| Burial Records of Reactive Iron in Cretaceous Black Shales and Oceanic Red Beds from Southern Tibet |
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| 作者姓名： | HUANG Yongjian WANG Chengshan HU Xiumian CHEN Xi |
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| 作者单位： | [1]1 Research Center for Tibetan Plateau Geology, China University of Geosciences （Beijing）, Beijing 100083 [2]Department of Earth Sciences, Nanjing University, Nanjing, Jiangsu 210093 |
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| 基金项目： | 国家重点基础研究发展计划(973计划)
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国家自然科学基金
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国家自然科学基金
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IGCP 463 |
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| 摘 要： | One of the new directions in the field of Cretaceous research is to elucidate the mechanism of the sedimentary transition from the Cretaceous black shales to oceanic red beds. A chemical sequential extraction method was applied to these two types of rocks from southern Tibet to investigate the burial records of reactive iron. Results indicate that carbonate-associated iron and pyrite are relatively enriched in the black shales, but depleted or absent in red beds. The main feature of the reactive iron in the red beds is relative enrichment of iron oxides （largely hematite）, which occurred during syn-depostion or early diagenesis. The ratio between iron oxides and the total iron indicates an oxygen-enriched environment for red bed deposition. A comparison between the reactive iron burial records and proxies of paleo-productivity suggests that paleo-productivity decreases when the ratio between iron oxides and the total iron increases in the red beds. This phenomenon could imply that the relationship between marine redox and productivity might be one of the reasons for the sedimentary transition from Cretaceous black shale to oceanic red bed deposition.
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| 关 键 词： | 页岩 白垩纪 西藏 反馈作用 |
| 修稿时间： | 2007-03-052007-05-15 |
Burial Records of Reactive Iron in Cretaceous Black Shales and Oceanic Red Beds from Southern Tibet |
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| Authors: | HUANG Yongjian WANG Chengshan HU Xiumian and CHEN Xi Research Center for Tibetan Plateau Geology China University of Geosciences |
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| Abstract: | One of the new directions in the field of Cretaceous research is to elucidate the mechanism of the sedimentary transition from the Cretaceous black shales to oceanic red beds. A chemical sequential extraction method was applied to these two types of rocks from southern Tibet to investigate the burial records of reactive iron. Results indicate that carbonate-associated iron and pyrite are relatively enriched in the black shales, but depleted or absent in red beds. The main feature of the reactive iron in the red beds is relative enrichment of iron oxides (largely hematite), which occurred during syn-depostion or early diagenesis. The ratio between iron oxides and the total iron indicates an oxygen-enriched environment for red bed deposition. A comparison between the reactive iron burial records and proxies of paleo-productivity suggests that paleo-productivity decreases when the ratio between iron oxides and the total iron increases in the red beds. This phenomenon could imply that the relationship between marine redox and productivity might be one of the reasons for the sedimentary transition from Cretaceous black shale to oceanic red bed deposition. |
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| Keywords: | reactive iron black shales oceanic red beds Cretaceous southern Tibet |
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