Crustal structure of the Rhenish Massif: results of deep seismic reflection lines Dekorp 2-North and 2-North-Q   总被引：1，自引：1，他引：0  

Prof. Dr. W. Franke  Prof. Dr. R. K. Bortfeld  Dr. M. Brix  Dr. G. Drozdzewski  Prof. Dr. H. J. Dürbaum  Prof. Dr. P. Giese  Dr. W. Janoth  Dr. H. Jödicke  Chr Reichert Dipl.-Geophys.  Dr. A. Scherp  J. Schmoll Dipl.-Geophys.  R. Thomas Dipl.-Geophys.  Dr. M. Thünker  Prof. Dr. K. Weber  Dr. M. G. Wiesner  Prof. Dr. H. K. Wong 《International Journal of Earth Sciences》1990,79(3):523-566

The reflection seismic line DEKORP 2-N reveals an almost complete cross section through the Rhenohercynian Zone, the most external part of the Variscan orogen in Europe.The northern part of DEKORP 2-N and a NE-directed branch (2-N-Q) reveal the Cretaceous of the Münsterland basin and the underlying folded Palaeozoic rocks. The northward decreasing intensity of folding is depicted in great detail by the highly reflective Late Carboniferous coal-measures and deeper reflections down to the level of the Givetian/Frasnian shallow-water carbonates.In the Devonian and older rocks of the Rhenish Massif, bedding is only represented by relatively weak, short and irregular reflections. These are truncated by stronger, southward dipping reflections, which exhibit the listric curvature and flat/ramp geometry characteristic of faults. In the northern part of the section, the thrusts appear to be blind. From the Ebbe Anticline southwards, prominent reflections can be correlated with important thrust faults known from the surface, such as the Ebbe-, Siegen-, Müsen- and Sackpfeife- Thrusts, as well as further important thrust faults in the Lahn- and Dill Synclines. The basal thrust of the extremely thin-skinned Giessen Nappe is only recognizable for a very short distance.At depth, the thrusts flatten out in a relatively transparent zone between 3–5 s TWT, with strongly reflective bands at its bottom and top. The transparent zone might correlate with a high-conductivity layer detected in a magnetotelluric survey; it represents either graphitic metapelites or a zone with an interconnected, brine-filled pore space. The seismic record relates either to lithological differences, or to rheological boundaries.The lower crust in the north is characterized by a relatively transparent zone, which wedges out towards south under the northern margin of the Siegen Anticline. Comparisons with a similar feature in the ECORS profile »Nord de la France« suggest that the transparent zones in both sections correspond to a pre-Palaeozoic basement, such as it underlies the Brabant Massif. Further south, the lower crust is increasingly reflective.The curvilinear, thrust-related reflections are cut by a conjugate set of much weaker, N- and S-dipping reflectors indicating a later deformation with pure shear. Displacement of some marker reflections suggests late- or post-Variscan compression.In an alternative interpretation, these straight and weak reflections represent the only thrust faults, while the curvilinear elements might relate to bedding.A southward rise of the Moho from approx. 11 to 8.5 s TWT is probably due to Tertiary rifting.

