长江口北支潮滩不同沉积微相有机地球化学元素分布*

利用在长江口崇明岛北支北四滧港（SY）、北堡港（BBG）以及新卫村（XW）潮滩获取的表层沉积物，测试总有机碳（TOC）、总氮（TN）及总硫（TS）含量，分析有机地球化学元素在潮滩微相的分布规律及影响因素，试图建立TOC/TN、TS/TOC等潮滩微相识别指标。研究结果显示，影响长江口潮滩TN、TS微相分布的重要因素为有机质含量及类型。在淤涨型潮滩，TOC/TN在高潮滩一般大于10，在中潮滩明显降至10以下；中潮滩植被带TS/TOC最高，平均值达0.063，其次为高潮滩互花米草带和中潮滩光滩（分别为0.055和0.054），高潮滩芦苇带最低；TS-TOC一元线性回归斜率在高潮滩芦苇带呈现为显著低值，自高潮滩米草带向光滩，逐渐增大。在侵蚀型潮滩，TOC/TN从高潮滩到低潮滩均大于10，而且中、低潮滩的比值大于高潮滩，潮下带骤降至小于10；TS/TOC自陆向海逐渐增大，TS-TOC一元回归斜率高潮滩最低，中潮滩最高。另外，侵蚀型潮滩各微相的TS-TOC一元线性回归斜率均明显低于淤涨型潮滩。上述研究结果表明，长江口沉积物的TOC/TN和TS/TOC及TS-TOC一元线性回归斜率与潮滩沉积微相之间存在一定的关系，具有应用于全新世钻孔识别潮滩沉积物微相的潜力。

Distribution of organic geochemical elements in different sedimentary microfacies of tidal flats from north branch of the Yangtze River mouth

We examined the spatial distribution of total organic carbon(TOC)，total nitrogen(TN)，and total sulfur(TS)in the surficial sediments of tidal flats from Beisiyaogang(SY)，Beipugang(BBG)，and Xinweicun(XW)，Chongming island at the north branch of the Yangtze River mouth.Factors controlling distribution of the organic elements were discussed and TOC/TN，TS/TOC ratios and TS-TOC relationship were analyzed to explore their potential for distinguishing different sedimentary microfacies of tidal flats in the study area.The results indicate that the content of TOC and the type of organic matter played a key role in the spatial distribution of TN and TS.In the progradational tidal flat，TOC/TN in upper tidal flat was generally larger than 10，but was smaller than 10 in middle tidal flat.The vegetation zone of the middle tidal flat had the highest average TS/TOC value of 0.063.The TS/TOC value in Spartina alterniflora zone of upper tidal flat and the bare area of middle tidal flat ranked the second(0.055 and 0.054，respectively);while in the Phragmites australis zone of upper tidal flat it showed the lowest value.The slope of TS-TOC linear regression was remarkably low in the Phragmites australis zone of upper tidal flat and gradually increased seaward.In the regradational tidal flat，TOC/TN in the whole intertidal zone exceeded 10，with higher values in mid-low tidal flat than in upper flat.However，TOC/TN was much smaller than 10 in the subtidal zone.TS/TOC increased gradually from land to sea.The slopes of TS-TOC regression lines were maximum in the middle tidal flat and minimum in the upper tidal flat.Moreover，the TS-TOC slope in regradational tidal flat was apparently lower than that in progradational tidal flat.We concluded that TOC/TN，TS/TOC and the liner regression of TS-TOC varied among different sedimentary microfacies of tidal flats in the study area，and therefore these proxies could be applied in the identification of different sedimentary microfacies of tidal flats for the Holocene core sediments.