Carbonate facies and biostromal distribution in a tectonically controlled platform in northwest Ireland during the late Viséan (Mississippian)

SUMMARY The North–West Carboniferous Basin (NWCB) contains a c. 3 km-thick succession of Mississippian (Courceyan to Arnsbergian) limestone, mudstone and sandstone, mostly of marine origin. The litho- and biostratigraphy of some sections in the basin are revised and new logged sections described in upper Visean, limestone-dominated platform successions. In the O’Donnell’s Rock area, a precise correlation of the Glencar Limestone Formation with the lower part of the Bricklieve Limestone Formation, and the Dartry Limestone Formation with the upper part of the Bricklieve Limestone Formation is confirmed. Consequently, in late Visean (Asbian) times the NWCB developed as an extensive (>12,000 km 2 ) carbonate platform, in which sediments of the facies typical of outer, middle and inner parts of the platform were deposited. The Asbian rocks of this platform contain abundant solitary and fasciculate rugose corals, with laterally persistent biostromes dominated by different species of Siphonodendron . Evidence of regional uplift and subaerial exposure occurs at the top of the Dartry Limestone/Bricklieve Limestone formations, especially in the northern half of the platform. The base of the succeeding Meenymore Formation is defined by a change from marine limestone below an erosional disconformity surface, to sediments deposited on a sabkha and in supra-tidal–peritidal facies. Evolution of the platform was controlled, in part, by syn-sedimentary faults, which allowed different thicknesses of sediment to accumulate. Between the margins of the NWCB there existed a turbid carbonate platform with relatively shallow to moderately deep water characterized by impoverished microfaunal assemblages. The platform margin extended SE into deeper water facies of the Dublin Basin.