关键词: 松辽盆地, 青山口组, 米兰科维奇旋回, 高频层序, 有机质富集

Abstract: There is great exploration and development potential of shale oil in Qingshankou Formation in the north of Songliao Basin, but its sedimentary cycle framework and organic matter enrichment response model are still unclear. Based on wavelet transform analysis and spectral analysis of the natural gamma logging data of Qingshankou Formation in Well Guye1, in combination with analysis results of the core, logging data and geochemical elements, the paper identifies the Milankovich cycle in the sedimentary strata, establishes the relationship between the theoretical orbital period and the single-well sedimentary cycle, and achieves the identification and division of the high-precision sedimentary cycles of Qingshankou Formation in Songliao Basin. The floating astronomical timescale of Qingshankou Formation is established according to the long eccentricity period of 400 ka. The sedimentary time of Qingshankou Formation is calculated to be 5.6 Ma. The organic-rich mud shale of Member 1 of Qingshankou Formation deposits during Late Cenomanian to Early Turonian of the Late Cretaceous. The Milankovitch cycle of Qingshankou Formation can be divided into 14 long eccentricity cycles and 46 short eccentricity cycles. The long and short eccentricity cycles correspond to the fourth and fifth levels of sequence stratigraphy respectively. On this basis, the sequence stratigraphic framework of astronomical cycles can be built in the study area, thus providing an idea for the unified stratigraphic division of deep and shallow water areas. Based on the established sedimentary model controlled by the long eccentricity cycle, it is found that when the eccentricity is close to the maximum, the corresponding sedimentary cycle will be in the organic-rich interval, which is the potential high-quality interval for shale oil exploration.

Key words: Songliao Basin, Qingshankou Formation, Milankovich cycle, high-frequency sequence, organic matter enrichment