黄河流域硅酸盐风化的讨论

根据2007年6月和7月采集的黄河干流及部分支流水样和河床砂样品数据,对黄河流域硅酸盐化学风化进行了探讨。在充分评估黄河流域的K+,Na+来源的基础上,确定了硅酸盐风化的K+量,并通过选定的硅酸盐风化(K/Na)比值,得到了硅酸盐风化的Na+量;通过测定流域内不同岩石类型分布的河床砂样品,得到河床砂样品硅酸盐部分(Ca/Na)和(Mg/K)的比值,确定了钙镁硅酸盐风化的Ca2+,Mg2+量;并据此估算了流域硅酸盐化学风化的CO2消耗率。如果选用黄河入海多年径流量58.02×109km3/a进行计算,则得到全流域硅酸盐风化CO2消耗率约为26.22×103mol/km2/a。若选用2007年的平均径流量24.83×109km3/a进行计算,则黄河流域硅酸盐风化引起的CO2消耗率约为11.19×103mol/km2/a。     

青藏高原东北部黄土沉积化学风化程度及古环境

通过对青藏高原东北部西宁盆地大墩岭剖面24种常微量元素的测定及数据的处理分析，研究了该地区黄土沉积的化学风化程度及某些地球化学特征。相对上部陆壳(UCC)元素平均值，大墩岭剖面显著富集Ca、Mg、Ti、V、Cr、Ni、Y、Zr等，而亏损Si、Al、K、Na、Sr、Nb等；相对于中国黄土(CL)元素平均值，大墩岭剖面明显富含Fe、Ca、Mg、K、Ti、Cr、Mn、Cu、Rb、Sr、Nb、Ba和P，而Si、Na、Co、Ni、Pb则表现为亏损；在UCC标准化图与CL标准化图中，大墩岭黄土与古土壤变化趋势基本一致。大墩岭剖面尚处于脱Ca、Na的大陆风化初期阶段。与其他地区的风尘沉积相似，大墩岭黄土沉积很可能也起源于上部陆壳，但不排除物源存在一定差别。风尘堆积时该区的气候环境比黄土高原要干冷，这与青藏高原第四纪以来的强烈隆升有直接关系。     

EPR evidence for maghemitization of magnetite in a tropical soil

Electron paramagnetic spectroscopy (EPR) was used in combination with standard rock magnetic methods to study magnetic minerals in a tropical soil. The susceptibility and hysteresis measurements showed magnetite grains with a Curie temperature near 850 K as the dominant magnetic remanence carriers in the soil. A minor Ti content in the magnetite was found by energy dispersive X-ray analysis. In order to get insight into the weathering status of the magnetite, different chemical treatments, including oxalate and citrate–bicarbonate–dithionite (CBD) extraction, were applied to the soil samples. The hysteretic properties exhibited no significant differences between the untreated and the CBD or oxalate treated samples. By contrast, the comparison of the EPR spectra revealed a significant broadening of the linewidth (δB) and a shift of the g -values ( g _eff) to lower fields after the CBD treatment. Furthermore, the spectral parameters g _eff and δB exhibited an angular dependence. At low temperature, the CBD treated samples showed a jump in δB between 120 and 100 K, the temperature range characteristic for the Verwey transition in magnetite. The changes in the spectral properties after the CBD treatment, which dissolves ferric oxides, were attributed to the removal of maghemite formed by the oxidation of magnetite, that is, during the maghemitization of the magnetite grains.     

京九铁路粤北段风化花岗岩、残积土的斜坡稳定性研究

文章总结了京九铁路广东段风化花岗岩、残积土路堑边坡病害的勘察、设计及治理经验，分析了沿线花岗岩风化壳综合分带特征，并对相关的滑坡形成机理、变形特征和治理措施作了简要阐述。     

石灰岩腐岩的基本特征及其形成机制

碳酸盐岩风化剖面非饱和带内的白色粉末状物质应属碳酸盐岩腐岩，剖面上部覆盖有一定厚度的土层是此类腐岩发育的必要条件。对昆明富民石灰岩风化剖面的研究表明，石灰岩腐岩呈白色或灰白色，结构疏松，密度、孔隙度和渗透率分别为1．8081g／cm^3、32．65％和774．8139×10^-3 μm^2，其母岩的对应指标分别为2．6966g／cm^3、0．05％和0．0084×10^-3 μm^2，综合差异显著。石灰岩腐岩吸水性强、给水能力差，容水度30％，持水度25％。基于铸体薄片的显微观察发现，腐岩粒间孔隙及溶蚀孔隙发育，面孔率达19％；扫描电子显微镜下，可见泥晶方解石集合体之间的蜂窝状溶孔和方解石颗粒之间的粒间孔。石灰岩向腐岩的转变是通过其结构体风化前锋的扩展实现的。微观尺度上，石灰岩结构体属非连续的颗粒集合体，具有巨大的比表面积和很强的潜在吸附能力。覆盖有土层的非饱和带多属潮湿环境，能保持较高的相对湿度。当在压力及浓度梯度驱动下侵入石灰岩结构体的水汽分子凝结为液态水时，可对方解石颗粒产生楔裂作用，削弱粒间或粒内的结构连接，使其集合体发生一定程度的体膨胀，从而形成腐岩壳。随着时间加长，风化前锋逐渐扩展，岩石结构体最终转化为腐岩结构体。石灰岩腐岩是在高湿度包气带环境中经吸湿膨胀作用形成的，是石灰岩物理风化的产物；渗入水的溶滤作用主要发生在腐岩的演化阶段。     

