Facies Pattern and Depositional Motif in an Immature Trench-Slope Basin, Eocene Mithakhari Group, Middle Andaman, India

Abstract Detailed facies analysis in Eocene Mithakhari Group reveals eight different lithofacies of wide ranging paleogeographic significance. These facies are i) disorganised matrix-supported conglomerate, ii) graded matrix-supported conglomerate, iii) graded pebbly sandstone, iv) massive and thick-bedded sandstone, v) plane laminated and cross-stratified sandstone, vi) interbedded sandstone and mudstone, vii) massive to faintly laminated shale and viii) interbedded shale and coal; which are grouped into-five different facies associations (FA). viz. Subaerial alluvial plain (FAl), Shallow water, wave dominated shelf (FA2), Delta slope (FA3), Prodelta slope (FA4) and Submarine fan (FA5). Lying unconformably on oceanic basement (ophiolite slices?) these sediments constitute short truncated successions. Litholog measurement in three isolated sections viz. Kaushalyanagar. Sagwannala and Rangat-Nimbutala reveal widely varying facies succession pattern. Frequent facies change, predominance of massflow deposits, signatures of synsedimentary basinal disturbance and wide paleogeographic variation indicate sedimentation in small isolated basins in an immature trench-slope setting. Profusion of progradational depositional cycles and evidences of emergence in the studied sections provide indication of frontal accretion and tectonic shoaling in the filling history of these basins.