ESCR - Grangemore and Castlerock Sand Dunes

Earth Science Conservation Review

Summary Full report
Grangemore and Castlerock Sand Dunes	Londonderry

Site number:	1140
ESCC:	IS
Locality Type:	Coastal section, Inland exposure	Status:	ASSI
Grid Reference:	C805355,C780361 Centroid, Not Entered
Google maps:	55.16056,-6.737
County:	Londonderry	Council area:	Causeway Coast & Glens Borough Council
Period:	Quaternary
Stages:	Holocene

Site Description
Highlights:
The sand dunes at Castlerock and Grangemore occur west and east, respectively, of the estuary of the Articlave River. The river is a south-bank tributary of the River Bann estuary and joins the latter 2.5km from the open sea. Although separated from the dunes of Portstewart by the River Bann, the Castlerock and Grangemore dune systems are part of the same, single physiographic unit (i.e. beach, dunes and river mouth) that has evolved during the last 6,000 years. Organic-rich deposits of both terrestrial and estuarine origins occur within and beneath the sand dunes and provide evidence for Holocene relative sea-level change and landsurface stability phases (vegetation colonisation and pedogenesis) during sand accumulation. Artifacts from earlier cultural periods have also been recorded from the dunes.
Introduction:
The Castlerock dunes are located on the north coast of Co. Londonderry immediately west of the River Bann (Nat. Grid Ref. C780361). They cover an area c. 1.0km2 and, with the exception of their seaward and estuary margins, are occupied by a golf course. The Grangemore dunes are located on the south side of the estuary of the River Bann (C805355) and cover an area of c. 0.6km2. They are managed by the National Trust and used as pasture for sheep and cattle. Both dune systems have a relatively subdued appearance when compared to those across the estuary at Portstewart. At Castlerock the dunes have been landscaped by the golf club; at Grangemore the subdued topography may be related to the position of the dunes within the estuary which has effectively isolated them from modern sediment sources. These dune systems first became of interest during the late 19th century when antiquarian collectors reported numerous finds of worked flints, hearth stones, bones, shells, and pottery (Gray, 1879; Knowles, 1887, 1891; Hass‚, 1890). Finds have continued to be reported during the present century (Hewson, 1934; May & Batty, 1948) and embrace cultures spanning the Neolithic to Medieval periods. Portlock (1843) was the first to report estuarine clays beneath the dunes and this was subsequently confirmed by Praeger (1893). More recently, Hamilton & Carter (1983) described a silt/organic- rich stratum interbedded in the dune sands and from the contained pollen, plant macro-fossils, and a radiocarbon date, related the material to the course of Holocene relative sea level. Buried podzolic soils were described by Wilson (1994) and used to construct a more detailed chronology of dune accumulation/ stability phases for sites around the Bann estuary.
Description:
Morphologically the Castlerock sand dunes are of little scientific merit. Most of the dune area has been landscaped for golf, while along the seaward and estuary margins the system has been severely impacted by recreational visitors. The dunes rise to 20m + O.D. and for the most part are well vegetated. Recent dune formation in close proximity to the west training wall at the Bann estuary was noted by Wilcock (1976) and attributed to the increased shelter provided by construction of the wall in 1887. At Grangemore the sand dunes rise to slightly in excess of 10m O.D. and with the exception of several small, active blowouts are covered by mature pasture and heathland vegetation. Unlike the Castlerock and Portstewart dunes, the sands at Grangemore lack calcium carbonate (shell fragments) and in this respect are anomalous in the context of north coast dune systems. Of greater scientific interest than dune surface morphology is the internal and sub-dune stratigraphy and structures. These characteristics have been documented at several locations. Praeger (1893), following a description given by Portlock (1843), reported a bluish clay, containing Foraminifera, interbedded with sands in the banks of the Articlave River. The clay layer was noted as being slightly above the high water mark. In the banks of a small stream about 1.3km west of the Articlave River, Praeger described a sequence of alternating sands and clays. The clays were regarded as estuarine on the basis of their contained fossil fauna. The surface of the upper clay unit was 3ft (0.9m) above the high water mark and was buried by blown sands. Hamilton & Carter (1983) described a silt/organic-rich interdune deposit, up to 0.5m thick, exposed in a meander of the Articlave River. The top of the silt/organic bed undulated between -0.1 and +0.1m O.D. The dune sands both above and below this bed consisted of poorly bedded quartz sands with low-angle concave cross-beds. Ripple drift structures were not apparent. Within the overlying sands, two distinct soil horizons with immature podzolic development were noted. The silt/organic bed contained pockets rich in leaves, fruits and mosses and a sample of these plant macro-fossils yielded a radiocarbon date of 5,315+/-135 years BP (UB-937). Pollen was rather uncommon but the spectrum obtained indicated a generally forested environment whose characteristics were compatible with the age estimate obtained. The macro-fossils suggested derivation from a single community and, along with their excellent state of preservation, indicated local derivation, probably from vegetation growing in or on the margins of a dune slack. Buried podzolic soils were described at two locations within the Grangemore dunes by Wilson (1994). These soils meet the morphological (i.e. horizon sequences and colours) and chemical criteria for classification as humoferric podzols. A radiocarbon date of 2,580+/-60 years BP (Beta-62957) was obtained on organic matter taken from the bAh horizon of one profile. The soils are developed in very well sorted, fine sand.
