华南沿海末次冰期类黄土沉积的漫反射光谱与激光粒度研究

摘要

野外调查发现，华南沿海广泛发育一套黄色粉土沉积。为研究其特征属性及成因，选择具有代表性的3条粉土剖面及1个钻孔采样，使用漫反射光谱（DRS ）分析和激光粒度（L PS ）分析的方法，率先尝试从沉积物铁矿物的产出形式和沉积物粒度配分特征的角度，综合判定沉积物的沉积环境、搬运营力及成因机制。DRS分析结果表明，在黄色粉土的漫反射光谱一阶导数曲线中，铁矿物的特征峰峰高总体有赤铁矿（565 nm ）＞针铁矿（505和435 nm ）的变化特征，与我国北方风成黄土的漫反射光谱一阶导数曲线形态吻合，均体现的是相对干冷的气候环境；而区内的河、海相沉积物曲线所反映的铁矿物特征峰的峰高变化与上述黄色粉土的变化方向相反，表明样品经历过充分的水化作用并长期处于潮湿的还原环境之中。L PS分析结果表明：各剖面（钻孔）黄色粉土的粒度组成均较为均一，粒组配分模式具显著的双峰式，两个峰值分别为主峰10～50μm 区段和次峰＜5μm区段，与黄土沉积的粒度配分模式一致，是风成沉积的特征粒组构成；而与区内河、海相沉积物粒组呈单向变化的配分模式有显著差异。结合黄色粉土的年龄介于10～80 ka之间，以及正负地形皆广泛存在的空间分布特征，最终认为该套沉积是形成于末次冰期的风成沉积（本研究称“类黄土”）。%Newly discovered yellow silt widely distributed in the coastal area of south China was analyzed using diffuse reflec-tance spectroscopy (DRS) and laser particle size(LPS)methods in the present paper .The authors take the lead in trying to syn-thetically judge the depositional enviro nment ,transporting agent and forming mechanism of the yellow silt from angles of output forms of iron minerals as well as grain size distribution features of the samples chose from three representative sections and a drill core .The DRS first derivative curves show the peak height of iron minerals decreasing from hematite (565 nm)to goethite (505 and 435 nm) ,which reflects a relatively dry ,cold climate that coincides with the aeolian loess widely distributed in the northwest China ,but reverses of the fluvial and marine deposits which experienced a well hydration in humid conditions over a long period of time in study area .LPS analysis show that grain size from top to bottom of the sections and drill core are homogeneous and typical of aeolian sediments .The grain size distribution in the yellow silt is characterized by double peaks with main peak of 10~50μm and a secondary peak of <5 μm ,similar to that of loess in northwest China but quite different from associated fluvial and marine deposits featured by unidirectional change of allocation mode of the grain size groups .Based on grain size analysis ,DRS results ,age range of 10~80 ka ,and spatial distribution that both of the positive landforms and buried topographies in the coast-al area of south China have this kind of sediments ,the yellow silt is considered to represent an aeolian deposit formed during the last glacial period ,which is called“loess-like deposits” in our study .