Source-sink characteristics of Weihe Graben and its controlling effect on deposition and reservoir characteristics

Property of provenance plays an important role in controlling Paleogene deposition and reservoir development in China's offshore basins. However, due to the cost of coring and the interpretation ambiguity of seismic data, the relevant understanding lacks visual evidence support. Weihe Graben is a Cenozoic rifting basin. Regional geological studies reveal that there are significant differences in provenance system between north and south of Weihe Graben, and its tectonic setting and provenance system show strong analogy with the offshore basins. Based on outcrops and systematic sampling in Weihe Graben, zircon U-Pb dating, cast thin section, backscattering and X-ray diffraction analysis are carried out to analyze the source system, deposition and reservoir characteristics of the northern and southern sandbodies in Weihe graben. The detrital zircons in the northern Huacheng section have two typical peaks of ~2500 Ma and ~1800 Ma reflecting the influence of North China Craton, and two younger peaks correspond to Caledonian and Hercynian movement. The conglomerate gravel types at the bottom of the sequence are mainly carbonate rocks, calcarenous clastic rocks and metamorphic rocks, which have distinct characteristics of Paleozoic carbonate rocks and clastic rock of Weibei Uplift in the north. The late Caledonian and Late Indosinian peaks dominate the detrital zircons in the southern profiles, and the gravel types are dominated by granites and metamorphic rocks, with distinct provenance characteristics of the southern Qinling Mountains. Typical profile observations show that the difference in provenance leads to significant differences between sedimentary system and reservoir characteristics. The carbonate provenance area of Weibei Uplift corresponds to a small and mud-rich sedimentary body, and the bottom conglomerate directly changes to silty sand and mudstone, with high calcium content in the reservoir. The southern Qinling orogenic belt is characterized by large distribution of sedimentary bodies, multi-cycle sand-rich deposits, and low calcium content. Different types of provenance systems provide material basis and prerequisite for reservoir and subsequent diagenesis. The outcrop system analysis of Weihe graben can provide references for offshore basin research in China.