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1.
Failure Mode and Spatial Distribution of Damage in Rothbach Sandstone in the Brittle-ductile Transition 总被引：4，自引：0，他引：4
— To elucidate the spatial complexity of damage and evolution of localized failure in the transitional regime from brittle faulting to cataclastic ductile flow in a porous sandstone, we performed a series of triaxial compression experiments on Rothbach sandstone (20% porosity). Quantitative microstructural analysis and X-ray computed tomography (CT) imaging were conducted on deformed samples. Localized failure was observed in samples at effective pressures ranging from 5 MPa to 130 MPa. In the brittle faulting regime, dilating shear bands were observed. The CT images and stereological measurements reveal the geometric complexity and spatial heterogeneity of damage in the failed samples. In the transitional regime (at effective pressures between 45 MPa and 130 MPa), compacting shear bands at high angles and compaction bands perpendicular to the maximum compression direction were observed. The laboratory results suggest that these complex localized features can be pervasive in sandstone formations, not just limited to the very porous aeolian sandstone in which they were first documented. The microstructural observations are in qualitative agreement with theoretical predictions of bifurcation analyses, except for the occurrence of compaction bands in the sample deformed at effective pressure of 130 MPa. The bifurcation analysis with the constitutive model used in this paper is nonadequate to predict compaction band formation, may be due to the neglect of bedding anisotropy of the rock and multiple yield mechanisms in the constitutive model. 相似文献
2.
This study present the result of conventional triaxial tests conducted on samples of Rothbach sandstone cored parallel, oblique (at 45 degrees) and perpendicular to the bedding at effective pressures ranging from 5 to 250 MPa. Mechanical and microstructural data were used to determine the role of the bedding on mechanical strength and failure mode. We find that samples cored at 45 degrees to the bedding yield at intermediate level of differential stress between the ones for parallel and perpendicular samples at all effective pressures. Strain localization at high confining pressure (i.e., in the compactive domain) is observed in samples perpendicular and oblique to the bedding but not in samples cored parallel to the bedding. However, porosity reduction is comparable whether compactive shear bands, compaction bands or homogeneous cataclastic flow develop. Microstructural data suggest that (1) mechanical anisotropy is controlled by a preferred intergranular contact alignment parallel to the bedding and that (2) localization of compaction is controlled by bedding laminations and grain scale heterogeneity, which both prevent the development of well localized compaction features. 相似文献
3.
Compaction and Failure in High Porosity Carbonates: Mechanical Data and Microstructural Observations
P. Baud S. Vinciguerra C. David A. Cavallo E. Walker T. Reuschlé 《Pure and Applied Geophysics》2009,166(5-7):869-898
We investigated systematically the micromechanics of compaction in two carbonates of porosity above 30%, Majella grainstone and Saint Maximin limestone. The composition, grain size and pore surface area of these rocks were determined. Hydrostatic compression experiments were performed under dry and wet conditions beyond the onset of grain crushing. A significant water weakening effect was observed in both rocks. A set of conventional triaxial experiments was also performed on both rocks under dry conditions at confining pressures ranging from 3 to 31 MPa. Microstructural observations were carried out on the deformed samples. The mechanical behavior of these high porosity carbonates is dominated by shear-enhanced compaction associated in most cases with strain hardening. Stress-induced cracking and grain crushing are the dominant micromechanisms of deformation in both rocks. In Majella grainstone, compactive shear bands appeared at low confinement, in qualitative agreement with the deformation bands observed in the field. At higher confining pressures, compaction localization was inhibited and homogeneous cataclastic flow developed. In Saint Maximin limestone, compaction localization was observed at all confining pressures. An increasing number of compactive shear bands at various orientations appeared with increasing strain. These new data suggest that compaction localization is important in the mechanical compaction of high porosity carbonates. 相似文献
4.
M. Fadavi A. Verveer J. Aymon D. Merlin K. Situ C. Pennypackker J. D. Biggs G. White A. Gould G. Greenberg V. Hoette K. McCarron K. Archer F. Pino M. Hibbs M. Ford J. Wetsch 《Astronomische Nachrichten》2006,327(8):811-813
The Pilot Small Telescope Network (PSTN) is a state‐of the art system of easily replicable and scalable hardware, software, servers, eXtensible Markup Language (XML) protocols, and network middleware connecting and developing a pilot array of robotic telescopes to one another and the user community. The PSTN is a developmental project that will allow growing access to these telescopes, and make available data to faculty, students and others in an environment of collaboration. The underlying goal of the PSTN is to broaden the quantity and quality of astronomical education and research, particularly with a focus on traditionally underserved populations. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
5.
