黄土高原褐土和黑垆土剖面中Rb和Sr分布与全新世成土环境变化

DISTRIBUTION OF Rb AND Sr ELEMENTS IN SOIL PROFILES AND CHANGES IN HOLOCENE PEDO GENIC ENVIRONMENT ON THE LOESS PLATEAU

对黄土高原 3个土壤剖面Rb和Sr分布规律的研究表明 ,全新世不同阶段的黄土和土壤中Rb和Sr分布存在明显的差异 ,Rb/Sr比值的变化反映了成土环境和成土作用强度的变化。全新世早期 ,气候比较温和干燥 ,风尘堆积速率降低 ,土壤发育表现为边沉积边成土 ;全新世中期 ,气候温暖湿润 ,沙尘暴很少发生 ,风尘堆积速率极低 ,生物风化成土作用达到最强 ,以至于在黄土高原面发育黑垆土 ,在关中盆地形成褐土。到了 3 10 0多年前 ,气候恶化变干 ,风尘堆积速率加快 ,土壤严重退化。从区域上看 ,冬季风对黄土高原南部的环境效应比夏季风对北部的环境效应要强 ;黄土高原南部季风场强的变化较北部大。

In this paper, three typical Holocene soil profiles in the Loess Plateau are stu died. The analytical results show that Sr concentration is higher in the loess b eds than that in the paleosol beds and that Rb concentration and Rb/Sr ratio is lower in the loess beds than that, respectively, in the paleosol beds. The chan g e in Rb/Sr ratio reflects changes in pedogenic environment during the Holocene, and spatial-temporal changes in monsoon circulation over the Loess Plateau, as well. In the early Holocene (11 500～ 8 500 years B.P.), dust deposition reduced becau se of climate warming, and biological weathering began. In the mid-Holocene ( 8 500～ 3 100 years B.P.), as the climate became warmer and wetter; the eff e ct of pedogenesis was getting stronger and stronger than that of the eolian dust depositio n, and thus black loessial soil developed on the surface of the plateau, and cin namon soil in the Guanzhong Basin. But beginning form 3 100 years BP, the clima t e has become dry, and dust storms and dust-fall occurred frequently. Recent loe s s (L 0) has begun to accumulate and gradually covered the mid-Holocene soil (S 0). As a result, the S 0 has become buried paleosoil, The change from soil formati o n to loess accumulation indicates environment deterioration and soil degradation . In the Loess Plateau, the environmental effect of the winter monsoon on the sou th is much stronger than that of the summer monsoon on the north, and so is the amplitude of the change in monsoon on the south than on the north.