中国中亚热带网纹红土的地球化学特征与沉积环境

130个样品的粒度、黏土矿物组成、地球化学特征以及Sr、Nd同位素分析表明,广泛分布在中亚热带地区并且具有一定厚度的第四纪网纹红土为加积型沉积。该类沉积粒度组成与北方风尘沉积类似,粉砂含量占优势,>50μm含量小于5%,5~50μm组分41.2%~61.5%,<5μm黏粒26.9%~55.8%;黏土矿物组成中含有较多的石英、云母和高岭石;全土体的平均硅铝率为7.96,硅铁铝率6.11;稀土元素丰度179.6 mg kg-1,与地壳平均值(178 mg kg-1)、北京郊区1998年12月大气粉尘稀土总量(178.0 mg kg-1)以及两块中国黄土标样(178.2mg kg-1)非常接近,并且表现为轻稀土强烈富集,重稀土淋失,Ce元素正异常;网纹红土全岩样品的87Sr/86Sr值界于0.725 657~0.727 714之间,Nd同位素0.511 989~0.512 098,与佳县上新世红黏土和黄土的酸不溶相性物质接近。理化特征指示,第四纪加积型网纹红土与北方黄土中的古土壤以及上新世红黏土的形成环境类似,并且具有稳定的物质来源。     

新疆博乐黄土磁化率特征及影响因素

博乐地区地处西风区,是新疆黄土的重要分布区之一。选择该区一个厚为11 m的黄土剖面作为研究对象,测试与分析了磁化率、粒度、TOC、CaCO(3%)等指标。结果显示,磁化率的平均值远远低于黄土高原典型黄土的磁化率值,磁化率的变化过程也同黄土高原典型黄土相反;粒度组成以粗粉砂(63~10μm)为主,粘土(<5μm)、细粉砂(5~10μm)和砂(>63μm)含量较少。相关性分析结果显示粘土和细粉砂与磁化率呈现较明显的负相关关系,而砂含量对磁化率的影响最为显著,分析其原因可能与沉积物的来源有关;由于TOC含量很少,对磁性矿物的生成和阻碍其老化方面贡献较小,再加上TOC自身的磁性也极其微弱,所以对磁化率的影响较小;CaCO3含量与磁化率相关关系不显著。由此可见,该区黄土沉积物磁化率影响因素较为复杂,进一步表明在该区如果用磁化率作为气候代用指标来恢复和重建古气候、古环境时需要更多的结合其它气候代用指标,多指标分析和合成解释其结果可能更可靠准确。     

镇江下蜀黄土的稀土元素地球化学特征研究

稀土元素(REE)作为示踪元素在各种岩石的成因、物源、演化及形成环境等方面均具有重要意义。对镇江大港下蜀黄土-古土壤剖面中稀土元素含量和分布特征的研究结果表明:镇江下蜀黄土-古土壤剖面∑REE变化于193.7~214.9μg g-1之间,平均值为207.7μg g-1。下蜀黄土REE绝对丰度明显高于黄土高原黄土,这主要是由于下蜀黄土中粘粒组分含量较高,对REE特别是轻稀土元素(LREE)产生较强的吸附作用造成的。镇江下蜀黄土和黄土高原黄土的REE特征参数及配分模式具有很好的相似性,它们均与上陆壳(UCC)具有相近的REE组成;下蜀黄土剖面不同时代样品的REE分布模式几乎完全一致。这些特征为下蜀黄土的“风成说”提供了新的地球化学证据,并揭示了下蜀黄土的物质来源区可能是一个广泛而开放的空间范围,下蜀黄土粉尘颗粒在搬运过程中经过了高度的混合。镇江下蜀黄土的稀土元素特征主要继承了原始物质的特征,粉尘物质堆积后虽经过较强的风化成土作用,轻重稀土间的分馏强于黄土高原黄土,但总体来说化学风化对REE的分馏作用并不十分显著,古土壤层与黄土层样品的REE组成差异不大,没有产生明显的Ce和Eu再分馏。     

