Structure of Lower Carboniferous basins of NW Ireland, and its implications for structural inheritance and Cenozoic faulting

The geometry of Lower Carboniferous basins across the northern part of Ireland is characterised by a gradual change in polarity of structure from a predominantly southward dipping fault system in Northern Ireland through the Lough Allen Basin and into a mainly northward dipping fault system of Connemara in the southwest. This polarity change is reflected in the emergence of northward facing uplifted footwall blocks, such as at Croagh Patrick and the Ox Mountains, in the southwest, with southward facing blocks in the northeast. Despite these structural changes, there is a great degree of along-strike continuity of Lower Carboniferous structure, strain and displacement, with the system forming a link between comparable sized and coeval basins in northern England and Scotland to the east and the Canadian Maritime Provinces to the west. The spatial distribution of Carboniferous normal faults suggests that Caledonian structure, such as the Fair Head-Clew Bay line, plays an important role in the localisation of Post-Caledonian strain, although the reactivation of individual Caledonian structures may be less common. The terrain of the west of Ireland is strongly influenced by major Carboniferous faults offsetting the base Carboniferous unconformity, as opposed to previously suggested Cenozoic normal faulting of a Tertiary peneplain.

► The geometry of Lower Carboniferous basins in NW Ireland was investigated. ► Polarity change from north to south-dipping Carboniferous faults across Ireland. ► Along-strike continuity of structure, strain and displacement across Ireland was observed. ► Structural inheritance and localisation of strain along Caledonian lineaments. ► Western Ireland terrain influenced by Carboniferous rather than Cenozoic deformation.