SEDIMENTOLOGICAL ANALYSIS OF PERMIAN BARAKAR FORMATION, KHUDIA NALA, RANIGANJ BASIN, INDIA, AND ITS IMPLICATIONS

Abstract

Permian Barakar Formation of the Raniganj Basin, peninsular India, was interpreted earlier as fluvial and mixed fiuvio-marine depositional systems on the basis of evidences from primary sedimentary structures and distribution of trace fossils. Those studies lack detailed facies analysis including petrographic and geochemical analysis. The present contribution reconstructs the depositional model of the Barakar Formation through detailed sedimentological analysis of the successions exposed along Khudia nala section in Raniganj Basin. The succession is composed of three facies associations. viz., (I) coarse- to medium-grained sandstone facies association, indicating distributary channel filling deposits. (ii) sandstone/siltstone-mudstOne facies association, forming the river mouth deposits, and (iii) carbonaceous shale-coal facies association, representing interdistributory flood plain (marshy land) sediments. Abundant tide-wave generated sedimentary structures within the distributary channel facies sequence and the river mouth facies sequence, and the presence of glauconite, kaolinite, illite indicates strong influence of marine depositional processes on the fluvial system. Presence of thick coal seams and the clay minerals suggests relatively humid, warm, acidic, anoxic climatic condition. Vertical and lateral shifting of the faci es types caused stacking of multiple fining-upward (transgressive) and coarsening-upward (regressive) sequences, resulting in an overall fining and shallowing upward sequence. Such facies sequence attest to a tide-wave influenced, fluvio-marine interactive estuarine depositional system for the Permian Barakar Formation in Raniganj Basin.