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1.
Microstructural observations on natural syntectonic fibrous veins: implications for the growth process 总被引：3，自引：0，他引：3
Syntectonic antitaxial and ataxial fibrous veins were investigated using SEM, microprobe, cathodoluminescence (CL) and optical microscopy. In antitaxial calcite veins, fibres and surrounding selvage grew simultaneously, with similar growth rates of crystallographically differently oriented grains. New material precipitated at the vein margin in antitaxial and bi-mineralic ataxial microstructures. Bridges of country rock material formed during vein growth in an initial en-echelon vein system. In our antitaxial and bi-mineralic ataxial samples, the spacing of solid inclusions does not reflect individual crack-seal openings. 相似文献
2.
The aim of this study is to recognize the basic clastic rock types on the basis of Hounsfield Units (HUs) by using statistical methods (hypothesis tests, distribution fitting, and confidence intervals). How does this recognition depend on depositional history of samples tested? Does the numerical pattern of HUs obtained from small-scale analyzing of some particular sedimentary structures coincide to the textural expectations of those sedimentary structures? Are the HU values provided by the CT measurements capable of evidencing micro-cycles belonging to a particular depositional history?For testing the numerical recognition, we analyze macroscopically homogeneous argillaceous marl, siltstone and fine sandstone samples with similar depositional background, age, and degree of diagenesis. The preliminary research shows that the Hounsfield Units can identify different sedimentary rocks considerably well. There are significant differences among the confidence intervals belonging to the different rock types. However, there also have been some slight overlaps among them.For analyzing the effects of the depositional processes in case of a particular rock type, samples from channel sandstone, distributary mouth-bar, massive (structureless) sandstone from a delta-fed turbidity fan, and channel sandstone with traction carpet origin from a delta-fed turbidity fan (all coming from Pannonian basin filling series) are used. The results prove again the significant differences in the terms of both confidence intervals and distribution-types; however, some overlapping also occurs. 相似文献
3.
Robyn Pickering Jan D. Kramers Tim Partridge Janos Kodolanyi Thomas Pettke 《Quaternary Geochronology》2010,5(5):544-558
Speleothems are found in association with hominin fossil-bearing cave deposits in South Africa and can be used to provide valuable chronological constraints. Such material is generally too old for U–Th dating and, although U–Pb geochronology presents a suitable alternative, bulk U concentrations are typically too low (<0.05 μg/g) to provide useful ages. For this reason, we used a simple non-invasive beta-scanner imaging screening step to identify U-rich (≥1 μg/g) domains that could be analyzed with MC-ICP-MS techniques to provide U–Pb ages. We demonstrate the technique using samples from Sterkfontein cave that exhibit infrequent <1 cm-thick layers with U concentrations ≥1 μg/g. Relict aragonite needles are found exclusively in these U-rich layers. We analyzed material from the same flowstone suite as Walker et al. (2006) and obtained a U–Pb age of ～2.3 Ma that agrees well with their estimate of 2.24 ± 0.09 Ma. We also obtained similar U–Pb (0.164 ± 0.026 to 0.200 ± 0.052 Ma) and U–Th (0.148 ± 0.003 Ma) ages for another sample exhibiting U-rich layers. We recognize that open-system behaviour during the partial transformation of aragonite to calcite is a potential problem and argue, on the basis of geochemistry and age consistencies, that recrystallization took place rapidly after speleothem formation and did not significantly affect the U–Pb ages. 相似文献
4.
Joyce Schmatz Marc Holland Steffen Giese Wouter van der Zee Janos. L. Urai 《Journal of the Geological Society of India》2010,75(1):74-88
The aim of this study is to improve our knowledge of the processes that lead to clay smear during faulting of a layered sand-clay
sequence in an analogue sandbox model. We carefully characterized mechanical properties of the materials used by a series
of geotechnical tests. Displacement field was quantified using PIV (Particle Image Velocimetry). The model is water-saturated
to allow the deformation of wet clay and sand in one experiment comprising a sand package with a horizontal layer of clay
above a predefined rigid basement fault. The thickness and rigidity of the clay layer are the parameters varied in this study.
