| 泥盆纪海水的碳、氧同位素变化——来自腕足化石的同位素记录 |
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| 关键词:Longmenshan oxygen isotope carbon isotope brachiopod sea level variation |
| 基金项目:国家自然科学基金项目(编号：40273011)和西北大学大陆动力学国家重点实验室开放课题基金项目(编号：07LCD13) |
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| Carbon and Oxygen Isotope Variations of Devonian Seawater:Isotopic Records from Brachiopod Shell |
| The stable isotopic information in biogenic calcite was used to calculate the isotopic composition of seawater in the geological history. Brachiopod shell, due to its resistant ability to diagenesis (low magnesium calcite) and widespread distribution, was considered to be one of the ideal samples in the study of seawater isotopic composition in Paleozoic. The authors measured carbon and oxygen isotopic compostion of well-preserved Longmenshan brachiopod shells, and established the seawater isotopic variation curve of Devonian and discussed the influencing factors. The results shows that: the δ13C value range from -2‰ to 2‰ (PDB) with three cycles, it every high value corresponding to one reef building event in Longmenshan area. The δ13C value shows different ranges in these cycles because of different variation degrees of sea level, indicating that the δ13C value of seawater was controlled jointly by biological growth and sea level variation, with the former being more important. The δ18O value ranges from -4‰ to -10‰. In Emsian stage, the oxygen isotope increased gradually from -10‰ to -6‰, being -2‰ ~ -4‰ lower than that of other areas. It may be suggested that, before Emsian stage, the Longmen sea was closed or the seawater circulation was not smooth, and its δ18O value was desalinized by the input of fresh water. With the transgression and the seawater assimilation in Emsian stage, the δ18O value unceasingly rises. From Eiferian stage to Frasian stage, the δ18O value varied from -4‰ to -6‰. Those results indicated that temperature is possibly the factor controlling the oxygen isotopic composition of sea water. |
| CHENG Hong-guang,LI Xin-qing,YUAN Hong-lin,WANG Ke-zhuo.2009.Carbon and Oxygen Isotope Variations of Devonian Seawater:Isotopic Records from Brachiopod Shell[J].Acta Geoscientica Sinica,30(1):79-87. |
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