Origin and emplacement of the impact formations at Chicxulub,Mexico, as revealed by the ICDP deep drilling at Yaxcopoil‐1 and by numerical modeling     

Dieter Stffler  Natalya A. Artemieva  Boris A. Ivanov  Lutz Hecht  Thomas Kenkmann  Ralf Thomas Schmitt  Roald Alberto Tagle  Axel Wittmann 《Meteoritics & planetary science》2004,39(7):1035-1067

We present and interpret results of petrographic, mineralogical, and chemical analyses of the 1511 m deep ICDP Yaxcopoil‐1 (Yax‐1) drill core, with special emphasis on the impactite units. Using numerical model calculations of the formation, excavation, and dynamic modification of the Chicxulub crater, constrained by laboratory data, a model of the origin and emplacement of the impact formations of Yax‐1 and of the impact structure as a whole is derived. The lower part of Yax‐1 is formed by displaced Cretaceous target rocks (610 m thick), while the upper part comprises six suevite‐type allochthonous breccia units (100 m thick). From the texture and composition of these lithological units and from numerical model calculations, we were able to link the seven distinct impact‐induced units of Yax‐1 to the corresponding successive phases of the crater formation and modification, which are as follows: 1) transient cavity formation including displacement and deposition of Cretaceous “megablocks;” 2) ground surging and mixing of impact melt and lithic clasts at the base of the ejecta curtain and deposition of the lower suevite right after the formation of the transient cavity; 3) deposition of a thin veneer of melt on top of the lower suevite and lateral transport and brecciation of this melt toward the end of the collapse of the transient cavity (brecciated impact melt rock); 4) collapse of the ejecta plume and deposition of fall‐back material from the lower part of the ejecta plume to form the middle suevite near the end of the dynamic crater modification; 5) continued collapse of the ejecta plume and deposition of the upper suevite; 6) late phase of the collapse and deposition of the lower sorted suevite after interaction with the inward flowing atmosphere; 7) final phase of fall‐back from the highest part of the ejecta plume and settling of melt and solid particles through the reestablished atmosphere to form the upper sorted suevite; and 8) return of the ocean into the crater after some time and minor reworking of the uppermost suevite under aquatic conditions. Our results are compatible with: a) 180 km and 100 km for the diameters of the final crater and the transient cavity of Chicxulub, respectively, as previously proposed by several authors, and b) the interpretation of Chicxulub as a peak‐ring impact basin that is at the transition to a multi‐ring basin.  相似文献   

GALACSI – The ground layer adaptive optics system for MUSE     

Remko Stuik  Roland Bacon  Ralf Conzelmann  Bernard Delabre  Enrico Fedrigo  Norbert Hubin  Miska Le Louarn  Stefan Strbele 《New Astronomy Reviews》2006,49(10-12):618

MUSE, the Multi-Unit Spectroscopic Explorer, is an adaptive optics (AO)-assisted Integral Field Spectrograph, currently in the Preliminary Design Phase as a second generation instrument for the VLT. MUSE will feature two modes, each with an associated AO mode. The first mode is the wide field mode, mainly aiming at the study of high redshift galaxies. For this mode, the AO system has to deliver an improvement of at least a factor of two over the full 1′ × 1′ field of view. The second mode, the narrow field mode, aims at the high-resolution spectroscopy of nearby extended objects, for example, galaxies and globular clusters. For this mode, the AO system will have to deliver near-diffraction limited performance over a small field of view. In this paper, we discuss the trade-offs in the current design of GALACSI – the MUSE AO system – and illustrate with a number of simulations the expected performance in the wide- and narrow field modes.  相似文献   

Storm-related sea level variations along the North Sea coast as simulated by a high-resolution model 1958–2002     

