Sediment properties of lithologic units and their correlation within the lower delta plain of the Nakdong River Delta, southeast Korea

Abstract

Multi-proxy sediment properties reveal that three cores (ND-01, ND-02, and ND-03) from the lower delta plain of the Nakdong River Delta, southeast Korea, are characterized by the same stratigraphic lithologic successions consisting of a upper sand unit (10–15 m thick and <1 ka), a middle mud unit (∼20 m thick and 1–9 ka), a lower sand unit (6–9 m thick and 9–10 ka), and a lower mud unit (10–15 m thick and >10 ka) overlying weathered gravelly fluvial sediments and weathered bedrock. The sediment properties of each lithologic unit are controlled by the balance between the marine influence from Holocene sea level rise and the freshwater influence from Nakdong River discharge. In particular, the middle mud unit is characterized by distinct peaks in CaCO3 content, P/T ratios (the ratio of planktonic foraminifera to the sum of benthic and planktonic foraminifera), total organic carbon and total nitrogen contents, and δ13Corg values at 7–8 ka, which indicates that the maximum marine forcing during the sea level rising and the greatest influence of the Tsushima Warm Current during the evolution of the river-mouth coastal depositional system from an estuarine to a deltaic environment. Although the vertical stacking of lithologic successions is stratigraphically consistent within the lower delta plain, the precise temporal evaluation and comprehensive depositional evolution in the Nakdong River Delta including the upper delta plain and the prodelta zones remain a topic of future investigation.