The Lincolnshire Limestone Formation is a geological formation in England, part of the Inferior Oolite Group of the (Bajocian) Middle Jurassic strata of eastern England.
[1] It was formed around 170 million years ago, in a shallow, warm sea on the margin of the London Platform and has estuarine beds above and below it.
[2] The dividing marker is the 'Crossi' bed which is distinguished by the fossils of the brachiopod Acanthothris crossi it contains.
The Crossi bed forms the top of the Lower Lincolnshire limestone.
It formed in warm, shallow seas where evaporation concentrated the dissolved calcium carbonate and then the precipitated material formed concentric layers building up around a nucleus of, usually, a shell fragment as the sea surface was disturbed by winds rolling the sea-bed material around: the resulting little rounded balls are called ooliths or ooids.