|Lincolnshire Limestone Formation
Stratigraphic range: Bajocian
|Unit of||Inferior Oolite Group|
|Sub-units||Upper Lincolnshire Limestone Member, Lower Lincolnshire Limestone Member|
|Underlies||Rutland Formation, Great Oolite Group or Hunstanton Formation, Chalk Group|
|Overlies||Grantham Formation, Northampton Sand Formation or Lias Group|
|Other||Sandy limestone, mudstone|
|Region||Market Weighton to Kettering, Peterborough|
The Lincolnshire limestone (now known as the Linconshire Limestone Formation) is part of the Inferior Oolite Group of the (Bajocian) Middle Jurassic strata of eastern England. It was formed around 165 million years ago, in a shallow, warm sea on the margin of the London Platform and has estuarine beds above and below it. The maximum known thickness is 40.2 metres, at around TF9730, while four kilometres further west it is 18.3 metres thick at its outcrop in the upper Witham valley. It fades out in the south, around Kettering in Northamptonshire.
There are two sub-divisions, the Upper and Lower Lincolnshire Limestone Members respectively. The dividing marker is the 'Crossi' bed which is distinguished by the fossils of Acanthothris crossi it contains. The Crossi bed forms the top of the Lower Lincolnshire limestone. The bottom of the Lower Lincolnshire limestone has some of the characteristics of the underlying Lower Estuarine Series, in that it tends to contain more than usual amounts of sand. A stone from this part of the formation which was commercially exploited is the Collyweston stone slate which was used for roofing for several centuries. It is now largely replaced in new work by concrete imitations.
Much of the rest of the Lower Lincolnshire limestone is oolitic. It formed in warm, shallow seas where evaporation concentrated the dissolved calcium carbonate and wave action rolled the precipitated material into tiny balls. It takes its name from its similarity to the hard roe of fish.
- Hains, B.A. & Horton, A. British Regional Geology Central England 3rd edn. (1969) ISBN 0-11-880088-4
- "Linconshire Limestone Formation". The BGS Lexicon of Named Rock Units. British Geological Survey. Retrieved 29 March 2015.