f Ecology of Lower Cretaceous Chalk

Chalk sediments, that is here biomicrite with a porosity of 10 – 50%, are widespread in the late Cretaceous of the Boreal Realm. Chalk, however, is uncommon in the Early Cretaceous where clays and mudstones dominate for example in the Lower Saxony Basin (LSB), northeast England (Speeton) and elsewhere. The Tuxen and Sola Formations (late Hauterivian – Aptian) of the southern North Sea (Danish Central Graben) represent this unusual Early Cretaceous chalk system.