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Earth Science Conservation Review
| Craigahilliar Quarry - Palaeogene | Antrim |
| Site number: | 65 | File Number: | C83 |
| ESCC: | IM | ||
| Locality Type: | Quarry (disused) | Status: | ASSI |
| Grid Reference: | C883389 Centroid | ||
| Google maps: | 55.18976,-6.61361 | ||
| County: | Antrim | Council area: | Causeway Coast & Glens Borough Council |
| Period: | Tertiary | ||
| Stages: | Eocene, Palaeocene | ||
| Lithostrat: | Lower Basalt Formation, Port Na Spaniagh Member, Tholeiitic Middle Basalt Member | ||
| Site Description | |
|---|---|
| Highlights: | |
The succession exposed in Craigahulliar quarry consists of the lowest member of the Interbasaltic Formation, the laterites of the Port na Spaniagh Member, representing the weathered and undulating surface of the Lower Basalts. This surface had been weathered and eroded to form a N-S trending river valley with a cover of vegetation, before being inundated by renewed volcanic activity producing the flows of the Causeway Tholeiite Member. Good examples of columnar basalts are exposed along with localized hyaloclastite deposits and interbasaltic sediments. Scree and waste material contain abundant zeolite minerals. | |
| Introduction: | |
Craigahulliar Quarry is located some 3 km southeast of Portrush and is just outside the area designated as the Causeway Coast AONB. Exposures in the quarry reveal an exhumed valley carved out of the Lower Basalt surface and represented by the laterites of the Port na Spaniagh Member, up to 5 m thick in places, with associated thin lignite and plant beds. These laterites at the base of the succession are overlain by up to five flows of the Causeway Tholeiites which successively overlap onto the sides of the valley. In a number of localities these eruptions have moved into lakes or shallow rivers and pillow-lava and hyaloclastite deposits have formed as a result of the inter-action between hot lava and water. Associated with the lava flows are thin deposits of mudstone or siltstone formed as river or lake deposits. Many of the quarry exposures show good examples of the colonnade and entablative sub-divisions which are typical of the columnar structure found in these basalts. There are also well developed "chisel-marks" which show the stages in the formation of the joint faces during cooling. Flows also contain an abundant zeolite suite including chabazite var. phacolite, and phillipsite. Wilson & Manning (1978) review much of the available literature and recent geochemical and volcanological interpretations have been made by Lyle & Preston (1993). | |
| Description: | |
The exhumed valley in the Lower Basalt surface trends roughly N-S and localities 1, 2a and 2b show the main features of the laterite surface and the overlying Causeway Tholeiite flows. Locality 1 (Grid Ref. C88153905): A steep bank behind the old workshop and conveyor buildings shows the upper part of the Port na Spaniagh laterite, overlain with thin pockets of blackish lignite containing abundant leaf and bark fragments and imprints. A range of pollens has been recognized from this horizon including cedar, spruce, pine, hazel and alder (Charlesworth 1963). The first flow of the Causeway lavas erupted over this surface and a crudely developed colonnade and entablature structure can be recognized. Large pipe vesicles have formed in this first flow, probably the result of gases released from the soil and vegetation, and unusually for Antrim these are filled with chalcedony, a crypto-crystalline form of quartz. They are 5-10 cm in diameter and up to 20 cms in length. The amygdales in the upper part of the flow are smaller and filled with zeolite minerals. Locality 2a (Grid Ref. C883389): The access road southeast into the quarry from locality 1 climbs to a higher level with the first flow of the Causeway Tholeiites again exposed over the Interbasaltic laterites. At this locality there is an excellent example of the flow-foot breccias formed of hyaloclastite material when lava flows into standing water. This shows a 2-3 m thick deposit of rounded pillow-like masses of chilled basalt in a matrix of yellow/orange palagonite. This palagonite is the clay alteration produce derived from the volcanic glass which formed when the hot lava chilled against the water. Locality 2b (~50 m SE of locality 2a): The basalt flow overlying this deposit is in turn overlain by a thin bed of fine sandstone or siltstone containing plant remains and probably representing a lake-bed or river-bed deposit. The flow top underlying this sediment has recently been exposed and shows a series of small domes and blisters. This occurrence is extremely rare within the Antrim Lava Group as a whole, and this exposure is the first found within the Causeway lavas. The amygdaloidal zones of the basalt around locality 2 yield excellent specimens of phacolite (a variety of chabazite), chabazite, phillipsite and analcite. Locality 3 (Grid Ref. C885390): To the north of locality 2 the final face worked in the quarry has left a spectacular vertical section through two Causeway flows. Along this face are examples of the colonnade/entablature columnar jointing so spectacularly exposed at the Giant's Causeway. Locality 4 (Grid Ref. C885392): To the north of the section exposed in locality 3 is an older and more overgrown part of the quarry. Here are very good examples of regular colonnade columns which show very clear horizontal markings known as "chisel marks". The precise origin of these marks is still under discussion but it seems certain that they represent stages in the gradual growth of the colonnade columns as the interior of the lava cooled. | |
| Importance: | |
