Woodleigh impact structure,Australia: Shock petrography and geochemical studies     

Wolf Uwe REIMOLD  Christian KOEBERL  Robert M. HOUGH  Iain MCDONALD  Alex BEVAN  Kassa AMARE  Bevan M. FRENCH 《Meteoritics & planetary science》2003,38(7):1109-1130

Abstract— The large, complex Woodleigh structure in the Carnarvon basin of Western Australia has recently been added to the terrestrial impact crater record. Many aspects of this structure are, however, still uncertain. This work provides a detailed petrographic assessment of a suite of representative drill core samples from the borehole Woodleigh 1 that penetrated uplifted basement rocks of the central part of this structure. Fundamental rock and mineral deformation data and high‐precision chemical data, including results of PGE and oxygen isotopic analysis, are presented. The sampled interval displays likely impact‐produced macrodeformation in the form of fracturing and breccia veining at the microscopic scale. Contrary to earlier reports that these breccias represent pseudotachylite (friction melt) or even shock/shear‐produced pseudotachylitic melt breccia cannot be confirmed due to pervasive post‐impact alteration. Abundant planar deformation features (PDFs) in quartz, in addition to diaplectic glass and partial isotropization, are the main shock deformation effects observed, confirming that Woodleigh is of impact origin. Over the investigated depth interval, the statistics of quartz grains with a variable number of sets of PDFs does not change significantly, and the patterns of crystallographic orientations of PDFs in randomly selected quartz grains does not indicate a change in absolute shock pressure with depth either. The value of oxygen isotopes for the recognition of meteoritic contamination, as proposed by earlier Woodleigh workers, is critically assessed. Neither INA nor PGE analyses of our samples support the presence of a meteoritic component within this basement section, as had been claimed in earlier work.  相似文献   

A taxonomic survey of comet composition 1985-2004 using CCD spectroscopy     

Uwe Fink 《Icarus》2009,201(1):311-334

A summary is presented of our spectroscopic survey of comets extending for roughly 19 years from 1985 to 2004 comprising data for 92 comets of which 50 showed good emissions. All data were re-analyzed using consistent reduction techniques. Our observations of comets over several apparitions and comets observed over an extended period indicate no major changes in compositional classification. To our regret, no major unidentified cometary features were found in our surveyed spectral region of 5200-10400 Å. Absolute production rates for the dominant parent molecule H₂O and the daughter species C₂, NH₂ and CN are determined within the limits of the Haser model as are values for the dust continuum, Afρ. From these data, production rate ratios are calculated for C₂/H₂O, NH₂/H₂O, CN/H₂O and Afρ/H₂O. Excluding the odd Comets Yanaka (1988r), 43P/Wolf-Harrington and 19P/Borrelly, with unusual spectra, our set of comets exhibited relatively uniform composition. Detailed analyses of our data resulted in four taxonomic classes:

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Comets of typical composition (∼70%); exhibiting typical ratios with respect to water of C₂, NH₂, and CN.

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Tempel 1 type (∼22%); having a deficiency in C₂ but normal NH₂ abundance.

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G-Z type (∼6%); having both low C₂ and NH₂ ratios.

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The unusual object Yanaka (1988r) (∼2%?); no detectable C₂ or CN emission but normal NH₂.

It is uncertain whether there is a clear separation between the comets of typical composition and those with C₂ depletion, or whether the latter consists of a group showing a continuum of decreasing C₂/CN ratios. Our spectroscopic investigations result in a visual record of the various compositional classes, which are illustrated in a number of figures. Production rate comparisons with the comet photometry program of Schleicher and A'Hearn [A'Hearn, M.F., and 4 colleagues, 1995. Icarus 118, 223-270] for 13 comets in common yielded good agreement once the different scale lengths are taken into account. An investigation into the possible origin of our compositional groups with respect to dynamical families of comets shows that the Halley family exhibits essentially no C₂ depletion. These objects were presumably formed in the region of Saturn and Uranus and scattered into the Oort cloud. Comets formed in the space near Neptune, responsible for the scattered Kuiper Belt show a mixture of “typical” and C₂ depleted objects, while we associate comets formed in-situ in the classical Kuiper belt with our C₂ depleted group.  相似文献   

The variation and controls of mean transit times in Australian headwater catchments     

Ian Cartwright  Uwe Morgenstern  William Howcroft  Harald Hofmann  Robin Armit  Michael Stewart  Chad Burton  Dylan Irvine 《水文研究》2020,34(21):4034-4048

