Abstract

• The present study would offer the Sedimentary Facies of Miocene clastic sedimentary rock units of Letkat Formation (Early Miocene), Natma Formation (Middle Miocene) and Shwethamin Formation (Late Miocene) exposed in the southwestern Chindwin Basin, situated in KalewaMawleik Townships, Sagaing Region. The study is mainly focus on outcrop-based sedimentary facies analysis. Eight lithofacies of Letkat Formation such as Trough cross-stratified sandstone (St) with basal erosional surface facies (Se) and lags (F.1), Pebbly gritty sandstone facies (Gm) (F.2), Sand-mud interlayer facies (Fl) (F.3), Thinly laminated fine sandstone facies (Sl) (F.4), Planar crossstratified sandstone facies (Sp) (F.5), Horizontal to low-angle stratified sandstone facies (Sh) (F.6), Massive, variegated silty clay facies with fine-grained sandstone facies (Fsc) (F.7) and Bluish grey silty shale with silt and sand lens facies (Fsc) (F.8), five lithofacies of Natma Formation such as Massive nodular clay with fine-grained sandstone facies (Fsc) (F.1), Medium to thick-bedded, coarse-grained to gritty trough–cross bedded sandstone (Gt) with basal erosional surface (Se) facies (F.2), Planar cross-stratified sandstone facies (Sp) (F.3), Thinly bedded siltstone or silty fine sandstone and shale facies (Fl) (F.4) and Massive, variegated silty clay facies (Fm) (F.5) and six lithofacies of Shwethamin Formation such as Gritty to pebbly sandstone facies (Gm) (F.1), Trough cross-bedded sandstone facies (St) (F.2), Planar cross-bedded sandstone facies (Sp) (F.3), Horizontal laminated sandstone facies (Sh) (F.4), Thinly laminated fine sandstone and siltstone facies (Fl) (F.5) and Massive, variegated silty clay facies(Fm) (F.6) were deposited in braided river environment. For more environmentally specific, individual facies is needed to combine together into facies associations to define environment. At least five lithofacies association can be established in the Miocene sequence of the research area which are Sandy Fluvial Channel Facies Association (CH), Sand Bar Facies Association (SB), Gravel Bar Facies Association (GB), Overbank Fines Facies Association (OF) and Laminated Sand Sheet Facies Association (LS).