The site is an important locality in the interpretation of the Lower Basalt and Interbasaltic Formations in north Antrim. The interpretations made in Craigahulliar have relevance to the overall interpretation of multi-tiered columnar lava flows occurring in the British Tertiary Volcanic Province in the Hebrides, and elsewhere in the world such as the Columbia River Basalt Group, USA, and in Iceland. | |
| Interpretation: | |
The quarry sections clearly record the lateritization of the Lower Basalt surface during the period of volcanic quiescence that occurred after the first cycle of Tertiary volcanism in Antrim (Lyle 1980). The development of soil and vegetation on that surface is recorded in the lignite and plant beds lying on the Interbasaltic surface. With the re-commencement of eruptions the Causeway tholeiite flows inundated the Lower Basalt surface and progressively overlapped the valley sides which had been eroded during the earlier Interbasaltic times. The volcanological conditions are indicated by the existence of hyaloclastite breccias and interbasaltic sediments, suggesting disrupted drainage and bodies of standing water on the lava surfaces. The presence of abundant water at the time of eruption is suggested as having played a role in the cooling history of the lavas. Inundation of the flow surface by water during cooling disrupts the cooling regime of the upper part of the flow and produces the curvi-columnar entablature (Lyle and Preston, 1993). In a regional context the exposures in Craigahulliar are similar to those elsewhere, particularly on the Causeway coast sections, but the quarry is unique in having such a range of typical features in such a compact area. | |
| Conclusions: | |
The site is unique in terms of its range of features, compactness and accessibility. It is a valuable research and teaching locality and is an important source of information in the interpretation of the volcanological history of the Antrim Lava Group in north Antrim. | |
| Notes: | |
The quarry is currently disused and is the subject of an enquiry into its use as a landfill site by the local authority. This proposal suggests preservation of localities 1, 2 and 4 as part of a geological trail. Preservation of locality 3 is also desirable even at the cost of some volume to the landfill site. The sections at localities 1 and 2 are potentially dangerous from falling blocks; thought will have to be given to providing access for those wishing to examine the flow surface and interbasaltic sediment. The flow surface is extremely vulnerable to weathering and indiscriminate sampling and may have to be treated with some form of hardener to assist preservation. The hyaloclastite breccia deposit is susceptible to over-sampling due to its friable state and this in turn exacerbates the tendency for blocks of basalt to fall from higher in the section. Zeolite collecting is possible from loose scree material but there is invariably a temptation by collectors to remove material from the face with a danger to themselves and others. This site is also important for Mineralogy and Metallogenesis. See Key Site 534 - Craigahulliar Quarry, near Portrush. | |
| Keywords | |
|---|---|
| Minerals: | Analcite, Chabazite, Chalcedony, Phillipsite |
| Rocks: | Basalt, Lignite, Palagonite, Tholeiite |
| Structures: | amygdales, columnar jointing, pipe vesicle |
| Relations: | Intrusion |
| Geomorph: | buried topography, laterite |
| Paleoenv: | river valley |
| Access | |
|---|---|
| Approach: | The quarry is 3 km south-east of Portrush. Access to localities is via the quarry road from Ballycraig Upper. |
| Restrictions: | The sections at localities 1 and 2 are potentially dangerous due to the possibility of falling blocks. In other areas of the quarry builders waste and other waste materials have accumulated, making access in places difficult and at times dangerous. |
| Management: | |
Unauthorized dumping has occurred in the past and there are areas in the quarry where builders waste and other waste materials have accumulated, making access in places difficult and at times dangerous. Unauthorized dumping must be prevented and areas such as those around localities 1-2 should be cleared of waste material and levelled. Vegetation cover and waste material around locality 4 also needs clearing to allow easier access to the quarry faces. | |
| Development: | The quarry is currently disused and is the subject of an enquiry into its use as a landfill site by the local authority. |
| Threats: | Development as a landfill site. Over-sampling and further weathering. |
| Uses | |
| Uses: | Industrial activity is currently carried on within the boundaries of the original quarry, but remote from any sections of geological significance. |
| Potential: | Landfill; geological trail |
| References (5) | |||
|---|---|---|---|
| Charlesworth, J.K., 1963. Historical Geology of Ireland., pp.565 Oliver and Boyd, London. | |||
| Lyle, P., 1980. A petrological and geochemical study of the Tertiary basaltic rocks of northeast Ireland. Irish Journal of Earth Sciences, vol. 2, pp.137-152. | |||
| 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. & Swaine, D.J., 1955. A petrochemical study of Tertiary tholeiitic basalts: the Middle Lavas of the Antrim plateau. Geochimica et Cosmochimica Acta, vol. 8, pp.173-181. | |||
| Wilson, H.E. & Manning, P.I., 1978. Geology of the Causeway coast. Memoir for one-inch geological sheet 7. Memoirs of the Geological Survey Northern Ireland, HMSO, Belfast. | |||
| Map(s): | For site location see the 1:50,000 O.S. Sheet 4 (Coleraine). | ||
| Record type: | Environment Serv. GIS, ESCR report, J. Preston l | ||
| Entered by: | Hamilton, M.J. | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Craigahilliar Quarry - Palaeogene, County Antrim, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=65. Accessed on 2026-11-06. |
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