Extensional Faulting and Related Fold Evolution along the Oseberg Øst Fault System, Norwegian North Sea

de Boer, Jord P.; Gawthorpe, Robert; Jackson, Christopher A.; Sharp, Ian; Whipp, Paul

Interaction between normal faulting and associated propagation folding has implications for the understanding of hangingwall trap geometries and syn-rift reservoir distribution. Three dimensional seismic and well data are used to understand the geometry and evolution of the Oseberg Øst normal fault system from the Jurassic North Sea rift. Integrated structural and stratigraphic analysis permits the reconstruction of initiation, growth, interaction and linkage of normal fault segments and highlights the role of fault-related folding in the development of a normal fault system. The 11 km long, planar normal fault system dips to the W, has up to 550 m displacement, and has a dominantly NNW-SSE strike, although prominent NNE-trending fault ‘jogs' are present. Overall, displacement and associated drag increases towards the southern end of the fault system. Local displacement minima occur at the linkage point between incipient fault segments.

Analysis of sequential isopachs, stratal geometries and displacement distribution show that isolated fault-parallel synclinal depocentres formed in the hangingwall of the propagating fault segments during a Late Bajocian - Bathonian rift initiation stage. The depocentres were associated with fault-parallel monoclinal folds above buried normal fault tips and their lengths were related to the length of the underlying, blind fault segments. In contrast, fault-perpendicular hangingwall anticlines located adjacent to the present day fault jogs and local displacement minima separated the synclinal fault-parallel depocentres along strike. The individual fault segments subsequently linked along-strike by breaching of existing relay ramps to form a single laterally extensive hangingwall depocentre during the rift climax (Middle-Late Oxfordian).

Resulting from the evolving fault system inferences can be made on geometries of hangingwall traps, the timing and origin of sediment sources, main sediment transport system(s) and the deposition of syn-rift reservoirs: (I) the orientations and interactions of normal faults and folds define the location of the hangingwall depocentres, (II) displacement minima are areas of segment linkage (e.g. breached relay ramps) result in intra-basinal highs, and (III) the fault scarp-related sediment input and the associated relay ramps defined the local pathways for coarse grained clastic sediments that have been delivered into the adjacent fault-parallel hangingwall depocentres.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013