Variation of the lithium-barium ratio in the Holocene loess-paleosol profiles in the south of the Chinese Loess Plateau: implications for pedogenic weathering intensity.

摘要

Lithium (Li) and barium (Ba) distributions in the Laoguantai and Liwan loess-paleosol profiles in the south of the Chinese Loess Plateau show distinct variations caused by pedogenesis. Mean Li contents in paleosols are higher than those in the upper or subjacent loess layer. Paleosol units at the two sites, respectively, contain 5% and 18% more Li than that the loess units. Conversely, mean Ba values in paleosol units are noticeably lower than in loess units. Paleosol units contain 33% and 46% less Ba than loess units at the Laoguantai and Liwan sites, respectively. Comparison of Li/Ba ratios shows that Li varied slightly throughout the weathering profiles, but was enriched in the paleosol layers. The Ba distribution showed greater variation throughout the weathering profiles and has a larger impact on the Li/Ba ratios. This indicates that Ba is more actively lost during pedogenesis, whereas Li is relatively stable and accumulates as a pedogenic product. Variations in the Li/Ba ratios in the weathering profiles reflect pedogenic changes after dust deposition. Accordingly, the Li/Ba ratio is a reasonably good proxy for reconstructing the climate change and pedogenesis history contained in the loess-paleosol sequences. The Li/Ba ratios reveal that pedogenic intensity underwent polyphase changes during the Holocene in the eastern Guanzhong Basin of South Central China, likely driven by shifts in the East Asian monsoon.