舞阳、襄城凹陷下第三系盐湖相有机地球化学与沉积环境研究

舞阳、襄城凹陷下第三系为一套盐湖相沉积物。研究表明,沉积环境与有机地化特征具有明显对应关系,咸水湖-盐湖相和盐湖相区有机质丰度相对较高,(扇)三角洲前缘与(扇)三角洲前缘-盐湖相区次之,(扇)三角洲平原区相对最差。烃源岩类中以页岩、油页岩最好,白云质、灰质泥岩、泥质白云岩、泥岩次之,含膏、含盐泥岩相对最差。有机质类型主要为1型,其次为Ⅰ型,少量Ⅱ₂型。且Ⅰ型、Ⅱ₁型有机质一般分布在盐湖相区内,而Ⅱ₂型和Ⅰ型有机质则主要分布于(扇)三角洲平原相和(扇)三角洲前缘相带。生物标志物指示烃源岩沉积环境为还原-强还原、高盐度咸化湖泊环境,其正烷烃多呈双峰态分布,高碳数部位具有一定的奇碳优势,OEP值大于1植烷、伽玛蜡烷含量高,Pr/Ph分布范围为0.04～0.72,β-胡萝卜烷和藿烯、ββ藿烷、芳香含硫化合物及脱羟基维生素E普遍存在,Tm/Ts大于1。根据Pr/Ph、Pr/nC₁₇、Ph/nC₁₈相对组成三角图可有效区分半咸水湖相与咸水湖-盐湖相。

Study of Lower Tertiary Organic Geochemistry and Their Sedimentary Environment in Wuyang and Xiangcheng Saline Sag, Henan, China

In lower tertiary,There are a suit of saline lacustrine sediments in Wuyang and Xiangcheng subdepression. A clear correlation exist between sedimentary environment and organic geochemistry in studying area. The organic matter content in salt water-saline lacustrine sediments is the highest and the abundance in the front of delta and fan-delta higher while the content in the plain lower. In hydrocarbon source rocks, shale and oil shale are characterized by the high content of organic matter while gypseous and salt mudstone by the low , between them are dolomitic and carbonaceous mudstone and muddy dolomite and mudstone. The organic matter types are dominated by Ⅱ₁ and secondly by Ⅰ.Also few Ⅱ₂ exist. Generally, Ⅰand Ⅱ 1 organic matter exist in saline lake while Ⅱ₂ and Ⅲ in the front and plain of delta and fan delta respectively. Biomarker compounds show that the source rocks are deposited in the high salinity and reducing to strong reducing environment. The n-alkanes of the source rock display a bimodal carbon number distribution with an odd-over-even predominance (OEP1). The content of pristine and gammacerane is high and the ratio of pristine/phytane is 0.04～0.72while the phytane/C 18 n-alkane greater than 4. The β-carrot alkane, hopene , hopanes and thionic aromatic hydrocarbons extend widely and the ratio of Ts/Tm is greater than unity. Dehydroxyltocopherols is widely spread with the 5 configurations of δ, 6-methyl-MTTC, β, γ and α. The hemi-saline water and saline facies can be distinguished availably by the triangle chart of Pr/Ph、Pr/nC₁₇ and Ph/nC₁₈ value.