Earth Science Conservation Review
| Cloghany pothole, Beighy Townland | Fermanagh |
| Site Type: | Pothole |
| Site Status: | ASSI |
| Council area: | Fermanagh District Council |
| Grid Reference: | H161302 |
| Google maps: | 54.22094,-7.75316 |
| Rocks | |
|---|---|
| Rock Age: | Carboniferous (Asbian, Visean) |
| Rock Name: | Cloghany Limestone Member, Dartry Limestone Formation |
| Rock Type: | Limestone, Shale |
| Interest | |
| Fossil Groups: | Foraminifera |
| Other interest: | Marine sediments |
Summary of site:
This record is of the type locality or stratotype of the Cloghany Limestone Member of the Dartry Limestone Formation. It is defined from a complete section seen in a minor karst pothole in this area, Cloghany Pot.
In this section the full thickness is 1.3m, commencing with 30cm of flaky, blue-grey shale and a thin, knobbly limestone full of broken fossil fragments, resting directly on the well bedded, cherty limestone of the typical Dartry Limestone beneath. The top of the shale is burrowed. Above them is a limestone bed 1m thick. It is grey with coarse fragments of crinoid (sea lily) plates in fine carbonate sand cemented with calcite. This limestone contains a rich fauna of the microscopic shells of foraminifera. The fourteen species identified imply a late Asbian age for the rock, around 337 million years ago.
The total area of outcrop of this member is little more than 2kmē, mostly a thin surface skim in the stratotype area but with sections exposed in the walls of the lower Owenbrean River before it sinks into the cleft of Pollasumera. It is around 1m thick wherever it is seen.
These rocks were formed in a shallow, tropical sea, at first with little or no sedimentation, allowing burrow feeding or inhabiting invertebrate animals to excavate deeply into the mud, stirring it up in the process. Immediately afterwards, lime shelled animals colonized the seabed which was now swept by strong currents leaving only carbonate grains behind.
This highly diagnostic member is an important marker horizon in this area, particularly useful for recognition of the top of the Dartry Limestone Formation. The stratotype in the pothole is not threatened but should be formally protected because of its unique status.
In this section the full thickness is 1.3m, commencing with 30cm of flaky, blue-grey shale and a thin, knobbly limestone full of broken fossil fragments, resting directly on the well bedded, cherty limestone of the typical Dartry Limestone beneath. The top of the shale is burrowed. Above them is a limestone bed 1m thick. It is grey with coarse fragments of crinoid (sea lily) plates in fine carbonate sand cemented with calcite. This limestone contains a rich fauna of the microscopic shells of foraminifera. The fourteen species identified imply a late Asbian age for the rock, around 337 million years ago.
The total area of outcrop of this member is little more than 2kmē, mostly a thin surface skim in the stratotype area but with sections exposed in the walls of the lower Owenbrean River before it sinks into the cleft of Pollasumera. It is around 1m thick wherever it is seen.
These rocks were formed in a shallow, tropical sea, at first with little or no sedimentation, allowing burrow feeding or inhabiting invertebrate animals to excavate deeply into the mud, stirring it up in the process. Immediately afterwards, lime shelled animals colonized the seabed which was now swept by strong currents leaving only carbonate grains behind.
This highly diagnostic member is an important marker horizon in this area, particularly useful for recognition of the top of the Dartry Limestone Formation. The stratotype in the pothole is not threatened but should be formally protected because of its unique status.
| Enlander, I., Dempster, M. & Doughty, P., 2024. Cloghany pothole, Beighy Townland, County Fermanagh, site summary. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/summary.php?item=193. Accessed on 2024-12-26 |
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