Late Miocene sedimentary architecture of the Ebro Continental Margin (Western Mediterranean): implications to the Messinian Salinity Crisis     

Alejandra L. Cameselle  Roger Urgeles  Ben De Mol  Angelo Camerlenghi  Jason C. Canning 《International Journal of Earth Sciences》2014,103(2):423-440

The Messinian Salinity Crisis (MSC) resulted from a significant multi-phase drop and subsequent reflooding of the Mediterranean Sea from 5.96 to 5.33 Ma. Well-developed drainage networks, characterized by step-like profiles and abrasion platforms, are associated to this event. The Ebro Continental Margin (Western Mediterranean) presents an additional complexity since the capture of the drainage of the adjacent subaerial Ebro Basin took place sometime prior to the Messinian stage. Using 3D seismic reflection data, this work provides new insights into the origin of the step-like profile of the Messinian erosional surface (MES) and timing of the capture of the subaerial Ebro Basin. The results obtained indicate a sedimentary-active continental slope and delta progradation during Middle-Late Miocene, in a normal regressive context associated to a pre-Messinian proto-Ebro River. The mature development attained by the Messinian Ebro River network during the MSC corroborates that the capture of the Ebro Basin occurred prior to the MSC. The configuration of the clinoforms below the MES suggests that deltaic sediments of the Messinian Paleo-Ebro River deposited during the Tortonian and initial Messinian sea-level drawdown. The MES formed at the top of the Tortonian Highstand, where a fluvial network was deeply carved, and in the topset region of the Messinian Falling Stage Systems Tract, where minor erosion occurred. Fluvial deposits are outstandingly preserved on the main valleys of the MES. Therefore, the step-like profile of the MES was not created during Zanclean inundation, but during the latest stages of the main Messinian sea-level fall and lowstand.  相似文献   

Promoting geodiversity: learning lessons from biodiversity     

Roger Crofts 《Proceedings of the Geologists' Association. Geologists' Association》2014

Progress made in promoting geodiversity in recent times is reviewed, concluding that it is now an established component of the Earth Sciences. However, it still lacks the status and standing of biodiversity in governmental, political and public forums. The paper assesses what can be learnt from the experience of the development and promotion of biodiversity. Based on this experience, eight suggestions for increasing the understanding and ownership of geodiversity beyond the Earth science community are provided as a basis for discussion.  相似文献   

Contrasting geochemical signatures on land from the Middle and Late Permian extinction events     

Nathan D. Sheldon  Ramananda Chakrabarti  Gregory J. Retallack  Roger M. H. Smith 《Sedimentology》2014,61(6):1812-1829

The end of the Palaeozoic is marked by two mass‐extinction events during the Middle Permian (Capitanian) and the Late Permian (Changhsingian). Given similarities between the two events in geochemical signatures, such as large magnitude negative δ¹³C anomalies, sedimentological signatures such as claystone breccias, and the approximate contemporaneous emplacement of large igneous provinces, many authors have sought a common causal mechanism. Here, a new high‐resolution continental record of the Capitanian event from Portal Mountain, Antarctica, is compared with previously published Changhsingian records of geochemical signatures of weathering intensity and palaeoclimatic change. Geochemical means of discriminating sedimentary provenance (Ti/Al, U/Th and La/Ce ratios) all indicate a common provenance for the Portal Mountain sediments and associated palaeosols, so changes spanning the Capitanian extinction represent changes in weathering intensity rather than sediment source. Proxies for weathering intensity chemical index of alteration, ?W and rare earth element accumulation all decline across the Capitanian extinction event at Portal Mountain, which is in contrast to the increased weathering recorded globally at the Late Permian extinction. Furthermore, palaeoclimatic proxies are consistent with unchanging or cooler climatic conditions throughout the Capitanian event, which contrasts with Changhsingian records that all indicate a significant syn‐extinction and post‐extinction series of greenhouse warming events. Although both the Capitanian and Changhsingian event records indicate significant redox shifts, palaeosol geochemistry of the Changhsingian event indicates more reducing conditions, whereas the new Capitanian record of reduced trace metal abundances (Cr, Cu, Ni and Ce) indicates more oxidizing conditions. Taken together, the differences in weathering intensity, redox and the lack of evidence for significant climatic change in the new record suggest that the Capitanian mass extinction was not triggered by dyke injection of coal‐beds, as in the Changhsingian extinction, and may instead have been triggered directly by the Emeishan large igneous province or by the interaction of Emeishan basalts with platform carbonates.  相似文献   

