South-east Ireland: Lower Palaeozoic stratigraphy and depositional history

Four lithostratigraphical groups are distinguished in the Lower Palaeozoics of SE Ireland. The sand-dominant Lower-Middle Cambrian Bray Group consists of laterally-derived flysch. The conformably overlying, and perhaps in part time-equivalent, mud-dominant Middle Cambrian-Llandeilo Ribband Group comprises axially-transported flysch with minor volcanics. Due to tilting and subsequent differential erosion of these trough sediments, the overlying mainly Caradoc Duncannon Group rests unconformably on the Ribband Group except in the west where there is a conformable passage. The Duncannon Group is a highly faulted, predominantly volcanic, platform sequence with local basal calcareous beds. In the northwest of the district, the Bray and Duncannon Groups are absent and a continuous period of flysch sedimentation is reflected by the upward passage of lower Ordovician Ribband Group sediments into sand-dominant turbidites of the Kilcullen Group (lower Ordovician to at least Llandovery). In contrast, the Slievenamon inlier in the southwest contains Ribband Group strata of Upper Cambrian age which palynological evidence suggests are separated by a major stratigraphical break from the entirely Silurian Kilcullen Group. In the Comeragh Mountains to the south, the Kilcullen Group is conformably underlain by the Ribband and Duncannon Groups. These features point to large-scale irregularities within the Leinster Basin, the main Lower Palaeozoic palaeogeographical feature of SE Ireland.