The negative effect of environmental geological conditions of some geo-archaeological sites of North Coast and Alexandria     

Hani Ibrahim  Gamal Kamh 《Environmental Geology》2005,49(2):179-187

Three geo-archaeological sites at the North Coast and Alexandria, namely, the Alexandria wall (El Shalalat Park site), Abu Soir temple, and Marina excavations, were investigated to determine the negative impact of a salty environmental condition. The monuments suffer from rock decay of different rates. The geo-archaeological sites were built mainly from oolitic limestone blocks (i.e., the Alexandria wall at the El Shalalat Park site and Abu Soir temple) or excavated on them (i.e., Marina excavations). Field inspection and a lab analysis were carried out to understand the weathering mechanism. Salt weathering criteria such as disintegration, pitting, scaling, exfoliation, and honeycomb are observed on the Alexandria wall and upper parts of the Abu Soir temple, while dangerous cracks are detected on the Marina excavation tombs. The petrographic study of the oolitic limestone samples shows that they consist mainly of oolities and drusy sparite as a cement (oolitic grainstone). Some oolities have quartz grains as nuclei. Hydrochemical analysis shows that the total dissolved salts of extracted solutions of the North Coast quarry samples range from 539 to 686 ppm and dramatically increase (i.e., ten times) for extracted solutions from monument samples, ranging from 5395 to 6880 ppm. The dominant cation is sodium while the dominant anion is chlorine. Acid insoluble residue analysis shows that the carbonate content ranges from 89.2% to 96.4% for fresh samples from quarries and from 9.2% to 94.8% for weathered monument samples. The weight loss of the quarry oolitic limestone samples range from 30.7% to 32.7% and its physical and mechanical properties become worse after being subjected to 15 cycles of a durability simulation soundness test (using a sodium sulphate solution). Our main recommendations are to use suitable grouting for binding the cracks, high durability reconstruction rocks, and suitable cleaning methods to remove salts from the monuments.  相似文献   

Late Glacial and Holocene Palaeoenvironmental Changes in the Rostov-Yaroslavl’ Area, West Central Russia     

Barbara Wohlfarth  Pavel Tarasov  Ole Bennike  Terri Lacourse  Dmitry Subetto  Peter Torssander  Fedor Romanenko 《Journal of Paleolimnology》2006,35(3):543-569

Three lake sediment sequences (lakes Nero, Chashnitsy, Zaozer’e) from the Rostov-Jaroslavl’ region north of Moscow were studied to provide information on palaeoclimatic and palaeoenvironmental changes during the past 15,000 cal yr. The multi-proxy study (i.e., pollen, macrofossils, mineral magnetic measurements, total carbon, nitrogen and sulphur) is chronologically constrained by AMS ¹⁴C measurements. Lake Nero provided the longest sedimentary record back to ca. 15,000 cal yr BP, while sediment accumulation began around ca. 11,000 cal yr BP in the two other lakes, possibly due to melting of permafrost. Limnic plant macrofossil remains suggest increased lake productivity and higher mean summer temperatures after 14,500 cal yr BP. While the late glacial vegetation was dominated by Betula and Salix shrubs and various herbs, it appears that Betula sect. Albae became established as early as 14,000 cal yr BP. Major hydrological changes in the region led to distinctly lower lake levels, starting 13,000 cal yr BP in Lake Nero and ca. 9000 cal yr BP in lakes Chashnitsy and Zaozer’e, which are situated at higher elevations. These changes resulted in sedimentary hiatuses in all three lakes that lasted 3500–4500 cal yr. Mixed broad-leaved – coniferous forests were widespread in the area between 8200 and 6100 cal yr BP and developed into dense, species-rich forests between 6100 and 2500 cal yr BP, during what was likely the warmest interval of the studied sequences. Agricultural activity is documented since 500 cal yr BP, but probably began earlier, since Rostov was a major capital by 862 A.D. This apparent gap may be caused by additional sedimentary hiatuses around 2500 and 500 cal yr BP.  相似文献   