长江中游地区第四纪红土的二元结构及古环境意义

在长江中游地区的湖南和湖北两省,选择宜昌、咸宁、常德、长沙、株洲5个第四纪红土剖面,分析第四纪红土的粒度组成特征,研究红土的成因及南方古环境的演变。结果表明,这些地区第四纪红土的粒度组成呈明显的二元结构:剖面上部(宜昌剖面0～320 cm,咸宁剖面0～220 cm,常德剖面0～270 cm,长沙剖面0～280 cm,株洲剖面0～150 cm)粒度细小而均匀,砂粒含量低,大部分小于1%;粗粉砂(又称风尘"基本粒组")相对富集,平均含量分别为34.38%、32.29%、32.48%、31.69%和31.86%。而且土壤样品粒度频率分布曲线与安徽宣城第四纪红土很相似,与镇江下蜀黄土也有明显继承性。这些特性均反映了剖面上层红土的风成特性。但研究剖面下部红土,粒度组成有明显不同:含有砾石,砂粒含量较高,不同粒度组分垂向变化明显,粒度频率分布曲线与宣城红土和下蜀黄土有显著差异,表现出明显的冲、洪积相特性。第四纪红土的"二元结构",反映了研究区域第四纪古环境的多变性和复杂性:早期红土形成后,因受间冰期湿热气候的影响,多受流水作用改造;而晚期红土更多地受风尘堆积的影响,沉积后虽经过了强烈的原位风化,但仍保留了风尘沉积的特性。     

黄土不同粒级稀土元素分布特征及其制约因素

对宁镇地区下蜀黄土和北方黄土高原黄土进行系统的分粒级稀土元素(REE)地球化学特征对比研究,结果表明:(1)无论是北方黄土还是下蜀黄土,REE分布均存在明显的粒级效应:北方黄土的REE主要在细粒端(4μm)富集,粗粒端(64μm)富集不明显;下蜀黄土在细粒端(4μm)和粗粒端(64μm)均呈明显的REE富集特征,且粗粒端的富集更加显著;(2)北方黄土和下蜀黄土在细粒端(4μm)的REE富集主要由风化成壤作用所控制,细粒组分中富集重稀土(HREE)的特征可能与Fe-Mn氧化物对HREE的专性吸附作用有关;(3)下蜀黄土在粗粒端(64μm)则主要以富集轻稀土(LREE)为主,这可能与下蜀黄土母质来源中多近源的区域性特征矿物(榍石等副矿物)有关,揭示下蜀黄土中的粗颗粒物质可能主要来源于近距离搬运。64μm可能是凸显下蜀黄土和北方黄土REE差异的敏感粒级,该粒级中LREE富集与否是区别两者的有效标志,这为REE应用于黄土的物源示踪研究提供了新途径。     

环青海湖表层土壤沉积物粒度分布特征及其指示意义

对环青海湖区38个表层土壤沉积物样品进行了粒度特征分布分析,结果表明:环青海湖表层土壤沉积物粒度组成以粉砂为主,占所有采样点土壤粒度组成的52%,砂含量次之,占37%,黏粒含量最少,占11%;环湖区38个采样点主要植被类型下表层土壤粒度百分比中也表现出粉砂砂黏粒;环青海湖区表层土壤沉积物粒度特征表明青海湖以东表层土壤沉积物粒度特征呈单峰模式、以西表层土壤沉积物粒度特征呈不对称双峰模式、以南表层土壤沉积物粒度特征近乎正态分布、以北表层土壤沉积物粒度特征呈多峰模式;环青海湖区表层土壤沉积物的平均粒径为1.96~6.71Ф,平均值为4.68Ф,为粉砂粒级;峰态值为0.75KG1.89,平均值为1.09;标准离差变化范围为0.81~2.63,平均值为1.77;偏度变化范围为-0.03~0.43,平均值为0.14。分析结果说明环青海湖区湖东区域为典型的风成砂沉积、湖西和湖南区域表层土壤沉积为风成黄土、湖北表层土壤沉积环境复杂多样。     

毛乌素沙地表土粒度特征及其空间变异

沙漠化土地表土粒度条件研究对于区域土地利用与恢复以及防控土壤风蚀沙化具有十分重要的意义。通过对毛乌素沙地表土粒度测定,采用矩法计算粒度参数,研究毛乌素沙地的表土粒度特征。结果表明：沙地内部各种土地类型的表土粒度主要集中于砂粒段（1000～50μm）,含量为41．22％～97．63％,粉砂粒（50～2μm）含量为0—51．61％,黏粒（〈2μm）含量为2．71％～10．38％;半固定沙丘和移动沙丘的平均粒径值分别为145．491和157．563μm,较为接近,处于各种土地类型的较低状态;固定沙丘与耕地的平均粒径值分别为128．782和118．175μm,居于中间状态;草地和林地的平均粒径值分别为94．667和108．819μm,颗粒级配较为细小;土地类型中以移动沙丘的粒度组成最为粗化。移动沙丘和半固定沙丘分选较好,表现出极强的正偏和较尖的峰值;耕地、林地、草地也表现出正偏,但其偏移值较小,峰值也较为平缓。毛乌素沙地不同土地类型间粒度特征值存在明显差异,充分表明不同土地类型受风蚀作用的差异性和风蚀作用的阶段性。从不同土地类型表土粒度的空间变异来看,毛乌素沙地表层土壤平均粒径存在比较明显的由东北向西南逐渐变细的空间变异规律。     

