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篇目详细内容 |
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【篇名】 |
Cretaceous black shale and the oceanic red beds: |
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【刊名】 |
Frontiers of Earth Science in China |
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【刊名缩写】 |
Front. Earth Sci. China |
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【ISSN】 |
1673-7385 |
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【EISSN】 |
1673-7490 |
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【DOI】 |
10.1007/s11707-008-0008-y |
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【出版社】 |
Higher Education Press and Springer-Verlag |
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【出版年】 |
2008 |
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【卷期】 |
2
卷1期 |
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【页码】 |
41-48
页,共
8
页 |
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【作者】 |
ZHANG Zhenguo;
FANG Nianqiao;
GAO Lianfeng;
GUI Baoling;
Cui Muhua;
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【关键词】 |
anoxic event; black shale; oceanic red bed; oxic process; oceanic volcanic activity; Cretaceous |
【摘要】 |
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The Cretaceous is an important period in which many geological events occurred, especially the OAEs (oceanic anoxic events) which are characterized by black shale, and the oxic process characterized by CORBs (Cretaceous oceanic red beds). In this paper, the causative mechanism behind the formation of black shale and the oceanic red beds are described in detail. This may explain how the oceanic environment changed from anoxic to oxic in the Cretaceous period. It is suggested that these two different events happened because of the same cause. On the one hand, the large-scale magma activities in Cretaceous caused the concentration of CO2, the release of the inner energy of the earth, superficial change in the ocean-land, and finally, the increase of atmospheric temperature. These changes implied the same tendency as the oceanic water temperature show, and caused the decrease in O2 concentration in the Cretaceous ocean, and finally resulted in the occurrence of the OAEs. On the other hand, violent and frequent volcanic eruptions in the Cretaceous produced plenty of Fe-enriched lava on the seafloor. When the seawater reacted with the lava, the element Fe became dissolved in seawater. Iron, which could help phytoplankton grow rapidly, is a micronutrient essential to the synthesis of enzymes required for photosynthesis in the oceanic environment. Phytoplankton, which grows in much of the oceans around the world, can consume carbon dioxide in the air and the ocean. Meanwhile, an equal quantity of oxygen can be produced by the phytoplankton during its growth. Finally, the oxic environment characterized by red sediment rich in Fe3+ appeared. The anoxic and oxic conditions in the Cretaceous ocean were caused by volcanic activities, but they stemmed from different causative mechanisms. The former was based on physical and chemical processes, while the latter involved more complicated bio-oceanic-geochemical processes. |
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