Age and significance of the Old Red Sandstone around Clew Bay, NW Ireland

Abstract

The stratigraphy of red bed successions in the Clew Bay area of County Mayo (Ireland) is described, and new palynological evidence for the age of some of the rocks is presented. The Old Red Sandstone in the Clew Bay area comprises several lithostratigraphic units. The Louisburgh succession is interpreted as part of a Silurian marginal marine sequence. Devonian strata are represented by the Islandeady Group which has yielded plant spores which suggest that these rocks should be assigned to the Lower Devonian (Siegenian to Emsian) and the Beltra Group which contains Middle Devonian (Eifelian) spores. These Lower and Middle Devonian strata are probably separated by an unconformity, and are overlain with clear unconformity by the highest unit, the Maam Formation, which is Dinantian (Carboniferous) in age. The Clew Bay Old Red Sandstone succession, therefore, shows important differences from that of the Midland Valley of Scotland, with which it has previously been compared.