Sedimentary Facies and Depositional Environment of Long Sediment Cores from the Nakdong Incised-valley Fills, Southeastern Korea

Hong, S.-H.; Chun, S.S.; Kim, J.-C.; Lee, G.-S.; Yoon, H.-H., and Yoo, D.-G., 2020. Sedimentary facies and depositional environment of long sediment cores from the Nakdong incised valley fills, southeastern Korea. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 511–515. Coconut Creek (Florida), ISSN 0749-0208.Two deep-drilled cores were obtained from the Nakdong River delta in 2016. Based on the sediment structure, composition and texture, the deposits can be divided into four depositional units: I) fluvial sediments, II) estuarine sediments, III) coastal sediments, and IV) delta sediments. The lowermost Unit I is about 25 m thick and comprised clast-supported gravel and massive sand. The age dates of the upper part of Unit 1 is 49.7 ± 5.3 ka. Unit II consists of thin silt laminations that vary rhythmically in thickness, suggesting tidal influences in the estuarine environment. The age dates of this unit range from 10.9 ± 0.18 to 9.6 ± 0.11. Unit III is composed of cross-bedded sand, which contains peat materials and shell fragments and is interpreted to rapidly deposited sand bars in coastal environment. The age of Unit III had 9.7 ± 0.18 ka. Unit IV is composed of extremely bioturbated sandy mud and cross-laminated sand. The age dates of Unit IV ranges from 7.4 ± 0.5 to 0.8 ± 0.09 ka, the deposits belonging to the Holocene. These results indicate that depositional units in the study area consists of fluvial deposits of forced regression formed during the MIS 3, estuarine to tidal flat deposits during deglacial transgression, prograding delta deposits during postglacial periods.