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The structural controls on Upper Jurassic and Lower Cretaceous reservoir sandstones in the Witch Ground Graben, UK North Sea

1990; Geological Society of London; Volume: 55; Issue: 1 Linguagem: Inglês

10.1144/gsl.sp.1990.055.01.14

2041-4927

Declan O'Driscoll, A. D. Hindle, David Long,

Geological and Geophysical Studies

Abstract The Witch Ground Graben is a product of Mid- and Late Cimmerian extensional tectonism. The principal orientation of normal faulting was NNE-SSW during the Mid-Cimmerian (Bajocian to Early Kimmeridgian) and a combination of NW-SE and E-W during the Late Cimmerian (Late Kimmeridgian to Barremian). Block rotation on the dominant Late Cimmerian trends, combined with reactivation of older structural grains formed the fault block traps in the area. Two major depositional systems form the reservoirs of the late Jurassic and early Cretaceous of the Witch Ground Graben, namely, the deltaic and shallow marine systems of the Sgiath and Piper Formations and the deeper water turbiditic sands of the Kimmeridge Clay and Valhall Formations. The transition between the systems is highly diachronous. The turbiditic sandstones are often enclosed within or onlap sealing strata, thus providing a stratigraphic element to many of the traps in the area. A chronostratigraphic framework was established and used as the basis for understanding firstly, the timing of the tectonic episodes responsible for moulding the Witch Ground Graben and secondly, the importance of these events in determining reservoir sandstone distribution and trap development.