Observations on the crystal structures of lueshite     

Roger H. Mitchell  Peter C. Burns  Kevin S. Knight  Christopher J. Howard  Anton R. Chakhmouradian 《Physics and Chemistry of Minerals》2014,41(6):393-401

Laboratory powder XRD patterns of the perovskite-group mineral lueshite from the type locality (Lueshe, Kivu, DRC) and pure NaNbO₃ demonstrate that lueshite does not adopt the same space group (Pbma; #57) as the synthetic compound. The crystal structures of lueshite (2 samples) from Lueshe, Mont Saint-Hilaire (Quebec, Canada) and Sallanlatvi (Kola, Russia) have been determined by single-crystal CCD X-ray diffraction. These room temperature X-ray data for all single-crystal samples can be satisfactorily refined in the orthorhombic space group Pbnm (#62). Cell dimensions, atomic coordinates of the atoms, bond lengths and octahedron tilt angles are given for four crystals. Conventional neutron diffraction patterns for Lueshe lueshite recorded over the temperature range 11–1,000 K confirm that lueshite does not adopt space group Pbma within these temperatures. Neutron diffraction indicates no phase changes on cooling from room temperature to 11 K. None of these neutron diffraction data give satisfactorily refinements but suggest that this is the space group Pbnm. Time-of-flight neutron diffraction patterns for Lueshe lueshite recorded from room temperature to 700 °C demonstrate phase transitions above 550 °C from Cmcm through P4/mbm to \(Pm\overline{3} m\) above 650 °C. Cell dimensions and atomic coordinates of the atoms are given for the three high-temperature phases. The room temperature to 400 °C structures cannot be satisfactorily resolved, and it is suggested that the lueshite at room temperature consists of domains of pinned metastable phases with orthorhombic and/or monoclinic structures. However, the sequence of high-temperature phase transitions observed is similar to those determined for synthetic NaTaO₃, suggesting that the equilibrated room temperature structure of lueshite is orthorhombic Pbnm.  相似文献   

Barriers in the science-policy-practice interface: Toward a knowledge-action-system in global environmental change research     

Juergen Weichselgartner  Roger Kasperson 《Global Environmental Change》2010,20(2):266-277

This paper presents the results of a case study analysis from the knowledge domains of vulnerability and resilience. We analyzed 20 scientific assessments to provide empirical evidence for successes and failures in collaborative knowledge production, i.e., the joint creation of assessments reports by researchers and decision makers in policy and practice. It became clear that the latter typically use insufficiently the research-based knowledge available and researchers typically produce insufficiently knowledge that is directly usable. We found a number of functional, structural, and social factors inhibiting a joint problem identification and framing of knowledge producers and potential users: divergent objectives, needs, scope, and priorities; different institutional settings and standards, as well as differing cultural values, understanding, and mistrust. Combining understanding from multiple sources and providing mechanisms for linking solutions proposed by research with articulated needs and problems of practitioners would reduce the discrepancies in activities of different actors and result in more timely and context-appropriate solutions. In the concluding section we argue for a more locally embedded and socially contingent production of actionable knowledge and make suggestions about ways to enhance effectiveness of research-based knowledge.  相似文献   

The Three Gorges Dam of the Yangtze River, China: engineering geology in China     

Roger Mason 《Geology Today》1999,15(1):30-33

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Rhomboidal versus triangular spherical harmonic truncation: Some verification statistics     

