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Earth Science Conservation Review
| Church Bay, Rathlin Island | Antrim |
| Site number: | 1137 | ||
| ESCC: | IS | ||
| Locality Type: | Pit, Scarp face | Status: | ASSI |
| Grid Reference: | D148506 Approximate | ||
| Google maps: | 55.28936,-6.19299 | ||
| County: | Antrim | Council area: | Causeway Coast & Glens Borough Council |
| Period: | Quaternary | ||
| Stages: | Holocene, Pleistocene | ||
| Site Description | |
|---|---|
| Highlights: | |
At Church Bay a massive solitary gravel barrier composed largely of chalk is present several metres above contemporary sea level. The feature is now vegetated and forms a smooth, undulating topography on which most of the village is built. A series of minor ridges oblique to the main feature have been interpreted as recurves on a spit. Its internal structure is visible in a few gravel pits. Dating of included shells indicated a Late Midlandian age for this feature. Seaward of the main ridge are a possible late Holocene feature composed of finer pebbles. This is succeeded seaward by a contemporary gravel beach and underlying chalk platform. | |
| Introduction: | |
Evidence of former shorelines associated with sea levels above present has long been recognised around the Irish coast (Synge & Stephens, 1966) and has been interpreted in terms of glacio- isostatic and glacio-eustatic changes in sea level. A series of shorelines at elevations up to 30m O.D. have been differentially uplifted during isostatic readjustment (Carter, 1994) and these present evidence of the nature and rate of uplift. Little direct evidence of the age of these raised features or of the conditions which created them is presently available and yet they formed at a time when climatic adjustment following glaciation and the physical constraints upon oceanic processes (sea level, tidal and wave regime) were undergoing rapid change. Such features thus offer the opportunity to investigate the nature of such changes and their morphological expression. In this regard the recent description of a raised gravel barrier at Church Bay (Carter, 1994) is an important, albeit preliminary, contribution. The feature has been known for some time (Wilson & Robbie, 1966) and the earlier account differs somewhat from that of Carter (1994). | |
| Description: | |
At the rear of Church Bay a scarp line may be traced between abandoned raised cliffs between Mill Bay and the north side of the harbour. The scarp is some 600m from the present coast behind Church Bay. Immediately landward of the settlement of Church Bay and seaward of the scarp is a large gravel barrier which is covered by vegetation (mostly grassed fields). This feature is about 1.2km long and extends from one cliffline to another across a low-lying section of land where the former cliffline diverges from the modern coast. In plan view the feature comprises an elongate shore-parallel ridge which bifurcates and produces a second ridge which extends obliquely landward. The ridge was estimated to comprise about 250-300,000m3 of sediment (Carter, 1994) and its crest is at just over 10m O.D. Exposures in a gravel pit revealed a 4.5m thick sequence of well rounded chalk gravel with a modal clast size in the range 20- 40mm. These gravels were deposited in graded beds which dip east at 25-28 deg. Both normal and inverse grading was present in the gravel beds which are typically clast supported. Dating of Littorina littorea shells yielded a 14C date of 12,320 +/- 80 years BP (Beta-48580) which when normalised and corrected yields an age of 12,335 +/- 80 years BP. | |
| Importance: | |
In the past ten years increasing evidence has proven the presence of glacio-marine environments at the margin of the last ice sheet. In this regard the radiocarbon date for the shell material at Rathlin is perhaps the most important element at this site. It provides a broad indication (perhaps within 10m) of the elevation of relative sea level in late Midlandian times. Further, it is the only gravel ridge feature of its type known in Ireland although contemporary examples occur in Canada (Carter, 1994). Carter (1994) drew attention to the difference in elevation of beach deposits from Rockall which are apparently contemporaneous with the Church Bay gravel ridge but are now submerged under 100-120m of water. Such a difference was tentatively ascribed to the collapse of a forebulge (located in the vicinity of Rockall) associated with the late Midlandian Scottish ice sheet. A hinge must have been located in the vicinity of the present coast since it is more than 100m higher than the Rockall platform deposits. The presence of a later raised beach as noted by Wilson & Robbie (1966) suggests a postglacial age for it and its associated erosional rock forms. | |
| Interpretation: | |
