Structural and tectonic setting of the Permo-Triassic basins of northwest Europe

The Permo-Triassic basins of NW Europe formed by (i) late-orogenic spreading of the Variscan mountain belt, eventually leading to ocean floor formation in the Mid-Atlantic, (ii) continental rifting propagating south from the Arctic and (iii) thermal subsidence following Carboniferous volcanic activity in the North Sea. Spreading values in the northernmost North Sea, west of Shetland and west and southwest of Britain, are relatively high but the sediments are dominantly continental; the Permo-Triassic rifting affected lithosphere thickened during Caledonian and Variscan orogenesis. However, subsidence associated with the Arctic rifting, together with global sea level changes, allowed marine incursions into the North Sea, producing the large Zechstein salt basins. Interference of the different basin formation mechanisms led to a complex three dimensional fault pattern and multidirectional extension across Britain and the North Sea. This fault pattern formed the basic framework for subsequent Jurassic and Cretaceous basin formation.