汉江上游黄坪村段古洪水滞流沉积物研究及意义

古洪水滞流沉积物是古洪水事件的直接产物,蕴含古洪水的重要信息。以汉江上游郧县黄坪村剖面为研究对象,对其粒度、磁化率、烧失量及碳酸钙等进行了分析。结果表明:古洪水滞流沉积物的粒度具有粉砂含量砂级颗粒黏粒含量的特征;磁化率值在78×10-8~81.2×10-8m3kg-1之间;烧失量值较低为23.9~27.7 g kg-1,碳酸钙为2.72%~3.20%。其宏观特征和上述参数与黄土和古土壤有明显的区别。沉积物的粒度组成特征及粒度参数、磁化率、烧失量、碳酸钙等对于鉴别古洪水滞流沉积层有重要的参考价值。     

下蜀黄土组成特征研究

本文研究了下蜀黄土的颗粒、矿物和化学组成,并对下蜀黄土的成因作一初步探讨。研究表明,下蜀黄土物质组成以粉砂和粘粒为主,并存有一定量的>0.25mm粗颗粒;粗颗粒中重矿物含量很少,轻矿物以石英、长石为主;粘粒矿物以水云母为主;伴有绿泥石、蛭石、高岭石、2:1/1:1型不规则混层矿物、无定型物质、氧化铁(针铁矿、赤铁矿)和石英,矿物结晶较差。下蜀黄土存在较弱的脱硅富铝化作用(SiO₂/Al₂O₃为3.29±0.19),且有东南部高于西北部趋势。     

花岗岩风化壳崩岗侵蚀剖面风化强度和粒度分布特征

结合粒度法和化学风化指标法分析了花岗岩风化壳崩岗侵蚀剖面,结果显示:（1）粒度组成以粉砂砾组分最多,平均值为52.52%,砂砾组分为38.38%,黏粒组分最少,平均值为9.09%。4~63 μm粉砂粒组分分别与<1 μm细黏粒组分、<4 μm黏粒组分正相关性较好;>63 μm的砂砾组分与中值砾径呈显著正相关性,与<1 μm细黏粒组分、<4 μm黏粒组分、4~63 μm粉砂粒组分呈显著的负相关性。剖面580~780 cm深度可能是崩岗侵蚀起源区域。（2）化学蚀变指数CIA、风化淋溶系数BA、残积系数Ki和退碱系数Bc一致表明,崩岗侵蚀剖面的化学风化程度高。风化强度从底部往上呈现先小幅度递减而后波动递增的变化趋势。（3）风化参数指标和粒度线性相关性分析得知,化学风化作用强度增强,<1 μm细黏粒组分、<4 μm黏粒组分、4~63 μm粉砂粒组分增加,>63 μm砂砾组分减少。化学风化作用减弱,<4 μm黏粒组分、4~63 μm粉砂粒组分减少,>63 μm砂砾组分增多。     

南京附近下蜀土中黄土层与古土壤层的差异性探讨

Xiashu loess strata are widely distributed along the middle-lower reaches of the Yangtze River in East China with the stratum near Nanjing, Jiangsu Province being typical. The cyclic variability of the stratum was investigated through comparison of geological features, chemical composition, and swelling-shrinkage properties between the loess and the paleosol layers. Based on the investigation of such a cyclic variability, soil behavior associated with the unsaturated state of the Xiashu loess stratum and its usefulness for geotechnical design and construction in the Nanjing area was analyzed. The stratum consisted of two types of cyclically alternating soil layers, namely the loess and the paleosol layers, which was the major cause for its cyclic variability. The loess and the paleosol layers were formed in different sedimentary environments. In order to avoid detrimental results from the differential engineering properties between them, this study suggested for the practitioners the importance of inspecting the variation of water content and controlling the downward net fluxes during geotechnical construction in the Nanjing area.     

