黄土高原黄土-古土壤的矿物组成及其环境意义

采自洛川和西峰剖面的34个黄土-古土壤样品分为砂、粉砂、粘土三个粒级进行了矿物成分分析。结果表明．黄土高原黄土和古土壤的矿物组成基本一致．除了方解石和褐铁矿、磁铁矿因在样品处理时已被剔除未予计算外，其主要矿物是石英、云母、长石和绿泥石。这4种矿物占总量的88％-91%，其他矿物有高岭石、蒙脱石、蛭石和少量重矿物。不同地质剖面和不同地层层位的矿物差异主要表现为组成矿物在含量和粒度上的变化。洛川与西峰剖面、古土壤与黄土以及相同古土壤层的上部与下部相比，它们的矿物组成主要表现为前者古有较少长石和较多云母和蛭石，而且颗粒较细，表明在土壤发育过程中使矿物转变的生物化学风化过程和使矿物颗粒由粗变细的物理风化过程并存。这一结果有利于这样一种土壤发育机制解释，即古土壤发育与黄土堆积过程同时进行，只是在古土壤发育时期黄土的堆积过程缓慢，成土作用大于黄土堆积作用而发育土壤。     

福建沿海地区表层土壤矿物分布特征及地质和环境意义

对福建沿海地区表层土壤矿物组分、含量、组合以及分布特征进行了分析研究。结果表明,不同地质背景形成的土壤其重矿物组成具有复杂性、一致性和差异性;不同的土壤类型其矿物组合可以较好地反映土壤与成土母岩的内在成因关系;不同沉积环境下形成的土壤矿物组成受外力影响具有一定的分选性;平原区土壤中汞、砷等元素的区域性高异常则与土壤中辰砂、雄黄矿物存在有关。     

新疆伊犁地区典型黄土磁学特征及其环境意义初探

黄土地层记录的磁学参数受控因素复杂,全球不同地区黄土磁化率的主要受控因子存在差别.文章在伊犁地区选取两个地层磁化率与成壤作用分别存在较明显正相关和负相关的典型黄土剖面,进行了系统磁性地层学研究.结果表明伊犁地区黄土地层中磁性矿物浓度较大,磁学性质主要受呈现准单畴状态磁铁矿控制,黄土沉积物中磁性矿物主要为原生矿物,后期改造作用弱,地层的磁学特征受物源影响明显.地层的成壤强度与地层中磁性矿物浓度无明显相关关系,与磁性矿物中细粒磁性矿物的含量呈正相关关系.本研究结果暗示伊犁地区黄土沉积物的磁化率增强模式既区别于典型的西伯利亚黄土"风速说"模型,也不同于中国黄土高原"成壤说"模型;当后期改造作用弱时,地层的磁学特征主要受物源影响;随着地层成壤作用的增强,对原生磁性矿物的改造作用逐渐增强,次生磁性矿物含量逐渐增加,磁化率变化规律趋近于"成壤说"模型.     

鞍本地区大孤山条带状铁建造含铁矿物和相分带特征及形成环境分析

鞍山-本溪条带状铁建造(Banded Iron Formation,简称BIF)位于华北克拉通东北缘,是世界上典型BIF之一,也是我国最重要的铁矿资源基地。大孤山位于鞍山地区南部矿带,为新太古代典型的Algoma型BIF,与华北克拉通其它大多数BIF相比,具有较低变质程度(绿片岩相-低角闪岩相)和较完整的沉积相分布特征。因此,通过大孤山BIF的研究有利于追踪Algoma型BIF的原生矿物组成及其后期成岩-变质过程,进而通过分析原生矿物形成的物理化学条件探讨古海洋环境。依据原生矿物共生组合及产出特征,可将大孤山BIF沉积相划分为氧化物相(30%)、硅酸盐相(50%)和碳酸盐相(20%)。氧化物相主要分布于主矿体南部,主要矿物组成为磁铁矿和石英;硅酸盐相分布于主矿体中部,主要矿物组成除了石英和磁铁矿之外,还有黑硬绿泥石、绿泥石、镁铁闪石等;碳酸盐相分布于矿体北部,主要矿物组成为菱铁矿、磁铁矿和石英等。本文通过大孤山BIF岩相学观察和含铁矿物化学成分研究,推测原生沉积物的组成为无定形硅胶、三价铁氢氧化物和富铝粘土碎屑,在经历了成岩和低级变质作用后转变为具不同相带的条带状铁建造。通过分析磁铁矿、菱铁矿和黑硬绿泥石等矿物在不同P_(O_2)-P_(CO_2)和pH-Eh条件下的共生相图可知,这些矿物均是在较低氧逸度、中到弱碱性环境下形成。综合考虑矿物成分、共生组合及受变质作用较弱等信息,本文推测制约原生矿物形成的控制因素主要是古海水氧化还原状态、酸碱度、CO_2含量和硫逸度。     

