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Earth Science Conservation Review
| Kilcoan, Island Magee | Antrim |
| Site number: | 1218 | ||
| ESCC: | ED | ||
| Locality Type: | Cutting | Status: | ASSI |
| Grid Reference: | J461986 Approximate | ||
| Google maps: | 54.81436,-5.72731 | ||
| County: | Antrim | Council area: | Mid & East Antrim Borough Council |
| Period: | Cretaceous | ||
| Stages: | Cenomanian, Coniacian, Santonian | ||
| Lithostrat: | Belfast Marls Member, Cloghfin Sponge Beds Member, Hibernian Greensands Formation, Island Magee Silts Member, Kilcoan Sands Member, Ulster White Limestone Formation | ||
| Site Description | |
|---|---|
| Highlights: | |
The section at Kilcoan is the type locality for the Island Magee Siltstones Member and the Kilcoan Sands Member of the Hibernian Greensands Formation. Also exposed here is the Belfast Marls Member. | |
| Introduction: | |
The Kilcoan site is a cutting leading to now infilled quarries. It is on the west coast of Island Magee, Co. Antrim, 7km SE of Larne. The area was mapped and an explanatory memoir produced by Hull (1876). This is the Barney's Point locality described by Hume (1897). The most detailed study of the site was by Fletcher (1967). A new map of the area has recently been produced (GSNI, 1994). | |
| Description: | |
The Belfast Marls Member, previously known as the Glauconitic Sands (Tate, 1865) is ~1.22m thick and consists of deep green glauconitic marly sands with a faunal assemblage dominated by individuals of Schloenbachia spp. and Acanthoceras (Hancock, 1961). The Island Magee Siltstones Member was previously known as the Grey Marls and Yellow Sandstones (Tate, 1865). This is the type locality for the member and the following section was previously exposed: ISLAND MAGEE SILTSTONES MEMBER Sandstone, light stone, fine-grained, tends to weather in lumps, 0.23m Sandstone, greenish, fine-grained, 0.05m Sandstone, greenish, fine-grained, 0.23m Silty sandstone, khaki, 0.76m Sandstone, greenish, fine-grained, 0.30m Silty sandstone, khaki, 0.76m Sandstone, 0.30m Silty Sandstone, 1.07m Sandstone, 0.03m Clayey sandstone, khaki, soft and massive, 0.91m This is also the type locality for the Kilcoan Sands Member (= Chloritic Sands and Sandstones of Tate (1865)). The basal conglomerate is 0.90m thick and contains small cobbles of quartzose sandstone which can be matched with sandstones from within the pre-Senonian greensands north of Larne. It is succeeded by rather coarse loosely cemented glauconitic quartz sand in which rhynconellids and Ostrea are common. Small phosphatic nodules occur, often in bands, and Inoceramus fragments increase in abundance 0.90m above the conglomerate. The next 1.52m contain much Inoceramus and Ostrea debris, the flat broken shells being aligned with the bedding and producing a banding effect. Rhynconellids continue into the Inoceramus beds but appear to give way in prominence to the terebratulids of which Gibbithyris and Carneithyris are particularly common. In the remaining 3.66m Inoceramus become quite rare and there is a general paucity of fossils. In the highest levels fossils again appear to be more abundant, especially the echinoids Conulus and Echinocorys. At the top, this member is overlain by the Cloghfin Sponge Beds Member of the Ulster White Limestone Formation. | |
| Importance: | |
This is the type locality for the Island Magee Siltstones Member and the Kilcoan Sands Member of the Hibernian Greensands Formation. The sequence is the thickest developed in the Larne-Lough Neagh Basin. It is of national importance and should be conserved. | |
| Interpretation: | |
