deposition from a subglacial conduit feeding into a proglacial lake. The deltas record temporary halts in the retreat of the glacier front to allow aggradation of sediments to the level of the waterbody surface (at approximately 40m a.s.l.). Both deltas with similar elevations indicate a static lake level of around 40m a.s.l. in the mid Bann valley. The esker deposits occurring to the south of and adjoining the southern (ice-contact) slopes of the flat-topped ridges are interpreted to represent the courses of efflux feeder channels. The enclosed depressions immediately south of the delta resulted from the melt-out of ice blocks buried under aggrading sediments i.e. kettle-holes, at or near the ice front. Their presence supports the hypothesis that the topography around Kilrea formed in the immediately proglacial zone. The steep-sided, sharp crested ridges south of Kilrea probably record ice-contact deposition in high-energy, subglacial tunnels. These are partially overlain and thus post-dated by the sediments exposed at Moneygeny interpreted to be deformed, subaqueous outwash which merges onto the southern slopes of the Kilrea delta fragment, indicating that the ponded water persisted as the ice margin retreated farther southwards. The sequence of deposits thus indicates the presence of a ponded proglacial waterbody during the retreat of the ice margin southwards from Vow to Moneygeny. The deposition of the subaqueous deposit at Vow only gives an indication of a minimum elevation of the waterbody surface at the time of its deposition. The elevation of the flat-topped deltaic deposits at Tully Hill and Kilrea relates them to a waterbody surface at 40m a.s.l. Superimposition of the deposits upon streamlined ridges and lack of streamlining/erosion of the sand and gravel indicates that the deposition of the complex post-dates the streamlining event in Northern Ireland c. 17ka B.P. (Mc Cabe et al., 1986). Evidence from other adjacent areas confirms this relative chronology, as a southward retreat of the ice margin and esker deposition (assumed to be deposited close to the glacier's margins) means that the Kilrea complex was deposited at approximately the same time as the Glarryford esker (located 13km due east) which has been shown to post-date the streamlining event (see Key Site 466 - Glarryford).
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 This site is also a Site of Local Nature Conservation Importance. See Key Site 734 - Kilrea.

Keywords
Rocks:	Gravel, Sand
Relations:	Glacial streamlining, Glaciolacustrine deposit, Subaqueous outwash
Geomorph:	anastomoses, esker, gravel ridge

Access
Management:
The deposits occur in rural lowlands along the banks of the River Bann, flanked by streamlined, gentle drumlin topography. Landuse on and around the esker is predominately agricultural grazing. Dispersed rural settlement occurs along most of the complex, apart from the town of Kilrea which utilises part of the complex's elevated deltaic topography. Extensive raised bogs have developed due to the detrimental effects upon water drainage of the ridged topography. This association of water ponding due to the enclosure of topographic depressions and the occurrence of mire ecosystems has developed most clearly in the southern portion of the complex, amid the esker ridges. These are presently in the process of being destroyed by drainage and strip cutting. Extensive areas e.g. Crossmore Hill (292800, 407500) are still however in pristine condition and add significant floral diversity to the area.

Access

Management:

The deposits occur in rural lowlands along the banks of the River Bann, flanked by streamlined, gentle drumlin topography. Landuse on and around the esker is predominately agricultural grazing. Dispersed rural settlement occurs along most of the complex, apart from the town of Kilrea which utilises part of the complex's elevated deltaic topography. Extensive raised bogs have developed due to the detrimental effects upon water drainage of the ridged topography. This association of water ponding due to the enclosure of topographic depressions and the occurrence of mire ecosystems has developed most clearly in the southern portion of the complex, amid the esker ridges. These are presently in the process of being destroyed by drainage and strip cutting. Extensive areas e.g. Crossmore Hill (292800, 407500) are still however in pristine condition and add significant floral diversity to the area.

References (5)
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.
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.
McCabe, A.M., Haynes, J.R. & MacMillan, N.F., 1986. Late-Pleistocene tidewater glaciers and glaciomarine sequences from north County Mayo, Republic of Ireland Journal of Quaternary Science, vol. 1, pp.73-84.
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. & Gorrell, G., 1991. Subglacially formed dunes with bimodal and graded gravel in the Trenton drumlin field, Ontario Geographie Physique et Quaternaire, vol. 45 pt. 1, pp.21-34.

Record type:	ESCR report
Entered by:	E M Porter

Enlander, I., Dempster, M. & Doughty, P., 2026. Kilrea, County Antrim, Londonderry, site details. [In] Earth Science Conservation Review.
https://www.habitas.org.uk/escr/site.php?item=467. Accessed on 2026-11-06.