塔里木盆地库车坳陷盐构造成因机制探讨   总被引：3，自引：0，他引：3  

邬光辉  蔡振中  赵宽志  董立胜  师骏 《新疆地质》2006,24(2):182-186

以盐构造解析的方法,综合地震与地质资料分析,在盐构造成因要素剖析的基础上探讨库车坳陷盐构造动力学特征.研究表明库车坳陷盐构造的成因受多重作用影响,差异负载是库车坳陷盐构造初始形成时的动力来源,中新世—上新世中晚期差异负载作用是盐构造形成与缓慢生长的主要动力.盐上盖层快速沉降是该期盐构造生长缓慢的主要原因.上新世中晚期以来强烈的区域挤压作用是库车坳陷盐构造发育的主控因素,构造挤压决定了盐构造的样式、分布与规模,并促进了差异负载、重力作用与浮力作用的发展,以区域挤压为主的多种作用因素造成了库车坳陷盐构造晚期异常高速的生长.  相似文献   

湖泊亚像元填图算法研究   总被引：4，自引：0，他引：4       下载免费PDF全文

张洪恩  施建成  刘素红 《水科学进展》2006,17(3):376-382

湖泊面积变化监测具有重要的科学和社会意义,使用中低分辨率卫星遥感数据进行大面积的湖泊面积变化监测有很多优势,但易受混合像元的影响。本文根据湖泊水体的遥感特性,发展了使用中低分辨率卫星遥感数据的混合像元分解算法,应用线性多端元混合像元分解技术,自动、快速地得到在每个像元中湖泊所占的面积百分比;在上述分类结果的基础上,基于地物的空间依存现象,建立空间吸引力的概念,用循环迭代的方法实现超过遥感影像自身分辨率的湖泊亚像元填图。在针对青藏高原不同季节不同地区的Modis影像的实践中,显示混合像元分解算法可以提供较高精度的软分类结果;使用迭代方法进行亚像元填图是简单高效的,具有很大的应用潜力。  相似文献   

湖芯沉积物揭示的末次冰消开始时期 普莫雍错湖区环境变化^*   总被引：14，自引：22，他引：14       下载免费PDF全文

朱立平  鞠建廷  王君波  西村弥亚  守田益宗  吴艳红  冯金良  谢曼平  林晓 《第四纪研究》2006,26(5):772-780

文章讨论了末次冰消开始时期青藏高原南部普莫雍错湖芯沉积反映的环境暖湿化以及原因。通过对现代湖泊和周边河流水文状况调查,发现流域内发育众多冰川,冰川融水构成维持湖面稳定的重要来源;湖面以及湖泊沉积环境的变化与冰川融水以及相应的温度改变具有密切的联系。利用湖泊沉积岩芯PM-1孔,通过加速器¹⁴ C测年和粒度、元素、碳酸盐含量、总有机碳以及有机碳同位素、总氮、分子标志化合物、孢粉等环境指标的分析,发现在16.4~15.4cal.kaB.P.有大量流水进入湖泊,使湖面扩大,湖水加深;流域地表产生大量有机碎屑,并被流水带入湖泊进行沉积;流域内的喜湿植被得以发展。该时段湖泊扩张、陆源植被发展的原因一方面得益于冰期过后气候向温暖湿润方向转化,另一方面温度上升带来大量冰川融水则可能具有更加重要的影响,对于深入理解当前青藏高原冰川普遍退缩和一些湖泊的水面上涨具有重要的参考价值。  相似文献   

云南茂租铅-锌矿床地质特征及成因研究   总被引：1，自引：1，他引：1  

贺胜辉  荣惠锋  尚卫  速建红 《矿产与地质》2006,20(4):397-402

阐述了茂祖铅．锌矿床的成矿地质背景、矿床地质特征，着重研究了赋矿地层、铅-锌矿体赋存及矿化特征，并通过该矿床的成矿时代、成矿物质来源、成矿温度方面的研究，综合分析后认为，茂祖铅-锌矿床的成因属同生断裂控矿的热水喷流-沉积改造型。  相似文献   

盐沼植被光谱特征的间接排序识别分析   总被引：1，自引：0，他引：1  

高占国  张利权 《国土资源遥感》2006,(2):51-56

运用ASD地物光谱仪,采用12个小型机载成像光谱仪(CASI)默认的植被波段组,以上海崇明东滩自然保护区的盐沼植物群落为对象,应用主成分分析法和相关分析研究了不同群落光谱特征与生态环境因子之间的关系。结果表明:运用PCA间接排序法能够识别盐沼植被中光滩、海三棱藨草群落、芦苇群落和互花米草群落等光谱特征;绝大多数盐沼植物的群落组成与所选波段的光谱特征之间有显著的相关关系;可见光和近红外波段数据可以分别识别低盖度的海三棱藨草群落和高盖度的互花米草和芦苇群落;对光谱反射率影响最大的生态环境因子是植物群落的高度和盖度,而高程和其它环境因子的影响次之。  相似文献   

