Early Tertiary sinistral transpression and fault reactivation in the western Voring Basin,Norwegian Sea:Implications for hydrocarbon exploration and pre-breakup deformation in ocean margin basins

摘要

The Nyk High is an approximately northeast-trending,Late Cretaceous to early Tertiary structural high situated in the western Voring Basin,offshore Norway.It is defined by a thick sequence of Upper Cretaceous to lower Tertiary sediments that dip toward the southeast and are cut by normal faults with throws up to 1500 m (4921 ft).Across-fault sediment thickness variations and strati-graphic onlap relationships show that these faults were active during Campanian to early Paleocene extension,prior to the separation of Norway from Greenland ca.55 Ma.Sediments preserved in the hanging walls of these rift-related normal faults are deformed by two populations of folds:one set is oriented clockwise of the fault strike;the other is oriented parallel to the fault strike.Stratigraphic relationships show that both sets of folds formed subsequent to rifting during the latest Paleocene to the earliest Eocene.We interpret these folds as having developed during minor sinistral transpression,which was partitioned between the northeast-southwest sinistral strike-slip reactivation of the normal faults and the northwest-southeast coaxial shortening (folding) within the fault hanging walls.The Nyk High is oriented counterclockwise to the inferred line of the continental breakup.We speculate that transpression was driven by north-northwest forces arising from the differential topography along the incipient plate boundary and the presence of hot,buoyant material beneath this elevated axial region.Such deformation will not necessarily impact significantly on source rock maturity or the distribution of reservoir sands but can give rise to unusual structural trap geometries.It is also likely to increase the connectivity of trap-bounding faults.