Controls on early post‐rift physiography and stratigraphy, lower to mid‐Cretaceous, North Viking Graben, Norwegian North Sea

Abstract

ABSTRACTThe transition from syn‐ to post‐rift is often poorly constrained and in contrast to syn‐rift systems, the controls on the development of post‐rift systems are poorly understood. This paper documents the timing of the post‐rift onset and discusses the controls that affected the subsequent development of the post‐rift infill of the North Viking Graben using an integration of seismic and well data. The study enhances our understanding of post‐rift system development in general and provides an analogue for other post‐rift systems. Within the early post‐rift infill of the North Viking Graben five key seismic surfaces were mapped [Base Cretaceous Unconformity (BCU), Intra‐Aptian, Top Albian, Top Cenomanian and Top Turonian], which divide the post‐rift interval into four key seismic stratigraphic units (K1–K4). The BCU has an intra‐Volgian age on the basin slopes and shelfal and terrace areas and is interpreted to mark the end of rifting in the study area. On the footwall crests adjacent to the graben the BCU represents a complex unconformity from the syn‐ and post‐rift combined, and in the graben it forms a conformable contact. Therefore, the BCU could not be used to date the onset of the post‐rift in these locations. The thickness variations and age relationships between the syn‐rift stratigraphy and the K‐units reveal that the early post‐rift infill of the North Viking Graben was dominantly controlled by the significant local syn‐rift topography, especially in the K1 and K2 stages. The Cretaceous post‐rift stratigraphy was also influenced by relative base level, which controlled the sediment source areas, the development of the basin geometry itself and subsequently the style of sediment deposition in the study area. Regional variations are also recognised in the post‐rift stratigraphy although these variances are strongly influenced by the local basin physiography.