| 柴西上干柴沟组中上段介壳微量元素古环境古气候意义 |
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| 引用本文： | 陈伟,李璇,曾亮,王庆同,焦学尧,杨平,江小青,马锦龙.柴西上干柴沟组中上段介壳微量元素古环境古气候意义[J].沉积学报,2019,37(5):992-1005. |
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| 作者姓名： | 陈伟 李璇 曾亮 王庆同 焦学尧 杨平 江小青 马锦龙 |
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| 作者单位： | 兰州大学地质科学与矿产资源学院,兰州 730000;甘肃省西部矿产重点实验室,兰州 730000;兰州大学地质科学与矿产资源学院,兰州 730000;甘肃省西部矿产重点实验室,兰州 730000;武警黄金第七支队,山东烟台 264004;中国石油青海油田分公司勘探开发研究院,甘肃敦煌,736202 |
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| 基金项目： | 第二次青藏科考综合考察研究专题（2019QZKK0704） |
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| 摘 要： | 介壳微量元素具有重要的沉积古环境古气候意义，结合介壳微量元素含量变化特征和介壳化石组合生态环境特征可得到柴达木盆地西部上干柴沟组中上段更为详尽的古环境古气候演化特征。柴达木盆地西部上干柴沟组中上段介壳微量元素比值Sr/Ca、Ba/Ca、U/Ca及元素Sr、Ba、U在A阶段（28.35~26.42 Ma）值较低，B阶段（26.42~23.08 Ma）值整体较高，段末值有所下降，C阶段（23.08~22.33 Ma）值明显上升，Mn/Ca和Mn值变化大致相反。A阶段Sr/Ca和Sr均值（分别为0.002 278、37.76×10-9）较低，B阶段均值（分别为0.003 347、41.46×10-9）较高，C阶段二者均值（分别为0.003 346、56.06×10-9）也较高，Ba/Ca、U/Ca、B、U有着类似的平均值变化特征，Mn/Ca和Mn值有着相反的平均值变化特征。同时相应各阶段介壳化石组合有所不同。通过介壳微量元素变化及化石组合特征，结合同期深海氧同位素及前人研究成果表明，上干柴沟组中上段柴西古湖古环境古气候演化特征为: A阶段，盐度较低和还原性较强，水位较高，气候相对温暖润湿；B阶段，整体盐度较高和氧化性较强，水位较浅，气候整体炎热干旱，段末气候干旱程度降低；C阶段，盐度和氧化性增高，湖水变浅，气候向冷干演化，响应了早中新世中国西北内陆干旱化。该地区该时段古气候主要受全球气候演化和青藏高原隆升的影响，与副特提斯海西退也有一定关系。
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| 关 键 词： | 柴达木盆地 上干柴沟组 介壳类 微量元素 古环境 |
| 收稿时间： | 2018-07-02 |
Paleoenvironmental and Paleoclimatic Significance of Trace Elements in Ostracod Shells in the Upper-Middle Section,Upper Ganchaigou Formation,Western Qaidam Basin |
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| Institution: | 1.College of Earth Sciences, Lanzhou University, Lanzhou 730000, China;2.Key Laboratory of Mineral Resources in Western China (Gansu Province), Lanzhou 730000, China;3.The 7th Gold Detachment of Chines Armed Police Force, Yantai, Shandong 264004, China;4.Research Institute of Petroleum Exploration and Development, PetroChina Qinghai Oilfield Company, Dunhuang, Gansu 736202, China |
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| Abstract: | Trace elements in ostracod shells in sedimentary deposits have important significance for studies of the paleoclimate and paleoenvironment. Variation in trace element content in ostracod shells combined with the characteristics of the ecological environment of ostracod fossil assemblages yielded more details about the paleoenvironmental and paleoclimatic evolution during the middle-upper section of Upper Ganchaigou Formation in the western Qaidam Basin. The trace element ratios Sr/Ca,Ba/Ca and U/Ca,and the trace amounts of Sr,Ba and U in the ostracod shells were low in phase A (28.35-22.33 Ma);their values were high in phase B (26.42-23.08 Ma),declining at the end of this phase. In phase C (23.08 22.33 Ma)they increased significantly,although the Mn/Ca ratio and Mn content showed approximately the opposite change. The average values of Sr/Ca and Sr (respectively 0.002 278 and 37.76×10-9)were low in phase A and higher in phase B (respectively 0.003 347 and 41.46×10-9),and their average values were also higher in phase C (respectively 0.003 346 and 56.06×10-9). The average values of Ba/Ca,U/Ca,Ba and U changed similarly,whereas the average values for Mn/Ca and Mn showed opposite changes. The ostracod shell assemblages also differed in the corresponding phases. Combining these trace element variations in the ostracod shell fossils and their assemblages with synchronous deep-sea oxygen isotopes,and noting previous research results,the evolution of the paleoenvironment and paleoclimate in the middle-upper section of Upper Ganchaigou Formation was determined to be the following. In phase A,the ancient lake of the western Qaidam Basin was a deep,low-salinity,strongly reducing lake environment with high water level;the climate was relatively warm and moist. In phase B,the lake was shallow,with high salinity,strongly oxidizing and low water level,and the overall climate was hot and arid. At the end of phase B,the salinity and oxidizing properties of the lake water decreased as the water level rose,and the climate became less arid. In phase C,the salinity and oxidation of the lake water increased as the water level fell, and the climate became cold and arid,similar to the inland aridity of northwestern China in the early Miocene. The paleoclimate during this geological period was mainly influenced by global climate evolution and uplift of the Tibetan Plateau, and also the retreat of the Paratethys Sea to the west. |
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