渤海湾盆地渤中凹陷西南部沙三段富有机质泥岩沉积环境及形成机理

Sedimentary environment and formation mechanism of organic-rich mudstone in the third member of Shahejie Formation in the southwestern Bozhong Sag, Bohai Bay Basin

有机质富集受多种因素影响,分析富有机质泥岩发育的控制因素对于页岩油气资源的勘探开发具有重要意义。通过对渤海湾盆地渤中凹陷西南部沙河街组三段(沙三段)中—下亚段(Es_(3)^(m-l))泥岩岩心样品进行总有机碳含量(TOC)以及主量、微量元素地球化学分析,讨论Es_(3)^(m-l)沉积期古气候、沉积水体环境、沉积速率及古生产力对有机质富集的影响,建立Es_(3)^(m-l)有机质富集模式。结果表明:Es_(3)^(m-l)泥岩有机质丰度较高,TOC含量介于1.05%~6.37%之间;CIA_(corr)反映整体为温暖湿润的古气候,Es_(3)^(l)下部相对干旱,Es_(3)^(l)中上部到Es_(3)^(m)气候变得更加温暖湿润;B含量和B/Ga值反映整体盐度较低,为淡水—半咸水,Es_(3)^(l)中上部到Es_(3)^(m)水体盐度变大;Mo-U协变模式和Corg/P摩尔比反映Es_(3)^(m-l)底水保存条件存在波动,整体为弱氧化—还原环境;Ti/Al、K/Al、Zr/Al表明Es_(3)^(m-l)沉积期陆源碎屑输入较强,具有较高的沉积速率,Es_(3)^(l)下部到Es_(3)^(m)沉积速率降低;古生产力定量恢复表明Es_(3)^(m-l)沉积期湖泊古生产力整体较高。渤中凹陷西南部Es_(3)^(m-l)泥岩有机质的富集是古气候、保存条件、沉积速率及古生产力共同作用的结果。

The enrichment of organic matter is affected by many factors.It is of great significance to analyze the controlling factors of the development of organic-rich mudstone for shale oil and gas exploration.Based on the geochemical analysis of total organic carbon(TOC),major and trace elements of mudstone core samples from Middle-Lower Shahejie Formation(Es_(3)^(m—l))in southwestern Bozhong Sag,the effects of paleoclimate,sedimentary water environment,sedimentation rate and paleoproductivity on organic matter enrichment during Es_(3)^(m—l)deposition were discussed,and the organic matter enrichment model of Es_(3)^(m—l)was established.The results show that Es_(3)^(m—l)mudstone has a high abundance of organic matter,with TOC content ranging from 1.05%to 6.37%.The CIAcorrreflects the overall warm and humid paleoclimate.The lower part of Es_(3)^(l)is relatively dry,and the middle and upper parts of Es_(3)^(l)to Es_(3)^(m)climate become warmer and wetter.B content and B/Ga reflect that the overall salinity is low,which is fresh-brackish water,and the salinity increases from the middle and upper parts of Es_(3)^(l)to Es_(3)^(m)The Mo-U covariation pattern and C_(org)/P molar ratio reflect the fluctuation of Es_(3)^(m—l)bottom water preservation conditions,and the overall environment is a weak redox environment.Ti/Al,K/Al,Zr/Al indicate that the terrigenous detritus input was strong during Es_(3)^(m—l),with a high deposition rate,and the deposition rate decreased from the lower part Es_(3)^(l)to Es_(3)^(m).The quantitative recovery of paleo-productivity showed that the paleo-productivity of the lake in Es_(3)^(m—l)period was high.The enrichment of organic matter in Es_(3)^(m—l)mudstone in southwestern Bozhong Sag is the result of the combined effects of paleoclimate,preservation conditions,sedimentation rate and paleoproductivity.