Sedimentary Environment And Coal Accumulation Of Yima Formation In Yima Coalfield

Based on the theories and methods of sedimentology, palaeontology, sequence stratigraphy, sedimentary petrology and coal geology, through the observation and laboratory study of drilling cores and outcrops in Yima coalfield, combined with the analysis of more than 150 wells, three sedimentary facies-Alluvial fan, Lake Delta, and Lacustrine-are identified in the study area, including 8 subfacies and 10 microfacies, and the characters of each sedimentary facies are summarized.On the basis of the recognition of sequence boundaries, the Yima formation can be divided into 2 third-order sequences and 6 system tracts. The thesis established the sequence stratigraphic framework of the study area, and discussed the characteristics of the sedimentary evolution within the sequence stratigraphic framework : the SQ1 LST period, the basin mainly developed alluvial fans; TST period, there distributed a lot of lakes in the southern area; HST period, the peat bogs formed in the fan front plain and gradually expand to the north until covering the whole region. SQ2 LST period, two lake deltas separately formed in northwest and northeast of Yima coalfield, and gradually develoed peat bogs; TST period, the whole study area covered by lakes; HST period, with the shrinking of the lakes, the peat bogs covered the bay in the south of the basin, until terminated by the conglomerate deposition of Ma’ao Formation.During the sedimentary period of Yima Formation, the tectonic movement in the study area was weak, the climate was warm and humid, and the plants flourished everywhere, all attribute to the development of peat bogs. The occurrence of coal accumulation also subjected to the control of sedimentary basement, sedimentary environment and the changing of lake level, and can be reduced to Alluvial fan, Lake Delta and Lacustrine 3 kinds of coal accumulation models.