共查询到20条相似文献，搜索用时 20 毫秒
1.
Field observations, chemical analysis, electron and light microscopy and radiolabelling experiments provide information on the characteristics, formation and distribution of Fe and Mn rock varnishes in southern Tunisia. Unstable rocks are not surface-coated, but when broken they commonly reveal internal microbial solution fronts. Stable rocks are coated in Fe, and more rarely Mn, rock varnishes. Radiolabelling indicates the presence of many respiring microbes on both Fe and Mn varnishes. Microscopy shows fungi and bacteria, both on the Fe varnishes and within the rock. Only rare, microcolonial fungi occur on Mn varnishes, suggesting that the microbes are within or beneath the varnish. The abundance of microorganisms supports a biogenic origin for rock varnishes. Different microbial communities appear to be involved in Fe and Mn varnish formation. Microbes appear to live beneath the surface of unstable rocks but coat stable rocks which cannot be penetrated, apparently to avoid u.v. light and desiccation. This explains the concentration of elements that form u.v. opaque minerals and clays. The origin of these elements is external to the substrate. These results suggest that rock varnish dating and paleoenvironmental techniques can be applied in southern Tunisia. 相似文献
2.
Ronald I. Dorn 《地球表面变化过程与地形》1989,14(2):167-170
This note queries the discussion of the origins of ‘desert varnishes’ (Smith and Whalley, 1988), with particular reference to manganese-rich conditions. The case for a biotic model of varnish development is proposed and illustrated as opposed to the abiotic model put forward by Smith and Whalley. 相似文献
3.
Two substrate-controlled varnish types were identified from arid southeast Morocco: (1) patchy varnish interspersed with ‘silica glaze’ on silicified limestone and (2) a complete varnish cover on partially-silicified limestone. Electron probe microanalysis was used in conjunction with scanning electron microscopy to investigate their chemical composition. In both instances, varnishes are predominantly silica and iron-rich with localized concentrations of manganese. Inorganic fixation of iron and manganese is the preferred explanation, with manganese and iron derived predominantly from external sources—possibly wind-blown dust. Some iron and silica may also be derived by outward migration from within the substrate, particularly on partially silicified limestone. 相似文献
4.
Manganiferous rock varnish, silica glaze and iron skins have formed on 20- to 40-year-old slag piles near Fontana, southern California. Rapid rock-varnish formation is associated with an unidentified cocci bacterium that grows rapidly in culturing experiments, combined with the likelihood that Mn-rich solutions flow over slag surfaces. A new model is proposed for the formation of silica glaze, involving soluble Al-Si complexes and the nature of wetting films. Iron skins occur where runoff is concentrated, and where iron bacteria grow. Observations indicate: (i) substrate can be important in supplying Mn, as well as maintaining a stable surface and channelling runoff to microspots where varnish grows; (ii) ignorance of boundary layer pH/Eh conditions makes chemical-physical models of varnish formation speculative; (iii) the balance between cementation of recently nucleated varnishes and erosional shear stresses is poorly understood, but is probably an important limiting factor on varnish growth rates; and (iv) there must be at least two steps in biotic varnishing-accretion of Mn-Fe in casts, followed by cementation of clays by either in situ cast residue or Mn-Fe remobilized from casts. Varnish accretion may be limited by the rate at which both steps occur. Rapid development of readily distinguishable manganiferous rock varnishes at this post-1952 site highlights the danger of speculation on the ages of landforms based solely on the appearance of rock-varnish coatings. 相似文献
5.
Peter A. Rigotti 《Earth and Planetary Science Letters》1978,39(3):417-426
A new method has been developed for recovering paleointensities from igneous rocks which requires only a single heating to the Curie temperature, utilizing partial ARM acquisition measurements before and after the heating to carefully separate distortions of the coercivity spectrum, caused by the heating, from viscous components present in the natural remanence. In addition, the changes in the partial ARM curves may be used to correct to some extent for chemical alterations that occur during the heating. As a result, the method allows one to use a number of samples for paleointensities that would normally be rejected by the Thellier-Thellier method, especially those contaminated by strong viscous overprints. The key to this process is the high sensitivity to changes in the TRM and ARM acquisition spectrum (and hence the coercivity spectrum) of partial ARM acquisition curves, which may be obtained at room temperature.Paleointensity results from recent historic Hawaiian lava flows have demonstrated the reliability of the ARM correction method. 相似文献
6.
本文以三层电剖面模型计算出由于电剖面参数变化而引起的视电阻率变化,进而说明因地下水位变化所引起的视电阻率变化是可能估计的。根据这个结果能够确定出由于地下水干扰所引起的视电阻率异常幅度,这将有利于视电阻率变化与地震关系的定性、定量分析研究。实际工作表明,视电阻率变化很复杂,许多因素都会使视电阻率发生变化,但水的影响很重要,因此,研究这个问题有重要意义。 相似文献
7.
