摘要
准噶尔盆地玛湖凹陷下二叠统风城组是一套罕见的碱湖沉积,活跃的火山背景和高pH值湖水性质,使风城组发育了碱岩-白云岩-燧石岩-泥岩-砂岩-砾岩-火山岩等复杂岩性组合。其中燧石岩和富硅泥页岩在风城组具有良好的油气显示,但整体研究较为薄弱。本次研究通过岩心观察、微观矿物学研究和主量、微量、稀土元素综合分析,划分出不同产状类型的燧石,以期揭示风城组火山-碱湖沉积中燧石成因。风城组燧石可分为层状、结核状和角砾状,其中层状燧石常发育帐篷构造和V字形收缩缝,燧石结核中发现硅质球体和交代残余的碳酸盐矿物,说明风城组燧石可能存在蒸发、生物、及交代成因。风城组燧石的Al/(Al+Fe+Mn)比值均在0.6左右,与生物成因燧石地球化学特征相似。总稀土含量介于2.26~116.17×10-6,平均36.65×10-6, LREE/HREE比值介于3.65~26.00,平均7.85,轻重稀土具有中等强度的分馏特征。Eu具有正异常和弱负异常特征,Ce大多落在正异常区域,反映风城组大部分燧石形成于较强的还原环境,且未受到明显热液活动的影响。结合碱湖-火山背景,本次研究提出风城组燧石主要以蒸发成因和生物诱导成因为主,交代成因也是风城组燧石岩的主要成因类型。
The Lower Permian Fengcheng Formation in Mahu Sag of Junggar Basin is a set of rare alkali lake sediments.Due to the active volcanic background and high pH water quality,the Fengcheng Formation developed complex lithologic assemblages,such as alkali rock,dolomite,silexite,mudstone,sandstone,conglomerate and volcanic rock.Among these rocks,the silexite and siliceous shale in Fengcheng Formation have good hydrocarbon signs of deposit,but its overall research is relatively weak.Based on core observation,microscopic mineralogy study and comprehensive analysis of major,trace and rare earth elements,the silexite with different occurrence types in the Fengcheng Formation is studied and classified in order to reveal the genesis of silexite in the volcanic-alkali lake deposits.The silexite in Fengcheng Formation can be divided into laminated,nodular and breccia form silexite.The laminated silexite usually develops tent-shaped structure and V-shaped contraction joints.The presence of siliceous spheres and meta-somatic residual carbonate minerals in the nodular silexite indicates that there are 3 possible geneses,including evaporation,biology and metasomatism for the silexite.Geochemical analysis shows that the Al/(Al+Fe+Mn)ratio of silexite in Fengcheng Formation is about 0.6,which is similar to the geochemical characteristics of biogenic chert.The total rare earth contents of the silexite range from 2.26〜116.17×10^(-6),with an average of 36.65×10^(-6) and the LREE/HREE ratio ranges from 3.65 to 26.00,with an average of 7.85.Eu has the characteristics of positive anomaly and weak negative anomaly,and Ce mostly falls in the region of positive anomaly,indicating that most of the silexite in Fengcheng Formation is formed in a strong reducing environment and is not affected by obvious hydrothermal activities.In consideration of above listed results,combined with the Jianghua volcanic background,it is proposed that the Fengcheng Formation silexite is mainly caused by evaporation and biological induction,and the metasomatism is also the a genetic type of the Fengcheng Formation silexite.
作者
魏研
郭佩
靳军
蒋宜勤
王剑
雷海燕
文华国
Wei Yan;Guo Pei;Jing Jun;Jiang Yiqing;Wang Jian;Lei Haiyan;Wen Huaguo(Institute of Sedimentary Geology,Chengdu University of Technology,Chengdu,Sichuan 610059,China;State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Chengdu University of Technology,Chengdu,Sichuan 610059,China;Research Institute of Experiment and Detection,PetroChina Xinjiang Oilfield Company,Karamay,Xinjiang 834000,China)
出处
《矿物岩石》
CAS
CSCD
北大核心
2021年第2期83-98,共16页
Mineralogy and Petrology
基金
国家自然科学基金(41572097,41972116)。
关键词
碱湖
燧石
风城组
蒸发浓缩
生物诱导
alkaline lake
silexite
Fengcheng Formation
evaporation concentration
biological induction
