Classification of CM chondrite breccias—Implications for the evaluation of samples from the OSIRIS‐REx and Hayabusa 2 missions     

Sarah Lentfort  Addi Bischoff  Samuel Ebert  Markus Patzek 《Meteoritics & planetary science》2021,56(1):127-147

CM chondrites are complex impact (mostly regolith) breccias, in which lithic clasts show various degrees of aqueous alteration. Here, we investigated the degree of alteration of individual clasts within 19 different CM chondrites and CM‐like clasts in three achondrites by chemical analysis of the tochilinite‐cronstedtite‐intergrowths (TCIs; formerly named “poorly characterized phases”). To identify TCIs in various chondritic lithologies, we used backscattered electron (BSE) overview images of polished thin sections, after which appropriate samples underwent electron microprobe measurements. Thus, 75 lithic clasts were classified. In general, the excellent work and specific criteria of Rubin et al. (2007) were used and considered to classify CM breccias in a similar way as ordinary chondrite breccias (e.g., CM2.2‐2.7). In BSE images, TCIs in strongly altered fragments in CM chondrites (CM2.0‐CM2.2) appear dark grayish and show a low contrast to the surrounding material (typically clastic matrix), and can be distinguished from TCIs in moderately (CM2.4‐CM2.6) or less altered fragments (CM2.7‐CM2.9); the latter are bright and have high contrast to the surroundings. We found that an accurate subclassification can be obtained by considering only the “FeO”/SiO₂ ratio of the TCI chemistry. One could also consider the TCIs’ S/SiO₂ ratio and the metal abundance, but these were not used for classification due to several disadvantages. Most of the CM chondrites are finds that have suffered terrestrial weathering in hot and cold deserts. Thus, the observed abundance of metal is susceptible to weathering and may not be a reliable indicator of subtype classification. This study proposes an extended classification scheme based on Rubin’s scale from subtypes CM2.0‐CM2.9 that takes the brecciation into account and includes the minimum to maximum degree of alteration of individual clasts. The range of aqueous alteration in CM chondrites and small spatial scale of mixing of clasts with different alteration histories will be important for interpreting returned samples from the OSIRIS‐REx and Hayabusa 2 missions in the future.  相似文献   

Experimental impact cratering: A summary of the major results of the MEMIN research unit          下载免费PDF全文

Thomas Kenkmann  Alex Deutsch  Klaus Thoma  Matthias Ebert  Michael H. Poelchau  Elmar Buhl  Eva-Regine Carl  Andreas N. Danilewsky  Georg Dresen  Anja Dufresne  Nathanaël Durr  Lars Ehm  Christian Grosse  Max Gulde  Nicole Güldemeister  Christopher Hamann  Lutz Hecht  Stefan Hiermaier  Tobias Hoerth  Astrid Kowitz  Falko Langenhorst  Bernd Lexow  Hanns-Peter Liermann  Robert Luther  Ulrich Mansfeld  Dorothee Moser  Manuel Raith  Wolf Uwe Reimold  Martin Sauer  Frank Schäfer  Ralf Thomas Schmitt  Frank Sommer  Jakob Wilk  Rebecca Winkler  Kai Wünnemann 《Meteoritics & planetary science》2018,53(8):1543-1568

