Origin and depositional paleoenvironment of Triassic polyhalite in the Jialingjiang Formation, Sichuan Basin
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ORIGINAL ARTICLE
Origin and depositional paleoenvironment of Triassic polyhalite in the Jialingjiang Formation, Sichuan Basin Yanjun Zhao1 · Chenglin Liu1 · Ting Ding2,3 · Luis A. Gonzalez3 · Zhaoqi Li4 · Mingquan Wang5 · Licheng Wang1 · Zhengjie Zhu6 Accepted: 17 May 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The Sichuan Basin contains the most prolific marine potash salt deposits in China. Although a vast amount of polyhalite has been found in the Triassic Jialingjiang Formation, the production of soluble potash deposits has yet to begin. The origin and sedimentary environment of polyhalite has remained unclear, and this information could have a significant economic impact. The recent discovery of protogenetic polyhalite co-existing with halite crystals in cores from the early Triassic Jialingjiang Formation in eastern Sichuan Basin provides vital clues to its origin and depositional environment. Two types of polyhalite have been identified, through the examination of sedimentary textures and fabrics, mineral composition and contents, and major and trace elements from cores. The first type is protogenetic polyhalite, which co-exists and is commingled with halite crystals. The second type is secondary in origin with a radiating texture and was formed by the metasomatism of gypsum. Triassic polyhalite and halite was deposited during periods of freshwater and sylvite-saturated, evaporated seawater mixing. Further dilution of the freshwater resulted in gypsum precipitation among the halite crystals. After periods of desalination, increasing evaporation leads to the formation of highly concentrated and dense brines that are rich in potassium and magnesium. These heavy brines sink downward through intercrystalline pores and fractures, replacing gypsum with polyhalite through metasomatism. These sequential phenomena occur because the Triassic marine basins were relatively small and tectonically active. Although these shallow, small salt basins can have a fast concentration rate, they can be easily desalinated by the peripheral freshwater input in an overall arid but fluctuating arid and wet climate. The alternating periods of evaporation and desalination are responsible for the formation of soluble potassium salt deposits. Our proposed mechanisms provide useful information for understanding the distribution of polyhalite. These mechanisms can be used to guide future exploration and production of Triassic marine potash salts in the periphery of the Tethys Ocean. Keywords Paleoenvironment · Polyhalite · Halite · Jialingjiang formation · Triassic · Sichuan basin Electronic supplementary material The online version of this article (https://doi.org/10.1007/s13146-020-00596-3) contains supplementary material, which is available to authorized users. * Chenglin Liu [email protected] 1
MNR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China
2
East China University of Technology, Jiangxi
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