鲕粒原生矿物识别及对海水化学成分变化的指示意义

鲕粒是碳酸盐沉积过程中一类非常特殊的颗粒类型, 为研究当时的沉积背景、水动力条件、气候环境, 甚至储层特征提供了重要线索。然而, 鲕粒的矿物组成及控制因素问题, 长期受到忽视。组成鲕粒的原生矿物类型在地质历史时期呈周期性变化, 在显生宙表现为三个以文石和高镁方解石占主导的时期以及两个以低镁方解石占主导的时期, 这也被称作“文石海”和“方解石海”时期。原生矿物的组成, 制约着鲕粒的纹层结构、保存程度以及成岩特征, 还蕴含着海水化学成分变化的线索。鲕粒原生矿物识别主要依据:①原生纹层结构;②保存程度;③微量元素浓度, 尤其是Sr-Mg的浓度。文石质鲕粒受文石不稳定性的影响, 原生结构保存程度较差;一般保存有典型的文石残余纹层结构(例如砖砌结构、溶解变形结构以及偏心结构等);在封闭成岩环境下原生矿物为文石质的鲕粒Sr浓度往往大于2 000 ppm;纹层结构主要为切线状(占主导)和放射状。方解石质鲕粒包括低镁方解石和高镁方解石两种类型:低镁方解石为稳定矿物, 原生结构一般保存良好。尽管高镁方解石也为亚稳定矿物, 但成岩转换后的保存程度好于文石。两者Sr含量一般均低于1 000 ppm, Mg含量一般在0~20 mol % MgCO₃(两者以4 mol % MgCO₃为界)。高镁方解石受成岩作用影响, 在纹层中往往保留有微粒白云石包裹体;海相地层中保存的方解石质鲕粒为放射状或同心-放射状结构。另外还存在一类由两种矿物共同构成的双矿物鲕粒, 可以通过分析两类纹层在结构和保存特征上的差异进行区分。鲕粒原生矿物成分随时间的波动变化受到海水化学条件, 尤其是Mg/Ca比值, 大气二氧化碳分压以及碳酸盐饱和度的控制。Mg/Ca比值的波动决定着鲕粒原生矿物类型的长期变化规律。一些突发性事件可能会扰动(区域)短时间尺度下鲕粒原生矿物的组成, 造成鲕粒原生矿物的转换。通过研究碳酸盐鲕粒原生矿物特征以及控制因素进而了解海水的化学特征, 是独立于古生物学和地球化学分析之外的一种较为可靠的沉积学方法。     

地层岩性对植物群落分布特征的影响

地层岩性是生态地质环境条件的重要组成部分,查明不同岩性对生长在其上植物群落的影响,对生态保护和生态修复具有重要意义。以江西赣州市相同地貌条件和气候条件下的岩石、土壤、植物群落为研究对象,通过对植被和土壤开展全面调查与采样分析,探索了岩石-土壤-植物群落间的对应关系。分析了不同成土母岩衍生的土壤在粒度组成、化学成分、物理性质等方面的特征,揭示了地质背景条件与植物群落分布的关系。结果表明: ①成土母岩岩性、土壤质地、土壤pH值、土壤养分、土壤中主量和微量元素含量的差异是影响植物群落分布的重要因素; ②研究区各岩性区的土壤养分含量从高到低为变余杂砂岩区土壤>粉砂岩区土壤>砂砾岩区土壤>长石石英砂岩区土壤>花岗岩区土壤。     

