Bathonian to mid-Oxfordian sequence stratigraphy of the South Viking Graben, North Sea

Abstract

Abstract Application of sequence stratigraphy to the analysis of the Middle Jurassic in the South Viking Graben provides the framework for a consistent, basinwide understanding of sedimentary facies distribution. The inherited lithostratigraphical nomenclature is found to be ambiguous and sequence stratigraphical principles have been useful in clarifying this problem. Biostratigraphical data aid in the delineation of five units, designated as sequences, which broadly correspond to Bathonian, early, mid- and late Callovian and early to mid- Oxfordian. These sequences are defined on the basis of the contemporaneous depositional systems which they each contain and the horizontal bounding surfaces which separate them from other sequences. The sequences represent transgressive-regressive episodes and the surfaces which separate them record maximum marine flooding. Three structural styles are recognized to have controlled basin development during the late Bathonian to Oxfordian syn-rift extension phase. Extension was accommodated by terrace block faulting, half-graben development, or movement over ramps and flats. Different rates of extension between these diverse structural zones were transferred by complex, strike-slip fault systems. The three structural styles gave rise to differential subsidence laterally in the hangingwall and there is an observed relationship between structural development and sedimentary facies distribution. The basinwide recognition of sequences, the analysis of their internal architecture and the change in this through time, is related to an interplay of changes in sea level, sedimentation rates and extensional tectonics. Sequence mapping shows that tectonically controlled subsidence was the major control on sedimentary facies distribution during the middle Jurassic in the South Viking Graben.