陆相深水环境层序识别标志及成因解释:以松辽盆地青山口组为例

Distinguishing features and their genetic interpretation of stratigraphic sequences in continental deep water setting:A case from Qingshankou Formation in Songliao Basin.

陆相盆地深水环境是油页岩、暗色泥岩沉积区域,深水层序研究是勘探开发此类能源的基础工作。但深水沉积多为暗色泥岩沉积,很难准确划分多级层序。在松辽盆地3口全取心井、测井及测试资料分析基础上,发现在深水区域,油页岩层或生物富集层底界面、TOC、含油率、生烃潜量、氢指数、氢/氧指数突然增高点及沉积物密度突变小处、伽马测井坎值均为准层序界面。根据层序四分观点,深水泥岩中有机质丰度在低水位-水进-高水体-水退体系域中呈现低值—增加—最高值—减少的趋势。依据从盆地深水区到盆地边缘沉积岩中有机质变化具有等时性,对比研究有机质垂向旋回变化,是划分层序的重要证据。通过沉积岩中有机质类型及来源分析,湖泊基准面较高,水体较深时期,沉积岩中有机质含量高,有机质来源主要为湖泊自生产力;基准面逐渐下降的层序内有机质含量逐渐减少,陆源有机质供给影响比较明显。该成果也可以应用到海相深水环境的层序地层学研究。

Oil shale and dark-mudstone are all in favor of developing in the deep water basins.Studies of deep water sequence stratigraphy belong to one aspect of the essential work for energy exploration and development.Because sediments in deep water were mostly dark mudstone,it is difficult to identify multi-scale stratigraphic sequences precisely.Here we performed detailed study of three complete drilling cores from Songliao Basin.There are several significant features corresponding to the boundaries of para-sequences.The observed features are bottoms of oil shale beds and organism-enriched layers;abrupt increase in TOC,oil yield,hydrocarbon-generation potential and hydrogen index;abrupt decrease in density of sediments;and notch of gamma logging.According to the four division framework for stratigraphic sequences,the abundance of organic matter in lowstand systems tract（LST）,transgressive systems tract（TST）,highstand system tract,and regressive systems tract（RST）,exhibits the trend of low-increasing-maximum value-decreasing correspondingly.Considering the fact that the changes of organism content from the edge to the center of the basin are synchronized,we pointed out that the comparison of vertical changes of organism content is an important method for dividing stratigraphic sequences in deep water setting.Through the analysis of organism types and provenance when the base-level of the lake was high,it is suggested that the mudstone was formed with abundant organism in deep water and the organism was originated within the lake.When the lake base-level went down,organism in sediments decreased and terrestrial organism was playing a significant role.These results can be also applied to sequence stratigraphic studies in marine deep water environment.