长江口北支潮滩不同沉积微相有机地球化学元素分布

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

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。

We examined the spatial distribution of total organic carbon （TOC）, total nitrogen （TN）, and total sulfur （TS） in the surficial sediments of tidal fiats from Beisiyaogang （SY）, Beipu-gang （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 ra- tios and TS-TOC relationship were analyzed to explore their potential for distinguishing different sedimenta- ry 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 val- ue 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 prograda- tional 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 ap- plied in the identification of different sedimentary microfacies of tidal flats for the Holocene core sediments.