塔里木盆地下寒武统西山布拉克组—西大山组沉积环境演化

Evolution of sedimentary environment of the Lower Cambrian Xishanbulake-Xidashan formations in the Tarim Basin

郭婷婷 朱碧 杨涛 陈永权

GUO Tingting ZHU Bi YANG Tao CHEN Yongquan

河海大学 地球科学与工程学院 地球关键带研究所, 南京 210098 南京大学 内生金属矿床成矿机制研究国家重点实验室, 南京 210046 中国石油 塔里木油田分公司, 新疆 库尔勒 841000

Institute of Earth's Critical Zone, School of Earth Sciences and Engineering, Hohai University, Nanjing 210098, Jiangsu, China State Key Laboratory for Mineral Deposits Research, Nanjing University, Nanjing, Jiangsu 210046, China Tarim Oil Field Company, PetroChina, Korla, Xinjiang 841000, China

寒武纪是生命与环境演化的关键时期，重建该时期的海洋沉积环境尤其是氧化还原状态，对探讨古海洋化学时空演化特征以及理解生物与环境之间的关系具有重要意义。通过对塔里木盆地塔东2井下寒武统西山布拉克组—西大山组开展主微量元素和有机碳含量（TOC）分析，对该地层的沉积环境进行了重构。该地层沉积时水体处于较弱的局限条件，底水氧化还原状态以缺氧为主，但缺氧程度存在明显的变化。其中，西山布拉克组中部相对上下部缺氧硫化程度明显增加，而西大山组中下部到上部缺氧程度逐渐减弱，底水氧化性总体增加，这种动态变化与前人提出的早寒武世海洋氧化还原状态存在动态变化的观点一致。对塔东2井西山布拉克组—西大山组有机质富集机制的分析显示，该地层中有机质积累并非受控于单一因素，西山布拉克组中下部缺氧/硫化的环境更有利于有机质的保存，而西山布拉克组上部—西大山组沉积过程中较高水平的初级生产力是有机质富集的主要控制因素。

The Cambrian is a critical period in the evolution of life and environment. Reconstructing the marine sedimentary environment, notably redox conditions during this period is key to explore the spatial and temporal evolutionary characteristics of seawater chemistry and the relationship between biological evolution and environmental changes. In this study, the major elements, trace elements and organic carbon content (TOC) of the Lower Cambrian Xishanbulake-Xidashan formations in well Tadong 2 in the Tarim Basin were analyzed, and the sedimentary environment of the formations was reconstructed. The results show that the water body was in weak restriction condition when the formation was deposited. The redox state of bottom waters was dominated by anoxia, but the degree of anoxia varied obviously. Specifically, the middle part of the Xishanbulake Formation showed elevated anoxia (euxinia) in bottom waters compared to the lower and the upper parts, while the Xidashan Formation showed a decrease in anoxia from the middle and the lower parts to the upper part and an expansion of bottom water oxidability. The results are consistent with the observation in previous studies that the Early Cambrian seawaters was characterized by dynamic changes in the redox state. The analysis of organic matter enrichment mechanism of Xishanbulake-Xidashan formations in well Tadong 2 shows that organic matter enrichments in the formations is not controlled by a single factor. The anoxic/euxinic environment in the middle and the lower parts of the Xishanbulake Formation is more conducive to the preservation of organic matter, while the higher level of primary productivity played a key role in the sedimentation of the upper part of the Xishanbulake Formation and the Xidashan Formation.

中央高校基本科研业务费专项资金 B200202009

https://doi.org/10.11781/sysydz202302252