杜家沟铝土矿成矿特征及成因分析

铝土矿和其下部的铁质粘土岩组成铝岩系.铝土矿的铝硅和铝铁均呈反比关系,硅铁呈正比关系,这一特征反映出第一期脱硅,第二期脱铁的两期风化成矿作用.粘土岩的铝含量稳定,铁含量变化大,硅铁是反比关系,显示第二期风化作用,脱出的铁质在粘土岩内沉淀,并生成山西式铁矿.铝岩系具有Al_2O_3/SiO_2和Fe_2O_3/SiO_2两值间同步正相关,显示铝土矿及其母质层粘土岩的陆壳风化成矿.     

Provenance of freshwater pulses in the Gulf of Mexico during the last deglaciation

During the last deglaciation, the decaying Laurentide Ice Sheet (LIS) delivered huge volumes of meltwater toward the Gulf of Mexico. The present investigation of clay mineralogy and grain-size characteristics of terrigenous sediments deposited in the Orca Basin (Gulf of Mexico) offers a unique opportunity to link the marine record of these meltwater floods with the reconstructed continental glacial history and the modeled drainage patterns. Five peculiar sedimentary levels, characterized by high smectite content and low CaCO₃ content, were identified and occurred simultaneously with major meltwater floods. According to recently published clay mineral distribution maps for North America, these results help to pinpoint the southwestern margin of the LIS as a main contributor to most of the meltwater discharges. In addition, the peculiar mineralogical composition (illite and chlorite-rich) of the sediments characterizing the meltwater episode associated with Heinrich event 1 suggests a provenance from the Great Lakes area, supporting the interpretation of destabilization of the LIS southeastern margin during this event. Decreased terrigenous contribution associated with changing provenance of sediments after 12.9 cal ka BP suggests strong modifications of the continental hydrography in relation to Lake Agassiz history and changes in the morphology of Mississippi delta due to rising sea level.     

甘肃西峰6.2～2.4MaB.P.红粘土中孢粉记录及古植被演化

通过对甘肃西峰赵家川6.2～2.4MaB.P.红粘土地层的孢粉学研究,建立了3个孢粉组合带。孢粉组合特征显示该区在此阶段总体为干旱的草原环境,6.2～5.8MaB.P.为灌丛草原;5.8～4.2MaB.P.是稀疏森林草原,植被由大量中生性草本植物和少量喜湿性的乔木植物组成,反映当时气候相对湿润;4.2～2.4MaB.P.植被中旱生植物藜科和麻黄明显增多,反映典型草原-荒漠草原。分析认为研究区自6.2MaB.P.干旱草原环境的格局就已经形成。红粘土中孢粉记录的植被演化信息与青藏高原隆升有时代上的耦合性,也与北极冰盖的起源和演化历史有着密切的联系。     

地面物探在岩溶地基工程勘察中的应用——以桂林某花园综合楼为例

岩溶地区工程建筑地基的地质情况比较复杂,存在土洞、软土等工程隐患。常规工程勘察手段,由于其自身的局限性,很难一一查清这些隐患的分布特征。地面物探是一种较为省时省力的工程辅助勘探方法。但物探方法有多种,在选用时,必须根据场地条件、探测目标、方法性能及工作成本等来综合考虑,选择适用的方法(或方法组合) ,才有可能取得令人满意的探测效果。桂林某花园综合楼地基主要以红粘土为主,软土、土洞发育,红粘土之下,桂林组灰岩表面起伏强烈,溶洞发育。根据场地地质特征及基坑开挖特点,本勘察采取浅层地震折射、反射波法,并配合高密度电阻率测量,较好地查明了场地软土和土洞的分布位置,为综合楼的地基处理提供了可靠的地质依据。      

长江口泥沙的来源分析与数量计算的研究

本文根据地学原理，建立了长江口泥沙的来源分析与数量计算的模式。定量分析了长江口泥沙来源，计算了泥沙的数量。通过验证表明沙量的计算值与验证值两者十分吻合。     

浅析北方红粘土对碳酸盐岩溶蚀作用的影响

北方碳酸盐岩发育的红色风化壳大都是第Ⅰ、Ⅱ间冰期湿热气候条件下溶蚀与风化作用的结果,形成硅铝—铁型风化壳。风化壳中红粘土化学成分R_2O_3(Al_2O_3+Fe_2O_3)含量达20—30％。当降水或地表水的垂直下渗、红粘土的氢离子浓度加大,溶蚀性增强,沿红粘土和碳酸盐岩接触面产生溶蚀作用,形成石芽、溶沟、溶槽、溶痕等岩溶地形,并在它们的表面保留有红粘土痕迹。     

华南二叠－三叠系的事件地层与生物地层界线

华南二叠－三叠系界线研究应严格区分事件地层界线与生物地层界线。“界线粘土”层的底界即为事件地层界线。生物地层界线定义不能与“混生层”或“过渡层”的概念连在一起。长兴煤山忠心大队剖面是最好的二叠－三叠系全球界线层型剖面点（ＧＳＳＰ）。二叠－三叠系生物地层界线定义为ＨｉｎｄｅｏｄｕｓｐａｒｖｕｓＭｏｒｐｈｏｔｙｐｅ１的首次出现,其位置就在长兴剖面界线层（混生层）２的内部,比事件地层界线高１５ｃｍ。ＨｉｎｄｅｏｄｕｓｐａｒｖｕｓＭｏｒｐｈｏｔｙｐｅ１的首次出现,即为长兴阶的顶界。     

