--> Late Jurassic to Cretaceous Structural evolution of the Witch Ground Graben, UK North Sea, by S. J. Harper; #90986 (1994).

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Abstract: Late Jurassic to Cretaceous Structural evolution of the Witch Ground Graben, UK North Sea

Simon J. Harper

The present morphology of the Witch Ground Graben was caused by active rifting during the Late Jurassic, with postrift subsidence occurring during the Cretaceous. The controlling factor in the structural evolution of the rift throughout this time was the reactivation of pre-existing basement structures. Two major lineaments can be recognized within the area, a NE-SW Caledonian trend and a NW-SE trend, which were originally activated during Devonian and Permian times, respectively. These features, combined with episodic extensional faulting approximately perpendicular to the NW-SE trend, between the late Jurassic middle Kimmeridgian and early Ryazanian, produced a complex array of intersecting, orthogonal NW-SE and NE-SW trending structures. This rift episode is termed the late Cimmeri n tectonic event.

Reconstruction of isopach maps for Upper Jurassic intervals suggests that oblique slip movements did occur, and influenced sedimentation patterns, especially turbidite input, into the rift basin. The sites of major hydrocarbon occurrences within the graben are located along intersecting NE-SW and NW-SE structures.

The Cretaceous Period was one of tectonic quiescence and considerable postrift subsidence. Currently published models of active Early Cretaceous tectonism are revoked with reference to a new, detailed sequence stratigraphic framework and modern, high-resolution seismic data. The integrated use of structural and fault analysis, palaeobathymetric studies and sequence stratigraphy to investigate subsidence and sedimentation patterns within the basin is presented. This approach has lead to a better understanding of structural geometry within the rift system.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994