Upper Carboniferous foreland basin evolution

Upper Carboniferous foreland basins of the Rhenohercynian and Sub-Variscan parts of the Variscan orogenic belt of SW Britain (Culm and South Wales Basins) developed during the structural inversion of previously thinned crust. The transition from an extensional (Middle Devonian-Lower Carboniferous) to compressional tectonic regime (Upper Carboniferous) occurred in early Namurian times and resulted in regional D1 basin inversion. In SW England a basic correlation existed between the thickness of Middle Devonian to Lower Carboniferous syn-rift sequences and the location of subsequent Upper Carboniferous sedimentation. Areas with thick syn-rift sequences such as the Trevone Basin and the North Devon Basin/Bristol Channel region emerged as topographic highs and acted as potential thrust loads as a result of inversion. In contrast, areas of thinner syn-rift sequences (beneath the Culm Basin) became relative lows and sites of subsidence following early Namurian compression. Uplift along the Bristol Channel Fault Zone (BCFZ)- a major Variscan thrust- took place from late Namurian into Westphalian times and resulted in emergence of a landmass which separated and sourced the Culm and South Wales Basins. E-W structures, active during sedimentation in the South Wales Basin are thought to represent Devonian-Lower Carboniferous extensional faults, reactivated during Dl shortening