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Zusammenfassung Das reflexionsseismische Profil DEKORP 2-N stellt einen fast vollständigen Querschnitt durch das Rhenohercynikum dar.Der nördliche Teil des Profiles 2-N sowie ein SW/NE-verlaufender Abzweig (2-N-Q) zeigen die Transgression der Münsterländer Kreide und das unterlagernde gefaltete Paläozoikum. Schichtgebundene Reflektoren (flözführendes Karbon, devonischer Massenkalk) bilden das Ausklingen der variscischen Faltung nach NW detailliert ab.In den devonischen und vordevonischen Sedimenten des rechtsrheinischen Schiefergebirges erzeugt die Schichtung nur relativ schwache, kurze und unregelmäßige Reflexionen. Diese werden von stärkeren, südfallenden Reflektoren abgeschnitten, die aufgrund ihrer listrischen Krümmung und flat/ramp-Geometrie wahrscheinlich als Überschiebungen zu interpretieren sind. Im Nordteil des Schiefergebirges sind diese Überschiebungen offenbar blind, werden also nahe der Oberfläche durch Faltung kompensiert. Im Ebbe-Sattel und weiter südlich lassen sich die meisten der starken, südfallenden Reflektoren zweifelsfrei mit bekannten Großüberschiebungen korrelieren (Ebbe-, Siegen-, Müsen-, Sackpfeife-Ü, sowie weitere Überschiebungen in der Lahn- u. Dill-Mulde). Die Basisüberschiebung der Giessen-Decke wird nur teilweise abgebildet.Zur Tiefe hin zeigen die Überschiebungen ein zunehmend flacheres Einfallen, und verschwinden in einer relativ transparenten Zone zwischen 3 und 5 s TWT, die im Hangenden und Liegenden durch dünne, stark reflektive Zonen begrenzt ist. Diese transparente Zone entspricht möglicherweise einer Zone hoher integrierter Leitfähigkeit, die in einem begleitenden magnetotellurischen Experiment nachgewiesen worden ist; es handelt sich entweder um einen Graphit-führenden Phyllit-Horizont oder eine mächtigere permeable Zone mit Elektrolyt-gefülltem Porenraum. Die hochreflektiven Bänder über und unter der transparenten Zone entsprechen entweder lithologischen Kontrasten oder rheologischen Grenzen, die vermutlich von einer scherenden Verformung überprägt worden sind.Die Unterkruste im N-Teil des Profiles enthält einen relativ transparenten Bereich, der nach Süden hin unter dem Nordteil des Siegener Sattels keilförmig ausläuft. Ein ähnliches Bild zeigt der Nordteil des ECORS-Profiles »Nord de la France«. Die transparenten Bereiche beider Profile entsprechen wahrscheinlich einem prä-paläozoischen kristallinen Basement, das das Brabanter Massif unterlagert und sich rechtsrheinisch fortsetzt. Südlich des transparenten Keiles wird die Unterkruste zunehmend reflexionsreicher. Die listrisch gekrümmten, an Überschiebungen gebundenen Reflektoren werden von einem konjugierten System schwächerer, N- u. S-fallender Reflektoren abgeschnitten, die auf eine jüngere, bruchhafte Verformung durch reine Scherung hindeuten. Der Versatz einiger älterer Reflektoren deutet auf spät- oder postvariscische Kompression hin.In einer alternativen Interpretation werden nur diese jüngeren Reflektoren als Überschiebungen gedeutet; die älteren, gekrümmten Elemente müßten dann primären lithologischen Grenzen entsprechen.Die Moho steigt von ca. 11 s TWT im N auf 8.5 s TWT unter dem Taunus an. Die Krustenverdünnung im Süden geht wahrscheinlich auf Dehnung im Tertiär zurück.

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Résumé Le profil sismique par réflexion DEKORP-2-N représente une transversale quasiment complète à travers la zone rhénohercynienne. La partie septentrionale du DEKORP-2-N ainsi qu'une branche de direction SW-NE (2-N-Q) mettent en évidence la transgression du Crétacé du Münsterland sur le Paléozoïque sous-jacent plissé. Des réflecteurs liés à la stratification (à savoir: le Houiller et les calcaires de plate-forme dévoniens) illustrent de façon détaillée la diminution vers le nord de l'intensité du plissement varisque.Dans les sédiments dévoniens et pré-dévoniens du Massif Rhénan à l'est du Rhin, la stratification ne fournit que que des réflexions relativement faibles, courtes et irrégulières. Elles sont tronquées par des réflecteurs plus intenses, à pendage sud qui, en raison de leur courbure listrique et de leur géométrie en «flat/ramp», doivent être interprétés comme des chevauchements. Dans la partie septentrionale du Massif, ces chevauchements sont apparemment aveugles, c'est-à-dire qu'ils sont compensés, près de la surface, par le plissement. Dans l'anticlinal d'Ebbe, ainsi que plus au sud, la plupart des réflecteurs intenses à plongement sud peuvent être corrélés avec des chevauchements majeurs connus, tels ceux de Ebbe, Siegen, Müsen, Sackpfeife et d'autres encore dans les synclinaux de la Lahn et de la Dill. Le chevauchement basai de la nappe de Giessen n'est que partiellement représenté.Les chevauchements deviennent de plus en plus plats en profondeur pour disparaître dans une zone relativement transparente qui se situe entre 3–5 sec TWT. Celle-ci est prise en sandwich par des zones minces à forte réflectivité. La zone transparente correspond probablement à une zone de conductivité intégrée élevée dont l'existence a par ailleurs été démontrée dans un essai magnétotellurique mené parallèlement. Il s'agit soit d'un horizon phyllitique graphiteux, soit d'une zone perméable plus épaisse dont les pores sont remplis d'électrolyte. Les bandes à haute réflectivité au-dessus et en-dessous de la zone transparente correspondent soit à des contrastes lithologiques, soit à des limites rhéologiques probablement accentuées par la déformation cisaillante.La croûte inférieure dans la partie septentrionale du profil comporte un domaine relativement transparent qui s'amincit vers le S et se termine, en dessous de la partie nord de l'anticlinal de Siegen, en forme de coin. La partie nord du profil ECORS «Nord de la France» montre une image semblable.Les domaines transparents des deux profils correspondent vraisemblablement à un soubassement cristallin pré-paléozoïque qui est sousjacent au Paléozoïque du Massif du Brabant et se prolonge vers l'est au-delà du Rhin. Au sud du coin transparent, la réflectivité de la croûte inférieure va en augmentant. Les réflecteurs listriques liés à des chevauchements sont recoupés par un système conjugué de réflecteurs plus faibles à plongement nord et sud qui indiquent des failles plus récentes. Le déplacement de quelques réflecteurs plus anciens suggère l'effet d'une compression tardiou post-varisque.Dans une interprétation alternative, seuls ces réflecteurs plus récents sont considérés comme correspondant à des chevauchements. Dans ce cas, les éléments courbes plus anciens devraient représenter des limites lithologiques primaires.Le Moho s'élève à partir de 11 sec TWT environ au nord jusqu'à 8.5 sec TWT en-dessous du Taunus. L'amincissement crustal au sud résulterait du régime de distension survenu au Tertiaire.

