Sedimentological analysis of the outcropping Sherwood Sandstone Group, northern Cheshire Basin, UK, documents the preserved stratigraphic expression of water table-controlled aeolian-dominated erg-margin successions (Wilmslow Sandstone Formation and lower Helsby Sandstone Formation), overlain by dryland fluvial deposits (middle Helsby Sandstone Formation). A quantitative assessment of sedimentary architectures and a comparison with analogous depositional systems reveals that strata of the Sherwood Sandstone Group are similar to other aeolian-dominated successions that also accumulated in rift basins, in erg-margin settings and where the water table interacted with the sediment surface. In stratal successions of erg-margin origin in the Wilmslow Sandstone Formation and Helsby Sandstone Formation, the dominant facies associations comprise: (i) thin cross-bedded dune sets characterized by foreset–toeset grainflow strata; and (ii) lenticular bodies of dry and damp-to-wet interdune strata. Together, these associations record accumulation of small, rapidly migrating transverse or oblique dunes, and intervening isolated interdune depressions. Two types of interdune deposits are observed: (i) near-horizontal wind-ripple laminated sandstone; and (ii) irregular to wavy-laminated sandstone with adhesion strata. These deposits indicate dry and damp–wet surface conditions, respectively. Dune climbing is demonstrated by the interfingering between dune toesets and interdune strata; this was enabled by accommodation generation driven by fault-related subsidence and associated relative water-table rise. Accumulation via climbing at very low angle but net positive, else by non-climbing mechanisms, is demonstrated by erosional, sharp dune–interdune bounding surfaces, which likely developed during slowdowns in subsidence rate. Episodic absolute water-table rise may have occurred during wet seasons or due to intense precipitation events, potentially in a monsoon climate. Water-table fluctuations may have also occurred in response to longer-term climatic perturbations following the Permian–Triassic mass extinction event. This study helps to constrain the factors controlling the accumulation of Triassic aeolian and mixed aeolian–fluvial successions, and their long-term preservation. Quantitative models are proposed to explain aeolian dune–interdune facies architectures. These can be used to guide predictions of three-dimensional sedimentary heterogeneity in the subsurface.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)