Circumgranular bassanite in a gypsum crust from eastern Algeria – a potential palaeosurface indicator

Detrital sand grains are surrounded by thin bassanite coatings in the upper part of a coarse-crystalline gypsum crust from the Algerian Sahara. The bassanite developed by topotactic replacement of the surrounding gypsum in the absence of a liquid phase. Heating experiments using a gypsum crystal with sand inclusions produced similar patterns and textures. In one experiment, bassanite developed around quartz and carbonate grains but not along the sides of the heated gypsum crystal. This is the result of differences in heat capacity between gypsum, quartz and calcite. Bassanite formation in the crust from Algeria was not controlled by differences in thermal properties. Instead, the bassanite apparently formed under conditions of thermal equilibrium. The occurrence of bassanite as circumgranular coatings in the crust is interpreted as being related to the availability of submicroscopic space along the contact between the gypsum cement and the enclosed sand grains. The presence of coatings of this type, or derived relict features, is a potential criterion for the recognition of palaeosurfaces.     

电感耦合等离子体发射光谱法测定石膏矿样品中的三氧化硫

样品用稀盐酸处理,在酸性条件下石膏样品中的三氧化硫以硫酸根状态存在于待测溶液中,过滤除去酸不溶物。处理好的待测溶液可直接上等离子体发射光谱仪ICAP-6300(美国热电制造)上测定。方法的检出限为0.01%,采用本法测定国家标准物质GBW03109,GBW03109a,GBW03110,GBW03111a,结果表明标准样品测定的相对误差为-0.411%~0.274%,相对误差允许限为1.07%,能够满足分析质量要求。     

石膏及其热转变产物的红外光谱

本文给出了石膏及其热转变产物－－烧石膏和硬石膏的红外光谱。在晶体结构资料基础上，对石膏和硬石膏分别进行了因子群分析和位置群分析，其结果清楚地表明，理论预测的光谱与实测光谱相当一致。根据烧石膏的红外光谱和位置群分析的结果可以肯定。SO4^2-离子的位置对称性不可能是D 2，只能为C2或C1。热转变产物的红外光谱表明，石膏－－烧石膏和烧石膏－硬石膏之间的热转变温度分别为80－100℃和350－400℃。     

Natural and human-induced sinkholes in gypsum terrain and associated environmental problems in NE Spain

The central Ebro Basin comprises thick evaporite materials whose high solubility produces typically karstic landforms. The sinkhole morphology developed in the overlying alluvium has been studied using gravimetry and ground-penetrating radar (GPR) on stream terraces, as well as analyzing the evolution of sinkhole morphologies observed in aerial photographs taken in 1928, 1957, and 1985. The sinkhole morphologies give some idea of possible subsurface processes as well as an indication of the final mechanisms involve in sinkhole development. On stream terraces and cover pediments the most commonly encountered dolines are bowl-shaped in their morphology with both diffuse and scarped edges. In contrast, dolines developed in the gypsiferous silt infilled valleys have a funnel and well-shaped morphology. The diffuse-edged bowl-shaped dolines are developed through the progressive subsidence of the alluvial cover, due to washing down of alluvial particles through small voids and cracks into deeper subsurface caves, resulting in a decrease alluvial density. Future compaction of the alluvial cover will produce surface subsidences. This type of dolines are associated with negative gravity anomalies. In contrast, the scarped-edge dolines are formed by the sudden collapse of a cavity roof. The cavities and cracks formed in the gypsum karst may migrate to the surface through the alluvial deposits by piping, and they may subsequently collapse. In this instance, the cavities can be detected by both gravity and GPR anomalies where the voids are not deeper than 4–5 m from the surface. These processes forming sinkholes can be enhanced by man-induced changes in the groundwater hydrologic regime by both inflows, due to irrigation, ditch losses, or pipe leakages, and by outflows from pumping activities.     

吉林省浑江盆地石膏矿地质特征及找矿方向

就浑江盆地而言,自南西向北东依次出现5个洼地:鹿圈子洼地、东热洼地、下四平洼地、浑江—大阳岔洼地、湾沟洼地。本文叙述了吉林省浑江盆地石膏矿床的地质特征及找矿方向。     

延安地区奥陶系马家沟组上组合膏盐岩成盐沉积演化模式研究

延安地区经过十余年油气勘探,在奥陶系马家沟组获得了一系列的突破,其中马家沟组上组合是天然气勘探的重要层位,该区是奥陶系碳酸盐岩-膏盐岩共生体系的主要沉积区,其中马家沟组上组合马五₄³-马五₃²膏盐沉积是海退蒸发环境的典型代表。本文基于延安气田奥陶系天然气勘探的最新进展,利用现场岩心观察、实验分析、钻井及测井资料,根据沉积构造、膏盐岩发育规模、岩性组合方式等,对研究区奥陶系马家沟组上组合膏盐岩的地质特征进行了详细的阐述,系统地总结了研究区马家沟组上组合膏盐岩的沉积背景及沉积相、建立了沉积演化模式,为延安气田膏盐岩研究提供基础资料。研究表明,在西高东低的沉积格局背景下,地层充填呈西薄东厚,南薄北厚的特点;自西南向东北依次为膏质白云岩-膏岩-盐岩沉积区;垂向发育三种岩石类型组合:Ⅰ型膏质白云岩-硬石膏结核白云岩-膏质白云岩-泥云岩组合,Ⅱ型膏岩-硬石膏结核白云岩-膏质白云岩-泥云岩组合,Ⅲ型盐岩-膏岩-硬石膏结核白云岩-膏质白云岩组合;沉积环境为相对安静且低能的潟湖沉积模式。沉积环境演化为极强蒸发盐化→蒸...     

