Experimental impact cratering: A summary of the major results of the MEMIN research unit

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.     

The first galaxies: assembly, cooling and the onset of turbulence

We investigate the properties of the first galaxies at   z ≳ 10  with highly resolved numerical simulations, starting from cosmological initial conditions and taking into account all relevant primordial chemistry and cooling. A first galaxy is characterized by the onset of atomic hydrogen cooling, once the virial temperature exceeds  ≃10⁴ K  , and its ability to retain photoheated gas. We follow the complex accretion and star formation history of a  ≃5 × 10⁷ M_⊙  system by means of a detailed merger tree and derive an upper limit on the number of Population III (Pop III) stars formed prior to its assembly. We investigate the thermal and chemical evolution of infalling gas and find that partial ionization at temperatures  ≳10⁴ K  catalyses the formation of  H₂  and hydrogen deuteride, allowing the gas to cool to the temperature of the cosmic microwave background. Depending on the strength of radiative and chemical feedback, primordial star formation might be dominated by intermediate-mass Pop III stars formed during the assembly of the first galaxies. Accretion on to the nascent galaxy begins with hot accretion, where gas is accreted directly from the intergalactic medium and shock heated to the virial temperature, but is quickly accompanied by a phase of cold accretion, where the gas cools in filaments before flowing into the parent halo with high velocities. The latter drives supersonic turbulence at the centre of the galaxy and could lead to very efficient chemical mixing. The onset of turbulence in the first galaxies thus likely marks the transition to Pop II star formation.     

Hydrocarbon distribution in coals and in dispersed organic matter of different maceral compositions and maturities

More than 60 samples from 5 coal seams and adjacent siltstones and sandstones were selected from a well through Westphalian B sediments from Northern Germany in order to study bitumen generation and migration. The cores were drilled between 1200 und 1530 metres depth. In this interval, vitrinite reflectance (Rr) is increasing from 0.70 to 0.92%. Results reveal high hydrocarbon generation potentials for all coal samples, but not for adjacent clastic rocks, although maceral compositions of both are quite similar. Yields and compositions of thermal extracts from the coals depend on maceral compositions and rank. However, the bulk of the already generated bitumen has not been removed during natural coalification and is not easily releasable by thermovaporisation. A mass balance based on elemental composition of dull coals indicates that in the rather narrow rank interval (0.70–0.92% Rr) a total mass loss of 20% may have occurred by migration. This is evidenced by a loss of about 20% of the original hydrogen, the rest being stored in the coals.

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Zusammenfassung Um die Entstehung und Migration von Bitumen zu untersuchen wurden in Norddeutschland mehr als 60 Proben aus 5 Kohleflözen und benachbarten Silt- und Sandsteinen aus einer Bohrung durch Westphal B-Sedimente bearbeitet. Die Entnahmetiefe der Bohrkerne liegt zwischen 1200 und 1530 Metern. Innerhalb dieses Intervales steigt die Vitrinit-Reflexion (Rr) von 0,70 auf 0,92%. Für alle Proben aus den Flözen ergeben sich hohe Kohlenwasserstoff-Bildungspotentiale, nicht aber für die benachbarten klastischen Gesteine, obwohl die Mazeral-Zusammensetzungen in beiden ähnlich sind. Die Ausbeute und Zusammensetzung thermaler Extrakte aus den Flözen hängen von Mazeral-Zusammensetzung und Reife ab. Allerdings wurden weder während der Inkohlung größere Mengen des Bitumens abtransportiert, noch ist dieses durch Thermovaporisation leicht freisetzbar. Eine Massenbalanzierung auf der Basis der Elementzusammensetzung ergibt für das relativ schmale Interval von C,70-0,92% Rr ein Massenverlust von 20% durch Migration. Diese Angabe basiert auf einer 20%igen Reduzierung der ursprünglichen Wasserstoffmenge, wobei die restlichen 80% in der Kohle gespeichert bleiben.

