Sedimentary structures and depositional environments

Gravel units All the units of waterlain, sorted gravel and sand repeatedly show suites of sedimentary structures that indicate deposition under broadly similar fluviatile conditions throughout the area. It is therefore possible, in general terms, to discuss the sedimentary sequences of deposits together. Previous investigations of the sedimentary structures of the gravel units have been presented in association with descriptions of fossiliferous fine sediment channel fills in gravels in neighbouring areas. For various reasons these have concluded that the sediments originated in a cold climate river depositional environment. However, detailed facies assemblage studies (e.g. Corner, 1975; Bryant, 1983a, b; Dawson, 1985; Dawson & Bryant, 1987) have not been presented for the Lower Thames region. In the same way as in the Middle Thames area (Gibbard, 1985), a generalised facies description is presented here for the gravel members, based on the sequences examined during this study. The sediments can be assigned to the braided or so-called wandering gravel river environment on the basis of facies models developed by Miall (1977, 1978). Individual gravel members may show minor deviations from the scheme. In addition, the facies descriptions can only be applied to those units that are exposed in large sections where the lateral and vertical relationships can unequivocally be observed.