Geochemical changes across the Proterozoic-Cambrian transition in the Durmala phosphorite mine section, Mussoorie hills, Garhwal Himalaya, India

The transition from the Neoproterozoic Nemakit-Daldynian(1) Krol-E dolomite to the Tommotian Lower Tal phosphorite-chert-black shale sequence denotes a period of drastic change in the depositional environment and the chemical milieu of the sedimentation basin. These changes are reflected by a marked negative excursion of carbon isotopes, phosphorus enrichment, trace-metal content, high organic carbon burial and notably the first appearance of prolific small shelly fauna and burrowing organisms. Recent studies have documented these changes along several stratigraphic profiles in the Mussoorie Hills of the Garhwal Himalaya for which a single profile from the Durmala phosphorite mine provides a key section discussed here. (C) 1997 Elsevier Science B.V.