Earth:Cushendall Formation
| Cushendall Formation Stratigraphic range: Early Devonian | |
|---|---|
 Outcrop at Port Obe | |
| Type | Geological formation |
| Unit of | Cross Sieve Group |
| Underlies | Igneous porphyry |
| Overlies | Ballyagan Formation |
| Thickness | up to 600 metres (1,970 ft) |
| Lithology | |
| Primary | conglomerate, sandstone |
| Other | Rhyolite, basalt |
| Location | |
| Region | County Antrim |
| Country | Northern Ireland |
| Extent | Cushendun Bay and Cushendun Caves |
| Type section | |
| Named for | Cushendall |
| Named by | Simon |
| Year defined | 1984[1] |
The Cushendall Formation is a geologic formation of Early Devonian age in Northern Ireland where it outcrops at Cushendall, County Antrim.[2]
History
Surveys of Cushendall were undertaken in 1886 and it was concluded that the rocks were metamorphic in origin.[3] The first geological maps of the area were produced by Bailey & McCallien (1934),[4] and Wilson (1953) was the first to conclude the rocks were Early Devonian in age and he placed them into the Old Red Sandstone as a new, unnamed member.[5]
Simon (1984b) defined the Cushendall Formation as a separate geological formation when he defined the Cross Sieve Group.[1]
Geology and location
The Cushendall Formation is formed of rhyolite and basalt clasts overlain by conglomerate.[6] The age of the formation can not be dated any more precisely than the Early Devonian due to the lack of fossils preserved,[7] and it was part of the Cross Slieve Group in the Old Red Sandstone; it is believed it is the youngest of the three formations of the Cross Slieve Group.[1] It is underlain by intrusive igneous porphyry and the formation is up to 600 metres (2,000 ft) thick in places.[7]
The Cushendun Formation outcrops only at Port Obe, Cushendall on the northeastern section of Cross Slieve;[1] the northeastern section is dominated by the Cushendun Formation.[6]
Paleogeography
It is believed that the Cushendall Formation represented an alluvial environment which at some point experienced volcanic activity.[7][8]
References
- ↑ 1.0 1.1 1.2 1.3 Simon, J B. (1984b). Provenance and depositional history of the Lower Old Red Sandstone of northeast Antrim. Irish Journal of Earth Sciences 6, 213-228.
- ↑ "Cushendall Formation". https://webapps.bgs.ac.uk/lexicon/lexicon.cfm?pub=CDAL.
- ↑ Cushendall, Sheet 14 Geological Survey of Ireland, 1886
- ↑ Bailey, E.B. and McCallien, W.J. (1934): The metamorphic rocks of North-east Antrim. Transactions of the Royal Society of Edinburgh: Earth Sciences, vol. 58, pp.163-177
- ↑ Wilson, H. E. (1953): The petrography of the Old Red Sandstone rocks of the north of Ireland. Proceedings of the Royal Irish Academy, vol. 55, pp.283-320
- ↑ 6.0 6.1 "Cushendun Formation". https://webapps.bgs.ac.uk/lexicon/lexicon.cfm?pub=CCC.
- ↑ 7.0 7.1 7.2 "Devonian - Cross Slieve Group; Cushendun to Port Obe". https://www2.habitas.org.uk/escr/summary.php?item=1146.
- ↑ "Conglomerate, County Antrim". https://www.geolsoc.org.uk/ks3/gsl/education/resources/rockcycle/page4002.html.
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