准噶尔盆地吉木萨尔南部中上二叠统沉积古环境分析——来自泥页岩生物标志化合物和元素地球化学方面的证据

Analysis of sedimentary paleoenvironment of Middle and Upper Permian in southern Jimsar,Junggar Basin:Evidence from biomarkers and elemental geochemistry of mudstone

准噶尔盆地东南缘吉木萨尔南部中上二叠统发育的泥页岩厚度大、分布广泛、有机质含量高,含有丰富的油气资源。通过对准噶尔盆地东南缘吉木萨尔南部中二叠统芦草沟组和上二叠统梧桐沟组进行了系统的采样,对泥页岩样品开展了生物标志化合物和元素地球化学分析,研究了该区中二叠统芦草沟组和上二叠统梧桐沟组泥页岩沉积时的氧化还原条件、古盐度和古气候特征。结果表明:(1)中二叠统芦草沟组沉积期处于贫氧的弱还原环境,有机质来源整体上以低等水生生物、沉水植物、原核生物等为主,芦草沟组中段混有少量高等植物输入;上二叠统梧桐沟组沉积期处于弱氧化—弱还原的环境,有机质来源整体上以低等水生生物、沉水植物、原核生物等为主,可能混有少量的高等植物,与芦草沟组相比有较多的沉水植物、泥炭藓、原核生物等;(2)中二叠统芦草沟组沉积时期湖盆为咸化—半咸化的水体,以干热的古气候条件为主;而上二叠统梧桐沟组沉积时期则为弱咸化—淡水的湖盆水体环境,以温暖湿润的古气候条件为主;(3)中二叠世至晚二叠世,研究区湖盆水体整体上呈现咸化程度降低,沉积有机质来源以低等水生生物、沉水植物、原核生物等为主,古气候呈由干热变为温暖湿润的演化趋势。

The mudstone developed in Middle and Upper Permian in the southern Jimsar area of the Junggar Basin is thick and widely distributed,with high organic matter content and rich oil and gas resources. In this study,we carried out biomarker and elemental geochemical analysis on mudstone samples from the Middle Permian Lucaogou Formation and Upper Permian Wutonggou Formation in the southern Jimsar area. On this basis,we studied the redox conditions,paleo-salinity and paleoclimate characteristics of the Middle Permian Lucaogou Formation and Upper Permian Wutonggou Formation mudstone in the southern Jimsar area. The results show that:(1)The Middle Permian Lucaogou Formation was in a weak reducing environment,the sources of organic matter are mainly lower aquatic organisms,submerged plants,and prokaryotes. The middle section of the Lucaogou Formation may be mixed with a small amount of higher plants. The Upper Permian Wutonggou Formation was in a weak oxidation and weak reducing environment,the sources of organic matter are mainly lower aquatic organisms,submerged plants,and prokaryotes,possibly mixed with a small amount of higher plants.Compared with Lucaogou Formation,Wutonggou Formation seems to have more submerged plants,sphagnum,and prokaryotes.(2)During the depositional period of the Middle Permian Lucaogou Formation,it was a saline-brackish water environment,which was dominated by dry and hot paleoclimate conditions. However,during the depositional period of the Wutonggou Formation in the Upper Permian,it was a weak salinity-fresh water environment,which was dominated by warm and humid paleoclimate conditions.(3)From the Middle Permian to the Late Permian,the salinity of lake basin in the study area decreased,the paleoclimate changed from dry and hot to warm and humid. The sources of organic matter are mainly lower aquatic organisms,submerged plants,and prokaryotes.