The barrier was interpreted by Carter (1994) as having formed during the late Midlandian as a spit which extended from south to north on the basis of the orientation of a recurve near the former distal end of the feature. This gradually extended until it isolated a low-lying area to landward which is now occupied by flat, low-lying ground. The spit was fed by erosion of chalk cliffs to the south (although none are present now) which supplied the chalk clasts to the barrier. Wilson & Robbie (1966) considered two gravel spits to be present enclosing depressions which were interpreted as former lagoons on a raised beach deposit (termed the second beach by Wilson & Robbie). West of this raised beach Wilson & Robbie identified another raised beach (the first beach) at 10ft (c. 3m) O.D. which they considered contemporaneous with a rock platform and raised sea stacks to the north. The internal structure of the gravel ridge described by Carter (1994) suggested two phases of deposition. Lower, finer-grained gravels were interpreted as a mid-beachface environment formed as the feature extended northward while the upper, coarser units dominated by discs are suggestive of overwashing of the former crest during an aggradation phase. Aggradation of over 3m is indicated, which could mean deposition under a rising sea level or the gradual elevation of the gravel crest under wave runup. The morphological evidence was unable to provide an estimate of former sea level with much accuracy other than that it was several metres above present. This is consistent with estimates of Late Glacial sea levels made from deposits at Portballintrae (McCabe et al., 1994). | |
| Conclusions: | |
A massive, solitary gravel barrier of late Midlandian age is present at Church Bay. It appears to have formed through spit elongation from the south followed by crestal build-up via barrier overwash. The feature provides dated evidence of former sea levels in late glacial times, although the dynamics of gravel barriers are such that precision in placing the former sea level is difficult. Although it has only been studied in a preliminary manner it affords the opportunity for further research on late glacial environmental change and is consequently of national importance. Although only studied superficially, it is the best studied of several gravel features of similar probable age in Northern Ireland. | |
| Notes: | |
The gravel ridge at Church Bay has been described only briefly by Wilson & Robbie (1968) and Carter (1994). On the basis of these descriptions and subsequent field visits it is clear that the site offers high potential for further study. This should ideally include a study of the stratigraphy and sedimentology of the Late Glacial feature, elucidation of the age and relationship of the apparently younger gravel feature which abuts it, and the morphodynamics of the contemporary beaches. There is topographical and limited sedimentary field evidence of potential back-barrier deposits to the rear of the gravel barrier. These are likely to offer a good potential for constraining Late Midlandian sea level more precisely than the gravel ridge itself, and may provide indications of late glacial environmental change. | |
| Keywords | |
|---|---|
| Fossil List: | Littorina littorea |
| Relations: | Glaciomarine deposit, Late-glacial deposit |
| Geomorph: | gravel barrier, raised shoreline |
| NonGeol: | The area is presently designated in terms of its a |
| Access | |
|---|---|
| Approach: | The gravel ridge underlies the settlement of Church Bay. |
| Management: | |
The gravel ridge underlies the settlement of Church Bay and is covered in agricultural land and a few houses and farm buildings. The gravel pit from which the stratigraphy of the ridge was described has been used as a dump and is presently filled with wrecked cars and disused household appliances. The section has thus largely been obscured. Temporary sections have been opened up (October 1995) presumably to provide aggregate for construction works adjacent to McCully's Public House. The widespread development on the ridge and evidence of opening of gravel pits pose potential management difficulties. Whereas gravel pits offer the only means of observing sections through the deposit, the widespread exploitation of the deposit could lead to reduction in its potential value before it is fully documented. The area is presently designated in terms of its archaeological interest (Viking cemetery). | |
| Threats: | Widespread exploitation of the deposit for gravel. |
| Uses | |
| Uses: | Agricultural land and dwellings. |
| Educ. Level: | Undergraduate / Postgraduate |
| References (4) | |||
|---|---|---|---|
| Carter, R.W.G., 1994. Age, origin and significance of the raised gravel barrier at Church Bay, Rathlin Island, County Antrim. Irish Geography, vol. 26, pp.141-146. | |||
| McCabe, A.M., Carter, R.W.G. & Haynes, J., 1994. A shallow marine emergent sequence from the northwestern sector of the last British ice sheet, Portballintrae, Northern Ireland. Marine Geology, vol. 117, pp.19-34. | |||
| Synge, F. & Stephens, N., 1966. Late Pleistocene shorelines and drift limits in north-east Ulster. Transactions of the Institute of British Geographers, vol. 39, pp.101-125. | |||
| Wilson, H.E. & Robbie, J.A., 1966. Geology of the country around Ballycastle. Memoirs of the Geological Survey Northern Ireland. | |||
| Map(s): | See the 1:50,000 O.S. Sheet 5 (Ballycastle). | ||
| Record type: | ESCR report | ||
| Entered by: | E M Porter | ||
| Last updated: | 8 Jan 2005 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Church Bay, Rathlin Island, County Antrim, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=1137. Accessed on 2026-11-06. |
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