青藏高原可可西里盆地晚白垩世—早中新世地层年代学新进展及其对地层和古环境的指示意义

青藏高原构造隆升是新生代重大地质事件之一,是东亚构造—气候演化的重要边界条件之一,也是研究全球气候变化绕不开的一个重要因素。目前,关于青藏高原的隆升历史和机制等存在较大的争议,其中,一个最重要的原因是地层年代学问题,可靠的地层沉积年龄是后续研究的基础。青藏高原中北部可可西里盆地保存有晚白垩世至中新世较连续的沉积,是研究青藏高原构造演化不可多得的研究材料。本文基于可可西里盆地最新的晚始新世至中新世地层年龄研究结果,同时,结合其他已发表的、有绝对年龄控制点的地层年龄,认为风火山群和沱沱河组是两套独立的地层单元,即在可可西里盆地,地层划分从老到新可划分为：风火山群、沱沱河组、雅西错组和五道梁组。在可可西里盆地地层沉积年龄最新进展基础之上,综合盆地的古高度、古纬度、古温度、古地磁、沉积相变化、地层接触关系、全球温度、大气二氧化碳以及亚洲季风和高原隆升之间关系的模拟等证据,指出：① 青藏高原面上类似于现在向东、东南逃逸的GPS速度运动场方向可能在始新世就已经形成,沱沱河盆地以东的物质向东南逃逸,以西没有这种趋势,沱沱河盆地可能是一个重要的边界;② 类似于现在的东亚季风—内陆干旱化格局形成于晚渐新世—早中新世;③ 青藏高原中北部晚始新世以来发生了明显的两阶段隆升,>38.5~26(24) Ma的隆升主要由印度与欧亚板块的碰撞挤压缩短所致,16 Ma~现在的隆升由岩石圈地幔对流拆沉引起,26(24)~16 Ma是隆升相对平静期;④ 青藏高原中北部主夷平面可能发育于26(24)~16 Ma期间;⑤ 角度不整合接触不是构造事件发生的可靠判别标志;⑥ 石膏等盐类矿物的出现不是干旱化的可靠指标,但似乎表明在盐类矿物沉淀析出之前,区域应该存在至少一期湿润的气候,按此结果,可能暗示了至少在古新世我国中东部可能已经存在季风气候。     

石膏尾矿墙体材料的研究

通过实验确定了生产石膏尾矿墙体材料的配合比及CaO、复合外加剂的最佳掺量，利用X射线衍射仪和扫描电子显微镜以水化产物的种类及结构形态进行了分析研究，并对其物理力学性能做了测试与分析。     

石膏岩中粘土矿物提取的一种新方法及在古气候重建中的应用

目前通用的前处理方法难以从石膏岩中有效提取足量粘土矿物进行测试分析,针对这一技术问题,本研究改进了原有的粘土矿物分析前处理方法,采用新的试剂乙二胺四乙酸二钠（以下简称EDTA）溶解石膏岩,释放其中所含的粘土矿物,有效提高石膏岩中粘土矿物的提取能力。本文以位于青藏高原东北缘西宁盆地塔山剖面（36.5°N,101.8°E） 始新世祁家川组、洪沟组和马哈拉沟组的9个石膏岩样品为研究对象,通过详细对比试验确定了EDTA的溶解条件,明确了采用EDTA提取石膏岩中粘土矿物的实验流程和方法,并探讨了溶解过程对粘土矿物的影响。实验结果表明,EDTA对石膏岩的最佳溶解条件为：温度=100℃、pH=10~12、浓度=0.32mol/L,改进后的前处理方法提取粘土矿物质量是原来的1~25倍,且不破坏粘土矿物的晶型结构。使用EDTA溶解法提取9个样品中的粘土矿物经X射线衍射分析结果表明,西宁盆地始新世石膏岩样品中粘土矿物含量以伊利石为主（62%~90%）,含少量绿泥石（3%~17%）,蒙脱石（含伊蒙混层矿物）含量变化较大（0~35 %）。粘土矿物组合特征反应该区域始新世以干旱气候为主,盆地内石膏岩地层形成时期的气候环境可能存在一定程度的干湿波动现象。     

山西中奥陶世石膏岩的成因类型及生成环境

山西中奥陶世石膏岩的沉积受到机械沉积作用的影响。区内九种石膏岩分别是不同水深条件下的沉积及交代产物,并可归纳为浪基面下洼地、浅水、滩岛潮坪等三种沉积环境。在空间上,它们彼此依存、转换并连为一体形成一个巨大的浅水蒸发岩沉积。