The south Celtic Sea/Bristol Channel Basin: origin, deformation and inversion history

Abstract

The South Celtic Sea/Bristol Channel Basin is a relatively narrow and elongated sedimentary trough, located within the northern part of the Hercynian fold belt and filled with ?Permo-Triassic redbeds to Jurassic marine sediments. Its present configuration is the result of a three-fold sequence of tectonic phases initiated during the late Palaeozoic. The origin of the basin appears to be related to localised extensional reactivation of Hercynian thrust zones during the ?Permian and Early Triassic, followed by regional subsidence during the Late Triassic and Jurassic. Uplift of the basin margins, together with dextral strike-slip movements in an east-west sense and large-scale erosion during the Late Jurassic to Early Cretaceous, resulted in the present elongated configuration of the Lower Mesozoic basin. Regional subsidence from Aptian time onwards resulted in widespread deposition of a relatively thin section of Wealden elastics and Upper Cretaceous chalk, unconformably overlying folded pre-Cretaceous strata. Sedimentation was interrupted during the Early Tertiary by a series of tectonic events that included emplacement of the Lundy igneous mass during the Early Eocene and mild basin inversion during the Oligo-Miocene. Inversion was accompanied by dextral reactivation of the NW-SE oriented Sticklepath fault zone. The total amount of uplift, probably not exceeding 350 m, reflects the rather stable configuration of the underlying lithospheric crust as indicated by seismic reflection and refraction data.