The importance of water in aeolian systems; an example from the Sherwood Sandstone of the West Midlands

The Triassic Sherwood Sandstone Group of the Cheshire Basin is a sand-rich succession that was deposited in a semi-arid ‘dryland’ setting (subject to deposition by both fluvial and aeolian systems). Whilst the aeolian and fluvial systems are primarily coeval, periods of fluvial and aeolian dominance are readily observed, and enable the formational sub-division of the Sherwood Sandstone locally. Fluvial sedimentation includes crossbedded, structureless, and rippled sandstones arranged in channel and sheetflood (non-channelised) elements. The aeolian architecture is dominated by stacked sequences of large-scale crossbedded sandstones that record the migration of sinuous crested sand dune elements. The sand dune elements are sometimes separated by interleaving interdune elements, comprised of parallel laminated sandstones, that together record deposition within a dunefield environment. In analogous modern and ancient dryland systems the presence of coeval aeolian and fluvial depositional systems is commonly thought to produce competitive relationships primarily in the form of system reworking. However, increasingly the presence of water in an active aeolian dunefield, via either fluvial incursions or watertable rises, enhancing the preservation potential of some of the aeolian lithofacies. Outcrop from the margin of the Cheshire Basin allows the identification of a series of aeolian-fluvial interactions on a variety of spatial scales. Examples of interaction include; i) fluvial incursion along interdune corridors, ii) aeolian interdune ponding and, iii) localised indirect watertable flooding. Whilst understanding the interactions between aeolian and fluvial systems is of interest in understanding the Earth’s ancient and correlative modern systems, it has applied considerations as the interactions generate heterogeneity at a variety of scales that can significantly impact fluid flow. This is relevant as the Sherwood Sandstone Group is; i) a principle aquifer in Northwest England, ii) hydrocarbon producing in the East Irish Sea, iii) host to a legacy of contamination and iv) a potential carbon store.