Permian-Triassic of the Tethys: Carbon isotope studies 总被引：19，自引：0，他引：19
Aymon Baud Mordeckai Magaritz William T. Holser 《International Journal of Earth Sciences》1989,78(2):649-677
Profiles of carbon isotopes were studied in marine limestones of Late Permian and Early Triassic age of the Tethyan region from 20 sections in Yugoslavia, Greece, Turkey, Armenian SSR, Iran, Pakistan, India, Nepal, and China. The Upper Permian sections continue the high positive values of 13C previously found in Upper Permian basins in NW Europe and western USA. In the more complete sections of Tethys it can now be demonstrated that the values of 13C drop from the Murgabian to the Dzhulfian Stages of the Upper Permian, then sharply to values near zero during the last two biozones of the Dorashamian. These levels of 13C sample the Tethys Sea and the world ocean, and equal values from deep-water sediments at Salamis Greece indicate that they apply to the whole water column. We hypothesize that the high values of 13C are a consequence of Late Paleozoic storage of organic carbon, and that the declines represent an episodic cessation of this organic deposition, and partial oxidation of the organic reservoir, extending over a period of several million years. The carbon isotope profile may reflect parallel complexity in the pattern of mass extinction in Late Permian time.
Zusammenfassung Untersucht wurden Profiie von Kohlenstoff-Isotopen mariner Karbonate aus dem Oberperm und der Untertrias der Tethys-Region aus 20 Lokalitäten in Jugoslawien, Griechenland, der Türkei, der Sowjet-Republik Armenien, dem Iran, Pakistan, Indien, Nepal und China. Die oberpermischen Proben zeigen dieselben hohen positiven gd13C Werte, wie sie vorher auch aus den oberpermischen Becken NW-Europas und dem Westen der USA berichtet wurden. Anhand von vollständigeren Abschnitten der Tethys kann dargelegt werden, daß die 13C Werte von der Murgabium- bis zur Dzhulfium-Phase des Oberperms abnehmen und dann innerhalb der letzten zwei Biozonen des Dorashamiums abrupt gegen Null verlaufen. Diese 13C Niveaus sind repräsentativ für die Tethys und den Weltozean. Sie gelten außerdem für alle Wassertiefen, wie durch ähnliche Werte aus Tiefsee-Sedimenten von Salamis (Griechenland) bestätigt wird. Unsere Annahme ist, daß die hohen 13C Werte auf spätpaläozoische Speicherung organischen Kohlenstoffs zurückzuführen ist. Die Abnahme stellt episodische Sedimentationsschwankungen des organischen Materials dar, während der die organischen Substanzen über einen Zeitraum von mehreren Millionen Jahren zum Teil aufoxidiert wurden. Das Kohlenstoff-Isotop Profil entspricht parallelisiert in etwa dem Muster des Massen-Aussterbens während des Oberperms.
Résumé Des profils isotopiques du carbone ont été établis dans des calcaires marins d'âge tardi-permien à éo-triasique répartis dans 20 endroits du domaine téthysien: Yougoslavie, Grèce, Turquie, République Socialiste dArménie, Iran, Pakistan, Inde, Népal et Chine. Les profils établis dans le Permien supérieur montrent les mêmes valeurs positives de 13C observées antérieurement dans des bassins de même âge en Europe occidentale et dans l'ouest des USA. Dans les profils les plus complets de la Téthys, il est maintenant établi que les valeurs de 13C décroissent depuis le Murgabien jusqu'au Dzhulfien (Permien supérieur) pour devenir proches de zéro dans les deux dernières biozones du Dorasharmen. Ces valeurs de 13C sont caractéristiques de la Téthys et de l'Océan mondial; elles s'appliquent à toutes les profondeurs d'eau, comme en témoignent les valeurs fournies par des sédiments de mer profonde à Salamis (Grèce). Nous formulons l'hypothèse que les hautes valeurs de 13C sont la conséquence du stockage du carbone organique au Paléozoïque supérieur et que leur décroissance traduit un arrêt épisodique de cette sédimentation organique, accompagné d'une oxydation partielle de la matière organique s'étendant sur une période de plusieurs Ma. L'influence parallèle des phénomènes d'extinction massive à le fin du Permien se refléterait également dans les profils isotopiques du carbone.
, 20 /, , , , , , / . 13, - . , 13 Murgabium'a Dzhulfium'a . 13 . , , / /. , 13 . , . / , , , .相似文献
6.
Sylvie Crasquin-Soleau Sylvain Richoz Jean Marcoux Lucia Angiolini Alda Nicora Aymon Baud 《Comptes Rendus Geoscience》2002,334(7):489-495
Very few data on Early Triassic marine ostracods are available. In most of cases, the data concern the upper part of the Early Triassic. The Çürük da? section, located in the Western Taurides (Turkey), well stratigraphically constrained by conodonts and foraminifera, has been re-sampled for ostracod study. A significant fauna has been discovered in the Late Permian and the levels of the Earliest Triassic (Hindeodus parvus and Isarcicella isarcica staeschei zones). The ostracods of the basis of the Kokarkuyu Fm. are the oldest Triassic forms ever discovered. The occurrence of Palaeocopes in the earliest Triassic and similarity between the Permian and Induan assemblages suggest that the Lower Triassic Çürük da? ostracods represent a survival assemblage after the Permo-Triassic mass-extinction. To cite this article: S. Crasquin-Soleau et al., C. R. Geoscience 334 (2002) 489–495. 相似文献
7.
