Abstract

• Pyawbwe – Minhlagyin area is located in Minbu Township, Magway Region. It is situated between North Latitude 19˚ 57' to 20˚ 02' and East Longitude 94˚ 37' to 94˚ 43' in one inch topographic maps of 84 L/12 and 85 I/9. The Pyawbwe Formation is characterized by thin to medium bedded, pale brown to bluish grey shale and mudstone with subordinate sandstone interbedded with buff coloured loose sand, laminated to large scaled cross-bedded, greenish grey silty clay and occasionally intercalated with hard sandstone bands. Gypsum, shell beds, lenticular and concretions are also observed. Pyawbwe Formation of the research area consists of at least 11 lithofacies and they are grouped into four lithofacies association: fan delta association, delta plain association, delta front association and prodelta association. Fan delta association is usually coarse grained resulting in higher sedimentation rate. Delta plain association may have occurred in swamp, marsh, lake and distributary channel area where are filled by overbank spilling of fine-grained material from the river during flood stages with quite energy condition. Delta front associations are present distributaries channel, subaqueous levee and distributary mouth bar. Prodelta is an environment where finer particles settle out from suspension and disperse over wide area by basinal processes. The lower part of Pyawbwe Formation is occupied by the wave and tidal influence delta front association. These include wavy laminated sandstone, laminated siltstone and clay, flaser and lenticular bedding of sandstone and shale. The middle and upper parts of Pyawbwe Formation are occupied by delta plain and prodelta. These include massive clay bearing burrow structure, shale intercalated with fossiliferous sandstone and sandstone intercalated with shale bearing gypsum.