Internal reflection pattern of Korea Strait shelf mud (Nakdong River subaqueous delta) off southeast Korea and implications for Holocene relative base-level change

Abstract

The Korea Strait shelf mud (KSSM) (Nakdong River subaqueous delta) is the most conspicuous Holocene sedimentary feature in the inner shelf off southeast Korea. Analysis of multi-channel sparker profiles and 14C ages of sediment cores reveals that the KSSM consists of three seismic units at the depocenter (> 60 m thick): (i) the thin transgressive bottom (> ca 8000 cal bp); (ii) thick (> 40 m) obliquely progradational middle (ca 8000-ca 2600 cal bp); and (iii) thin transgressive top (ca 2600 cal bp-present) units. The relative base level, predicted from the internal reflection pattern of the KSSM, remained significantly deeper (up to > 70 m) than global sealevel during much of the Holocene. The apparent gradual drop (similar to 20 m) of the relative base level during the deposition of the middle unit, followed by a rise, further suggests that base level does not conform to sealevel and is more sensitive than the relative sealevel is to the local oceanographic regime and processes.