Trace element depth profiles in presolar silicon carbide grains     

Ashley J. KING  Torsten HENKEL  Detlef ROST  Ian C. LYON 《Meteoritics & planetary science》2012,47(10):1624-1643

Abstract– We have analyzed eleven presolar SiC grains from the Murchison meteorite using time‐of‐flight secondary ion mass spectrometry. The Si isotopic compositions of the grains indicate that they are probably of an AGB star origin. The average abundances of Mg, Fe, Ca, Al, Ti, and V are strongly influenced by their condensation behavior into SiC in circumstellar environments. Depth profiles of Li, B, Mg, Al, K, Ca, Ti, V, Cr, and Fe in the SiC grains show that trace elements are not always homogenously distributed. In approximately half of the SiC grains studied here, the trace element distributions can be explained by condensation processes around the grains’ parent stars. These grains appear to have experienced only minimal processing before their arrival in the presolar molecular cloud, possibly due to short residence times in the interstellar medium. The remaining SiC grains contained elevated abundances of several elements within their outer 200 nm, which is attributed to the implantation of energetic ions accelerated by shockwaves in the interstellar medium. These grains may have spent a longer period of time in this region, hence increasing the probability of them passing through a shockfront. Distinct groups of presolar SiC grains whose residence times in the interstellar medium differ are consistent with previous findings based on noble gas studies, although some grains may also have been shielded from secondary alteration by protective outer mantles.  相似文献   

Hydraulic fracturing in unconventional gas reservoirs: risks in the geological system part 1   总被引：2，自引：2，他引：0  

Torsten Lange  Martin Sauter  Michael Heitfeld  Kurt Schetelig  Karolin Brosig  Wiebke Jahnke  Alexander Kissinger  Rainer Helmig  Anozie Ebigbo  Holger Class 《Environmental Earth Sciences》2013,70(8):3839-3853

Hydraulic fracturing of unconventional gas reservoirs rapidly developed especially in the USA to an industrial scale during the last decade. Potential adverse effects such as the deterioration of the quality of exploitable groundwater resources, areal footprints, or even the climate impact were not assessed. Because hydraulic fracturing has already been practised for a long time also in conventional reservoirs, the expansion into the unconventional domain was considered to be just a minor but not a technological step, with potential environmental risks. Thus, safety and environmental protection regulations were not critically developed or refined. Consequently, virtually no baseline conditions were documented before on-site applications as proof of evidence for the net effect of environmental impacts. Not only growing concerns in the general public, but also in the administrations in Germany promoted the commissioning of several expert opinions, evaluating safety, potential risks, and footprints of the technology in focus. The first two publications of the workgroup “Risks in the Geological System” of the independent “Information and Dialogue process on hydraulic fracturing” (commissioned by ExxonMobil Production Deutschland GmbH) comprises the strategy and approaches to identify and assess the potential risks of groundwater contamination of the exploitable groundwater system in the context of hydraulic fracturing operations in the Münsterland cretaceous basin and the Lower Saxony Basin, Germany. While being specific with respect to local geology and the estimation of effective hydraulic parameters, generalized concepts for the contamination risk assessment were developed. The work focuses on barrier effectiveness of different units of the overburden with respect to the migration of fracking fluids and methane, and considers fault zones as potential fluid pathway structures.  相似文献   

Modeling the effect of stratification on cemented layer formation in sulfide-bearing mine tailings     

Jeannet A. Meima  Torsten GraupnerDieter Rammlmair 《Applied Geochemistry》2012

Reactive transport simulations have been applied to investigate possible effects of stratification on the potential of sulfide-bearing mine tailings to form protective cemented layers. The simulations are based on characteristic strata found at a German tailings site, including sulfide-enriched heavy mineral layers, mica-enriched silt layers, and homogeneously mixed layers. The simulated secondary phases (jarosite, gypsum, amorphous ferric arsenate, amorphous Fe hydroxide, alunite, amorphous silica, and kaolinite) are similar to those observed in the field. Using scanning electron microscope analyses of cemented layers, it has been observed that the pore area becomes disconnected if the porosity is decreased to values below 15%, which would indicate a strong decrease in permeability. Stratification was found to play a crucial role in cemented layer formation. Cemented layers are absent or insignificant in systems with a homogeneous distribution of Fe-bearing sulfides. They are extensively developed in systems with (a) an arsenopyrite-rich layer or (b) a mica-enriched layer situated immediately below an Fe-sulfide enriched layer. The modeling results have clearly demonstrated that the key processes operating in scenario (a) are very different from the key processes in scenario (b). In scenario (a), the oxidation of arsenopyrite is followed by the precipitation of amorphous ferric arsenate, which can be solely responsible for significant pore reduction. In scenario (b), the presence of a large amount of reactive aluminosilicates (e.g. biotite and Ca-bearing plagioclase) immediately below the Fe-sulfide rich layer appears to be crucial. Key processes are extensive formation of Acid Rock Drainage (ARD) followed by enhanced (pH-driven) weathering of aluminosilicates, resulting in the accumulation of secondary phases directly below the Fe-sulfide rich layer. In both scenarios, a cemented layer is formed that effectively retards the further downward movement of the oxidation front. The presented details on the role of stratification in the formation of cemented layers could be considered in the construction of mining heaps as a possible measure to stimulate natural attenuation.  相似文献   

