PALEOCLIMATIC SIGNIFICANCE OF CHANGES IN CLAY MINERALOGY ACROSS THE JURASSIC-CRETACEOUS BOUNDARY IN ENGLAND AND FRANCE

Clay mineralogical changes across the Jurassic-Cretaceous boundary from the northern to the southern part of western Europe show similar patterns in: the mudrocks exposed on the Yorkshire Coast, the paralic sediments of the Dorset Wessex Basin, and the Jura and Vocontian Trough of S.E. France, This comprises a change from smectite-poor sediments in the Jurassic (with correspondingly abundant illite and kaolinite) to sediments with abundant smectite in the Jurassic-Cretaceous boundary beds, depleted in kaolinite. This change occurs in the Oxfordian in the south, to ?latest Volgian in the north of the study area. Kaolinite reappears in abundance in the late Ryazanian or stratigraphic equivalent in all the locations studied. Comparision with other climatic indicators and other areas suggest that these variations can be ascribed to a phase of latest Jurassic-earliest Cretaceous aridity, the onset of which appears to be diachronous across W. Europe. Possible causes for the climatic change towards aridity are examined: the orographic effect of mountains or plateaus to the east of the study area is considered most likely.