Sedimentary response to tectonism and rifting in basins on the Norwegian shelf and onshore Norway

Abstract

The Norwegian sedimentary basins offshore and onshore have in variable degree been influenced by tectonism as rifting and faulting during deposition. This stems from post Caledonian extensional events that affected both the Devonian and Mesozoic sedimentary basins in Norway. The Mesozoic northern North Sea region experienced well-known multiple rift-phases with intervening intervals of reduced tectonic activity. This resulted in a complex sedimentary infill of the basin. However, the significance of the tectonic influence in the stratigraphy of the sedimentary basin has, to some extent, been downplayed. In many cases, this is caused by the application of the sequence stratigraphic method which conventionally has placed greatest and dominating weight on eustatic sea level changes. Among other things, this has led to the interpretation of many of the sedimentary units offshore Norway as being deposited during tectonic quiescence. This dissertation documents and discusses the sedimentary response to tectonism based on several case-studies offshore and onshore Norway at three levels of scale: at basinal scale, at the infill style and architectural scale, and at local fault-induced depositional environment scales. At basinal scale, the impact of tectonism must be distinguished from the impact of other allogenic forces such as climate or eustasy, not least because tectonic changes cause changes in both supply and accommodation. Basins at various stages of rifting show different infill styles dependent on the interplay between accommodation space and the sediment supply. This is sometimes reflected in the depositional environments in terms of wave and fluvial influence in relative open, shallow seascapes of overfilled basins, typically during proto- and rift-initiation stages. Underfilled rift basins are sometimes dominated by tidal depositional environments, typically during syn-rift stage when rapid burial and topography allows good preservation of tidal signals. The sequence stratigraphic method can be applied to the sedimentary infill of a rift basin where parts of fault blocks have been subjected to near uniform subsidence. This implies that the method has some important limitations. At local scale, fault movement has a direct impact on the depositional environment by creating local depressions or elevating fault-footwall crests. It is suggested that the results herein benefit our understanding of: modern sedimentary basins in terms of environmental challenges and hazards; the subsurface parts of sedimentary basins with regard to hydrocarbon exploration, production and CO2 storage; and the general geological evolution of these sedimentary basins in Norway with application to other areas.