Permian-Triassic tectonic-stratigraphic evolution of the Stord Basin, northern North Sea

Abstract

The Stord Basin is one of the less explored areas of the northern North Sea, hence the Permian- Triassic tectono-stratigraphic evolution of the basin is not well known. This MSc thesis aims to use available 2D seismic and well data covering the Stord Basin to investigate the evolution of the multiphase rift-basin, with focus on the Permian-Triassic rifting phase. The study is based on seismic interpretation of deep (9 s TWT) 2D seismic lines. Different methods were used to investigate the tectono-stratigraphy in the Stord Basin. Generation of thickness maps allows to illustrate stratigraphic units and indicate fault activity. Creation of throw-length (T-x) plots illustrate the map-view growth history. Heave and throw calculations have been used to evaluate the strain distribution in the Stord Basin through time. The major Permian-Triassic faults are found to have a more curved appearance at depth and consist of multiple subsegments. Most of the displacements along the faults were obtained during the first Permian- Triassic rifting phase. Evidence of inter-rifting has been further investigated in this thesis. The influence of pre-existing Devonian shear zones on later Permian-Triassic faults’ orientation and geometry has also been investigated. The Utsira Shear Zone and the Hardangerfjord Shear Zone have affected the orientation and geometry of later Permian-Triassic faults in their proximities. The shear zones roughly divide the Stord Basin into a structural domain. Analyses of surface and thickness maps have resulted in the determination of the Permian-Triassic rift succession into syn-tectonic and post-tectonic. The collected results have been used to make an evolutionary model of the Stord Basin from the initial Permian-Triassic rifting to the present day configuration.