Early to mid-Cretaceous tectonics and unconformities of the Wessex Basin (southern England)

Abstract

Sediment distribution patterns, time-subsidence plots, seismic data and outcrop analysis of the Lower Cretaceous (?Ryazanian-Albian) of the Wessex Basin, southern England, suggest that a number of unconformable horizons exist and that there is no single ‘late Cimmerian unconformity’ surface. A tectonic change, from areally restricted deposition in the Weald and Channel sub-basins to extensive sedimentation across the whole of southern England, began in the mid-Aptian. This change ended with transgression of basement ‘highs’ in the early Albian of the Dorset area, and later Albian of the Devon and London Platform basin margin areas: its onset can be linked to the Austrian tectonic phase of Europe. The onset of marine deposition in the Aptian is coincident with periodic transgression of the margins of the Wessex Basin throughout the Aptian-Albian. Mid-late Aptian and early/mid-AIbian transgressions were preceded by periods of erosion. The Aptian-Albian Lower Greensand is characterized by transgressive-regressive phases, suggesting a short-term controlling process (third-order eustatic changes or intra-plate mechanisms). Tectonic changes in the mid-Aptian include uplift followed by widespread subsidence. This change coincides with a time of plate reorganization in the European and North Atlantic areas.