2.5Ma以来大陆风化强度的演变

本次研究得出了２．５ＭａＢＰ以来洛川剖面黄土－古土壤序列的酸不深物＾８７Ｓｒ／＾８６Ｓｒ、Ｒｂ／Ｓｒ、磁化率和沉积速率的变化曲线。黄土和古土壤酸不深物＾８７Ｓｒ／８６Ｓｒ、Ｒｂ／Ｓｒ和磁化率的变化具有类似的阶段性和周期性，这与晚新生代以来古气候的主要变化以及行星轨道参数相一致。研究证明，黄土和古土壤酸不深物＾８７Ｓｒ／＾８６Ｓｒ值得化学风化强度的替代指标，沉积速率是物理风化强度的替代指标。自２．５

Variations in Continental Weathering Intensity over the Past 2.5 Ma

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.