Cretaceous

Abstract

AbstractEarly CretaceousThe Cretaceous Period lasted for about 70 million years. During this time there was a major change in the sedimentary history of the area as tectonism died down and deposition started of an extensive blanket of coccolith ooze: the Chalk. The change took place mainly over a brief interval across the Albian/Cenomanian (Lower/Upper Cretaceous) boundary, at about 95 Ma. Until that time crustal extension along the Arctic-North Atlantic megarifts continued to influence the tectonic evolution of northwest Europe (Ziegler 1982, 1988). This tensional régime caused rifting and block faulting, particularly across the Jurassic-Cretaceous boundary (Late Cimmerian movements) and in the mid Aptian (Austrian phase). During the latter phase, sea-floor spreading commenced in the Biscay and central Rockall Rifts. The northern part of the Rockall Rift began to widen too, possibly by crustal stretching rather than sea-floor spreading (Ziegler 1988, p. 75). During the Albian the regional pattern began to change and by the beginning of the Cenomanian rifting had effectively ceased away from the Rockall/Faeroe area.Most of the Jurassic sedimentary basins continued as depositional areas during the Early Cretaceous, but the more extensive preservation of Lower Cretaceous sediments provides firmer constraints on some of the geographical reconstructions. The marked sea-level fall across the Jurassic-Cretaceous boundary isolated the more southerly basins as areas of non-marine sedimentation, and it was not until the beginning of the Aptian that they became substantially marine.The extent of emergence of highs in the North Sea area is difficult to assess, especially where