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1.
Nanomechanics of organic-rich shales: the role of thermal maturity and organic matter content on texture 总被引：2，自引：2，他引：0
Despite the importance of organic-rich shales, microstructural characterization and theoretical modeling of these rocks are limited due to their highly heterogeneous microstructure, complex chemistry, and multiscale mechanical properties. One of the sources of complexity in organic-rich shales is the intricate interplay between microtextural evolution and kerogen maturity. In this study, a suite of experimental and theoretical microporomechanics methods are developed to associate the mechanical properties of organic-rich shales both to their maturity level and to the organic content at micrometer and sub-micrometer length scales. Recent results from chemomechanical characterization experiments involving grid nanoindentation and energy-dispersive X-ray spectroscopy (EDX) are used in new micromechanical models to isolate the effects of maturity levels and organic content from the inorganic solids. These models enable attribution of the role of organic maturity to the texture of the indented material, with immature systems exhibiting a matrix-inclusion morphology, while mature systems exhibit a polycrystal morphology. Application of these models to the interpretation of nanoindentation results on organic-rich shales allows us to identify unique clay mechanical properties that are consistent with molecular simulation results for illite and independent of the maturity of shale formation and total organic content. The results of this investigation contribute to the design of a multiscale model of the fundamental building blocks of organic-rich shales, which can be used for the design and validation of multiscale predictive poromechanics models. 相似文献
2.
Gurri Francisco D. Ruiz-García Wilma Molina-Rosales Dolores O. Vallejo-Nieto Mirna I. 《Natural Hazards》2019,96(1):149-171
Natural Hazards - We built an easy-to-interpret individual vulnerability index to floods that is amenable for empirical testing and may be adapted to any perceived hazard or ecological setting. An... 相似文献
3.
Comparison of Linear Regression Models for Quantitative Geochemical Analysis: An Example Using X-Ray Fluorescence Spectrometry 总被引：1，自引：0，他引：1
Mirna Guevara Surendra P. Verma Fernando Velasco-Tapia Rufino Lozano-Santa Cruz Patricia Girón 《Geostandards and Geoanalytical Research》2005,29(3):271-284
This paper presents statistical aspects related to the calibration process and a comparison of different regression approaches of relevance to almost all analytical techniques. The models for ordinary least-squares (OLS), weighted least-squares (WLS), and maximum likelihood fitting (MLF) were evaluated and, as a case study, X-ray fluorescence (XRF) calibration curves for major elements in geochemical reference materials were used. The results showed that WLS and MLF models were statistically more consistent in comparison with the usually applied OLS approach. The use of uncertainty on independent and dependent variables during the calibration process and the calculation of final uncertainty on individual results using error propagation equations are the novel aspects of our work. 相似文献
4.
Igor Brautovi&#; Natalia Bojani&#; Mirna Batisti&#; & Marina Cari&#; 《Marine Ecology》2006,27(2):124-132
Temporal variability and population structure of planktonic ostracods were investigated for the first time in the South Adriatic Sea during 1996. The maximal total ostracod abundance (1167 ind·100 m−3; 69% juveniles, 18% females and 13% males) was recorded in February. Thirteen species of marine planktonic ostracods were identified. Porroecia spinirostris and Archiconchoecia striata dominated the ostracod assemblage, accounting respectively for 62% and 18% of the total abundance. Their annual peaks were recorded during the cold season, which was the period of their intense reproduction, with favourable temperature conditions and lack of predators. The females surpassed the males in abundance in most species. The presence of the mesopelagic species indicated a strong influence of intermediate layer water masses from the Eastern Mediterranean Sea. 相似文献
5.
Abundance, Biomass, C- and N-
Content of Flaccisagitta enflata and
Mesosagitta minima (Chaetognatha)
Mirna Batisti&#; 《Marine Ecology》2003,24(1):1-13
Abstract The annual variability in abundance and biomass of Flaccisagitta enflata (Grassi, 1881) and Mesosagitta minima (Grassi, 1881), along with the C‐ and N‐content of their different maturity stages, were investigated in the South Adriatic Sea on a weekly basis throughout 1996. Increases in abundance and biomass of F. enflata [maximum 554 indiv. · (10 m3)–1 and 16.3 mg C · (10 m3)–1] and M. minima [maximum 336 indiv. · (10 m3)–1 and 3.1 mg C · (10 m3)–1] were found in summer and autumn, a time of intense reproduction for these species. Mean carbon content (as a percentage of dry weight) varied from 30.41 to 40.39 % among maturity stages for F. enflata, and from 27.73 to 39.31 % for M. minima. Nitrogen contents of both species were ～ 3 to 3.5 times less than carbon contents and varied less. Accurate estimates of chaetognath biomass as carbon should be based on the separate contribution of each maturity stage present in the total population. 相似文献
6.
Davor Lu&#;i&#; Adam Benovi&#; Mira Morovi&#; Mirna Batisti&#; & Ivona Onofri 《Marine Ecology》2009,30(1):16-32
Diel vertical migration (DVM) of medusae was investigated at a fixed station in the oligotrophic Southern Adriatic Sea at several depths during summer (July) 2003. We hypothesized that medusan DVM is considerably influenced by environmental variables such as hydrographic features, light intensities, and potential prey densities. We used short-term repetitive sampling as an approach to detail these relationships. Of the 26 species collected, the highest abundance was in the layer between the thermocline (15 m) and 100 m depth, where Rhopalonema velatum predominated, reaching the maximum count of 93 individuals per 10 m3 . Seven species were observed over a wide depth range: Solmissus albescens (15–1200 m), R. velatum (0–800 m), Persa incolorata (50–1200 m), Octophialucium funerarium (200–1200 m), Arctapodema australis (200–1200 m), Amphinema rubra (100–800 m), and Rhabdoon singulare (15–600). According to the medusan weighted mean depth (WMD) calculations, the longest DVMs were noted for the deep-sea species S. albescens , O. funerarium , and A. australis . The shallowest species, Aglaura hemistoma , was primarily non-migratory. Certain medusan assemblages were associated consistently with a particular depth layer characterized by a particular light intensity. The interplay of environmental factors and trophic relationships explains some of the features of medusan migratory patterns. These findings thus contribute to understanding the variables that determine patterns of medusan vertical migratory behavior. 相似文献
7.
