长江口启东嘴潮滩黏土矿物沉积特征及环境意义

Clay Mineral Characteristics of Tidal Flat and Environmental Significance at Qidong Cape, the Changjiang River Estuary

黏土矿物是认识沉积环境变化和示踪物质来源的重要环境指标。应用粉晶X射线衍射(XRD)方法对长江口启东嘴潮滩的岩芯沉积物的黏土矿物组成进行分析,结果表明:伊利石含量最高,均值为54.11%;其次为绿泥石和蒙脱石,均值分别为21.30%、16.21%;高岭石最低,均值为8.37%。组合类型多样,主要为Ⅰ型(伊利石+绿泥石+蒙脱石+高岭石)、Ⅱ型(伊利石+绿泥石+高岭石+蒙脱石)、Ⅲ型(伊利石+蒙脱石+绿泥石+高岭石)。物源分析结果显示,研究区沉积物与南黄海物质的关系最为密切。南黄海沉积物受到长江和黄河的共同影响,在长期的地质过程作用下具有混合源特征。沉积物来源的变化与沉积动力环境的变化密切相关。人类围垦活动造成分流角加大,接近90°,导致长江北支分流比急剧下降,河槽性质发生质的变化,涨潮流成为主要动力作用。来自口外南黄海的悬浮泥沙,在涨潮动力的携带下扩散倒灌成为研究区主要的物质来源。

Clay minerals are important environmental indicators for understanding sedimentary environment changes and provenance tracing.The X-rays diffraction analysis (XRD) is employed to measure the clay mineral compositions of core sediments at tidal flat around Qidong cape,the Changjiang River estuary.The results show that the content of illite is the highest,average up to 54.11%;the second is chlorite and smectite,respectively is 21.30% and 16.21%;kaolinite is the lowest for 8.37%.There is a variety of the clay minerals assemblage,mainly including Ⅰ assemblage (illite-chlorite-smectite- kaolinite),and Ⅱ assemblage (illite-chlorite-kaolinite-smectite),and Ⅲ assemblage (illite-smectite-chlorite-kaolinite). According to provenance tracing,sediments of the study area are most closely related to the sediments of South Huanghai Sea.It is well known that the continental shelf sediments in China mainly come from the Changjiang River and the Huanghe River.The South Huanghai Sea is influenced by the two rivers,and indicating mixed provenance characteristics under the long-term geological process.The provenance change is closely related to change of sedimentary dynamic environment. The division angle increased to almost 90°under human activities,and then the water and sediment diversion ratios declined sharply.The hydrodynamic forces transform from runoff to tide,and both the velocity and duration of the flood tide are larger than those of the ebb tide.Suspended sediments from the South Huanghai Sea,spread by the tidal power,have developed as the main source of this area.