Edernery Quarry
Also within
Geology & landscape
Geological Feature: Geological Fault · Mining / Industrial: Quarry · Geological Period: Carboniferous · Rock Type: Limestone, Sandstone, Shale
Description
Ederney Quarry Carboniferous stratigraphy, Structural The area is of special scientific interest because of its important geology. Edemey Quarry exposes rocks from the Tyrone Group of early Carboniferous age, about 345 million years old. The site includes the type locality of the Edemy Limestone Member of the Ballyshannon Limestone Formation. The basal beds of the Bundoran Shale Formation and the plane of the Aghaleague fault and associated folding are also exposed in the site. The Edemy Limestone Member is found at the floor level at the north end of the quarry, the type locality being located on the north west corner of the site. The Edemy Limestone reaches 4.8m thickness here and it is typically pale to medium grey, rubbly and nodular, poorly bedded micritised limestone. It is directly underlain by a thin shale bed and grainstones and packstones of the Crockanaver Limestone Member, and overlain by a band of pale green-yellow-brown clay. Succeeding this clay horizon is a 1.38m thick bed of medium grey, sandy limestone containing crinoid ossicle debris and fragments of brachiopods. This is exposed on both sides of the quarry and is the local, distal representative of the Skea Sandstone Member, the basal unit in the Kesh-Omagh area of the Bundoran Shale Formation. Above this bed are about 1.3m of grey shaley mudstones with thin, calcareous bioturbated sandstones and very thin sandy limestones containing bivalves, brachiopods, bryozoa and echinoid spines. These are only exposed at the top southeast corner of the quarry and represent the basal beds of the Bundoran Shale Formation. The rock sequence at Edemey Quarry records a series of depositional environments in a shallowing upward sequence. The available evidence suggests micritisation of the top few metres of the Ballyshannon Limestone, and the distinctive Edemy Limestone Member, occurred by the percolation of carbonate rich brines through the bedrock. The extent of downward micritisation appears to have been controlled by shale horizons; at the Edemy stratotype, the Crockanaver Limestone is capped by a shale bed and has not been micritised. This is believed to have occurred in very shallow water as there is no evidence of subaerial exposure of the Ballyshannon Limestone. Asymmetrical uplift of land areas to the north of the Kesh-Omagh area resulted in the erosion of coarse debris and inundation of the shallow sea by coarse clastic sediment, the Skea Sandstone Member. In Edemey Quarry this member is represented by a quartz-bearing crinoidal limestone, representing a truly marine shelf deposit beyondthe distal extremity of the depositional fan of the Skea Sandstone. Increasing water depths accompanying the regional transgression at the base of the Bundoran Shale resulted in the disappearance of coarse clastic sediment as the coastline moved northwards. Sediment then changed to mud and silt grade particles, with an abundant marine benthos. The exposed plane of the Aghaleague Fault forms the southern face of Ederney Quarry. The plane of the fault trends NE-SW and dips at about 500 towards the north-west. This structure was originally Caledonian in age part of the regionally important Castle Archdale Fault Zone and was reactivated during the Variscan Orogeny. On the south west face of the quarry, there is a rollover anticline and synclinal fold formed through reverse movement in the hanging wall of the Aghaleague Fault. This is taken as evidence of the compressive nature of the Variscan deformation. https://www.daera-ni.gov.uk/publications/ederney-quarry-assi