本文分析了简化模型下声波测井时裸眼井（内充流体一般是泥浆）中弹性波的传播,此波场可看成是轴向传播有不同波矢的分波的叠加。分析表明,对于井外只有单一均匀岩层且无限深的井,仅对如（18）式所示的特征频率成分才存在具有轴向传播最大相速度vzm=c2的所谓“首波”;而vx > c2及c2 > vz>b2的分波却不存在,此处c2和b2分别是井外岩层的纵波和横波速度。这正解释了文献[3]中所报道的裸眼井的“过滤效应”。分析还表明,对于井外具有多层岩层的井,只在一定条件下才存在与上述特性相近的“首波”。本文结果对声速测井显然是重要的。 相似文献
8.
数学形态学是一门新兴科学,它建立在严格的数学理论基础之上,是研究数字信号（图像）形态结构特征及其快速并行处理方法的理论,已经成功应用于图像处理、医学信号处理和语音信号处理等领域.地震信号去噪处理和裂缝检测的研究一直都是地质学家和油气藏工程学家感兴趣的问题.本文将数学形态学与地震信号处理相结合,重点探讨了数学形态学在地震信号处理中的应用,针对地震信号的特点,设计了形态滤波器,应用于合成地震资料,得到了理想的结果.在此基础上,本文研究并构造了形态学边缘检测算子,通过理论和实际资料检验,该方法具有良好适用性.以上研究表明,基于形态学的地震信号处理是可行的,具有推广应用前景. 相似文献
9.
J.S. Young 《Marine pollution bulletin》1973,4(5):70-73
A kill of lobsters around wrecks off the New Jersey coast seem not to be a direct result of pollution but may have been due to an influx of water causing reduced oxygen levels combined with high temperatures. Mortalities of this kind have been observed before in the area but it is not known if this is an annual event or due to abnormal circumstances. It would be worth keeping the situation under review in the future. 相似文献
10.
James R. Allen 《地球表面变化过程与地形》1981,6(2):139-150
Many of the world's beaches have recently been eroding, even on progradational landforms. This study uses the sediment budget approach to identify and rank the causes of the hazard along Sandy Hook spit where the primary recreational beach has been eroding at about 10 m/yr since 1953 and 23 m/yr in the 1970s. Large spatial variations in longshore sediment transport are found to result from differences in refracted wave energies and intersegmental sediment transport. Erosion results from a 60 per cent deficit (-270,000 m3/yr) in the sediment budget that is primarily caused by (1) refraction induced locally high waves that increase the transport rate by 100,000 m3, and (2) shore protection structures that have lessened the longshore sediment inputs by an additional 100,000 m3/yr. A storm index is presented to analyse secular climatic variation. It suggests that the annual sediment transport rate may vary by as much as ±50 per cent about the mean and that recently, above normal storm wave energies are responsible for about 60,000 m3/yr of the budget deficit. Rising sea levels and storm overwash each account for only about one per cent of the sediment loss. Pulses of sediment, induced by accelerated erosion at the feeder beach locale of spit segments, are found to move downdrift. They alter the geomorphology of the spit through episodic extensions of the spit segments with lag times exceeding one year per segment. 相似文献
11.
A detailed gravity survey over the Chattolanee Baltimore Gneiss Dome in the Maryland Piedmont suggests that the dome is an arched recumbent fold. The Baltimore Gneiss, which cores the dome, has a negative density contrast with the surrounding Cambro-Ordovician marbles and schists and is coincident with a large minimum in the simple Bouguer gravity. Three north-south profiles, which cut across the east-west-trending surface exposure of the dome were modeled two-dimensionally. The models suggest that the Baltimore Gneiss is thickest and tightly folded in an inverted V shape to the east and thinner and broadly arched to the west. It is also possible to fit the gravity data with a mushroom-shaped body at the easternmost profile, which could suggest a diapiric origin for the dome, but this interpretation is not favored based on geological arguments. The Baltimore Mafic Complex, located to the south of the Chattolanee Dome, can be modeled as an approximately 1 km thick slab with a subhorizontal base, suggesting that it is a thrust sheet. By analogy with the Phoenix Baltimore Gneiss Dome, mapped by Crowley [2], the Cambro-Ordovician sediments surrounding the Chattolanee Dome may also be involved in the recumbent folding which would suggest that the dome was formed during the Ordovician Taconic orogeny. 相似文献
12.
