Depositional model for peat swamp and coal facies evolution using sedimentology, coal macerals, geochemistry and sequence stratigraphy
Depositional model for peat swamp and coal facies evolution using sedimentology, coal macerals, geochemistry and sequence stratigraphy
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DOI：
10.1007/s12583-016-0942-7
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发表时间：
2017-12
影响因子：
3.3
通讯作者：
Jing Lu;L. Shao;Minfang Yang;Kai Zhou;J. Wheeley;Hao Wang;J. Hilton
中科院分区：
文献类型：
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作者：
Jing Lu;L. Shao;Minfang Yang;Kai Zhou;J. Wheeley;Hao Wang;J. Hilton
泥炭沼泽作为非常规天然气最重要的烃源岩和储集层之一，（煤层的前身）对煤层的空间分布、物质组成、生烃潜力、储层物性等都有重要意义。为了揭示陆相盆地泥炭堆积时期的沉积特征和环境变化史，对柴达木盆地高泉中侏罗统7号煤进行了沉积学、显微组分、地球化学和层序地层学研究。通过对沉积岸线破碎带、波能亏损点和波基面位置的识别，将泥炭沼泽系统划分为（1）湖滨平原亚相、（2）低能湖岸亚相、（3）高能湖岸亚相和（4）浅湖亚相。提出了一种综合考虑氧化还原程度、能量条件和陆源沉积物影响的煤相判别方法。煤层演化表明，泥炭主要沉积在低能湖滨和湖滨平原亚相中。识别出5种层序地层面和2种准层序。强制湖退和正常湖退是层序界面形成的原因。层序地层格架由6个层序和相应的体系域组成，每个层序的基准面曲线均表现出缓慢上升-快速上升-缓慢上升的特征。提出了基准面变化、煤相演化与沼泽环境特征的关系模式，表明沼泽环境特征受基准面变化和煤相的共同控制。随着基准面上升速率的加快，沉积环境由湖滨平原向湖滨、浅湖转变，水体古盐度、酸度和木本植物比例降低，沼泽类型由低沼泽向高沼泽转变。
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.