Sr-Nd isotopic characteristics of eolian deposits in the Erdos Desert and Chinese Loess Plateau: Implications for their provenances

Abstract

Material sources of the northern deserts and the Loess Plateau in China are always one of the critical focuses in Quaternary and paleoclimate fields. In this paper, the method of Sr-Nd isotope geochemistry is applied to explore the relationship in material source between the Erdos desert and Chinese Loess Plateau. The eNd(0) value of the <75 μm silicate fraction between -11.8 and -17.2 is more positive in the west than in the east, and its 87Sr/86Sr ratio varies from 0.719218 to 0.714824 without similar characteristics in the Erdos desert. In addition, there are Sr-Nd isotopic differences between different grain-size fractions of eolian sand in the Erdos desert. The coarse-grained fractions mainly originated from local parent rock weathering, but the fine-grained fractions were probably affected by the input of foreign materials. Geographical distribution of Sr-Nd isotopes (especially Nd isotopes) of <75 μm silicate fractions indicates that the input of foreign materials into the Erdos desert decreases gradually from its west to east. The eNd(0) and 87Sr/86Sr values of eolian silicate fractions in the Chinese Loess Plateau vary from -9.2 to -13.56 and from 0.719957 to 0.714424, respectively in this study. The eNd(0) and 87Sr/86Sr values of eolian silicate fractions are different between the western-central and eastern Loess Plateau. According to Sr-Nd isotopic data from previous and present studies, the eNd(0) values of eolian silicate fractions in the western-central Loess Plateau mostly fall in a very narrow range of -9∼-11.5, suggesting a uniform source region. However, there is a large Sr isotope variation resulting from different pretreating methods employed by researchers. The eNd(0) and 87Sr/86Sr values of eolian silicate fractions in the eastern Loess Plateau both change markedly. The differences in Sr-Nd isotopes of eolian silicate fractions between the eastern and western-central Loess Plateau indicate that there are different sources for eolian silicate materials in the two sub-areas. Sr-Nd isotopes, especially Nd isotopes of the <75 μm silicate fractions in the Erdos desert are clearly different from those of eolian silicate fractions in the western-central part, but roughly close to those of eolian silicate fractions in the eastern part of the Chinese Loess Plateau, which shows that the Erdos desert was perhaps a main source for the eastern Loess Plateau but not for the western-central Loess Plateau.