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31.
The crucial role of stone pavements in arid environments for aeolian or alluvial processes and as numerical dating tools is increasingly acknowledged. This role is based on the assumption that stone pavements are stable landforms, formed gradually over time and predominantly by vertical processes. However, this is challenged by evidence of stone‐pavement clast reworking or burial. Bimodal, mostly slope aspect‐symmetrical clast orientation is a frequent phenomenon in various study areas. It implies that stone pavements may be influenced by unidirectional lateral processes besides vertical ones. Here, the finding of lateral processes contributing to stone‐pavement evolution is supported by numerical modelling and physical experiments. These unequivocally show that unconcentrated overland flow can transport clasts to form a closely packed stone mosaic with characteristics similar to those of natural stone pavements. The commonly observed length‐axes orientation angle of 40 ± 14° for natural stone‐pavement clasts is consistently reproduced by angle‐dependent force equilibrium. Monte Carlo runs confirm the natural scatter and allow characterization of the control parameters of clast orientation. The model explains up to 70% of the natural variance. It is further validated by flume experiments, which confirm model predictions of single object orientation angles. Experiments with multiple objects yield artificial stone pavements with properties similar to those found in the field. The unidirectional lateral process acting on natural stone pavements requires the presence of a vesicular horizon. This underlines the tight genetic coupling of this common epipedon feature and the clast cover. The presented findings highlight the role of stone pavements as process and environment proxies. However, stone pavements represent information since the last surface disturbance only. This has to be considered when using them as age indicators. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
32.
Physics of seasonally ice-covered lakes: a review 总被引：2，自引：0，他引：2
33.
This paper gives an overview of the published literature on laboratory testing of the stress dependence of rock-permeability.
Additionally results of personal research on the stress dependence of the permeability of a low-porosity sandstone are presented.
Stress-dependent permeability is examined in the laboratory under different stress fields and stress paths, depending on the
intended application of the research. The most commonly applied stress paths are hydrostatic compression, triaxial compression,
uniaxial strain conditions, and testing under a constant stress path. The published results of several studies on different
rock types under one or more of the mentioned stress conditions are described and compared.
A general trend of permeability evolution under hydrostatic and triaxial conditions can be established for sandstones and
some crystalline rocks such as granite or rocksalt. For uniaxial strain tests and stress path tests the published results
are limited to a few rock types (mainly sandstones). Therefore, a general conclusion for the stress dependence of permeability
under these conditions is not possible.
Electronic Publication 相似文献
34.
Juliane Kasten 《Limnologica》2003,33(2):99-111
The flood plains of the Lower Odra are inundated in winter and spring and are desiccated in summer and autumn. Phytoplankton composition as well as its seasonal succession in permanent oxbows and separate lakes were investigated between 1993 and 1996. Solitary centric diatoms were the characteristic phytoplankton taxa of these flood plain waters. They dominated the main channel non-seasonally, the flood plains during the entire inundation phase and long periods of the isolation phase. Only during long phases of low mixing (maximal 1.5-2 months in summer) separate water bodies were dominated by Cyano- and/or Dinophyceae. This special feature of the Lower Odra Valley is explained by the Inundation-Isolation-Model of phytoplankton development influenced by inundation. Out of a high diverse algal spectrum of 495 taxa, specialities such as 9 endangered taxa and 6 halophilous taxa were discussed. Additionally, taxon specific cell-volumes and maxima of biovolumes were given. 相似文献
35.
