| dc.description.abstract | In rift systems, extensional fault-related folds play an important part on the deformation pattern, and they are key to understand fault and sediment growth. In this thesis, the Beta structure in the Smeaheia area, Horda platform, northern North Sea is studied. This structure is an anticline in the hanging wall of the Øygarden fault complex (ØFC), which is a west-dipping, non-planar normal fault juxtaposing Precambrian basement on the east with Permian to Cretaceous sediments on the west. The thesis focuses on improving the understanding of the structural evolution of the Beta structure along two selected cross-sections, using seismic data in combination with kinematic modelling and discrete element modelling (DEM). From the DEM modelling, the Beta structure was formed by the normal movement of Permian-Jurassic strata along the non-planar ØFC, together with Late Jurassic-Early Cretaceous sedimentation. Fault bends are critical, with antithetic (to the ØFC) normal faults forming above concave upwards bends and offsetting the forelimb, and synthetic reverse or normal faults forming above convex upwards bends and offsetting the backlimb and crest of the structure. The fit of the DEM to the actual structure is better in section 2, which displays a more complex ØFC geometry with more bends than in section 1. However, extensional fault-bend folding alone cannot simulate a local syncline in the pre-growth and growth-strata close to the ØFC. Tectonic inversion and reactivation of the ØFC as a reverse fault during the Neogene improves the model fit, but it does not replicate the syncline. This “drag fold” is likely due to compaction and/or fault propagation folding. I test this last hypothesis using a trishear model. | |
