南黄海辐射沙脊群大北槽东沙沉积物地球化学特征及沉积模式研究

The geochemical characteristics and sedimentary environment evolution of the Dabeicao channel and Dongsha shoal area among the radial tidal sand ridge system,southern Yellow Sea

根据南黄海辐射沙脊群大北槽东沙07SR03钻孔的沉积相及沉积物中的δ13 C和C/N特征,来研究晚更新世以来大北槽东沙地区海平面波动和沉积模式.07SR03孔AMS14 C测年得到钻孔年龄自深到浅处于(41420±615)^(5630±50)14C yrB.P..沉积相中主要以砂,粉砂和黏土为主,以粉砂居多.沉积物的δ13 C处于-26.504‰^-21.812‰之间,C/N为0.045~64.156,表现出大北槽东沙地区的晚更新世以来陆海交互作用显著,在07SR03孔的18~20m和55.6~70m均出现了δ13 C高值区,认为是陆地C4植物的有机质沉积影响,与冰期海退情况相符.研究南黄海大北槽区域晚更新世以来的海平面波动变化,40kaB.P.以来海侵海退交替,20kaB.P.左右迎来末次盛冰期,海平面降至-100m左右,之后气候回暖,海平面逐渐升高,12kaB.P.新仙女木期间小幅度海退,随后进入全新世海侵时期,经过海平面迅速升高后,海平面缓慢下降并趋于稳定.综合07SR03钻孔沉积相信息和有机质地球化学指标δ13 C和C/N,将大北槽东沙晚更新世以来自下而上的沉积分为河流相→潮滩相→陆地硬粘土相→潮滩相→滨岸相→近代潮流沙脊相的沉积模式.

07SR03core was collected from the Dabeicao channel and Dongsha shoal area of the radial tidal ridge system offshore of Jiangsu Province,in the southern Yellow Sea.Analyses of sedimentary facies,14 C dating,δ^13 C,and C/N were carried out,together with the geological and geomorphological data available from the literatures.In the present study,the 28 sediment samples recorded ages ranging from（41420±615）to（5630±50）14 C yr B.P..The sedimentary materials consist of fine to coarse grained sands with parallel lamination or cross stratification and massive or laminated muds.The characteristics of δ^13 C（-26.504‰to-21.812‰）and C/N（0.045 to 64.156）indicate most-ly marine and freshwater phytoplankton sources for the organic matter.These results reveal paleoenvironment change in the southern Yellow Sea since the late Pleistocene.Two δ^13 C high values appear at 18～20mand 55.6～70mof07SR03core,corresponding to a glacial regressive situation,which is indicated by the terrestrial organic matter deposition of C4 plants.On the basis of the 07SR03 data and relevant literature,sea level fluctuations in the study area since the late Pleistocene are identified,with alternating transgressive and regressive periods sine 40 ka B.P..Around20 kaB.P.with the Last Glacial Maximum coming the relative sea level dropped to-100 m.With the temperature increase,the sea level rose gradually,except for the little regression during the Younger Dryas period.From then on,sea level rise became rapid with the advent of the Holocene transgression,followed by slow falling and relatively stable periods.The distribution of δ^13 C,and C/N,together with facies associations,show that the depositional settings are related to fluvial,tidal flat,terrestrial（characterized by the stiff mud deposit）,tidal flat,shoreface and tidal sand ridge facies,respectively,from the bottom towards the top parts within the core.