On mineralogical and geochemical criteria in the genesis of red beds

The article discusses a concept on the origin of hematite in red-bed deposits as a result of the alteration of ferrihydrite (a hydrous iron oxide with a composition 2.5 Fe₂O₃ · 4.5 H₂O). The formation of ferrihydrite is associated with a predominantly bacterial oxidation of ferrous iron contained in discharged groundwaters. Clastogenic material and ferrihydrite flakes have been supplied to the site of sedimentation from different sources. The climate in the areas of their deposition has been hot and arid. Owing to an absence of organic matter during the diagenesis, the iron remained in the form of an Fe³⁺ oxide.Sedimentary rocks united under the name of “red beds” are of different ages. A great number of papers deals with the conditions of formation of these rocks and yet the genesis of the hematite contained in them has not been satisfactorily explained. The significance of red beds in paleoclimatology is also not clear. This paper is an attempt to discuss these problems on the basis of mineralogical and geochemical data.