冲积平原区重金属元素异常解析中的矿物学方法

冲积平原区生态地球化学调查方法技术研究中矿物鉴定和化学分析结果对比研究表明，土壤中化学元素的含量及其分布特征主要取决于土壤对成壤母质中各种矿物成分的继承，元素的区域地球化学背景差异和在不同深度的含量变化均可通过矿物和矿物组合特征较为直接地示踪显现，土壤中矿物组成对其化学元素含量的影响是直接的、决定性的。因此，利用土壤的矿物组成确定其常量和微量元素的初始值具有重要意义。据此可进一步解析土壤中元素地球化学异常成因，判别土壤的元素地球化学异常类型。     

包气带土壤组成对三氯乙烯的吸附影响研究

有机质和矿物质是包气带土壤中的主要吸附介质,其吸附特性直接影响有机污染物在环境中的迁移、转化等过程。分别采用分析纯石英砂和典型粘土矿物高岭石模拟土壤的原生矿物和粘土矿物,利用批实验的方法研究土壤中各组成部分对三氯乙烯(TCE)的吸附行为。土壤有机质的吸附行为通过全土样和矿物质的对比得出。结果表明,粘土矿物是吸附氯代烃的主要矿物质,原生矿物对氯代烃的吸附量很小;土壤有机质含量和土壤吸附量之间有很好的正相关性;土壤有机碳含量与土壤粘土矿物含量的比值是影响吸附行为的另一重要因素,比值越小,Koc值越大,土壤对TCE的亲和力就越强。由于自然界中的土壤有机质大都与矿物质形成有机质-粘土矿物结合体,据此推测有机质-矿物质结合体会影响有机质的组成和形态,从而对其吸附行为有重要作用。     

浙江土壤矿物组成特征

对浙江省29种母质和16种土类或亚类构成的69个母质一土类单元共194个土壤样品中的矿物成分进行测定，分析得出矿物种类及矿物百分含量。在此基础上分析了浙江省土壤矿物组成特征。不同土类或亚类土壤中矿物组成存在明显差异，矿物种数和含量变化较大。突出的特征是，相同母质类型土壤含有相似的矿物种类，而且相同母质不同样品中同一矿物含量变化也较小，表现出同母质土壤矿物组成与含量具有相似性。在69个土壤剖面中，由A层到C层矿物种类和含量变化较小，土壤矿物组成明显受基岩影响和控制。宜把地质背景相同、矿物组成相近、土壤环境相似的成土母质作为划分土壤重金属污染评价单元，土壤类型只能作为评价单元的辅助划分依据。     

原生矿物组分对CO_2地质储存地球化学过程的影响

CO2的地质储存是迅速减少温室气体向大气排放最直接、最有效的方法之一,其封存量受很多因素影响,储层原生矿物组分是其中之一。本文以松辽盆地、美国墨西哥湾、日本Nagaoka场地资料为基础,对CO2矿物封存过程进行数值摸拟。结果表明:原生矿物组成及含量相差不大时,地球化学反应过程相似,原生矿物组成较为复杂时,地球化学反应过程也更复杂;在以石英、长石为主的砂岩储层中,长石和绿泥石是重要的溶解矿物,铁白云石和片钠铝石是主要的固碳矿物;CO2矿物封存量随着原生矿物中奥长石和绿泥石含量增加而增大,其中奥长石的影响更大。以上研究对CO2地质储存储层的选取有指导意义。     

Mineral Composition of Loess—Paleosol Samples from the Loess Plateau of China and Its Environmental Significance

