Loess-paleosol sequences have been applied to retrieve palaeoenvironment change in the study of the paleoclimatic evolution.Chafangcun (CFC) at Shangdan basin,Shaanxi provides such a loess-paleosol profile.At this profile,loess sequence's color and structure were investigated,and 210 samples were systematically collected for grain-size analysis.The results showed that:① Chafangcun loess-paleosol sequence in the first river terrace with typical atmospheric dust sediment along the Danjiang River,has formed since 55 000 a BP.② This loess sequence is mainly composed of silt (5 ～50 μm) and cla y (＜5 μm),with an average proportion of 86.65％.The coarse silt of 10 ～ 50 pm in size is dominant composition in CFC profile,accounting for 46.81％ on average,and clay (＜5 μm in size) accounts for 23.94％ in total composition.The sequence's grain-size composition varies from bottom to top stratigraphic unit,and the paleosol is smaller in grain size than that of their loess stratum.These properties reflect that the weathering intensity in paleosol is stronger than in loess.③ The grain-size characteristics in the Shangdan Basin reveal that the palaeo-climate changed successively in the following four stages:a cold and dry climate during the last glacial (55 000 ～ 11 500 a BP),a climate from dry & cold to warm & humid during the early Holocene (11 500 ～ 8 500 a BP),a warm and humid climate during the middle Holocene (8 500 ～ 3 100 a BP),and the lower temperature and reduced precipitation climate during the late Holocene (3 100 ～ 0 a BP).

以陕西丹凤县茶房村黄土剖面为研究对象,对其微量元素含量进行了系统的元素测定分析.选取Rb/Sr、磁化率作为参比,探讨了微量元素分布和其所反映的气候演化特征及其与成壤强度的关系.结果表明:微量元素(Mn、Pb、Ga、Cr、Cu、Ni、As、V、Zn、Ti)的含量变化与磁化率曲线、Rb/Sr曲线变化相同,呈极显著相关关系,即微量元素含量变化与气候关系密切,表明元素动态变化受气候变化和成壤环境的影响;微量元素(Mn、Ga、Cr、Cu、Ni、As、V、Zn)的含量在古土壤层最高,指示全新世中期主要受夏季风影响,气候温暖湿润,黄土风化成壤作用强,黄土层(L0、Lt、L1)气候相对冷干,受冬季风活动影响较大.

阐明商丹盆地黄土母质发育土壤的微形态特征及其诊断意义.以茶房村土壤剖面为研究对象,在Lical偏光显微镜下对土壤形成物、粗颗粒、孔隙等微形态单元的类型、空间分布及变化进行了研究.结果表明,与上部淋溶层和下部母质层相比,Bt层(110～230 cm)黏土大量聚集且淀积黏土含量/残积黏土含量的比值(Ki/r)很高、但黏土胶膜不发育,粗颗粒数量减少、粒径降低,孔隙个体增大及边沿更加平滑;矿物成分趋于单一.这些微形态特征证实了Bt属于典型的“黏化层”,结合成土因素检索,此土壤可归为简育湿润淋溶土.

The extensive and careful fieldwork was carried out on the first river terrace in Danjiang River valley.The typical loess -paleosol sedimentary sequence in Chafang Village of Danfeng County from top to bottom was as follows:surface soil layer (TS )-loess layer (L0 )-weak paleosol layer (S0 -upper)-loess lay-er (Lx )-paleosol layer (S0 -lower)-transitional loess layer (Lt )-Malan loess layer (L1 )-alluvial flat faci-es sand gravel layer (T1 -al ).The quartz grains of 90 ~125 μm was choosed to detect the stratigraphic age by single aliquot regeneration (SAR)of OSL dating technique.The sedimentary sequences from bottom to top were as follow.The upper limit was S0 -lower of 6.16 ±0.12 ka,Lx of 5.86 ±0.14 ka,S0 -lower of 4.83 ± 0.12 ~2.51 ±0.17 ka,L0 of 1.94 ±0.07 ka.Combined with the physical and chemical data,the analysis results showed that at Holocene Megathermal period (6.16 ka),the climate was warm and moist with good developement soil and density vegetation in the south of Qinling Moutain.Around 5.86 ±0.14 ka,the climate was arid and cold and the typical loess was developed.At 4.83 ±0.12 ka,the climate was warm and moist and the weak paleosol was developed.From 1.94 ka,the climate was arid and cold and the loess was devel-oped.The paleosol layer developed about 2.5 ka,which was later than the ending deadline of Holocene Megathermal period of around 3 ka in the Loess Plateau.The cold event of 5.86 ka was one of the rapid cool-ing climate event and regional response of climate fluctuate.

