Volcanogenic clays in Jurassic and Cretaceous strata of England and the North Sea basin

The nature and origin of authigenic clay minerals and silicate cements in t he Jurassic and Cretaceous sediments of England and the North Sea are discu ssed in relation to penecontemporaneous volcanism in and around the North S ea Basin. Evidence, including new REE data, suggests that the authigenic cl ay minerals represent the argillization of volcanic ash under varying diage netic conditions, and that volcanic ash is a likely source for at least the early silicate cements ill many sandstones. The nature and origin of smect ite-rich, glauconite-rich, berthierine-rich and kaolin-rich volcanogenic cl ay mineral deposits are discussed. Two patterns of volcanogenic clay minera ls facies are described. Pattern A is related to ash argillization in the n on-marine and marine environments. Pattern B is developed by the argillizat ion of ash concentrated in the sand and slit Facies belts in the seas borde ring ash-covered islands and massifs. It is associated with regression/tran sgression cycles which may he related tu thermal doming and associated volc anism, including the submarine release of hydrothermal fluids rich in Fe. T he apparent paucity of volcanogenic clay deposits in the Jurasssic and Earl y Cretaceous sediments of the North Sea is discussed.