34samples of loess-paleosol from the Luochuan and Xifeng sections in the Loess Plateau,northern China were eparated into sand,silt and clay fractions and analyzed for their mineral compositions.The results indicate that there is almost no difference between loess and paleosol in mineral composition.Major mineral species are quartz,mica,feldspar and chlorite,accounting for about 88-92% of the total;other minerals are kandite,smectite,vermiculite and a few heavy minerals.The calcite,magnetite and hematite were not taken into consideration because of their removal in the process of sample preparation.The main difference with respect to the mineral composition of samples collected from different sections and different statigraphic levels lies in the amount and grain size of minerals hosted.Comparisons between the Luochuan section and the Xifeng section,between paleosol and loess and between the upper part and the lower part of some paleosol layers show that the formers contain less feldspar but more mica and vermiculite and are finer in grain size,indicating the co-occurrence of both biochemical weathering process responsible for mineral change and physical weathering process leading to grain-size change during the soil-forming processes.This result favours such an explanation of the soil-forming mechanism that loess deposition and paleosol development occurred synchronously,though the rate of soil formation was greater than that of loess deposition,thus leading to soil development.     

辽西黄土的物质组成与微观结构特征

黄土的物质组成和结构特征对深入研究黄土的工程地质特性和湿陷机理具有重要的意义。利用颗分试验、X射线衍射技术、化学分析技术及扫描电镜测试技术,对阜新一朝阳高速公路沿线黄土的颗粒组成、化学成分、矿物成分、易溶盐,以及原状黄土的微观结构进行了测试、分析。结果表明：①黄土的颗粒成分以粉粒为主,粉粒中又以粗粉粒为主;粘粒含量变化较大;②黄土中的碎屑矿物以石英和长石为主,粘土矿物以伊利石、伊蒙混层为主;③黄土中的易溶盐和难溶盐较其他地区偏低;④浅层黄土结构较松散,为支架大孔微胶结结构和支架大孔-镶嵌微孔半胶结结构;深层黄土结构较为密实,多为絮凝状胶结结构和凝块状胶结结构。     

黄土的本质与形成模式

根据显微结构鉴定,有机质分析,颗粒分析,CaCO₃测定和野外观察、统计等资料,研究了黄土的本质和形成模式。资料表明,黄土具有土壤的各种结构,具有指示草原和森林草原土壤发生特征的CaCO₃和CaSO₄淀积成分,含有土壤的有机质;黄土的本质是土壤,是在相对冷干气候条件下发育的多种灰黄色狭义土壤,而且是在当时当地气候条件下处于稳定状态的发育成熟的古土壤;黄土形成模式是风尘经草原、森林草原和荒漠草原区的成壤作用形成土壤的模式。黄土高原是世界上土壤资源最深厚、最富集的地区,黄土的工程地质性质和水文地质性质在很大程度上取决于成壤作用的强弱。     

我国不同气候带黄土中粘土矿物组合特征分析

在兰州黄土和下蜀黄土中粘土矿物的X衍射分析基础上,对我国不同纬度和气候带的五个黄土剖面(点)中的粘土矿物组合和空间分布进行了对比分析,并探讨了与古气候的关系。结果表明,黄土中粘土矿物组合具有明显的地带性特征。从西北到东南,随着纬度的逐渐降低,黄土中的粘土矿物组合也发生有规律的变化。主要表现为绿泥石含量的逐渐减少和蛭石含量的逐渐增多。位于温带半干旱区的兰州黄土以伊利石和绿泥石为主要粘土矿物,而位于亚热带湿润区的大港下蜀黄土则以伊利石和蛭石为主要粘土矿物。黄土中含有较多量的绿泥石可作为黄土母质堆积后干冷气候和微弱风化的标志,而蛭石和蛭石/绿泥石混层矿物含量的增加指示了风化强度的增强。因此,黄土粘土矿物组合特征不仅反映物源区古环境信息,而且指示了黄土堆积期后的生物气候环境。     

