Abstract:

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.

Key words: deepwater setting, Organic geochemical parameters, oil shale, distinguishing features of stratigraphic sequences, genetic interpretation, Songliao Basin