Magnetic field seeding by galactic winds     

Serena Bertone  Corina Vogt  Torsten Enßlin 《Monthly notices of the Royal Astronomical Society》2006,370(1):319-330

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Hydroxymanganopyrochlore: A new mineral from the Eifel volcanic region, Germany     

N. V. Chukanov  G. Blass  N. V. Zubkova  I. V. Pekov  D. Yu. Pushcharovskii  H. Prinz 《Doklady Earth Sciences》2013,449(1):342-345

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Hypocenter migration of fluid-induced earthquake swarms in the Tjörnes Fracture Zone (North Iceland)     

Martin Hensch  Carsten Riedel  Jrg Reinhardt  Torsten Dahm  The NICE-People 《Tectonophysics》2008,447(1-4):80

The Tjörnes Fracture Zone separates Iceland's North Volcanic Zone from Kolbeinsey-Ridge (Greenland-Sea). Seismicity mainly occurs in swarms, often 100 and more per day, with similar waveforms and frequently offshore.We analysed three earthquake swarms between June and September 2004, recorded by 35 stations, i.e. the permanent Icelandic SIL network and a temporary setup of land and ocean-bottom-seismometers, and 5 swarms of the years 1994-1997 only using the sparser SIL network. Events occurring in the same swarm often show similar waveforms at the same station. We cross-correlated these time series by using a new approach of three component cross-correlation in order to relocate the hypocenters relative within the swarms and to precisely determine the direction and velocity of migration. Our method delivered good relocations with small spatial and temporal errors. This allows the interpretation and characterisation of the observed earthquake swarms. We try to classify observed migration velocities by comparing them to typical fluid- and crack-propagation velocities and determine focal-mechanisms and orientation of the best fitting plane through the hypocenter distribution.We separate the investigated events into two types of earthquake swarms, supposedly dike-induced and hydrothermally- or gas-induced swarms, by pointing out typical characteristics of both types and by comparing them to similar events of other volcanic regions. Based on different migration velocities, we will discuss possible mechanisms and their triggers of all single clusters within a swarm. Hypothetic models will be established, trying to explain the processes during the swarm episodes and to derive possible pre-eruptive patterns from the character of seismicity.  相似文献   

An experimental database for the development,calibration and verification of constitutive models for sand with focus to cyclic loading: part II—tests with strain cycles and combined loading     

Torsten Wichtmann  Theodoros Triantafyllidis 《Acta Geotechnica》2016,11(4):763-774

For numerical studies of geotechnical structures under earthquake loading, aiming to examine a possible failure due to liquefaction, using a sophisticated constitutive model for the soil is indispensable. Such model must adequately describe the material response to a cyclic loading under constant volume (undrained) conditions, amongst others the relaxation of effective stress (pore pressure accumulation) or the effective stress loops repeatedly passed through after a sufficiently large number of cycles (cyclic mobility, stress attractors). The soil behaviour under undrained cyclic loading is manifold, depending on the initial conditions (e.g. density, fabric, effective mean pressure, stress ratio) and the load characteristics (e.g. amplitude of the cycles, application of stress or strain cycles). In order to develop, calibrate and verify a constitutive model with focus to undrained cyclic loading, the data from high-quality laboratory tests comprising a variety of initial conditions and load characteristics are necessary. It is the purpose of these two companion papers to provide such database collected for a fine sand. Part II concentrates on the undrained triaxial tests with strain cycles, where a large range of strain amplitudes has been studied. Furthermore, oedometric and isotropic compression tests as well as drained triaxial tests with un- and reloading cycles are discussed. A combined monotonic and cyclic loading has been also studied in undrained triaxial tests. All test data presented herein will be available from the homepage of the first author. As an example of the examination of an existing constitutive model, the experimental data are compared to element test simulations using hypoplasticity with intergranular strain.  相似文献   

Plant–Arthropod Associations from the Lower Miocene of the Most Basin in Northern Bohemia (Czech Republic): A Preliminary Report     

Jakub PROKOP  Torsten Wappler  Stanislav Knor  Zlatko Kva?ek 《《地质学报》英文版》2010,84(4):903-914

