Detrital zircon geochronology of Palaeozoic Novaya Zemlya – a key to understanding the basement of the Barents Shelf     

Henning Lorenz  David G. Gee  Evgeny Korago  Galina Kovaleva  William C. McClelland  Jane A. Gilotti  Dirk Frei 《地学学报》2013,25(6):496-503

The Novaya Zemlya fold‐and‐thrust‐belt is the northern continuation of the late Palaeozoic Uralide Orogen. Little is known about its deeper structure and the basement history of the adjacent Barents and Kara shelves. Based on geological evidence and detrital zircon analysis of 28 samples from the northeastern and stratigraphically deepest part of the archipelago, we demonstrate that Cambro‐Ordovician turbidite‐dominated deposition was almost exclusively sourced from rocks consolidated during the Timanian orogeny (Timanian basement). A profound change in provenance occurred near the end of the Ordovician. Over 90% of the zircons from Silurian and about 80% from Devonian strata have ages characteristic of the Sveconorwegian Orogen, implying uplift of these rocks in the vicinity of Novaya Zemlya. The presence of Sveconorwegian and Grenvillian rocks in the high Arctic suggests revision of recent reconstructions of the Rodinia supercontinent, its break‐up and subsequent Caledonian orogeny.  相似文献   

The accessibility of nodes in the Belgian road network     

Walter Lannoy  Dirk Oudheusden 《GeoJournal》1991,2(1):65-70

This paper presents an analysis of the accessibility of nodes in the Belgian road network. The intersection of roads are considered as the nodes and their connecting roads as the edges of a network. By means of the Dijkstra algorithm accessibility values are computed for each node by summing shortest travel times to a reference system of 158 nodes spread evenly over the Belgian territory. A comparison of the measured actual accessibility with that determined from an optimal situation provides an indication of the quality of directness of the Belgian road system. Accessibility and directness are shown cartographically. An isochronal map illustrates the access to Brussels.  相似文献   

The granulometrical characteristics of a slowly-moving dust cloud   总被引：1，自引：0，他引：1  

Dirk Goossens 《地球表面变化过程与地形》1985,10(4):353-362

A torn-up road offered the opportunity to sample a dust cloud continuously at different heights during a time interval of 51 hours. In particular the granulometrical characteristics of the dust caught were investigated. It appears that if the air layer in the vicinity of a dust cloud is not too turbulent, the cloud will be clearly granulometrically stratified. The coarse material moves chiefly at the bottom of the cloud, whereas the fine material will occur both at the bottom and at the top. The experiment also shows that the higher the dust in the cloud, the worse it is sorted. Above a critical height, however, the degree of sorting increases again. The variation of the mean dust diameter d₅₀, as a function of the height z, can be expressed in a simple semi-logarithmic equation. The variation of the dust quantity G, as a function of the height z, can also be expressed in a semi-logarithmic form but the correlation is higher when a power equation is used. The ratio of fine silt to coarse silt seems to vary parabolically with height. One can only speak of an optimal transport height in the case of particles > 16 μm. For finer particles, the turbulence of a normal air stream is usually high enough to carry the particles anywhere in the dust cloud, so that one can no longer speak of an optimal transport height. The granulometrical border between aeolian transport in saltation and aeolian transport in suspension lies, according to the results of the experiment, at a diameter of about 63 μm.  相似文献   

Hafnium/rare earth element fractionation in the sedimentary system and crustal recycling into the Earth's mantle     

P.J. Patchett  W.M. White  H. Feldmann  S. Kielinczuk  A.W. Hofmann 《Earth and Planetary Science Letters》1984,69(2):365-378

