Holocene Depositional Patterns of the Subaqueous Nakdong Delta on the Korea Strait with Respect to Sequence Stratigraphy

Abstract

A sequence stratigraphic analysis was conducted using high-resolution 'Chirp' seismic profiles and a long core data off the Nakdong River where Holocene deltaic deposition prevails in the Korea Strait. The depositional sequence comprises a group of transgressive and highstand systems tracts, intercalated with their bounding surfaces of maximum flooding surfaces, above a sequence boundary. It is formed by an erosional process within an incised valley, indicating the Nakdong River at the lowstand of sea level. The transgressive systems tract consists of the lower and upper depositional units, bounded by a ravinement surface, formed during the early Holocene when sea-level rose between 12.0 and 6.0 ka BP. The lower depositional unit mostly occurs in the incised valley area, comprising fluvio-estuarine sediments, whereas the upper one nearshore environments consist of sand sheet and ridges. The overall stacking pattern of these sequences demonstrates retrogradation. During the late Holocene sea-level highstand of around 6.0 ka BP, the highstand systems tract overlying the maximum flooding surface consists of the deltaic sequence, formed as a seaward sigmoid progradational pattern. The subaqueous Nakdong delta system has evolved to depositional units of the retrogradational transgressive and then the progradational highstand systems tract over a sequence boundary during the Holocene transgression.