A storm-dominated offshore sandstone interval from the Corallian Group (Upper Jurassic), Weald Basin, southern England

Abstract

The Upper Jurassic Corallian Group of the subsurface of the Weald Basin, southern England, contains two stacked marine sand bodies. They have an elongate geometry (9–25 m thick, 100 km long, 30 km wide) and consist predominantly of cross-bedded, fine to medium grained, glauconitic sandstones with bioturbated, low angle cross-laminated silty sandstones. The sandbodies trend east-west, subparallel to the palaeoshoreline, but oblique with respect to the south-easterly palaeocurrent direction. In general, facies are stacked in progressively upward-coarsening sequences with lower clays passing up into bioturbated siltstones, followed by various types of cross-bedded, medium grained sandstones. The characteristics and distribution of the lithofacies indicate that these sandbodies are not shoreline deposits. However, they are strikingly like offshore sand ridges widely documented from the Cretaceous Western Interior seaway of North America. The lack of any typical features of tidal sandbodies and the common occurrence of erosively based, low angle cross-lamination resembling hummocky cross-stratification in the lower part of the coarsening upwards sequences indicate that storm currents may have been important in generating the Corallian offshore sandbodies.