BISHOP, DANIEL J., The University of Edinburgh, Edinburgh, United Kingdom

ABSTRACT: Tertiary Extension and Halokinesis in the Western Central North Sea Basin

Interpretation of commercial 2-D seismic reflection data and exploration well data in the western Central North Sea basin shows that halokinesis and associated normal faulting have been an important control on deposition and subsequent deformation of the Tertiary strata. Basement rocks beneath the salt are predominantly Devonian and Permian sandstones. The salt belongs to the Permian Zechstein Group. Very low-angle detachments are developed within the salt, which link strongly concave-up listric normal faults that deform the overlying Mesozoic - Cenozoic sequence. The listric faults have nucleated at sites of salt diapirism, and generally dip in the same direction as the top basement surface, toward the main axis of the Central North Sea basin. The fault blocks have rotated so that Te tiary strata dip away from the basin axis. Thickening of strata adjacent to listric faults shows that these faults were a control on sedimentation during the Tertiary. Antithetic normal faults in the hanging-wall blocks are clearly imaged on the seismic data, so that complex extensional geometries can be recognised, similar to those developed during analog modelling experiments. Faults are known to

be important conduits for oil migration from the Jurassic source rocks near the basin axis, to the reservoirs along the basin margin. The linked extensional fault system described here may allow migration further westward than previously thought. Listric faults also control thickness of potential reservoir sandstones of Paleocene age, which are equivalent to the reservoir sandstones in the nearby giant Forties and Montrose oil fields.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.