松辽盆地青山口组二段下部湖泊水体环境变化  

The variation of paleo-lake environment in the Lower Member 2 of Qingshankou Formation in the Songliao Basin

作　　者：曹怀仁 胡建芳[1] 彭平安[1] 席党鹏[3] 

机构地区：[1]中国科学院广州地球化学研究所有机地球化学国家重点实验室,广东广州510640 [2]中国科学院大学,北京100049 [3]中国地质大学生物地质与环境地质国家重点实验室,北京100083

出　　处：《地学前缘》2017年第1期205-215,共11页Earth Science Frontiers

基　　金：国家重点基础研究发展计划"973"项目(2012CB822002);国家自然科学基金项目(41372110;41321002)

摘　　要：以松辽盆地李家坨子露头剖面为研究对象,利用热解和生物标志化合物数据研究了青山口组二段下部(K_2qn^2)的沉积水体环境。该剖面样品成熟度均较低,氢指数和氧指数分别介于210~773(mg HC/g TOC)和2~188(mg CO_2/g TOC),其交叉图表明有机质主要来源于水生生物。根据地球化学数据,整个剖面湖泊水体环境演化可分为3个演化时期:阶段Ⅰ的伽马蜡烷指数及芳基类异戊二烯/菲比值较低,结合低的重排甾烷/规则甾烷比值及姥鲛烷/植烷比值和脱羟基维生素指数交叉图,指示湖水以半咸水的缺氧条件为主。阶段Ⅱ中,24-正丙基-胆甾烷和24-异丙基-胆甾烷含量变化证明该阶段发生短时间尺度的海水入侵事件,并导致半深湖到深湖相的缺氧环境;海水入侵带来大量的海洋生物、氧气、营养有机质及含硫物质,使得湖水盐度升高并以半咸水到咸水为主;高丰度的芳基类异戊二烯化合物反映该时期水体中富含自由态的H_2S,并且伴随水体分层、透光带缺氧及化跃层上移现象。但是,阶段Ⅱ演化的后期阶段湖水以淡水到半咸水沉积为主,同时氧含量升高,指示淡水输入量增加。阶段Ⅲ沉积时期因受到半干旱气候条件的影响,水体出现高盐度、缺氧且化跃层较浅的沉积环境,此时期动荡的水体不利于绿硫细菌的生长发育及游离态H_2S的保存。The data of rock-eval and biomarkers in the samples of the Lijiatuozi Section were analyzed for better understanding the paleo-lake environment of the Lower Member 2of the Qingshankou Formation（K_2qn^2）in the Songliao Basin.The organic matters（OMs）were mainly originated from aquatic organisms according to plot of hydrogen index（210-773 mg HC/g TOC）and oxygen index（2-188 mg CO_2/g TOC）in low maturity source rock.The evolution of paleo-lake environment could be divided into three stages based on geochemical data.In the stageⅠ,low values of gammacerane index and aryl isoprenoid/phenanthrene ratio,corresponding with low ratios of diasterane/sterane and the plot of pristane/phytane and dehydroxyl vitamin-E index,parameters mentioned above all indicated that the lake was considered as being anoxic and brackish water conditions.In the stageⅡ,the occurrence of short time marine incursion was defined by variable contents of 24-n-propylcholestanes and 24-i-propyl-cholestanes,leading to semi-deep or deep water environment;seawater intrusion with sea creatures,oxygen,nutrition,organic matter and sulfurous substances,which were helpful with formation of increasing salinity for brackish water and salt water;abundant composition of aryl isoprenoid displayed that stratified lake water was rich in free state of H_2S with euphotic zone of anoxia and upward chemocline during this period.However,the lake was dominantly given priority to fresh water to the brackish water deposition with increasing oxygen content at the same time,which suggested that fresh water input increased in the latter stages of stage Ⅱ.The lake was in high salinity water,anoxia,and the shallow chemocline due to being influenced by semi-arid climate conditions during the sedimentary period of stageⅢ,and turbulent water body was against growth of green sulfur bacteria and preservation of free H_2S.

关 键 词：松辽盆地 生物标志化合物 盐度 水体分层 缺氧 

分 类 号：P534.53[天文地球—古生物学与地层学] P342[天文地球—地质学]