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Earth Science Conservation Review
| Bovevagh Old Church | Londonderry |
| Site number: | 3 | File Number: | C61 |
| ESCC: | IS | ||
| Locality Type: | River bank | Status: | ASSI |
| Grid Reference: | C668140 Centroid | ||
| Google maps: | 54.9695,-6.95693 | ||
| County: | Londonderry | Council area: | Causeway Coast & Glens Borough Council |
| Period: | Quaternary | ||
| Stages: | Early Midlandian | ||
| Site Description | |
|---|---|
| Highlights: | |
The stratigraphy includes glaciomarine mud rich in marine shells, foraminifera and ostracods. Marine shells from the mud provided 14C dates older than 45ka B.P. and amino acid ratios which suggest that the deposit is Early Midlandian in age. The sequence demonstrates deep isostatic depression and glaciomarine conditions in the Dungiven depression as the ice sheet decayed. The stratigraphic importance of the site is therefore critical for palaeoenvironmental reconstructions in the early part of the last cold stage. | |
| Introduction: | |
The site at Bovevagh Old Church is 200m north west of the Bovevagh grave yard on the west bank of the Bovevagh river. The section is poorly-exposed and is 21m in length by 4m in height. It occurs 12km inland at a height of about 95m O.D. It is therefore of critical scientific importance with respect to its location and altitude. Early records such as Portlock (1843) described the shelly drift as a result of ice transport. More recently Charlesworth (1939) and Colhoun (1971) regarded the fossiliferous muds as glacial tills. More recent sedimentological and palaeoecological work which is still in progress suggests that the deposit is more complex than hitherto realised, and is a remnant of a low angle, prograded glaciomarine delta. Workers such as Charlesworth (1939), Colhoun (1971) and Mitchell et al. (1973) regarded all of the shelly drifts of the Dungiven basin as sea floor deposits reworked by ice advances from Scottish sources. | |
| Description: | |
The exposure consists of poorly-stratified gravels, sands and sandy diamicts which interfinger laterally with massive, fossiliferous mud. Poorly-sorted gravel at the base of the exposed sequence consists of amalgamated beds of cobble to pebble gravel which are generally ungraded and massive. At several horizons in the gravels strong imbricated fabrics indicate a palaeoflow to the north. Openwork pods and lags of cobbles and pebbles are common. The gravel consists mainly of schist, quartzites sandstones and occasional red sandstones many of which are weathered. Thin beds (10cm) of silty-clay within the gravels thicken northwards and pass below the base of the exposure. The basal gravels are overlain abruptly by a flat-lying bed of silty-clay which is highly variable internally and ranges from massive to faintly-laminated. The upper surface of the clay is planar and overlain by contorted and laminated sands containing whorls and masses of sand overturned to 340°T. This unit is interbedded with the fossiliferous marine muds towards the northern end of the section. It contains comminuted marine shell fragments. The contact with the overlying pebble and cobble gravel is sharp and marked by a discontinuous stone lag. The upper unit of gravels is similar in clast composition and sedimentological characteristics to the lower gravel unit. The upper 10m to 15m of the sequence is not exposed though small slumps immediately behind the grave yard suggest that a brown, massive to stratified diamict is present. On the opposite side of the Bovevagh river (Knockbrack) an old slump exposed a massive, diamict with dispersed clasts. It is up to 8m thick and is rich in Triassic detritus and schist. The interbedded relationships between massive grey mud at the northern end of the sequence and the coarse clastic units at the southern end of the sequence show that both were deposited contemporaneously. Slickensided surfaces within the mud are common, along with discontinuous silty and sandy stringers and occasional small pebbles. The most common fossil is Turritella communis which occurs in profusion and about 50% of the specimens are perfectly preserved. Some mud samples contain low concentrations of poorly-preserved foraminifera. Others however contain very distinct, well-preserved, foraminiferal assemblages. One assemblage is boreal in aspect and is similar to environmental settings of western Norway today. The other reflects shallow water glaciomarine conditions with a distinct Arctic aspect. These samples require farther processing before more definite statements can be made. Two AMD dates on a whole shell of Aporrhais perplelicani (>34kam B.P.) and several whole shells of Turritella communis (>44ka B.P.) are infinite. | |
| Importance: | |
Although there are two possible interpretations for the Bovevagh sequence there is no doubt that the sequence is important locally and nationally. Its importance concerns the development of lowland ice masses and extent of isostatic depression during the Early Midlandian and the associated palaeoclimatic inferences. On a wider scale however the site may well achieve an international significance if the reconnaissance surveys on the palaeoecological trends of the fauna prove reliable. In any case this site contains critical palaeocecological evidence on glaciomarine conditions within the Dungiven basin at about 95m O.D. and 12km inland. No other site known in Ireland demonstrates this setting during the Early Midlandian and preservation is probably a result of weak glacial activity in the Dungiven basin during the Late Midlandian. | |
