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Burial Records of reactive iron in Cretaceous Black Shales and Oceanic Red Beds from Southern Tibet

Acta Geologica Sinica(English Edition) 2007年第3期81卷 463-469页

作者： HUANG Yongjian WANG Chengshan HU Xiumian CHEN Xi 1 Research Center for Tibetan Plateau Geology China University of Geosciences （Beijing） Beijing 100083 Department of Earth Sciences Nanjing University Nanjing Jiangsu 210093

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.

关键词： reactive iron black shales oceanic red beds Cretaceous southern Tibet

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Geochemistry of iron,Sulfur and Related Heavy Metals in Metal-Polluted Taihu Lake Sediments

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Pedosphere 2008年第5期18卷 564-573页

作者： YIN Hong-Bin FAN Cheng-Xin DING Shi-Ming ZHANG Lu ZHONG Ji-Cheng State Key Laboratory of Lake Science and Environment Nanjing Institute of Geography and Limnology ChineseAcademy of Sciences Nanjing Z10008 （China）. Graduate University of the Chinese Academy of Sciences Beijing 100049 （China）

To understand the geochemical characteristics of iron and sulfur and the extent of iron-sulfide minerals influencing heavy metal behaviour in metal-polluted sediments of Talhu Lake, two sites, in Meiliang Bay （ML） and Wuli Lake （WL）, were selected to study the fractionation of iron, sulfur and related heavy metals. There were relatively high concentrations of Fe^2＋ and low concentrations of total S^2- in porewaters, indicating that conditions in these sediments favored iron reduction. The concentrations of acid volatile sulfides in sediments were 1.9-9.6 μmol g^-1 at ML and 1.0-11.7 μmool g^-1 at WL, both in the range of values detected in unpolluted lakes. Pyrite-S was 10.2-49.4 μmol g^-1 at ML and 10.3- 33.0 μmol g^-1 at WL, accounting for more than 69% of the reduced inorganic sulfur at both sites. The low degree of sulphidization （〈 14%） and pyritization （〈 10%） indicate that sulfate may be the limiting factor for pyrite formation. The extractability of Mn, Cu, Pb, Zn, Ni, and Cr in sediments all suggest that sulfides are not the major binding phase for these metals during early diagenesis. Sulfur may play a modest role in the geochemistry of iron and traced metals in the sediments.

关键词： heavy metals reactive iron reduced inorganic sulfur Taihu Lake

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