Geology of the Greywell area, Basingstoke, Hampshire

This report gives a brief account of the geology of the Greywell area near Basingstoke, Hampshire. The Greywell area lies approximately 8 km east-south-east of Basingstoke, and is located on the 1:50 000 scale geological map sheet 284 (Basingstoke). The area was last completely mapped during the six-inch survey of the Basingstoke district, which was published in 1897 (Figures 1 and 2). A partial revision of the Chalk outcrop was undertaken in 2007 by K A Booth, but did not include the Palaeogene outcrop. The published geological map is based on the 1897 six-inch survey of the Basingstoke district (Figures 1 and 2). Consequently the map does not show the new Chalk lithostratigraphy, nor is the bedrock related to modern topographical contours. Thus there is considerable uncertainty in the location of the Chalk- Palaeogene contact in the Greywell area. As part of a groundwater modelling investigation in the Whitewater River catchment, focussed on the Greywell pumping station, BGS was asked by the client (Jacobs Engineering) to undertake a partial revision of the Basingstoke geological map sheet around the Whitewater valley. The present survey was commissioned to obtain additional field data and combine that with borehole records and topographic data to provide a more accurate indication of the Chalk– Palaeogene boundary. The area between Up Nately, Greywell, North Warnborough and Odiham was resurveyed in mid September 2012 by A R Farrant, in particular focussing on the Chalk– Palaeogene boundary, including a zone up to 0.5 km either side of the contact. Superficial deposits were also mapped, but no additional boreholes or sections were excavated or logged. Existing BGS records including old field-slips, borehole records and historic maps, along with information on the Greywell Canal Tunnel from the Surrey & Hampshire Canal Society (see http://www.basingstoke-canal.org.uk/engineering/tunnels.htm) were also used in the compilation of the new line work. Fieldwork was undertaken by a standard walkover survey with a soil auger. The new line-work is shown in Figures 3, and also in Figures 5 and 6 at the end of the report.