The Geology of Oliver’s Battery – by Dr Tom Gernon

Oliver’s Battery is situated on a chalk ridge that forms part of an undulating landscape characteristic of the West Winchester Downs.

HCC’s Integrated Character Assessment (HICA, 2010) defines the area as consisting of open downland, mixed (some ancient) woodland, scenic chalk ridges and downland scarps (e.g. the adjacent Hursley Scarps), dry valleys and dispersed settlements. Oliver’s Battery occupies one of a chain of north east to south west trending chalk hills within this character area, having a maximum elevation of approximately 125 metres in the north (Oliver’s Battery Road South), and a minimum of approximately 80 metres in the southwest (at the junction with Port Lane). These hills are gentle folds formed over the
past 65 million years by tectonic forces linked to the collision of the African and European tectonic plates, the same event that formed the Alps Mountains in continental Europe.

Our settlement is largely built on sedimentary rocks of the Seaford Chalk Formation. These flint-bearing chalks were gradually laid down in warm, shallow seas during the Cretaceous Period, 84-90 million years ago, and are largely composed of microscopic fossil organisms called coccoliths (a type of plankton).  Although chalk outcrops are sparse, the surface layer of chalky soil is very shallow in most areas, typically 30 to 100 cm deep, so chalk is often excavated in ground works, providing very good foundations.

Chalk is a highly absorbent material, readily soaking up water. Therefore, surface water quickly filters down into aquifers, or deep underground layers of water-bearing chalk, meaning there is very little naturally occurring open water. Instead, the land is very free draining with low fertility, flinty and chalky soils, supporting vegetation tolerant of alkaline conditions (for example, beech and yew).

The Yew Hill Butterfly Reserve to the south consists of open downland atop slightly younger sedimentary rocks of the Newhaven Chalk Formation (72-86 million years ago) and the Culver Chalk Formation (72-84 million years ago). The youngest deposits in Oliver’s Battery are surface channels of clay, silt, sand and gravel (collectively termed ‘head’), formed over the past approximately three million years by downslope movement (i.e. hillwash) probably linked to periods of flooding. One such channel originates in land at Pitt, traverses South Winchester Golf Course and proceeds in a south westerly direction to Hursley. Another ancient drainage channel, originating in Texas Drive, curves round to the southeast joining the floodplain of the River Itchen.

Taken together, these factors—ranging from the elevated nature of the land providing far-reaching views over valued landscapes, to the limiting properties of the chalky soils – all shape how life is lived in Oliver’s Battery.

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