Importance:
The dunes and underlying clays at Castlerock and Grangemore are of international (Irish) importance as they record the course of sea level from early in the Holocene to the mid-Holocene and have figured prominently in construction of the north coast sea-level curve. Furthermore, within the Grangemore dune system are found the earliest known coastal dune sands in Ireland. The buried soils within the dunes offer the opportunity to assess development stages and pedogenic processes in the evolution of temperate dune soils, and as such they are of international (W. European) interest. The dune systems form part of a single physiographic unit at the estuary of the longest river in Northern Ireland. Their place in understanding the evolution of the estuary in terms of land-ocean interactions renders them of national importance.
Interpretation:
Estuarine clays similar to the sub-dune clays recognised at Castlerock and Grangemore by Portlock (1843) and Praeger (1893) have since been identified at several other sites within the estuary of the River Bann (Jessen, 1949; Batterbee et al., 1985), and on the basis of their elevations are considered to relate to the Holocene marine transgression that culminated c. 6,000 years BP. Although these clays have not been investigated in detail at either Castlerock or Grangemore, Jessen (1949) recorded that they were underlain by early Holocene peat at two sites (Somerset and Farrenlester), while Batterbee et al. (1985) obtained a radiocarbon date of 6,120+/-70 years BP (Lu-2130) from close to the top of the clay sequence at Sandelford. This date for the timing of the maximum relative height of the transgression agrees well with a date of 5,920+/-80 years BP (Beta-36943) from peat at Portrush that was buried by beach sand. The recorded elevations of the clays (0-+1.3m O.D.) indicate that the Holocene transgression rose above present O.D. The estuarine clays thus record sea-level rise and flooding of the Bann estuary during the early and mid-Holocene. The interdune silt/organic-rich bed reported by Hamilton & Carter (1983) was interpreted as resulting from periodic flooding of a dune slack by the ancient Articlave River. The aeolian sands below the dated horizon are the earliest Holocene dunes so far identified in Ireland. Furthermore they indicate that sea level must have fallen below 0m O.D. before c. 5,300 years BP to facilitate dune formation at this site. This information was used by Carter (1982) in construction of a Holocene sea-level curve for the north coast of Northern Ireland. Together, the estuarine clays that underlie the dunes and the interdune silt/organic-rich bed constrain the maximum relative height of the Holocene transgression in the Bann estuary to the period 6,000-5,500 years BP and demonstrate it to have been a short-lived event. The buried podzolic soils at Grangemore indicate a period of landsurface stability (vegetation colonisation and pedogenesis) during dune sand accumulation. This period, dated at around c. 2,600 years BP, probably correlates with one of the phases of stability marked by buried soils in the banks of the Articlave River (Hamilton & Carter, 1983). The radiocarbon date is in broad agreement with the archaeological evidence from the sand dunes at Portstewart for a landsurface stability phase during the Bronze Age. Thus, the available evidence for dune development phases on both sides of the Bann estuary appears to indicate synchronous periods of stability. The presence of buried podzolic soils at Grangemore is indicative of freely-drained conditions and favourable circumstances for the mobilisation and translocation of iron and organic matter at the time of their formation. This suggests that the soils progressed through a sequence of development stages similar to those outlined by Wilson (1992) for soils in freely-drained sites on aeolian sand. The absence of calcium carbonate from the Grangemore dunes may be because of pedogenic leaching in association with podzolisation, but the possibility exists that for some reason as yet undetermined calcium carbonate was never present. Even the modern soils, in the uppermost sand unit, lack carbonate.
Conclusions:
The Castlerock and Grangemore sand dunes and underlying estuarine clays represent facets of coastal evolution at the estuary of the River Bann. The clays record sea level rise in the early and mid-Holocene, whereas the dunes contain evidence for several phases of aeolian sand deposition (including the earliest known dune sands in Ireland), separated by phases of landsurface stability. The stability phases are marked by morphologically and chemically distinctive buried soils.
Notes:
The details given above are drawn from relatively few locations within the Castlerock and Grangemore dunes and there is no information concerning the lateral continuity or extent of the organic-rich materials and buried soils. In order to determine whether the information and inferences drawn from these sites is applicable to the dune systems as a whole, a programme of coring at selected sites is suggested. Note: all age estimates used in this report are in uncalibrated radiocarbon years Before Present (BP).