李家岗下蜀黄土剖面的反射光谱研究

采用色度学方法,系统研究了下蜀黄土典型剖面的反射光谱特征。结合磁化率、微量元素Ｒｂ、Ｓｒ的含量和比值,讨论了色度参数的古气候意义,初步把下蜀黄土形成以来的古气候划分为３个波动旋回。下蜀黄土和黄土高原色度参数的对比,揭示了长江中下游地区更强的化学风化作用和成壤强度。     

中国南方金衢盆地红土多元成因的粒度证据

Six typical red clay profiles were sampled from Tangxi (TX),Langyaz (LYZ),South Shangshanwen (SSW),Xianqiao (XQ),Qijian (QJ) and Huhaitang (HHT) of Jinhua-Quzhou Basin,Zhejiang Province of China to evaluate the characteristics of grain size composition,distribution and parameters of red clays and to reveal the origin of red clays and interpret possible implications for paleoclimate in subtropical China.The results showed that red clays in TX,LYZ and SSW were fine and uniform,with no>2mm gravels and little>63μm fraction.They had a high content of 10–50μm fraction,so-called"basic dust fraction",and showed unimodal distributions,which were very comparable to those of the Xiashu Loess in southeastern China and the loess in North China.All these features reflected marked aeolian characteristics of the red clays in these areas.Red clays in XQ and QJ were much coarser than those in TX,LYZ and SSW,with high contents of >63μm fraction and even containing>2 mm gravels in some layers.The grain size distribution patterns showed significantly progressive trends from the lower profile to the upmost layer and could not be compared with those of the loess in North China or the Xiashu Loess,implying they might be derived from underlying parent rocks and had some inherited properties from bedrock.Red clays in HHT had high contents of>63μm fraction and contain many >2mm gravels in each layer.The grain size frequency curves showed multiple-peaks and some abrupt variations were also observed on the profile,revealing its alluvial or diluvial origin in HHT.The multiple origins of red clays reflected the diversity and complexity of the Quaternary environment in South China.It can be concluded that grain size is an efective proxy indicator for the origin of most deposits.     

PALEOsolS DEVELOPED ON CHALKY BOULDER CLAY IN ESSEX

Soils with paleosol features occur at the surface on the Chalky Boulder Clay in the Chelmsford area, Essex. Their particle size distribution, micromorphology and sand, silt and clay mineralogy indicate periods of weathering, clay illuviation and hydromorphism before deposition of loess in the Late Devensian. These periods are provisionally related to the Ipswichian and/or Hoxnian Interglacials.     

Physical and Chemical Characteristics of Urban Snow Residuals Generated from Traffic Activities

Urban transportation activities generate a wide gradation of anthropogenic solids with varying physical and chemical properties. These solids accumulatein urban highway snow and remain as residual deposition material after the melting and recession of the snow from the pavement shoulder. This study analyzed the physical characteristics of these residuals and the associatedheavy metals for 10 urban highway sites located throughout metropolitan Cincinnati. Results from the residuals analyses indicate that for all sites particle gradations ranged from greater than 5000-μm to less than 25-μm with a mean d₅₀ of 1225-μm. Specific gravity (ρ_sg) of residual solids ranged from 2.5 to 3.2 as evaluated for intervals across thegradations, with the lower specific gravity associated with particles less than 100-μm. For each gradation, specific surface area (SSA) generally increased with decreasing particle size while the predominance of total surface area (SA) was associated with the coarser size fractions. Cumulativeanalysis for Pb, Cu, Cd and Zn associated with snow residuals indicated that more than 50% of the heavy metal mass was associated with particles greaterthan 250-μm and more than 80% was associated with particles greater than 50-μm. Results provide guidance for management of urban snow residuals and design of treatment strategies focused on these residuals.     

黄土古土壤的抗剪强度特性

[目的]对原状和扰动古土壤抗剪强度随含水量和干密度的变化进行研究,为黄土地区的边坡工程、隧道工程以及地下建筑工程设计施工中参数的选取提供依据。[方法]分别对相同干密度、不同含水量的原状样,不同干密度、不同含水量的扰动样及与原状样相同干密度、相同含水量的扰动样进行室内直剪试验。[结果]在干密度相同的条件下,原状和扰动古土壤的黏聚力随含水量的增大而减小;在同一含水量指标下,原状古土壤的黏聚力大于扰动古土壤,二者的内摩擦角亦随含水量的增大而减小。[结论]黄土古土壤的抗剪强度指标随着含水量的增大而减小,黏聚力与含水量呈指数函数关系,内摩擦角与含水量呈二次抛物线关系。     

