Controls on Deposition Within Arid Continental Basin Margin Systems: Implications for Basin-Scale Fluid Migration

Abstract

Continental basin margins are commonly dominated by alluvial fan environments, which are long-lived throughout basin development. Fan deposition is influenced by: 1) varied transport and depositional mechanisms; 2) interactions between the fan and contemporaneous environments in the basin centre; 3) long-term allocyclic climatic variations; and, 4) localised autocyclic variations. Towards the distal extent of the basin, the alluvial fan interdigitates through a zone of interaction with contemporaneous environments in the basin centre. The sedimentology of the zone of interaction can have a significant impact upon basin-scale fluid flow by generating or restricting fluid migration pathways between the fan and permissible reservoir or seal lithologies in the basin centre. This work considers a well-exposed analogue for continental basin margin systems through the examination of the Cutler Group sediments of the Paradox Basin, western U.S.A. The work presents generalised spatial facies models across the Cutler Group alluvial fans and the zone of interaction. Temporal facies models have been constructed to highlight how long-term allocyclic climatic variations and short-term and localised autocyclic variations control deposition in the Cutler Group. The identified cyclicity highlights clear horizons which can be used to cyclostratigraphically correlate through the deposits, allowing for the further examination of basin-scale fluid migration pathways. The generic facies models derived from this work are applied to the basin margin sediments of the Permian Brockram Facies, of the East Irish Sea Basin, U.K. The application of the Cuter Group models provides significant insight into the sedimentology, geometry, and flow pathway connectivity of the Brockram Facies. This work highlights the impact of the deposits of both the alluvial fan and the zone of interaction on basin-scale fluid migration pathways and prospectivity in continental basins. The facies models show that basin margin sedimentation controls: 1) the connectivity of otherwise isolated potential reservoirs in the distal extent of the basin; 2) the development of ‘thief zones’ away from distal reservoirs; 3) the creation of bypass routes to charge distal reservoirs; and, 4) the introduction of baffles into an otherwise productive system. The net effect on fluid flow can be examined through the generation of a climate-based cyclostratigraphical framework.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015