Difference between revisions of "Geology of the Andover area: Exposed strata - Upper Greensand Formation"
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Revision as of 12:47, 7 July 2014
|This page is part of a category of pages providing a summary of the geology of the Andover district (British Geological Survey Sheet 283), which extends over approximately 600 km2 of north-west Hampshire and a small part of eastern Wiltshire. Links to other pages in this category can be found at the foot of the page.
Authors: J Thompson, K A Lee, P M Hopson, A R Farrant, A J Newell, R J Marks, L B Bateson, M A Woods, I P Wilkinson and N J Smith.
This formation consists of pale, yellow-brown, grey and greenish grey, bioturbated siltstone and silty, very fine-grained sandstone, with variable amounts of mica and glauconite. In places the formation is indurated to form a ‘malmstone’ and there are common occurrences of grey and brown colloidal silica chert within the higher part of the succession.
During the recent survey of the Andover district the component members of the formation recognisable in other districts could not be identified consistently and as a result the Upper Greensand Formation is shown as a single unit.
The unit thickens from about 34 to 40 m in the north of the district and about 45 m in the south to over 70 m in the centre of the region.
In the Andover district, the Upper Greensand Formation forms the oldest unit at outcrop. It is present in the north-eastern and north-western corners of the district within the core of the Kingsclere Anticline and in the closure of the Pewsey Vale Anticline respectively.