四川盆地志留系龙马溪组有机质特征与沉积环境的关系  

Relationship between organic matter characteristics and depositional environment in the Silurian Longmaxi Formation in Sichuan Basin

作　　者：张小龙[1] 李艳芳[1] 吕海刚[1] 闫建萍[1] 妥进才[2] 张同伟[1] 

机构地区：[1]兰州大学甘肃省西部矿产资源重点实验室,甘肃兰州730000 [2]中国科学院地质与地球物理研究所兰州油气资源中心,甘肃兰州730000

出　　处：《煤炭学报》2013年第5期851-856,共6页Journal of China Coal Society

基　　金：国家重点基础研究发展计划(973)资助项目(2012CB214701);国家自然科学基金资助项目(41072092)

摘　　要：选择四川盆地长宁县双河镇上奥陶统五峰组—下志留统龙马溪组新鲜露头剖面,对124个样品进行碳硫含量、Rock-Eval热解分析和有机质碳同位素组成分析。结果显示,五峰组—龙马溪组底部约20 m段TOC含量较高,达3.04%~7.28%,向上残余有机质含量变低(0.81%~1.83%)并趋于稳定。硫含量在0.02%~4.69%,平均为0.95%。龙马溪组页岩δ13Corg值在-31.2‰^-29.4‰,平均-30.1‰,显示有机质以Ⅰ,Ⅱ型为主。TOC与硫含量、δ13Corg之间存在着一定的相关关系。结合龙马溪页岩的岩石学和化石特征,认为控制龙马溪组烃源岩有机质富集的主要原因是海平面升高、气候变暖和深水还原环境,导致有机质产率高且保存好。奥陶系五峰组和志留系龙马溪组底部高有机质海相泥岩是页岩气富集的最有利层段。The carbon and sulfur content,Rock-Eval pyrolysis and the carbon isotopes of organic matter were analyzed using 124 fresh outcrop samples collected from the Ordovician Wufeng Formation to the Lower Silurian Longmaxi Formation in Shuanghe Town,Changning County in Sichuan Basin.The results show that TOC content is high（3.04% to 7.28%） in the Wufeng Formation and the lower part of the Longmaxi Formation,and the thickness of high TOC interval is about 20 m.The TOC content sharply decreases from 0.81% to 1.83% in the upper part of the Longmaxi Formation and then becomes stable with its content values less than 1%.The sulfur content ranges from 0.02% to 4.69%,with an average of 0.95%.The δ13Corg values of the Longmaxi shale are concentrated in the range of-31.2‰ to-29.4‰,with an average of-30.1‰,indicating that organic matter is dominated by Type Ⅰ and Type Ⅱ.Combined with petrology and fossils characteristics of the Longmaxi Formation,the authors suggest that the main controls to the organic matter enrichment are sea level rise caused by global warming and the deep water reducing environment favorable for organic matter high productivity.In addition,a relatively slow deposition rate and reducing conditions lead to the better preservation of the organic matter.Therefore,the Wufeng Formation and the lower part of Longmaxi Formation marine shales with abundant TOC content in Sichuan basin is the main target for shale-gas exploration.

关 键 词：四川盆地 龙马溪组 有机质 沉积环境 碳同位素 页岩气 

分 类 号：P618.13[天文地球—矿床学]