Among long-lived radioactive parent-daughter element pairs, the ratio Lu/Hf is strongly fractionated relative to constant Sm/Nd in the Earth's sedimentary system. This is caused by high resistance to chemical weathering of the mineral zircon (Zr,Hf)SiO₄. Zircon-bearing sandy sediments on and near continents have very low Lu/Hf, while deep-sea clays have up to three times the chondritic Lu/Hf ratio. Turbidity currents mechanically carry the low-Lu/Hf sandy material onto the ocean floor. The results are important for the crust-to-mantle recycling discussion, where most recycled materials would be subducted oceanic sediments. Such sediment should be capable of explaining the HfNd mantle isotopic variation by mixing with peridotite, but in fact any average pelagic sediment has Nd/Hf and Lu/Hf too high to allow mixing curves to pass through the Hf/Nd isotopic array. The array could only be reproduced by subduction of turbidite sandstone with pelagic sediment in the approximate ratio 1.2 to 1, and by maintaining a good mixture between the two components. At least today, turbidites are available for subduction only at locations quite different and distant from those where pelagic sediments may be recycled; furthermore, mantle isotopic variation shows that the mantle often cannot mix itself well enough to homogenize these widely-separated sedimentary components to the degree required. The Lu/Hf fractionations place a severe restriction on the ability of recycled sediments to explain mantle isotopic patterns.  相似文献   

Slip rates variability and sediment mobilization on a shallow landslide in the northern Swiss Alps     

Marco Schwab  Christine Läderach  Dirk Rieke-Zapp  Fritz Schlunegger 《Swiss Journal of Geoscience》2007,100(2):281-292

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Stratigraphic filtering and source penetration depth     

Mirko van der Baan  James Wookey  Dirk Smit 《Geophysical Prospecting》2007,55(5):679-684

Seismic exploration underneath highly heterogeneous layers such as basalt flows is possible by lowering the principal source frequency. Unfortunately this also reduces resolution. Wave‐localization theory is a multiple scattering theory that can be used to study stratigraphic filtering in chaotic lithologies. It predicts the apparent attenuation due to scattering of a plane wave traversing a layer with high velocity fluctuations. It can therefore predict the optimum principle source frequency in the trade‐off between loss of resolution and increased penetration depth. We show how this can be done with the help of a few statistical parameters derived from a well‐log analysis; namely, the average background velocity, the expected standard deviation in the velocity fluctuations, the typical scale length of the heterogeneities and the thickness of the basalt layer. In the likely situation that no local well logs exist, a multitude of scenarios can easily be examined at low cost.  相似文献   

On the meridional circulation and balance of momentum in the Southern Ocean of POP     

Dirk Olbers  Vladimir O. Ivchenko 《Ocean Dynamics》2001,52(2):79-93

 The circulation of the Southern Ocean is studied in the eddy-resolving model POP (Parallel Ocean Program) by an analysis of zonally integrated balances. The TEM formalism (Transformed Eulerian Mean) is extended to include topography and continental boundaries, thus deviations from a zonally integrated state involve transient and standing eddies. The meridional circulation is presented in terms of the Eulerian, eddy-induced, and residual streamfunctions. It is shown that the splitting of the meridional circulation into Ekman and geostrophic transports and the component induced by subgrid and Reynolds stresses is identical to a particular form of the zonally integrated balance of zonal momentum. In this balance, the eddy-induced streamfunctions represent the interfacial form stresses by transient and standing eddies and the residual streamfunction represents the acceleration of the zonal current by density fluxes in a zonally integrated frame. The latter acceleration term is directly related to the surface flux of density and interior fluxes due to the resolved and unresolved eddies. The eddy-induced circulation is extremely vigorous in POP. In the upper ocean a shallow circulation, reversed in comparison to the Deacon cell and mainly due to standing eddies, appears to the north of Drake Passage latitudes, and in the Drake Passage belt of latitudes a deep-reaching cell is induced by transient eddies. In the resulting residual circulation the Deacon cell is largely cancelled and the residual advection of the zonal mean potential density is balanced by diapycnal eddy and subgrid fluxes which are strong in the upper few hundred meters but small in the ocean interior. The balance of zonal momentum is consistent with other eddy-resolving models; a new aspect is the clear identification of density effects in the zonally integrated balance. We show that the wind stress and the stress induced by the residual circulation drive the eastward current, whereas both eddy species result in a braking. Finally, we extend the Johnson–Bryden model of zonal transport to incorporate all relevant terms from the zonal momentum balance. It is shown that wind stress and induction by the residual circulation carry an eastward transport while bottom form stress and the stress induced by standing eddies yield westward components of transport. Received: 26 June 2001 / Accepted: 2 November 2001  相似文献   

