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Earth Science Conservation Review
| Castle Espie | Down |
| Site number: | 290 | File Number: | J46 |
| ESCC: | ED | ||
| Locality Type: | Lough Shore | Status: | ESCR |
| Grid Reference: | J4967 1 km square | ||
| Google maps: | 54.52988,-5.69835 | ||
| County: | Down | Council area: | Ards & North Down Borough Council |
| Period: | Carboniferous | ||
| Stages: | Brigantian, Visean | ||
| Lithostrat: | Castle Espie Limestone Formation | ||
| Site Description | |
|---|---|
| Highlights: | |
Carboniferous limestones of the Castle Espie Group formerly exposed at Castle Espie are the sole occurrence of late-Vis‚an strata in north Co. Down. The rocks are highly fossiliferous and rest unconformably on Lower Palaeozoic greywackes of the Down- Longford massif. | |
| Introduction: | |
The Carboniferous outcrop at Castle Espie is believed to cover an area of about 1km2 and is confined to the SW shore of Strangford Lough, 4km SE of Comber. According to the 6 inch field maps (Down 11SW) of the Geological Survey of Ireland (1867) only one natural outcrop of limestone was ever known (J494 672) towards the eastern end of the outcrop. Limestone was however formerly extracted from large quarries that were opened a short distance west of this exposure although even on the 1867 map these were described as "old limestone quarries" with the inference that they had, by this date, ceased operations. All of these quarries are now completely flooded and no limestone can be seen in situ although numerous blocks of rock, presumably quarry spoil, lie strewn on the ground close by and cover the seaward side of the seawall between the emergence of the Graffan Burn onto the lough shore and the Pier some 600m to the east. Location: The full extent of the coastal outcrop of Carboniferous rocks at Castle Espie, County Down is very poorly constrained but is believed to extend from the south side of the estuary of the Comber River (J478 678) south-eastwards for about 2km to J497 670 and to be about 600m wide on land. Because of the absence of exposures and of any additional information that might help define the boundaries of the limestone outcrop, the position of the sub-Carboniferous unconformity, with the lower Silurian Strangford Group, is taken as that defined in the original geological survey (1869). Bibliographic Review: With the exception of the geological maps and memoirs of the Geological Survey of Ireland (1869 and 1871) and the Geological Survey of Northern Ireland (1989 and 1991) no other research has been carried out on these rocks. General Geology: Because of the flooding of the limestone quarries at Castle Espie, our knowledge of the field relationships of the Castle Espie Group is restricted to those observations contained in the original geological memoir for this area (Hull et al., 1871). He described the limestone as red or salmon-coloured and finely crystalline in beds of variable thickness with layers and partings of light green shale being at the quarry thirty-five feet thick and at the engine shaft forty-one feet. In the quarry the limestones were seen to lie on "dark purplish red and green mottled shales" which were penetrated to a depth of nearly 2m without reaching either their base or the underlying Silurian rocks. Nevertheless Hull illustrated their conjectured field relationships as limestone and shale dipping north and resting unconformably on Silurian basement. In the absence of positive evidence it is equally possible that the Castle Espie Group is much thicker than Hull surmised. The paucity of limestone exposures in this area is quite understandable in view of the fact that the original survey geologists described the top limestone surface in the quarry as being overlain unconformably by a thin, but persistent, layer of horizontal soft, red Triassic sandstone (Sherwood Sandstone Group) and up to 52 ft (16m) of glacial drift. This relationship is depicted by G.V. duNoyer in the first geological memoir of the Newtownards area (Sheet 37; 1871, p.37). | |
| Description: | |
The only lithological information available was obtained from the abundant loose blocks of limestone and shale that occur on the foreshore and in the vicinity of the old quarries. The limestone are secondarily stained pale pink to red and are very coarse- grained crinoidal packstones/grainstones that frequently contain an abundance of Saccaminopsis fusulinaformis, all of which are infilled with clear calcite spar. Bioclast debris occurs in the limestones and comprises an abundant macrofauna dominated by brachiopods and coiled and orthocone nautiloids, with one incomplete specimen of the latter type attaining a length of over 70cm. Loose blocks of pale purple calcareous shale always contain abundant bioclast fragments, in particular of brachiopod spines and bryozoa and small abraded crinoid ossicles. The only macro- fauna recovered during the preparation of this report include a specimen of the small solitary coral Axophyllum vaughani Sal‚e, a long-ranging species found from the Holkerian to the early Brigantian and a trilobite pygidium. The precise age of the Castle Espie Group is however determined by the occurrence of abundant foraminifera including the following forms that are diagnostic of the Brigantian Stage: Asterarchaediscus sp. and Loeblichia paraammonoides. | |
| Interpretation: | |
There is little doubt that the late Asbian-early Brigantian Castle Espie Group rests directly on Lower Palaeozoic basement although its precise thickness, and age of the basal beds, is not known. Nevertheless these marine limestones are the youngest Carboniferous strata in Northern Ireland that rest on the Down-Longford massif. Although formerly much more extensive, a great deal of erosion clearly occurred in later Carboniferous and early Permian times (Variscan Orogeny) and, in many areas adjacent to the outcrop at Castle Espie, Permo-Triassic rocks succeed unconformably the Lower Palaeozoic basement. The precise shape of the depositional basin that these rocks were deposited in can only be guessed at; whether it occurred in a 'narrow', fault-bounded trough of only localised extent or was part of a regionally transgressing sea that affected all of, and probably submerged the last upstanding remnants (land area) of the Down-Longford massif, is not known. | |
| Conclusions: | |
Although there are no exposures of the Castle Espie Group in this area a great deal of information is known about these rocks and they are of significance in helping to reconstruct the palaeogeography of Northern Ireland during early Carboniferous times. | |
| Notes: | |
For information on other sites in Subarea-10 see Key Site 1183 - Subarea-10; North County Down. | |
| Keywords | |
|---|---|
| Rocks: | Limestone, Shale |
| Fossil Groups: | Brachiopod, Coral, Crinoid, Nautiloid, Polyzoan, Trilobite |
| Fossil List: | Axophyllum vaughani Salee, Saccaminopsis fusulinaformis |
| Relations: | Marine sediments |
| Access | |
|---|---|
| Approach: | The SW shore of Strangford Lough, 4km SE of Comber. |
| References (2) | |||
|---|---|---|---|
| Hull, E., Warren, J.L. & Leonard, W.B., 1871. Explanatory memoir to accompany sheets 37, 38 and part of 29 including the country around Bangor, Newtownards, Comber and Saintfield in the County of Down. Memoirs of the Geological Survey of Ireland. | |||
| Smith, R.A., Johnston, T.P. & Legg, I.C., 1991. Geology of the country around Newtownards Memoirs of the Geological Survey Northern Ireland, pp.42 PP. | |||
| Map(s): | Geological Survey of Ireland (1869) 1:63,360 Geological map of the Newtown Ards area (Sheet 37). Dublin. Geological Survey of Northern Ireland (1989) 1:50,000 Solid Geology of Sheet 37 and part of 38 (Newtownards). Belfast. | ||
| Record type: | ESCR report | ||
| Entered by: | Doughty, P.J. | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Castle Espie, County Down, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=290. Accessed on 2026-11-06. |
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