Transition from Deep- to Shallow-Marine Deposition: The Craven Basin, UK
Turbidite systems may terminate due to switch-off and abandonment, tectonic occlusion of the basin or as a basin transition from being under- to overfilled. The close association of turbiditic and deltaic sandstones in the Craven Basin suggests that the top seal of turbidite systems is more likely compromised in settings where their termination is caused by overfilling of the basin. Connection to the fluvial feeder system might provide a further pathway for hydrocarbon migration.
The Craven Basin is bounded proximally by the Askrigg Block (to the north), a tectonically stable high on top of which a carbonate platform developed during the Early Carboniferous. During the Early Serpukhovian the basin was in transition from syn- to post-rift tectonic domains; at this time incised valleys cut across the platform and fed coarse-grained siliciclastics into the basin, commencing with a sand-rich turbiditic succession up to 500 m thick. Exposures show depositional settings varying from slope channel to proximal lobe. Directly above this succession is a predominantly fine-grained interval (50-350 m) containing distributary channel and mouth bar sands, indicative of deltaic development which is followed by a sand-rich delta system (50-100 m) showing Gilbert-type deltas with newly recognised mass-flow deposits in the delta toe. This system developed south of the Askrigg Block in a zone of rapidly increasing accommodation space. On the Askrigg Block feeders to the turbiditic and deltaic successions are present enabling correlations with the source area of the basin.
Mini-basin experiments at the Eurotank Laboratories provide a controlled environment with source to sink control on the sediment flux to examine block-basin transitions and the transition from under- to overfilled basins. Base level variations, tectonic regime and sediment input are used as input parameters and provide control on the evolution of the succession in these settings. Analyses include digital elevation models at predetermined intervals providing volumetric constraints on deposition, bypass and erosion; video coverage; and lacquer peels showing the resultant deposits.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California