TL dating of loess in China

Abstract

TL ages of 56 loess samples collected from Xinjiang and the middle reaches of the Yellow River were determined by using fine-grained quartz and man-made light source bleaching techniques. The results indicate that: 1. The well-preserved loess sections in Xinjiang began depositing 400000 a ago. The loess/paleosol series may be comparable with that observed in the middle reaches of the Yellow River but the depositing time was probably delayed by 30000–50000 a. 2. The bottom boundary age of the Malan loess varies from one place to another. The TL dates can be divided into two groups: 70000–130000 a and 30000–50000 a. The TL data are consistent with the appearance of two warmer climate periods since the Pleistocene, indicating obvious regional differences in stratigraphic development of loess, i.e., paleosol occurred in the warm climate period in the same location, but loess was deposited in other locations. The initial age of loess deposition tends to become older from west to east and from south to north. In contrast, the cold climatic belt showed an opposite trend. The TL ages of loess provide strong evidence for the Quaternary stratigraphy throughout geological times and the shift tendency of climatic belt. 3. The depositing rate of the Malan loess along the middle reaches of the Yellow River varies from place to place but the TL age shows a linear relationship with the depositing thickness. The depositing rate of loess in the north is higher than that in the south, suggesting that loess materials are derived from desert areas of northern China.