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A geological model of the North Downs of Kent : the River Medway to the River Great Stour

Farrant, A.R.; Aldiss, D.T.. 2002 A geological model of the North Downs of Kent : the River Medway to the River Great Stour. Nottingham, UK, British Geological Survey, 39pp. (CR/02/310N) (Unpublished)

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Abstract/Summary

This report describes the geological modelling of the North Downs in Kent, between the River Medway at Chatham and the River Great Stour at Canterbury, and north to the Thames estuary. This work was co-funded by the Environment Agency to support an investigation of the local hydrogeology, with particular reference to maintaining spring flow in the North Kent marshes. Most of the area is underlain by the Upper Cretaceous Chalk Group. The Palaeogene Thanet Sand Formation, the Lambeth Group and the Thames Group occur in the north. The project included a desk study revision of the Chalk of the North Downs, using the new Chalk lithostratigraphy. The revisions to the geology are shown on the 1:50 000 scale geological map which accompanies this report. Together with evidence from boreholes and from seismic surveys, the new outcrop patterns have been incorporated into a geological model, using both computer software (earthVision) and manual methods. The introduction describes the background to the project. The subsequent chapter describes the sources for the data used in the model: published and unpublished geological maps, borehole records, seismic surveys, biostratigraphic collections and records, and the published literature. Each Chalk formation present in the area is briefly described, noting its relationship to the older lithostratigraphic divisions, and to biostratigraphic zones. The local Chalk sequence extends from the base of the Chalk Group to high in the Seaford Chalk Formation. The early Palaeogene formations (the Thanet Sand, the Upnor Formation, the Woolwich Formation and the Harwich Formation) and the major local superficial deposits are also briefly described. Apart from minor adjustments to the outcrop of the basal surface, no revision of these formations was done for this study. An account of the processes that led to the generation of the geological model includes notes on their inherent limitations, and on the criteria used to subdivide the Chalk according to the new lithostratigraphy. A discussion of the structure starts with observations on the kinds of influence exerted on the Chalk by tectonic structures, and on the difficulties of specifically identifying faults in the Chalk. Evidence for folding and faulting both subparallel to strike and subparallel to dip is described. Geological factors influencing the local hydrogeology are noted. It is likely that most groundwater movement in the Chalk occurs in the Seaford Chalk and the Lewes Chalk. There is a distinct possibility that a dual control constrains the position of the major spring-line at the northern foot of the North Downs: a relatively impermeable, clay-rich facies in the lower part of the Thanet Formation is combined with concentration of groundwater flow on north-north-east trending fracture zones within the Chalk.

Item Type: Publication - Report (UNSPECIFIED)
Programmes: BGS Programmes > Geology and Landscape Southern
Funders/Sponsors: Environment Agency
Additional Information. Not used in RCUK Gateway to Research.: This item has been internally reviewed but not externally peer-reviewed
Date made live: 22 Jan 2015 09:06 +0 (UTC)
URI: http://nora.nerc.ac.uk/id/eprint/509479

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