Morphology and mineralogy of weathering crusts on highly porous oolitic limestones, a case study from Budapest     

Á. Török  N. Rozgonyi 《Environmental Geology》2004,46(3-4):333-349

Black crusts are very common on limestones in polluted urban environments, but white crusts are less frequently developed. On the soft, porous and inherently weak oolitic limestone of Budapest both crusts are frequent, and indeed white ones are more common on the stone walls of the studied fortress. In this paper, black and white crusts and the host rock have been described using morphological criteria, mineralogical analyses (XRD, DTA), elements analyses (microprobe) and micro-morphological (SEM) tests. The analyses have shown that on white crusts the surface dissolution is combined with the precipitation of gypsum and calcite in the pores and accumulation of gypsum on the underside of the crust. Thin white crusts are removed by a combination of salt crystallisation (gypsum) and frost action while very thick stone layers scale off due to freeze-thaw cycles. Black crusts are enriched in gypsum relative to white crusts. Gypsum accumulates on the crust surface and signs of dissolution have not been observed. Airborne particulates (flyash, silt-sized quartz, and organic debris) adhere to the crust surface of sheltered black crusts. These particles are later incorporated into the expanding gypsum crystals, that are visible on the underside of the crust. The host rock also contains gypsum, but it is washed off the surface when the crust is removed. Further exposure of the host rock may lead to the dissolution of calcite crystals as it is observed by SEM. The micro-environment influences the crust formation and adherence of the crusts. On frequently wet and dry surfaces crust removal is more common. The crust serves as a protective layer on the stone surface, but this protection is temporary since trigger mechanisms such as salt crystallisation or frost action can cause rapid surface loss.Special Issue: Stone decay hazards  相似文献   

The effects of fire on the surface properties and seed germination in two shallow monoliths from a rangeland soil subjected to simulated raindrop impact and water erosion     

C. J. Chartres  H. J. Mücher 《地球表面变化过程与地形》1989,14(5):407-417

This paper describes the methods used and some preliminary results of simulated erosion studies on soils with cryptogamic crusts from a semiarid rangeland environment. Two 0·3 m² shallow monoliths were collected from the upper 20 cm of a Typic Haplargid from the semiarid Australian rangelands and subjected to a range of rainfall intensities and durations representing potentially erosive summer and winter rainfall events. One of the monoliths was cleared of vegetation by a simulated low intensity bushfire. Macro- and micromorphological properties of the surface, as well as runoff and erosion losses, were measured during the experiment. Runoff and erosion losses were, as expected, greater for all conditions on the burned than on the unburned monolith. Intensive rainfall damaged the cryptogamic crust unprotected by vegetation by widening and deepening desiccation cracks around the cryptogams, and breaking away and dispersing larger soil fragments from the crack margins. The burned and eroded surfaces provided a much poorer environment for seed entrapment, germination, and growth than did the unburned surface.  相似文献   

Environmental impact on the Roman monuments of Tarragona,Spain     

M. Vendrell-Saz  M. Garcia-Vallès  S. Alarcón  J. Molera 《Environmental Geology》1996,27(4):263-269

The extant remains of the Roman monuments of Tarragona, Spain are made of different types of Miocenic rocks from the quarries surrounding the city, which vary from calcarenite to bioclastic limestones, showing different degrees of dolomitization, depending on their diagenetic evolution. The decay of these monuments is highly dependent on the mineralogy and the fabric of the stone as well as on the environmental conditions to which the monument subjected. As a consequence, different forms of decay are observed on these monuments, namely, granular disintegration, differential erosion between sparitic and micritic areas of the rock, and development of black crust and orange patinas, some of them attributed to a sulfation process. A number of processes have been established as being responsible for the decay forms observed: sulfation on sheltered areas of the building in the urban environment; differential dilatation because of the NaCl of the marine spray that crystallizes inside the porosity; hydric and thermal expansion of the stone, both related to the amount and crystallinity of the clay minerals forming the rock matrix; and biocolonization on the stone surface. An empirical model is proposed to explain the decay forms studied in relation to these factors (rock and environment).  相似文献   