古玉器的化学风化机理初探之二——块状模拟实验

在前文粉末态模拟实验基础上,初步模拟古玉埋藏的酸性以及碱性环境,通过对不同材质玉料的块状形态在酸、碱缓冲溶液中的浸泡实验,并与粉末态玉料的浸泡结果进行对比分析,以深化对古玉器风化机理的认识。     

Hydrochemical framework of groundwater in the Ankobra Basin,Ghana

Hydrochemical and stable isotope (¹⁸O and ²H) analyses of groundwater samples were used to establish the hydrochemistry of groundwater in the Ankobra Basin. The groundwater was generally mildly acidic, low in conductivity and undersaturated with respect to carbonate phases. Major ions except bicarbonate were low and dissolved silica was moderately high. Silicate minerals weathering is probably the main process through which major ions enter the groundwater. Groundwater samples clustered tightly along the Global Meteoric Water Line suggesting integrative, smooth and rapid recharge from meteoric origin. The majority of the boreholes and a few hand dug wells cluster towards the Ca–Mg–HCO₃ dominant section of the phase diagram, in conformity with the active recharge and short residence time shown by the isotope data. Aluminium, arsenic, manganese, iron and mercury were the only trace metals analysed with concentrations significantly above their respective detection limits. Approximately 20%, 5%, 40% and 25% respectively of boreholes had aluminium, arsenic, iron and manganese concentrations exceeding the respective WHO maximum acceptable limits for drinking water. The relatively large percentage of boreholes with high concentration of aluminium reflects the acidic nature of the groundwater.     

Landslide susceptibility mapping using GIS and digital photogrammetric techniques: a case study from Ardesen (NE-Turkey)

Ardesen is a settlement area which has been significantly damaged by frequent landslides which are caused by severe rainfalls and result in many casualties. In this study a landslide susceptibility map of Ardesen was prepared using the Analytical Hierarchy Process (AHP) with the help of Geographical Information Systems (GIS) and Digital Photogrametry Techniques (DPT). A landslide inventory, lithology–weathering, slope, aspect, land cover, shear strength, distance to the river, stream density and distance to the road thematics data layers were used to create the map. These layer maps are produced using field, laboratory and office studies, and by the use of GIS and DPT. The landslide inventory map is also required to determine the relationship between these maps and landslides using DPT. In the study field in the Hemsindere Formation there are units that have different weathering classes, and this significantly affects the shear strength of the soil. In this study, shear strength values are calculated in great detail with field and laboratory studies and an additional layer is evaluated with the help of the stability studies used to produce the landslide susceptibility map. Finally, an overlay analysis is carried out by evaluating the layers obtained according to their weight, and the landslide susceptibility map is produced. The study area was classified into five classes of relative landslide susceptibility, namely, very low, low, moderate, high, and very high. Based on this analysis, the area and percentage distribution of landslide susceptibility degrees were calculated and it was found that 28% of the region is under the threat of landslides. Furthermore, the landslide susceptibility map and the landslide inventory map were compared to determine whether the models produced are compatible with the real situation resulting in compatibility rate of 84%. The total numbers of dwellings in the study area were determined one by one using aerial photos and it was found that 30% of the houses, with a total occupancy of approximately 2,300 people, have a high or very high risk of being affected by landslides.     

Short‐term rock surface expansion and contraction in the intertidal zone

Transverse micro‐erosion meter (TMEM) stations were installed in rock slabs from shore platforms in eastern Canada. The slabs were put into artificial sea water for 1, 6 or 11 hours, representing high, mid‐ and low tidal areas, respectively. The TMEMs were used to record changes in surface elevation as the rocks dried during the remainder of the 12 h of a semi‐diurnal tidal cycle. A similar technique was used on the same rock types at intertidal TMEM stations in the field, as the rocks dried during low tide. Argillite and basalt surface contraction was from 0 to 0·04 mm: there was little surface expansion. Sandstones contracted by up to 0·03 mm in the field, but there was almost no contraction in the laboratory. Argillite and basalt contraction tended to be greatest in the upper intertidal zone, and to increase with rates of longer‐term surface downwearing, but there was little relationship with rock hardness or air temperature and humidity. Changes in elevation at the same points at TMEM stations in the laboratory and field were quite consistent from one tidal cycle to the next, but there were considerable variations within single tidal cycles between different points within each station. The data suggest that contraction within the elevational zone that is normally submerged twice a day by the tides is by alternate wetting and drying. Short‐term changes in elevation are generally low compared with annual rates of downwearing owing to erosion, but they may generate stresses that contribute to rock breakdown. Copyright © 2007 John Wiley & Sons, Ltd.