Sedimentary Characteristics and Coal-accumulation Pattern of the Xishanyao Formation in the Toksun Coalfield of Xinjiang

Based on analyzing a mass of data concerning bore cores,loggings,outcrops and palaeophyte,the authors used the basic theory and method of classic sequence stratigraphy to divide the sequence stratigraphy of the Xishanyao Formation in the Toksun coalfield.As a result,two sequences of SQ1 and SQ2 were identified.Then,according to the style of stratigraphic superposition and cycles of sedimentation,the Xishanyao Formation was subdivided into six system tracts.Through the study of basic deposition maps and the analysis of sedimentary environment,the authors defined the characteristics of sedimentary evolution.For SQ1 sequence,rivers dominated delta development to form stable peat swamps on the lake edge and in flood plain areas,and the long and intense coal accumulation led to the formation of a stable thick coal seam.As for SQ2 sequence,due to frequent changes in structure and subsequent strong denudation,the coal accumulation was gradually weakened.The analysis of sedimentary characteristics and coal accumulation of the Xishanyao Formation in the Toksun coalfield has provided a basis for further coal exploration.