广西环江凹陷深部岩溶缝洞充填物碳氧同位素特征及古环境意义  

Carbon and oxygen isotope characteristics and paleoenvironmental significance of deep karst fracture-cave fillings in Huanjiang sag,Guangxi

作　　者：董红琪 张庆玉[1,2] 梁嘉鹏 淡永 梁彬[1,2] 聂国权 季少聪[1,2] DONGHongqi;ZHANG Qingyu;LIANG Jiapeng;DAN Yong;LIANG Bin;NIE Guoquan;JI Shaocong(l.Institute of Karst Geology,CAGS/Key Laboratory ofKarst Dynamics f MNR&GZAR,Guilin,Guangxi 541004,China;Guangxi Karst Resources and Environment Research Center(rfEngineering Technology^Guilin,Guangxi 541004,China;China University of Geosciences^Wuhan),School ofEnvironmental Studies,Wuhan,Hubei 430074,China)

机构地区：[1]中国地质科学院岩溶地质研究所/自然资源部、广西岩溶动力学重点实验室,广西桂林541004 [2]广西岩溶资源环境工程技术研究中心,广西桂林541004 [3]中国地质大学(武汉)环境学院,湖北武汉430074

出　　处：《中国岩溶》2022年第5期838-846,837,共10页Carsologica Sinica

基　　金：国家重点研发计划课题(2018YFC0604301);中国地质调查局项目(DD20190562,DD20190723,DD20221658)。

摘　　要：深部岩溶是碳酸盐岩地区深部油气资源勘探中不可避免的问题。深部岩溶发育期次的确定是岩溶储层地质的技术难题。广西环江凹陷在页岩气钻井中发现大量深部溶洞且充填物丰富多样,成为深部岩溶发育期次研究的良好素材。文章对HD1-4钻井揭露的深部岩溶缝洞充填物及地表岩溶缝洞充填物进行碳氧同位素分析,揭示出环江地区的4种不同岩溶环境:同生期或准同生期岩溶环境、表生期大气淡水岩溶环境、中浅埋藏岩溶环境、深埋藏或热液岩溶环境,环江地区深部岩溶发育为4期不同岩溶环境叠加的效果,主要受到热液岩溶环境和大气淡水岩溶环境的影响。In recent years,deep karst caves are commonly met in deep resource exploration and engineering construction.However,the deep-buried caves lead to the insufficient research on the genesis and development mechanism of deep karst caves.As good research samples,a large amount of complete drilling cores in deep kars caves are founded in Huanjiang sag in Guangxi.The karst morphology analysis of the drilling core in Well HD1-4 reveals that the deep karst in Huanjiang area is mainly composed of net cracks and holes expanding along cracks and dolomite honeycomb pores,and large karst caves are also developed,with the maximum height of 20 m.The types of fillings in deep karst caves are diverse.Through the observation of the whole well core,it is found that the deep kars cave fillings are of four characteristics.(1) Calcification growth,the mixed growth pattern of chemical and argillaceous substances reflects periodic growth in the cave,which may be associated with surface hydrological systems.(2) Flowerlike growth pattern,white calcite with multi-stage growth can be identified in pores,but the growth direction and growth environment of each stage are different,hence forming flower-like growth pattern.(3) Primary chemica fillings of the hole,the hole is filled with calcite or dolomite,and the crystal form of calcite in part of the hole is good(4) Argillaceous fillings in the cave,argillaceous fillings can be seen at 230 m,432 m,880 m and even 1,132 m in Well Huandi 1-4,which are far lower than the local discharge datum or the sea level.These argillaceous fillings may come from the surface mud seepage along the fracture or the mud beneath the ancient exposed surface.In this paper,the carbon and oxygen isotope analyses of deep karst cave fillings and surface karst cave fillings in Well HD1-4 drilling show the wide distribution of carbon and oxygen isotope of deep karst fracture.δC values are between-5.2‰ and-2‰ with the average value of-0.33‰. δO values are between-16.78‰ and-5.3‰ wtih the average value of-11.45‰

关 键 词：碳氧同位素 深部岩溶 古环境 岩溶期次 环江凹陷 

分 类 号：P618.13[天文地球—矿床学] P597[天文地球—地质学]