Ralf Weisse  Andreas Plüβ 《Ocean Dynamics》2006,56(1):16-25

Storm-related sea level variations 1958–2002 along the North Sea coast from a high-resolution numerical hindcast are investigated and compared to the results of earlier studies. Considerable variations were found from year to year and over the entire period. The large-scale pattern of these variations is consistent with that derived from previous studies, while the magnitudes of the long-term trends differ. The latter is attributed to different analysis periods, improvements in the atmospheric forcing, and the enhanced spatial resolution of the numerical simulation. It is shown that the different analysis periods, in particular, represent an issue as the increase in storm-related sea levels was found to be weaker over the last few years that have not been included in earlier studies. These changes are consistent with observed changes of the storm climate over the North Sea. It is also shown that observed and hindcast trends may differ significantly. While the latter are in agreement with observed changes in the storm climate, it may be concluded that observed sea level changes along the North Sea coast comprise a considerable fraction that cannot be attributed to changes in the large-scale atmospheric circulation.

Ralf WeisseEmail:

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Optimal experimental design for reservoir property estimates in geothermal exploration     

Ralf Seidler  Kateryna Padalkina  H. Martin Bücker  Anozie Ebigbo  Michael Herty  Gabriele Marquart  Jan Niederau 《Computational Geosciences》2016,20(2):375-383

During geothermal reservoir development, drilling deep boreholes turns out to be extremely expensive and risky. Thus, it is of great importance to work out the details of suitable borehole locations in advance. Here, given a set of existing boreholes, we demonstrate how a sophisticated numerical technique called optimal experimental design helps to find a location of an additional exploratory borehole that reduces risk and, ultimately, saves cost. More precisely, the approach minimizes the uncertainty when deducing the effective permeability of a buried reservoir layer from a temperature profile measured in this exploratory borehole. In this paper, we (1) outline the mathematical formulation in terms of an optimization problem, (2) describe the numerical implementation involving various software components, and (3) apply the method to a 3D numerical simulation model representing a real geothermal reservoir in northern Italy. Our results show that optimal experimental design is conceptually and computationally feasible for industrial-scale applications. For the particular reservoir and the estimation of permeability from temperature, the optimal location of the additional borehole coincides with regions of high flow rates and large deviations from the mean temperature of the reservoir layer in question. Finally, the presentation shows that, methodologically, the optimization method can be generalized from estimating permeability to finding any other reservoir properties.  相似文献   

A data model for moving regions of fixed shape in databases     

Florian Heinz  Ralf Hartmut Güting 《International journal of geographical information science》2018,32(9):1737-1769

Moving object databases are designed to store and process spatial and temporal object data. An especially useful moving object type is a moving region, which consists of one or more moving polygons suitable for modeling the spread of forest fires, the movement of clouds, spread of diseases and many other real-world phenomena. Previous implementations usually allow a changing shape of the region during the movement; however, the necessary restrictions on this model result in an inaccurate interpolation of rotating objects. In this paper, we present an alternative approach for moving and rotating regions of fixed shape, called Fixed Moving Regions, which provide a significantly better model for a wide range of applications like modeling the movement of oil tankers, icebergs and other rigid structures. Furthermore, we describe and implement several useful operations on this new object type to enable a database system to solve many real-world problems, as for example collision tests, projections and intersections, much more accurate than with other models. Based on this research, we also implemented a library for easy integration into moving objects database systems, as for example the DBMS Secondo (1) (2) developed at the FernUniversität in Hagen.  相似文献   

Temperature-dependent dissolution of residual non-aqueous phase liquids: model development and verification     

Steffi Popp  Christof Beyer  Andreas Dahmke  Nicolas Koproch  Ralf Köber  Sebastian Bauer 《Environmental Earth Sciences》2016,75(11):953

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Erratum to: 3D thermal history and maturity modelling of the Levant Basin and its eastern margin,offshore–onshore Lebanon     

Samer Bou Daher  Mathieu Ducros  Pauline Michel  Nicolas Hawie  Fadi H. Nader  Ralf Littke 《Arabian Journal of Geosciences》2016,9(9):550