J. C. Correnza G. L. Hutchinson
A. M. Chandler
《Soil Dynamics and Earthquake Engineering》1992,11(8):465-484This paper reviews the various forms of reference model adopted for studies that evaluate inelastic seismic torsional effects and assess their implications for building design. Both qualitative and quantitative comparisons are presented. The importance of selecting an appropriate reference model is in accordance with the above aims is emphasised. It is found that variations in the reference models adopted in analyses of inelastic seismic torsional effects may lead to significant differences in the results obtained and, hence, to the conclusions drawn from such studies. It is demonstrated that accidental torsional effects, as incorporated in code design provisions, result in significant changes to the distribution of element strengths and the inelastic response behaviour of symmetric and generalised torsionally balanced reference models. Such changes should be considered when employing such models to evaluate the ineslatic response of torsionally unbalanced building systems. 相似文献
13.
14.
本文发展了一种加权平均方法，用于综合考虑地震危险性分析中的专家意见。其中假定接近综合结果的专家意见具有的权系数较大，这样可以合理反映专家意见的一致性与差异性，另外，利用随机加权方法估计综合结果及权系数的不确定性，给出其统计特征量。 相似文献
15.
North Menan Butte is a tuff cone near Idaho Falls, Idaho. It is a result of the eruption of basaltic magma through shallow water-saturated river alluvium of the Snake River. The cone is characterized by primary fractures that can be classified into four groups on the basis of their physical properties and their orientations relative to the symmetry elements of the cone. Type I fractures are short, closely spaced and usually confined to individual beds. They strike approximately at right angles to cone radii and always dip toward the rim of the tuff cone. Bed segments separated by these fractures have undergone rotation, resulting in normal displacements. Type II fractures have similar attitudes but are more continuous, less frequent, and show no shear displacement. Type III fractures also strike at right angles to cone radii, but they dip away from the cone rim. They cut across several beds and reveal inconsistent senses of shear displacement. Type IV fractures are radial, steeply dipping and tend to be the most continuous of all fracture types. Type I fractures were the earliest to develop; age relationships otherwise are uncertain. Examples of all four types of fractures are exposed on the inner and outer eroded slopes of the cone.Evidence from the cone indicates that the fractures developed in an unconsolidated aggregate of tuff with low cohesion; therefore, analysis of fracture genesis should be constrained by principles of soil mechanics. Type I fractures originated as tension fractures related to early downslope mass movement. Later movement on Type I fractures accompanied the development of Type III shear fractures and possible bedding plane displacements, all caused by overloading the crest of the cone by late-stage eruptive products. The origin of Type II fractures is unknown; shrinkage due to desiccation or large-scale creep are possible explanations. The radial Type IV fractures may be a consequence of desiccation shrinkage or possibly of subcone processes such as magma doming or radial hydraulic fracturing. 相似文献
16.
Summary It is shown that non-divergent vortices may induce, as a result of the resonance effect, a rapid surface development. 相似文献
17.
18.
一、前言观测表明,在地壳形变区域中,如果发生一次较大的地震,那么由主震所激发而与主震有关的余震便立即进行活动,余震释放能量的总和与主震释放能量的比值,取决于地震序列活动的类型、根据我国境内6.0级以上地震统计的研究,大致分为下列几种类型。1.孤立型这种类型的地震序列活动,其能量基本上通过主震一次释放;前震和余震能 相似文献
19.
运用CAP方法反演2018年9月4日新疆伽师MS5.5地震及MS≥3.0余震的震源机制解,计算得出伽师MS5.5地震的震源机制解为:节面Ⅰ:走向48°,倾角83°,滑动角3°;节面Ⅱ:走向318°,倾角87°,滑动角173°;主压应力P轴方位角为3°,倾角为3°,主张应力T轴方位角273°,倾角为7°;矩震级为MW5.3。使用双差定位法对主震及余震共计129个MS≥1.5地震进行重新定位,并对震源机制解和重定位结果进行综合分析,发现此次重定位地震结果与CAP方法反演结果的展布方向一致,地震集中分布在NEE向,因此认为节面I是此次地震的主破裂面;重定位后NS、EW和UD方向的平均相对误差分别为0.25、0.23及0.09 km,平均走时残差为0.026 s,震源深度集中分布在5~15 km。此次地震及其余震附近地表无明显的断层出露,所以初步判定2018年新疆伽师MS5.5地震可能受控于柯坪断裂带附近的隐伏断裂。 相似文献
20.
W. H. Ward 《水文科学杂志》2013,58(1):85-101
AbstractA new method is presented to generate stationary multi-site hydrological time series. The proposed method can handle flexible time-step length, and it can be applied to both continuous and intermittent input series. The algorithm is a departure from standard decomposition models and the Box-Jenkins approach. It relies instead on the recent advances in statistical science that deal with generation of correlated random variables with arbitrary statistical distribution functions. The proposed method has been tested on 11 historic weekly input series, of which the first seven contain flow data and the last four have precipitation data. The article contains an extensive review of the results.Editor D. KoutsoyiannisCitation Ilich, N., 2014. An effective three-step algorithm for multi-site generation of stochastic weekly hydrological time series. Hydrological Sciences Journal, 59 (1), 85–98. 相似文献