Multistage Diagenetic Fluid Shaping Miocene Island Dolostones on One Isolated Atoll in the South China Sea: Insights from LA-ICP-MS U–Pb Dating and Geochemical Characterization
Cenozoic dolomitization of reefal carbonates has been widely found on many tropical islands worldwide. However, most ages and geochemical data obtained from bulk samples prevent a clear understanding of the previous complex diagenetic processes of these island dolostones due to a lack of in situ age...
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MDPI AG
2024-01-01
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| author | Yun Luo Gang Li Xiyang Zhang Weihai Xu Xiaowei Zhu Wanqiu Zhou Huiwen Huang Wen Yan Fuchang Zhong |
| author_facet | Yun Luo Gang Li Xiyang Zhang Weihai Xu Xiaowei Zhu Wanqiu Zhou Huiwen Huang Wen Yan Fuchang Zhong |
| author_sort | Yun Luo |
| collection | DOAJ |
| description | Cenozoic dolomitization of reefal carbonates has been widely found on many tropical islands worldwide. However, most ages and geochemical data obtained from bulk samples prevent a clear understanding of the previous complex diagenetic processes of these island dolostones due to a lack of in situ age and fluid composition. In this study, one deep borehole penetrated Cenozoic carbonates on Meiji Island in the southern South China Sea and massive dolostones with thicknesses over 400 m were uncovered. The in situ U–Pb geochronology and elemental analysis were conducted on the lower Nanwan Formation (upper Miocene) comprising undolomitized calcite (bioclast), replacive dolomite, and dolomite cement. Strontium isotope ages and U–Pb dates show that the penecontemporaneous replacive dolomitization occurred at 11.0–8.5 Ma, close to the deposition of precursor limestone. The dolomite cement precipitated at 8.5–6.0 Ma. In situ elemental analyses indicate that the formation of replacive dolomite and dolomite cement in the Nanwan Formation was probably controlled by seawater. The higher Mg/Ca ratio and lower Mn and Sr contents in dolomite cements show that their fluid underwent more evaporation. The dolomite content is positively related to the porosity of reefal limestones in the Nanwan Formation, suggesting that primary voids play an important role in fluid transportation during following dolomitization. Coralline algae and lime mud with algal fragments are beneficial for the rapid nucleation of dolomite. This study demonstrates that in situ elemental analysis using laser ablation has great potential for identifying the source of multistage dolomitizing fluids and can help refine the existing dolomitization model of isolated atolls. |
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| spelling | doaj.art-c6299048933b412fb66c4ebfbb5834822024-02-23T15:28:36ZengMDPI AGMinerals2075-163X2024-01-0114215710.3390/min14020157Multistage Diagenetic Fluid Shaping Miocene Island Dolostones on One Isolated Atoll in the South China Sea: Insights from LA-ICP-MS U–Pb Dating and Geochemical CharacterizationYun Luo0Gang Li1Xiyang Zhang2Weihai Xu3Xiaowei Zhu4Wanqiu Zhou5Huiwen Huang6Wen Yan7Fuchang Zhong8Key Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, ChinaKey Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, ChinaKey Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, ChinaKey Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, ChinaKey Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, ChinaKey Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, ChinaKey Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, ChinaKey Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, ChinaKey Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, ChinaCenozoic dolomitization of reefal carbonates has been widely found on many tropical islands worldwide. However, most ages and geochemical data obtained from bulk samples prevent a clear understanding of the previous complex diagenetic processes of these island dolostones due to a lack of in situ age and fluid composition. In this study, one deep borehole penetrated Cenozoic carbonates on Meiji Island in the southern South China Sea and massive dolostones with thicknesses over 400 m were uncovered. The in situ U–Pb geochronology and elemental analysis were conducted on the lower Nanwan Formation (upper Miocene) comprising undolomitized calcite (bioclast), replacive dolomite, and dolomite cement. Strontium isotope ages and U–Pb dates show that the penecontemporaneous replacive dolomitization occurred at 11.0–8.5 Ma, close to the deposition of precursor limestone. The dolomite cement precipitated at 8.5–6.0 Ma. In situ elemental analyses indicate that the formation of replacive dolomite and dolomite cement in the Nanwan Formation was probably controlled by seawater. The higher Mg/Ca ratio and lower Mn and Sr contents in dolomite cements show that their fluid underwent more evaporation. The dolomite content is positively related to the porosity of reefal limestones in the Nanwan Formation, suggesting that primary voids play an important role in fluid transportation during following dolomitization. Coralline algae and lime mud with algal fragments are beneficial for the rapid nucleation of dolomite. This study demonstrates that in situ elemental analysis using laser ablation has great potential for identifying the source of multistage dolomitizing fluids and can help refine the existing dolomitization model of isolated atolls.https://www.mdpi.com/2075-163X/14/2/157island dolostoneearly dolomitizationU–Pb datingWell NK-1southern South China Sea |
| spellingShingle | Yun Luo Gang Li Xiyang Zhang Weihai Xu Xiaowei Zhu Wanqiu Zhou Huiwen Huang Wen Yan Fuchang Zhong Multistage Diagenetic Fluid Shaping Miocene Island Dolostones on One Isolated Atoll in the South China Sea: Insights from LA-ICP-MS U–Pb Dating and Geochemical Characterization Minerals island dolostone early dolomitization U–Pb dating Well NK-1 southern South China Sea |
| title | Multistage Diagenetic Fluid Shaping Miocene Island Dolostones on One Isolated Atoll in the South China Sea: Insights from LA-ICP-MS U–Pb Dating and Geochemical Characterization |
| title_full | Multistage Diagenetic Fluid Shaping Miocene Island Dolostones on One Isolated Atoll in the South China Sea: Insights from LA-ICP-MS U–Pb Dating and Geochemical Characterization |
| title_fullStr | Multistage Diagenetic Fluid Shaping Miocene Island Dolostones on One Isolated Atoll in the South China Sea: Insights from LA-ICP-MS U–Pb Dating and Geochemical Characterization |
| title_full_unstemmed | Multistage Diagenetic Fluid Shaping Miocene Island Dolostones on One Isolated Atoll in the South China Sea: Insights from LA-ICP-MS U–Pb Dating and Geochemical Characterization |
| title_short | Multistage Diagenetic Fluid Shaping Miocene Island Dolostones on One Isolated Atoll in the South China Sea: Insights from LA-ICP-MS U–Pb Dating and Geochemical Characterization |
| title_sort | multistage diagenetic fluid shaping miocene island dolostones on one isolated atoll in the south china sea insights from la icp ms u pb dating and geochemical characterization |
| topic | island dolostone early dolomitization U–Pb dating Well NK-1 southern South China Sea |
| url | https://www.mdpi.com/2075-163X/14/2/157 |
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