Keywords
Fossil Groups:	Foraminifera, Plant
Relations:	Beach deposit, Coastal processes, Estuarine deposits
Geomorph:	buried podzol, decalcified sands, estuarine clays, pollen analysis, radiocarbon dating, sand dune

Access
Management:
Current management of the dune systems by Castlerock Golf Club and the National Trust appears adequate to maintain the scientific interest of these systems.
Uses
Uses:	Recreation; golf; pasturing of sheep and cattle.

References (15)
Batterbee, R.W., Scaife, R.G. & Phethean, S.J., 1985. Palaeoecological evidence for sea-level change in the Bann estuary in the early Mesolithic period. Northern Ireland Archaeological Monographs, numb. 2 In Excavations at Mountsandel 1973-77., pp.111-120.
Carter, R.W.G., 1982. Sea-level changes in Northern Ireland. Proceedings of the Geologists Association of London, vol. 93, pp.7-23.
Gray, W., 1879. The character and distribution of the rudely-worked flints of the north of Ireland, chiefly in Antrim and Down. Journal of the Royal Historical and Archaeological Association of Ireland, vol. 5 (ser.4), pp.109-143.
Hamilton, A.C. & Carter, R.W.G., 1983. A mid-Holocene moss bed from eolian dune sands near Articlave, Co. Londonderry. Irish Naturalists Journal, vol. 21, pp.73-75.
Hasse, L., 1890. Objects from the sandhills at Portstewart and Grangemore, and their antiquity. Proceedings and Papers of the Royal Society of Antiquaries of Ireland, vol. 1 (ser.5), pp.130-138.
Hewson, L.M., 1934. Notes on Irish sandhills. Journal of the Royal Society of Antiquaries of Ireland, vol. 4 (ser.7), pp.231-244.
Jessen, K., 1949. Studies in Late Quaternary deposits and floral history of Ireland. Proceedings of the Royal Irish Academy, vol. 52B, pp.85-290.
Knowles, W.J., 1887. The prehistoric sites of Portstewart, County Londonderry. Journal of the Royal Historical and Archaeological Association of Ireland, vol. 8 (ser.4), pp.221-237.
May, A.McL. & Batty, J., 1948. The sandhill cultures of the River Bann estuary, Co. Londonderry. Journal of the Royal Society of Antiquaries of Ireland, vol. 78, pp.130-156.
Portlock, J.E., 1843. Report on the Geology of the County of Londonderry and of parts of Tyrone and Fermanagh. HMSO, Dublin.
Praeger, R.L., 1893. Report on the estuarine clays of the north-east of Ireland. Proceedings of the Royal Irish Academy, vol. 2 (ser.3), pp.212-289.
Wilcock, F.A., 1976. Dune physiography and the impact of recreation on the north coast of Ireland (D. Phil. thesis). (Thesis) University of Ulster.
Wilson, P., 1992. Trends and timescales in soil development on coastal dunes in the north of Ireland. In Coastal Dunes: Geomorphology, Ecology and Management for Conservation., pp.153-162 Balkema, Rotterdam.
Wilson, P., 1994. Characteristics, age and significance of buried podzols in the Grangemore sand dunes, Co. Londonderry. Irish Naturalists Journal, vol. 24, pp.475-480.
Wilson, P. & Carter, R.W.G., 1990. Portrush - Mill Strand. In Field Guide No. 13. North Antrim and Londonderry., pp.35-39 Irish Association for Quaternary Studies, Dublin.

Map(s):	See the 1:50,000 O.S. Sheet 4 (Coleraine).
Record type:	ESCR report
Entered by:	E M Porter
Last updated:	6 Jun 2005

Enlander, I., Dempster, M. & Doughty, P., 2026. Grangemore and Castlerock Sand Dunes, County Londonderry, site details. [In] Earth Science Conservation Review.
https://www.habitas.org.uk/escr/site.php?item=1140. Accessed on 2026-11-06.