UNDERHILL, JOHN R., Univ. of Edinburgh, Department of Geology, Edinburgh, Scotland; and MARK A. PARTINGTON, British Petroleum, Glasgow, Scotland

ABSTRACT: The Tectonic Modification of Classic Sequence Stratigraphic Models: Controls on Late Jurassic Deposystems of the Central North Sea

Considerable advances have been made in the predictive exploration of siliciclastic deposition a systems using classic sequence stratigraphic models. However, the emphasis to date has been on two-dimensional shelf-break settings with little consideration of the effects of active tectonism or the three-dimensional variation in basin floor topography. The Late Jurassic succession of the Central Graben of the North Sea affords an ideal opportunity to assess the potential for introducing tectonic modifications to the classic models, since deposition occurred in an area which experienced rifting and halokinesis following a phase of pre-rift thermal subsidence. Analysis of over one hundred and fifty wells in the UK and Norwegian sectors allows the construction of a rigorous genetic sequence stratigraphic framework in which to investigate any temporal or spatial depositional variation. This scheme shows that the Late Jurassic section may be subdivided into at least ten genetic stratigraphic sequences bounded by maximum flooding surfaces with demonstrable chronostratigraphic significance. The results demonstrate that stratigraphic separation occurs between the sands in the Puffin (late Oxfordian), Fulmar (early Kimmeridgian) and Ula/Gyda fields (late Kimmeridgian-early Portlandian) and show that each clastic pulse represents a major basinward shift in facies resulting from minor regressive intervals which punctuate the overall transgression. The Late Jurassic succession forms part of a complex retrogradational clastic stack deposited during progressive southward-directed mari e flooding controlled largely by tectonic activity in this terraced embayment. Theresult suggests that considerable modification of classic sequence stratigraphic models is needed in the Central Graben to account for tectonics.

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