The model shows a range of structures that are related to competence contrast between sand and different clay types. Results
show ductile shearing of soft clay with a transition to brittle fracturing of stiff clay accompanied by the formation of rotating
clay blocks in the fault zone. Localized deformation is observed through time showing (i) the propagation of one active fault
migrating laterally through the sediment package, and (ii) the formation of a stable prism between two or more active faults
that gets progressively smaller with minor rotation of the hanging wall fault. Continuous clay smear is observed resulting
from the lateral injection of clay as well as from a reworked mixture of sand and clay. 相似文献
5.
Evaporation can be an important control on stream temperature, particularly in summer when it acts to limit daily maximum stream temperature. Evaporation from streams is usually modelled with the use of a wind function that includes empirically derived coefficients. A small number of studies derived wind functions for individual streams; the fitted parameters varied substantially among sites. In this study, stream evaporation and above-stream meteorological conditions (at 0.5 and 1.5 m above the water surface) were measured at nine mountain streams in southwestern British Columbia, Canada, covering a range of stream widths, temperatures, and riparian vegetation. Evaporation was measured on 20 site-days in total, at approximately hourly intervals, using nine floating evaporation pans distributed across the channels. The wind function was fit using mixed-effects models to account for among-stream variability in the parameters. The fixed-effects parameters were tested using leave-one-site-out cross-validation. The model based on 0.5 m measurements provided improved model performance compared to that based on 1.5 m values, with RMSE of 0.0162 and 0.0187 mm h−1, respectively, relative to a mean evaporation rate of 0.06 mm h−1. Inclusion of atmospheric stability and canopy openness as predictors improved model performance when using the 1.5 m meteorological measurements, with minimal improvement when based on 0.5 m measurements. Of the wind functions reported in the literature, two performed reasonably while five others exhibited substantial bias. 相似文献
6.
Timothy O. Lawrence Chad T. Ritter Janos Gergely 《Geotechnical and Geological Engineering》2011,29(5):919-926
Over fifty percent of our nation’s 560,000-plus bridges are obsolete or structurally deficient. To upgrade or replace these
structures would require a serious budget. In order to shorten this list of bridges and to improve their ratings, state DOTs
are investigating new repair techniques and better performance evaluation tools in order to implement the new drive to sustainability
within the infrastructure. The research presented herein focused on the evaluation of current US bridge analysis and rating
procedures for the North Carolina Department of Transportation (NCDOT). To evaluate these procedures, several bridges were
rated with commercially available software and a newly developed spreadsheet program. In parallel, the bridges were also load
tested for comparison, from which, it was concluded that the NCDOT’s bridge rating software directly follows the latest AASHTO
requirements. The experimental results, however, also proved that the bridges had significant strength reserves associated
to several factors, such as, girder/deck composite action, impact and distribution factors, material strength, and contribution
of non-structural elements. In this research, a simplified bridge testing protocol was developed from which it was concluded,
that a relatively simple instrumentation setup could be effective in the load rating of bridges through testing. The data
gathered through these instruments provide vital performance data for normal traffic conditions, as well as during extreme
loading conditions and evacuations, which could lead to less restrictive load ratings and removal of the structurally deficient
classification, yielding a more sustainable structure. 相似文献
7.
Jozsef Szilagyi Vitaly A. Zlotnik John B. Gates Janos Jozsa 《Hydrogeology Journal》2011,19(8):1503-1513
Mean annual recharge in the Sand Hills of Nebraska (USA) over the 2000?C2009 period was estimated at a 1-km spatial resolution as the difference of mean annual precipitation (P) and evapotranspiration (ET). Monthly P values came from the PRISM dataset, while monthly ET values were derived from linear transformations of the MODIS daytime land-surface temperature values into pixel ET rates with the help of ancillary atmospheric data (air temperature, humidity, and global radiation). The study area receives about 73?mm of recharge (with an error bound of ±73?mm) annually, which is about 14?±?14% of the regional mean annual P value of 533?mm. The largest recharge rates (about 200?±?85?mm or 30?±?12% of P) occur in the south-eastern part of the Sand Hills due to smoother terrain and more abundant precipitation (around 700?mm), while recharge is the smallest (about 40?±?59?mm or 10?±?14% of P) in the western part, where annual precipitation is only about 420?mm. Typically, lakes, wetlands, wet inter-dunal valleys, rivers, irrigated crops (except in the south-eastern region) and certain parts of afforested areas in the south-central portion of the study area act as discharge areas for groundwater. 相似文献
8.
