The Stratigraphy And Sedimentary Environment Evolution Of Continental Shelf Since The Late Quaternary,Southern Yellow Sea

As an important storage sites for the terrigenous sediments,continental shelf is the most active and concentrated area about sea despoting,it's also the main channel of errestrial sediments transporting to the deep basins.Studying it can reveal the trend of marine environment evolution and the couse in the shelf areas of the southern yellow sea,and to provide a scientific basis for the development of Jiangsu offshore sea.In different part of the southern yellow sea,the hydrodynamic is different,and different area means different sedimentary environment in the same time.The study of southern yellow sea focused on the radial sand ridges area,but much fewer in the deep sea area,through the study of the core at the depth of 5 0-60m in continental shelf,enriched the mechanism and the dynamic development of the yellow sea,and the result can guide the development of the shelf to promote the development of China's marine economy.A long core of 13YZ02(33°32.982'N,121°24.170'E)was drilled on the continental shelf,southern yellow sea on 26-28,August,2014.The depth of the core was 80.1 m.The core was logged and sampled in June,2016,Based on grain size,foraminifera,loss of ignition,magnetic susceptibility,combined with 14C dating,we seriously analyzed the long term evolution of study area.The result has shown that the core is mainly consist of sand and silt,with the average of 29.4%and 66.2%,clay with the average of 8.9%.The average particle size is 5.725?.The average sorting is 1.977,with a relatively poor sorting.The average Skewness is 0.225,with a positive skewness.The average Kurtosis is 1.049,with a moderate kurtosis.The results of loss of ignition shown significant correlation with sedimentary environments.6 sedimentary units have been distinguished from top to bottom:U1 unit:1)Middle shelf(0-6.4m):It mainly consists of interbeded silt and mud,has some wavy beddings and riches in organic matter.Foraminifera includes:Lagena sulcata?Lagena hispida?Bulimina marginata.2)Inland shelf(6.4?11.8m):It mainly consists of interbeded silt and mud,gray,and the organism burrows increase form top to bottom,rich in carbon spot.Foraminifera includes:Pseudorotalia schroeteriana?Quinqueloculina lamarckiana?Quinqueloculina seminula and Globigerina bulloides.3)Swamp(11.8?13.7m):It mainly consists of gray clay,intercalated with silt layers,has carbon spot?calcareous concretions and bioturbation.Foraminifera includes:Ammonia annectens?Elphidium decorum and Elphidium advenum.U2 unit:1)Flooding plain(13.7?16.8m):It mainly consists of silty clay?clayey silt and sand,yellow-brown.See some iron rust?Fe/Mn concretions which are exposure sighs.Never find foraminifera.2)River(16.8?21.1m):It mainly consists of interbeded silt and fine sand,brown-gray,contains some calcareous concretions.Never find foraminifera.U3 unit:1)Inland shelf(21.1?29.0m):It mainly consists of clay.See some mollusk shells?burrows and calcareous concretions.There is a erosion interface on the top of the sedment.Foraminifera includes:Ammonia annectens?Elphidium decorum and Elphidium advenum.2)Middle shelf(29.0?36.0m):It mainly consists of dark gray clay.See some carbon spots?burrows which filled with silt and mollusk shell.Foraminifera includes:Nonionella spp.?Bulimina subula.U4 unit:1)Inland shelf(36.0?43.2m):It mainly consists of gray silt at the top part,and consists of interbeded silt and mud at the last part,rich in shells?burrows.Foraminifera includes:Ammonia beccarii?Elphidium advenum and Spiroloculina communis.2)Middle shelf(43.2?53.7m):It mainly consists of interbeded silt and mud,rich in carbon spots.Foraminifera includes:Hanzawaia mentaensis?Hanzawaia convexa?Ammonia compressiuscula and Buccella frigida.3)Estuary-Tidal influenced river-The leading edge of the estuary((53.7?63.9m):It mainly consists of gray silt at the top part,and consists of interbeded silt and mud at the last part,rich in shells?burrows.Foraminifera includes:Ammonia beccarii?Pseudorotalia yabei and Florilus scaphum.U5 unit:1)River(63.9?69.7m):It mainly consists of gray silt,some part intercalated with clay and wavy beddings.Never find foraminifera.2)Tidal influenced river(69.7?72.1m):It mainly consists of gray silt,some part intercalated with clay and wavy beddings.Never find mollusk shells,find a few foraminiferas,may be taking here by tide.3)River(72.1?79.7m):It mainly consists of gray fine sand,intercalated with clay layers at the top of this facies.See lots of mollusk shells and rocky clasts.It is only contains a few oraminiferas,may be taking here by tide.U6 unit:Inland shelf(79.7?80.1m):It mainly consists of brown-gray clay,fine and smooth,small burrows filled with silt,no beddings.Foraminifera includes:Rosalina bradyi?Ammonia beccarii and Pseudorotalia yabei.Organic matter and carbonate content analysis shown that their percentage in different sedimentary environments are different,dating from far to near,there are 6 major environmental changes in the study area.The results of loss of ignition and interpretation of sedimentary facies are in good agreement.So it's feasible to use loss of ignition as a indicator to environment.Facies in continental shelf,southern yellow sea,show the core experienced continental shelf?river?estuary-continental shelf?continental shelf?land facies?swamp-continental shelf since the late Quaternary.MIS7 is a transgressive stage,the study area are submerged and developed inland shelf MIS6 stage has a colder climate and the sea level dropped,the study area exposed in this period,forming fluvial environment.MIS5 stage,the South Yellow Sea into another transgression period,sea level rise,the study area was flooded again and developed a sedimentary sequence as the estuary to continental shelf.We didn't find sediment in MIS4stage,maybe because it's to short to deposit anything.During the warm interglacial stage as MIS3,South Yellow Sea experienced the fluctuation of a significant climate raising.Sea-level raised during this period,the study area formed shelf facies.During the MIS2 period,global climate became cold again and sea-level falling,the study area subaerially exposed and the river and flooding plain were formed.When sea level rose again during the MIS 1 period,the study area became the shelf environment.Foraminifera identification results,14C dating data,grain size data,loss on ignition analysis and the comparison between the 13YZ02 and other core in southern yellow sea,provide a basis for discrimination of the sedimentary environment evolution.