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高校地质学报 ›› 2019, Vol. 25 ›› Issue (6): 838-.DOI: 10.16108/j.issn1006-7493.2019077

• 烃源岩地球化学专栏 • 上一篇    下一篇

松辽盆地后金沟剖面上白垩统烃源岩氧化还原环境重建

宋力,陈睿倩,商斐   

  1. 1. 中国石油大学(北京) 地球科学学院,北京 102249;
    2. 油气资源与探测国家重点实验室,中国石油大学(北京),北京 102249;
    3. 中国石油勘探开发研究院,北京 100083
  • 收稿日期:2019-10-12 修回日期:2019-11-12 出版日期:2019-12-20 发布日期:2020-01-06

Reconstructing Redox Conditions of Upper Cretaceous Source Rocks in the Houjingou Section of the Songliao Basin

SONG Li,CHEN Ruiqian,SHANG Fei   

  1. 1. College of Geosciences, China University of Petroleum, Beijing 102249, China;
    2. State Key Laboratory of Oil and Gas Resources and Exploration, China University of Petroleum, Beijing 102249, China;
    3. Research Institute of Petroleum Exploration and Development , Beijing 100083, China
  • Received:2019-10-12 Revised:2019-11-12 Online:2019-12-20 Published:2020-01-06

摘要: 松辽盆地是中国大型陆相湖盆,其上白垩统嫩江组一段(K2n1) 和二段(K2n2) 烃源岩沉积时期的形成环境一直备受争议。文章选取盆地后金沟剖面为研究地区,通过测定和分析烃源岩中的稳定氮同位素等地球化学指标,重建了氧化还原条件。结果表明,后金沟剖面嫩一段(H 层位) 和嫩二段(N2 层位) 具有明显的差异:嫩二段相较嫩一段而言,有机碳(TOC) 值偏高、有机碳同位素(δ13Corg) 值负偏,而且稳定氮同位素(δ15N) 值偏小,一致指示海侵事件发生之后导致嫩二段形成了缺氧环境。结合微量元素比值分析,古生产力参数Ba/Al、Ba/Ca,反映嫩二段具有更高的生产力,这与TOC 的含量变化一致;Mo/Al、V/Cr 等氧化还原参数表明嫩二段沉积时的水体环境还原性更强,这与δ15N 值偏小指示嫩二段形成缺氧环境的结论相符,重建了沉积时期水体的氧化还原环境。研究结果不仅可以预测优质烃源岩的沉积分布,还可以为国内其它湖相页岩沉积环境的研究提供借鉴,为油气勘探提供新的依据。

关键词: 松辽盆地, 嫩江组, 稳定氮同位素, 微量元素, 氧化还原环境

Abstract: The Songliao Basin is a large-scale continental lacustrine basin in China. The Upper Cretaceous Nenjiang Formation developed high-quality source rocks, which were mainly formed in the first (K2n1 ) and second members of the Nenjiang Formation (K2n2 ). However, the redox environment has been debated over years. The Houjingou section, in the typical area of Songliao Basin, is selected as the study site. By measuring and analyzing organic carbon and nitrogen isotopes, trace elements and other geochemical indicators of the source rocks in this area, it is found that there are obvious differences between K2n1 and K2n2 . The higher TOC value, the negative deviation of δ13Corg value and the smaller value of δ15N in K2n2 than those in K2n1 indicate that the anoxic environment formed in K2n2 after marine transgression. Combined with trace element ratios, the paleo-productivity parameters such as Ba/Al and Ba/Ca reflect the higher productivity of K2n2, which is consistent with the change of TOC; the redox parameters such as Mo/Al and V/Cr indicate the water environment is more reductive in K2n2 deposition, which is consistent with the conclusion that the δ15N value is small indicating the formation of anoxic environment in K2n2. The redox environment of the water body during the deposition period is reconstructed. The research results can not only predict the distribution of high-quality source rocks, but also provide a reference for the study of sedimentary environment of other lacustrine shales in China, and provide a new basis for oil and gas exploration.