MICROBIAL SIGNATURES IN LACUSTRINE AND FLUVIAL CARBONATES - GONDWANA (PERMIAN) AND HOLOCENE EXAMPLES, INDIA

Laminated microbial carbonates occur in the siliciclastic sequence of the Talchir Formation (Lower Permian) of Gondwana basin, Orissa State, India. The microbial mat largely thrived in a lake-deltaic setting in near-shore, very shallow part of the lake and in peri-lacustrine swam ps and marginal fluvial regime, Petrographic and stable isotope studie s suggest periodic saline (marine?) groundwater input and evaporation under semi-arid condition. A nearby marine setting seems probable. Lat e Holocene microbial travertines-tufas (dominantly of stromatolitic cr usts) occur in parts of Orissa State and appear to be constructed of p ossible Phormidium, Scytonema, Schizothrix and diatoms. Stable isotope s suggest dominantly an inorganic precipitation from freshwater in flu vial regime of streams and small river.