Seawater normalized REE patterns of dolomites in Geshan and Panlongdong sections,China: Implications for tracing dolomitization and diagenetic fluids |
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| Institution: | 1. Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;2. Department of Earth, Ocean and Ecological Sciences, University of Liverpool, Liverpool L69 3GP, UK;3. Energy Resource Department, China University of Geosciences Beijing 100083, China;4. State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Nanjing 210008, China;5. Hangzhou Research Institute of Geology, Hangzhou 310023, China;6. Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;1. Guangxi Laboratory on the Study of Coral Reefs in the South China Sea, Coral Reef Research Center of China, School of Marine Sciences, Guangxi University, Nanning 530004, China;2. Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T5R 3C8, Canada;3. School of Earth Sciences, University of Queensland, QLD 4067, Australia;4. School of Earth Science and Engineering, Nanjing University, Nanjing 210093, China;1. State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing, Jiangsu 210093, China;2. Institute of Energy Sciences, Nanjing University, Nanjing, Jiangsu 210093, China;3. Northwest Exploration and Production Company, SINOPEC, Xinjiang, Urumqi 830011, China;1. State Key Laboratory of Biogeology and Environmental Geology, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China;2. State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, China;3. Key Laboratory of Carbonate Reservoir of CNPC, Department of Sedimentology and Hydrocarbon Accumulation, Southwest Petroleum University, Chengdu 610500, China;4. Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia;5. School of Earth and Environmental Sciences, The University of Queensland, Brisbane, QLD 4072, Australia;6. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China;7. Department of Geology, University of Cincinnati, Cincinnati, OH 45221-0013, USA |
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| Abstract: | In conventional studies of tracing dolomitization and diagenetic fluids, REEs of dolomites were widely used as been normalized by PAAS, NASC or chondrite. However, most dolomites are formed in seawater or seawater-derived fluids. Thus, we conduct a new attempt to normalize the REEs of dolomite using seawater standard, based on case studies on 36 Triassic limestone–dolomite samples from the Geshan section of southeast China and 26 Permian–Triassic dolomite samples from the Panlongdong section of northeastern Sichuan Basin, southwest China.The Geshan seawater-normalized (SN) REE patterns are characterized by notable positive CeSN (average CeSN/Ce* = 6.823, SD = 0.192) and negative PrSN anomalies (average PrSN/Pr* = 0.310, SD = 0.010), and slightly negative GdSN anomalis (average GdSN/Gd* = 0.864, SD = 0.053), with no obvious EuSN anomaly (average EuSN/Eu* = 1.036, SD = 0.094). The signatures of REE patterns barely changed during the dolomitization process. For the REE compositions of the Panlongdong dolomite, it can be found that (1) the recrystallization process can result in varied total REE concentrations (between 7.16 ppm and 37.87 ppm), but do not alter the REE patterns, including consistent positive CeSN anomalies (average = 4.074, SD = 0.27) and LREE enrichment (average NdSN/YbSN = 3.164, SD = 0.787); (2) meteoric incursion can reverse Ce anomaly, from the strong positive Ce anomalies (CeSN/Ce* = 5.059) to slightly positive (CeSN/Ce* = 2.459) or even negative Ce anomalies; and (3) hydrothermal fluid altered REE pattern is complicated by fluctuated distribution curve, negative Ce anomaly and positive Eu anomaly (EuSN/Eu* = 1.862). These results suggest that the seawater normalized REE patterns of dolomite can serve as an index to study the source of the dolomitization fluids and distinguish complex diagenetic processes, providing a complement to previous works. |
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| Keywords: | Dolomite Seawater normalized REE pattern Diagenesis Geshan section Panlongdong section |
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