This paper reviews major findings of the Multidisciplinary Experimental and Modeling Impact Crater Research Network (MEMIN). MEMIN is a consortium, funded from 2009 till 2017 by the German Research Foundation, and is aimed at investigating impact cratering processes by experimental and modeling approaches. The vision of this network has been to comprehensively quantify impact processes by conducting a strictly controlled experimental campaign at the laboratory scale, together with a multidisciplinary analytical approach. Central to MEMIN has been the use of powerful two-stage light-gas accelerators capable of producing impact craters in the decimeter size range in solid rocks that allowed detailed spatial analyses of petrophysical, structural, and geochemical changes in target rocks and ejecta. In addition, explosive setups, membrane-driven diamond anvil cells, as well as laser irradiation and split Hopkinson pressure bar technologies have been used to study the response of minerals and rocks to shock and dynamic loading as well as high-temperature conditions. We used Seeberger sandstone, Taunus quartzite, Carrara marble, and Weibern tuff as major target rock types. In concert with the experiments we conducted mesoscale numerical simulations of shock wave propagation in heterogeneous rocks resolving the complex response of grains and pores to compressive, shear, and tensile loading and macroscale modeling of crater formation and fracturing. Major results comprise (1) projectile–target interaction, (2) various aspects of shock metamorphism with special focus on low shock pressures and effects of target porosity and water saturation, (3) crater morphologies and cratering efficiencies in various nonporous and porous lithologies, (4) in situ target damage, (5) ejecta dynamics, and (6) geophysical survey of experimental craters.  相似文献   

A multi‐storage groundwater concept for the SWAT model to emphasize nonlinear groundwater dynamics in lowland catchments          下载免费PDF全文

Matthias Pfannerstill  Björn Guse  Nicola Fohrer 《水文研究》2014,28(22):5599-5612

Hydrological models are useful tools to analyze present and future conditions of water quantity and quality. The integrated modelling of water and nutrients needs an adequate representation of the different discharge components. In common with many lowlands, groundwater contribution to the discharge in the North German lowlands is a key factor for a reasonable representation of the water balance, especially in low flow periods. Several studies revealed that the widely used Soil and Water Assessment Tool (SWAT) model performs poorly for low flow periods. This paper deals with the extension of the groundwater module of the SWAT model to enhance low flow representation. The current two‐storage concept of SWAT was further developed to a three‐storage concept. This was realized due to modification of the groundwater module by splitting the active groundwater storage into a fast and a slow contributing aquifer. The results of this study show that the groundwater module with three storages leads to a good prediction of the overall discharge especially for the recession limbs and the low flow periods. The improved performance is reflected in the signature measures for the mid‐segment (percent bias ?2.4% vs ?15.9%) and the low segment (percent bias 14.8% vs 46.8%) of the flow duration curve. The three‐storage groundwater module is more process oriented than the original version due to the introduction of a fast and a slow groundwater flow component. The three‐storage version includes a modular approach, because groundwater storages can be activated or deactivated independently for subbasin and hydrological response unit level. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Tailoring spatial reference in early warning systems to administrative units     

Matthias Lendholt 《Earth Science Informatics》2011,4(1):7-16

This paper presents a novel approach for early warning systems to transform the spatial reference of dispersion models into addressable administrative units enabling an intelligible warning message reception and spatial awareness. The spatial reference along the entire information chain from sensor measurements via dispersion model to warning dissemination is discussed. Core concept behind this approach is the application of the Egenhofer-Model for analysis of binary topologic relations. It is used to identify topologic relations between dispersion model forecasts and administrative units. The result set of intersection matrices defines the relations that are counted for area classification with hazard specific parameters. Following the design for a generic and hazard-independent web service based on Open Geospatial Consortium (OGC) standards is presented in combination with results of the reference implementation.  相似文献   

Contextual factors influencing sustainable fisheries in Mexico     

Alejandro Espinoza-Tenorio  Ileana Espejel  Matthias Wolff  José Alberto Zepeda-Domínguez 《Marine Policy》2011

Sustainable fisheries take into consideration that managed fisheries ecosystems shift over time in response to evolving environmental as well as market and political factors. These contextual forces are especially valuable in understanding developing countries such as Mexico, where the unconsolidated fisheries administration faces productive marine ecosystems but unsustainable fisheries. To recognize the issues that have inhibited the consolidation of a regulatory system for sustainable fisheries, a contextual factor analysis was applied to the co-development of two current policies in the Mexican fishery regime: fisheries and environmental policies. Six historical phases have been identified in which there are few long periods of stability and frequent short periods of radical change that alternate between stable and adverse contextual situations. These short and contrasting contextual situations cause a kind of tug-of-war in Mexican fisheries policy-making. On the one hand, domestic economic, scientific, and technological forces seem to slowly lead toward the consolidation of sustainable fisheries; on the other hand, domestic policies drift from one position to another at other timing than the international fisheries and environmental policies. Although recent crises seem to highlight new periods of radical change in Mexico, they also provide an opportunity to adopt new structural plans to consolidate domestic forces as a basis for long-term strategies.  相似文献   

