南黄海辐射沙脊群西洋潮道晚更新世晚期以来沉积环境

Sedimentary environments of Xiyang tidal channel of radial tidal sand ridge system since the late period of Late Pleistocene in South Yellow Sea

利用首次在江苏大丰港岸外西洋潮流通道内获取的钻孔沉积物,通过沉积相分析和浅地层剖面解译,结合同位素测年,对西洋长周期演变和成因机制进行了综合分析。共识别出7种沉积相,即:潮道底部滞留相、潮间—潮下相、贝壳层、潟湖相、泛滥平原相、滨海湖沼相及滨海沙坝相。西洋潮流通道长周期演化显示,晚更新世晚期以来研究区经历了滨海沙坝→滨海湖沼→泛滥平原→滨岸潟湖→潮流沙脊→潮道充填→潮道侵蚀一系列复杂的沉积环境演变。进入全新世,随着海侵的加剧,潮流作用逐渐增强并改造下伏沉积物形成潮流沙脊。晚全新世期间,中全新世形成的潮流沙脊沉积体系面临调整,西洋潮流通道在此期间通过沙脊蚀低形成。公元1128—1855年黄河夺淮,带来大量泥沙,充填了西洋潮流通道。随着黄河北归、沙源被切断,潮道底部遭受强烈冲刷和侵蚀,遂成为强潮水道。

A core （33°15.84′N,120°53.761′E）was drilled in Xiyang tidal channel,aimed to reveal the genesis and history of sedimentary environment of the channel based on sedimentary facies and seismic explanation combined with isotope dating analysis.Seven sedimentary facies such as channel bottom lag deposit,inner-tidal-subtidal facies,shell bed,lagoon facies,flooding plain,littoral swamp and sand bar facies have been distinguished on the basis of lithology,sedimentary structures,grain size,and fossils contained.The results show that the study area experienced a complex sedimentary environment evolution of coastal sand bar→littoral lake swamp→flooding plain→lagoon→tidal ridge→channel infilling→channel erosion.With the intensive Holocene transgression,the increased tidal currents reworked the underlying sediments,a tidal ridge-channel system was developed.During the Late Holocene,the tidal ridges were cut and eroded partly.The Xiyang tidal channel was formed during this period.When the Yellow River delivered to the South Yellow Sea coast from 1128 to 1855 AD,the channel was filled.After the Yellow River switched to the Bohai Bay,the sediments were cut and the channel encountered intensive scouring and erosion.As a result,the channel bottom became expansion and relief.