Ballagh
Also within
Geology & landscape
Geological Feature: Rock Outcrop · Mining / Industrial: Quarry · Geological Period: Carboniferous · Rock Type: Limestone, Shale
Description
Ballagh Carboniferous Stratigraphy Ballagh is of importance because of its geology. Specifically the site is the stratotype for the Ballagh Limestone Member, a new lithostratigraphical unit within the Carboniferous Dartry Limestone Formation. The Ballagh Limestone Member is also the uppermost member within the Dartry Limestone Formation. The Ballagh Limestone Member is partially exposed in this former quarry. While it is not possible to define the full thickness of the Ballagh Limestone here due to limited exposure, it still provides the most accessible section of this geological unit. In outcrop the limestone consists of very coarse-grained crinoidal grainstone. Other bioclastic material forms only a small part of the rock and consists of tiny fragments of brachiopod shells. Bedding is massive with crude internal laminations produced by grain size variations. No fossils diagnostic of the age of this limestone have been recovered from this site. The very fine-grained limestone that forms the bulk of the Dartry Limestone Formation appears to reflect deposition in relatively deep water of low energy. The occurrence of the Ballagh Member, near the top of the Dartry Formation, could be an indication of an episode of turbulent conditions in a shallow water environment. This is problematic in terms of sudden bathymetric shallowing followed equally abruptly by a return to deep water, anoxic conditions as evidenced by the black, ferruginous shale that rests directly on top of the Ballagh Member elsewhere in the wider area. It is thought that the material forming the Ballagh Limestone was initially deposited in relatively shallow water but subsequently transported downslope into a deep water location. https://www.daera-ni.gov.uk/publications/ballagh-assi