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Geology and hydrogeology ... …

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

Sources of Imperfection in the Kimmeridge Clay

The Kimmeridge Clay can be highly fossiliferous; it can also contain palaeo channels filled with alluvial, or other permeable, material. Finally, although the Kimmeridge Clay and the underlying Corallian Rag can each lie in fairly thick deposits, the rag can be faulted, and the clay can be disturbed. All three of these possibilities have to be investigated before specifying the use of Kimmeridge Clay for bunding, because all three can lead to loss of sealing capability. There is no evidence that this has been done by RWE npower or their associates. Nor is there a protocol in place to deal with such imperfections as they arise.

(a) Fossils

Kimmeridge Clay and Corallian Rag lie in the Jurassic sequence of rocks, wherein almost

all common marine a wealth of fossil

invertebrates show evidence of progressive diversification, and there is

remains

in

the

English

Jurassic

rocks.

The

ammonoids

vigorously

evolved. An important palaeographical distinction, as far as Europe continuance of a belt of deeper water from Spain eastward along Himalayan line (the Tethys Ocean). Shallow waters to the north of

is concerned, is the a Mediterranean to this were colonised

periodically,

largely

according

to

changes

in

sea

level.

On

land

dinosaurs

flourished

and

pterodactyls developed flight. The first bird, the Archaeopteryx developed of the Jurassic. The coccoliths developed in the lower Jurassic and were

towards the end the herald of the

major development of such rocks introduced to the wealth of fossils

in to

the Cretaceous.

In the 1970’s,

be

found

at

Curtis’s

gravel

works

this writer at Radley.

was He

obtained 13 dinosaur vertebrae from the base of the terrace Kimmeridge Clay). Ammonites and Bellumnites were common. now professor at the University of Cantabria, Spain, was visiting at

gravels (i.e. from the The author’s nephew, the time and was totally

absorbed

by

an

interest

in

the

fossil

record,

having

already

established

a

fine

collection

of

fossils from

the North of

Spain. On

spent a day

investigating

the fossils.

visiting Curtis’s quarry at Radley, by He returned home saying this must

invitation, he have been a

massive dinosaur graveyard. from the very same belt of observed the fossil richness

I have seen his collection of small and large fossils obtained blue Kimmeridge Clay in the North of Spain and I have found therein. Further evidence of the fossiliferous nature,

and indeed of the occurrence of very large plesiosaur, the arm itself being a number of m long. This was found in Lake F, towards

fossils, comes from the finding of the arm of a metres long. Such creatures reached up to 12 the Southern shore, and lay in the Kimmeridge

Clay, being found when Lake F was being dug. This fossil was of Natural History in Oxford. Numerous complete marine reptiles including pleiosaurs, icthyosaurs and turtles. Many millions of place. Fish species included Lepidotes spp.

exhibited at the Museum have been found12 at H/I bivalves etc were left in

Fossils, large and small, can be the cause of failure of a clay seal. The fossils interrupt the continuity of the clay and allow flow channels to develop along their surfaces. In extreme cases the fossil can be ejected from the clay by hydraulic pressure. There will be high hydraulic pressure at the base of the clay bunds when Lake E has been filled, perhaps 0.5 bar above the groundwater pressure. Unless the majority of fossils are removed, leaching will occur.

12

Eeles R M G, pers. comm.

Page 9 of 23

© SAVE RADLEY LAKES 2006

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