Eolian dune types preserved in the Tensleep Sandstone (Pennsylvanian-Permian), north-central Wyoming

Abstract

The Tensleep Sandstone is one component of an erg system that prograded southward out of north-central Wyoming from Middle Pennsylvanian to Early Permian time. Each erg advance was temporarily interrupted by regional marine transgression. Interpretation of dune types deposited in these ergs is developed from an analysis of the relative proportions of eolian stratification types comprising foreset strata, geometry and relationships of bounding surfaces, and paleodispersal patterns. Two basic morphologic dune types are inferred: simple dunes and compound crescentic dunes. The simple dunes are dominant and are subdivided into 1–2 km wavelength and 1.0 km saddle-spacing slightly crescentic, and 0.1–0.2 km wavelength straight-crested subtypes based on their first-order bounding surface geometries. Foresets are composed of grainfall and wind-ripple strata; avalanche strata are rare. The compound crescentic dunes had wavelengths of 0.5–1 km and saddle spacings of 0.8 km. Foresets are dominated by avalanche and wind-ripple strata. A morphodynamic classification of the dune types is inferred from considerations deduced from paleodispersal patterns and comparison with paleocirculation models. The simple dunes were demonstrably oblique to some elements of the wind field and less oblique to others. The compound crescentic dunes had a predominantly transverse configuration.