Current models for the structural evolution of the western flank of the North Viking Graben concentrate on a pattern of Late Jurassic extension controlled by a series of north-south striking, eastward down-throwing, normal faults. Due to the extensive tectonic overprinting by this event, the evolution of previous rift systems is difficult to ascertain.
Using data integrated from extensive three-dimensional seismic coverage, wells, and field analogues, an analysis and restoration of the sub-Jurassic structural and depositional regimes was undertaken for an area between the Dunbar and Snorre fields. This restoration indicates that Triassic extension was initiated during the Lower Triassic (Teist Formation), ~20 Ma earlier than comparable Upper Triassic rifting in the Atlantic region. Initially, several small sub-basins developed, controlled by northeast-southwest striking and westward-dipping boundary faults, with sediment thickening toward the border fault. At the boundary between the Teist and Lomvi Formations (~238 Ma), fault-linkage caused some faults to become more dominant, with cessation of movement on others. Continued movement through the Lunde Formation was pulsatory, leading to a series of internal unconformities within the basin fill.
Sedimentology of the fill, determined through well data (geophysical logging, core, and well-cutting lithology), and complemented by field analogues, has enabled a spatial and temporal model to be generated. Results show that syn-rift sedimentation reflected a typical continental transition during basin formation from an open to a partially-closed system. Integration of sedimentation and structural geometries will improve the regional view of the Triassic and potentially aid evaluation of Triassic hydrocarbon potential.
SEPM: Eustatic, Tectonic and Sedimentary Control on Depositional Sequences: Relative Importance - II