Five million year Be-10 record in Chinese loess and red-clay: Climate and weathering relationships

Be-10 measurements in bulk samples, in different size fractions, in selective chemically leached fractions of several representative loess-paleosol sequences and in the underlying red-clay sediments from the Chinese Loess Plateau, back to ca. 5 Ma, were made using the AMS (accelerator mass spectrometer). Our data support but considerably extend the earlier studies of Shen and Beer and their colleagues in the upper 0.75 Ma Luochuan loess-paleosol sequences. The effect of climatic change is dramatically expressed by Be-10 concentrations: (1) in the red-clay sediments, for which we estimate model accumulation rates of 5.8 and 8.7 m Ma(-1) for the upper sequences in Lingtai and Baoji, respectively; (2) in the paleosols where soil maturation processes are manifest in the Be-10 distribution within different size fractions, accompanied by downward movement to zones of high authigenic mineral concentration; and (3) in loess samples which, at deposition, had an appreciable endowment of Be-10 from the dust source regions. On the basis of leaching experiments, we estimate that, on average, the paleosol layers lost about 3+/-3% of their initial Be-10 content to the underlying layers by transport with water. Finally, we estimate that the relative average zonal precipitation rate during glacial periods was similar to(2/3)x the average interglacial value. The estimates of the initial Be-10 concentrations and dust composition are consistent with the measured values for the recent atmospheric dust falls sampled from the Loess Plateau and the Shandong Peninsula.