四川盆地东部地区早侏罗世湖泊古水深恢复  

Paleo-water-depth Reconstruction of Early Jurassic Lakes in the Eastern Sichuan Basin

作　　者：王昌勇[1] 常玖 李楠 洪海涛 李雅楠 王小娟 李胡蝶 WANG ChangYong;CHANG Jiu;LI Nan;HONG HaiTao;LI YaNan;WANG XiaoJuan;LI HuDie(Institute of Sedimentary Geology,Chengdu University of Technology,Chengdu 610059,China;Institute of Exploration and Development,Southwest Oil and Gas Field Company,PetroChina,Chengdu 610041,China;Institute of Exploration and Development,Qinghai Oil and Gas Field Company,PetroChina,Dunhuang,Gansu 736202,China)

机构地区：[1]成都理工大学沉积地质研究院,成都610059 [2]中国石油西南油气田公司勘探开发研究院,成都610041 [3]中国石油青海油田分公司勘探开发研究院,甘肃敦煌736202

出　　处：《沉积学报》2024年第1期158-170,共13页Acta Sedimentologica Sinica

基　　金：中国石油天然气股份有限公司科学研究与技术开发项目(2019B-0505);国家科技重大专项(2016ZX05007-003)。

摘　　要：[目的]川东地区下侏罗统湖泊—三角洲沉积具有较大的勘探潜力,但基础地质研究的滞后制约了勘探进程,古水深恢复对川东地区下侏罗统岩相古地理恢复及页岩油气勘探具有重要指导意义。[方法]根据岩石类型、沉积构造和古生物化石分布特征,结合Fe/Mn比值、(Al+Fe)(/Ca+Mg)比值及干酪根类型对川东地区自流井组和凉高山组古水深变化趋势进行分析,并采用La-Co法、TOC法及Th/U比值法对早侏罗世古水深进行定量恢复。[结果与结论]沉积构造及古生物分布特征表明早侏罗世川东地区中部长期处于湖盆低洼位置,Fe/Mn比值和(Al+Fe)(/Ca+Mg)比值的变化趋势反映研究区东北部和南部为近岸浅水区。La-Co法、TOC法及Th/U比值法古水深恢复结果存在一定差异,La-Co法恢复的古水深与沉积相存在较大矛盾,Th/U比值法对浅湖沉积区古水深恢复较为可靠、但在滨湖及半深湖沉积区可靠度较低,而基于TOC法的古水深恢复结果最为可靠、与沉积相吻合度最高。早侏罗世川东地区湖泊浪基面约15 m,TOC法古水深恢复结果表明川东地区下侏罗统半深湖广泛发育,早侏罗世湖泊最大水深约60 m,广安—万州一带广泛发育半深湖—深湖沉积,有利于有机质的富集和保存,是页岩油气勘探的有利位置。[Objective]The Lower Jurassic lacustrine and delta deposits in the eastern Sichuan Basin have signifi-cant hydrocarbon exploration potential,but the lag of basic geological research restricts the exploration process.Paleo-water-depth reconstruction of the Lower Jurassic helps guide lithofacies paleogeography and shale oil-gas ex-ploration in the eastern Sichuan Basin.[Methods]Based on the rock types,sedimentary structures,and distribution characteristics of paleontological fossils,combined with the Fe/Mn ratio,(Al+Fe)/(Ca+Mg)ratio,and kerogen type,the paleo-water-depth variation trend of the Ziliujing and Liangshan Formations in the eastern Sichuan Basin is studied.The Early Jurassic paleo-water-depth was reconstructed quantitatively using the La-Co,total organic carbon(TOC),and Th/U ratio methods.[Results and Conclusions]The characteristics of sedimentary structure and pale-ontological distribution indicate that the central part of the eastern Sichuan Basin was in a low-lying lake basin for an extended period during the Early Jurassic,and the variation trend of the Fe/Mn and(Al+Fe)/(Ca+Mg)ratios indi-cates that the northeast and south of the study area are derived from nearshore shallow water.The results of paleowater-depth reconstruction for the three methods are quite different.The paleo-water-depth reconstructed based on the La-Co method contradicts that of the sedimentary facies.The Th/U ratio method is more reliable for paleo-water-depth reconstruction in shallow lake sedimentary areas,but less reliable in lakeside and semi-deep lake sedimentary areas.The paleo-water-depth reconstruction result based on the TOC method is the most reliable and has the highest coinci-dence with sediments.The base surface of the lake-wave in the eastern Sichuan Basin was approximately 15 m in the Early Jurassic.Paleo-water-depth reconstruction results based on the TOC method indicate that the Lower Jurassic semi-deep lakes were widely developed in the eastern Sichuan Basin,and the maximum water depth of the Early Ju-rassic lak

关 键 词：自流井组 凉高山组 古地理重建 页岩油气 川东地区 

分 类 号：P512.2[天文地球—地质学]