- Blisworth Limestone
The Blisworth Limestone is a
stratum oflimestone of theBathonian stage, found in theJurassic ridge which extends north and south throughEngland . It was laid down in the shallows of the Jurassic sea and is part of the more widely defined Great Oölite Series. It is also known as the Great Oolite Limestone. From the Jurassic ridge it extends eastwards below the later deposits and in the North Sea terminology, it is part of the West Sole Group. (Cameron p.74)Formation
The Blisworth limestone lies above the
Upper Estuarine Series of strata. The latter was formed close to the coast where rivers flowed from theLondon-Brabant Island . The land sank a little in relation to the sea so the site lay a little further offshore. In the hot, shallow sea, the water partially evaporated so that the dissolved calcium carbonate (CaCO³) was precipitated onto minute nuclei to form tiny spheres which together resemble hard fish roe. This is composed of eggs; hence the name oölite. The process goes on today in the seas off theBahamas (Kirkaldy p.59). Much of it also contains marine shells, notably of oyster. Subsequently, the site was submerged less deeply so that the overlying Blisworth Clay was deposited in brackish conditions. (Gallois p.20)The stratum is known as Blisworth Limestone because it was first studied at Blisworth in
Northamptonshire when theBlisworth tunnel was being dug for what is now called the Grand Union Canal. The tunnel finally opened in1805 .Occurrence
Blisworth limestone is a generally thin but widely spread deposit in eastern England. It becomes thicker as one progresses southward from north Lincolnshire or westward from Norfolk. In the
King's Lynn district, it is a shelly oolitic limestone 1 to 2 m thick. At Wiggenhall it is around 190m below mean sea level (OD) and at Tydd St Mary, around 140m. (Gallois) AtBourne, Lincolnshire , at the eastern edge of the Jurassic ridge, it is around 15m below OD. (BGS sheet 144) It is exposed at the surface around the valleys of the East and West Glen rivers (River Glen, Lincolnshire ) in which vicinity it is 2.4 to 4.8 metres thick. (BGS sheet 143). Its exposure continues southward in a similar relationship to the Jurassic ridge, to the west ofPeterborough . (BGS sheet 157) AroundTowcester it reaches a thickness of 9m. (Hains & Horton p.85)References
*British Geological Survey, 1:50,00 Series. (1992)
*Cameron, T.D.J. "et al". "The geology of the southern North Sea" (1992) ISBN 0-11-884492-X
*Gallois, R.W. "Geology of the country around King's Lynn and The Wash" (1994) ISBN 0-11-884495-4
*Hains, B.A. & Horton, A. "British Regional Geology: Central England" 3rd edn. (1969) ISBN 0-11-880088-4
*Kirkaldy, J.F. "Field Geology" (1988) ISBN 1-85079-133-3ee also
*
List of types of limestone
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