The Formation Mechanism and Geological Significance of Graptolite from the Longmaxi Formation: Constraints from in situ Multi-element Imaging Analysis
BACKGROUND The black shale of the Longmaxi Formation in the Upper Yangtze region is rich in graptolites. Most of them were preserved as a carbonaceous film, and enriched in organic-rich layers. Previous research focuses mainly on the graptolite morphology and evolution process after diagenesis, but...
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| Format: | Article |
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Science Press, PR China
2019-05-01
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| Series: | Yankuang ceshi |
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| Online Access: | http://www.ykcs.ac.cn/en/article/doi/10.15898/j.cnki.11-2131/td.201810110113 |
| _version_ | 1797953794030436352 |
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| author | ZHU Cheng-lin WANG Hua-jian YE Yun-tao WANG Xiao-mei HUANG Jia-xuan ZHU Yu-mei YANG Rui-dong |
| author_facet | ZHU Cheng-lin WANG Hua-jian YE Yun-tao WANG Xiao-mei HUANG Jia-xuan ZHU Yu-mei YANG Rui-dong |
| author_sort | ZHU Cheng-lin |
| collection | DOAJ |
| description | BACKGROUND The black shale of the Longmaxi Formation in the Upper Yangtze region is rich in graptolites. Most of them were preserved as a carbonaceous film, and enriched in organic-rich layers. Previous research focuses mainly on the graptolite morphology and evolution process after diagenesis, but the direct evidence for the fossil formation is still lacking. OBJECTIVES To explore the formation mechanism of graptolite in the Longmaxi Formation and its geological significance on organic matter enrichment. METHODS Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) was used for the in situ multi-element imaging of graptolites and surrounding rocks from the Longmaxi Formation of the N203 well. RESULTS Analysis of the distribution and enrichment degree of major ore-forming elements indicates that Mg, Al, Si, Fe were rich in the carbonaceous film surface of graptolite, with a enrichment degree ranging from 1.5 to 10. However, Sr/Ba values (1.4-2.3) of the carbonaceous film type graptolite were lower than that of the surrounding rocks (>5.0). This indicated that embedding by clay minerals was the main process of graptolite preservation. The sulfidic micro-environment caused by embedding of clay minerals benefited the pyritization of the graptolite organism. Combing with the vertical variation and correlation analysis of the cross-section graptolite ratio, organic matter, pyrite, clay mineral content and δ13Corg value, it can be concluded that the flourishing of the microbial mat in early stage and sulfate-reducing bacteria in later stage consumed oxygen in the pore water and caused anoxic bottom water, and should be the main reason of massive burial of graptolite and organic matter. CONCLUSIONS The result revealed the burial and mineralization mechanism of graptolite in the Longmaxi Formation, and also provided a new method for studying the controlling factors of organic matter enrichment and black shale formation. |
| first_indexed | 2024-04-10T23:07:44Z |
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| institution | Directory Open Access Journal |
| issn | 0254-5357 |
| language | English |
| last_indexed | 2024-04-10T23:07:44Z |
| publishDate | 2019-05-01 |
| publisher | Science Press, PR China |
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| spelling | doaj.art-461803c6533541cc8419e7653fa24ca72023-01-13T10:06:13ZengScience Press, PR ChinaYankuang ceshi0254-53572019-05-0138324525910.15898/j.cnki.11-2131/td.201810110113ykcs-38-3-245The Formation Mechanism and Geological Significance of Graptolite from the Longmaxi Formation: Constraints from in situ Multi-element Imaging AnalysisZHU Cheng-lin0WANG Hua-jian1YE Yun-tao2WANG Xiao-mei3HUANG Jia-xuan4ZHU Yu-mei5YANG Rui-dong6College of Resources and Environmental Engineering, Guizhou University, Guiyang 550025, ChinaKey Laboratory of Petroleum Geochemistry, Research Institute of Petroleum Exploration and Development, Beijing 100083, ChinaKey Laboratory of Petroleum Geochemistry, Research Institute of Petroleum Exploration