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Earth Science Conservation Review
| Binevenagh | Londonderry |
| Site number: | 1187 | ||
| ESCC: | EO | ||
| Locality Type: | Crag | Status: | ASSI |
| Grid Reference: | C690310 Approximate | ||
| Google maps: | 55.12188,-6.91848 | ||
| County: | Londonderry | Council area: | Causeway Coast & Glens Borough Council |
| Period: | Tertiary | ||
| Stages: | Eocene, Palaeocene | ||
| Lithostrat: | Antrim Lava Group, Upper Basalt Formation | ||
| Site Description | |
|---|---|
| Highlights: | |
A good exposure of the Tertiary basalt sequence of the western part of the Antrim Plateau, overlying Cretaceous Chalk. | |
| Introduction: | |
The basalt scarp at Binevenagh represents the northwestern limit of the Antrim Lava Group and is exposed from the north coast at Downhill - Castlerock, SW to Binevenagh and then in a generally southerly direction to the hills around Benbraddagh near Dungiven, a distance of around 30km. The geology of the basalts was described in some detail by Patterson (1955) with later studies by Lyle (1985 & 1988). The succession is included in Sheet 12 and part of Sheet 6 (Limavady) of the Geological Survey of Northern Ireland. The succession consists of a series of olivine basalts overlying Cretaceous Chalk except in the Glenshane area to the south where the basalts overlie Trias sandstone. Patterson (1955) on the basis of field evidence concluded that most belonged to the Upper Basalt Formation while Lyle (1985) presented further field evidence from the Binevenagh area to confirm their likely UBF age, but showed that chemical characteristics of these basalts had similarities to both Lower and Upper Basalts from the eastern part of the plateau. The apparent absence of a laterite horizon correlating with the Interbasaltic Formation makes a definitive age determination difficult. | |
| Description: | |
(i) Petrography and field occurrence of the Binevenagh basalts Patterson (1955) described the petrography of the lavas in some detail and recorded intergranular through sub-ophitic to ophitic textures. The basalts are olivine-bearing and intergranular textures in the lower part of the succession pass up into ophitic/poikilitic textures. Lyle (1985) recorded the occurrence of flowbanded olivine-phyric basalts towards the top of the succession, similar to a chemically distinct group of flows recorded near the top of the Upper Basalts on the Garron Plateau in east Antrim (Lyle, 1980). The Binevenagh basalts all show some degree of post-crystallization alteration with serpentine, chlorite and fibrous zeolites as the commonest alteration products. The succession at Binevenagh consists of around 100m of basalts overlying Cretaceous Chalk. The base of the succession contains a number of flows made up of thin flow units often with marked pahoehoe tops. These flows pass up into a number of prominently columnar flows separated by distinctive red boles and the upper flows in the sequence are olivine-phyric with convoluted flow banding. Lyle (1988) has attempted to correlate this Binevenagh section with other sections through the basalts as far south as Benbraddagh and the Glenshane Road (Fig 4., Lyle op. cit.). A feature of the base of the Binevenagh cliffs is the presence of extensive slipped masses of basalt overlying Cretaceous, Liassic and Triassic rocks. These are considered to be of late- and post- glacial age (Wilson, 1972). (ii) Geochemistry of the lavas Recent major and trace element data have been presented by Lyle (1985 & 1988). In general terms the major element concentrations are similar to the Upper Basalts particularly total alkali values, while the incompatible and rare earth element values are closer to those of the Lower basalts. Normative analyses show that all the basalts are hypersthene-normative and like the Lower and Upper Basalts in Antrim they are olivine tholeiites. | |
| Importance: | |
The basalt successions at Binevenagh show a typical section through the Tertiary lavas of the western edge of the lava plateau and are largely representative of the sections exposed from Castlerock to Benbraddagh. They occur on the NW of the Tow Valley Fault which forms the northern edge of the Highland Border Ridge. The petrogenesis of the Binevenagh basalts may have involved decompression melting of the underlying mantle initiated by movement along the fault (Lyle and Preston, 1993). There are significant geochemical differences between these western basalts and those of the rest of the Antrim plateau and they represent an important contribution to an understanding of the petrogenesis of the Antrim Lava Group as a whole. The volcanic features such as the occurrence of flow units and pahoehoe surfaces are among the best examples seen anywhere within the basalt plateau. | |
| Interpretation: | |