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DEKORP 2 Nord. x-t- ray-tracing'a. 6,0 6,6 /, — 7,0 8,2 /. 6,25 /. 28 30 . , .

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Abbreviations MORB Mid-Ocean Ridge Basalt - TWT two-way travel time, seconds (s) - CMP common mid-point - VP vibration point - SNR signal to noise ratio  相似文献   

Holocene record of productivity in the NW Iberian continental shelf     

V. Alves Martins  C. Patinha  E. Ferreira da Silva  J.-M. Jouanneau  O. Weber  F. Rocha   《Journal of Geochemical Exploration》2006,88(1-3):408

A multiproxy approach (textural characteristics, heavy metal concentrations and benthic foraminifera data) was adopted to study the OMEX core KSGX 40, collected at the Galicia Mud Deposit (NW Iberian outer continental shelf) and recording the last ca. 4.8 ka cal BP. Geochemical profiles of Fe, Mn, Zn, Co, Cr, Cu, Ni, Pb, Al and Ca show significant temporal variations. Benthic foraminifera productivity proxy suggests that the recorded muddy events were contemporaneous of a higher C_org flux to the marine benthic environment. The higher flux of organic matter, following a long-term intensification of the upwelling and coinciding with a finer sedimentation, led to depressed levels of oxygen beneath the water-sediments interface and to early diagenetic processes of several redox-sensitive elements.  相似文献   

Variations in water clarity and chlorophylla in Tampa Bay, Florida, in response to annual rainfall, 1985–2004     

Gerold Morrison  Edward T. Sherwood  Richard Boler  Joe Barron 《Estuaries and Coasts》2006,29(6):926-931

In the Tampa Bay region of Florida, extreme levels of annual and seasonal rainfall are often associated with tropical cyclones and strong El Niño episodes. We used stepwise multiple regression models to describe associations between annual and seasonal rainfall levels and annual, bay-segment mean water clarity (as Secchi depth [m]), chlorophylla (μg I^?1), color (pcu), and turbidity (ntu) over a 20-yr period (1985–2004) during which estimated nutrient loadings have been dominated by non-point sources. For most bay segments, variations in annual mean water clarity were associated with variations in chlorophylla concentrations, which were associated in turn with annual or seasonal rainfall. In two bay segments these associations with annual rainfall were superimposed on significant long-term declining trends in chlorophylla. Color was significantly associated with annual rainfall in all bay segments, and in one segment variations in color were the best predictors of variations in water clarity. Turbidity showed a declining trend over time in all bay segments and no association with annual rainfall, and was significantly associated with variations in water clarity in only one bay segment. While chlorophylla, color, and turbidity a affected water clarity to varying degrees, the effects of extreme rainfall events (El Niño events in 1998 and 2003, and multiple tropical cyclone events in 2004) on water clarity were relatively short-lived, persisting for periods of months rather than years. During the 20-yr period addressed in these analyses, declining temporal trends in chlorophylla and turbidity, produced in part by a long-term watershed management program that has focused on curtailing annual loadings of nitrogen and other pollutants, may have helped to prevent the bay as a whole from responding more adversely to the high rainfall periods that occurred in 1998 and 2003–2004.  相似文献   

Land-surface scheme validation using the Oklahoma Atmospheric Surface-layer Instrumentation System (OASIS) and Oklahoma Mesonet data: Preliminary results     

