The Pleistocene fluvial stratigraphy and palaeogeography of Essex

Abstract

Four main types of fluvial gravel aggradation are recognised in Essex, distinguished regionally, lithologically and by stratigraphic and altitudinal position. Firstly, deposits which are widespread in the northern and central parts of the county form part of the Kesgrave Sands and Gravels, which represent terrace aggradations of the pre-diversion Thames. A second type comprises the terrace gravels of the Lower Thames, which continue the history of the river after its glacial diversion into its modern valley through London. The third type, the High-level East Essex Gravel, comprises the degraded remnants of Medway deposits laid down by that river in eastern Essex at broadly the same time as the deposition by the Thames of the Kesgrave Sands and Gravels. Finally, a number of further aggradations, grouped together under the title Low-level East Essex Gravel, complete the terrace sequence in eastern Essex. These last deposits are of Thames-Medway origin, therefore representing a downstream continuation of the Lower Thames terraces. The change from Medway to Thames-Medway gravels in eastern Essex indicates that the glacially diverted Thames adopted the pre-existing valley of the Medway. This post-diversion route of the Thames-Medway was progressively modified in successive terrace aggradations, culminating in the pre-Flandrian buried valley which underlies the modern Thames estuary. The reconstruction of palaeodrainage and terrace stratigraphy in Essex promises to provide important links between the Quaternary sequences of the Thames basin and East Anglia.