| 07SR03core was collected from Dabei trough eastern sand ridge of radial tidal sand ridge system in Jiangsu offshore, South Yellow Sea. We measured total organic carbon (TOC), total nitrogen (TN), inorganic carbon (TIC) and organic carbon isotope (δ13C), and obtained the vertical variation of these indices since the late Pleistocene. In this paper, we use C/N (TOC/TN) and δ13C to trace the change in organic matter sources and analyse the cause for formation at different times. The results show that:0-15.5m:(1) These indices change stable, which shows that the sedimentary environment is stable since the Holocene.(2) The C/N ratio changes stable and ranges from9.7to21.2. The δ13C value ranges from-25‰to-22‰. These values show that the material source in this region is a mixture of terrestrial and marine material.15.5-18.1m:(1) Upslope from18.1m, particle is fining, TOC increased from0.22%to0.585%and TN increased from0.023%to0.04%. These changes may be caused by the Changjiang River runoffs into the South Yellow Sea in the northern Jiangsu, and brings a large number of fine particles and high organic matter.(2) The content of TIC is low ranged from0.037%to0.226%, which may be caused by a large number of poor carbonate material brought by the Changjiang River.(3) Although the climate was warmer, but the temperature was still lower than now, so the vegetation was mixed by coniferous and broad-leaved forest and grassland. And some herbage is C4plant, such as Artemisia, Cyperaceae, Compositae. Local and the Changjiang River bring Some C4plants, which is the reason of higher δ13C value(-24.679‰～-22.267‰). 18.1-25m:(1) The content of TOC ranges between0.001%to0.329%, and TN ranges between0.007%and0.038%, which changed stable at a low value. At this time the earth entered late Dali ice age, so the climate changed drier and colder, and sea level continued to decrease. So the shelf of south yellow sea was exposed and formed continental sedimentary. Due to the cold climate, less plant grew, so the preservation of the organic matter is less.(2) From25m upward, inorganic carbon content decreased gradually, dropped from1.091%to0.01%, which caused by reduction of calcareous biological productivity and enhancement of dissolved calcium carbonate. The change of TIC shows the process of marine to continental.(3) Native some C4plants, which is the reason of higher δ13C value(-24.507‰～-22.222‰).(4) According to the change of organic matter and δ13C and the color of the sediment, we correct the lower limit of silt clay sedimentation to25m.25-55.5m:Because the influences of the tide, the sediment were eroded and redeposit, and the lack of core, so these indices changed complex. A large number of pollen deposited formerly were washed away and redeposit by the strong hydrodynamic, so the δ13C value changed severely.Below55.5m:(1) The core is missing, so the organic matter fluctuates strongly.(2) At this time the earth entered early Dali ice age, so sea level continued to decrease. The sedimentary facies is fluvial facies. The river brings a lot of terrigenous matter, and the dilution effect is stronger, so the inorganic carbon content is low(0.047%～0.795%).(3) The climate is colder, and vegetation is composed of meadow steppe (Artemisia, Cyperaceae, Compositae). The C4plants, which is the reason of higher δ13C value(-24.679‰～-22.267‰). |
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