西安地区全新世气候变化与土壤侵蚀研究

为了揭示西安地区全新世环境变化和黄土地层的侵蚀期,利用野外调查和化学分析等方法,研究了西安地区全新世黄土与古土壤发育时的气候变化和不同气候阶段的土壤侵蚀。通过野外调查,在西安白鹿塬区发现了在黄土塬区很少见到全新世中期古土壤分为3个层次,整个全新世黄土剖面可分为5层,表明黄土塬区全新世气候变化与沙尘暴活动与河谷地区一样可分为5个阶段。土层氧化物、微量元素、CaCO3含量和磁化率测定结果显示,西安白鹿塬区全新世8 500~6 000年和5 000~3 100年古土壤发育时较10 000~8 500年、6 000~5 000年和3 100年以来的黄土发育时夏季风活动强,降水量多,气候湿润,沙尘暴活动弱。中全新世8 500~6 000年间发育的S02古土壤中Fe2O3和Al2O3有一定富集,该层土壤类型相当于黄棕壤,指示当时年平均降水量较现今多150 mm左右。虽然沙尘暴活动很弱的间冰期是黄土地层理论上的侵蚀期,但是实际上这一时期的土壤侵蚀很弱。全新世黄土的侵蚀主要发生在气候冷干时期,不是发生在温湿时期。全新世中期6 000~5 000年间的黄土侵蚀率一般大于堆积率,使得广大地区全新世中期的薄层黄土在绝大多数地区受到侵蚀而消失。全新世中期薄层黄土发育时气候变冷干引起的植被退化是当时土壤侵蚀加强和出现侵蚀期的原因。     

巫山黄土成因及其发育土壤特征研究

  目的  为探明巫山黄土成因,了解该类母质发育土壤的发生学特征。  方法  以典型巫山黄土及其发育土壤剖面为研究对象,通过野外调查采样和室内分析,详细考察剖面形态、颗粒组成、常量元素地球化学特征及其他相关理化性质,计算探讨硅铝率（ Sa ）、化学蚀变指数（ CIA ）、钠钾比（ Na/K ）、铁游离度等风化指标。  结果  （1）巫山黄土的颗粒组成以粉粒为主,平均含量为53.29%,与典型风尘沉积物相似,同时,巫山黄土与其他区域风成黄土的主要元素硅、铝、铁含量非常接近,上陆壳（UCC）标准化曲线也较为相似;（2）该剖面100 ~ 140 cm深度与其他深度相比,有机碳和硒含量较高,CaCO₃相当物含量和δ13C值较低,推测在此深度堆积过程中的气候较为温湿,并可能出现过植物的生长;（3）巫山黄土剖面的 Sa 为8.73 ~ 9.17、 CIA 为65.96 ~ 69.10、 Na/K 为0.74 ~ 0.89、铁游离度为22.88% ~ 29.74%,与其他地区风成黄土相比,巫山黄土风化程度强于洛川黄土而弱于下蜀黄土和成都黏土,与汉江黄土和甘孜黄土十分接近。  结论  巫山黄土应为风积成因,处于中等化学风化程度,以脱盐基为主,脱硅富铁铝化程度弱,可能与汉江黄土或甘孜黄土同源。     

Sangamon paleosols of southwestern Indiana,U.S.A.

In southwestern Indiana, the Sangamon paleosol transgresses Illinoian glacial drift and weathered bedrock of Pennsylvanian and Mississippian ages in an unglaciated area. The paleosol is buried beneath Wisconsin age loess that thins from 3.2 to 0.5 m in a distance of 83 km eastward from the Wabash River Valley. The buried soil is redder, has more clay in the illuvial horizon, and also has a thicker solum than overlying ground soils formed in loess. Base saturation and pH states of the paleosol relate to secondary enrichment after burial. Free iron-oxide content relates to redder colors and is a genetic property of the buried soils. Greater depletion of illite and chlorite in the paleosol shows that it is more weathered than the overlying ground soil. Pedologic contrasts permit recognition of the Sangamon stage as an event of greater magnitude in the Quaternary than all postloess and Recent time in southwestern Indiana.The Sangamon paleosol has the redder colors and forest-soil profiles on well-aerated, upland, paleogeomorphic sites for a distance of 1000 km to the west. The Sangamon environment probably was uniformly warm, humid forest and woodland not unlike the climatic-vegetation pattern in southern United States today. The present ground soils have more diverse patterns ranging from forest soils in Indiana westward through grassland prairie soils to grassland chernozemic soils of the easternmost Great Plains and with related humid to dry subhumid climates.