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The presence of methane (CH4) in groundwater is usually only noticed when it rises to high concentrations; to date rather little is known about its production or natural ‘baseline’ conditions. Evidence from a range of non-polluted groundwater environments in England, including water supply aquifers, aquicludes and thermal waters, reveals that CH4 is almost always detectable, even in aerobic conditions. Measurements of potable waters from Cretaceous, Jurassic and Triassic carbonate and sandstone aquifers reveal CH4 concentrations of up to 500 μg/l, but a mean value of < 10 μg/l. However, aquiclude and thermal waters from the Carboniferous and Triassic typically contain in excess of 1500 μg/l. Such high concentrations have so far only been found at redox (Eh) potentials below 0 mV, but in general CH4 concentration and Eh value are poorly correlated. This suggests a lack of thermodynamic equilibrium, which is confirmed by comparing pe values calculated from the redox couple C(4)/C(− 4) with those derived from Eh. Genesis of CH4 appears to occur on two timescales: a rapid if low rate of production from labile carbon in anaerobic microsites in the soil, and a much longer, millennium scale of production from more refractory carbon. Methane is rarely measured in groundwater; there is no single ionic determinand which acts universally as a proxy, but a combination of high HCO3 and low SO4 concentrations, or the reverse, is an indication that high amounts of CH4 may be present. 相似文献
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Abstract: Carbonate rocks of Cambrian (18 samples) and lower-middle Ordovician (11 samples) ages from South Korea were analyzed for sulfur contents of structurally substituted sulfate (SSS) and sulfides and their δ34 S values. The δ34 S values of SSS ranging from +25.9 to +45.2 permil, are averaged as +33.6 and +33.5 permil for the Cambrian and Ordovician rocks, respectively, which indicate high δ34 S values of the Cambro-Ordovician seawater. The SSS contents in the carbonate rocks are low being 2.9 to 17.3 ppm S (averaged as 7.0 ppm S). Sulfide sulfur, on the contrary, is much abundant containing 3 to 1,880 ppm S and the δ34 S values range widely between –17.6 and +31.1 permil. Sulfide sulfur of the studied rocks excluding impure carbonates has an average content of 187 ppm S and δ34 S value of +12.8 permil (n=24). The estimated δ34 S (sulfate–sulfide) values, which range from 13.8 to 25.4 permil in general with a few exceptions from 36.5 up to 52.3 permil for some impure carbonates, may provide evidence for the persistent oceanic anoxia with its temporary recovery during the Cambro-Ordovician time.
The SSS and sulfide sulfurs have often higher δ34 S values than the Mesozoic-Cenozoic ore sulfur (Ishihara et al., 2000). Since carbonate rocks are very reactive with circulating hydrothermal ore solution, high δ34 S values of the Korean ore deposits might be caused to some extent by 34 S enrichment from the host carbonates, resulting in the low SSS contents observed. 相似文献
The SSS and sulfide sulfurs have often higher δ
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Different diagenetic transformations and their relative chronological sequence are studied in the meteoric diagenetic zone from the Upper Oligocene limestone at the North of the Aquitaine Basin (France), by combining high-resolution cathodoluminescence spectroscopy and electron-microprobe analyses. More than 128 spot analyses by electron microprobe and 60 analyses by cathodoluminescence spectroscopy are done on different meteoric cements firstly identified by classic optical microscopy. Three cement types are identified according to the relative intensity of the bands of their respective cathodoluminescence spectra (350, 380, 430, 500, and 620 nm). From these investigations, we could identify for each meteoric cement different phases of crystalline growth and crystalline dissolution. As a result, a better and more realistic meteoric diagenetic model is proposed. It illustrates the cyclic transformations from vadose zone (unsaturated) to meteoric zone (saturated). To cite this article: R. Chapoulie et al., C. R. Geoscience 337 (2005). 相似文献
6.
GIS-based detachment susceptibility analyses of a cut slope in limestone, Ankara—Turkey 总被引:3,自引:0,他引:3
Due to the rapidly growing population of the city of Ankara (Turkey) and increased traffic congestion, it has become necessary to widen the Ankara-Eskişehir (E-90) highway connecting the newly built areas west of the city to the city center. During widening, several cut slopes were formed along the highway route. As a result, some instability problems (small-sized rock falls/sliding, sloughing, raveling) produced detachment zones along a cut slope in highly jointed, folded and sheared limestone, causing local degradation of the cut slope. Identification of the areas that are likely to detach from the cut slope in the future is considered to be very important for the application of remedial measures. For this purpose, the relationships between the existing detachment zones and various parameters (e.g., point load strength index, weathering, block size, daylighting, shear zone) were investigated using GIS-based statistical detachment susceptibility analyses in order to predict the further aerial extension of the detachment zones with time. During the overlay analyses, statistical index and weighting factor methods were used. The outcomes of the analyses were compared and evaluated with the field observations to check the reliability of the methods and to assess the detachment zones that may develop in the future. The detachment susceptibility map without the block-size layer gives the best result and indicates some risky zones where detachments are likely to occur in the future. Recommendations on remedial measures of the cut slope should consider these risky zones. 相似文献
7.