The structural vulnerability in the framework of natural hazard risk analyses and the exemplary application for storm loss modelling in Tyrol (Austria)     

Matthias Huttenlau  Johann Stötter 《Natural Hazards》2011,58(2):705-729

In the context of natural hazard-related risk analyses, different concepts and comprehensions of the term risk exist. These differences are mostly subjected to the perceptions and historical backgrounds of the different scientific disciplines and results in a multitude of methodological concepts to analyse risk. The target-oriented selection and application of these concepts depend on the specific research object which is generally closely connected to the stakeholders’ interests. An obvious characteristic of the different conceptualizations is the immanent various comprehensions of vulnerability. As risk analyses from a natural scientific-technical background aim at estimating potential expositions and consequences of natural hazard events, the results can provide an appropriate decision basis for risk management strategies. Thereby, beside the preferably addressed gravitative and hydrological hazards, seismo-tectonical and especially meteorological hazard processes have been rarely considered within multi-risk analyses in an Alpine context. Hence, their comparative grading in an overall context of natural hazard risks is not quantitatively possible. The present paper focuses on both (1) the different concepts of the natural hazard risk and especially their specific expressions in the context of vulnerability and (2) the exemplary application of the natural scientific-technical risk concepts to analyse potential extreme storm losses in the Austrian Province of Tyrol. Following the corresponding general risk concept, the case study first defines the hazard potential, second estimates the exposures and damage potentials on the basis of an existing database of the stock of elements and values, and third analyses the so-called Extreme Scenario Losses (ESL) considering the structural vulnerability of the potentially affected elements at risk. Thereby, it can be shown that extreme storm events can induce losses solely to buildings and inventory in the range of EUR 100–150 million in Tyrol. However, in an overall context of potential extreme natural hazard events, the storm risk can be classified with a moderate risk potential in this province.  相似文献   

IFKIS-Hydro: an early warning and information system for floods and debris flows     

Hans Romang  Massimiliano Zappa  Nadine Hilker  Matthias Gerber  François Dufour  Valérie Frede  Dominique Bérod  Matthias Oplatka  Christoph Hegg  Jakob Rhyner 《Natural Hazards》2011,56(2):509-527

IFKIS-Hydro is an information and warning system for hydrological hazards in small- and medium-scale catchments. The system collects data such as weather forecasts, precipitation measurements, water level gauges, discharge simulations and local observations of event-specific phenomena. In addition, IFKIS-Hydro incorporates a web-based information platform, which serves as a central hub for the submission and overview of data. Special emphasis is given to local information. This is accomplished particularly by human observers. In medium-scale catchments, discharge forecast models have an increasing importance in providing valuable information. IFKIS-Hydro was developed in several test regions in Switzerland and the first results of its application are available now. The system is constantly extended to additional regions and may become the standard for warning systems in smaller catchments in Switzerland.  相似文献   

Coherent structures and flux contribution over an inhomogeneously irrigated cotton field     

Yu Zhang  Heping Liu  Thomas Foken  Quinton L. Williams  Matthias Mauder  Christoph Thomas 《Theoretical and Applied Climatology》2011,103(1-2):119-131

