泌阳凹陷核三段主力富有机质页岩层地球化学特征

Geochemical Characteristics of Organic-Rich Shales of He-3 Member of Hetaoyuan Formationin Biyang Sag

泌阳凹陷中部深凹区古近系核桃园组发育多套含油气页岩层。采用ICP-MS分析法对第5套页岩层稀土元素和微量元素特征进行了分析,讨论了泥页岩地球化学特征、沉积环境及其有机质富集机制。结果表明,B、Sr和Th含量及B/Ga值与古盐度呈正相关,显示该套页岩层为咸水湖泊沉积,纵向上古盐度逐渐降低,这与藻类含量及组合特征反映的古盐度一致。各样品稀土元素分异明显,轻稀土富集而重稀土亏损,（La）N/（Yb）N值明显大于1,δCe值为0.93-1.17,平均0.99,Ce异常性不明显或为正异常,反映沉积物沉积速率相对较低。V/（V＋Ni）值为0.71-0.84,Ce异常指数均大于-0.1,显示为还原环境。综合研究认为,核三段第5套富有机质页岩层形成于干旱—半干旱气候条件下缓慢沉积的咸水湖泊环境。

Several organic-rich shales with oil and gas were developed in the Paleogene Hetaoyuan formation of deep area in Biyang sag. Thetrace and rare earth elements＇ contents and indexes from the fifth shale were analyzed using ICP-MS method, including the geochemistry,the sedimentary environment and the organic-rich mechanism in this area. The results show that the changes in content of B, Sr, Th and B/Gahave a positive correlation with the change of paleosalinity, reflecting that such shales were deposited in saltwater lakes, and the gradual de-cline of the paleosalinity from bottom to top was consistent with the content and composition characteristics of the algae. The obvious differ-entiation of individual rare earth element indicates the enrichment of the light rare earth elements and the loss of the heavy ones, and thesefacts that the ratio of（La）N/（Yb）Nis obvious greater than 1, the value of δCe ranges from 0.93 to 1.17 with an average of 0.99, being of unob-vious or positive anomaly, which implies relatively low depositonal rate of the deposit. The value of V/（V＋Ni） is between 0.71 and 0.84, andthe value of Ce anomaly index of larger than-0.1 indicates the reducing environment. It is suggested that the fifth organic-rich shales of He-3member of Hetaoyuan formation was developed in saltwater lake environment with low depositional rate and semiarid climate.