Sedimentary environment and formation mechanism of the mud deposit in the central South Yellow Sea during the past 40kyr

Abstract

Abstract Sedimentary environment and formation mechanism of the mud deposit in the central South Yellow Sea of China during the last 40 kyr are studied based on the analysis of particle size, sediment density, chemical features, magnetic properties and AMS 14 C ages of a new core YS01A together with other available core data. The results show that there exist four sedimentary sections during this 40 kyr period, including two marine sections (A and C) and two terrestrial/intertidal sections (B and D). Sedimentary indexes of section D, which were formed before 40 kyr, show that strong weathering and erosion occurred in this section. In contrast, sedimentary environment of section B was wetter and warmer and weathering and erosion were not as strong as in section D. Marine deposits in both sections A and C indicated the effects of sea level rise and section C was deposited when the climate was much wetter than in section A. Variations of climate and local hydrodynamics created different sediment features of two marine sections. From the estimated river discharges of the Huanghe, Changjiang and relevant Korean rivers and calculation of mud deposit volumes of section A during the past 9.7 kyr, it is found that the sediment inputs from these river sources can only account for about 48% of sediments in the two mud deposits of the central and southeastern South Yellow Sea. The other main source of sediments is identified to be the seabed erosion, resuspension and redeposition from the Yellow Sea and, to a lesser extent, from the biogenesis and diagenesis. It provides a unique opportunity of understanding the formation and source of mud deposits by comparing the sedimentary properties of sections A and C in core YS01A. It is found that formation of mud deposits is not related directly to the Yellow Sea Warm Current, which only changed the sediment properties of mud deposits in section A since it formed from Holocene by bringing a large amount of organic mass and finer particles. However, cold water mass developed in this area is important as it helped to trap more and finer particles in the two marine sections. Upwelling usually occurs around 50 m bathymetry which is at the juncture of two opposite water currents and has induced the thickest sediment layer. This study also confirmed that formation of the mud deposit in the central South Yellow Sea is caused mainly by the tidal currents on the continental shelves.