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Earth Science Conservation Review
| Cloghan Head - site of local interest | Down |
| Site number: | 713 | ||
| Locality Type: | Coastal section, Foreshore | Status: | local interest |
| Grid Reference: | J578387 Centroid | ||
| Google maps: | 54.27321,-5.57757 | ||
| County: | Down | Council area: | Newry, Mourne & Down District Council |
| Period: | Silurian | ||
| Lithostrat: | Ardglass Formation | ||
| Site Description | |
|---|---|
| Highlights: | |
The coast at Cloghan Head exposes a section through the Silurian Ardglass Formation with well-developed sedimentary structures, several well-developed bentonite horizons and several lamprophyre intrusions. | |
| Description: | |
The Ardglass Formation is the thickest and most unvaried succession of the Silurian distal turbidites within Lecale and comprises a monotonous repetition of 2-50cm thick grey, or greenish-grey greywacke-siltstones, parallel- and current-laminated flaggy siltstones and well cleaved shales. The sediments are markedly calcareous. Within coastal exposures of the formation, sedimentary structures are well preserved including delayed graded lamination, sole markings, flute moulds, chevron moulds and rilled tool marks. At Cloghan Head, climbing ripple drift cross-lamination, arcuate ripples and sand volcanoes are well preserved on the upper surfaces of several beds. The sand volcanoes are elongated with the elongation being interpreted as tectonic. A 13cm thick primary red bed unit can be seen, one of only two localities within the Ardglass Formation where such horizons are seen. Metabentonites are abundant at Cloghan Head with a multiple unit occurring. This unit consists of four metabentonite seams, ranging from 0.1-1.5cm thickness, separated by thin siltstone beds. This has been interpreted by Cameron (1977) as representing repeated interruption of the deposition of a single ash fall by discrete turbidite flows and implies a low rate of bentonite sedimentation. Lamprophyre dykes are also exposed at Cloghan Head. One multiple intrusion, some 2m across, has well-developed joints at its edge and parallel to its margins. Furthermore the central surface of the dyke is pitted. The intrusion lies just below Saint Patrick’s Holy Well [J577 388] and is known locally as Saint Patrick’s Causeway. | |
| Importance: | |
The site is of limited significance scientifically though the sequence does provide sedimentological evidence for the environment of deposition of the Ardglass Formation. | |
| Notes: | |
The site has some cultural significance as the multiple dyke is associated with the nearby Holy Well and, through it, with Saint Patrick. | |
| Keywords | |
|---|---|
| Rocks: | Greywacke, Shale, Siltstone, Turbidite, Bentonite, Lamprophyre |
| Structures: | cross-bedding, dyke, ripple marks, graded bedding, sole marks |
| Access | |
|---|---|
| Approach: | This site is located 3km northeast of Ardglass. |
| Uses | |
| Educ. Level: | The site is of educational significance as the relatively small section provides good examples of several sedimentological, igneous and structural features. |
| Record type: | SLNCI Report | ||
| Entered by: | E M Porter | ||
| Last updated: | 09/10/03 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Cloghan Head - site of local interest, County Down, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=713. Accessed on 2026-11-06. |
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