Asymmetric evolution of incised-valley deposits in response to sea-level changes since the Penultimate Glacial Maximum, southeastern Korea

The recognition of lowstand fluvial deposits in incised valleys below coastal plains is important for establishing the evolution of depositional systems over one glacial period in response to sea-level changes. The Penultimate Glacial Maximum lowstand was lower than the Last Glacial Maximum lowstand, making it imperative to consider it as a beginning-point for documenting incised valley fills. The preservation of whole deposits owing to weathering and erosional processes during glacial periods pose of challenge for studying the Penultimate Glacial Maximum. Here, we carefully conducted core analyses of sedimentary facies, grain size, and OSL age dating from the two cores, in addition to documenting younger valley infills. Seven facies associations were defined in the cores: braided river, tributary channel and land swamp, mud flat and marsh, fluvial channel and floodplain, central basin to bayhead prodelta, bayhead delta front, and bayhead delta plain. Overall, the sedimentary analyses indicate that the depositional environments of each stage produced during the five successive stages and correspond to the relationship between sediment supply and accommodation spaces in response to sea-level changes in the Nakdong incised-valley system. The Nakdong incised-valley fills shows that one and a half sea-level cycle was preserved in an incised-valley system during Last Glacial Maximum periods. The wedge-shaped geomorphology influenced the architecture and preservation of the Nakdong incised-valley deposits characterized by the asymmetric development of depositional successions since the Penultimate Glacial Maximum.