C01_P05

Sedimentary environment and depositional process of reworked materials in the subaqueous Yangtze Delta during the middle and late Holocene

Wang K^1,2, Saito K², Tada R^2,3, Irino T¹, Zheng H⁴, Sugisaki S⁵, Uchida M⁶

¹Hokkaido University, Sapporo, Japan, ²University of Tokyo, Hongo, Japan, ³Chiba Institute of Technology, Tsudanuma, Japan, ⁴Yunnan University, Kunming, China, ⁵National Institute of Advanced Science and Technology (AIST), Tsukuba, Japan, ⁶National Institute for Environmental Studies (NIES), Tsukuba, Japan

Origin and formation mechanism of the subaqueous Yangtze Delta is of primary importance owing to massive inputs of terrestrial materials from the Yangtze River. It is necessary to examine the transportation mechanism of Yangtze-derived sediment including sediment reworking / re-deposition by coastal current, tide and local input, the migration of shoreline and estuary of the Yangtze River, as well as changes of depocenter in the Yangtze Delta associated with the postglacial sea-level rise in order to interpret and further understand paleoclimatic information record in the Yangtze Delta. YD13 core recovered from the subaqueous Yangtze Delta at 37-m water depth was used to examine the depositional process through time. The age model of YD13 core was established on the basis of the AMS¹⁴C dates of shell fossil, which revealed that the top 10 m of YD13 core corresponds to the last 5.1 ka. The top 10 m of YD13 core sediments are mainly composed of gray silt with intercalations of many thin coarse silt to sand layers. Comparison among ages of shell fossil, benthic foraminifera, particulate organic carbon (POC) and optically stimulated luminescence (OSL) dating, we assumed that YD13 core sediments deposited during 5.1 to 2.3 ka were significantly affected by the reworked materials, which were originally deposited during the transgression in the early to middle Holocene in addition to the riverine sediments discharged directly from the Yangtze estuary.