and Development, Beijing 100083, ChinaKey Laboratory of Petroleum Geochemistry, Research Institute of Petroleum Exploration and Development, Beijing 100083, ChinaKey Laboratory of Petroleum Geochemistry, Research Institute of Petroleum Exploration and Development, Beijing 100083, ChinaKey Laboratory of Petroleum Geochemistry, Research Institute of Petroleum Exploration and Development, Beijing 100083, ChinaCollege of Resources and Environmental Engineering, Guizhou University, Guiyang 550025, ChinaBACKGROUND The black shale of the Longmaxi Formation in the Upper Yangtze region is rich in graptolites. Most of them were preserved as a carbonaceous film, and enriched in organic-rich layers. Previous research focuses mainly on the graptolite morphology and evolution process after diagenesis, but the direct evidence for the fossil formation is still lacking. OBJECTIVES To explore the formation mechanism of graptolite in the Longmaxi Formation and its geological significance on organic matter enrichment. METHODS Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) was used for the in situ multi-element imaging of graptolites and surrounding rocks from the Longmaxi Formation of the N203 well. RESULTS Analysis of the distribution and enrichment degree of major ore-forming elements indicates that Mg, Al, Si, Fe were rich in the carbonaceous film surface of graptolite, with a enrichment degree ranging from 1.5 to 10. However, Sr/Ba values (1.4-2.3) of the carbonaceous film type graptolite were lower than that of the surrounding rocks (>5.0). This indicated that embedding by clay minerals was the main process of graptolite preservation. The sulfidic micro-environment caused by embedding of clay minerals benefited the pyritization of the graptolite organism. Combing with the vertical variation and correlation analysis of the cross-section graptolite ratio, organic matter, pyrite, clay mineral content and δ13Corg value, it can be concluded that the flourishing of the microbial mat in early stage and sulfate-reducing bacteria in later stage consumed oxygen in the pore water and caused anoxic bottom water, and should be the main reason of massive burial of graptolite and organic matter. CONCLUSIONS The result revealed the burial and mineralization mechanism of graptolite in the Longmaxi Formation, and also provided a new method for studying the controlling factors of organic matter enrichment and black shale formation.http://www.ykcs.ac.cn/en/article/doi/10.15898/j.cnki.11-2131/td.201810110113longmaxi formationgraptolitemulti-element imaginglaser ablation-inductively coupled plasma-mass |
| spellingShingle | ZHU Cheng-lin WANG Hua-jian YE Yun-tao WANG Xiao-mei HUANG Jia-xuan ZHU Yu-mei YANG Rui-dong The Formation Mechanism and Geological Significance of Graptolite from the Longmaxi Formation: Constraints from in situ Multi-element Imaging Analysis Yankuang ceshi longmaxi formation graptolite multi-element imaging laser ablation-inductively coupled plasma-mass |
| title | The Formation Mechanism and Geological Significance of Graptolite from the Longmaxi Formation: Constraints from in situ Multi-element Imaging Analysis |
| title_full | The Formation Mechanism and Geological Significance of Graptolite from the Longmaxi Formation: Constraints from in situ Multi-element Imaging Analysis |
| title_fullStr | The Formation Mechanism and Geological Significance of Graptolite from the Longmaxi Formation: Constraints from in situ Multi-element Imaging Analysis |
| title_full_unstemmed | The Formation Mechanism and Geological Significance of Graptolite from the Longmaxi Formation: Constraints from in situ Multi-element Imaging Analysis |
| title_short | The Formation Mechanism and Geological Significance of Graptolite from the Longmaxi Formation: Constraints from in situ Multi-element Imaging Analysis |
| title_sort | formation mechanism and geological significance of graptolite from the longmaxi formation constraints from in situ multi element imaging analysis |
| topic | longmaxi formation graptolite multi-element imaging laser ablation-inductively coupled plasma-mass |
| url | http://www.ykcs.ac.cn/en/article/doi/10.15898/j.cnki.11-2131/td.201810110113 |
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