Rock magnetic and geochemical proxies for iron mineral diagenesis in a tropical lake: Lago Verde, Los Tuxtlas, East–Central Mexico     

Beatriz Ortega  Margarita Caballero  Socorro Lozano  Gloria Vilaclara  Alejandro Rodríguez 《Earth and Planetary Science Letters》2006,250(3-4):444-458

Magnetic and non-magnetic mineral analyses were conducted on a lacustrine sequence from Lago Verde in the tropical coast along the Gulf of Mexico that covers the last 2000 years. The site witnessed the transformation of the environment since the early Olmec societies until forest clearance in the last century. Through these analyses we investigated the processes that affected the magnetic mineralogy in order to construct a model of past environmental changes, and compare this model with the archeological record and inferred climatic changes in the northern hemisphere of tropical America. Volcanic activity has played a major influence on sediment magnetic properties, as a purveyor of Ti-magnetites/Ti-maghemites, and as a factor of instability in the environment. Anoxic reductive conditions are evident in most of Lago Verde's sedimentary record.

Direct observations of magnetic minerals and ratios of geochemical (Fe, Ti), and ferrimagnetic (χf) and paramagnetic (χp) susceptibility (χ) data, are used as parameters for magnetite dissolution (χp/χ, Fe/χf), and precipitation (χf/Ti) of magnetic minerals. Intense volcanic activity and anoxia are recorded before A.D. 20, leading to the formation of framboidal pyrite. Increased erosion, higher evaporation rates, lower lake levels, anoxia and reductive diagenesis in non-sulphidic conditions are inferred for laminated sediments between A.D. 20–850. This deposit matches the period of historical crisis and multiyear droughts that contributed to the collapse of the Maya civilization. Dissolution of magnetite, a high organic content and framboidal pyrite point to anoxic, sulphidic conditions and higher lake levels after A.D. 850. Higher lake levels in Lago Verde broadly coincide with the increased precipitation documented during the Medieval Warm Period (A.D. 950–1350) in the northern tropical and subtropical regions of the American continent. For the Little Ice Age (A.D. 1400–1800), the relatively moist conditions inferred are in concordance with the glacial advances recorded in central Mexico. Higher erosion rates reflect destruction of the rainforest over the last 40 years.  相似文献   

博斯腾湖面积定量遥感   总被引：6，自引：0，他引：6       下载免费PDF全文

刘瑞霞刘玉洁  郑照军黄彦彬 《应用气象学报》2006,17(1):100-106

采用NOAA/AVHRR资料, 利用水体与地物光谱特性的差异, 结合通道2方案和通道2/通道1方案, 对4月博斯腾湖水体进行判识, 而利用通道2、通道2/通道1并结合通道4的方案判识了10月博斯腾湖水体, 在此基础上利用线性混合模式对混合像元做了处理, 定量估算了1990—1998年4月和10月博斯腾湖的面积, 调研了9年来博斯腾湖面积变化情况, 表明9年间博斯腾湖面积呈增加趋势。进一步采用主成分分析方法对博斯腾湖面积增大原因做了初步的气候分析, 表明1988年以来博斯腾湖地区气温升高、蒸发量减少、降水有所增加, 而人类活动用水和出流稳定并有减少是博斯腾湖面积增加的主要原因。而博斯腾湖及上游地区季节性积雪的特征, 使冬季积雪水资源注入博斯腾湖, 导致春季博斯腾湖面积较秋季大。  相似文献   

Earthquake-induced deformation structures in lake deposits: A Late Pleistocene to Holocene paleoseismic record for Central Switzerland   总被引：1，自引：0，他引：1  

Katrin Monecke  Flavio S. Anselmetti  Arnfried Becker  Michael Schnellmann  Michael Sturm  Domenico Giardini 《Eclogae Geologicae Helvetiae》2006,99(3):343-362

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