Late Pleistocene loess-like deposits in the coastal area of south China

Abstract

A layer of yellow silt with thickness from tens of centimeters to a few meters is widely distributed on low hills and terraces in the coastal area of south China. The yellow silt has different sedimentological characteristics from other common types of Quaternary sediments and the bedrock weathering material in the area. Five representative sections were studied using scanning electron microscopy, grain size analysis, diffuse reflection spectroscopy, geochemical analysis and optically-stimulated luminescence (OSL) dating to reveal the sedimentary characteristics, deposition environment, origin and age of the yellow silt. Subrounded-subangular quartz grains showed typical aeolian impact pits, such as dish-like and crescent pits, and chemical precipitation and corrosion on grain surfaces. The grain size composition, grain size parameters and unimodal frequency distribution curves of the yellow silt were similar in all sections examined and consistent with those of north and central China loess. The iron mineral content of the yellow silt was dominated by hematite, indicating a similar sedimentary environment to that of typical Chinese loess. The major oxide composition of the yellow silt with respect to normalized upper continental crust (UCC) distribution patterns was close to that of the UCC and similar to north China loess and other aeolian deposits in China. However, the data suggested that the yellow silt in the coastal area of south China had suffered strong weathering after deposition. The OSL ages of the yellow silt indicated a deposition age of late Pleistocene. The results of the various analytical methods all showed an origin correlation and regular transition of loess deposits from northwest to southeast China. Hence, it was concluded that the yellow silt widely distributed in the coastal area of south China is a loess-like deposit formed during the late Pleistocene. It probably mostly originated from northwest inland China and constitutes the south extension of other loess in China.