Geometry-and-late-stage-structural-evolution-of-Central-Graben-salt-diapirs,-North-Sea.pdf

Marine and Petroleum Geology 17 (2000) 499±522
Geometry and late-stage structural evolution of Central Graben
salt diapirs, North Sea
I. Davison a,*, I. Alsop b, P. Birch c, C. Elders a, N. Evans d, H. Nicholson e,
P. Rorison f, D. Wade g, J. Woodward h, M. Young a
aDepartment of Geology, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK
bCrustal Geodynamics Group, School of Geography and Geosciences, University of St. Andrews, Fife, Scotland KY16 9ST, UK
cEnterprise Oil, Victoria Tower, 62 Market St, Aberdeen, Scotland AB11 5PJ, UK
dBHP Petroleum Ltd, 1 Neathouse Place, London SW1V 1LH, UK
eBP Exploration Operating Co., Fairburn Industrial Estate, Dyce, Aberdeen, Scotland AB21 7PB, UK
fConoco (UK) Ltd, Rubislaw House, North Anderson Drive, Aberdeen, Scotland AB15 6FZ, UK
gRanger Oil (UK), Walnut Tree Close, Guildford, Surrey GU1 4US, UK
hDepartment of Geological Sciences, University College London, Gower St, London WC1E 6BT, UK
Received 5 March 1999; received in revised form 8 November 1999; accepted 16 November 1999
Abstract
Central Graben salt diapirs may have initiated along extensional faults and evolved into diapirs in Triassic times. The lack of
primary rim synclines indicates that the structures became diapiric without going through a pillow phase. Diapirs grew mainly
by downbuilding, probably with sporadic periods of subtle bathymetric relief created at diapir crests through to the Miocene
period. Sea-bed relief controlled the deposition of Palaeocene turbidite sandstones, which thicken away from the diapir crests
from 0 up to 300 m. However, highest-density turbidity currents ¯owed across diapir crests and good-quality channel sandstones
were deposited across the tops of the diapirs. Radial faults at top Palaeocene level concentrate at the elongate terminations of
elliptical diapirs, or above deeper cross-fault intersections above more circular diapirs. In map view, the radial faults tend to
cluster in thr