西太平洋海山富钴结壳稀土元素(REE)组成原位LA-ICPMS测定   总被引：3，自引：0，他引：3  

薛婷  孙晓明  张美  刘珊珊  何高文  王生伟  陆红锋 《岩石学报》2008,24(10):2423-2432

利用激光剥蚀电感耦合等离子体质谱(LA-ICPMS)微区原位分析方法,对采自西太平洋海山具完整三层结构的富钴结壳样品进行了稀土元素(REE)含量测定,结果表明, 虽然均产于西太平洋海山且均具有明显的三层结构,富钴结壳化学组成受地理位置和沉积环境影响很大。绝大多数西太平洋富钴结壳具有高ΣREE、高LREE/HREE、δCe正异常和δEu基本无异常或微弱正异常的特点, 显示它们主要由正常海水沉积形成。结壳不同层圈之间REE组成有较大的区别, 其原因主要在于其形成环境和矿物组成不同。样品0327稀土元素总量(∑REE)由亮煤层到疏松层到外层逐渐升高,且亮煤层δCe和Y/Ho变化非常大,最大值分别为38.61和105.5,显示该层生长环境较为氧化且相对动荡,而样品0346中三层结构的∑REE都非常高,且变化趋势与0327正好相反,从亮煤层到致密层∑REE有降低的趋势。 亮煤层形成时海水相对较氧化的环境有利于铁锰氧化物的形成和Ce⁴⁺等稀土元素的吸附,导致其中ΣREE较疏松层和外层为高,而后期磷酸盐化导致REE元素的迁移和亏损。在结壳生长剖面上,由最外层到疏松层和亮煤层,δCe呈明显上升趋势,且变化范围趋大,说明该结壳所处的海水环境在由老至新的生长过程中由相对动荡和氧化变为相对平静和还原。  相似文献   

富钴铁锰结壳的控矿要素和成矿过程——以西太平洋为例   总被引：4，自引：0，他引：4  

石学法  任向文  刘季花  S.I. Andreev 《矿物岩石地球化学通报》2008,27(3)

以西太平洋海山的麦哲伦海山群和马尔库斯-威克海山群为例,研究了富钴铁锰结壳（富钴结壳）形成过程中地质要素和海洋要素的作用,重点分析了海山漂移和沉降、水道开合、最小含氧带（OMZ）、大洋环流,以及气候变化等要素对富钴结壳形成的控制作用。基于对麦哲伦海山和马尔库斯-威克海山结壳样品剖面Mn／Fe值曲线的综合研究,结合控矿要素和成矿背景分析,将该区白垩纪以来富钴结壳的成矿过程划分为五个阶段：（1）自垩纪-始新世,（2）始新世末-晚渐新期,（3）晚渐新期-中中新期早期,（4）中中新期早期晚中新期早期,（5）晚中新期早期-现代,其中（2）、（3）阶段有利于发育富钴结壳。  相似文献   

辽南地区晚第三纪红色风化壳及更新世高海面问题探讨     

蒋伟  李永化  魏东岚  沈俊杰  李爽 《地理科学》2018,38(8):1391-1396

以辽南地区石槽剖面与城山头剖面的红色风化壳为研究对象,利用X射线荧光光谱仪,对风化壳剖面样品进行分析。结果表明：剖面中各采样点样品的主要化学元素含量自剖面底部到顶部无规律性变化,显示了主要化学元素在风化过程中的地球化学行为较为一致,符合风化壳沉积类型特征;剖面的主要化学成分为SiO₂、Al₂O₃、Fe₂O₃,结合各采样点样品的主要化学元素含量及SiO₂/Al₂O₃及SiO₂/R₂O₃系数,可以认为这套红色风化壳应是在高温高湿的环境条件下风化作用的产物。通过与山东庙岛群岛风化壳的对比及风化壳厚度的计算,可以认为该套风化壳的形成时代应在上新世或更早。依据风化壳在滨海地区的残存高度可以推断,自第三纪晚期以来辽南地区最高海平面高度未超过今天的海平面高度。  相似文献   

