Paleo-water-depth Reconstruction of Early Jurassic Lakes in the Eastern Sichuan Basin
[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 paleo-water-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 lakes was approximately 60 m.Semi-deep lake to deep lake deposits were widely developed in the Guang'an-Wanzhou area,which benefits the enrichment and preservation of organic matter,creating a favorable position for shale oil and gas exploration.
Ziliujing FormationLianggaoshan Formationpaleogeography reconstructionshale oil and gaseastern Sichuan Basin
万方数据
维普
