Sedimentolology of the Vempalle Formation of Proterozoic Cuddapah Basin on Dharwar Craton, India: Implications for the Palaeoenv ironmental dynamics and Precambrian biosphere evolution

摘要

The sedimentological study in the Palaeoproterozoic Vempalle Formation of the Cuddapah Basin, in and around Kottalu village (78°3'30", 14°1 37 ) reveals two major facies associations, viz mixed facies association consisting of heterolithic facies and microbialite facies and stromatolite facies association comprising of columnar stromatolite facies and domal stromatolite facies. Facies association and associated stromatolites morphology clearly demonstrate that the Vempalle Formation in the study area is deposited in a shallow carbonate shelf that evolve to a stromatolitic ramp within fair weather wave base during sea-level low-stand. The Vempalle Formation also shows significantly depleted δ~(13)C (-0.03 to -5.74) and δ~(18)O (-8.19 to -18.25%o). This negative carbon isotope value of the said formation indicates the contribution of CO_2 or bicarbonate derived from oxidation of organic matter. Diagenetic carbonate concretions associated with the stromatolitic dolomites of the Vempalle Formation is also an important event in biosphere evolution linked to the emergence of modern style recycling of organic matter which has been taken place globally at the end of Lomagundi-Jatuli Event.