SEDIMENTARY CHARACTERISTICS OF CORE YE-2 FROM THE CENTRAL MUD AREA IN THE SOUTH YELLOW SEA DURING LAST 8 400 YEARS AND ITS INTERSPACE COARSE LAYERS

Based on chronological, sedimentological, micropaleontological and U₃₇^K'-sea surface temperature data of core YE-2 from the central mud area of the South Yellow Sea, evolution of the marine environment in the past 8 400 years and three interspace sandy layers in the core were studied. The core is mainly composed of clayey silt, and evolution of marine environment during the last 8 400 years experienced three phases:(1) Near-shore shallow water environment with sand content of 13% at about 8.4~6.9 kaBP; (2) Transitional marine environment from near-shore shallow water to stable shallow sea with sand content of 8% at about 6.9~6.1 kaBP; (3) Stable shallow sea environment with sediment without sand at about 6.1~0 kaBP. Sea surface temperature (SST) was low in the near-shore shallow water phase, about 14.2℃ on average. And the SST began to increase at the beginning of the second phase, about 6.9 kaBP, indicating intrusion of the Yellow Sea Warm Current with the highest SST up to 18.1℃. The SST stopped increasing at 6.4 kaBP. After that the SST was stable from 15℃ to 16℃ with some fluctuations in the shallow sea phase, excluding three low temperature periods at about 5.7~5.2, 3.7~3.2 and 2.3~1.8 kaBP respectively, whose temperature was about 13.9℃ on average. Three abnormal sandy silt coarse interlayers deposited in stable shallow sea environment,were speculated to have formed in 6.0, 3.9 and 2.5 kaBP respectively. Grain-sizes of the sandy layers show characteristics of storm deposition.Heavy mineral compositions of the sandy layers show characteristics of the origin of metamorphic rocks. U₃₇^K'-SST and clay mineral compositions of the sandy layers indicate a sedimentary environment with higher temperature than that in shallow sea. These characteristics of sandy layers are different from other sediment in the core, indicating great differentce between the sandy layer and other strata in provenance.Therefore, the three coarse layers are speculated to be the storm deposition. Without consideration of three storm depositions, the sedimentation rates in core YE-2 range from 50.7 to 75.6 cm/ka, based on AMS ¹⁴C data.