Jean Riotte Laurent Ruiz Stéphane Audry Benjamin Baud Jean-Pierre Bedimo Bedimo Laurie Boithias Jean-Jacques Braun Bernard Dupré Jean-Louis Duprey Mikael Faucheux Christelle Lagane Jean-Christophe Marechal Hemanth Moger Mandalagiri Subbarayappa Mohan Kumar Harshad Parate Olivier Ribolzi Emma Rochelle-Newall Buvaneshwari Sriramulu Murari Varma Muddu Sekhar 《水文研究》2021,35(5):e14196
Despite the importance of tropical ecosystems for climate regulation, biodiversity, water and nutrient cycles, only a few Critical Zone Observatories (CZOs) are located in the tropics. Among these, most are in humid climates, while very few data exist for semi-arid and sub-humid climates, due to the difficulty of estimating hydro-geochemical balances in catchments with ephemeral streams. We contribute to fill this gap by presenting a meteorological and hydro-geochemical dataset acquired at the Mule Hole catchment (4.1 km2), a pristine dry deciduous forest located in a biosphere reserve in south India. The dataset consists of time series of variables related to (i) meteorology, including rainfall, air temperature, relative humidity, wind speed and direction, and global radiation, (ii) hydrology, including water level and discharge at the catchment outlet, (iii) hydrogeology, including manual (monthly) and/or automated (from 15 min to hourly) groundwater levels in nine piezometers and (iv) geochemistry, including suspended sediment content in the stream and chemical composition of rainfall (event based), groundwater (monthly sampling) and stream water (storm events, 15 min to hourly frequency with an automatic sampler). The time series extend from 2003 to 2019. Measurement errors are minimized by frequent calibration of sensors and quality checks, both in the field and in the laboratory. Despite these precautions, several data gaps exist, due to occasional access restriction to the site and instrument destruction by wildlife. Results show that large seasonal and interannual variations of climatic conditions were reflected in the large variations of stream flow and groundwater recharge, as well as in water chemical composition. Notably, they reveal a long-term evolution of groundwater storage, suggesting hydrogeological cycles on a decadal scale. This dataset, alone or in combination with other data, has already allowed to better understand water and element cycling in tropical dry forests, and the role of forest diversity on biogeochemical cycles. As tropical ecosystems are underrepresented by Critical Zone Observatories, we expect this data note to be valuable for the global scientific community. 相似文献
8.
AbstractThe study of the exotic blocks of the Hawasina Nappes (Sultanate of Oman) leads to give apposit data that allow us to propose a new paleogeographic evolution of the Oman margin in time and space. A revised classification of exotic blocks into different paleogeographical units is presented. Two newly introduced stratigraphic groups, the Ramaq Group (Ordovician to Triassic) and the Al Buda’ah Group (upper Permian to Jurassic) are interpreted as tilted blocks related to the Oman continental margin. The Kawr Group (middle Triassic to Cretaceous) is redefined and interpreted as an atoll-type seamount. The paleogeography and paleoenvironments of these units are integrated into a new scheme of the Neotethyan rifting history. Brecciae and olistoliths of the Hawasina series are interpreted to have originated from tectonic movements affecting the Oman margin and the Neotethyan ocean floor. The breccias of late Permian age were generated by the extension processes affecting the margin, and by the creation of the Neotethyan oceanic floor. The breccias of mid-late Triassic age coincide in time with the collision of the Cimmerian continents with Eurasia. In constrast, the breccias of late Jurassic and Cretaceous age are interpreted as resulting to the creation of a new oceanic crust (Semail) off the Oman margin. 相似文献
9.
Isa Baud Monika Kuffer Karin Pfeffer Richard Sliuzas Sadasivam Karuppannan 《International Journal of Applied Earth Observation and Geoinformation》2010
Analyzing the heterogeneity in metropolitan areas of India utilizing remote sensing data can help to identify more precise patterns of sub-standard residential areas. Earlier work analyzing inequalities in Indian cities employed a constructed index of multiple deprivations (IMDs) utilizing data from the Census of India 2001 (http://censusindia.gov.in). While that index, described in an earlier paper, provided a first approach to identify heterogeneity at the citywide scale, it neither provided information on spatial variations within the geographical boundaries of the Census database, nor about physical characteristics, such as green spaces and the variation in housing density and quality. In this article, we analyze whether different types of sub-standard residential areas can be identified through remote sensing data, combined, where relevant, with ground-truthing and local knowledge. The specific questions address: (1) the extent to which types of residential sub-standard areas can be drawn from remote sensing data, based on patterns of green space, structure of layout, density of built-up areas, size of buildings and other site characteristics; (2) the spatial diversity of these residential types for selected electoral wards; and (3) the correlation between different types of sub-standard residential areas and the results of the index of multiple deprivations utilized at electoral ward level found previously. 相似文献
10.