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1.
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.
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
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.
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.
DEKORP 2 Nord. x-t- ray-tracing'a. 6,0 6,6 /, — 7,0 8,2 /. 6,25 /. 28 30 . , .
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
2.
GUNNAR ØSTREM NILS HAAKENSEN HANS CHR. OLSEN 《Geografiska Annaler: Series A, Physical Geography》2005,87(1):243-258
ABSTRACT. The retreat of Nigardsbreen, an outlet glacier from the ice-cap Jostedalsbreen in south-central Norway, from its largest extent during the Little Ice Age, uncovered a proglacial lake during 1936–1967. This lake, Nigardsvatn, has been studied since 1968 in order to obtain data on solid material carried by the meltwater stream from the glacier, both in suspension and as bottom load. Between 70 and 85% of the suspended sediment has been deposited on the lake bottom, forming annual varves. The coarse material has been deposited in a delta, the formation of which started in 1968. Its growth, and hence the volume of total annual bottom load, has been surveyed annually for the past 36 years. In 1969 the entire bottom load was collected by building a fence-like net across the river. Material >3 cm was caught by this net, and formed approximately half the amount of suspended sediment transport during the same three-week period. Annual average deposition on the delta was 11800×103 kg for the period 1968–2003. This is almost the same amount as carried in suspension from the glacier on an annual mean basis for the 36-year period. If conditions remain constant, the lake will be completely filled in about 500 years. The glacier erosion is calculated to be 0.3 mm/a. 相似文献
3.
4.
5.
HANS PIRLET LAURA M. WEHRMANN BENJAMIN BRUNNER NORBERT FRANK JAN DEWANCKELE DAVID VAN ROOIJ ANNELEEN FOUBERT RUDY SWENNEN LIEVEN NAUDTS MATTHIEU BOONE VEERLE CNUDDE JEAN‐PIERRE HENRIET 《Sedimentology》2010,57(3):786-805
Authigenic gypsum was found in a gravity core, retrieved from the top of Mound Perseverance, a giant cold‐water coral mound in the Porcupine Basin, off Ireland. The occurrence of gypsum in such an environment is intriguing, because gypsum, a classic evaporitic mineral, is undersaturated with respect to sea water. Sedimentological, petrographic and isotopic evidence point to diagenetic formation of the gypsum, tied to oxidation of sedimentary sulphide minerals (i.e. pyrite). This oxidation is attributed to a phase of increased bottom currents which caused erosion and enhanced inflow of oxidizing fluids into the mound sediments. The oxidation of pyrite produced acidity, causing carbonate dissolution and subsequently leading to pore‐water oversaturation with respect to gypsum and dolomite. Calculations based on the isotopic compositions of gypsum and pyrite reveal that between 21·6% and 28·6% of the sulphate incorporated into the gypsum derived from pyrite oxidation. The dissolution of carbonate increased the porosity in the affected sediment layer but promoted lithification of the sediments at the sediment‐water interface. Thus, authigenic gypsum can serve as a signature for diagenetic oxidation events in carbonate‐rich sediments. These observations demonstrate that fluid flow, steered by environmental factors, has an important effect on the diagenesis of coral mounds. 相似文献
6.
The replacement by ferroan calcite with preservation of the original structures can be used as a new criterion for identifying skeletons originally composed of high-magnesian calcite. This applies to bryozoa, rugose corals, echinoderms, many foraminifera, most ostracods, red algae, and serpulids. On the other hand, skeletons originally composed of low-magnesian calcite were never replaced by ferroan calcite, as shown by belemnites, brachiopods, and most of the pelecypods. Using this criterion, an original low-magnesian calcite composition is inferred for Tentaculites and some ostracods and foraminifera, whereas a previous high-magnesian calcite composition is inferred for trilobites, oligostegina and certain ooids. Chemical instability of high-magnesian calcite is suggested to be the driving force of the replacement by ferroan calcite. In most of the thirty-seven samples investigated, of Oligocene to Devonian age, the ferrous iron concentration of the interstitial fluid increased during diagenesis, as shown by well established sequences of cement A and B and fissure fill. This offers a relative time scale for diagenetic processes. Ferroan calcites contain up to 6 mol % FeCO3 and up to 5 mol % MgCO3. In this range of concentration, the distribution coefficients for Fe and Mg between calcite and solution at about 25°C are about 1 to 0-03, respectively, according to experiments. Possible sources of iron are iron oxides and hydroxides as well as clay minerals including glauconite. Though a submarine origin below the sediment surface is conceivable for ferroan calcite, there are serious limiting conditions such as low Eh and, at the same time, lack in sulphate-reducing bacteria. On the other hand, ferroan ‘dedolomite’, compositional zonality in individual ferroan calcite overgrowths, low δ18C and δ18O values, and low Mg concentrations point more to a meteoric-phreatic origin of many ferroan calcite occurrences. 相似文献
7.
A symposium on the genesis of till entitled Till/Sweden-76 was held in Stockholm 16–18 August 1976. This issue of Boreas contains most of the papers presented at the symposium. 相似文献
8.
KAREN LUISE KNUDSEN HANS PETTER SEJRUP 《Boreas: An International Journal of Quaternary Research》1988,17(3):347-354
Isoleucine epimerization (alle/Ile) ratios have been measured on foraminiferal tests from interglaical sites in the southern North Sea region. In order to evaluate the possibilities of this amino acid method on benthic foraminifera, sites were chosen from areas where the stratigraphy was already well known. The study demonstrates that the isoleucine epimerization reaction in benthic foraminifera can be used for correlation and as a means of relative age estimation within a limited geographic area. Previous suggestions of a Holsteinian age for the Rugrd, Tornskov, and Wacken sites are supported for the Kås Hoved site. The age of most presumed Eemian sites is supported by the amino acid results; the Reighton site also seems to belong in this interglacial. 相似文献
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10.
Late Weichselian glaciation history of the northern North Sea 总被引:8,自引:1,他引:8
HANS PETTER SEJRUP HAFLIDI HAFLIDASON INGE AARSETH EDWARD KING CARL FREDRIK FORSBERG DAVID LONG KÅRE ROKOENGEN 《Boreas: An International Journal of Quaternary Research》1994,23(1):1-13
Based on new data from the Fladen, Sleipner and Troll areas, combined with earlier published results, a glaciation curve for the Late Weichselian in the northern North Sea is constructed. The youngest date on marine sedimentation prior to the late Weichselian maximum ice extent is 29.4 ka BP. At this time the North Sea and probably large parts of southern Norway were deglaciated (corresponding to the Alesund interstadial in western Norway). In a period between 29.4 and c. 22 ka BP, the northern North Sea experienced its maximum Weichselian glaciation with a coalescing British and Scandinavian ice sheet. The first recorded marine inundation is found in the Fladen area where marine sedimentation started close to 22 ka BP. After this the ice fronts receded both to the east and west. The North Sea Plateau, and possibly parts of the Norwegian Trench, were ice-free close to 19.0 ka, and after this a short readvance occurred in this area. This event is correlated with the advance recorded at Dimlington, Yorkshire, and the corresponding climatostratigraphic unit is denoted the Dimlington Stadial (18.5 ka to 15.1 ka). The Norwegian Trench was deglaciated at 15.1 ka in the Troll area. The data from the North Sea, together with the results from Andwa, northern Norway (Vorren et al . 1988; Møller et al . 1992), suggest that the maximum extent of the last glaciation along the NW-European seaboard from the British Isles to northern Norway was prior to c . 22 ka BP. 相似文献