Determining mean transit times in headwater catchments is critical for understanding catchment functioning and understanding their responses to changes in landuse or climate. Determining whether mean transit times (MTTs) correlate with drainage density, slope angle, area, or land cover permits a better understanding of the controls on water flow through catchments and allows first-order predictions of MTTs in other catchments to be made. This study assesses whether there are identifiable controls on MTTs determined using ³H in headwater catchments of southeast Australia. Despite MTTs at baseflow varying from a few years to >100 years, it was difficult to predict MTTs using single or groups of readily-measured catchment attributes. The lack of readily-identifiable correlations hampers the prediction of MTTs in adjacent catchments even where these have similar geology, land use, and topography. The long MTTs of the Australian headwater catchments are probably in part due to the catchments having high storage volumes in deeply-weathered regolith, combined with low recharge rates due to high evapotranspiration. However, the difficulty in estimating storage volumes at the catchment scale hampers the use of this parameter to estimate MTTs. The runoff coefficient (the fraction of rainfall exported via the stream) is probably also controlled by evapotranspiration and recharge rates. Correlations between the runoff coefficient and MTTs in individual catchments allow predictions of MTTs in nearby catchments to be made. MTTs are shorter in high rainfall periods as the catchments wet up and shallow water stores are mobilized. Despite the contribution of younger water, the major ion geochemistry in individual catchments commonly does not correlate with MTTs, probably reflecting heterogeneous reactions and varying degrees of evapotranspiration. Documenting MTTs in catchments with high storage volumes and/or low recharge rates elsewhere is important for understanding MTTs in diverse environments.  相似文献   

Analysis of uncertainties in the hydrological response of a model‐based climate change impact assessment in a subcatchment of the Spree River,Germany          下载免费PDF全文

Anne Gädeke  Herwig Hölzel  Hagen Koch  Ina Pohle  Uwe Grünewald 《水文研究》2014,28(12):3978-3998

Climate change impact assessments form the basis for the development of suitable climate change adaptation strategies. For this purpose, ensembles consisting of stepwise coupled models are generally used [emission scenario → global circulation model → downscaling approach (DA) → bias correction → impact model (hydrological model)], in which every item is affected by considerable uncertainty. The aim of the current study is (1) to analyse the uncertainty related to the choice of the DA as well as the hydrological model and its parameterization and (2) to evaluate the vulnerability of the studied catchment, a subcatchment of the highly anthropogenically impacted Spree River catchment, to hydrological change. Four different DAs are used to drive four different model configurations of two conceptually different hydrological models (Water Balance Simulation Model developed at ETH Zürich and HBV‐light). In total, 452 simulations are carried out. The results show that all simulations compute an increase in air temperature and potential evapotranspiration. For precipitation, runoff and actual evapotranspiration, opposing trends are computed depending on the DA used to drive the hydrological models. Overall, the largest source of uncertainty can be attributed to the choice of the DA, especially regarding whether it is statistical or dynamical. The choice of the hydrological model and its parameterization is of less importance when long‐term mean annual changes are compared. The large bandwidth at the end of the modelling chain may exacerbate the formulation of suitable climate change adaption strategies on the regional scale. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Regaining momentum for international climate policy beyond Copenhagen     

Michael Huettner  Annette Freibauer  Constanze Haug  Uwe Cantner 《Carbon balance and management》2010,5(1):2

The 'Copenhagen Accord' fails to deliver the political framework for a fair, ambitious and legally-binding international climate agreement beyond 2012. The current climate policy regime dynamics are insufficient to reflect the realities of topical complexity, actor coalitions, as well as financial, legal and institutional challenges in the light of extreme time constraints to avoid 'dangerous' climate change of more than 2°C. In this paper we analyze these stumbling blocks for international climate policy and discuss alternatives in order to regain momentum for future negotiations.  相似文献   

Meteorology and oceanography of the Atlantic sector of the Southern Ocean—a review of German achievements from the last decade     

Hartmut H. Hellmer  Monika Rhein  Günther Heinemann  Janna Abalichin  Wafa Abouchami  Oliver Baars  Ulrich Cubasch  Klaus Dethloff  Lars Ebner  Eberhard Fahrbach  Martin Frank  Gereon Gollan  Richard J. Greatbatch  Jens Grieger  Vladimir M. Gryanik  Micha Gryschka  Judith Hauck  Mario Hoppema  Oliver Huhn  Torsten Kanzow  Boris P. Koch  Gert König-Langlo  Ulrike Langematz  Gregor C. Leckebusch  Christof Lüpkes  Stephan Paul  Annette Rinke  Bjoern Rost  Michiel Rutgers van der Loeff  Michael Schröder  Gunther Seckmeyer  Torben Stichel  Volker Strass  Ralph Timmermann  Scarlett Trimborn  Uwe Ulbrich  Celia Venchiarutti  Ulrike Wacker  Sascha Willmes  Dieter Wolf-Gladrow 《Ocean Dynamics》2016,66(11):1379-1413

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Mutual validation of GNSS height measurements and high-precision geometric-astronomical leveling     

Christian Hirt  Martin Schmitz  Uwe Feldmann-Westendorff  Gerhard Wübbena  Cord-Hinrich Jahn  Günter Seeber 《GPS Solutions》2011,15(2):149-159

