Depositional Model for Peat Swamp and Coal Facies Evolution Using Sedimentology, Coal Macerals, Geochemistry and Sequence Stratigraphy

查看全文 作　　者：Jing [1,2]Lu;Longyi [1]Shao;Minfang [3]Yang;Kai [1]Zhou;James [2]R.Wheeley;Hao [1]Wang;Jason [2]Hilton

机构地区：[1]State Key Laboratory of Coal Resources and Safety Mining, China University of Mining and Technology;[2]School of Geography, Earth and Environmental Sciences, the University of Birmingham;[3]Langfang Branch of Petroleum Exploration and Development Research Insitute,Petro China

出　　处：《Journal of Earth Science》索引2017年第28卷第6期,共15页

基　　金：the National Natural Science Foundation of China (Nos. 41472131, 41772161);New Century Excellent Talents Fund of Chinese Ministry of Education (No. 2013102050020) 摘　　要：As one of the most important source rocks and reservoirs of unconventional natural gas, the sedimentary environment and mode of peat swamp(the predecessor of coal seam) is important to the coal seam's spatial distribution, material composition, hydrocarbon generation potential, reservoir physical properties, etc. To reveal the depositional characteristics and history of environmental change in a terrestrial basin during a period of peat accumulation, the Middle Jurassic aged #7 coal from Gaoquan in the Qaidam Basin(NW China) was investigated using sedimentology, maceral composition, geochemistry and sequence stratigraphy. Based on identification of the sedimentary shoreline break belt, wave energy depletion point and position of wave base, the peat swamp system can be subdivided into(1) lakeside plain,(2) low energy lakeshore,(3) high energy lakeshore, and(4) shallow lake subfacies. A new method for determining coal facies is proposed based on the combination of environmental parameters including oxidation-reduction levels, energy conditions and the influence of terrigneous sediments. The evolution of the coal seam shows that peat was deposited mainly in the low energy lakeshore and lakeside plain subfacies. Five types of sequence stratigrpahic surface and two types of parasequence were identified. Forced lake regressions and normal lake regressions are attributed as the causes of sequence boundaries. The sequence stratigraphic framework comprises six sequences and corresponding system tracts, and the curve of base-level for each demonstrates a characteristic initial period of slow rising followed by fast rising and then returning to slow rising. A model indicating the relationship among base-level changes, coal facies evolution, and the environmental features in the swamp is proposed that shows the environmental features of the swamp were controlled by both base-level changes and coal facies. Accompanying depositional environment changes from a lakeside plain to lakeshore and shallow lake caused by increasing rate of base-level rise, water paleosalinity, acidity and the percentage of woody plants decrease, and the bog type alters from the low marsh to raised bog. 关键词：peat swamp sedimentary model coal facies base level coal maceral

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Depositional Model for Peat Swamp and Coal Facies Evolution Using Sedimentology, Coal Macerals, Geochemistry and Sequence Stratigraphy

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