松辽盆地北部白垩纪青山口组黑色页岩元素地球化学特征及沉积古环境恢复  

Element geochemical characteristics of black shale and paleo-sedimentary environmental restoration of Qingshankou Formation of the Cretaceous in the northern Songliao Basin

作　　者：王岚 周海燕[1] 商斐 周学先 Wang Lan;Zhou Haiyan;Shang Fei;Zhou Xuexian(PetroChina Research Institute of Petroleum Exploration&Development,Beijing 100083)

机构地区：[1]中国石油勘探开发研究院,北京100083

出　　处：《地质科学》2022年第1期156-171,共16页Chinese Journal of Geology(Scientia Geologica Sinica)

基　　金：国家科技重大专项“重点盆地致密油资源潜力、甜点区预测与关键技术应用”(编号:2016ZX05046-006)资助。

摘　　要：对松辽盆地北部青山口组118块页岩样品进行有机碳和元素地球化学测试,运用一系列判别古气候、古盐度、古生产力和古氧化还原条件的地化指标,恢复青山口组黑色页岩的沉积环境,探讨富有机质页岩成因机制。青山口组沉积期为温暖半湿润亚热带气候,古气温>15℃,水体为陆相微咸水—半咸水环境,盐度5‰~10‰。青山口组底部发育厚度约30 m的富有机质页岩,TOC最高达到9.39%,自下而上有机碳含量逐渐变低。富有机质页岩Cu、Ni、Mo和Zn含量高,发育大量胶磷矿、藻席,表明青山口组早期湖盆生产力达到峰值,为有机质富集提供物质基础。U元素含量以及V/(V+Ni)、V/Sc比值较高,表明青山口组早期水体为强还原环境,为富有机质页岩保存提供有利条件。中-晚期随着湖盆收缩、水体变浅,还原环境遭到破坏,有机碳含量降低。TOC与古生产力及氧化还原指标呈正相关关系,表明有机质含量的变化主要受控于湖盆生产力和氧化还原环境。古海侵事件带来丰富营养物质,极大提高了湖盆生产力,保证有机质大量供应;同时海侵造成盐度分层,使底部水体的强还原环境不受破坏,促进了有机质的保存。松辽盆地青山口组在白垩纪全球缺氧事件影响下形成了面积约5×10^(-3)km;的黑色页岩,是页岩油勘探的重要目标。In this study, a test were carried out on organic carbon, major and trace elements of 118 shale samples of Qingshankou Formation in the northern Songliao Basin. Moreover, this study analyzed a series of geochemical indicators were used to distinguish the paleoclimatology,paleo-salinity, paleo-productivity and paleo-redox condition. The sedimentary environment of black shale of Qingshankou Formation were restored and the genetic mechanism of organic-rich shale were explored. The sedimentary period of Qingshankou Formation had a warm sub-humid subtropical climate, and the ancient temperature was more than 15 ℃. The water body was continental brackish water-brackish water with a salinity of 5‰~10‰. Organic-matter-rich shale with a thickness of about 30 m was developed at the bottom of Qing-1 Member, and the TOC reached up to 9.39%. The organic carbon content in the upper part gradually decreased.The organic-matter-rich shale at the bottom of Qing-1 Member has high contents of Cu, Ni, Mo and Zn, and a large amount of gelophosite and algal mat are developed, indicating that the productivity of Early Qingshankou Formation reached the peak, providing material basis for organic matter enrichment. V/(V+Ni), V/Sc, U elements and other sensitive indicators of oxidative reduction indicate that the early water of Qing-1 Member is a strong reducing environment, which provides favorable conditions for the formation of organic-rich shale. With the contraction of the lake and the shallow water, the environment was destroyed and the organic carbon content decreased. TOC was positively correlated with paleo-productivity and REDOX indicators, indicating that the change of organic matter content was mainly controlled by lake basin productivity and REDOX environment. The event of ancient transgression brought rich nutrients, which greatly improved the productivity of the lake basin and ensured a large supply of organic matter. Marine transgression resulted in salinity stratification, which protected the strong reductive environm

关 键 词：元素地球化学 氧化还原环境 海侵 白垩纪全球缺氧事件 松辽盆地 

分 类 号：P593[天文地球—地球化学] P618.13[天文地球—地质学]