基于SEM-EDS的湿陷性黄土黏土矿物定量分析

黄土在压力作用下受水浸湿后,其特有的孔隙体系内颗粒间胶结作用的丧失而导致颗粒发生相对滑动所产生的变形是黄土发生湿陷的根本原因,而黄土中的胶结物以附于碎屑颗粒或团聚体等骨架颗粒表面的黏土矿物为主。黄土中有多种黏土矿物,由于各种黏土矿物的水理性质不同,对黄土湿陷性的影响亦各有不同,因此在某种程度上黏土矿物成分及其所占比例能够反映黄土的湿陷性。本文通过对延安地区不同深度黄土中的主要矿物元素进行能谱分析,建立了质量守恒方程组。把该方程组问题转化为最优化问题——线性规划标准形问题,采用数学规划问题中的单纯形法来计算矿物构成,分析了延安地区黄土中主要黏土矿物的含量,结合化学分析测试结果对该方法的可行性进行了探讨。结果表明:本方法计算精度满足要求,是一种行之有效的测定黄土中黏土矿物含量的途径,该方法最大的优势在于数据获取便捷,可实现SEM环境下的即时定点定量分析。     

原状黄土土水特征滞后性研究

现有的土水特征曲线(SWCC)滞后性的研究多针对重塑土,原状黄土土水特征曲线滞后性特征的研究较少。为研究全吸力范围内原状黄土的滞后特征,以泾阳马兰黄土(L1)和离石黄土(L5)为研究对象,采用压力板仪和滤纸法测定增湿和减湿SWCC,采用压汞法测定孔隙分布特征,X衍射分析矿物成分。结果表明,在压力板仪测试基质吸力范围内(0~600 kPa),滤纸法和压力板仪测定的SWCC具有一致性,且在减湿过程中两种方法的测试结果更为一致。滤纸法测得的全吸力范围(0~30 000 kPa)内,黄土SWCC滞后性存在三段性特征。即在天然含水率(L1 14.2%、L5 17.3%)附近,黄土SWCC几乎无滞后性;含水率高于天然含水率一定范围(L1大于19.2%、L5大于18.3%),存在极为明显的滞后性;低于天然含水率一定范围(L1小于11.2%、L5小于15.4%),存在弱滞后性。天然状态下反复干湿循环,导致黄土SWCC在天然含水率附近无滞后性;黄土限制孔隙对墨水瓶效应的增益作用,导致高含水率下黄土SWCC呈强滞后性;黏土矿物的水合作用,导致低含水率下SWCC呈弱滞后性。     

Rock Magnetism Study on Loess-Paleosol Sequence at Huixinggou Section of Sanmenxia Basin

Rock magnetism is the foundation of paleomagnetism and environmental magnetism study, and is effective in identifying the components, grain size and content of magnetic minerals in rocks and sediments. A systematic rock magnetism investigation has been conducted on the Huixinggou loess-paleosol sequence at Shuigou-Huixinggou Paleolithic site of Sanmenxia Basin in the southeastern Loess Plateau. Results show that the magnetic assemblage of the section is dominated by magnetite and maghemite, as well as hematite, exhibiting the average grain size of magnetic minerals is attributed to Pseudo-Single Domain (PSD). The variation curves of magnetic parameters are consistent and well comparable to marine oxygen isotope curves, with low values corresponding to the loess deposition during glacial periods, and high values corresponding to the paleosol development during interglacial periods, jointly demonstrating the glacial-interglacial cyclicities of magnetic mineral types, composition, and grain size of Chinese loess-paleosol sequences under the influence of alternating strengthening and weakening of Eastern Asian paleomonsoon over the Quaternary period. Comprehensive analysis reveals that the relative content of high-coercivity antiferromagnetic minerals is higher in loess than in paleosol, whilst the absolute content of high-coercivity antiferromagnetic minerals in paleosol is generally higher than that in loess accompanying increasing intensity of pedogenesis. The mass-specific magnetic susceptibility (χ) shows distinctly positive correlations with anhysteretic susceptibility (χ_ARM), Saturation Isothermal Remanent Magnetization (SIRM) and magnetic grain size dependent parameters (χ_ARM/SIRM and χ_ARM/χ), indicating that the pedogenic producing Single Domain (SD) and small PSD ferrimagnetic particles contribute significantly to the magnetic susceptibility enhancement.     

