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BROOK, ANTONY M., Department of Earth Sciences, The University of Liverpool, UK

ABSTRACT: Controls on Turbidite Sedimentation in Half-Grabens: The Heather Formation (Upper Jurassic), Nevis and Beryl Fields, UK Previous HitNorthNext Hit Previous HitSeaNext Hit

Relative Previous HitseaNext Hit-level variation, local and regional tectonics and sediment provenance are among the factors which may influence the development of turbidite systems. Any attempt to generate a predictive model of a system must seek to understand these controls, and their interactions through time.

The Nevis and Beryl Fields in the UK Previous HitNorthNext Hit Previous HitSeaNext Hit (Beryl Embayment, western margin of the Viking Graben) produce hydrocarbons from the Callovian-Oxfordian Heather Formation. This formation comprises several units of fine to very fine grained sandstone turbidites interbedded with thick marine siltstones, deposited during late Jurassic extension in the south Viking Graben.

In the Nevis Previous HitfieldNext Hit, synrift deposits are limited to the mid to late Callovian. Sediment derived from the East Shetland Platform progressively onlapped the hanging wall of the Nevis half graben, locally overtopping the Nevis high during the post-rift phase (Oxfordian). These areas are identified as sediment supply paths for Beryl Previous HitfieldNext Hit turbidites, with sediment entry points commonly localized by cross- fault lows in the hanging wall. Within the Beryl Previous HitfieldNext Hit, fault-controlled intrabasin bathymetry was the major control on patterns of turbidite deposition. Relative Previous HitseaNext Hit level variations also influenced sediment supply by partially controlling source area exposure.

This study illustrates the importance of structural controls on the distribution of turbidite elements and the overall geometry of turbidite systems in an active extensional basin. In the Beryl Previous HitfieldTop, the turbidites are too thin to allow direct seismic resolution, but the locations and characteristics of sandstone accumulations can be predicted from structural geometries.

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