Abstract
Santanghu Coalfield is the largest integrated coalfield exploration area in China. The major coal seams developing in Xishanyao Formation (Middle Jurassic) are the high-quality steam coals characterized by large thickness, favorable horizontal continuity and high coal quality. In this paper, twenty-two samples were collected from the three typical boreholes in Hanshuiquan district, representing the 11 coal seam sequences (7#, 8#, 9#, 13#, 14#, 15#, 17#, 18#, 19#, 20#, 22#), respectively. The petrographic characteristics of the coal-bearing sequence in Xishanyao Formation were firstly summarized systematicly, and then the coal-forming swamp characteristics and succession mechanism of the coal seam in Xishanyao Formation were defined by analyzing the samples. The maceral composition, structure, geochemical and geophysical characteristics of coal are included in original genetic criteria of coal-forming swamp analysis. And the composition of coal petrography, maceral and microlithotype are the most frequently used parameters. Coal is composed of microscopic constituents and inorganic substances. The Xishanyao Formation maceral mainly consists of vitrinite (65.74%–97.01%), inertinite (1.93%–34%), and the exinite shows the mode of regular change. The coal-forming swamp in Xishanyao Formation possesses the characteristics of mainly marsh, wet forest swamp facies, and shallow water covered forest swamp facies, and a few of coal seams distribute in the deep water covered forest swamp facies. In addition, the sporopollens in Xishanyao Formation are mainly Pinaceae evergreen broad leaf and needle-leaved plants, Osmundaceae, Cyatheaceae and Lygodiaceae, indicating that the warm and humid tropic-subtropical climate conductive to the persistent growth of coal-forming plants in the Middle Jurassic. The coal-forming swamp shows the characteristics of vertically upward fluctuation through the periodic transition. It indicates a shallow-deep-shallow change process of the water covered depth in the swamp. This is the principal factor for the formation of the high-quality and continuous coal seam in Hanshuiquan district, Santanghu Coalfield.
Highlights
The contents of ash and sulphur in high-quality coal developing in Jurassic System of northwest China are low (Huang et al 2010), which is conducive to the development of industrial economy and ecological environment, and its et al 2009; Dai et al 2012; Ao et al 2012)
The major coal seams developing in Xishanyao Formation (Middle Jurassic) are the high-quality steam coals characterized by large thickness, favorable horizontal continuity and high coal quality
The coal-forming swamp in Xishanyao Formation possesses the characteristics of mainly marsh, wet forest swamp facies, and shallow water covered forest swamp facies, and a few of coal seams distribute in the deep water covered forest swamp facies
Summary
The contents of ash and sulphur in high-quality coal developing in Jurassic System of northwest China are low (Huang et al 2010), which is conducive to the development of industrial economy and ecological environment, and its. Zhang et al (2015) studied the Jurassic coal-forming swamp in Santanghu, and believed that the major coal seam in Xishanyao Formation is transited from wide water marsh to wet forest swamp, and through the research of its coal petrography and coalforming swamp, he found that exinite content is zero. This might be resulted from the small quantity of sample, which fails to accurately reflect the evolutionary characteristics of the coal-forming swamp in this area. The characteristic and evolution of coal-forming swamp in Hanshuiquan district, Santanghu
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