J. A. Brotzge  D. Weber 《Meteorology and Atmospheric Physics》2002,80(1-4):189-206

Summary The Oklahoma Atmospheric Surface-layer Instrumentation System (OASIS) is a recently-developed observational system that collects, archives, and quality controls atmospheric, surface, and soil data in real-time from 90 stations across Oklahoma. Ten of the 90 sites, termed “super sites”, are equipped with additional sonic anemometry and four-component net radiometers to provide complete observations of the surface energy balance. Oklahoma Mesonet and OASIS data are used in this study to validate the sensitivity and accuracy of a land-surface scheme within a numerical prediction model. The Advanced Regional Prediction System (ARPS) is a three-dimensional, nonhydrostatic mesoscale model developed by the Center for Analysis and Prediction of Storms (CAPS) at the University of Oklahoma. The land-surface model (LSM) used within ARPS is the Interactions Soil Biosphere Atmosphere (ISBA) scheme. Mesonet and OASIS data collected from the super site located in Norman, Oklahoma, are used as verification for the ISBA. Research presented in this study outlines the challenges in developing, maintaining, and using in-situ data for model validation. Such problems as instrument error, surface heterogeneity, and non-closure of the surface energy budget limit data accuracy. Preliminary results of model validation focus on the sensitivity of the soil physics within the ISBA scheme. Model sensitivity to vegetation cover, surface roughness, and soil type are investigated. Furthermore, several recent improvements to ISBA are evaluated and compared to observations. This study concludes that the sensitivity of the ISBA to a priori soil and vegetation type is detrimental for this scheme to be used in a mesoscale model without improved treatment of surface heterogeneity. Received November 18, 2001 Revised December 28, 2001  相似文献   

Late Cretaceous reactivation of major crustal shear zones in northern Namibia: constraints from apatite fission track analysis     

Matthias J. Raab  Roderick W. Brown  Kerry Gallagher  Andrew Carter  Klaus Weber   《Tectonophysics》2002,349(1-4)

Namibia's passive continental margin records a long history of tectonic activity since the Proterozoic. The orogenic belt produced during the collision of the Congo and Kalahari Cratons in the Early Proterozoic led to a zone of crustal weakness, which became the preferred location for tectonism during the Phanerozoic. The Pan-African Damara mobile belt forms this intraplate boundary in Namibia and its tectonostratigraphic zones are defined by ductile shear zones, where the most prominent is described as the Omaruru Lineament–Waterberg Thrust (OML–WT). The prominance of the continental margin escarpment is diminished in the area of the Central and Northern Zone of the Damara belt where the shear zones are located. This area has been targeted with a set of 66 outcrop samples over a 550-km-long, 60-km-broad coast-parallel transect from the top of the escarpment in the south across the Damara sector to the Kamanjab Inlier in the north. Apatite fission track age and length data from all samples reveal a regionally consistent cooling event. Thermal histories derived by forward modelling bracket this phase of accelerated cooling in the Late Cretaceous. Maximum palaeotemperatures immediately prior to the onset of cooling range from ca. 120 to ca. 60 °C with the maximum occurring directly south of the Omaruru Lineament. Because different palaeotemperatures indicate different burial depth at a given time, the amount of denudation can be estimated and used to constrain vertical displacements of the continental crust. We interpret this cooling pattern as the geomorphic response to reactivation of basement structures caused by a change in spreading geometry in the South Atlantic and South West Indian Oceans.  相似文献   

Seismic image of the deep crust at the eastern margin of the Alps (Austria): indications for crustal extension in a convergent orogen     

H. Graßl  F. Neubauer  K. Millahn  F. Weber 《Tectonophysics》2004,380(1-2):105-122

A 39-km-long deep seismic reflection profile recorded during two field campaigns in 1996 and 2002 provides a first detailed image of the deep crust at the eastern margin of the Eastern Alps (Austria). The ESE–WNW-trending, low-fold seismic line crosses Austroalpine basement units and extends approximately from 20 km west of the Penninic window group of Rechnitz to 60 km SSE of the Alpine thrust front.The explosive-source seismic data reveals a transparent shallow crust down to 5 km depth, a complexly reflective upper crust and a highly reflective lowermost crust. The upper crust is dominated by three prominent west-dipping packages of high-amplitude subparallel reflections. The upper two of these prominent packages commence at the eastern end of the profile at about 5 and 10 km depth and are interpreted as low-angle normal shear zones related to the Miocene exhumation of the Rechnitz metamorphic core complex. In the western portion of the upper crust, east-dipping and less significant reflections prevail. The lowermost package of these reflections is suggested to represent the overall top of the European crystalline basement.Along the western portion of the line, the lower crust is characterised by a 6–8-km-thick band of high-amplitude reflection lamellae, typically observed in extensional provinces. The Moho can be clearly defined at the base of this band, at approximately 32.5 km depth. Due to insufficient signal penetration, outstanding reflections are missing in the central and eastern portion of the lower crust. We speculate that the result of accompanying gravity measurements and lower crustal sporadic reflections can be interpreted as an indication for a shallower Moho in the east, preferable at about 30.5 km depth.The high reflectivity of the lowermost part of the lower crust and prominent reflection packages in the upper crust, the latter interpreted to represent broad extensional mylonite zones, emphasises the latest extensional processes in accordance with eastward extrusion.  相似文献   