腾格里沙漠东南缘生物土壤结皮对土壤理化性质的影响   总被引：3，自引：1，他引：2  

都军  李宜轩  杨晓霞  李云飞  马晓俊 《中国沙漠》2018,38(1):111-116

生物土壤结皮是荒漠生态系统地表景观的重要组成部分,在沙化土地恢复和流沙固定中起着重要作用。研究了腾格里沙漠东南缘固沙植被区不同类型生物土壤结皮理化性质及结皮发育对下层土壤性质的影响。结果表明：结皮层厚度、孔隙度、黏粉粒和田间持水量以及有机碳、无机碳、全氮、碱解氮、速效磷、速效钾含量和电导率均表现为藓类结皮 > 混生结皮 > 地衣结皮 > 藻类结皮;砂粒含量和容重表现为藻类结皮 > 地衣结皮> 混生结皮 > 藓类结皮。结皮下0~2 cm和2~5 cm土层理化性质表现出与结皮层相同的变化规律。总体上,生物土壤结皮对下层土壤理化性质的影响表现为藓类结皮和混生结皮大于地衣结皮和藻类结皮;而结皮对下层土壤理化性质的影响随土壤深度的增加而减小。生物土壤结皮的拓殖和发育是荒漠生态系统成土过程和土壤质量的关键影响因素。  相似文献   

A review of progress in identifying and characterizing biocrusts using proximal and remote sensing     

《International Journal of Applied Earth Observation and Geoinformation》2017

Biocrusts are critical components of desert ecosystems, significantly modifying the surfaces they occupy. The mixture of biological components and soil particles that form the crust, in conjunction with moisture, determines the biocrusts’ spectral signatures. Proximal and remote sensing in complementary spectral regions, namely the reflective region, and the thermal region, have been used to study biocrusts in a non-destructive manner, in the laboratory, in the field, and from space. The objectives of this review paper are to present the spectral characteristics of biocrusts across the optical domain, and to discuss significant developments in the application of proximal and remote sensing for biocrust studies in the last few years. The motivation for using proximal and remote sensing in biocrust studies is discussed. Next, the application of reflectance spectroscopy to the study of biocrusts is presented followed by a review of the emergence of high spectral resolution thermal remote sensing, which facilitates the application of thermal spectroscopy for biocrust studies. Four specific topics at the forefront of proximal and remote sensing of biocrusts are discussed: (1) The use of remote sensing in determining the role of biocrusts in global biogeochemical cycles; (2) Monitoring the inceptive establishment of biocrusts; (3) Identifying and characterizing biocrusts using Longwave infrared spectroscopy; and (4) Diurnal emissivity dynamics of biocrusts in a sand dune environment. The paper concludes by identifying innovative technologies such as low altitude and high resolution imagery that are increasingly used in remote sensing science, and are expected to be used in future biocrusts studies.  相似文献   

中国干旱区沙化土地绿色环保治理技术综述   总被引：1，自引：1，他引：0  

赵洋  潘颜霞  苏洁琼  张志山 《中国沙漠》2021,41(1):195-202

土地沙化是中国面临的严重生态问题。沙化土地治理是中国生态文明建设的重点和难点,也是建设美丽中国必须要面对和解决的问题。在干旱区使用人工植被和草方格机械沙障等措施治理沙化土地效果显著,但同时也存在一定的局限性。针对这些问题,近年来中国学者研发和探索了人工生物土壤结皮等诸多新型、快速的沙化土地绿色环保治理技术。本文评述了2000年以来中国学者在这一领域开展的系列创新性研究,分析了其研究前沿和未来发展趋势,以期为全面、准确认识和评估绿色环保沙化土地治理技术提供重要依据。  相似文献   

约翰斯顿岛附近海域铁锰结壳矿物学和地球化学研究   总被引：11，自引：4，他引：11  

姚德 Wilts.  J 《海洋地质与第四纪地质》1996,16(1):33-49

铁锰结壳存在两种不同的产状，一种是铁锰氧化和的围绕“核心”生长形成的球状结壳，另一种是铁锰氧化物在基底岩石上生长形成的被状结壳。本文对Ｒ／Ｖ，Ｋａｉｍｉｋａｉ－Ｏ－Ｋａｎａｌｏａ船１９９３年１１月在约翰期顿岛附近海域取得铁锰结壳进行了矿物学和地球化学分析。该区铁锰结壳主要组成矿物为δ－ＭｎＯ２，Ｍｎ／Ｆｅ比值为２．０２，富Ｃｏ（０．８８１％），盆Ｃｕ（０．１％），稀土总量（∑ＲＥＥ）１９１８．２７  相似文献