The Meso-Cenozoic sedimentary system in the southern depression of the South Yellow Sea Basin: A case study of the Nanwu Sag

Abstracts: The southern part of the South Yellow Sea Basin has complex geological structures, many exploration layers, and great resource potential. However, the current level of exploration in the sea area of the basin is still low; especially the sedimentary characteristics and source-sink systems of the Mesozoic and Cenozoic continental deposits in the southern depression belt have not been systematically studied, and whether the sources in the central uplift area can be transported to the southern depression belt over long distances remains controversial, which has more or less restricted the exploration work to find favorable reservoir facies zones. We took the Nanwu Sag in the southern depression of the basin as an example, compared and analyzed the surrounding depressions, used fine interpretation of two-dimensional and three-dimensional seismic data, as well as compared new and old drilling rock electrical characteristics and core samples, based on which the sedimentary types and characteristics of the Meso-Cenozoic key strata in the southern depression of the South Yellow Sea Basin were identified, and the provenance, transport channels, and convergence areas of the basin were divided. Meanwhile, a set of sedimentary models for the Nanwu Sag was formed, and a reasonable temporal and spatial configuration relationship of sedimentary facies was established. Results show that during the Mesozoic and Cenozoic eras, water body in Nanwu Sag experienced from shallow to deep, then to shallow, and to deep water again. The sedimentary facies belt in the steep slope zone in the southern part of the depression is dominated by materials from short-axis sources, of which a semi-lacustrine-alluvial fan-fan delta sedimentary system was developed, and the materials came from the southern Bunansha uplift, while the northern gentle slope zone is dominated by materials from a shallow lake-braided river delta front, and the source mainly came from the west of the central uplift area of the South Yellow Sea Basin, and a some from the Nan’er Uplift.