汉江上游前坊村黄土剖面化学风化程度及其环境意义

通过对郧县前坊村黄土剖面常量元素及相关参数分析,采用Al为标准的变化率参数计算。结果表明：(1)古土壤S0形成时期，土壤磁化率、粘粒成分、CIA值较典型黄土L1高，Na/K值低于典型黄土L1。这表明古土壤形成时期，气候温暖湿润，土壤风化淋溶较强,反映了较强的成壤过程，在黄土堆积时期气候相对干冷，沙尘暴频繁出现，土壤的成壤作用较弱；(2)碳酸盐含量的剧烈变化是影响黄土元素分布特征很重要的因素，其中,一些元素如Mn和Fe在剖面中的含量较高，主要是碳酸盐被强烈淋溶造成的相对富集；(3)前坊村剖面中，常量元素风化成土过程中，Na、Ca、Mg、K、Si和Ti在古土壤S0为主要迁移元素，其迁移顺序为：Na>Ca>Mg>K>Si>Ti；Mn和Fe表现的轻微富集；常量元素的迁移特征指示了汉江上游谷地黄土已经完成初级的脱Ca、Na阶段，应进入了早期去K的中等风化阶段

CHEMICAL WEATHERING INTENSITY OF THE QFC PROFILE AND ITS ENVIRONMENTAL SIGNIFICANCE IN THE UPPER OF THE HANJIANG RIVER VALLEY，CHINA

This paper presents data from QFC loess palaeosol profile in the Hanjiang River Valleytry to illustrate weathering intensity and its environmental significance. To evaluate the degree of weathering using major elements content and related parameters, using Al as the standard rate of change of parameter calculation. Experimental results showed that: (1) magnetic susceptibility, clay composition, and CIA value of the paleo sol S0 is higher than those of typical loess L1, while Na/K value is lower than that of the typical loess L1. It indicates that it was warm and humid climate, with stronger weathering and leaching during the palaeosol S0 formation period, reflecting the strong pedogenesis; while it was relatively dry and cold, and dust storms occur frequently during loess accumulation period, reflecting weak pedogenes．(2)The dramatic changes of carbonate content is an very important factor influencing the element distribution of loess.Elements content such as Mn and Fe increased in palaesol is mainly caused by the leaching of the carbonate.(3) In the QFC profile the major elements such as Na, Ca, Mg, K, Si and Ti in paleosol S0 are the main migration elements whose migration order is Na＞Ca＞Mg＞K＞Si＞Ti; Mn and Fe expressed relative slightly enriched, other major elements in the profile are expressed as relative migration. This indicates loess in upper reaches of Hanjiang valley has completed primary off the Ca and Na phase, and should go into the early off K, with moderate weathering stages．(4) Difference is clear in the value of climatic proxies in paleosol and loess. Susceptibility, clay content, clay/coarse silt ratio and the CIA are higher values in paleosol S0 while they are relatively low in loess. It indicates that the water and heat conditions was the most appropriate during paleosol S0 formation period, with strong pedogenesis; while the climate was cold and dry during the loess accumulation period, with weak pedogenesis.Weathering intensity order is paleosol S0＞ Holocene loess L0＞transition Lt＞ Malan loess L1．(5) It was cold and dry, and dust storms occur frequently, forming Malan loess L1 in the late Pleistocene (11 500 aBP). Climate shift from cold wet to warm humid during the early Holocene (between 11 500-8 500 aBP) and dust storm activity gradually decreased to form a transitional loess layer Lt．It was warm and humid, and dust storm sediments were strongly modified to form paleosol S0 during the mid Holocene (between 8 500-3 000 aBP).It tended to be cooler and drier during the late Holocene (since 3 000 aBP), and dust storms were obviously intensified to form loess L0.