Facies pattern and depositional motif in an immature trench-slope basin, Eocene Mithakhari group, middle Andaman, India

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 s andstone, v) plane laminated and cross-stratified sandstone, vi) interbedde d sandstone and mudstone vii) massive to faintly laminated shale and viii) interbedded shale and coal; which are grouped into;five different facies as sociations (FA), viz. Subaerial alluvial plain (FA1), Shallow water, wave d ominated 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 isol ated sections viz. Kaushalyanagar, Sagwannala and Rangat-Nimbutala reveal w idely varying facies succession pattern. Frequent facies change, predominan ce of massflow deposits, signatures of synsedimentary basinal disturbance a nd wide paleogeographic variation indicate sedimentation in small isolated basins in an immature trench-slope setting. Profusion of progradational dep ositional cycles and evidences of emergence in the studied sections provide indication of frontal accretion and tectonic shoaling in the filling histo ry of these basins.