| 西藏羌塘盆地双湖地区毕洛错黑色页岩稀土元素特征及地质意义 |
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| 引用本文：孙玉琪,伊帆,伊海生,夏国清,李高杰,徐鸿彬.2025.西藏羌塘盆地双湖地区毕洛错黑色页岩稀土元素特征及地质意义[J].地球学报,46(3):544-560. |
| DOI：10.3975/cagsb.2025.011721 |
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| 基金项目:国家自然科学基金青年科学基金项目(编号: 41902107)和甘肃省油气资源研究重点实验室开放基金(编号: SZDKFJJ2022002) |
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| 中文摘要:南羌塘盆地双湖地区的毕洛错黑色页岩是南羌塘最具代表性的优质烃源岩, 在羌塘盆地的油气勘探中受到广泛关注。本文选取毕洛错剖面底部有机质初始沉积的层位进行稀土元素地球化学分析, 结果表明: 毕洛错剖面样品稀土元素总量(ΣREE)平均值为61.97 μg/g, 明显低于大陆上地壳和北美页岩; 轻、重稀土元素比值(ΣLREE/ΣHREE)平均值为8.44, (La/Yb)N平均值为1.27, 具有轻稀土较为富集、重稀土相对亏损的特征; δCe值为0.77~0.95, 平均值为0.85, 显示较弱的Ce负异常, δEu值为0.90~1.11, 平均值为1.00, 几乎无Eu异常。稀土元素配分模式和La/Th-La/Yb、Co/Th-La/Sc、La/Yb-ΣREE以及La/Th-Hf图解显示源岩主要为沉积岩和长英质火山岩; ΣREE、ΣLREE/ΣHREE、Al、Ti以及CIA特征显示随着有机质开始富集, 风化作用增强, 陆源输入增加; δEu、δCe、Ceanom的参数特征以及V/(V+Ni)、MoXS/UXS特征显示剖面整体为贫氧环境; (La/Yb)N、Nd/La及ΣREE/P2O5参数特征显示稳定且较高的沉积速率; 沉积环境指标与TOC的相关性指示风化作用增强导致的陆源输入增加是有机质富集的核心因素, 推测在早中侏罗世温暖湿润的气候背景下, 地表径流带来的营养盐促进了藻类繁盛, 提供有机质来源, 同时较高的沉积速率和贫氧的水体环境有利于有机质的埋藏与保存, 造成有机质富集。 |
| 中文关键词:羌塘盆地 黑色页岩 稀土元素 有机质富集 |
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| REE Characteristics and Geological Implications of the Bilong Co Black Shale in the Shuanghu Area, Qiangtang Basin, Southern Tibet |
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| Abstract:The Bilong Co black shales in the Shuanghu area are most representative high-quality source rock in the southern Qiangtang Basin. They draw significant substantial attention in oil and gas exploration within the basin. This study focuses on the rare earth elements geochemical research present in the strata, where or-ganic matter originally accumulated at the base of the Bilong Co section. The findings reveal that the av-erage value of rare earth element (ΣREE) in the Bilong Co section amounts to 61.97 ?g/g. This value is significantly lower than that of the continental crust and North American Shale Composite. The ΣLREE/ΣHREE average ratio is 8.44, with the (La/Yb)N ratio averaging at 1.27. This indicates an enrich-ment in the light rare earth elements while experiencing a shortage of heavy rare earth elements. The δCe is 0.77–0.95, with a mean of 0.85, demonstrating a weak negative anomaly. The δEu is 0.90–1.11, with a mean of 1.00, indicating almost no anomaly. The NASC normalized pattern of black shale and the diagram of La/Th-La/Yb, Co/Th-La/Sc, La/Yb-ΣREE, and La/Th-Hf jointly suggest that the source rocks are mainly sedimentary rocks and felsic volcanic rocks. The changes in ΣREE, ΣLREE/ΣHREE, Al, Ti, and CIA demonstrate the enhancement of weathering and the increase of terrigenous input with the beginning of organic matter enrichment. The δEu, δCe,Ceanom, V/(V+Ni), and MoXS/UXS demonstrate the suboxic environment in the entire strata. (La/Yb)N, Nd/La, and ΣREE/P2O5 parameters reflect stable and high depo-sition rates. The major factor for organic matter enrichment is the increase in terrigenous input caused by enhanced weathering, as revealed from the analysis of the correlation between the deposition environ-ment index and TOC. Meanwhile, it is speculated that in the warm and humid climate of the Early-Middle Jurassic periods, nutrient influx from rivers fosters algae proliferation and provides organic matter. Simul-taneously, the high deposition rate and suboxic conditions favor the burial and preservation of organic matter, culminating in its enrichment. |
| keywords:Qiangtang Basin black shale rare earth element organic matter enrichment |
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