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Résumé Dans un forage pratiqué à travers le Westphalien B du nord de l'Allemagne, on a sélectionné plus de 60 échantillons provenant de 5 couches de charbon ainsi que des siltites et grès adjacents, dans le but d'étudier la formation et la migration du bitume. Les carottes proviennent de profondeurs situées entre 1200 et 1530 m. Dans cet intervalle, le pouvoir réflecteur de la vitrinite (Rr) passe de 0,70 à 0,92%. L'étude révèle des potentiels élevés en hydrocarbure pour tous les échantillons de charbon, mais pas pour les roches détritiques voisines, bien que les compositions «macérales» soient analogues dans les deux cas. L'importance et la composition des extrait athermiques des charbons dépendent de la composition «macérale» et du degré d'évolution. Toutefois, la plus grande partie du bitume engendré est restée sur place au cours de la houillification naturelle et elle est difficile à extraire avex la methode de thermovaporisation. Une balance des masses d'éléments indique pour cet intervalle relativement étroit (0,7–0,92% Rr) une perte totale de masse de 20% due à la migration. Ce résultat correspond à une perte d'environ 20% de l'hydrogène originel, les 80% restants étant demeurés dans le charbon.

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60 5 , , . 1200 1530 . /Rr/ 0,7 0,92. , , . , , . , , . , , 20% 0,7 0,92 %. 20%; , 80%, .

     

Evaluation and Monitoring of Service Quality: Discussing Ways to Meet INSPIRE Requirements

Service oriented architectures (SOA) are widely used nowadays. As the name implies such architectures rely on services. Germany developed a marine‐specific service oriented data infrastructure (MDI‐DE – Marine Dateninfrastruktur Deutschland) from 2010 to 2013. The services in MDI‐DE can contribute to fulfilling reporting commitments for various European and national legislation. The services of MDI‐DE (just like other services affected, for instance, by INSPIRE) have to meet specific requirements regarding performance, availability and conformity (quality of service, QoS). Although SOA is an important field in scientific research there are very few publications and studies available on QoS, especially regarding INSPIRE requirements. The services of MDI‐DE were analyzed using various existing tools. Their usefulness to reflect where either the aspect's performance, availability or conformity needs improvement was partly verified. Due to varying results and the neglect of some services for various reasons it can be stated that the more tools are used, the more conclusive the outcome. Furthermore, service quality was not coherent when measured with different tools. This means that measuring QoS in terms of INSPIRE will be very difficult to do in the future and there is the danger that people will choose the tools with which their services perform best.     

Assimilation and diffusion during xenolith-magma interaction: a case study of the Variscan Karkonosze Granite, Bohemian Massif

Magmatic enclaves from the Rudolfov quarry near Liberec (Czech Republic) are interpreted to represent remnants of lamprophyric melt that intruded the Karkonosze granite at a stage at which the granite was not fully solidified. Based on the observation that larger enclaves are generally more circular than the smaller ones, we conclude that bigger blobs of mafic magma became more spherical during flow in the gravity field (sink or float). This flow is also interpreted to be responsible for the incorporation of mineral grains into the enclaves and may have facilitated the assimilation of granitic melt. Linear mixing trends on Harker diagrams for most network-forming and mainly slow-diffusing or fluid-immobile elements indicate such an assimilation process between granite and lamprophyre. In contrast, all fast-diffusing or fluid-mobile elements display scattered element distributions, implying that chemical diffusion also played a role. Pressure and temperature for this late magmatic stage are estimated at around 1 kbar and 500°C. These results suggest that two processes modified the composition of the enclaves in the Karkonosze granite: (1) assimilation (mechanical mixing) of granitic melt during the injection of the lamprophyric melt and the subsequent flow of the forming enclaves in the gravity field (responsible for the linear mixing trends) and (2) diffusion-controlled redistribution of elements between both solidifying rock types at the magmatic stage and/or due to late-stage magmatic fluids (responsible for the scattering and deviation from the linear mixing trends).     

