Aeolian dune and wet interdune sedimentation in the Middle Proterozoic Dala sandstone, Sweden

Abstract

The Middle Proterozoic Dala sandstone covers an extensive area in west-central Sweden and the adjacent parts of Norway, but it is poorly exposed. However, a series of quarries in the lower part of the sandstone provides good exposures that allow an interpretation of the environment of deposition in this part of the unit.Only two facies have been distinguished: Facies A, an aeolian dune facies, and Facies B, a wet interdune facies. Facies A consists of large-scale cross-stratified sandstone in which cross-stratified sets are up to almost 4 m thick, while the maximum foreset dip is 25°. Sandflow and subcritically climbing translatent strata have been recognized in this facies, but the identification of grainfall strata is uncertain. Penecontemporaneous folding and brecciation of cross-strata has taken place locally. Facies B, which was deposited simultaneously with Facies A, consists of sandstone with thin mud laminae, an irregular wavy structure, and numerous wave-rippled and mud-cracked surfaces. The increasing proportion of Facies B relative to Facies A passing up the stratigraphic section may herald an approaching coastline.Lack of recognition, rather than preservational bias, is thought to be the reason for the apparent scarcity of aeolianites in the Precambrian.