Evolution of late Quaternary mud deposits and recent sediment budget in the southeastern Yellow Sea

Analysis of high-resolution seismic reflection profiles and sediment samples has revealed the evolution and sediment budget of the southeastern Yellow Sea mud belt (SEYSM) along the southwestern Korean Peninsula. The SEYSM, up to 50 m thick, over 250 km long and 20–55 km wide, can be divided into three stratigraphic units (A1, A2, and B, from oldest to youngest). Unit A1, overlying the acoustic basement, comprises the northern part of the SEYSM. Unit A2 comprises the southern part of the SEYSM; much of unit A2 is exposed at the seafloor. Unit B completely covers unit A1 and pinches out southward.

¹⁴C data suggest that evolution of each unit is closely related to the postglacial sea-level changes. Unit A1 consists of estuarine/deltaic or shallow-water muds deposited during the early to middle stage of postglacial sea-level rise (ca. 14,000–7000 yr B.P.). Unit A2 corresponds to relict muds deposited during the last, deceleration stage of sea-level rise (ca. 7000–3.500 yr B.P.). Unit B consists of shelf muds deposited during the recent sea-level highstand (ca. <3500 yr B.P.).

Very low background activities of ²¹⁰Pb of the surface sediment of unit A2 suggest that the present-day sediment accumulation is negligible in the southern SEYSM. On the other hand, ²¹⁰Pb excess activity profiles in unit B yield an average sediment accumulation rate of 3.9 mm/yr, indicating active sediment accumulation in the northern SEYSM. The annual sink (3.0×10⁷ tons/yr) of fine-grained sediment in unit B is about an order of magnitude greater than can be explained by the sediment input from the Korean rivers alone. We propose that reworking of unit A2 has provided large volumes of muds to unit B, resulting in excessive sediment accumulation in the northern SEYSM. Much of unit A2, in turn, is likely to have originated from erosion of unit A1 in the north. This rather unique erosional/depositional regime of the SEYSM is probably owing to the tidal and regional currents characteristic in the southeastern Yellow Sea.