The Bayesian approach to an internally consistent thermodynamic database: theory, database, and generation of phase diagrams

An internally consistent thermodynamic dataset has been derived for 148 endmember phases (145 solids and 3 fluids) comprising the elements Li, Na, K, Be, Mg, Ca, Ti, Cr, Mn, Fe, Zn, Al, Si, C, H, and O. This has been achieved by simultaneous treatment of phase property (like standard enthalpy of formation, standard entropy, molar heat capacity, molar volume, thermal expansivity, bulk modulus etc.) and reaction reversal data by the Bayesian method. The theory underlying the approach, and the computational methods involved, are briefly outlined. (For the benefit of readers unfamiliar with inference statistics, the basic concepts of the Bayes method are also presented in such a way that they can be grasped intuitively.) Although not yet addressed, this method can be extended to refine the thermodynamic mixing properties of crystalline solutions. The sources of the input data, culled from the literature, are summarized in the Appendix. The resulting database is succinctly documented in this paper. It includes the enthalpies of formation and entropies, their uncertainties, and the correlation among them. The database allows calculation of P-T, T-X _CO2, P-X _CO2, and T-f _O2 sections, with error propagation into the computed phase diagrams on a routine basis. A user-friendly computer program has been written to generate such phase diagrams. It is public domain software. The software and the thermodynamic database (which includes a complete documentation of the thermodynamic data above and beyond those listed (Table 2, here) may be downloaded from the web site http://homepage.ruhr-uni-bochum.de/niranjan.chatterjee/Index.htm. Examples of computed phase diagrams are given to illustrate the quality of the data and the capabilities of the software. Received: 11 March 1998 / Accepted: 11 June 1998     

Fifteen days of continuous activity survey at Stromboli volcano, Italy, in late September 2000: Doppler radar, seismicity, infrared, soil humidity, and mapping of the crater region

The intention of our study was to gain new insight into the complex interplay between different types of eruption of the Stromboli volcano by combining detailed field observation with different geophysical methods. We recorded more than 600 eruptions by use of continuous Doppler radar measurements. We detected the onset of the seismic precursor and the beginning of the visible eruption by use of seismic and infrared data. Two soil samples per day were used to monitor the effect of humidity on the eruptive style. We mapped the crater region as a reference base for the long-term morphological changes of the active region and for the exact positions of our measurement systems. Two distinct types of eruption were distinguished from each other on the basis of seismic and radar data - short, wide-angle Strombolian explosions and pulsating, sharp angle fountain-like eruptions. Data and visual observations imply that weather conditions significantly effect volcanic activity. We also interpret the intensification of eruptive activity during our field study as replenishment of the reservoir with a new batch of magma in late September 2000.     

Methane exchange between coal-bearing basins and the atmosphere: the Ruhr Basin and the Lower Rhine Embayment, Germany

A precise knowledge of methane exchange processes is required to fully understand the recent rise of atmospheric methane concentration. Three of these processes take place at the lithosphere/atmosphere boundary: bacterial consumption of methane and emission of bacterial or thermogenic methane. This study was initiated to quantify these processes on a regional scale in the Ruhr Basin and the Lower Rhine Embayment. Since these areas are subject to bituminous coal and lignite mining, natural and anthropogenically-induced methane exchange processes could be studied. The methane emission and consumption rates and their carbon isotope signal were measured at the lithosphere/atmosphere boundary using flux chambers. On most of the soils studied, methane consumption by bacteria was identified. Thermogenic methane was released only at some of the natural faults examined. In active and abandoned bituminous coal mining areas methane emissions were restricted to small areas, where high emission rates were measured. The carbon isotope composition of methane at natural faults and in mining subsidence troughs was typical of thermogenic methane (−45 to −32 ‰ δ¹³C). Methane exchange balancing revealed that natural methane emissions from these two basins represent no source of atmospheric importance. However, methane release by upcast mining shafts dominates the methane exchange processes and is by about two orders of magnitude greater than methane consumption by bacterial oxidation in the soils.     

Node-centered finite volume discretizations for the numerical simulation of multiphase flow in heterogeneous porous media

Three node-centered finite volume discretizations for multiphase porous media flow are presented and compared. By combination of these methods two additional discretization methods are generated. The ability of these schemes to describe flows at textural interfaces of different geologic formations is investigated. It was found that models with nonzero-entry pressures for the capillary pressure-saturation relationship in conjunction with the Box discretization may give rise to spurious oscillations for flows around low permeable lenses. Furthermore, the applicability and sensitivity of the discretization methods with regard to the used computational grids is discussed. The schemes are used for the numerical study of two-phase flow in porous media with zones of different material properties. This revised version was published online in July 2006 with corrections to the Cover Date.