The Guinevere field in the UK Southern North Sea is characterized by the presence of complex Mesozoic grabens trending in the NW-SE. A prominent feature of these grabens is the presence of a Lower Triassic Separation Zone (LTSZ), which is characterized by the absence of the Lower Triassic Bunter Group (Bunter Shale and Sandstone Formations). These grabens are bounded by basinward and landward listric growth faults which detach on the Permian Zechstein and Triassic Haisborough Groups.
Graben1 shows crestal collapse structure containing series of synthetic and antithetic faults, which probably developed as a result of accommodating extension on the listric growth faults. Graben2 on the other hand developed from an asymmetric half graben to a full graben with no crestal collapse structures. An array of domino style faults with an oblique extensional direction (ENE) relative to the graben bounding faults (NW-SE) detaching on the Triassic Haisborough Group developed during the Jurassic extension. The change in direction of these domino faults is attributed to a reorientation of the stress field.
A 3D structural evolution model is proposed for the formation of these grabens, the suggested mechanisms are salt tectonics and extensional faulting utilizing multiple detachment layers of the Permian Zechstein and Triassic Haisborough Group in two different phases of extension. Listric extensional faults cut and caused the rotation of the hanging wall units within the Upper Triassic sequences and detached on the Upper Permian Zechstein. The subsequent development of an antithetic listric fault detaching on the inclined Haisborough Group causes the separation zone to form during the Lower Jurassic.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California