Mesozoic structural evolution of the UK Southern North Sea: insights from analysis of fault systems

Abstract

An understanding of the Mesosoic fault systems in the UK Southern North Sea is important in modelling the burial history of source and reservoir rocks, in determining the time of formation of structural traps in the Permian and older section and in mapping seismic velocity fields in Mesozoic rocks for accurate time to depth conversion.The evolution of Mesozoic fault systems in the Southern North Sea can be understood by examination of several faults with different amounts of movement across them, and by analysis of fault patterns. Structural analysis has been undertaken in selected areas where complications due to salt movement are minor. Local fault analysis is illustrated by balanced cross-sections and maps from Blocks 49/28,48/23 and 48/11. The faults studied are shown to have been active extensional faults during the Jurassic and early Cretaceous, but have in general undergone only limited movement during later Cretaceous and Tertiary phases of subsidence and uplift.The Mesozoic faults are detached from basal Permian and Carboniferous rocks by decollement in the Zechstein evaporites and are linked by transfer zones to form a basin-wide system of faults. Mesozoic fault systems overlie zones of weakness in pre-Zechstein rocks, but are not directly connected to them, so their orientation is controlled by Mesozoic forces rather than pre-existing structural grain.