The turbulence data measured at two levels (i.e., 8.7 and 2.7?m) in the Energy Balance Experiment (EBEX), which was conducted in San Joaquin Valley in California during the period from July 20 to August 24, 2000, are used to study the characteristics of coherent structures over an irrigated cotton field. Patch-to-patch irrigation in the field generated the dry-to-wet horizontal advection and the oasis effects, leading to the development of a stably internal boundary layer (SIBL) in the late mornings or the early afternoons. The SIBL persisted in the rest of the afternoons. Under this circumstance, a near-neutral atmospheric surface layer (ASL) developed during the period with a stratification transition from the unstable to stable conditions during the daytime. Therefore, EBEX provides us with unique datasets to investigate the features of coherent structures that were generated over the patches upstream and passed by our site in the unstable ASL, the near-neutral ASL, and the SIBL. We use an objective detection technique and the conditional average method that is developed based on the wavelet analysis. Our data reveal some consistencies and inconsistencies in the characteristics of coherent structures as compared with previous studies. Ramp-like structures and sweep?Cejection cycles under the daytime SIBL have similar patterns to those under the nocturnal stable ASL. However, some features (i.e., intermittence) are different from those under the nocturnal stable ASL. Under the three stratifications, thermal and mechanical factors in the ASL perform differently in affecting the ramp intensity for different quantities (i.e., velocity components, temperature, and specific humidity), leading to coherent structures that modulate turbulence flow and alter turbulent transfer differently. It is also found that coherent structures contribute about 10?C20% to the total fluxes in our case with different flux contributions under three stratifications and with higher transporting efficiency in sensible heat flux than latent heat and momentum fluxes.  相似文献   

Northwest Africa 11024—A heated and dehydrated unique carbonaceous (CM) chondrite     

Samuel Ebert  Addi Bischoff  Dennis Harries  Sarah Lentfort  Jean‐Alix Barrat  Andreas Pack  Jrme Gattacceca  Robbin Visser  Peter Schmid‐Beurmann  Stephan Kimpel 《Meteoritics & planetary science》2019,54(2):328-356

Based on the high abundance of fine‐grained material and its dark appearance, NWA 11024 was recognized as a CM chondrite, which is also confirmed by oxygen isotope measurements. But contrary to known CM chondrites, the typical phases indicating aqueous alteration (e.g., phyllosilicates, carbonates) are missing. Using multiple analytical techniques, this study reveals the differences and similarities to known CM chondrites and will discuss the possibility that NWA 11024 is the first type 3 CM chondrite. During the investigation, two texturally apparent tochilinite–cronstedtite intergrowths were identified within two thin sections. However, the former phyllosilicates were recrystallized to Fe‐rich olivine during a heating event without changing the textural appearance. A peak temperature of 400–600 °C is estimated, which is not high enough to destroy or recrystallize calcite grains. Thus, calcites were never constituents of the mineral paragenesis. Another remarkable feature of NWA 11024 is the occurrence of unknown clot‐like inclusions (UCLIs) within fine‐grained rims, which are unique in this clarity. Their density and S concentration are significantly higher than of the surrounding fine‐grained rim and UCLIs can be seen as primary objects that were not formed by secondary alteration processes inside the rims. Similarities to chondritic and cometary interplanetary dust particles suggest an ice‐rich first‐generation planetesimal for their origin. In the earliest evolution, NWA 11024 experienced the lowest degree of aqueous alteration of all known CM chondrites and subsequently, a heating event dehydrated the sample. We suggest to classify the meteorite NWA 11024 as the first type 3 CM chondrite similar to the classification of CV3 chondrites (like Allende) that could also have lost their matrix phyllosilicates by thermal dehydration.  相似文献   

Investigating suspended particulate matter in coastal waters using the fractal theory     

Chapalain  Marion  Verney  Romaric  Fettweis  Michael  Jacquet  Matthias  Le Berre  David  Le Hir  Pierre 《Ocean Dynamics》2019,69(1):59-81

Ocean Dynamics - Suspended particulate matters (SPM) in coastal waters were investigated with an approach combining suspended particulate matter concentrations (SPMCs) measured by an optical...  相似文献