Olga-Joan Ktenidou Zafeiria Roumelioti Norman Abrahamson Fabrice Cotton Kyriazis Pitilakis Fabrice Hollender 《Bulletin of Earthquake Engineering》2018,16(6):2311-2336
Accelerometric data from the well-studied valley EUROSEISTEST are used to investigate ground motion uncertainty and variability. We define a simple local ground motion prediction equation (GMPE) and investigate changes in standard deviation (σ) and its components, the between-event variability (τ) and within-event variability (φ). Improving seismological metadata significantly reduces τ (30–50%), which in turn reduces the total σ. Improving site information reduces the systematic site-to-site variability, φ S2S (20–30%), in turn reducing φ, and ultimately, σ. Our values of standard deviations are lower than global values from literature, and closer to path-specific than site-specific values. However, our data have insufficient azimuthal coverage for single-path analysis. Certain stations have higher ground-motion variability, possibly due to topography, basin edge or downgoing wave effects. Sensitivity checks show that 3 recordings per event is a sufficient data selection criterion, however, one of the dataset’s advantages is the large number of recordings per station (9–90) that yields good site term estimates. We examine uncertainty components binning our data with magnitude from 0.01 to 2 s; at smaller magnitudes, τ decreases and φ SS increases, possibly due to κ and source-site trade-offs Finally, we investigate the alternative approach of computing φ SS using existing GMPEs instead of creating an ad hoc local GMPE. This is important where data are insufficient to create one, or when site-specific PSHA is performed. We show that global GMPEs may still capture φ SS , provided that: (1) the magnitude scaling errors are accommodated by the event terms; (2) there are no distance scaling errors (use of a regionally applicable model). Site terms (φ S2S ) computed by different global GMPEs (using different site-proxies) vary significantly, especially for hard-rock sites. This indicates that GMPEs may be poorly constrained where they are sometimes most needed, i.e., for hard rock. 相似文献
36.
Monitoring CO2 saturation using time‐lapse amplitude versus offset analysis of 3D seismic data from the Ketzin CO2 storage pilot site,Germany 
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下载免费PDF全文 Monika Ivandic Peter Bergmann Juliane Kummerow Fei Huang Christopher Juhlin Stefan Lueth 《Geophysical Prospecting》2018,66(8):1568-1585
The injection of CO2 at the Ketzin pilot site commenced in June 2008 and was terminated in August 2013 after 67 kT had been injected into a saline formation at a depth of 630–650 m. As part of the site monitoring program, four 3D surface seismic surveys have been acquired to date, one baseline and three repeats, of which two were conducted during the injection period, and one during the post‐injection phase. The surveys have provided the most comprehensive images of the spreading CO2 plume within the reservoir layer. Both petrophysical experiments on core samples from the Ketzin reservoir and spectral decomposition of the 3D time‐lapse seismic data show that the reservoir pore pressure change due to CO2 injection has a rather minor impact on the seismic amplitudes. Therefore, the observed amplitude anomaly is interpreted to be mainly due to CO2 saturation. In this study, amplitude versus offset analysis has been applied to investigate the amplitude versus offset response from the top of the sandstone reservoir during the injection and post‐injection phases, and utilize it to obtain a more quantitative assessment of the CO2 gaseous saturation changes. Based on the amplitude versus offset modelling, a prominent decrease in the intercept values imaged at the top of the reservoir around the injection well is indeed associated solely with the CO2 saturation increase. Any change in the gradient values, which would, in case it was positive, be the only signature induced by the reservoir pressure variations, has not been observed. The amplitude versus offset intercept change is, therefore, entirely ascribed to CO2 saturation and used for its quantitative assessment. The estimated CO2 saturation values around the injection area in the range of 40%–60% are similar to those obtained earlier from pulsed neutron‐gamma logging. The highest values of 80% are found in the second seismic repeat in close vicinity to the injection and observation wells. 相似文献
37.
Ocean Dynamics - Many ports and navigation channels around the world suffer from silting and the presence of fluid mud layers, which can cause reductions in nautical depth. In this context, the... 相似文献
38.
