PALEOLIMNOLOGICAL SIGNIFICANCE OF CARBON AND OXYGEN ISOTOPIC RATIOS OF OSTRACODA FROM OIL SOURCE ROCKS IN DONGYING DEPRESSION
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摘要: 对山东东营凹陷沙河街组一段2 7个生油岩样品中的介形虫进行了氧、碳同位素分析, 其δ(18O) 全为负值, δ(13C) 多为正值, 两者之间有明显的相关性, 相关系数(r) 为0. 92. 同时, δ(18O) 与δ(13C) 垂向变化明显, 沙一段下、中亚段明显高于上亚段. 通过与现代湖泊碳酸盐氧、碳同位素特征的比较得出: 沙一段生油岩沉积时期的古湖泊是一封闭咸水或半咸水湖泊, 中、下亚段沉积时期, 气候干燥、蒸发作用强烈、湖水面较低、盐度高、生产力高, 而上亚段沉积时期, 气候较湿润、降雨量大、湖水面高、盐度偏低、生产力降低.Abstract: Stable-isotopic analyses of 27 ostracoda samples from oil source rocks in Dongying depression (Bohai Gulf basin, East China) have been carried out. The results show that the δ(18O) of the ostracoda is negative and the δ(13C) is positive except one sample (δ(18O) : -4.853×10-3 to -0.341×10-3; δ(13C) : -0.360×10-3 to 2.961×10-3), which displays the characteristics, highly correlated in covariance between oxygen and carbon isotopic variations (r=0.92). This characteristics is similar to the stable oxygen and carbon isotopic compositions of primary carbonates from modern hydrologically closed lakes. Therefore, we concluded that the paleolake during the oil source rocks deposition in Dongying depression is a closed saline or brackish lake. Based on the vertical variation of δ(18O) and δ(13C), the changes of the paleoclimate, paleolake level and paleoproductivity have been discussed. In the early stage of oil source rocks deposition, the climate was dry, the lake level, lower and the productivity, high, but it became wet, and the high water level and lower productivity occurred in the late depositional period.
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Key words:
- oxygen and carbon isotope /
- ostracoda /
- oil source rocks /
- paleolimnology
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图 2 2-2-18井沙一段介形虫壳体δ (18O) 和δ (13C) 值散点图
Fig. 2. Scatter plot of δ (18O) and δ (13C) of ostracoda from the first member of Shahejie Formation in well 2-2-18
图 3 2-2-18井沙一段介形虫壳体δ (18O) 和δ (13C) 及生油岩TOC垂向变化曲线
Fig. 3. Vertical variation of δ (18O) and δ (13C) of ostracoda and TOC of oil source rocks in well 2-2-18
表 1 东营凹陷2-2-18井沙一段介形虫壳体氧、碳同位素成分
Table 1. Oxygen and carbon isotopic compositions of ostracoda from the first member of Shahejie Formation
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