湘中坳陷泥盆系碳氧同位素特征及其古环境意义  

Carbon and Oxygen Isotopic Characteristics of Devonian in Central Hunan Depression and Its Paleoenvironmental Significance

作　　者：刘安[1] 陈林 陈孝红[1] 田巍 李海[1] 郄文昆[2] 周鹏[1] Liu An;Chen Lin;Chen Xiaohong;Tian Wei;Li Hai;Qie Wenkun;Zhou Peng(Wuhan Center of China Geological Survey,Wuhan 430205,China;Nanjing Institute of Geology and Palaeontology,Chinese Academy of Sciences,Nanjing 210008,China)

机构地区：[1]中国地质调查局武汉地质调查中心,湖北武汉430205 [2]中国科学院南京地质古生物研究所,江苏南京210008

出　　处：《地球科学》2021年第4期1269-1281,共13页Earth Science

基　　金：国家科技重大专项(No.2016ZX05034001-002);中国地质调查局基金项目(Nos.DD20190781,DD20190558)。

摘　　要：基于系统碳氧同位素和有机碳测试,在充分论证样品测试数据有效性的基础上,对湘中坳陷地区泥盆系碳氧同位素特征展开分析,探讨了研究区地层对比、古海洋环境发育特征及其对富有机质页岩形成的影响.结果表明,湘中地区泥盆系δ^(13)C受后期蚀变成岩作用影响较小.区内泥盆系δ^(13)C表现出自下而上逐渐变轻,并在欧家冲组底部发生显著的负偏、之后向上逐渐增大的发育趋势.以上曲线与全球泥盆系碳氧同位素曲线相似,具有较为一致的变化趋势.区内泥盆系δ^(13)C曲线形态及偏移程度与四川龙门山剖面、独山其林寨剖面、广西拉利剖面及欧美地台剖面可对比性强,可作为区内地层划分与对比、古海洋环境演化分析的依据.对比结果显示,区内棋梓桥组顶部-佘田桥组底部δ^(13)C曲线与海平面变化存在差异,指示区域性地壳构造升降与全球海平面变化综合主导了区域的古水深变化.区内泥盆系δ^(13)C正漂移与高TOC页岩具有良好对应关系,表明佘田桥组下部、孟公坳组上部富有机质页岩发育层段是大范围海侵阶段的产物,也是构成区内泥盆系页岩气勘探的主要目的层系.Based on the systematic carbon and oxygen isotope and organic carbon testing, the carbon and oxygen isotope characteristics of the Devonian in the Central Hunan depression were analyzed by fully proving the validity of the testing data.Results show that the δ^(13) C values of Devonian are less affected by later alteration in the Central Hunan area. The δ^(13) C of Devonian gradually decreases from the bottom to the top and shows a significant negative shift at the bottom of the Oujiachong Formation,and then gradually increases upward. The δ18 O curve shows a slowly increasing trend from Middle Devonian to Upper Devonian.The above curves are similar to the carbon and oxygen isotopic curves of the global Devonian strata, and have a relatively consistent trend of change. The shape and migration degree of δ^(13) C curve of Devonian strata in the area are highly comparable with Longmenshan Section in Sichuan Province, Qilinzhai Section in Dushan, Lali Section in Guangxi, and Euramerican platform section, which can be used as the basis for stratigraphic division and correlation in the area and analysis of paleo-marine environment evolution. Results show that there are differences between the δ^(13) C curve and the sea level change from the top of Qiziqiao Formation to the bottom part of Shetianqiao Formation, indicating that the regional paleowater depth change is comprehensively dominated by the regional tectonic activities and the global sea level changes. There is a significant correlation between the δ^(13) C positive drift and the high TOC in the shale of this area, which indicates that the organic-rich shale intervals at the lower part of Shetianqiao Formation and the upper part of Menggongao Formation are the products of large-scale transgression.The intervals consist of the main shale gas exploration target strata of Devonian in the study area.

关 键 词：湘中坳陷 泥盆系 碳氧同位素 沉积环境 富有机质页岩 页岩气 

分 类 号：P597[天文地球—地球化学]