Allan H. TREIMAN Amy K. MALOY Charles K. SHEARER Jr. Juliane GROSS 《Meteoritics & planetary science》2010,45(2):163-180
Abstract– Fragments of magnesian anorthositic granulite are found in the lunar highlands meteorites Allan Hills (ALH) A81005 and Dhofar (Dho) 309. Five analyzed clasts of meteoritic magnesian anorthositic granulite have Mg′ [molar Mg/(Mg + Fe)] = 81–87; FeO ≈ 5% wt; Al2O3 ≈ 22% wt; rare earth elements abundances ≈ 0.5–2 × CI (except Eu ≈ 10 × CI); and low Ni and Co in a non‐chondritic ratio. The clasts have nearly identical chemical compositions, even though their host meteorites formed at different places on the Moon. These magnesian anorthositic granulites are distinct from other highlands materials in their unique combination of mineral proportions, Mg′, REE abundances and patterns, Ti/Sm ratio, and Sc/Sm ratio. Their Mg′ is too high for a close relationship to ferroan anorthosites, or to have formed as flotation cumulates from the lunar magma ocean. Compositions of these magnesian anorthositic granulites cannot be modeled as mixtures of, or fractionates from, known lunar rocks. However, compositions of lunar highlands meteorites can be represented as mixtures of magnesian anorthositic granulite, ferroan anorthosite, mare basalt, and KREEP. Meteoritic magnesian anorthositic granulite is a good candidate for the magnesian highlands component inferred from Apollo highland impactites: magnesian, feldspathic, and REE‐poor. Bulk compositions of meteorite magnesian anorthositic granulites are comparable to those inferred for parts of the lunar farside (the Feldspathic Highlands Terrane): ～4.5 wt% FeO; ～28 wt% Al2O3; and Th <1 ppm. Thus, magnesian anorthositic granulite may be a widespread and abundant component of the lunar highlands. 相似文献
39.
Arya Udry Zoë E. Wilbur Rachel R. Rahib Francis M. McCubbin Kathleen E. Vander Kaaden Timothy J. McCoy Karen Ziegler Juliane Gross Christopher DeFelice Logan Combs Brent D. Turrin 《Meteoritics & planetary science》2019,54(4):785-810
We present petrologic and isotopic data on Northwest Africa (NWA) 4799, NWA 7809, NWA 7214, and NWA 11071 meteorites, which were previously classified as aubrites. These four meteorites contain between 31 and 56 vol% of equigranular, nearly endmember enstatite, Fe,Ni metal, plagioclase, terrestrial alteration products, and sulfides, such as troilite, niningerite, daubréelite, oldhamite, and caswellsilverite. The equigranular texture of the enstatite and the presence of the metal surrounding enstatite indicate that these rocks were not formed through igneous processes like the aubrites, but rather by impact processes. In addition, the presence of pre‐terrestrially weathered metal (7.1–14 vol%), undifferentiated modal abundances compared to enstatite chondrites, presence of graphite, absence of diopside and forsterite, low Ti in troilite, and high Si in Fe,Ni metals suggest that these rocks formed through impact melting on chondritic and not aubritic parent bodies. Formation of these meteorites on a parent body with similar properties to the EHa enstatite chondrite parent body is suggested by their mineralogy. These parent bodies have undergone impact events from at least 4.5 Ga (NWA 11071) until at least 4.2 Ga (NWA 4799) according to 39Ar‐40Ar ages, indicating that this region of the solar system was heavily bombarded early in its history. By comparing NWA enstatite chondrite impact melts to Mercury, we infer that they represent imperfect petrological analogs to this planet given their high metal abundances, but they could represent important geochemical analogs for the behavior and geochemical affinities of elements on Mercury. Furthermore, the enstatite chondrite impact melts represent an important petrological analog for understanding high‐temperature processes and impact processes on Mercury, due to their similar mineralogies, Fe‐metal‐rich and FeO‐poor silicate abundances, and low oxygen fugacity. 相似文献
40.
A grain of light‐blue sulfate material was reported in the lunar highlands regolith meteorite PCA 02007 (Satterwhite and Righter 2013). Allocated grains of that material are, in fact, aluminosilicate glass with a chemical composition like that of the bulk meteorite and other lunar highlands regoliths. The calcium sulfate detected in PCA 02007 was likely a surface coating, and reasonably of Antarctic (not lunar) origin. 相似文献