Mid to Upper Viséan facies and palaeoenvironments of the Shannon Basin, Western Ireland

Abstract

The Shannon Basin, located in southwest Ireland, was a long-lived structure, with sediments accumulating there from earliest Tournaisian to late Bashkirian times (Carboniferous: Mississippian-Pennsylvanian). The basin is identified during the early Tournaisian only on the evidence of thickness changes. In late Tournaisian times, Waulsortian mudbanks developed across Ireland and reached an acme in terms of thickness in the area of the Shannon Basin. During the Visean, clear differences in carbonate facies developed between the basin and the surrounding shelf, exemplified by a southward passage from cyclic platform carbonates in the Burren area of County Clare, through carbonate mudmounds into basinal limestone sequences, which include breccias, evidence of local, perhaps fault controlled, slopes, and a conspicuous and widespread unit of striped limestones. The latter unit, a laminite, is late Visean in age and forms an important marker horizon across the basin.