Palynofacies Analysis and Depositional Environment of Bihpuria Well-a, North Bank of Brahmaputra River, Upper Assam Basin

Dispersed organic matter of Cenozoic sediments are analyzed for palaeoenvironmental purposes of Bihpuria well - A, situated in the North Bank of River Brahmaputra, Upper Assam Basin Distribution pattern of the organic matter types with respect to various strata has been assessed to observe changes tn depositional environment Desptite using well cutting samples, quantitative and qualitative panlynofacies analyses in various sequences v17 , Late Palaeocene - Upper Eocene and Late Miocene to Pho-Pleistocene have been defined by core lithotypes, log data and characteristics ot organic matter content The results show a significant difference between anoxic and oxic facies with relative distribution of structured and non-structured debris Depositional set-up of anoxic/oxic facies is directly related to the supply of detritus fiom various sources, lithotypes and organic particles embedded therein, which also affect their preservation and biodegradation Palaeocene-Eocene sediments deposited under shallow marine conditions exhibit highly degraded phytoclasts (amorphous, grey and highly pyritized amorphous and biodegraded terrestrial/aquatic organic matter types) supplied from both terrestrial and marine sources These accumulated at basal horizons of the basin leading to anoxic conditions Carbonaceous shale of Kopili Formation (Late Eocene) IS represented here by thin bed than in other sections In the Assam-Arakan Basln, deposited under restricted marine conditions Upper part of the sections represented by the Tipam Group and Namsang Formation, which are examples of fluvio-lacustrine deposits, characterized by land derived, less biodegraded and moderate to richly oxidized phytoclasts The nature, occurrence and frequency of organic matter in these sedimentary sequences is discussed in detail.