[Objective]The basement buried hill in Weixinan sag is an important target area for oil and gas exploration in the South China Sea. However, its stratigraphic age is vague, lithology is complex and diverse, boundary characterization is difficult and distribution law is unknown, which seriously restricts the buried hill oil and gas exploration. [Methods]This study integrates drilling cuttings, core samples, well logging data, and 3D seismic data from the basement. By employing methods from petrology, zircon U-Pb dating, structural geology, and geophysics, it systematically determines the ages and geophysical characteristics of different strata. Subsequently, the spatial distribution of lithologies is characterized, a structural evolution model of the buried hill is established, and the distribution patterns of the strata are revealed.[Results]The results show that there are three types of lithology in the basement. First, the Carboniferous carbonate rocks containing and coral fossils were formed in the expansion stage of the Qinfang Trough in the Hercynian period. The second is the early palaeozoic granite with zircon U-Pb age of 460~430 Ma, which is the magmatic response product of Caledonian orogeny. The third is the Precambrian metamorphic rocks with a peak age of 1180 Ma. The combination of well and seismic analysis shows that the velocity and impedance of the three types of rocks are significantly different. The velocity of carbonate rock formation is the highest (6000-6500m/s), followed by granite (5000-6000m/s), and metamorphic rock is the lowest (4500-5200m/s). [Conclusion]Through comprehensive seismic configuration and multi-attribute analysis, the lithological boundaries were delineated, revealing that the basement is divided by fault zones. The No.1 fault zone is dominated by carbonate rocks, the No.2 fault zone shows mixed granite-carbonate lithology, the No.3 fault zone exhibits mixed granite-metamorphic rock assemblages, while the slope area is primarily composed of granite.This results in a planar distribution pattern characterized by stable granitic basements in the north and south, and mixed lithologies in the central area. Differential multi-phase tectonic uplift and erosion are identified as the main controls on lithological distribution in the buried hills: Caledonian uplift exposed granite, Hercynian subsidence controlled carbonate rock overlap deposition, Indosinian-Yanshan movements influenced differential preservation of strata, and the Himalayan movement established the present basement structural framework. The results effectively guide the exploration evaluation and breakthrough of granite and metamorphic buried hills in No.2 and No.3 fault zones, and have important practical significance for oil and gas exploration in similar cross-lithologic buried hills.
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