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Comparison of Estimated Atmospheric Boundary Layer Mixing Height in the Arctic and Southern Great Plains under Statically Stable Conditions: Experimental and Numerical Aspects   总被引：1，自引：0，他引：1  

A.A. Aliabadi  R.M. Staebler  J. de Grandpré  A. Zadra  P.A. Vaillancourt 《大气与海洋》2016,54(1):60-74

The atmospheric boundary layer mixing height (MH) is an important bulk parameter in air quality (AQ) modelling. Formulating this parameter under statically stable conditions, such as in the Arctic, has historically been difficult. In an effort to improve AQ modelling capacity in North America, MH is studied in two geographically distinct areas: the Arctic (Barrow, Alaska) and the southern Great Plains (Lamont, Oklahoma). Observational data from the Atmospheric Radiation Measurement program, Climate Research Facility and numerical weather forecasting data from Environment Canada's Regional Global Environmental Multiscale (GEM15) model have been used in order to examine the suitability of available parameterizations for MH under statically stable conditions and also to compare the level of agreement between observed and modelled MH. The analysis period is 1 October 2011 to 1 October 2012. The observations alone suggest that profile methods are preferred over surface methods in defining MH under statically stable conditions. Surface methods exhibit poorer comparison statistics with observations than profile methods. In addition, the fitted constants for surface methods are site-dependent, precluding their applicability for modelling under general conditions. The comparison of observations and GEM15 MH suggests that although the agreement is acceptable in Lamont, the default model surface method contributes to a consistent overprediction of MH in Barrow in all seasons. An alternative profile method for MH is suggested based on the bulk Richardson number. This method is shown to reduce the model bias in Barrow by a factor of two without affecting model performance in Lamont.  相似文献   

On the Response of the Greenland Ice Sheet to Greenhouse Climate Change     

Ralf Greve 《Climatic change》2000,46(3):289-303

Numerical computations are performed with the three-dimensional polythermal ice-sheet model SICOPOLIS in order to investigate the possible impact of a greenhouse-gas-induced climate change on the Greenland ice sheet. The assumed increase of the mean annual air temperature above the ice covers a range from T = 1°C to 12°C, and several parameterizations for the snowfall and the surface melting are considered. The simulated shrinking of the ice sheet is a smooth function of the temperature rise, indications for the existence of critical thresholds of the climate input are not found. Within 1000 model years, the ice-volume decrease is limited to 10% of the present volume for T 3°C, whereas the most extreme scenario, T = 12°C, leads to an almost entire disintegration, which corresponds to a sea-level equivalent of 7 m. The different snowfall and melting parameterizations yield an uncertainty range of up to 20% of the present ice volume after 1000 model years.  相似文献   

Composition of organic matter in subducted and unsubducted sediments off the Nicoya peninsula, Costa Rica (ODP Leg 170, Sites 1039 and 1040)     

Rüdiger Lutz  Birgit Gieren  Andreas Lückge  Heinz Wilkes  Ralf Littke 《Organic Geochemistry》2000,31(12)

Investigation of sediment samples from Sites 1039 and 1040 (ODP Leg 170) drilled off the Nicoya peninsula (Costa Rica) by organic geochemical and organic petrological methods has revealed that subduction has only little influence on the composition of the sedimentary organic matter. Organic carbon contents reached 1.5% in the Pleistocene samples but Miocene and Pliocene sediments had an average organic carbon content of less than 0.5%. Organic carbon/sulfur ratios are generally below 2.8, reflecting an intense sulfate reduction in the uppermost sediments which was enhanced by sulfate supply both from sea water and deeper strata. Microscopical examinations indicate that the organic matter is mainly derived from marine sources. A small amount of terrigenous organic matter is, however, present as well according to n-alkane and fatty acid distributions. The alkenone unsaturation index U₃₇^k′ shows only a slight decrease during the Miocene and Pliocene, and stronger variations in the Pleistocene, probably indicating more stable sea surface temperatures during the Miocene and Pliocene. Variations in the Pleistocene can possibly be related to glacial/interglacial changes.  相似文献