Patterson (1955) discussed the age of the Binevenagh lavas relative to the basalts in the eastern part of the Antrim plateau. He concluded they were likely to be of Upper Basalt age on the basis of: (a) the much greater thickness of the lavas in the Binevenagh area (150m) compared with around 50m of Lower Basalts east of the River Bann some 15km away; (b) the absence of a recognizable Interbasaltic Formation within the lava succession; (c) the occurrence of a ferruginous bole beneath the basalts at Downhill which has affinities with typical Interbasaltic Formation elsewhere on the plateau; and (d) outside the immediate area at Coagh 50km to the south, the presence of rhyolite pebbles in the Coagh conglomerate under- lying the basalts. Rhyolite occurrences elsewhere on the plateau, e.g. at Tardree, are considered Interbasaltic in age. Additional field evidence was presented by Lyle (1985) who recognized flowbanded olivine-phyric basalts near the top of the Binevenagh succession, similar in appearance to flowbanded olivine-phyric flows occurring near the top of the succession on the Garron Plateau in east Antrim. This was interpreted as further supporting the correlation of the Binevenagh basalts as Upper Basalt in age. The presence of thin pahoehoe flow units within the Binevenagh succession suggests that flows were erupted from nearby vents (Lyle, 1988) and Lyle and Patton (1989) suggest that flowbanded olivine-phyric lavas are also found close to source, since otherwise the olivine phenocrysts would be lost by flow-separation. Geochemical data in Lyle (1985 & 1988) were used to erect a petrogenetic model whereby volcanic activity extended westwards from Antrim in Upper Basalt times and the lavas in the Binevenagh area are the products of a first melting of a less depleted mantle than that which produced the Upper Basalts in Antrim. | |
| Conclusions: | |
A relatively accessible lava sequence which demonstrates clearly inter-flow relationships in the building of a basalt lava plateau and which contains important geochemical evidence on the petrogenetic history of the Antrim Lava Group. | |
| Keywords | |
|---|---|
| Rocks: | Basalt, Olivine Basalt, Pahoehoe, Tholeiite |
| Structures: | flow-banding, phenocrysts |
| Relations: | Extrusion |
| Measurements | |||||
|---|---|---|---|---|---|
| Length: | Width: | Height: | ~100 m | ||
| Depth: | Area: | ||||
| Access | |
|---|---|
| Approach: | Access to the top of the Binevenagh cliffs is by the path through the Binevenagh Forest with car parking at the Binevenagh Lake which is used for fishing. The cliffs are to the north and west of the lake. Access to the base of the cliffs can also be made from Binevenagh Forest tracks. |
| Management: | |
The sections through the basalts at Binevenagh are generally steep and inaccessible and particularly dangerous if approached from above. Access to the lavas is via gulleys generally formed along faults, and there is considerable risk of falling rocks. The sections to the south towards Croaghan offer the best opportunity to examine the section closely but even here great care must be exercised, particularly in misty or windy weather. Pressure from geological sampling is not considered to be a likely problem. No management actions are envisaged. | |
| Uses | |
| Uses: | Recreation, fishing. As well as extensive forest cover in the area there is hill sheep-farming and bogland. A standing stone is marked at the NE limit of the National Nature Reserve. |
| References (6) | |||
|---|---|---|---|
| Lyle, P., 1985. The geochemistry and petrology of Tertiary basalts from the Binevenagh area, Co. Londonderry. Irish Journal of Earth Sciences, vol. 7, pp.59-64. | |||
| Lyle, P., 1988. The geochemistry, petrology and volcanology of the Tertiary lava succession of the Binevenagh-Benbraddagh area of Co. Londonderry. Irish Journal of Earth Sciences, vol. 9, pp.141-152. | |||
| Lyle, P. & Patton, D.J.S., 1989. The petrography and geochemistry of the Upper Basalt Formation of the Antrim Lava Group in northeast Ireland. Irish Journal of Earth Sciences, vol. 10, pp.33-41. | |||
| Lyle, P. & Preston, J., 1993. The geochemistry and volcanology of the Tertiary basalts of the Giant's Causeway area, Northern Ireland. Journal of the Geological Society of London, vol. 149, pp.109-120. | |||
| Patterson, E.M., 1955. The Tertiary lava succession in the northern part of the Antrim plateau. Proceedings of the Royal Irish Academy, vol. 57B, pp.79-122. | |||
| Wilson, H.E., 1972. Regional Geology of Northern Ireland. HMSO, Belfast. | |||
| Map(s): | GSNI 1:50,000 Sheet 12 and part of Sheet 6 (Limavady). | ||
| Record type: | ESCR report | ||
| Entered by: | E M Porter | ||
| Last updated: | 23 Dec 2003 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Binevenagh, County Londonderry, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=1187. Accessed on 2026-11-05. |
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