Influence of salt on fault geometry: examples from the UK salt basins

Abstract

Abstract The influence of salt layers on cover faulting during thick-skinned extensional faulting is examined using seismic examples from the salt basins offshore UK. The ratio of salt layer thickness to basement fault displacement is a key geometric parameter governing spatial offset between cover and basement fault segments. The influence of geological factors such as stratigraphic variation in salt thickness, basement fault zone geometry and basement fault growth through time on this parameter are individually examined. 3D models are constructed to illustrate the spectra of possible fault geometries which result from variations in these factors. Lateral stratigraphic variations within individual ‘salt’ layers are also considered, as are complications introduced by the addition of further salt layers into cover stratigraphy. Since diapiric intrusions occur after cover fault geometries are established and are localized by such faulting, an understanding of basement-cover fault relationships also illuminates salt diapir-basement fault relationships. An example from the Central North Sea diapir province is subject to such a genetic analysis, relating the diapir and its location to an underlying basement fault. The influence of salt on cover fault reactivation during basin inversion is discussed, focusin on the southern North Sea, where inhibition of reverse fault propagation from basement to cover is noted. It is suggested that analysis of local basement-cover relationships should form a first step in any attempt at a genetic classification of salt bodies.