The aeolian dust accumulation curve     

Dirk Goossens 《地球表面变化过程与地形》2001,26(11):1213-1219

This article presents a simple physical concept of aeolian dust accumulation, based on the behaviour of the subprocesses of dust deposition and dust erosion. The concept is tested in an aeolian dust wind tunnel. The agreement between the accumulation curve predicted by the model and the accumulation curve obtained in the experiments is close to perfect and shows that it is necessary to discriminate between the processes of aeolian dust deposition and aeolian dust accumulation. Two important thresholds determine the accumulation process. For wind speeds below the deflation threshold, the aeolian accumulation of dust increases linearly with the wind speed. For wind velocities between the deflation threshold and the accumulation limit, the sedimentation balance is above unity and there is still accumulation, though it rapidly drops once the deflation threshold has been exceeded. At wind speeds beyond the accumulation limit, the sedimentation balance is below unity and there will no longer be an accumulation of dust. The thresholds have been determined in a wind tunnel test at friction velocity u_* = 0·34 m s^?1 (deflation threshold) and u_* = 0·43 m s^?1 (accumulation limit), but these values are only indicative since they depend heavily on the characteristics of the accumulation surface and of the airborne grains. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Big Earth data: disruptive changes in Earth observation data management and analysis?     

Martin Sudmanns  Dirk Tiede  Stefan Lang  Helena Bergstedt  Georg Trost  Hannah Augustin 《International Journal of Digital Earth》2020,13(7):832-850

ABSTRACT

Turning Earth observation (EO) data consistently and systematically into valuable global information layers is an ongoing challenge for the EO community. Recently, the term ‘big Earth data’ emerged to describe massive EO datasets that confronts analysts and their traditional workflows with a range of challenges. We argue that the altered circumstances must be actively intercepted by an evolution of EO to revolutionise their application in various domains. The disruptive element is that analysts and end-users increasingly rely on Web-based workflows. In this contribution we study selected systems and portals, put them in the context of challenges and opportunities and highlight selected shortcomings and possible future developments that we consider relevant for the imminent uptake of big Earth data.  相似文献   

A Late Tournaisian synmetamorphic folding and thrusting event in the eastern Variscan foreland: 40Ar/39Ar evidence from the phyllites of the Wolsztyn–Leszno High,western Poland     

Żelaźniewicz  Andrzej  Marheine  Dirk  Oberc-Dziedzic  Teresa 《International Journal of Earth Sciences》2003,92(2):185-194

A Variscan foreland in western Poland comprises two NW-trending basement highs, which are concealed under Carboniferous through Triassic strata of the Fore-Sudetic Monocline (FSM). Both highs consist of multiply deformed quartz-sericite - albite - chlorite phyllites of unknown protolith age. ⁴⁰Ar/³⁹Ar laser probe dating of white micas in up to 0.5-mm-thick mica layers, which form the S₂ axial-plane foliation in phyllites of the Wolsztyn-Leszno High, yielded an age of 340.1DŽ.6 Ma for the lower greenschists facies metamorphism and probably also for the F₂ folding. This deformation was associated and followed by thrusting, which brought about the basement highs. The latter delivered clasts to overlying late Viséan-early Namurian flysch basin that was mainly sourced from the Saxothuringian Sudetes in which most of the deformation occurred between 345-335 Ma. The FSM basement may represent an independent terrane, referred to as the Wielkopolska terrane, belonging to the Armorican Terrane Assemblage.  相似文献