中国科学院南京地质古生物研究所机构知识库

塔里木盆地下寒武统玉尔吐斯组是国内已发现的最优质海相烃源岩(TOC=29.8%),但针对该层段开展的古环境地球化学研究较匮乏.选取柯坪地区于提希剖面,开展野外勘查、薄片鉴定、主微量元素及总有机碳含量测试,探究富有机质烃源岩形成环境.研究表明,玉尔吐斯组岩石富集了包括V、U、Ni、Ba、Mo、Cu、Zn等微量元素;其底部硅质页岩展现的"负Ce异常、正Y异常、正Eu异常"的左倾稀土配分模式,较低的Ce/Ce*(均值0.45),较高的Y/Ho(均值39.77)和极高的Eu/Eu*(均值35.32)与重晶石、磷结核等,表明塔里木地台北缘在早寒武世初期处于硫化还原和强烈热液活动的海水背景.氧化还原指标U/Al、V/Al、Th/U、V/Sc及Mo-U共变分析,揭示了早寒武世塔里木地台北缘是开阔海;同时,海水经历了"硫化缺氧(玉尔吐斯组A组Th/Uavg=0.070)→次氧化(B组Th/Uavg=1.21;C组Th/Uavg=0.62;D组Th/Uavg=1.21)→硫化缺氧(肖尔布拉克组Th/Uavg=0.13)"的变化过程;并具备较高的古生产力(TOCmax=17.2%,玉尔吐斯组ex-Baavg=8634.85×10-6)和有利的有机质保存条件.据此,建立了玉尔吐斯组"周期性缺氧事件-热液活动-沿岸上升洋流"背景的缓坡型海相烃源岩发育模式.研究可为塔里木盆地深层-超深层远景油气资源评价与我国西北地区早寒武世古环境演化研究提供重要科学参考.

The lower Cambrian Yuertusi Formation has been confirmed as the best high-quality source rocks of marine rocks in China,and the source rocks of the Cambrian pre-salt play in the Tarim and crucial research field of the Ediacaran-Cambrian transition.However,little work has been published about the paleo-environments.Yutixi section in Keping is intensively investigated by a multi proxy analysis including thin-sections identification,major elements,trace elements and TOC contents,for revealing the accumulation mechanisms of the sources rocks in this study.Results demonstrate that the samples are rich in trace elements comprising V,U,Ni,Ba,Mo,Cu and Zn.Along with the weakly positive Ce anomalies(Ce/Ce*=0.45),extremely positive Eu anomalies(Eu/Eu*=35.32),Y/Ho(39.77)and barite for samples of basal Yuertusi Fm.,the REEs patterns of negative Ce anomalies,positive Y anomalies and positive Eu anomalies verified the drastic hydrothermal activities and anoxic conditions of the Early Cambrian.Specifically,many proxies including U/Al,V/Al,Th/U,V/Sc,and Mo-U covariation ascertained the paleocean in the northern Tarim was an open sea.The paleocean was under sulfide in period of Yuertusi Fm.Group A(Th/Uavg=0.070).Then it changed into suboxic in periods of Yuertusi Fm.Group B(Th/Uavg=1.21),Group C(Th/Uavg=0.62)and Group D(Th/Uavg=1.21)with generally increased oxidation level.Finally it was under sulfide conditions in period of Xiaoerbulake Fm.(Th/Uavg=0.13).In addition,the elevated productivity and well preservation are implied by the high TOC contents(TOCmax=17.2%)and ex-Baavg(8634.85×10-6)for Yuertusi Fm.Group A.Ultimately,development pattern of the source rocks of the Lower Cambrian Yuertusi Fm.,northern Tarim platform is proposed,which is characterized by hydrothermal activities,coastal upwelling and anoxic to sulfide conditions.This study will facilitate both the prospect evaluation of deep and super-deep oil and gas resources in Tarim basin,and studies of Ediacaran-Cambrian paleo-environments transition in NW China.