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Ederny QuarryFermanagh
South face and SW wall of Ederny Quarry, Co. Fermanagh; inclined S face is fault plane of Aghaleague Fault; limestones of Crockanaver Limestone Member in SW wall show rollover anticline and synclinal fold caused by fault movement.
Summary Full report
Site Type: Quarry (disused)
Site Status: PASSI
District: Fermanagh District Council
Grid Reference: H224641
Rocks
Rock Age: Carboniferous (Arundian, Visean)
Rock Name: Ballyshannon Limestone Formation, Bundoran Shale Formation, Crockanaver Limestone Member, Dromore Sandstone Member, Ederny Limestone Member, Mullaghmore Sandstone, Skea Sandstone Member, Tyrone Group
Rock Type: Limestone, Sand, Sandstone, Shale
Interest
Fossil Groups: Bivalve, Brachiopod, Crinoid, Echinoderm, Gastropod, Polyzoan, Trilobite
Other interest: fault, Marine sediments

Summary of site:

When a rock formation is named, it is usually defined from one exposure, normally where it is most typically developed and its base can be identified. Such localities are called ‘stratotypes’ and the significance of the Ederny Quarry site is centred on the Ederny Limestone Member for which it is the stratotype. It is therefore the standard of comparison for all other outcrops of the member. The very top of the Ballyshannon Limestone Formation and the base of the overlying Bundoran Shale Formation are exposed in the quarry and the Ederny Limestone is the last member of the Ballyshannon Limestone. Its top marks the base of the Bundoran Shale.

The thickness of the Ederny Limestone varies between 2.5m and 5.5m but in the stratotype section, at the north-west edge of the quarry, it is 4.8m thick. It is a pale to medium grey, rubbly and nodular, micritised limestone with wisps of clay. Micritisation is the reduction of a coarse grained limestone to fine particles either by the action of bacteria or certain types of filamentary algae (plants) soon after formation, but in this case it appears to have been due to a chemical change caused by the flow of calcareous (lime-rich) brine through the sediment. No trace of the original fabric of the rock or its fossils is preserved. The effect of the brine is confined to the Ederny Limestone by a 15cm shale bed immediately below it. The coarse grained limestone immediately beneath is unaffected. The top of the Ederny Limestone in the type section is immediately below 18cm of laminated, pale green, yellow and brown clay with flecks of mica that are not seen elsewhere in the quarry. 1.4m of medium grey, gritty limestone follow, full of crinoid ossicles and brachiopod fragments. This is the Skea Sandstone Member, defining the base of the Bundoran Shale Formation. Shaley mudstones above these are rich in fossils, particularly bivalve molluscs, brachiopods, bryozoa and sea urchin spines. Despite its relative thinness, the Ederny Limestone covers an area of 300km˛ and is the top of a sequence of rocks in the Ballyshannon Limestone that become progressively finer from base to top. This indicates a shallow sea, a marine basin steadily filling with sediment. The purity of the limestone with no contamination of sediment from the land (such as sand, grit or shale) also implies deposition at some distance from shore, and the thin coloured clays on top of the member at the stratotype could represent the final settling of very fine sediments. The Skea Sandstone at the base of the succeeding Bundoran Shale Formation is obviously marine in this area, still some distance from land, but elsewhere it is a sand fan with clear evidence of emergence above sea level. As a stratotype, the section of the Ederny Limestone Member of the Ballyshannon Limestone Formation is an essential component of the geological history of Northern Ireland and should be preserved. The stratotype also clearly shows the relationship with the overlying Bundoran Shale Formation. The main threat, as in all disused quarries, is of dumping.


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