a complex of sedimentary rocks consisting primarily of clays, siltstones, and sandstones, with layers of limestones and gypsums, having a red color caused by iron hydroxides and oxides forming a thin film around the sand and clay particles.

The red color, the presence of carbon, and in some cases the presence of gypsum indicate that the red beds were formed under conditions of a dry climate. In places where red beds have been reworked by underground waters, which are contained in sand and gravel horizons, green gleyed horizons may appear in the red beds as a result of the redistribution of iron and other elements. As a result of epigenetic gleying, the red beds sometimes become multicolored. Red beds were deposited primarily on piedmont alluvial plains and in intermontane areas, in the channels, flood-plains, and deltas of rivers and lakes, partially in shallow seas, and at the foot of mountain slopes (proluvium, for example). They have formed over virtually the entire period of geological history, from the Precambrian to the Neocene. (Cambrian, Devonian, Permian, Triassic, Cretaceous, and Paleogene-Neo-cene red beds are most widespread.) Deposits of copper (copper sandstones), uranium, vanadium, fluorite, celestite, gypsum, salts, and oil are associated with red beds.