Inversion, reactivated faults and related structures: seismic examples from the southern North Sea

Summary This study examines the geometry and timing of inversion features in offshore Quadrants 53/54 of the UKCS. The area studied lies south of the Zechstein salt basin and is dominated by two major and temporally-persistent structural elements, the Wales-Brabant Massif (in the SW of the area) and the South Hewett Fault (in the centre of the area). The Wales-Brabant Massif is a stable basement block, flanked to the north by an inverted Triassic basin. This Triassic basin in turn forms the footwall block to the South Hewett Fault. NE, and locally SW, of the South Hewett Fault lies a series of Jurassic tilted fault blocks symmetrically disposed about a central ‘keystone’. These central blocks contain no synextension sediment fill and are interpreted as outer-arc extensional structures parasitic on a large wavelength uplift produced by an underlying thermal anomaly. All major structural features lying to the NE of the Wales-Brabant Massif were inverted during the late Cretaceous. This inversion produced forced folds in the cover rocks above deeper basement faults, and harpoon-shaped structures at the sites of earlier rotational half-grabens. This account considers the effects of both this late Cretaceous inversion and a succeeding period of inversion during the Miocene on earlier extensional structures.