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 ε Nd (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 87 Sr/ 86 Sr 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 ε Nd (0) (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 ε Nd (0) and 87 Sr/ 86 Sr 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.

Sr–Nd isotopic and REE geochemical constraints on the provenance of fine-grained sands in the Ordos deserts, north-central China

“…There are no N830 μm grain-size fractions in any of the samples. The grain-size result of this study agrees with the study of Rao et al (2008), but is greatly different from those of the Chinese loess (Sun, 2004). The N75 μm fractions in alluvial sand samples from mountains near Yinchuan and Baotou comprise 70% and 81%, respectively, and consist of N90% in other alluvial sand samples (Table 1).…”

“…In this case, the given components are required to be extracted through mechanical separation and chemical leaching from bulk sediment samples for Sr-Nd isotopic and REE geochemical analyses Chen et al, 2007). In recent years, Sr-Nd isotopic and REE geochemical methods have been widely used to trace the cycle of mineral dust (Liu et al, 1993(Liu et al, , 1994Greaves et al, 1999;Pettke et al, 2000;Svensson et al, 2000;Sun, 2002aSun, ,b, 2005Honda et al, 2004;Nakano et al, 2004Nakano et al, , 2005Yokoo et al, 2004;Chen et al, 2007;Yang et al, 2007b;Rao et al, 2008;Lee et al, 2010). Comparatively, Sr-Nd isotopic and REE geochemical studies of the desert provenance are still few (Chang et al, 2000;Roy and Smykatz-Kloss, 2007;Yang et al, 2007a).…”

Geochemical studies on the source region of Asian dust

“…Rao et al [59] found that the ε Nd value of fine grained fraction of Mu Us Desert Based on the age distribution of zircon grains, Xie et al [48] found that the sand in central and south Mongolia comes from the Central Asia Orogen (CAO) and the sand in Ontin Daga Sandy Land is derived from both the CAO and the mountains of North China Craton. This remarkable study demonstrated that sand in the low relief should originate from the surrounding high mountains.…”

Sr isotopic and elemental characteristics of calcites in the Chinese deserts: Implications for eolian Sr transport and seawater Sr evolution

“…Eolian dust in the Chinese Loess Plateau is usually considered to originate from the desert areas of northern China, however, which deserts are the source areas of eolian dust deposits in the Loess Plateau is controversial at present (Liu, 1985;Liu et al, 1994;Zhang et al, 1997;Sun, 2002a;Nakano et al, 2004;Yokoo et al, 2004;Chen et al, 2007;Rao et al, 2008a). Northern China is climatically controlled by the upper-level westerly and the low-level East Asian monsoon.…”

“…Primary silicate rocks are responsible for the silicate fraction in the desert sand whereas the carbonate fraction is probably associated with weathering of both marine carbonate and silicate rocks. In recent years, detailed investigations on the bulk samples and silicate fractions of the Chinese deserts have been carried out by using the methods of isotopic and elemental geochemistry to trace the provenance, transport and precipitation of mineral dust (Nakai et al, 1993;Liu et al, 1994;Asahara et al, 1995;Chang et al, 2000;Pettke et al, 2000;Bory et al, 2002;Kanayama et al, 2002a,b;Nakano et al, 2004;Yokoo et al, 2004;Grousset and Biscaye, 2005;Nakano et al, 2005;Rao et al, 2006;Chen et al, 2007;Rao et al, 2008a). However, the knowledge of carbonate geochemistry of the Chinese deserts is still limited (Wang et al, 2005a,b,c).…”