以丹凤县茶房村黄土—古土壤剖面为对象,研究了该区黄土色度参数的变化规律及其主控因素.结果表明,L+(亮度)在黄土层中出现峰值,a+(红度)、a*/b*(红度/黄度)在古土壤层出现峰值,色度参数的峰谷变化特征与该区黄土—古土壤地层旋回相吻合.L*(亮度)的变化与有机质含量密切相关;a+(红度)、a*/b*(红度/黄度)的变化则受控于铁氧化物的种类和含量.尽管三者的受控因素不同,但都与风化成壤强度密切相关,且与磁化率形成良好的对比,可作为良好的气候代用指标,间接地反映该区气候和成壤环境的变化规律.

对陕西丹凤县茶房村黄土剖面的地层学、沉积学特征以及常量元素、磁化率、粒度等进行了研究.结果表明:茶房村剖面具有表土(MS)→全新世黄土(k)→古土壤(S0)→过渡黄土(Lt)→马兰黄土(L1)的地层序列;化学风化过程中元素Ca、Na、Mg、K和Si表现为迁移特征,Fe则相对富集,呈现Na＞Si＞Mg＞K＞Ca＞Al＞Fe的迁移序列;剖面总体风化程度处于初等向中等过渡的阶段,不同地层的风化强弱顺序为S0＞Lt＞L1＞L0.化学风化强度的变化表明该区自晚更新世以来气候经历了气候干冷→气候回暖→温暖湿润→气候转凉的变化过程.

比较汉江上游谷地及渭河谷地典型黄土剖面的元素组成、化学风化强度及常量元素迁移特征,揭示秦岭南北两侧黄土—古土壤剖面的成壤强度及其所指示的环境演变特征,两者差异及共性如下:①两剖面化学组成均以SiO2、A12O3和Fe2O3为主,元素组成均一且高度混合,与上部陆地壳(UCC)的化学成分十分接近,该些证据均指示两区域黄土是来源广泛并经过充分混合的风尘堆积产物.②据CIA值可判定MTS及YHC剖面均经历了中等风化作用,比较两剖面CIW值、A-CN-K三角图投点特征及元素迁移率知,汉江上游谷地的黄土—古土壤序列经历的化学风化作用更强,Ca及Na元素的丢失率更高,A1、Na、Mg、Si等常量元素的迁出率更大.③依据Fe、Na迁移率的全剖面变化曲线知,汉江上游谷地与渭河谷地自全新世以来经历了相同的气候演变阶段,均记录了6000-5000a BP的干冷气候事件.

Stratigraphic sequence and constant elements were studied in Mituosi's loess profile,Yun County,Hubei Province,China. And optically stimulated luminescence(OSL)was carried out on dating the loess sediments. The aim is to discuss the chemical weathering characteristics and the palaeoenvironmental change based on comprehensive approaches,such as Chemical Index of Alteration(CIA),A-CN-K diagram,Na/K and Fe/Mg. Results showed that the major composition of Mituosi's loess section was made up with Si O2 and Al2O3. Na2 O,Mg O,Ca O were performed leaching in the profile,while Fe2O3,K2 O and Al2O3 were enriched. Moreover these elements behaved leaching or enriching more intensely in the palaeosol. The leaching of Na,Mg and Ca is due to the weathering of plagioclase and pyroxene. While Fe and Al's relative enrichment is because of leaching of other elements. The K enrichment is likely to be its ion adsorpted by relevant clays. These elements' geochemical variations could reflect the pedogenic modification of loess in Mituosi. The CIA(65.41)and A-CN-K diagram showed the profile experienced the primary chemical weathering processes in which Ca,Na loss was serious,but almost no leaching of K. And it was transited to middle stage of chemical weathering. The weathering products mainly are montmorillonite and illite. It has not reac- hed kaolinite and gibbsite-based degree of weathering.The CIA,Na/K and Fe/Mg's curves all indicated the weathering was from weak to strong degrees and then weakened,which from Malan loess to palaeosol then to Holoncene loess. This information revealed the palaeoenvironment,especially the palaeoclimate change since the late Pleistocene. The climate was characterized by cold and dry climate at about the late Pleistocene 18 000-11 500 a BP;Then that came to the Holocene,it was becoming warm. And the Holocene warm period was during 8 500-3 100 a BP,after about 3 100 a BP. The climate turned cool again. All above indicated the climate wascold-dry→warm→warm-wet→cool-dry. Meanwhile the climatic cold fluctuation events at about 6 000-5 000 a BP. have been recorded and responded by Mituosi's loess.