Sedimentary flow heterogeneities in the Triassic UK Sherwood Sandstone Group: Insights for hydrocarbon exploration

Fluvial and aeolian sedimentary successions host important hydrocarbon resources as well as major groundwater aquifers. This review of the lithological characteristics of Triassic fluvio-aeolian successions of the Sherwood Sandstone Group (United Kingdom) demonstrates how distance from a fluvial sediment source and rate of rift-related tectonic subsidence play important roles in governing reservoir quality in continental successions. Increasing distance from the fluvial sediment source area results in increased porosity and permeability in deposits of mixed fluvial and aeolian reservoir successions that accumulated in arid and semiarid settings. Indeed, successions of the U.K. Sherwood Sandstone Group reveal an increase in the proportion of highly permeable deposits of aeolian origin with increasing distance from the principal uplands, represented by the Armorican Massif in northern France, which formed the main source for delivery of fluvial sediment to a series of rift basins. A progressive reduction in the discharge of fluvial systems entering and passing through a series of interlinked rift basins encouraged aeolian accumulation in more distal basins. Extensional tectonics enabled preservation of highly permeable aeolian facies in basins subject to high rates (100m/Myr) of tectonic subsidence by rapidly placing such deposits below the water table. However, successions exclusively characterized by fluvial lithofacies record decreases in both porosity and permeability with increasing distance (similar to 250-750km) from the sediment source due to the coupling of porosity reduction and increasing clay content.