Holocene paleosols of the Upo wetland, Korea: Their implications for wetland formation

摘要

A 4.490 m long core UP-1 was recovered from the marginal part of the Upo wetland. The wetland is a typical riverine wetland in Korea and has been designated as a Protected Wetland in accordance with the International Ramsar Treaty. We studied the Holocene environmental changes of the Upo wetland and the depositional conditions under which the Upo wetland formed. The core is divided into four units on the basis of grain size distribution, abundance of mottles and vertical color variation. Unit 1 has undergone pedogenic processes, resulting in variably weak to moderate soil profile development. Unit 1 paleosols are regarded as synsedimentary soils of floodplain origin, and the radiocarbon data suggest that the whole paleosol profile spans the last 5790 years. The boundaries between the soil horizons are not clear-cut, probably due to a repeated cycle of accumulation, denudation and soil-forming processes. The recurrence of these processes initiated the development of the Upo wetland. The lower boundary of Unit 2 lies at about 2300 ~(14)C yr BP, the beginning of the Subatlantic age in Korea. The lack of intense soil formation and abundant clay content in Unit 2 indicate that the geomorphologically stable wetland was developed around the coring site at that time. This means that the depositional environment changed from a floodplain to a stable, continuously submerging wetland setting. An abrupt change in sediment textures was detected in Unit 3, which commenced formation around 1000-900 ~(14)C yr BP, indicative of geological events such as inundations or inflows of slope-wash sediments. Anthropogenic deforestation and plowing around the Upo wetland area might have started at that time.