滇黔北地区筇竹寺组元素地球化学特征及古环境意义

Geochemical characteristics of element Qiongzhusi Group in Dianqianbei area and paleoenvironmental significance

关键词:  滇黔北地区  筇竹寺组  元素地球化学  古环境

Key words:  Dianqianbei area  Qiongzhusi formation  elemental geochemistry  ancient environment

摘要:

南方下志留统龙马溪组页岩气已实现规模效益开发,下寒武统筇竹寺组为滇黔北地区潜在的页岩气接替层系。筇竹寺组页岩元素地球化学特征及形成的古环境研究,对于筇竹寺组页岩气评层选区具有一定的指导作用。通过A井筇竹寺组有机碳、主微量元素和稀土元素的系统测试,结合测井资料,按层段分析A井黑色页岩相关元素地球化学参数的变化特征,探讨黑色页岩形成的古环境和沉积模式。结果表明:滇黔北探区筇竹寺组相关主、微量元素富集程度与总有机碳含量(TOC)相关；氧化还原敏感参数比值显示筇竹寺组沉积期水体整体由缺氧到贫氧再向氧化环境过渡,与Mo/TOC图解和UEF-MoEF协变图所表征的水体滞留程度基本一致；滇黔北地区筇竹寺组沉积期处于被动大陆边缘,筇一段受热液作用影响,筇一段相对筇二段和筇三段古生产力较高；筇一段沉积期水体强滞留性形成的缺氧古环境是有机质有效富集保存的关键,筇一段是滇黔北地区筇竹寺组页岩气勘探有利的层段。

Abstract:

The Lower Silurian Longmaxi formation shale gas in southern China has achieved scale benefit development, and the lower Cambrian Qiongzhusi formation is a potential shale gas replacement formation in Dianqianbei area. The study on the geochemical characteristics and paleoenvironment of shale elements has a certain guiding role in the shale gas assessment area of Qiongzhusi formation. Through systematic tests of organic carbon, main trace elements and rare earth elements of well A in the Qiongzhusi formation, combined with logging data, the geochemical parameters of the related elements in black shale in well A are analyzed according to the layer section, and the paleoenvironment and sedimentary model of black shale formation are discussed. The results show that the concentration of main and trace elements in Qiongzhusi formation is related to then TOC content in Dianqianbei exploration area. The ratio of redox sensitive parameters shows that the whole water body in the sedimentary period of Qiongzhusi formation is transformed from hypoxia to oxygen poor to oxidation environment, which is consistent with the retention degree of water body as shown by the Mo/TOC diagram and UEF-MOEF covariant map. The sedimentary period of Qiongzhusi formation in Dianqianbei area is on a passive continental margin. The first section of Qiongzhusi formation is affected by the hydrothermal action, and the paleoproductivity of the first section is relatively high. The anoxic paleoenvironment formed by strong retention of water body in the first sedimentary period is the key to the effective enrichment and preservation of organic matter. The first section is a favorable shale gas exploration section of Qiongzhusi formation in Dianqianbei area.