Bounding surfaces in a mixed aeolian–fluvial system (Rotliegend, Wessex Basin, SW UK)

The Dawlish Sandstone Formation is a Late Permian succession of mixed aeolian and fluvial deposits in the Wessex Basin (SW England). It is used to illustrate two contrasting types of fluvial/aeolian bounding surface (planar and incised). Planar bounding surfaces separate tabular bodies of fluvial conglomerate and aeolian dune sandstone. They were produced primarily by wind scour to groundwater table, with the later emplacement of conglomerates resulting in local fluvial erosion of cemented aeolian dune sandstones. Incised bounding surfaces were produced by fluvial downcutting. The erosive relief was infilled with mixed aeolian/fluvial deposits. The Dawlish Sandstone Formation may provide the first outcrop example of these incised valley fills, which have recently been identified as a major component of the subsurface Rotliegend in the Southern North Sea Basin. The potential variability of aeolian/fluvial sedimentary architecture has important implications for well-to-well correlation and reservoir modelling.