The presence of unconformities within this sequence demonstrates gaps in sedimentation particularly during the Turonian which is not found here. The area from Portmuck to Kilcoan shows the greatest thickness of the Kilcoan Sands Member and is typical of sedimentation in the Hillsport Basin, a sub-basin of the Larne- Lough Neagh Basin. Much of the detrital content of the greensands derived from the north. The basal conglomeratic material was derived from the pre-existing Devonian and Triassic conglomerates exposed in the Dalradian ridge area. Fossils from sediments not known to be present in Ireland have been found within the basal conglomerate. Some of these specimens especially those of Middle Liassic age may have been swept in from the Mesozoic sedimentary basin a little to the NW. Away from the sediment source area pebbles are reduced in size with a reduction in the thickness of the conglomerate. In the extreme south much of the debris is fragmentary Cretaceous sediment and cobbles of the Island Magee Siltstones Member are not uncommon. It is to be expected therefore that pre-Senonian fossils will be present within the basal bed. In South Antrim the basal faunal assemblage contains typical Cenomanian forms. Their presence is considered to be the result of remani‚ emplacement. Tectonic controls have had a major effect on the preservation of these greensands. The basin of preservation was centred on the area to the south of Larne and sediments thin to the north and south. | |
| Conclusions: | |
The history of Cretaceous sedimentation in the Hibernian Greensands Formation of the Hillsport Basin is best seen at this site, the type locality for two members of the formation. It allows the relationships between tectonism and sedimentation to be demonstrated. The site should be conserved but would need to be cleaned up so that the sequence can be studied. | |
| Notes: | |
For general information on the Cretaceous System in N. Ireland see Key Site 1194 - The Cretaceous System in N. Ireland - Introduction. For information on other Cretaceous sites see Key Site 1207 - White Rocks - Cretaceous, Key Site 1208 - White Park Bay, Key Site 1209 - Dunnaglea-Larry Bane Bay, Key Site 1210 - Port Calliagh-Ballycastle, Key Site 1211 - Capecastle Quarry, Key Site 1212 - Garron Point-Cloghastucan, Key Site 1213 - Glenarm Quarry, Key Site 1214 - Creggan Quarry, Key Site 1215 - Portmuck, Island Magee, Key Site 1216 - White Head, and Key Site 1217 - Clarehill Quarry. | |
| Keywords | |
|---|---|
| Rocks: | Sand, Sandstone, Siltstone |
| Fossil Groups: | Belemnite, Brachiopod, Echinoderm |
| Fossil List: | Acanthoceras sp., Echinocorys sp. , Gibbithyris sp. , Inoceramus sp. |
| Relations: | Marine sediments |
| Access | |
|---|---|
| Approach: | West coast of Island Magee, 7km SE of Larne. Access to the site is from an abandoned farmhouse on the road leading to the quay. Then across fields to the western end of the cutting. |
| Management: | |
The exposure is very overgrown at present and could usefully be cleaned up and restored to the state when it was described as `presenting one of the finest sections'. | |
| References (5) | |||
|---|---|---|---|
| Fletcher, T.P., 1967. Correlation of the Cretaceous exposures of East Antrim. (Thesis) Unpublished M.Sc. Thesis, Queen's University of Belfast. | |||
| Hancock, J.M., 1961. The Cretaceous System in Northern Ireland. Quarterly Journal of the Geological Society of London, vol. 117, pp.11-36. | |||
| Hull, E., 1876. The country around Antrim, Larne and Carrickfergus. Memoirs of the Geological Survey of Ireland. | |||
| Hume, W.F., 1897. The Cretaceous strata of County Antrim. Quarterly Journal of the Geological Society of London, vol. 53, pp.540-606. | |||
| Tate, R., 1865. On the correlations of the Cretaceous formations of the NE of Ireland. Quarterly Journal of the Geological Society of London, vol. 21, pp.15-44. | |||
| Map(s): | GSNI (1994) 1:50,000 Geological Sheet 21 (Larne). | ||
| Record type: | ESCR report | ||
| Entered by: | E M Porter | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Kilcoan, Island Magee, County Antrim, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=1218. Accessed on 2026-11-06. |
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