Controls on sediment architecture and deposition in arid continental basin margin systems

Abstract

Continental basin margin systems are dominated by alluvial fan environments throughout basin development. As the fan is long-lived, the sediments interdigitate with contemporaneous environments of deposition in the basin centre. The facies and architectures of alluvial fan deposits are influenced by: 1) the varied environments of the fan; 2) the interactions of the fan with contemporaneous distal environments; 3) allocyclic controls on these environments; and, 4) smaller-scale, and more localised, controls of climate, tectonics, base level, and sediment supply.

This work considers the Cutler Group sediments of the Paradox Basin, western U.S.A. The proximal extent of the Cutler Group comprises a well exposed continental basin margin system. This work presents generalised spatial facies models across the proximal Cutler Group to ascertain the varied environments of the fan, and the zone of interaction between the fan and the contemporaneous distal environments. Temporal facies models have been constructed to highlight how long-term allocyclic climatic changes, and localised autocyclic variations control the deposition of the Cutler Group. The identification of this cyclicity is used to cyclostratigraphically correlate through the basinal deposits.

The deposits of the basin margin system have the potential to significantly impact upon basin-scale fluid migration pathways. These impacts include: 1) interconnecting isolated permeable lithologies of the distal basin; 2) creating ‘thief zones’ away from distal permeable lithologies; 3) providing a bypass route to charge the distal permeable lithologies; and, 4) introducing baffles into an otherwise productive system.

Generic facies models derived from this work are applied to the sediments of the Brockram Facies, northern England: a poorly exposed arid continental depositional system dominated by alluvial fan sediments at the basin margin. The application provides significant insight into the sedimentology, geometry and connectivity of the Brockram Facies. This research provides a sedimentological framework to better understand basin margin deposits in poorly exposed basins.