Sedimentary Characteristics And Implication To Provenance And Sedimentary Environment Since The Last Deglaciation In The North Yellow Sea

In order to identified the provenance and sedimentary environment, and reconstruct the depositional history of ancient epicontinental seas, it is important to understand sediment characteristics and transport processes of modern and cores deposition in the continental shelf environments. A large number of surface and core sediments were obtained during cruise to the North Yellow Sea (NYS). Base upon grain size, mineral analyses, and AMS14C and 210Pb dating, the sediment characteristics and evolution were discussed, and the provenance and sedimentary environment were analyzed in addition. Grain size of surface sediment samples were analyzed, indicating that the surface sediments in the study area could be identified as mud, silt, sandy silt, silty sand and sand, and became coarser and coarser from southwestern part to northeastern. The NYS could be divided into five sediment environmental zones according to grain size analysis, which was dominated by factors such as provenance and hydrodynamic environment respectively.The clay minerals in the <2μm fraction of surface sediment samples from the NYS have been identified. Illite was the most abundant component in the modern clay minerals of NYS, followed by smectite, chlorite and kaolinite. The results of the K-means clustering analysis discriminated the fine-deposition in the western part and the coarse-deposition in the northeastern part on the basis of clay mineral assemblages. Fine materials from Huanghe, as well as west coastal erosion and other rivers supplied clay minerals for western part of NYS, while Yalujiang River offered plenty of illite and chlorite with clear abrasive edge and lower crystallography index for northeastern NYS. The spatial distribution of clay minerals has a close relationship with the local circulation system. The Yellow Sea Warm Current (YSWC) and Yellow Sea Coastal Current (YSCC) exerted good control on transportation clay minerals in western NYS. Liaonan Coastal Current (LCC) brought more illite and chlorite from Yalujiang to deposit near Dalian Bay. The enrichment of smectite in the central part of the investigated area was considered to be northward transported by YSWC.Modern detrital minerals in NYS were absolutely dominated by light minerals (97% in average). Mineral assemblages were characterized by relatively high content of feldspar, quartz in light minerals and hornblende, chlorite, epidote, muscovite in heavy minerals. In sandy deposition of northeastern NYS, the dynamic sorting under strong tidal currents largely affected the distribution of detrital minerals, which derived from Yalujiang River and residual deposition before Holocene. Near the Dalian Bay—Changshan Islands area, dynamic sorting in shallow water exerted a dominant control on detrital minerals distribution, and sediments were mainly derived from the coastal erosion. Schistose minerals were extremely enriched in fine-grained deposition in southwestern NYS, hydrodynamic was weak therein and differentiation during long-distance transporting was responsible for the distribution of detrital minerals, which was considered to be subjected to great influence from Yellow River. The center of NYS, which was a multi-source deposition zone affected by multiple factors, was speculated to be the response of the YSWC, which obstruct water and sediment exchange between west and east regions as well as south and north regions to a large extent.To decipher the sedimentary evolution and sedimentary environment changes since the Last Deglaciation, two gravity cores, B-L44 and B-U35 from the western NYS were analyzed in grain size, clay minerals, detrital minerals, and 14C dating. The two cores are correlated with each other, and the succession observed are divided into four depositional units in lithology and mineral assemblages, which record the postglacial transgression. Depositional unit 4 (DU 4) (before 11.5 ka) was characterized by great enrichment of sand, and was diagnosed as nearshore deposits in shallow water during the Younger Dryas Event. DU 3 (11.5-9.6 ka) displayed a fining-upward succession composed of sediment from local rivers, such as Yellow River, and from coastal erosion, clearly related to the early Holocene transgression. Stable fine deposition (DU 2) in NYS began to form at about 9.6 ka and received direct supply of fine materials from the Shandong subaqueous clinoform. It is believed that the Yellow Sea circulation system played a major role in controlling the formation of DU 1 (after 6.4 ka) after the sea level maximum.In a word, the modern sediment in the NYS is dominated by terrigenous depositions from such as Yellow River, Yalujiang River and so on. Additionally, erosion, including coastal erosion and sea erosion, contributed to the NYS more coarse particles. The strong tidal current in eastern, the YSWC in central and YSCC in southern jointly dominated the distribution pattern in the NYS.