Marine influence and incursion in the Gondwana basins of Orissa, India: A review

The Permian–Triassic succession of the Indian Gondwana Sequence was previously considered to have been deposited in a fluviatile-lacustrine environment. Similarly, earlier Lower Gondwanas of Orissa State (a major part of the Mahanadi Master basin) were considered entirely fresh water deposits. Faunal evidence is still scanty in this master basin. Ichnology and palynology along with a few sedimentary records are reviewed and analysed for inferring marine signature. The marine nature of the Talchir, Karharbari, Barakar, Barren Measures and Kamthi sediments of three major basins (Talcher, Ib River and Athgarh) in Orissa State was predicted on the basis of typical marine ichnofossils. Most of these sediments also contain acritarchs reflecting marine marginal environment throughout the Permian. Moreover, evidence of wave activity, salinity raise and discovery of phosphorite in Permian sediments also strengthen this view.Hence, the previous model of continental facies for the Lower Gondwanas is found to be incorrect. The ichnofossils (Skolithos and Cruziana ichno-facies), acritarchs (Foveofusa, Leiosphaeridia, Greinervillites, etc.) and other palynofossils of marine origin can be utilized as a tool for palaeoenvironmental reconstruction. In the Gondwana basins of Orissa (Mahanadi Master basin), consistent occurrence of marine acritarchs and trace fossils with some typical sedimentary structures such as wave ripples has been studied and reviewed from the Talchir (Early Permian) to Upper Kamthi (Triassic) formations at various time intervals. Here marine incursion could have occurred due to the well known global transgressions during Permian and Triassic.