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Abstract:
The Silverpit Crater consists of a set of concentric faults up to 20 km in diameter in the southern North Sea. Although formerly described as the first impact structure to be recognized in the UK, its spatial association with local tectonic and stratigraphic features suggests that it is unlikely to have been caused by a random extra-terrestrial event. This paper proposes a terrestrial origin for the Silverpit Crater as a Palaeogene pull-apart basin linked to strike-slip faulting in the Carboniferous basement. Faulting and thinning of Permian cvaporites underlying the crater acted as a buffer to basement extension and caused both a flexural collapse of the overlying Triassic strata and circumferential listric faulting in the Cretaceous succession. Reactive diapirism in Lower Jurassic shales may have contributed to the formation of a central uplift at base Cretaceous level. The paper compares the tectonic setting of two contemporaneous strike-slip-related structures in southern England (Bovey Basin in Devon and the Compton Valence structure in Dorset) with that of the Silverpit Crater, and concludes by briefly considering whether a pull-apart model can help to explain the formation of Upheaval Dome, a similar putative impact structure in the Canyonlands National Park of Utah.
Keywords: Silverpit Crater, Upheaval Dome, impact crater, strike-slip faults, salt tectonics.
The Silverpit Crater lies at a depth of 300-1500 m beneath the UK sector of the southern North Sea and consists largely of a set of closely spaced circumferential faults centred on UKCS Block 43/25 and extending to 20 km in diameter (Figs 1-3). The faults were first recognized at top Upper Cretaceous level on 3D seismic reflection data and have been attributed to deformation associated with the impact of an extra-terrestrial body during the Palaeocene (about 60 Ma) (Stewart & Allen 2002). Before its discovery, the Silverpit Crater was penetrated by two hydrocarbon exploration wells (43/24-3 and 43/25-1; O'Mara et al. 1999), but unequivocal evidence of impact in the form of shock-related metamorphic effects has yet to be obtained from the area. A key element in the impact interpretation is the presence of a cone-shaped uplift beneath the centre of the inferred crater. Best defined at base Cretaceous level, the uplift is c. 250 m high and 750 m across, and is cut by...