Variations in Continental Weathering Intensity over the Past 2.5 Ma
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P512.1

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    Abstract:

    In this paper, 87Sr/86Sr and Rb/Sr ratios of acid-insoluble residues, and magnetic susceptibilities and deposition rates of loess and palaeosols from the Luochuan loess section are presented. The 87Sr/87Sr, Rb/Sr, and magnetic susceptibilities of palaeosol residues are generally higher than those of loess residues. This is attributed to the difference in chemical weathering intensity related to palaeoclimate, which leads to the formation of either loess or palaeosol. Temporal variations in these parameters can be divided into two stages. The first stage, from -2. 5 Ma to 1. 2 Ma, is characterized by low-frequency oscillations of 87Sr/86Sr, Rb/Sr and magnetic susceptibility and low deposition rate, while the second stage, from -1. 2 Ma to the present, is characterized by high-frequency oscillations of 87Sr/86Sr, Rb/Sr and magnetic susceptibility and high deposition rate with a cycle of -100 ka. The second stage can be further divided into two sub-stages with the boundary at -0. 6 Ma. This investigation reveals a long-term decrease in residue 87Sr/86Sr ratios and a long-term increase in deposition rates from 2. 5 Ma to the present. This may imply a general rise of mechanical erosion intensity coupled with a general decline of chemical weathering intensity over the past 2. 5 Ma. These long-term trends may be a combined result of the uplift of the Himalayas and Qinghai-Tibet Plateau, general intensification of glaciation and a decline of the Asian summer monsoon.

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Yang Jiedong, Chen Jun, Li Chunlei, Tao Xiancong, Ji Junfeng, Chen Yang.2000. Variations in Continental Weathering Intensity over the Past 2.5 Ma[J]. Geological Review,46(5):472-480.

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