We present five new discriminant function diagrams based on an extensive database representative of basic and ultrabasic rocks
from four tectonic settings of island arc, continental rift, ocean-island, and mid-ocean ridge. These diagrams were obtained
after loge-transformation of concentration ratios of major-elements — a technique recommended for a correct statistical treatment of
compositional data. Higher % success rates (overall values from ∼ 83 to 97%) were obtained for proposing these new diagrams
as compared to those (∼82 to 94%) obtained from the discriminant analysis of the raw major-element concentration data (i.e.,
without the loge-transformation and without taking ratios of the compositional data, but using exactly the same database to provide an unbiased
comparison), suggesting that such a data transformation constitutes a statistically correct and recommended technique. The
new diagrams also resulted in less mis-classification of basic and ultrabasic rocks from known tectonic settings than the
diagrams obtained from the raw data. The use of these highly successful new discriminant function diagrams is illustrated
using Miocene to Recent basic and ultrabasic rocks from three areas of Mexico with complex or controversial tectonic settings
(Mexican Volcanic Belt, Los Tuxtlas volcanic field, and Eastern Alkaline Province), as well as older rocks from three areas
(Deccan, Malani, and Bastar) of India. Additionally, the major-element data from two ‘known’ continental arc settings are
used to show that they are similar to those from the island arc setting. Continental rift setting is inferred for all Mexican
cases and for one cratonic area of India (Malani) and an IAB setting for the Bastar craton. The Deccan flood basalt province
of India is used to warn against an indiscriminate use of those discrimination diagrams that do not explicitly include the
likely setting of the area under evaluation. An Excel template is also provided for an easy application of these new diagrams
for discriminating the four settings considered in this work. 相似文献
8.
Well productivity controlling factors in crystalline terrains of southeastern Brazil 总被引：1，自引：0，他引：1
Over the last decades, increasing water demands have fostered research to obtain high well yields in crystalline terrains where, besides the intrinsic properties of rocks, the groundwater flow depends on several factors. The depth of the wells, the lithotypes, the presence and thickness of sedimentary coverings and weathered layers, the landforms, the geological structures, and the effects of tectonic stresses are among the most investigated factors considered as determinant of well productivity. The influence of these factors on productivity of wells that exploit the Crystalline Aquifer System in the Jundiaí River Catchment, southeastern Brazil, is investigated in this work. The largest region of the studied area is located on the Precambrian Basement, partially covered by sedimentary deposits. The results show that the sedimentary deposits and the weathered layer are important for high well yield, but it also depends on the existence of a net of open fractures, in order to maintain high productivity. The sites that have more possibility of occurrence of such structures are the regional shear and fault zones and other minor structures with NW–SE and E–W directions, which characterize areas subjected to transtensional stress related to the neotectonics. 相似文献
9.
Topographic stress and rock fracture: a two‐dimensional numerical model for arbitrary topography and preliminary comparison with borehole observations 
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下载免费PDF全文 Theoretical calculations indicate that elastic stresses induced by surface topography may be large enough in some landscapes to fracture rocks, which in turn could influence slope stability, erosion rates, and bedrock hydrologic properties. These calculations typically have involved idealized topographic profiles, with few direct comparisons of predicted topographic stresses and observed fractures at specific field sites. We use a numerical model to calculate the stresses induced by measured topographic profiles and compare the calculated stress field with fractures observed in shallow boreholes. The model uses a boundary element method to calculate the stress distribution beneath an arbitrary topographic profile in the presence of ambient tectonic stress. When applied to a topographic profile across the Susquehanna Shale Hills Critical Zone Observatory in central Pennsylvania, the model predicts where shear fractures would occur based on a Mohr–Coulomb criterion, with considerable differences in profiles of stresses with depth beneath ridgetops and valley floors. We calculate the minimum cohesion required to prevent shear failure, Cmin, as a proxy for the potential for fracturing or reactivation of existing fractures. We compare depth profiles of Cmin with structural analyses of image logs from four boreholes located on the valley floor, and find that fracture abundance declines sharply with depth in the uppermost 15 m of the bedrock, consistent with the modeled profile of Cmin. In contrast, Cmin increases with depth at comparable depths below ridgetops, suggesting that ridgetop fracture abundance patterns may differ if topographic stresses are indeed important. Thus, the present results are consistent with the hypothesis that topography can influence subsurface rock fracture patterns and provide a basis for further observational tests. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
10.
This work presents a comparison of relative efficiency of fourteen statistical tests to detect outliers in normally distributed samples. These tests include deviation/spread, Grubbs-type, Dixon-type, and high-order moment statistics. Performance for the statistical tests is evaluated using Geochemical Reference Material databases from the United States Geological Survey. Test efficiency is compared for the first application of statistics in version k = 1 and k = 2, as well as for tests in version k = 1 applied consecutively against block procedures in which k = 2, 3, or 4 values are evaluated at the same time. In both evaluations, the sensitivity of the statistical tests shows a general strong dependence on sample size. The best performance is observed for the block procedures compared to consecutive statistical tests affected by masking effects. 相似文献