Biostratigraphic research has been conducted over the last four decades in the southwestern Ulleung Basin and has provided a chronostratigraphic framework to understand basin evolution. However, absolute geologic ages for the basin are almost absent owing to the lack of deep-drilled cores. To obtain the absolute age from the zircon, we extensively sampled and measured five deep-drilled conventional cores previously obtained fo...

The Daeri Member, a Cretaceous volcanic–sedimentary succession, can be divided into lower, middle, and upper parts based on vertical changes in its lithologic characters. The lower Daeri Member is composed of siliciclastic deposits formed in a semi‐arid floodplain environment, which is overlain by the middle Daeri Member consisting mainly of andesite lava flow. After the emplacement of the andesite, activities of intrabasinal...