Geology & Soils

Geology and Soil Types

Cretaceous geology dominates the landscape at Wimpole with Gault to the south on the lower land

Middle chalk strata can be seen as  a light beige

Middle chalk strata can be seen as a light beige

20-40m OD, while Lower/Middle Chalk lies to the north forming the escarpments 40-70m OD. 450,000 year old glacial deposits of Chalky Boulder clay overlay the Middle Chalk at 70 OD on the high plateau to the north and it is some of these deposits that have slumped down from the slopes and formed the Drift clay deposits above the Gault clay valley floor in places.

Rectory farm

There is an important thin band of Upper Cambridge Greensands lying between the Gault clay and Lower/Middle Chalk. This allows calcareous spring water to seep out at around 40m OD forming springs. These can form wet flushes where Alder, Willow and Poplar do particularly well.

Soils reflect the geology.  Evesham on the Gault and Drayton on the Drift clays while Didmarton, Landwade and Abingdon dominate the Lower/Middle Chalk, Hanslope, Canamore and Radford are found on the Chalky Boulder clay. All the soils are alkaline to some depth, so would preclude those species preferring acid conditions such as Sweet Chestnut, Sessile oak, Scots Pine  etc.

The effects of the post glacial landscape are related initially to the periglacial effects of solifluction and this is where the Drift clays are derived from. The Chalky Boulder clay on the steeper south facing slopes slumped onto the Gault clay valley floor and formed the Drift clays with their associated Drayton soil series.  High energy erosion through very high rainfall later washed down and dumped the larger stones and sands and then at a later date the finer clays were deposited as the energy source dissipated; this formed the St Lawrence soil series, gravelly at depth then becoming more clayey to the surface,  oak seems to do very well on this soil series.

Later, as the climate settled, much finer organic soil debris accumulated in the brook and river flood zone. It is fairly narrow but is discernable. This consists of alluvium and is associated with the Thames soil series with silt, organic debris and freshwater snails within its matrix. In certain parts the brook and river have deposited banks of fine gravel and sand, these banks are sporadic and associated to the Milton soil series and may well have been exploited for brick production.

Some calcareous soils have become acidic in the A horizon.  Two typical soils are the St Lawrence which becomes Lawford and suffers from loss of soil structure if inappropriate land work is carried out and Hanslope which becomes Radford due to the decalcification of the A horizon from rainfall and thousands of years under ancient woodland.  Haley and Eversden woods are good examples.

 

Gault and Drift soils suffer from serious seasonal water-logging in wet years and when saturated in winter have caused large trees to become unstable in strong winds and kill roots on certain trees e.g. Black Walnut because of the anoxic conditions prevailing. Tree species choice should reflect the geological and soil type.

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