Facies Analysis, Markov Model and Linking of Sub-environments in the Early Permian Barakar Coal Measures of Godavari Gondwana Basin of Southeastern India

Abstract

The early Permian Barakar coal measures Formation of Gondwana Supergroup in the Godavari basin comprise siliciclastic fluvial facies of passive continental margin. The lithofacies relationship and their sequences are analyzed quantitatively using embedded Markov Chain analysis along with improved binomial probability method. Summarized lithofacies sequence show the following order: (CGSD= Matrix supported conglomerate, gritty to pebbly/coarse-grained tabular and trough cross bedded sandstones)→(MGSD= Medium grained trough and planar cross bedded sandstones)→(FGSD= Fine-grained parallel and ripple drift cross-laminated sandstones)→(SH= Shale/inter-bedded sandstone-shale and gray shale)→(C=coal/shaly coal and carbonaceous shale)→(CGSD= Matrix supported conglomerate, gritty to pebbly/coarse-grained planar and trough bedded sandstones). These repetitive cycles accumulated in a low sinuosity, high gradient braided streams which became moderately sinuous at places. The lithofacies relationships showing fining upward tendency suggest a progressive upward decline in current competency. The sequence is considered as the classical example of a sand dominated braided river. The lateral changes in lithofacies association indicate shifting of sub-environments from stream channel, overbank levee and peat forming back swamp to flood plains of fluvial system. It is suggested that the channel wandering along with differential intra-basinal tectonism and subsidence controlled cyclic repetition during early Permian sedimentation in the Godavari basin.