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Geology and hydrogeology ... …

Report No. SRL/FP/004.1 (10/05/2006)

(c)

Faulting in the Corallian Rag and associated interruption in the continuity of the Kimmeridge Clay

The Corallian Rag, which underlies the Kimmeridge Clay at Radley, outcrops over a partial U-shaped region around Oxford. Between Faringdon and Oxford its height is sufficient to

separate the Oxford Clay Vale from the Vale of and Boars Hill are such outcrops to the west Corrallian escarpment, Headington Hill, which

White Horse. Wytham Hill, Cumnor Hill

of Oxford. consists of

To the East is the largest the very shelly ragstone

originally used to build the Oxford Colleges with disastrous effect; there also lies a Corrallian villages, in an arc from Iffley through Beckley, Otmoor and Waterperry. owe their existence to the springs-line associated with large-scale landslips

line of These in the

Corallian escarpment, initiated by these springs Oxford Clay. Many of the springs in Abingdon

occurring where the limestone overlies the (e.g. Spring Terrace, Spring Road, Spring

Gardens etc) are probably also related to this pressure under the rag due to its slope and to Abingdon, so water finding its way into and applies pressure to the aquifer in and under

effect. Here there is considerable hydraulic the greater height of the land to the north of under the rag at Boars Hill, for example, the Corrallian to the South. Another likely

location springs

for in

springs associated with faulting in the Long Furlong Park, North Abingdon,

ragstone is the

extensive

array of

lying between

the Long

Furlong

Community Centre South Avenue and

and Tilsley Park. were sufficiently

These springs also occur impressive to the original

under the developer

lower part of of the South

Avenue estate, back in the 1930s, that Mr Smith slope over the region of the springs. Subsequent continuing distress of the present residents!

chose not to build the estate down developers ignored this problem to

the the

Faulting has long been known to occur in the Kimmeridge Clay in the vicinity of the Radley Lakes. Corser13, in 1978, records

“…minor faults trending east-west occur near Lockwood16…downthrowing to the south.”

Faulting is also reported17 to occur in the Kimmeridge beneath Lakes H/I. The palaeo- channel running E-W across these lakes seems to be associated with a fault where concreted greensand runs E-W. The same phenomenon occurs underneath Longmead (Lake L2) - so it is fairly extensive. The concreted greensand was rather odd in that it was bedded vertically. Dr Christine Buckingham, Dr Kate Scott and Dr Eeles have speculated that this is related to a major faulting event comtemporaneous with the formation of the Alps and the famous buckling at Lulworth Cove. It was definitely in situ. The palaeo- channel that runs alongside the fault under H/I was packed full of Lower Greensand, but with less Greensand and more coarse gravels at Longmead.

It is important to investigate the extent of the breaks in the ragstone at Lake E at Radley and the related breaks in the continuity of the Kimmeridge Clay. These discontinuities together with the remnants of palaeo channels will lead to leaching from the ash-filled lake,

which will then be entrained in the redirected

potentially

serious

consequences.

There

groundwater flows is no evidence,

towards in the

Abingdon, with RWE npower

Environmental Statement, that such an assessment has been made, and indeed, npower seemed oblivious to these risks when preparing and filling previous lakes.

RWE

16 17

The woodland across the Thames, opposite Lakes A-D Observed by R M G Eeles and J Wallis, pers. comm.

Page 11 of 23

© SAVE RADLEY LAKES 2006

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