Scribbagh
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Geology & landscape
Geological Feature: Rock Outcrop · Mining / Industrial: Quarry · Geological Period: Carboniferous · Rock Type: Breccia, Limestone, Shale
Description
Scribbagh Carboniferous stratigraphy Scribbagh is of significant geological importance. The limestones exposed at Scribbagh occur near the top of the Carboniferous Dartry Limestone Formation and the quarry exposes a suite of sediments that are unique in the outcrop of the Dartry Limestone in Northern Ireland. Near the base of the section is a thin palaeokarst horizon that contains an abundant fossil fauna and yields what is probably the most prolific fossil macrofauna at this level anywhere in the Dartry Formation. The former quarry at Scribbagh exposes 12m of strata, located near the top of the Dartry Formation. The bulk of the quarry face is composed of laminated dolomitic grainstones with limestone breccias, the latter commonly developed as lag deposits at the base of channel features in the grainstones. At the top of the face are thinly bedded bioclastic limestones. The greater thickness of strata is exposed in the main face of the quarry but the dip slope that occurs stratigraphically below this face on the west side of the site is of particular interest. The lowest 0.5m of rock on the west side consists of fawn-grey, pink-stained rubbly palaeokarst packstone in which the top 0.1m is intensely karstified, taking the form of a breccia. Overlying this are thin dark grey shales containing an abundant fossil macrofauna. This mainly consists of solitary corals, and more rarely goniatites an extinct group of ammonoids, brachiopods lampshells, orthocone nautiloids an extinct group of straight-shelled cephalopod and trilobites. The sedimentary features found at Scribbagh are indicative of very shallow marine conditions. At the base, the palaeokarst limestone and 'breccia' is produced by subaerial exposure but the origin of the prolific macrofauna in the thin shale is somewhat puzzling in view of the fact that most specimens are either abraded and broken or coated with a thin film of micrite. Both factors indicate a shallow water environment but the micrite coating is usually associated with hypersaline conditions, which would, under normal circumstances, not favour the development of a rich marine benthic community. It seems probable that all components of the macro-fauna are reworked and were subsequently transported into a shallow water environment. https://www.daera-ni.gov.uk/publications/scribbagh-assi