干旱区生态环境知识资源中心

The Re-Os isotope system is a potentially powerful tool for obtaining information on source regions and transportation processes of aerosols such as mineral dust. Re-Os isotopic systematics were studied in two Pleistocene loess-paleosols exposed at Kuerdenengbulake and Zeketai in the Yili Basin, northwestern China. In the late Pleistocene Malan Loess, Os-187/Os-188 ratios (0.90-1.45) varied inversely with Os abundances (28-61 pg/g). In the middle Pleistocene Lishi Loess section, fluctuations in Os abundances (25-50 pg/g) were accompanied by a limited range of variation in Os-187/Os-188 ratios (generally 1.21-1.40). Four samples of Malan Loess from the Kuerdenengbulake section had higher Os concentrations and less radiogenic Os-187/Os-188, coupled with higher zoisite/tourmaline ratios but uncorrelated with abundances of other minerals, paleomagnetic parameters, grain-size characteristics, major-element composition, or Rb-Sr and Sm-Nd isotopic systematics. The correlation between Os and zoisite/tourmaline ratio suggests that the source material of the loess changed when these samples were deposited, but this change was not evident in the other data in this study. Depth profiles show how Re-Os isotopic compositions varied with age of deposition. By characterizing Os abundances and Os-187/Os-188 ratios of late Pleistocene loess-paleosol samples in the Yili Basin, local paleoclimatic changes occurring over intervals of several thousand years could be identified that had not been found by traditional paleoclimatic proxies. When the Nd-143/Nd-144 ratio alone cannot distinguish the provenance of global eolian sediments, a combination of Nd-143/Nd-144 and Os-187/Os-188 can sometimes be effective. However, for the Yili Basin’s loess-paleosol, the range of Os-187/Os-188 overlapped with ratios in eolian sediments from other areas, offering no improvement over Nd-143/Nd-144 alone in this respect. (C) 2014 Elsevier B.V. All rights reserved.