| 南堡凹陷古近系沙河街组沉积环境和物源: 来自微量和稀土元素地球化学的证据 |
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| 引用本文： | 静禹钱,雷闯,刘克栋,李振华.南堡凹陷古近系沙河街组沉积环境和物源: 来自微量和稀土元素地球化学的证据[J].地质科技通报,2023,42(1):350-359. |
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| 作者姓名： | 静禹钱 雷闯 刘克栋 李振华 |
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| 作者单位： | 1.中国石油大学(北京)油气资源与探测国家重点实验室, 北京 102249 |
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| 基金项目： | 国家科技重大专项子课题2016ZX05006-006油气资源与探测国家重点实验室开放课题PRP/open-2004 |
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| 摘 要： | 为深入认识南堡凹陷沙河街组富有机质泥页岩形成机理, 通过详细分析微量和稀土元素地球化学特征, 对其水体沉积环境及物源进行研究。结果表明: 微量元素Li, Cs, Bi较为富集; Cr, Sn较为亏损; 其他微量元素接近于上地壳元素含量。稀土元素总量变化范围宽泛, 接近或高于大陆上地壳的平均值, 指示陆源碎屑供给较为充足。REE分配模式表现为轻稀土元素富集, 分异程度较高; 重稀土元素相对亏损, 分异程度较低。铕元素异常值(δEu)负异常明显, 铈元素异常值(δCe)基本正常。根据锶丰度和锶/钡比值的变化, 反映出沙三段沉积时期湖泊水体具有一定的分隔性, 淡水、半咸水和咸水环境共存; 沙一段沉积时期湖泊水体的连通性增强, 以半咸水环境为主。根据V/(V+Ni)、Th/U比值及δCe、铈异常指数(Ceanom)值特征, 反映出湖泊水体为分层较强的贫氧环境。源生Ba含量揭示出湖泊水体古生产力较高。通过稀土元素组合特征分析, 认为沙河街组物源主要来自燕山褶皱带于燕山期发育的花岗岩, 且混有少量沉积岩。南堡凹陷沙河街组泥页岩有机质富集程度与其古环境和古地理密切相关: 一是适宜的水体古盐度和丰富的水体营养物质适应多种浮游藻类的共同繁盛, 提高了湖泊水生有机质生产效率; 二是贫氧的水体环境减缓有机质在埋藏过程中的降解, 提高了沉积有机质保存效率。
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| 关 键 词： | 南堡凹陷 沙河街组 微量元素 稀土元素 沉积环境 物源 |
| 收稿时间： | 2021-06-28 |
Deposition environment and provenance of the Palaeogene Shahejie Formation in Nanpu Sag: Evidences from trace and rare earth element geochemistry |
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| Affiliation: | 1.State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum(Beijing), Beijing 102249, China2.College of Mining Engineering, North China University of Science and Technology, Tangshan Hebei 063210, China3.Shandong Provincial Nuclear Industry 248 Geological Brigade, Qingdao Shandong 266041, China4.Dongying Market Supervision and Administrtion Bureau, Dongying Shandong 257091, China |
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| Abstract: | In order to reveal the formation mechanism of the organic-rich shales of the Shahejie Formation in Nanpu Sag, the depositional environment and provenance were investigated in detail through analyzing trace and rare earth elements(REE) geochemical characteristics. The results show that the trace elements Li, Cs and Bi are enriched, Cr and Sn are relatively depleted, and other trace elements are close to those in the upper continental crust(UCC).The total amount of REE vary widely, which is close to or higher than the average value in the UCC, and the supply of terrestrial source debris is adequate. The REE allocation pattern shows light rare earth element(LREE) enrichment with a high degree of divergence, and a relative deficit of heavy rare earth element(HREE) with a low degree of divergence. Eu negative anomaly is obvious, Ce is basically normal. The variations of Sr abundance and Sr/Ba ratio reflect that, in Nanpu Sag, the lake water was separated to a certain extent, and the fresh water, brackish water and saline water coexisted during sedimentary period of the third member of Shahejie Formation(Es3), and during these dimentary period of the first member of Shahejie Formation(Es1), the connectivity of lake water was enhanced, which was dominated by brackish water.The values of the V/(V+Ni), Th/U, δCe, and Ceanom comprehensively delineate the water body presented suboxic environment with moderate stratification. Respectively, the source Ba content indicated the water body was dominated by high paleoproductivity. The REE assemblage characteristics suggests that the provenance of Shahejie Formation were primarily derived from Yanshanian granites developed in Yanshanian fold belt and a small amount of sedimentary rocks. The development of organic-rich shales in the Shahejie Formation in Nanpu Sag is closely related to paleoenvironment and paleogeography, which can be summarized as the followings: ①suitable paleosalinity as well as sufficient nutrients at water body contributed to the booming of various planktonic algae, improving the production efficiency of the aquatic organic matter; ②suboxic water column slowed down the degradation of oxygen-sensitive material during the burial process, enhancing the preservation efficiency of sedimentary organic matter. |
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