Mechanisms of salinization in a middle Eocene lake in the Tanggu area of the Huanghua Depression |
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| Institution: | 1. State Key Laboratory of Biogeology and Environmental Geology, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China;2. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;3. School of Resources and Environment, Henan Polytechnic University, Jiaozuo 454003, China;4. Hubei Shale Gas Development Co. Ltd, Wuhan 430060, China;1. Geological Survey of Japan, AIST, 1-1-1 Higashi, Tsukuba 305-8567, Japan;2. Department of Earth System Science, Faculty of Science, Fukuoka University, Fukuoka 814-0180, Japan;3. Akiyoshi-dai Museum of Natural History, Shuho-cho, Mine 754-0511, Japan;1. College of Earth Sciences, Jilin University, Changchun, Jilin 130061, China;2. Key-Lab for Evolution of Past Life and Environment in Northeast Asia, Ministry of Education, Changchun, Jilin 130026, China;3. Key-Lab for Oil Shale and Paragenetic Minerals of Jilin Province, Changchun, Jilin 130061, China;4. Senckenberg Research Institute and Natural History Museum, Frankfurt 60325, Germany;5. College of paleontology, Shenyang Normal University, Shenyang, Liaoning 110034, China |
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| Abstract: | The Sha-3-5 Submember of the Shahejie Formation in the Tanggu area of the Huanghua Depression contains analcime-bearing dolomite, indicating salinization of an ancient lake during deposition. Solar evaporation and hydrothermal salinization have both been proposed as ways to generate these saline conditions. Based on a comprehensive analysis of core data, thin sections, spore and pollen data, elemental geochemistry, pyrolysis results, and vitrinite reflectance, we assessed the mechanisms driving salinization in light of provenance evolution, geothermal evolution, paleoclimate, mineral responses to evaporation, and the relationship between fluid temperature and salinity. The vertical profiles of ΣREE, Eu/*Eu, and Tmax exhibit little variation, and the maximum paleotemperatures attained by organic matter are comparable to present-day drill hole temperature. No major changes in provenance or paleotemperature and no petrological fabrics that would indicate a hydrothermal input are observed in the studied section. However, evidence for a semi-humid to semi-arid climate, primary evaporitic textures and structures, and a positive relationship between fluid temperature and salinity all support evaporation as the primary mechanism driving rising salinity. Solar evaporation, rather than hydrothermal eruption, appears to have been the primary factor driving lake salinization during middle Eocene deposition of the dolomitic Sha-3-5 Submember. |
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| Keywords: | Sha-3-5 submember Evaporation Hydrothermal eruption Provenance Paleotemperature Climate |
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