Distribution and facies patterns of Lower Cretaceous sediments in northernGermany: a review

Marine sediments of Early Cretaceous age (Berriasian-Albian) have a widespr ead distribution in the Lower Saxony Basin of northern Germany. This basin, which is about 400 km long and 100 km wide, formed the southernmost extens ion of the North Sea Basin. Sediments attaining a maximum thickness of up t o several hundred metres are represented by shallow marine siliciclastics i n the west, south and easternmost part of the basin. These interfinger with the basin facies represented by dark mudstones up to 2000 m thick. The dis tribution and facies patterns of the sediments as well as thicknesses are r elated to three factors: differential subsidence, local tectonics and sea-l evel changes. For various parts of the basin and certain stratigraphic inte rvals it is possible to distinguish between these causes. Sedimentary thick nesses are clearly a result of differential subsidence from Kimmeridgian to Albian times onwards, being controlled by tectonic movements along northwe st-southeast trending faults. These result in an asymmetric trough, bound t o the north and south by synsedimentary faults with sedimentation rates hig hest in the north. Local tectonics are clearly caused by salt diapirs mainl y in the eastern part of the basin and along the western, southern and east ern margins. These areas in particular include parts of the western Emsland and the Salzgitter area. Sedimentary patterns vary considerably over less than a kilometre, showing an extreme range of different lithologies. This i s ideally observed in the Salzgitter area. Sea-level changes finally are re flected by widespread facies patterns and particularly by fossils of differ ent provenance. The following sea-level-related events can be followed thro ughout the basin: the Wealden regressive phase, the Early Valanginian trans gression, the early Late Valanginian transgression, the mid Hauterivian tra nsgression, the Barremian regression, deposition of the Early Aptian anoxic sediments, and accumulation of the mid Albian hemipelagic marls. (C) 2000 Academic Press.