New constraints on the timing of late Carboniferous-early Permian volcanism in the central North Sea

The Permo-Carboniferous evolution of the central North Sea is characterized by three main geological events: (1) the development of the West European Carboniferous Basin; (2) a period of basaltic volcanism during the Lower Rotliegend (latest Carboniferous-early Permian); and (3) the development of the Northern and Southern Permian Basins in late Permian times. The timing of the late Carboniferous-Permian basaltic volcanism in the North Sea is poorly constrained, as is the timing of extensional tectonic activity following the main phase of inversion during the Westphalian, due to the diachronous propagation of the Variscan deformation front. Results of high precision Ar-Ar dating on basalt samples taken from a core from exploration well 39/2-4 (Amerada Hess) in the UK sector of the central North Sea suggests that basaltic volcanism was active in the late Carboniferous, at c. 299 Ma. The presence of volcanics below the dated horizon suggests that the onset of Permo-Carboniferous volcanism in the central North Sea commenced earlier, probably at c. 310 Ma (Westphalian C.). This is contemporaneous with other observations of tholeiitic volcanism in other parts of NW Europe, including the Oslo Graben, the NE German Basin, southern Sweden and Scotland. Interpretations of available seismic data show that main extensional faulting occurred after the volcanic activity, but the exact age of the fault activity is difficult to constrain with the data available.