Refined U-Pb zircon age of the Kusandong Tuff: A key stratigraphic marker for Cretaceous arc magmatism in northeast Asia

The Kusandong Tuff is a prominent stratigraphic unit within the Gyeongsang Basin, the largest Cretaceous sedimentary basin on the Korean Peninsula in East Asia. Extending approximately 200 km in a north–south direction, it serves as a key marker bed within the basin. Located in the upper part of the Hayang Group, the Kusandong Tuff records the onset of subduction-related arc magmatism that followed extension-related volcanism in the Gyeongsang Basin. Overlying the Hayang Group with Kusandong Tuff, the Yucheon Group in the eastern basin reflects the development of the Gyeongsang Arc System through subduction. The Kusandong Tuff thus represents an initial phase of subduction-related volcanism prior to Yucheon deposition. Despite its significance, establishing the precise eruption age of the tuff has been challenging, with previous zircon U-Pb dating studies reporting ages ranging from approximately 97 Ma to 103–104 Ma. These discrepancies have hindered consistent stratigraphic correlations and geological interpretations. In this study, we analyzed five samples from different outcrops using three zircon U-Pb dating methods to refine the eruption age. The results confirmed that the tuff erupted during the late Albian of the Early Cretaceous, approximately 103 Ma. These findings provide a refined temporal framework for understanding the tectonic evolution, stratigraphy, and volcanic activity of the Cretaceous in northeast Asia, and enhance the stratigraphic correlation within the Gyeongsang Basin.