Delta or coastal plain? With an example of the controversy from the Middle Jurassic of Yorkshire

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Abstract
Summary: Deltaic and coastal plain deposits can be distinguished from each other in the rock record where enough data are available to interpret the three-dimensional distribution of facies and unconformities over a wide area. This distinction is based on the distribution of facies rather than purely on a marine-to-alluvial transition as has been the case in the past. The distinction between deposits of the two environments is often very difficult or impossible, and if based on limited data may lead to inaccurate and even incorrect models that can cause problems with prediction of reservoir rocks or coal location in the subsurface. Models of the gross facies distribution for tectonically, eustatically and autocyclically controlled coastal plains are seen as the end-members of a continuum between coastline depositional styles. The Middle Jurassic sedimentary rocks of the Yorkshire Basin are used to illustrate the controversy that can arise from imprecise definitions and the application of incorrect facies models. The Middle Jurassic Ravenscar Group is interpreted here as the deposits of a tectonically and eustatically influenced coastal plain. Repeated fluctuations between shallow-marine and non-marine conditions are interpreted as mainly caused by vertical tectonic movements and sea-level changes rather than by autocyclic processes.