Genesis of alkaline lacustrine deposits in the Lower Permian Fengcheng Formation of the Mahu Sag, northwestern Junggar Basin: insights from a comparison with the worldwide alkaline lacustrine deposits

被引：0
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作者：
Li W. [1 ]
Zhang Y. [1 ]
Ni M. [1 ]
Tang W. [1 ]
机构：
[1] Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing
来源：
Dizhi Xuebao/Acta Geologica Sinica | 2020年 / 94卷 / 06期
关键词：
Alkaline lacustrine deposits; Climate; Diagenesis; Fengcheng Formation; Mahu Sag; Shale oil; Volcanism;
D O I：
10.19762/j.cnki.dizhixuebao.2020087
中图分类号：
学科分类号：
摘要：
The alkaline lacustrine deposits are distributed all over the world and formed under special tectonic and climate conditions with volcanic and hydrothermal activities. The old, deeply buried alkaline lacustrine deposit in the Lower Permian Fengcheng Formation of the Mahu Sag provides a unique opportunity to study its sedimentary and diagenetic evolution. In addition, the distribution of alkaline lake deposits in the Fengcheng Formation is closely related to the distribution of shale reservoirs, thus a study of their formation and evolution provides important support towards the study of the shale reservoirs.A comprehensive study of sedimentary characteristics and genesis of worldwide alkaline lacustrine deposits was carried out to provide new insights into the genesis of the alkaline lacustrine deposits in the Lower Permian Fengcheng Formation of the Mahu Sag, northwestern Junggar Basin. An overview of the literature indicates that both contemporaneous volcanic activity and specific climatic could control the formation of the alkaline lacustrine deposits. The formation of alkaline lacustrine deposits required hydrologically closed basins, adequate solute supply of sodium and carbon, low concentration of sulfate, and a strong evaporative environment. The relationship between the mineral types and burial depth of the global alkaline lacustrine deposits indicated that the minerals were transformed by diagenesis. Diagenesis resulted in the conversion of gaylussite to pirssonite and finally into shortite. Meanwhile, wegscheiderite was formed diagenetically from nahcolite and trona. Comparative analysis showed that shortite and wegscheiderite in the alkaline lacustrine deposits from the Fengcheng Formation were formed by diagenetic mineral transformation. Searlesite was formed from pyroclastic deposits under burial alteration and diagenesis, and reedmergnerite was related to hydrothermal activity. The characteristic minerals were associated with the sediments formed by weathering of surrounding alkaline volcanic rocks. The depocenter of the alkaline lacustrine deposits in the Fengcheng Formation was covered by high alkaline brines and the depositional environment was anoxic as a result of perennial salinity-based lake water stratification. The alkaline lacustrine deposits in the study area were controlled by specific climate, tectonism, volcanism and diagenesis. © 2020, Science Press. All right reserved.
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页码：1839 / 1852
页数：13
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