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古近系心组红岗段是广东三水盆地的主要生油层,以一套黑—灰黑色页岩沉积为主,其富含有机质、纹层理发育良好的岩层与相对贫有机质、含微体生物化石的微扰动层交替出现。根据纹层状页岩与生物扰动页岩的C-S-Fe关系以及对氧化还原条件敏感的痕量元素(Mo、U、V、Co、Ni、Pb和Cu)地球化学记录,对这两种不同岩相的地球化学特征及其所反映的水体氧化还原条件进行了分析。纹层状页岩的TOC、S含量和DOPT值均较高,TOC-S、TOC-DOPT显示较弱的相关性;而生物扰动页岩的TOC、S含量和DOPT值相对较低,TOC-S、TOC-DOPT相关性显著。痕量元素在两种岩相中的分布也有差别,各元素在纹层状页岩中的丰度均高于生物扰动页岩,尤其是Mo和U具有较高的丰度水平、且在不同岩相中显示明显差别。黑色页岩中的C-S-Fe关系和痕量元素(特别是Mo和U)分布反映了心组红岗段沉积时期湖盆水体的氧化还原条件变化。生物扰动页岩沉积期间,底部水体主要为氧化环境,间歇性出现贫氧条件,硫酸盐还原作用发生于沉积物/水界面及其以下沉积物中。纹层状页岩形成于缺氧的底部水体条件下,水体和沉积物中均可含H2S,为有机质保存以及对氧化还原条件敏感的痕量元素的富集提供了有利条件。
The Paleogene Qiongxin Formation Honggang section is the main oil reservoir in the Sanshui Basin of Guangdong Province. It is dominated by a set of black-gray-black shale deposits. Its rich organic-matter-rich, well-developed strata and relatively poor organic matter, Micro-disturbing layers of body fossils alternate. Based on the CS-Fe relationship between laminar shales and bioturbated shales and the geochemical records of trace elements (Mo, U, V, Co, Ni, Pb and Cu) sensitive to redox conditions, The geochemical characteristics of lithofacies and the redox conditions of the water body are analyzed. The TOC, S content and DOPT values of laminar shale are higher than that of TOC-S and TOC-DOPT, while the TOC, S content and DOPT value of bioturbated shale are relatively low. TOC- S, TOC-DOPT significant correlation. There are also differences in the distribution of trace elements between the two lithofacies. The abundance of each element in laminar shale is higher than that of bioturbated shales, especially Mo and U, which have higher abundance levels. The lithofacies show a clear difference. The C-S-Fe relationship and the distribution of trace elements (especially Mo and U) in the black shale reflect the redox conditions of the lake waters during the sedimentation of the Honggang section of the Chengxin Formation. During the bioturbation shale deposition, the bottom water body is mainly oxidized environment with intermittent oxygen depletion conditions. Sulfate reduction occurs at the sediment / water interface and below sediments. The formation of laminar shales under the hypoxic bottom water conditions may contain H2S in water and sediments, which provides favorable conditions for the preservation of organic matter and the enrichment of trace elements sensitive to redox conditions.