Sequence-palaeogeography and coal accumulation of the upper Triassic Wayaobu Formation in central Ordos Basin
Li Ming-Pei1,2, Shao Long-Yi3, Xia Yu-Cheng1, Li Zhi-Xue2,4, He Dan5, Li Li3
1 School of Geology and Environment,Xi'an University of Science and Technology,Xi'an 710054,China; 2 Innovation Technology Research Institute of Shaanxi Investment Group Co.,Ltd.,Xi'an 710061,China; 3 School of Geoscience and Surveying Engineering,China University of Mining & Technology(Beijing),Beijing 100083,China; 4 Shaanxi Investment Group Co.,Ltd.,Xi'an 710061,China; 5 Shaanxi Coal Geology Group Co.,Ltd.,Xi'an 710026,China
Abstract：In order to study the evolution of the sequence and paleogeography and the coal accumulation law of the upper Triassic Wayaobu Formation in the central Ordos Basin,the field outcrops,boreholes and logging data are used to identify five types of lithology and 17 types of lithofacies in the Wayaobu Formation. Based on the sequence stratigraphic interfaces such as regional unconformity surface,the abrupt change of formation surface and the erosion surface by the incised river valley,the Wayaobu Formation is divided into three third-level sequences,i.e., SQ1,SQ2 and SQ3. The sedimentary range,lithofacies assemblages and sedimentary system of them are identified. It shows that the sedimentary units of SQ1,SQ2 and SQ3 in the Wayaobu stage are mainly composed of meandering river,alluvial plain,delta plain,delta front and lake. From the SQ1 period to the SQ3 period,the alluvial plain and delta gradually advanced to the lake area,while the area of lake gradually shrinked. The development of delta plain provided a favorable place for coal accumulation and the coal seam of industrial importance formed. Between the SQ1 period and the SQ3 period,the coal accumulation mainly occurred in the lacustrine transgressive system tract. With the gradually development of coal accumulation,the rate of peat accumulation and the growth rate of accommodation space gradually reached a balance,and the total thickness of coal seam and the maximum single layer thickness of coal seam gradually increased too. The results can provide geological basis for coal resource potential prediction and formation mechanism research of oil-rich coal in the upper Triassic Wayaobu Formation of Ordos Basin.
Li Ming-Pei,Shao Long-Yi,Xia Yu-Cheng et al. Sequence-palaeogeography and coal accumulation of the upper Triassic Wayaobu Formation in central Ordos Basin[J]. JOPC, 2021, 23(2): 375-388.
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