六盘山盆地马东山组泥页岩干酪根地球化学特征分析

Kerogen Geochemical Characteristics of Mud-shale in Madongshan Formation,Liupanshan Basin

以六盘山盆地马东山组泥页岩露头与钻孔样品为研究对象,通过干酪根地球化学特征如干酪根显微组分、元素组成和碳同位素组成研究其泥页岩有机质类型。结果显示,显微组分鉴定、H/C和O/C原子比及Tmax-HI、Tmax-D均显示六盘山盆地马东山组泥页岩有机质类型总体表现为Ⅱ型,兼有Ⅰ型和Ⅲ型,与其沉积时期母质来源主要为藻类等浮游动植物一致;钻孔样品比露头样品的有机质类型更好。有机质类型越好(由Ⅲ-Ⅱ-Ⅰ型为越好),TOC含量和生油潜力(S1+S2)也相对更高。马东山组泥页岩干酪根元素以C、H为主,平均质量分数分别达78.44%,4.8%,H/C原子比值介于0.09~0.19,平均0.13;O/C原子比值介于0.41~1.51,平均0.90。钻孔样品H元素含量相对更高,露头样品C元素含量相对更高;干酪根碳表现出重碳同位素特征,分布范围为-1.9%^-2.5%,主频率为-2.2%^-2.4%。分析认为,六盘山盆地泥页岩有机质干酪根地球化学参数主要受沉积-构造-热演化的地质过程控制,具体表现为干酪根化学成分组成及其后期非线性变化受古沉积环境控制的有机质多源输入配比不同、沉积相带分布及风化、氧化作用等因素控制。

The kerogen type study is carried out via determining maceral on the whole rock polished surfaces, element composition and the carbon isotope taken the outcrop and well as samples from the Madongshan Formation in Liupanshan basin. The determining maceral, H/C and O/C, Tmax-H I, Tmax-D results show that the main organic type of Madongshan formation is Ⅱ type with the combined Ⅰ type and Ⅲ type. It indicates that the main source of parent material during the period of Madongshan Formation is algae and other zooplankton. The well samples have a better kerogen type compared with the outcrop samples. The better kerogen type samples have a higher TOC and S1+S2 content. The Kerogen elements of Madongshan Formation are C and H, and the average content is 78.44% and 4.8%, with H/C of 0.09-0.19, O/C of 0.41-1.51. What’s more, the well samples have a higher H content while the outcrop samples have a higher C content. The carbon isotope show a high value which is distributed in the range of-2.5% to 1.9%, and the dominant frequency is-2.2%to-2.4%. It indicates that the organic kerogen elements of mud-shale in Liupanshan basin is mainly controlled by the geological processes of sedimentary-tectonic-thermal evolution. The non-linear change of kerogen elements with multi-source input ratio of organic matter is controlled by sedimentary environment, sedimentary facies distribution and weathering and oxidation.