Comparative analysis of contributing parameters for rainfall-triggered landslides in the Lesser Himalaya of Nepal

In the Himalaya, people live in widely spread settlements and suffer more from landslides than from any other type of natural disaster. The intense summer monsoons are the main factor in triggering landslides. However, the relations between landslides and slope hydrology have not been a focal topic in Himalayan landslide research. This paper deals with the contributing parameters for the rainfall-triggered landslides which occurred during an extreme monsoon rainfall event on 23 July 2002, in the south-western hills of Kathmandu valley, in the Lesser Himalaya, Nepal. Parameters such as bedrock geology, geomorphology, geotechnical properties of soil, and clay mineralogy are described in this paper. Landslide modeling was performed in SEEP/W and SLOPE/W to understand the relationship of pore water pressure variations in soil layers and to determine the spatial variation of landslide occurrence. Soil characteristics, low angle of internal friction of fines in soil, medium range of soil permeability, presence of clay minerals in soil, bedrock hydrogeology, and human intervention were found to be the main contributing parameters for slope failures in the region.     

Stabilization of swelling clays by Mg(OH)2. Changes in clay properties after addition of Mg-hydroxide

Stabilization of the swelling clay structure is attempted by intercalation of Mg(OH)₂ and the development of a brucite interlayer between the clay layers. The properties of the product obtained by applying the technique, formulated as described in a previous work, are considered here. The materials used were Wyoming bentonite (USA), Fuller's Earth (UK), kaolinite, illite, lignite, and silica gels. The Mg(OH)₂-clay products were examined by the methylene blue dye test, X-ray diffraction analysis (XRD), differential thermal analysis (DTA), and derivative thermogravimetry analysis (DTGA). From the results obtained it is concluded that: the Mg-hydroxide is adsorbed by swelling clays both on their external and internal surface, whereas it is adsorbed on the external surface by non-swelling clays. The internally adsorbed phase of Mg-hydroxide forms an ill-defined interlayer of brucite, retarding swelling, whereas the external phase covers the particles modifying drastically their surface properties, like the adsorption of the MB dye. The material produced after precipitation of Mg-hydroxide on swelling clays (smectites) did not re-expand on wetting or after glycolation. The adsorption of MB dye was also reduced by some 80–90%, due to coating effect, preventing the measurements of the external surface area of the clay by polar molecules. The principal forces involved in the process are believed to be physical adsorption on the external surface, along with chemisorption and some chemical bonding, mostly in the internal surface. Cementation due to crystallization and, in the long term, some pozzolanic reactions take also place. Internal adsorption of the Mg-hydroxide is postulated to be in the form of positively charged mono- and/or small polymers and it is, chiefly, diffusion controlled. Since Mg-hydroxide is internally adsorbed by swelling clays, whereas Ca-hydroxide(lime) is not, and the (Mg, Ca)-clay aggregates are more stable than the Ca-clay or the Mg-one, the combination of the two hydroxides could give better results in soil stabilization than each hydroxide alone.     

新疆库车凹陷侏罗系多粒级黏土矿物分析方法及其对沉积-成岩环境的指示

本文选取库车坳陷侏罗系阿合组—齐古组的碎屑岩样品,利用 Stokes 原理,通过同步跟进与离心分析相结合的多粒级提取的方式提取不同粒径的黏土矿物,包括>20μm;20μm～5μm;5μm～2μm;2μm～0.2μm和<0.2μm。不同粒径组分的黏土矿物呈现出不同的型貌特征,在20～2μm范围内的样品中,自生黏土矿物少见,大量可见碎屑来源的黏土矿物,由于经过了长期的机械搬运,难见完整的晶型。在<2μm的样品中大量存在自生黏土矿物,大量成集合体,同时也存在碎屑蚀变成因的黏土矿物。通过 XRD 方法定量分析了所分离出的不同粒径黏土矿物的相对含量,黏土粒径范围内的黏土矿物相对含量呈现些规律变化。碎屑伊利石含量有随着粒级的减小而减少的趋势,而自生伊利石和伊蒙混层只在2～0.2μm及0.2μm以下粒级才出现,并且集中在0.2μm以下粒级范围内;在古气候,沉积环境和母岩特性及分布基本一致的情况下,高岭石的分布有随着岩性的变粗呈现升高的趋势,而伊利石呈负相关关系。碎屑岩中黏土矿物的形貌特征表明,黏土矿物有陆源碎屑来源与自生两种成因,应用 Decoform 软件对0.2μm以下黏土矿物中不同成因的伊利石进行了计算,并就存在的比例与粒径的关系进行了讨论。黏土矿物组合揭示侏罗纪沉积环境由酸性环境向微碱性环境过渡,早侏罗世和中侏罗世早期为气候潮湿时期,高岭石的含量明显高于侏罗世晚期地层,恰克马克期到齐古期高岭石含量开始出现减小的趋势。从恰克马克期开始,气候缓慢向干旱变化,高龄石含量降低,而伊利石的平均含量明显增加,反映黏土矿物组合主要受沉积环境和成岩作用共同影响。