Coal-accumulating processes and base level cycles of the Taiyuan Formation in the Datong coalfield

Abstract: Based on the base-level cycle principle, the authors studied high-resolution sequence stratigraphic characteristics and coal accumulation of Taiyuan Formation in the Datong coalfield by using borehole, logging and geological data. One long-term base level cycle, three medium-term base level cycles and seven short-term base level cycles were identified. Various sedimentary facies sequences, structure and stacking pattern of short cycle sequences and controlling factors for coal accumulation in different middle cycle sequences were analyzed emphatically and, as a result, the distribution features and log responses of sand bodies and coal seams in the interior were obtained. The research results also show that the accumulation of the coal of Taiyuan Formation was controlled by medium-term base-level changes under the conditions of slight extension and slow subsidence of tectonic setting and humid climate. The late rising half medium-term base-level was favorable for depositing wide and thick coal seams, while thin layers of carbonaceous mudstone and coal were developed in the early-to-middle period of the rising half medium-term base level or the late period of the falling half level, where the coal seams were distributed sporadically with poor continuity laterally.