Terrestrial plants and insects currently account for the majority of the Earth's biodiversity, and approximately half of insect species are herbivores. Thus, insects and plants share ancient associations that date back more than 400 Myr. However, investigations of their past interactions are at the preliminary stages in Western Europe. Herein, we present the first results of our study of various feeding damage based on a dataset of nearly 3500 examined plant specimens from the Lower Miocene of the Lagerst?tte Bílina Mine in the Most Basin, Czech Republic. This site provides a unique view of the Neogene freshwater ecosystems. It has long been studied by scientists working in different branches of sedimentology, paleobotany, and paleozoology. The fossils are preserved in three characteristic horizons overlaying the coal seam (Clayey Superseam Horizon, Delta Sandy Horizon, and Lake Clayey Horizon), reflecting paleoenvironmental changes in a short time period of development. The trace fossils are classified as functional feeding groups or “guilds”, without searching for a direct cause or a recent analog host relation. Approximately 23% of specimens of dicotyledonous plant leaves were found to be damaged and associated with some leaf “morphotypes”. Deciduous plant–host taxa, and those with a chartaceous texture typical of riparian habitats, were frequently damaged, such as Populus, recorded with two species Populus zaddachii and Populus populina (57.9% and 31% herbivory levels, respectively), followed by Acer, Alnus, and Carya, averaging almost 30% of damaged leaves/leaflets. There has been evidence of 60 damage types (DT) representing all functional feeding groups recorded at the Bílina Mine, including 12 types of leaf mines and 16 gall-type DT. In total, Lower Miocene of the Lagerst?tte Bílina Mine exhibits a high level of external foliage feeding types (23.7%), and a low level of more specialized DT, such as galls (4.3%) and leaf mines (<1%). A broader comparison based on DT of the main sedimentary environments shows significance supporting different biomes by frequency of damage levels and DT diversities.  相似文献   

Robust methods for the decomposition and interpretation of compound dunes applied to a complex hydromorphological setting     

Leon Scheiber  Oliver Lojek  Axel Götschenberg  Jan Visscher  Torsten Schlurmann 《地球表面变化过程与地形》2021,46(2):478-489

Underwater dunes are a morphological feature that are explored by marine scientists and coastal engineers alike. This study presents new methodologies in order to simplify bedform identification and morphodynamic analyses. Specifically, subaqueous compound dunes are decomposed with a simple yet extensive tracking algorithm, which relies on a repeated evaluation of unfiltered bed elevation profiles according to five predefined length classes. In a second step, morphological trends are assessed in the form of bed migration rates, bed slope asymmetries and net sediment changes, in which all parameters are referred to equidistant sections of the examined fairway stretch. This integrated approach not only avoids the challenges in weighting the varying size and abundance of dunes of different scales but also ensures comparability between dune-specific and areal parameters, which significantly improves the interpretation of the morphological setting as a whole. The developed methods are applied to the Outer Jade fairway, an anthropogenically influenced and regularly maintained waterway in the German Bight, and allow scrutiny of spatio-temporal trends in this region. Based on a unique data set of 100 sequential high-quality echo-sounding surveys, various types of bedforms are identified, comprising large-scale primary as well as superimposing secondary dunes that are assumed to interfere with each other. Temporal trends show a long-term rise of the troughs of major bedforms and constant maximum crest elevations near the official maintenance depth, which matches the observed long-term aggradation of sediments. The spatial distribution of integrated morphodynamic parameters reflects a previously described zone of primary dune convergence and facilitates the precise localization of this geophysical singularity. The presented findings both confirm the robustness of the proposed methodologies and, in return, enhance the understanding of morphological processes in the Outer Jade. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

Observing upper troposphere–lower stratosphere climate with radio occultation data from the CHAMP satellite     

Ulrich Foelsche  Michael Borsche  Andrea K. Steiner  Andreas Gobiet  Barbara Pirscher  Gottfried Kirchengast  Jens Wickert  Torsten Schmidt 《Climate Dynamics》2008,31(1):49-65

High quality observations of the atmosphere are particularly required for monitoring global climate change. Radio occultation (RO) data, using Global Navigation Satellite System (GNSS) signals, are well suited for this challenge. The special climate utility of RO data arises from their long-term stability due to their self-calibrated nature. The German research satellite CHAllenging Minisatellite Payload for geoscientific research (CHAMP) continuously records RO profiles since August 2001 providing the first opportunity to create RO based climatologies for a multi-year period of more than 5 years. A period of missing CHAMP data from July 3, 2006 to August 8, 2006 can be bridged with RO data from the GRACE satellite (Gravity Recovery and Climate Experiment). We have built seasonal and zonal mean climatologies of atmospheric (dry) temperature, microwave refractivity, geopotential height and pressure with 10° latitudinal resolution. We show representative results with focus on dry temperatures and compare them with analysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF). Although we have available only about 150 CHAMP profiles per day (compared to millions of data entering the ECMWF analyses) the overall agreement between 8 and 30 km altitude is in general very good with systematic differences <0.5 K in most parts of the domain. Pronounced systematic differences (exceeding 2 K) in the tropical tropopause region and above Antarctica in southern winter can almost entirely be attributed to errors in the ECMWF analyses. Errors resulting from uneven sampling in space and time are a potential error source for single-satellite climatologies. The average CHAMP sampling error for seasonal zonal means is <0.2 K, higher values occur in restricted regions and time intervals which can be clearly identified by the sampling error estimation approach we introduced (which is based on ECMWF analysis fields). The total error of this new type of temperature climatologies is estimated to be <0.5 K below 30 km. The recently launched Taiwan/U.S. FORMOSAT-3/COSMIC constellation of 6 RO satellites started to provide thousands of RO profiles per day, but already now the single-satellite CHAMP RO climatologies improve upon modern operational climatologies in the upper troposphere–lower stratosphere and can act as absolute reference climatologies for validation of more bias-sensitive climate datasets and models.  相似文献