渤海海域石臼坨凸起东段元素特征与古环境关系

Relationship between element characteristics and paleoenvironment in the eastern section of Shijiutuo uplift in Bohai Sea area

渤海海域石臼坨地区是渤海油田精细化勘探的重点区域,但该区沉积环境变化较快。结合元素地球化学特征,对石臼坨东部东营组、沙河街组等层位展开沉积环境分析,结果表明,各层位MgO/CaO平均值的最大值与最小值相差3.2%,说明研究区从石炭系到东营组时期的沉积环境发生了巨大的变化,东营组为较温暖的潮湿沉积环境,沙一段与沙二段存在干旱或蒸发沉积环境。Fe^(3+)/Fe^(2+)比值显示研究区东营组以还原环境为主,沙河街组以弱氧化环境为主,且砂体相对发育的层位Fe^(3+)/Fe^(2+)比值均比泥岩段略大。

Shijiutuo area in Bohai Sea area is the key area of fine exploration in Bohai oilfield,but the sedimentary environment changes rapidly.In combination with the element geochemical characteristics,the sedimentary environment of Dongying formation and Shahejie formation in the eastern section of Shijiutuo uplift is analyzed.The results show that the difference between the maximum and the minimum MgO/CaO average values in each layer is 3.2%,indicating that the sedimentary environment in the study area has changed greatly from Carboniferous to Dongying formation.Dongying formation is a relatively warm and humid sedimentary environment,and there are arid or evaporative sedimentary environments in members 1 and 2 of Shahejie formation.The Fe^(3+)/Fe^(2+) ratio shows that the Dongying formation in the study area is dominated by reducing environment,and the Shahejie formation is dominated by weak oxidation environment,and the Fe^(3+)/Fe^(2+) ratio of the layer with relatively developed sand body is slightly larger than that of the mudstone section.