贵州豹子洞石灰岩与红土型金矿藓类植物比较研究 总被引:8,自引:1,他引:8
红土型金矿是岩溶地区新发现的一类金矿类型,其特点是石灰岩基岩与金矿红土混生。为了探索岩溶地区苔藓植物特征, 2004年8月我们对贵州安龙县豹子洞石灰岩和红土型金矿苔藓植物进行了比较研究。野外在红土型金矿区和石灰岩各设5个采样点, 共观察和采集了105份苔藓标本。对苔藓植物的区系组成、地理成分、结构及物种多样性进行统计分析,结果表明: 该地区两种基质上共有40种,隶属9科25属,未发现苔类和角苔类。其中,石灰岩上有7科、11属、12种藓类植物; 红土型金矿上有6科、18属、28种藓类植物。豹子洞石灰岩与红土型金矿区藓类植物其种相似性系数为0. 05。Sha nno n-Wiene r 指数和种间相遇机率指数较低, Simpso n 指数则较高,表明苔藓植物分布受基质影响明显。 相似文献
8.
It is often necessary to locate the original quarry which supplied the stone for a particular historical building. This stones could be used for future restoration work and for testing in the laboratory (artificial aging tests, physical properties determination, control of the efficacy of conservation treatments, etc.). Generally, reviewing historical documentation gives information about the geographical setting of quarries and location of the stones in the monument, but this information needs to be proved by field and laboratory studies. The comparative study of stone from quarries and monuments should basically include the following: (1) mineralogical and petrographical studies; (2) the chemical analysis of major, minor and trace elements; (3)stable isotopes determinations; (4) physical properties of quarry materials and unweathered building stone (water absorption, ultrasound transmission velocity, porosity and porous system, density, bulk density, compressive strength, etc.). This methodology was applied to Málaga Cathedral stones represented in the main façade, towers, and the western zone of the terrace, which, according to historical literature, came from Almayate (Miocene–Pliocene limestones) and Cerro Coronado (Permotriassic sandstone) in Málaga. The conclusion of the comparative study carried out on quarries and building stones was consistent with the information available from the historical documentation. 相似文献
9.
岩性不均一的灰岩风化壳发育特征——贵阳花溪剖面粒度分布特征的指示 总被引:1,自引:2,他引:1
通过贵阳花溪夹泥质薄层的灰岩风化壳剖面的粒度分布特征的研究,结合矿物成分分析,揭示出岩性不均一的灰岩风化壳的发育特征: 灰岩作为剖面主体的成土母岩,风化早期,其以碳酸盐矿物的大量溶蚀及酸不溶物的残余积累为特征,同时方解石的溶解也延缓了酸不溶物的风化; 后期,随着易溶盐类消失殆尽,酸不溶物作为风化主体,开始了类似其它岩类的风化过程。而灰岩中的泥质薄层夹层,作为风化壳的次要组分,在灰岩风化过程中,由于存在巨大的体积缩小变化,泥质薄层被错断并被灰岩的风化产物所包裹,延缓了其风化发育进程。于是,各端元组分由于所处的微环境的差异,受风化溶液的影响程度不同,按照各自的风化方向和演化方式进行。随着风化程度不断增强,泥质薄片的包裹体分解,端元组分逐渐混合、趋同,风化壳趋于均质化,以统一的风化成土作用向表生稳定的矿物转变。 相似文献
10.
对安徽巢湖地区平顶山和马家山剖面下二叠统栖霞组和下三叠统南陵湖组进行了地层沉积特征及暗色石灰岩生烃潜力的综合分析,并对这两个层位的样品进行了饱和烃生物标志物特征研究。结果表明,两个层位的石灰岩都属于有效烃源岩,均具有一定的生烃潜力。南陵湖组石灰岩饱和烃以高丰度的长链三环萜烷、重排藿烷、重排甾烷为特征,表明其形成于偏弱氧化的沉积环境。栖霞组沉积期水体能量相对较低,受陆源物质影响明显,栖霞组石灰岩萜烷系列为常规的分布模式,但其甾烷成熟度参数明显低于平衡值,认为高的热演化程度是造成栖霞组石灰岩20S/(20S+20R)-ααα-C29甾烷值和ββ/(ββ+αα)-C29甾烷值"倒转"的主要原因。 相似文献