Weathering histories of Chinese loess deposits based on uranium and thorium series nuclides and cosmogenic 10Be

The long, continuous deposition of dust in the Chinese loess plateau (Liu et al., 1985; Kukia and An, 1989; Ding et al., 1991a) offers an unique opportunity to study the nature of soil weathering in a wide range of climatic conditions. In this paper we report on measurements of concentrations of U-and Th-series nuclides and of major cations in 150 loess and paleosol samples from five sites, going back 2.5 Ma. Using the results for Be-10 concentrations in these soils (Gu et al., 1996), we determined the absolute amounts of water added to several soil units and obtained: (1) first-order leaching constants for U and several cations and (2) the compositions of the soils contributing to the dust-source regions and of the dust at deposition. Further, based on analyses of Th-230 in soils deposited in the past ca. 140 ka, we determined when the soils weathered in the source regions. We conclude that most of the weathering in the dust-source regions may have occurred during the interglacials. Copyright (C) 1997 Elsevier Science Ltd.