Sequence stratigraphic frameworks in different scales and sandstone-type uranium ore-formation of Minghuazhen Formation in Dagang area, Bohai Bay Basin

Objective The Bohai Bay Basin, situated within the Eurasian metallogenic belt, is one of the world's two largest belts for sandstone-type uranium deposits, exhibiting significant potential for uranium mineralization. Well logging data indicate the development of extensive high gamma-ray anomalies within the Minghuazhen Formation in the Dagang area. Methods To investigate uranium ore formation and guide exploration efforts, a multiscale sequence stratigraphic framework of the Minghuazhen Formation was established, including a detailed study of sedimentary microfacies and the delineation of redox zones. Results The Minghuazhen Formation was subdivided into five sequences based on variations in log responses and lithological characteristics. Gamma-ray anomalies predominantly occur in the upper part of the lower member (SPNmxs) and the lower part of the upper member (SPNmsx) of the Minghuazhen Formation. Four sedimentary microfacies were identified: meandering river channel, levee, overbank, and floodplain. Uranium anomalies are primarily associated with the levee and channel sand bodies. The redox zones in these sections were classified into oxidation, transition, and reduction zones, with uranium anomalies mainly occurring in the transition zone. Conclusion The integration of sedimentary facies, redox zone distribution, uranium anomaly distribution, and oil and gas distribution suggests that the most favorable conditions for uranium mineralization are present in the levee and river channel microfacies within the transition zone near oil-gas enrichment areas. Consequently, the X7-14-2, X1603, G3-6-20, and G8-15-1 well areas are identified as the most prospective targets for sandstone-type uranium deposits in the Dagang area. This study provides valuable insights for the exploration of sandstone-type uranium deposits in the Bohai Bay Basin.