Hydrochemical Groundwater Evolution in the Bunter Sandstone Sequence of the Odenwald Mountain Range,Germany: A Laboratory and Field Study

Field and laboratory investigations were performed to identify the principal mechanisms of the hydrochemical groundwater evolution among low mineralised groundwater in the Triassic Bunter sandstone aquifer of the Odenwald low mountain range, central Germany. Hydrochemical composition comprises low pH, SO₄-rich shallow groundwaters issued by springs (Ca-Mg-SO₄-type) grading to SO₄-poor deep groundwaters with near-neutral pH (Ca-HCO₃-type). Batch experiments of the original rock were run to determine primary mineral alteration reactions and the origin of dissolved ions. Principal experimental reactions comprise the decomposition of anorthite, K-feldspar, biotite and jarosite as mineral components of the original sandstone rock and the formation of clay minerals of the smectite group (Ca-montmorillonite, beidellite), and iron hydroxides as secondary minerals. Mobilisation of fluid inclusion in quartz grains contributes to Na and Cl concentrations in the leachates. The evolution of deep groundwater circulation proceeds by mineral alteration reactions calculated by the inverse modelling of both primary and secondary minerals to produce low-T mineral phases. The dissolution of K-feldspar converts Ca-montmorillonite to illite (illitisation). The formation of Na-beidellite correlates with decreasing concentration of Na in solution. Mineral reactions further proceed to the formation of kaolinite as stable mineral phase. As indicated by modelled adsorption curves, the decrease of SO₄ concentrations during groundwater evolution relates to the adsorption of SO₄ on iron hydroxides. The leaching of calcite indicated for individual groundwaters relates to the distribution of loess in the appropriate catchment areas.     

The loess of North-East Essex, England

A thin mantle of cover-loam over much of North-East Essex has been recognised as consisting largely of loess. The cover-loam represents the intermixing, to a varying degree, of a layer of loessial silt with a thin layer of underlying sand which is also of likely aeolian origin. The heavy mineral content of the coarse silt fraction of North-East Essex loess is generally similar to that of last glaciation age loesses elsewhere in Eastern England, Belgium and the Netherlands. This suggests the North-East Essex loess is part of a single loess sheet deposited over Eastern England and parts of Western Europe. Nevertheless, detailed examination of the heavy minerals content from all of these areas reveals slight areal variations especially in the proportion of hornblende. These differences show the coarse silt from North-East Essex loess to have closest affinities with that from Norfolk. A distant source for the loess within the present North Sea Basin is proposed on textural evidence. Loess accumulation in North-East Essex probably commenced in the few thousand years leading up to the maximum extent of Devensian ice (about 18,000 years B.P.) and may have continued to about 14,000 years B.P.     

GEOBOTANICAL INVESTIGATIONS IN PROSPECTING FOR ORE DEPOSITS

The use of plants as indicators in prospecting for minerals is discussed on a broad scale from the standpoints both of available literature and field experiments. The method of isoline mapping of mineral deposits by means of metal content in ashes of plant parts is detailed,. The author cautions against too broad use of any single species as a “direct” indicator or too heavy reliance on ash content, as some species tend to concentrate certain minerals, regardless of soil composition. Instead, a combination of species as indicators and a combination of factors, such as appearance of leaves, luxuriance of the plant, and color and time of blooms is recommended. The tendency of some minerals to nullify the effect of others–iron counteracting the effect of copper, for instance — is noted, as well as different effects on plants of different salts of the same mineral. In spite of these qualifications and the early, stage of development of this technique, the method has particular merit in areas where the strata overlying the metal-bearing deposits is relatively thick. Analyzing the ash content of leaves of deep-rooted trees is particularly helpful in detecting the presence of an ore mineral in such a situation. — A. Eustus