Study on the geochemical character of carbon and nitrogen and sedimentary environment evolution of radial tidal sand ridges system in the South Yellow Sea, China

Abstract:

07SR03 core was collected from Dabei trough eastern sand ridge of radial tidal and ridge system in Jiangsu offshore, South Yellow Sea in China. The present work integrates sedimentary facies,¹⁴C dating, δ¹³C, and C/N with geologic and geomorphologic data available from literature. Twenty-eight sediment samples recorded ages ranging from 7490±50 to 41420±61514C yr B.P.. Facies analysis indicated fine to coarse grained sands with parallel lamination or cross stratification, massive or laminated muds . δ¹³C values are in the range of −26.504‰ to −21.812‰, and C/N ratios are in the range of 0.045 to 64.156. These indicate the organic matters have typical characteristics of mixed terrigenous and marine provenance. The results confirm an obvious land-sea interaction in the South Yellow Sea since late Pleistocene. At the depth of 18-20 m and 55.6 to 70 m corresponding to the sedimentary facies of land clay and river deposition respectively, which indicate the regression period in lower sea level, δ¹³C values are higher obviously. These may result from the C4 plant growing in the study area during those times. According to the 07SR03 information and relevant literature, determine the sea level fluctuations in DaBei trough area around the South Yellow Sea since late pleistocene. Transgressive and regressive were alternating since 50kaB.P.. About 20kaB. P. with the Last Glacial Maximum coming the relative sea-level dropped to -100m. With the increasing temperature, the sea level rises gradually except for the little regression during Younger Dryas period. From then on, the sea level rises rapidly with the advent of Holocene transgression, followed by the slow falling and then being relatively stable. The distribution of δ¹³C, and C/N with the depth of the core, together with facies associations, led to identify depositional settings related to tidal sand ridge facies, shoreland, tidal flat, land clay sedimentation, tidal flat and river deposition (from the top downward).