An Eifelian U-Pb zircon date for the Enagh Tuff Bed from the Old Red Sandstone of the Munster Basin in NW Iveragh, SW Ireland

Abstract

The first geochronological data from the Minister Basin (SW Ireland) contradict the accepted biostratigraphical maximum age (late Givetian-early Frasnian) of the oldest alluvium in the basin depocentre. Magmatic zircons from the Enagh Tuff Bed, a sub-plinian air-fall tuff within fluviatile Old Red Sandstone of NW Iveragh, give a Pb/Pb isotope age of 384.9 ± 0.7 Ma. This confirms Middle Devonian (probably Eifelian) sedimentation and allows possible Early Devonian basin initiation. Associated second-cycle gravels suggest a pre-385 Ma minimum age for the Caherbla Group of the Dingle Basin. Correlation with alluvium containing tetrapod trackways indicates a pre-385 Ma age for the trace maker.