Largy Quarry
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Geology & landscape
Geological Feature: Rock Outcrop · Mining / Industrial: Quarry · Geological Period: Carboniferous · Rock Type: Conglomerate, Granite, Mudstone, Sandstone
Landscape processes: Fluvial, Volcanic / Igneous
Description
Largy Quarry Carboniferous stratigraphy The area is of special scientific interest because of its important geology, which is found at outcrop in a quarry on the north east side of Largy hill. The rocks exposed are of Carboniferous age, some 320 million years old. The outcrop consists of interbedded sandstone, mudstone and conglomerates from the Ballyreagh Conglomerate Formation of the Kilskeery Group. Coarse grained pale grey, pink-brown arkose like sandstones are the predominant lithology in the quarry. The sandstones are interbedded with mudstones, pebbly sandstones and fine to coarse, matrix supported conglomerates. The beds exposed in the quarry are dipping at 20° to the north west. The sandstone beds exhibit low angle planar cross lamination and sand filled desiccation cracks are observed in the mudstone beds. The conglomerate and pebbly sandstones contain a range of clasts, notably dominated by Lower Palaeozoic greywacke. Other clast lithologies include trachyandesite, quartz, rare granite and reworked contemporaneous mudstone and sandstone. Rocks of the Kilskeery Group were originally deposited as sediment in a subsiding, non marine sedimentary basin. There is evidence that two basins developed at the same time, separated by a topographic high composed of metamorphic and Lower Palaeozoic sedimentary rocks. The Ballyreagh Conglomerate Formation, exposed in Largy Quarry, was deposited in the southern of these two basins. Increased uplift during the early Brigantian Stage of the Carboniferous, led to increased erosion of the central high, producing alluvial fans that prograded south depositing the coarse grained sandstones and conglomerates of the Ballyreagh Conglomerate Formation. https://www.daera-ni.gov.uk/publications/largy-quarry-assi