Sr isotope ratios of acid-leached loess residues from Luochuan, China: A tracer of continental weathering intensity over the past 2.5 Ma

Abstract

We present 87Sr/86Sr ratios of acid-washed residues, Rb/Sr, magnetic susceptibilities and deposition rates of loess and paleosols from the Luochuan loess section, China, covering the last 2.5 Ma. Paleosol residues have consistently higher 87Sr/86Sr than loess residues. This is attributed to the paleoclimate-related differences in chemical weathering intensity of the source area. This study indicates that the 87Sr/86Sr ratio of residues of loess and paleosols may be a proxy for chemical weathering intensity. This investigation reveals a long-term decrease in residue 87Sr/86Sr ratios and a general increase in deposition rates from 2.5 Ma to the present. This may imply a general rise in mechanical erosion intensity coupled with a general decline in chemical weathering intensity over the past 2.5 Ma. The regular oscillations of residue 87Sr/86Sr, Rb/Sr, and magnetic susceptibilities of loess and paleosols began at ∼ 1.0 Ma and display a ∼ 100 Ka cyclicity, which is consistant with the climate change being associated with the eccentricity-driven insulation cycle of ∼ 100 Ka.