The environmental conditions that prevailed during the formation of the Rohtas carbonates have been delineated on the basis of the Eh-pH diagrams for V, Mn, Fe⁺² and Fe⁺³ compounds. The high content of vanadium in the insoluble residue is indicative of the prevalence of reducing environment. During early-diagenesis manganese seems to have been mobilised from the soft sediments. Higher manganese content in the carbonates is a result of late-diagenesis. Prior to late diagenesis, ferric iron appears to have been precipitated from the waters while manganese remained in solution, and this process accounts for the low iron content of the carbonates.