摘要
元素地球化学在沉积环境判别中发挥重要的作用,尤其是沉积物形成时的氧化-还原环境和底层水体状况。本文对南大巴山上奥陶统五峰组-下志留统龙马溪组泥岩开展了元素地球化学分析,结果表明:临湘组Al_(2)O_(3)含量高于五峰组,五峰组-龙马溪组向上逐渐增加,TiO_(2)和Al_(2)O_(3)具有相似的特征,二者与TOC呈负相关;氧化-还原敏感元素U、V和Mo较为富集,表明沉积时处于缺氧环境,不同剖面不同层位存在两次强烈富集异常,指示其为硫化环境;稀土元素均表现为轻稀土富集、重稀土亏损,略微右倾的稀土元素配分模式,具有明显Eu负异常,其中五峰组-龙马溪组Ce负异常,缺氧环境,栗子坪少数Eu正异常,可能存在热液活动;氧化-还原敏感元素比值、Mo/TOC及Mo_(EF)-U_(EF)的协变模式揭示了南大巴山奥陶纪-志留纪之交主体上处于弱滞留贫氧-中等滞留缺氧的开阔海环境,主要受控于海平面升降变化和沉积时古海底地形,局部受北侧秦岭洋盆内洋流影响。
Element geochemistry plays an important role in judging sedimentary environments such as redox environment and bottom water condition during deposition process of sediments.A detailed element geochemistry study of mudstones from the upper Ordovician Wufeng Formation to lower Silurian Longmaxi Formation in southern Dabashan mountain is carried out in this paper.The results show that Linxiang Formation has a higher Al_(2)O_(3) content than Wufeng Formation,and from bottom Wufeng Formation to upper Longmaxi Formation,the contents of Al_(2)O_(3) increase gradually.Both contents of Al_(2)O_(3) and TiO_(2) have a negative correlation with TOC.Redox-sensitive elements such as U,V and Mo are enriched,indicating an anoxic environment during the deposition of the sediments.Two dramatically enriched anomalies of U,V and Mo in different strata from different profiles show a sulfidic condition.The distributions of NASC-normalized REEs display slightly right-tilted patterns,which are enriched in LREEs and depleted in HREE sand have an obvious Eu negative anomaly.The Ce negative abnormalies of Wufeng Formation and Longmaxi Formation signify an anoxic environment in bottom water and the minor Eu positive abnormalies from Liziping profile probably imply hydrothermal activities during precipitating.Covariation of ratios of redox-sensitive elements such as Mo/TOC and Mo_(EF)-U_(EF) reveal that southern Daba Mountain during Ordovician-Silurian transition is generally in an open oceanic environment with weak stagnant oxygen depletion or medium stagnant anoxia.The sedimentary environment of study area at that time is mainly controlled by fluctuations of sea level and paleo-seafloor topography,locally influenced by oceanic hydrothermal currents from Qinling Ocean in the north.
作者
熊国庆
刘春来
董国明
崔伟
XIONG Guoqing;LIU Chunlai;DONG Guoming;CUI Wei(Chengdu Center,China Geological Survey,Chengdu 610081,China;Key Laboratory of Sedimentary Basin&Oil and Gas Resources of MNR,Chengdu 610081,China;The 2nd Geological Brigade of Hebei Bureau of Geology and Mineral Resource Exploration,Tangshan 063004,China)
出处
《沉积与特提斯地质》
CAS
CSCD
北大核心
2021年第3期398-417,共20页
Sedimentary Geology and Tethyan Geology
基金
四川盆地龙马溪组页岩气战略选区调查(编号:DD20160193)
贵州凯里-都匀地区页岩气地质调查(编号:DD20190722)
重庆市页岩气勘探有利区带优选及资源量评价研究(渝东北地区)。
