松辽盆地晚白垩世湖相白云岩碳氧同位素特征及其古环境意义  

Carbon and Oxygen Isotope Characteristics of Late Cretaceous Lacustrine Dolomite in the Songliao Basin and their Paleoenvironmental Implications

作　　者：张一范 高远[1] 陈积权 黄帅 海伦 毋正轩 杨柳[1] 董甜 ZHANG Yifan;GAO Yuan;CHEN Jiquan;HUANG Shuai;HAI Lun;WU Zhengxuan;YANG Liu;DONG Tian(School of Earth Sciences and Resources,China University of Geosciences(Beijing),Beijing 100083,China)

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083

出　　处：《现代地质》2023年第5期1243-1253,共11页Geoscience

基　　金：国家自然科学基金项目(41972096);中国地质大学(北京)求真学人项目(265QZ202207)。

摘　　要：松辽盆地上白垩统青山口组和嫩江组是重要的烃源岩层位,以暗色泥岩为主,夹有数层白云岩层和白云岩结核层。湖泊碳酸盐岩是分布范围最广泛的一类陆相碳酸盐岩,是陆相盆地在特殊环境下的产物,其形成与盆地气候-环境演化密切相关,是深时古地理、古气候、古环境等信息的良好记录载体。另外,白云岩是碳酸盐岩层系中最主要的油气储渗体,因此开展重要含油层系白云岩研究有助于了解陆地古环境演化及烃源岩储层特征。本文对松辽盆地东南缘鸟河剖面青山口组一段和李家坨子剖面嫩江组一段湖泊白云岩开展碳、氧同位素特征分析,探讨其古环境意义。结果表明,松辽盆地晚白垩世白云岩具有重碳(δ^(13)C_(鸟河)=5.89‰~0.78‰,δ^(13)C_(李家坨子)=-8.36‰~6.70‰)、轻氧(δ^(18)O_(鸟河)=-10.03‰~-7.84‰,δ^(18)O_(李家坨子)=-11.30‰~-3.82‰)特征,且δ^(13)C-δ^(18)O相关性较高(R^(2)>0.7),表明松辽盆地晚白垩世白云岩是湖水滞留时间较长的封闭型咸水-半咸水湖泊体系的产物。根据经验判别式Z=2.048×(δ^(13)C+50)+1.498×(δ^(18)O+50)计算,青山口组、嫩江组白云岩Z平均值分别为124和126.5,表明白云岩形成过程中可能受到海水入侵作用影响。进一步通过海水与淡水氧同位素混合模型,估算了海侵作用的规模,综合认为松辽盆地晚白垩世湖相白云岩沉积于海侵背景下、湖水长期滞留的封闭型咸水-半咸水湖泊。The Late Cretaceous Qingshankou and Nenjiang Formations in the Songliao Basin,extensively deposited with dark mudstone,and interspersed with layers of dolomite and dolomite nodules,are regarded as important source rock strata.Studying important oil-bearing dolomite can help to understand the terrestrial paleoenvironment evolution and source rock reservoir characteristics.In this study,carbon and oxygen isotopes of dolomites from the Qingshankou Formation(the first member)in Niaohe section and the Nenjiang Formation(the first member)in Lijiatuozi section in the southeastern margin of Songliao Basin are analyzed to explore paleoenvironmental significance.The results show thatδ^(13)C values of dolomites in both sections are relatively high(δ^(13)CNiaohe=-5.89‰~0.78‰,δ^(13)CLijiatuozi=-8.36‰~6.70‰),whileδ^(18) O values are relatively low(δ^(18) ONiaohe=-10.03‰~-7.84‰,δ^(18) OLijiatuozi=-11.30‰~-3.82‰),and the correlation betweenδ^(13)C andδ^(18) O is high(R^(2)>0.7).This demonstrates that the late Cretaceous dolomites in the Songliao Basin were the product of closed(semi-)brackish lacustrine system with a long retention time.According to the empirical equation Z=2.048×(δ^(13)C+50)+1.498×(δ^(18) O+50),the average values of dolomites in Qingshankou and Nenjiang Formations are 124 and 126.5,respectively,indicating that the dolomites may be affected by seawater intrusion during the formation process.Furthermore,we estimated the scale of transgression using a mixing model of seawater and freshwater oxygen isotopes.In conclusion,we consider that the Late Cretaceous lacustrine dolomite in the Songliao Basin was deposited in closed(semi-)brackish lacustrine system with a long retention time,under a transgressive background.

关 键 词：松辽盆地 白垩纪 白云岩 碳氧稳定同位素 古环境 

分 类 号：P534.53[天文地球—古生物学与地层学]