Basinal subsidence history, constructed after corrections of sediment thickness for tectonic strain, suggests
Arenig stretching by a lithospheric dyking mechanism followed by thermal subsidence from Llandeilo to
Pridoli and load-induced flexural subsidence in the Lower Devonian. Sedimentary studies across the
basin margin faults augmented by palaeo-waterdepth estimates from volcanic evidence allow quantitative
refinement of this conclusion. Consideration of likely crustal and lithospheric thicknesses, constrained
by analysis of Middle Devonian basin inversion to a present-day 35 km crust, suggests an initial stretching
factor of about 2 with a normal crustal thickness and a somewhat attenuated lithospheric thickness
adjacent to the volcanic are to the NW.