2.5Ma以来黄土高原灵台剖面黄土-古土壤^(87)Sr/^(86)Sr比值的变化

Variations in ^(87)Sr/^(86)Sr Ratios of Loess-Paleosols of Lingtai Section over the Past 2.5 Ma

研究提出了2.5MaB.P.以来黄土高原灵台剖面黄土-古土壤序列的酸不溶物87Sr/86Sr、Rb/Sr、Zr/Rb、平均粒径和磁化率的变化曲线.黄土和古土壤酸不溶物87Sr/86Sr、Rb/Sr、Zr/Rb和磁化率的变化具有类似的阶段性.研究证明,黄土和古土壤酸不溶物87Sr/86Sr比值是化学风化强度的替代指标,Zr/Rb是物理风化强度的替代指标.自2.5MaB.P.以来大陆化学风化强度在总体上呈下降趋势,而物理风化强度呈上升趋势.

We present the results for ^(87)Sr/^(86)Sr ratios of residues, Rb/Sr and Zr/Rb ratios, average grain size and magnetic susceptibility of loess_paleosols from the Lingtai section, China covering the last 2.5 Ma. Paleosols have consistently higher ^(87)Sr/^(86)Sr, Rb/Sr and magnetic susceptibilities, but lower Zr/Rb than loess and average grain size. This is attributed to the differences in chemical weathering intensity related to paleoclimate, under which either loess or paleosol was formed. Temporal variations in these parameters can be divided into three stages. The first stage is from 2.5 Ma B.P. to 1.2 Ma B.P., the second stage from 1.2 Ma B.P. to (0.6) Ma B.P., the third stage from 0.6 Ma B.P. to the present. All these stage boundaries coincide with major climate change events during the Plio_Pleistocene: (1) the onset of the NH great glaciation at ～ 2.4 Ma B.P., (2) the onset of quasiperiodic 100 Ka ice age cyclicity by the eccentricity in NH ice sheets at ～ 1.2 Ma B.P., and (3) amplification of ～ 100 Ka cycles at ～ 0.6 Ma B.P., respectively. This investigation reveals a long_term decrease in residue ^(87)Sr/^(86)Sr ratios and a long_term increase in Zr/Rb from 2.5 Ma B.P. to the present. This implies a general rise in mechanical erosion rates might couple with a general decline in chemical weathering rates over the past 2.5 Ma. These long_term trends may be a combined result of Himalayan_Tibetan Plateau uplift and a change in the Asian monsoon circle current.