Volcanological and paleoenvironmental implications of charcoals of the Nari Formation in Nari Caldera, Ulleung Island, Korea

The volcanic activity of Ulleung Island generated considerable amount of pyroclastic materials composed of volcanic ash, lapilli tuff, pumice, and breccia, during the period ranging from the Pleistocene to the Holocene. The Nari Formation exposed in the southern part of the Nari caldera can be divided into four units; Nari-I, Nari-II, Nari-III and Nari-IV. Nari-I, Nari-II, and Nari-III are characterized by dense gray pumice, white and gray pumices, and brown and black pumices, respectively. In this study, we dated radiocarbon ages and identified species of four charcoal fragments collected from the pumiceous deposits of Nari-I and Nari-II. Radiocarbon ages for Nari-I and Nari-II are 15,880 ± 60~15,560 ± 100 BP and 7,660 ± 40~7,600 ± 40 BP, respectively. Calibrated ages from these ages are 19,055 ± 95~18,840 ± 150 cal BP for Nari-I and 8,465 ± 75~8,400 ± 40 cal BP for Nari-II. This result indicates that the interval between Nari-I and Nari-II might be about 10,000 years. Nari-III was formed after 5,600 cal BP that records the youngest age data correlated with Nari-II. Therefore, it can be concluded that Albong lava dome, the youngest volcanic activity of the island, is more likely to cease a few thousands of years ago. On the basis of the anatomical characteristics of the charcoal fragments, they were identified to be Picea spp. and Fagus crenata. To summarize, the paleovegetation around the Nari caldera consisted of Picea spp. until 19,055~18,840 cal BP and Fagus crenata, representing a broadleaf forest of Ulleung Island at present, flourished after about 8,465 cal BP.