Geochemistry of Sediments from a Subalpine Lake Sedimentary Succession in the Western Nanling Mountains, Southern China: Implications for Catchment Weathering During the Last 15 400 Years

In the present work, 15 400 yr old geochemical records of a core from the subalpine Daping swamp are presented with the aim to examine the relationship between the chemical weathering and the climatic changes in the region of the western Nanling Mountains, China. The climate of the study region was deeply controlled by the East Asian summer monsoon. The results indicate that, in the past 15 400 yrs, the values of chemical index of alteration (CIA) ranged from 73.9% to 88.2% (mean: 85.3%), suggested a medium and high intensity of chemical weathering. The local exogenous clastic materials, which were derived from the weathered residues, played a key role in contributing towards the sediments. Since the climate-induced chemical weathering exerted strong influences on the geochemical features of weathered residues, the geochemical characteristics of the sediments were deeply impacted by climatic conditions. Wetter and warmer conditions would favor increased chemical weathering, resulting in more leaching of soluble and mobile elements (e.g., Ba and Sr) and leaving the resistant and immobile elements (e.g., Al and Ti) enriched in the weathered residues. These materials were then eroded and transported into the lake, and led to the sediments characterized by the characteristic of having depleted soluble elements. In contrast, dry and cold conditions would result in an opposite trend. In this sense, the geochemical records can serve as proxies to indicate changes of chemical weathering intensity, which were closely related to the evolution of summer monsoon.