The method of geometric-astronomical leveling is presented as a suited technique for the validation of GNSS (Global Navigation Satellite System) heights. In geometric-astronomical leveling, the ellipsoidal height differences are obtained by combining conventional spirit leveling and astronomical leveling. Astronomical leveling with recently developed digital zenith camera systems is capable of providing the geometry of equipotential surfaces of the gravity field accurate to a few 0.1 mm per km. This is comparable to the accuracy of spirit leveling. Consequently, geometric-astronomical leveling yields accurate ellipsoidal height differences that may serve as an independent check on GNSS height measurements at local scales. A test was performed in a local geodetic network near Hanover. GPS observations were simultaneously carried out at five stations over a time span of 48 h and processed considering state-of-the-art techniques and sophisticated new approaches to reduce station-dependent errors. The comparison of GPS height differences with those from geometric-astronomical leveling shows a promising agreement of some millimeters. The experiment indicates the currently achievable accuracy level of GPS height measurements and demonstrates the practical applicability of the proposed approach for the validation of GNSS height measurements as well as the evaluation of GNSS height processing strategies.  相似文献   

Biomass to Biofuels: Strategies for Global Industries     

Uwe Schröder 《洁净——土壤、空气、水》2011,39(11):1022-1022

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Ries crater and suevite revisited—Observations and modeling Part I: Observations     

Dieter Stöffler  Natalia A. Artemieva  Kai Wünnemann  W. Uwe Reimold  Juliane Jacob  Birgit K. Hansen  Iona A. T. Summerson 《Meteoritics & planetary science》2013,48(4):515-589

We report results of an interdisciplinary project devoted to the 26 km‐diameter Ries crater and to the genesis of suevite. Recent laboratory analyses of “crater suevite” occurring within the central crater basin and of “outer suevite” on top of the continuous ejecta blanket, as well as data accumulated during the past 50 years, are interpreted within the boundary conditions imposed by a comprehensive new effort to model the crater formation and its ejecta deposits by computer code calculations (Artemieva et al. 2013). The properties of suevite are considered on all scales from megascopic to submicroscopic in the context of its geological setting. In a new approach, we reconstruct the minimum/maximum volumes of all allochthonous impact formations (108/116 km³), of suevite (14/22 km³), and the total volume of impact melt (4.9/8.0 km³) produced by the Ries impact event prior to erosion. These volumes are reasonably compatible with corresponding values obtained by numerical modeling. Taking all data on modal composition, texture, chemistry, and shock metamorphism of suevite, and the results of modeling into account, we arrive at a new empirical model implying five main consecutive phases of crater formation and ejecta emplacement. Numerical modeling indicates that only a very small fraction of suevite can be derived from the “primary ejecta plume,” which is possibly represented by the fine‐grained basal layer of outer suevite. The main mass of suevite was deposited from a “secondary plume” induced by an explosive reaction (“fuel‐coolant interaction”) of impact melt with water and volatile‐rich sedimentary rocks within a clast‐laden temporary melt pool. Both melt pool and plume appear to be heterogeneous in space and time. Outer suevite appears to be derived from an early formed, melt‐rich and clast‐poor plume region rich in strongly shocked components (melt ? clasts) and originating from an upper, more marginal zone of the melt pool. Crater suevite is obviously deposited from later formed, clast‐rich and melt‐poor plumes dominated by unshocked and weakly shocked clasts and derived from a deeper, central zone of the melt pool. Genetically, we distinguish between “primary suevite” which includes dike suevite, the lower sublayer of crater suevite, and possibly a basal layer of outer suevite, and “secondary suevite” represented by the massive upper sublayer of crater suevite and the main mass of outer suevite.  相似文献   

Geochemical studies of the SUBO 18 (Enkingen) drill core and other impact breccias from the Ries crater,Germany     

Wolf Uwe Reimold  Iain McDonald  Ralf‐Thomas Schmitt  Birgit Hansen  Juliane Jacob  Christian Koeberl 《Meteoritics & planetary science》2013,48(9):1531-1571

Suevite and melt breccia compositions in the boreholes Enkingen and Polsingen are compared with compositions of suevites from other Ries boreholes and surface locations and discussed in terms of implications for impact breccia genesis. No significant differences in average chemical compositions for the various drill cores or surface samples are noted. Compositions of suevite and melt breccia from southern and northeastern sectors of the Ries crater do not significantly differ. This is in stark contrast to the published variations between within‐crater and out‐of‐crater suevites from northern and southern sectors of the Bosumtwi impact structure, Ghana. Locally occurring alteration overprint on drill cores—especially strong on the carbonate‐impregnated suevite specimens of the Enkingen borehole—does affect the average compositions. Overall, the composition of the analyzed impact breccias from Ries are characterized by very little macroscopically or microscopically recognized sediment‐clast component; the clast populations of suevite and impact melt breccia are dominated consistently by granitic and intermediate granitoid components. The Polsingen breccia is significantly enriched in a dioritic clast component. Overall, chemical compositions are of intermediate composition as well, with dioritic‐granodioritic silica contents, and relatively small contributions from mafic target components. Selected suevite samples from the Enkingen core have elevated Ni, Co, Cr, and Ir contents compared with previously analyzed suevites from the Ries crater, which suggest a small meteoritic component. Platinum‐group element (PGE) concentrations for some of the enriched samples indicate somewhat elevated concentrations and near‐chondritic ratios of the most immobile PGE, consistent with an extraterrestrial contribution of 0.1–0.2% chondrite‐equivalent.  相似文献