The lower Carboniferous (Chadian-Brigantian) geology of shallow marine carbonate rocks in the central and southeast Irish Midlands and the Wexford Outlier

This is the first comprehensive study, consisting of integrated petrographical, paleontological and geochemical analyses on the post-Waulsortian strata in the central and southeast Irish Midlands. This study reveals that the style of sedimentation and early diagenesis substantially influenced the late diagenesis, and the characteristics of Zn-Pb mineralization in the Rathdowney Trend. The study also demonstrates the fundamental difference in the style of sedimentation and tectonic history between the basins in the Irish Midlands and the Wexford Outlier.; Sedimentation of shallow marine carbonates and evaporites in the southeast Irish Midlands developed through various stages before achieving a typical shelf configuration. During the Late Chadian platform interior carbonate sandbodies and peritidal sediments with evaporites were formed within beach-barrier island - lagoonal depositional settings on a gentle sloping ramp, which evolved from the Tournaisian mixed siliciclastic-carbonate ramp. During the Arundian - Holkerian transgressive event, carbonate production on the ramp could keep up with the gradual subsidence and/or eustatic sea-level change, which lead to the regional deposition of shelf carbonates during the Asbian - Brigantian.; Analysis of the sedimentary strata in the Wexford Basin indicates that there was a strong tectonic influence on deposition. Reactivation of a former NE-SW-trending Caledonian structure (Wexford Boundary Fault) in response to NW-SE and N-S extension resulted in enhanced tectonic activity during the late Chadian. This event is analogous to tectonic episodes observed in the Dublin Basin and the northern English basins.; Viséan carbonate sediments and evaporites were affected by multiple diagenetic events. Cementation of limestones and dolomitization by modified seawater and refluxing hypersaline brines controlled porosity distribution in the carbonates. The early diagenetic fluids may have been involved in regional dolomitization of Chadian and possibly underlying Courceyan strata. They may also have been a source of high-salinity fluids associated with nearby base-metal sulfide deposits. The original textural and geochemical signatures of these carbonates were altered by late diagenetic dolomitization and precipitation of open space-filling dolomite, calcite, quartz, and fluorite associated with Zn-Pb sulfide mineralization.; The sedimentary sequences, deposited in the southeast Irish Midlands and Wexford Basin, indicate substantial differences in the style of sedimentological processes and basin evolution. The subsidence/exhumation history of the Wexford Basin suggests its close relationship with the Late Paleozoic - Mesozoic Irish Sea basins.