Abstract

New seismic reflection data from the Bristol Channel area provide direct evidence of a major Variscan thrust in the Palaeozoic basement beneath the Mesozoic Bristol Channel syncline. The thrust has an average southerly dip of about 25° and it rises into the major fault (the Central Bristol Channel fault zone, CBCFZ) at the northern margin of the Bristol Channel syncline. The CBCFZ is attributed to reactivation in extension of the Variscan thrust, probably during the early Cretaceous. There is no evidence for major synsedimentary movement on the CBCFZ, and the Bristol Channel syncline does not represent a rollover structure. Section restoration suggests that the CBCFZ has cut up through a previously tilted sequence of Triassic and Jurassic strata. Pervasive NNW–SSE cross faults are interpreted as original Variscan transfer faults that have been reactivated in the Mesozoic and Tertiary.