Sequence-palaeogeography and coal accumulation of the Lower Cretaceous Saihantala Formation in the Bayanbaolige Coalfield, Erlian Basin, Inner Mongolia
Wang Shuai1, Shao Long-Yi1, Sun Qin-Ping2, Zhang Yun-He1, Shi Ming-Jian1, Sun Bin2, Lu Jing1
1 School of Geoscience and Surveying Engineering,China University of Mining & Technology(Beijing),Beijing 100083; 2 Langfang Branch of Research Institute of Petroleum Exploration and Development,PetroChina,Langfang 065007,Hebei;
Abstract：The Bayanbaolige Coalfield of Erlian Basin is rich in coal and coalbed methane resources. In this paper, we studied the palaeogeographic evolution and coal accumulation in sequence stratigraphic framework of the Lower Cretaceous Saihantala Formation based on data of boreholes and logging curves. Three types of sequence boundary, including regional unconformities, basal erosional surfaces of the incised valley fills and correlative conformities, were recognized. Accordingly, the Saihantala Formation was divided into two third-order sequences, and thick coal seams were developed in the early and late transgressive system tract of Sequence Ⅰ. The palaeogeographic pattern were reconstructed based on the single factor analysis and multifactor comprehensive mapping method, and the palaeogeographic units include alluvial fan, fan delta plain and shoreline-shallow lake. The favorable coal-forming sites were in the lakeshore-shallow lake, the transitional zone between fan delta plain and lakeshore-shallow lake where moderate subsidence was maintained and there was little input of coarse-grained sediments. Seam thickness and coal accumulation decreased from Sequence Ⅰ to Sequence Ⅱ. The development of the thick coal seams of multilayers, which were affected by intermittence and periodicity of subsidence, were controlled by the continuous change of ratio between the accommodation increase rate and the peat accumulation rate. For the Sequence Ⅰ,the central study area is the favorable area for the exploration of coal and coalbed methane resources in the future.
Wang Shuai,Shao Long-Yi,Sun Qin-Ping et al. Sequence-palaeogeography and coal accumulation of the Lower Cretaceous Saihantala Formation in the Bayanbaolige Coalfield, Erlian Basin, Inner Mongolia[J]. JOPC, 2018, 20(2): 325-336.
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