Diffuse Reflectance Spectroscopy Study of Mottled Clay in the Coastal
Area of Fujian and Guangdong Provinces and the Interpretation of Its
Origin and Sedimentary Environment
WANG Jing1, 2*, CHEN Zhen3, GAO Quan-zhou1
1. School of Geography and Planning, Sun Yat-sen University, Guangzhou 510275, China
2. Museum (History Museum) of Sun Yat-sen University, Guangzhou 510275, China
3. GDZD Institute on Deep Earth Sciences, Guangzhou 510275, China
Abstract：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.
Key words：Diffuse reflectance spectroscopy; Iron oxide; Mottled clay; Aeolian deposit
王 晶，陈 震，高全洲. 漫反射光谱法对闽粤沿海花斑粘土沉积环境及成因的指示[J]. 光谱学与光谱分析, 2022, 42(08): 2494-2498.
WANG Jing, CHEN Zhen, GAO Quan-zhou. Diffuse Reflectance Spectroscopy Study of Mottled Clay in the Coastal
Area of Fujian and Guangdong Provinces and the Interpretation of Its
Origin and Sedimentary Environment. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2022, 42(08): 2494-2498.
