External Controls on the Evolution of a Prograding Shelf Margin: the Craven Basin, UK

Bijkerk, Jochem F.; Wignall, Paul; Waters, Colin; Eggenhuisen, Joris T.; Kane, Ian A.; McCaffrey, William D.

Turbidite system style depends in part on controls that are external to the loci of deposition. Here, analogue modelling experiments at the Eurotank Laboratories are used to examine the interplay between basin configuration and sea-level fluctuations.

The generic concepts derived from the analogue experiments are that inherited basin configuration is a significant control on fluvial system behaviour, the style of basin infill, and the position of incised valley formation. Specifically, in complex post-rift margins, the deepest sections of basins are attractors for incised valley formation. This concept has been applied to outcrop studies in the Carboniferous Craven Basin, UK, where it can account for the variations in style of turbiditic sand-body development and determines which parts of such successions form viable targets for hydrocarbon exploration.

The proximal margin of the Craven Basin is formed by a fault-bounded high. As the basin underwent syn- to post-rift transition, an early Serpukhovian fluvial system prograded over this high and built a prograding shelf and slope system into the basin during early sea-level fall. This predominantly fine-grained delta front succession contains mouth bar and distributary channel deposits that are traceable down-dip into unconfined slope deposits cut by numerous isolated gullies. The unconfined system is succeeded by an incised valley that cut across the sub-aerial shelf during late sea-level fall. This conduit carried coarse-grained siliciclastics into the deepest parts of the basin to form a sand-rich turbidite succession up to 500 m thick. The focused routing of sediment into the deep basin led to sediment starvation laterally, and resulted in development of a slope dominated by siltstone and shale deposition in most locations.

The difference between confined and unconfined feeder systems has major implications for turbiditic sand-body development in the Craven Basin and only the confined system would be considered a viable hydrocarbon target in such succession. The observations are in close correspondence with the concepts derived from analogue modelling and imply that the recognition of basin configuration as external control allows for a better understanding of basin infill.

We further test our ideas on basin configuration governance of depositional style further by means of literature case-studies, and demonstrate a wide application, thus providing a potential tool for hydrocarbon exploration.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013