Extensional Faulting and Folding in Sedimentary Growth Basins: Case Studies from Seismic and Outcrop Data

This PhD thesis addresses how fault and fold growth affect accommodation development and sediment routing and fill in extensional basins. Extensional basins are key constituents of passive continental passive and intra-continental rift systems and hold great potential accumulation of reservoir-grade successions of sediments. These types of basins differ widely in terms of e.g. fault and fold properties, duration of faulting, accommodation development, tectono-climatic setting and lithology of basin substrate and fill. Accordingly, constructing general models for extensional basin evolution is challenging. Combining different types of datasets that offer different observation scale and resolution can mitigate this. This thesis presents seismic case studies from the Fingerdjupet Subbasin, southwestern Barents Sea and outcrop studies from the Bandar Jissah Basin, northeastern Oman. Seismic analyses include interpretations of faults and horizons bounding seismic reflector packages; age control was achieved through seismic ties to hydrocarbon exploration wells. Additional insight was gained from analysis of isochore thickness maps and horizon and fault attributes. Outcrop data consists of measured sedimentological sections and structural data that are coupled to a collection of high-resolution photomosaics. Results from both datasets highlight how extensional fault-related folding significantly impacts accommodation evolution and sedimentary architecture. The Fingerdjupet Subbasin evolved as a semi-regional rollover associated with displacement on the Terningen Fault Complex. On a smaller scale, growth of a fault-bend anticline limited deposition near the Terningen East fault, causing sediments to accumulate in a fault-bend syncline further into the hangingwall, away from the fault. The history of fault growth, fault linkage and fold growth in the Fingerdjupet Subbasin is deduced by examining sedimentary architecture. In the Bandar Jissah Basin, rollover folding was set up by displacement along the Banurama detachment, causing drainage diversion and deposition of growth packages on the rollover flank. Transverse folds reflect lateral fault segmentation and constrain the lateral extent of early syn-rift basins in the Fingerdjupet Subbasin. Transverse fold trajectory analysis determines segmentation and linkage in the fault array that control folding, accommodation distribution, sediment entry points to hangingwall basins and potential trapping structures. The longevity of transverse folds through several phases of vertically decoupled faulting in the Fingerdjupet Subbasin emphasizes the importance of inherited structural fabrics during rifting. There is a transition from supradetachment basin to rift-style basin setting in the Bandar Jissah Basin that is reflected in a changing accommodation pattern. Displacement on late, steep faults (Marina and Yiti Beach) set up local E-W to N-S proximal-distal trends. This pattern is superimposed onto the regional Ndirected accommodation increase that resulted from displacement along an older detachment (Banurama). Additional evidence for a rift-style basin setting include growth packages in the proximal hangingwall of the steep Marina fault, alignment of distinct facies belts to fault strike and reduced siliciclastic input to hangingwall basins. A similar major structural transition is inferred for the Fingerdjupet Subbasin, where steep basin-bounding faults sole out in a low-angle detachment at depth. This thesis adds to the general understanding of extensional basins through investigations of basins differing in age, location and tectonic setting. Utilizing different datasets and observation at various scales allows knowledge-building. This work adds to ongoing – and will guide future research on synsedimentary faulting and folding in extensional settings