The second member of Paleogene Dongying formation of Jiyang Depression was deposited during faulted period, in the 4th sandstone units of which the gravity flow deposits is dominated in the study area. Onlap develops in the Dongying Formation from northeast to southwest, forming draping structure units. Under the control of palaeogeomorphology of pitching northeast (about 56°), it forms incised gully of various scales where the gravity flow deposit system develops, which can be generalized into two models in the study area——channelized system and non-channelized system. The main types of non-channelized system are sandy debris flow sediment and turbidite, followed by the slump deposits and muddy debris flow sediment. These were first recognized in this area on cores, based on characteristics of sliding surface in slide deposits, convolute bedding and slump deformation structure in slump deposits, massive sandstone associated with dark mudstone as well as boulder clays and torn mudstone fragments in sandy debris flow sediment, muddy with several sandy particles and clumps interiorly in muddy debris flow sediment, and typical positive grading in turbidite. Channelized system is formed by subaqueous braided channels, terrace, sheet-like turbidite sandstone, which were identified from core analysis and log interpretation.
Restricted by the research techniques and methods, the distribution of these facies is unclear yet, especially that of the gravity flow deposit system. Under the guidance of the theory of seismic sedimentology, the sliced cubes were made and the sandbodies of the typical slices were interpreted subtly, in order that the distribution of sedimentary facies are predicted. The channelized system is mainly formed in the east slope, including four braided channels that originate from the West Chengbei Lower Uplift and gradually prograde to the eastern depression area. The non-channelized system deposits is due to the slump of delta front sediments. From provenance to sedimentary area, slide deposits, slump deposits, sandy debris flow sediment, muddy debris flow sediment and turbidite are successively found in the gully.
This study established typical gravity flow deposit system in Chengdao Area, Jiyang Depression, which can also be referred for seismic sedimentology study in non-marine basins, especially areas with high-quality 3D seismic dataset.