| Interpretation: | |
Flat-lying beds together with the absence of obvious glacitectonic structures at this site suggest that the sequence is in situ and has not been transported by ice. Rapid interbedding of facies and the preservation of many primary sedimentary structures and bedding planes are also indicative of an undisturbed succession. Slickensides in the mud are probably a response to sediment loading or overburden rather than ice induced. However the exposure is small and could be part of a much larger deformed unit which is not exposed. The marked lateral and vertical facies changes at the site reflect a range of processes. Coarse-grained gravels are the result of mass flow and traction activity with a northwards palaeoflow. Grain size variability simply shows that flows ranged from fluidal to more dense flows and debris flow events. The delicate, interbedded relationship between these flow units and the mud shows that both are contemporaneous. The most likely depositioned setting is where a stream formed a low-angle delta which prograded into a shallow water glaciomarine setting dominated by plume deposition from suspension. If the muds are in situ then the succession records deep isostatic depression and glaciomarine conditions in the Dungiven basin. The implications are that extensive ice masses developed probably during the Early Midlandian in northwest Britain. An alternative explanation involves ice transport of sea floor muds followed by reworking in a shallow proglacial water body which would explain the sediment geometry of the section. This hypothesis requires large onshore ice masses during the Early Midlandian, but does not require deep isostatic depression, to explain the present height of the muds and their inland position. The second model would explain the presence of mixed faunas in a simpler way than the first model which would require sustained isostatic compensation during the deglacial phase and boreal-type environmental settings. Further work is in progress to resolve this problem. | |
| Conclusions: | |
The Bovevagh site occurs 12km inland at 95m O.D. and is an example of a shallow deltaic setting where gravelly sediment prograded northwards into fossiliferous glaciomarine clays. If the sequence is in situ it records the development of major lowland ice masses during the Early Midlandian and marked isostatic depression. This association of large lowland ice sheets and isostatic depression during the early part of the last cold stage has important palaeoenvironmental and palaeoclimatic implications for Quaternary research in northwestern Europe. | |
| Notes: | |
The lateral extent of the muds and associated sediments is unknown. | |
| Keywords | |
|---|---|
| Fossil Groups: | Foraminifera |
| Fossil List: | Turritella communis |
| Relations: | Glaciomarine deposit |
| Geomorph: | prograded delta |
| Paleoenv: | delta |
| Measurements | |||||
|---|---|---|---|---|---|
| Length: | 21 m | Width: | Height: | 4 m | |
| Depth: | Area: | ||||
| Access | |
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| Approach: | The site at Bovevagh Old Church is 200m NW of the Bovevagh grave yard on the W bank of the Bovevagh river, approximately 6km NW of Dungiven. |
| Management: | |
The site is in a poor state of preservation for proper geological investigation largely because the course of the river has been moved away from the outer bank of the once active meander scar. As a consequence the sediments have started to slump over the site and the mud is extremely mobile when lubricated by water. This condition is exacerbated by the constant trampling and poaching by cattle as they traverse the northern slopes of the site. An active management policy would be to allow the river to erode the site and expose the stratigraphy. An interesting development here would be that the eroded debris, especially the gravelly detritus, would provide the stream with the bedload necessary to sustain fish life in general and more specifically aid spawning banks. Similarly in many rivers rather than dredging away the sand and gravel it may be more appropriate to encourage river erosion along slumps and scars which would have distinct biological and geological benefits. Notifiable operations include: 1: Disturbance or modification of the land surface, water levels or water courses. Whether by engineering works or storage (eg. wood, piles of wood cuttings) or by any other means. 2: Field drainage or field boundary drainage. 3: Use of vehicles or machinery likely to obliterate the site. 4: Constant trampling by animals is particularly relevant at this specific site and is a major problem. 5: Afforestation or tree planting. 6: Burning of vegetation or waste material. 7: Dumping, spreading, discharge or storage of any materials. | |
| Threats: | Slumping of river banks; trampling by cattle. |
| Uses | |
| Uses: | Current land use around the site is mainly grazing. Small- scale attempts have deflected the present course of the river away from the formerly active meander scar. The site will now degrade and will soon disappear as a section available for study. |
| Map(s): | See the 1:50,000 O.S. Sheet 7 (Londonderry). | ||
| Record type: | Environment Serv. GIS, ESCR report | ||
| Entered by: | Crowther, P.R. | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Bovevagh Old Church, County Londonderry, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=3. Accessed on 2026-11-05. |
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