Guillaume Desbois Janos L. Urai Peter A. Kukla Uwe Wollenberg Fabián Pérez-Willard Zsolt Radí Sandor Riholm 《Contributions to Mineralogy and Petrology》2012,163(1):19-31
We report observations from room temperature static recrystallization experiments (annealing times from minutes to year) of
cold-pressed, synthetic, coarse-grained, wet sodium chloride, prepared by broad ion beam polishing and SEM observations at
cryogenic temperature to observe directly the brine in grain boundaries. At all stages of annealing, the majority of the brine
in the samples is connected in 2D sections along grain boundaries. Another part of the brine is in isolated brine inclusion
arrays along grain boundaries and in brine inclusions left behind by migrating brine-filled grain boundaries. Most of these
boundaries are mobile because the aggregate is coarsening. We interpret that the boundaries without observable brine films
(<15 nm) and brine inclusion arrays are healed and immobile. Evolution of grain boundary structure involves three major processes.
First, dissolution on one side of the grain boundary and precipitation on the other side, resulting in grain boundary migration.
Second, the development of facets formed by low-index crystallographic planes of the grains bounding the grain boundary brine.
When both sides of a grain boundary are able to develop low-index facets in a thick brine film, the resulting impingement
boundary is interpreted to be immobile and may prevent the new grain from migrating into a deformed neighbor. When one side
of a faceted boundary consists of low-index crystallographic planes and the other side passively follows this faceted shape
along irrational surfaces, the boundary is mobile. Third, the healing of grain boundary brine films, producing solid–solid
grain boundaries without resolvable brine films. 相似文献
9.
Heijn W. van Gent Marc Holland Janos L. Urai Ramon Loosveld 《Journal of Structural Geology》2010,32(9):1375-1391
We present analogue models of the formation of dilatant normal faults and fractures in carbonate fault zones, using cohesive hemihydrate powder (CaSO4·½H2O). The evolution of these dilatant fault zones involves a range of processes such as fragmentation, gravity-driven breccia transport and the formation of dilatant jogs. To allow scaling to natural prototypes, extensive material characterisation was done. This showed that tensile strength and cohesion depend on the state of compaction, whereas the friction angle remains approximately constant. In our models, tensile strength of the hemihydrate increases with depth from 9 to 50 Pa, while cohesion increases from 40 to 250 Pa. We studied homogeneous and layered material sequences, using sand as a relatively weak layer and hemihydrate/graphite mixtures as a slightly stronger layer. Deformation was analyzed by time-lapse photography and Particle Image Velocimetry (PIV) to calculate the evolution of the displacement field. With PIV the initial, predominantly elastic deformation and progressive localization of deformation are observed in detail. We observed near-vertical opening-mode fractures near the surface. With increasing depth, dilational shear faults were dominant, with releasing jogs forming at fault-dip variations. A transition to non-dilatant shear faults was observed near the bottom of the model. In models with mechanical stratigraphy, fault zones are more complex. The inferred stress states and strengths in different parts of the model agree with the observed transitions in the mode of deformation. 相似文献
10.
Monthly evapotranspiration (ET) rates (2000 to 2009) across Nebraska at about 1‐km resolution were obtained by linear transformations of the MODIS (MODerate resolution Imaging Spectroradiometer) daytime surface temperature values with the help of the Priestley–Taylor equation and the complementary relationship of evaporation. For positive values of the mean annual precipitation and ET differences, the mean annual net recharge was found by an additional multiplication of the power‐function‐transformed groundwater vulnerability DRASTIC‐code values. Statewide mean annual net recharge became about 29 mm (i.e., 5% of mean annual precipitation) with the largest recharge rates (in excess of 100 mm/year) found in the eastern Sand Hills and eastern Nebraska. Areas with the largest negative net recharge rates caused by declining groundwater levels due to large‐scale irrigation are found in the south‐western region of the state. Error bounds of the estimated values are within 10% to 15% of the corresponding precipitation rates and the estimated net recharge rates are sensitive to errors in the precipitation and ET values. This study largely confirms earlier base‐flow analysis‐based statewide groundwater recharge estimates when considerations are made for differences in the recharge definitions. The current approach not only provides better spatial resolution than available earlier studies for the region but also quantifies negative net recharge rates that become especially important in numerical modeling of shallow groundwater systems. 相似文献