赤铁矿和针铁矿是自然界最常见的两种铁氧化物, 广泛分布于沉积物中, 其相对含量关系不仅可以反映沉积环境, 同时也为成因判别提供依据。 由于传统测试方法操作复杂、 效率低下, 因此难以快速而准确的测定铁氧化物的种属及含量。 近年来, 基于紫外-可见光-近红外分光光度计的漫反射光谱分析法因操作简单、 测试速度快、 检测限低等优势, 被广泛地应用于沉积物的研究中。 在我国闽粤沿海的晚第四纪盆地中, 广泛发育一套末次盛冰期的黄色粉土层, 有时混杂红、 灰色, 也被称为“花斑粘土”。 对于该套花斑粘土层, 前人多将其归因于海进期的水下沉积物在全球低海面时期, 顶部因暴露地表风化所致。 而研究发现, 大部分花斑粘土与下伏沉积在岩性上没有过渡, 截然相交, “风化”难以解释该现象; 花斑粘土中也并无发现其下伏沉积层所富含的海相生物化石, 表明两者在沉积环境及物源上存在较大差异。 为了进一步判定花斑粘土的沉积环境及成因, 在以往研究的基础上, 使用漫反射光谱分析法, 从铁矿物特征的角度对珠江三角洲第四纪钻孔进行研究。 结果表明, 花斑粘土的赤铁矿特征峰峰高>针铁矿特征峰峰高, 而其下伏沉积层的赤铁矿特征峰峰高<针铁矿特征峰峰高。 赤铁矿是干燥温暖、 陆上氧化条件的产物, 针铁矿是长期潮湿、 水下还原条件的产物。 因此, 花斑粘土并没有经过长期水化作用的改造, 并非水下沉积原地风化形成, 应属陆上外来粉尘堆积。 各钻孔垂向上, 花斑粘土两种铁矿物峰高值的变异系数较小, 一阶导数曲线形态相似, 表明不同深度成分均一, 堆积前经历了充分的混合与分选, 这为风成成因的判定提供新的证据。 可见, 漫反射光谱分析法不仅对沉积物中铁氧化物的鉴定提供技术支持, 同时也为沉积环境及成因的判别提供新的思路。

Hematite and goethite, the two most common iron oxides in nature, are widely distributed in sediments. Their relative content relationship can reflect the sedimentary environment and provide provides a basis for origin discrimination. Due to the complex operation and low efficiency of traditional methods, it is difficult to quickly and accurately determine iron the species and content of iron oxide within the sediments. Recently, diffuse reflectance spectroscopy(DRS) based on ultraviolet-visible-near infrared spectrophotometer has been widely used in sediments because of its simple operation, fast test and low detection limit. A set of Last Glacial yellow silt, sometimes mixed with red and gray and known as “mottled clay”, is widely developed in the late Quaternary basins of Fujian and Guangdong Provinces in the coastal areas south China. This layer was often attributed to exposed weathering of the underwater sediments during the global low sea-level period. However, there is no transition between mottled clay and its underlying deposit, which is difficult to explain by weathering. Moreover, marine fossils rich in the underlying layer are not found in the mottled clay layer, indicating great differences in the sedimentary environment and provenance between these two layers. In order to further determine the sedimentary environment and origin of the mottled clay, four Quaternary drill cores in the Pearl River delta with the method of DRS are analyzed from the perspective of iron mineral characteristics in this study. The results show that the peak value of hematite within the mottled clay is higher than that of goethite, suggesting that the sample is rich in hematite and relatively low in goethite. This trend is opposite to that of the underlying sediments. Hematite is formed in a dry, warm and onshore oxidation environment, where as goethite is the product of long-term wet and underwater reduction conditions. Hence, the mottled clay had not undergone long-term hydration transformation and is therefore not formed by weathering of in-situ underwater deposition but constitutes a subaerial exotic dust accumulation. The small coefficient of variation of the two iron mineral peak values and the similar DRS first derivative curves from the top to bottom of the mottled clay layer in every drill coreindicate that the composition of the mottled clay in different depths is uniform, and the samples had suffered a sufficient mixing and sorting before accumulation. It gives new evidence for the determination of mottledaeolian clay. It can be seen that the DRS method provides not only technical support for iron oxide identification of sediment but also contributes new ideas for the determination of sedimentary environment and origin.