The control of astronomical cycles on lacustrine fine-grained event Sedimentation--A case study of the Chunshang sub-member of the upper Es4 in the Dongying Sag.

Fine-grained lacustrine sedimentation controlled by astronomical cycles remains a research weakness in sedimentology studies, as most studies have concentrated on how astronomical cycles affect the normal lacustrine fine-grained sedimentation, but how they affect the lacustrine fine-grained event sedimentation has been rarely studied. Therefore, this work researched the characteristics of event sedimentation by systematically observing the cores from 30 cored wells in the Shahejie Formation of the Dongying Sag at a depth of over 1800 m, with more than 4000 thin sections being authenticated and over 1000 whole rocks being analyzed by X-ray diffraction (XRD). The research object was the Chunshang Sub-member of Upper Es4 in the Fanye 1 well, as it had the most comprehensive analysis data and underwent the most continuous coring. We divided astronomical cycles into different orders and made corresponding curves using the gamma-ray (GR) curve, spectral analysis, power spectrum estimation, and module extreme values, there were 6 long eccentricity periods, 22 short eccentricity periods, 65.5 obliquity cycles, and 110.5 precession cycles in this sub-member. On this basis, this study analyzed the control of astronomical cycles on the lacustrine fine-grained event sedimentation, and the research shows deposits were developed by slide-slump, turbidities, hyperpycnites, and tempestites in the Chunshang Sub-member of the Upper Es4, with higher long eccentricity, the monsoon climate contributes to the formation of storm currents, while with lower long eccentricity, the surface deposits are severely eroded by rivers and rainfalls, thus developing the slide-slump, turbidities, and hyperpycnites. The relationship between the lacustrine fine-grained event sedimentation and astronomical cycles was studied in this case study, which can promote research on fine-grained sedimentary rocks in genetic dynamics and boost the theoretical and disciplinary development in fine-grained sedimentology. [ABSTRACT FROM AUTHOR]