Roger Daley  Yvon Bourassa 《大气与海洋》2013,51(2):187-196

Abstract

In the construction of global primitive equation models, based on the spherical harmonic method, two forms of truncation are in general use. Theoretical considerations suggest the triangular truncation method is superior, but the easily coded rhomboidal truncation is more commonly used. A verification experiment employing the Canadian Operational Spectral Model has been performed to determine if the theoretical superiority of the triangular truncation can be realized in practice. It was found that at least in the restricted case of extra‐tropical forecasts of less than 48 h, that the two truncation methods produced forecasts of equivalent accuracy.  相似文献   

A system for line profile studies at the 150-foot tower on Mount Wilson     

Roger K. Ulrich  Larry Webster  John E. Boyden  Nick Magnone  Richard S. Bogart 《Solar physics》1991,135(2):211-241

We describe enhancements to the hardware and software for the 150-foot tower system on Mt. Wilson which make possible the acquisition of high precision line profile measurements. This system utilizes the 75-foot pit spectrograph with a photomultiplier detector system to scan line profiles repeatedly in order to study variations induced by the passage of waves vertically through the solar atmosphere. Oscillations of line profile parameters with an amplitude as low as 1.7 m s^–1 have been detected with this system using integrated sunlight. Phase relations between oscillations of different parts of the line profile are appropriate to upward energy transport. Consistent with the previous conclusion by Mein and Schmieder (1981), we find that the magnitude of the energy transport is compatible with the 5-min oscillations making an important contribution to the heating of the low chromosphere.The Mount Wilson Observatory is operated by the Mount Wilson Institute under agreement with the Carnegie Institution of Washington.  相似文献   

Assessing the impact of the hydraulic properties of a crusted soil on overland flow modelling at the field scale     

Nane Chahinian  Marc Voltz  Roger Moussa  Gwenn Trotoux 《水文研究》2006,20(8):1701-1722

Soil surface crusts are widely reported to favour Hortonian runoff, but are not explicitly represented in most rainfall‐runoff models. The aim of this paper is to assess the impact of soil surface crusts on infiltration and runoff modelling at two spatial scales, i.e. the local scale and the plot scale. At the local scale, two separate single ring infiltration experiments are undertaken. The first is performed on the undisturbed soil, whereas the second is done after removal of the soil surface crust. The HYDRUS 2D two‐dimensional vertical infiltration model is then used in an inverse modelling approach, first to estimate the soil hydraulic properties of the crust and the subsoil, and then the effective hydraulic properties of the soil represented as a single uniform layer. The results show that the crust hydraulic conductivity is 10 times lower than that of the subsoil, thus illustrating the limiting role the crust has on infiltration. Moving up to the plot scale, a rainfall‐runoff model coupling the Richards equation to a transfer function is used to simulate Hortonian overland flow hydrographs. The previously calculated hydraulic properties are used, and a comparison is undertaken between a single‐layer and a double‐layer representation of the crusted soil. The results of the rainfall‐runoff model show that the soil hydraulic properties calculated at the local scale give acceptable results when used to model runoff at the plot scale directly, without any numerical calibration. Also, at the plot scale, no clear improvement of the results can be seen when using a double‐layer representation of the soil in comparison with a single homogeneous layer. This is due to the hydrological characteristics of Hortonian runoff, which is triggered by a rainfall intensity exceeding the saturated hydraulic conductivity of the soil surface. Consequently, the rainfall‐runoff model is more sensitive to rainfall than to the subsoil's hydrodynamic properties. Therefore, the use of a double‐layer soil model to represent runoff on a crusted soil does not seem necessary, as the increase of precision in the soil discretization is not justified by a better performance of the model. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Structural properties of discs and bulges of early-type galaxies     

Roelof S. de Jong  Luc Simard  Roger L. Davies  R. P. Saglia  David Burstein  Matthew Colless  Robert McMahan  Gary Wegner 《Monthly notices of the Royal Astronomical Society》2004,355(4):1155-1170

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