Imaging the Dead Sea Transform with scattered seismic waves   总被引：2，自引：0，他引：2  

N. Maercklin  C. Haberland  T. Ryberg  M. Weber  Y. Bartov  the DESERT Group 《Geophysical Journal International》2004,158(1):179-186

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Force interactions between magnetite,silica, and bentonite studied with atomic force microscopy     

I. Dobryden  E. Potapova  A. Holmgren  H. Weber  J. Hedlund  N. Almqvist 《Physics and Chemistry of Minerals》2015,42(4):319-326

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Testing the suitability of geologic frameworks for extrapolating hydraulic properties across regional scales     

Benjamin B Mirus  Keith Halford  Don Sweetkind  Joe Fenelon 《Hydrogeology Journal》2016,24(5):1133-1146

The suitability of geologic frameworks for extrapolating hydraulic conductivity (K) to length scales commensurate with hydraulic data is difficult to assess. A novel method is presented for evaluating assumed relations between K and geologic interpretations for regional-scale groundwater modeling. The approach relies on simultaneous interpretation of multiple aquifer tests using alternative geologic frameworks of variable complexity, where each framework is incorporated as prior information that assumes homogeneous K within each model unit. This approach is tested at Pahute Mesa within the Nevada National Security Site (USA), where observed drawdowns from eight aquifer tests in complex, highly faulted volcanic rocks provide the necessary hydraulic constraints. The investigated volume encompasses 40 mi³ (167 km³) where drawdowns traversed major fault structures and were detected more than 2 mi (3.2 km) from pumping wells. Complexity of the five frameworks assessed ranges from an undifferentiated mass of rock with a single unit to 14 distinct geologic units. Results show that only four geologic units can be justified as hydraulically unique for this location. The approach qualitatively evaluates the consistency of hydraulic property estimates within extents of investigation and effects of geologic frameworks on extrapolation. Distributions of transmissivity are similar within the investigated extents irrespective of the geologic framework. In contrast, the extrapolation of hydraulic properties beyond the volume investigated with interfering aquifer tests is strongly affected by the complexity of a given framework. Testing at Pahute Mesa illustrates how this method can be employed to determine the appropriate level of geologic complexity for large-scale groundwater modeling.  相似文献   

Evaluating Tidal Wetland Restoration Performance Using National Estuarine Research Reserve System Reference Sites and the Restoration Performance Index (RPI)     

Kenneth B. Raposa  Scott Lerberg  Craig Cornu  John Fear  Nina Garfield  Christopher Peter  Robin L.J. Weber  Gregg Moore  David Burdick  Michelle Dionne 《Estuaries and Coasts》2018,41(1):36-51

Evaluations of tidal wetland restoration efforts suffer from a lack of appropriate reference sites and standardized methods among projects. To help address these issues, the National Estuarine Research Reserve System (NERRS) and the NOAA Restoration Center engaged in a partnership to monitor ecological responses and evaluate 17 tidal wetland restoration projects associated with five reserves. The goals of this study were to (1) determine the level of restoration achieved at each project using the restoration performance index (RPI), which compares change in parameters over time between reference and restoration sites, (2) compare hydrologic and excavation restoration projects using the RPI, (3) identify key indicator parameters for assessing restoration effectiveness, and (4) evaluate the value of the NERRS as reference sites for local restoration projects. We found that the RPI, modified for this study, was an effective tool for evaluating relative differences in restoration performance; most projects achieved an intermediate level of restoration from 2008 to 2010, and two sites became very similar to their paired reference sites, indicating that the restoration efforts were highly effective. There were no differences in RPI scores between hydrologic and excavation restoration project types. Two abiotic parameters (marsh platform elevation and groundwater level) were significantly correlated with vegetation community structure and thus can potentially influence restoration performance. Our results highlight the value of the NERRS as reference sites for assessing tidal wetland restoration projects and provide improved guidance for scientists and restoration practitioners by highlighting the RPI as a trajectory analysis tool and identifying key monitoring parameters.  相似文献