Detrital zircon U-Pb dating was performed using LAMC-ICP-MS on a total of six samples to determine the depositional period of the Dadaepo Formation (DF) in the Dadaepo Basin (DB) located in the Busan area, Korea. Cretaceous zircons accounted for 81% (LD-1), 49% (LD-2), and 34% (LD-3) in the lower Dadaepo Formation (LDF), 88% (IG-1) in the ignimbrite at the boundary of the upper and lower Dadaepo formations, and 80% (UD-1) and 100% (UD-2) in the upper Dadaepo Formation (UDF). The ²⁰⁶Pb/²³⁸U weighted mean ages using the youngest clusters of zircons were calculated to be 98.0 ± 0.3 Ma in LD-1, 96.8 ± 0.2 Ma in LD-2, 97.1 ± 0.3 Ma in LD-3, 93.6 ± 0.2 Ma in IG-1, 93.3 ± 0.2 Ma in UD-1, and 92.8 ± 0.2 Ma in UD-2. Therefore, the DF was deposited from the early Cenomanian to the Turonian in the Late Cretaceous, and the formation is correlated with the lowermost Yucheon Group. In addition, the synthesized chronostratigraphy of the Cretaceous basins in Korea indicates that the sinistral strike-slip movement of the NE–SW-striking fault systems in the Korean Peninsula decreased starting at about 85 Ma.