A new biostratigraphic correlation for Late Cretaceous–Paleocene strata of the Gulf of Guinea: Evidence from dinoflagellate cysts     

Raquel Sánchez-Pellicer  Edwige Masure  Loïc Villier 《Comptes Rendus Geoscience》2017,349(1):32-41

A new biostratigraphic correlation for Late Cretaceous and Palaeocene strata of the Côte d’Ivoire–Ghana continental margin has been developed from the identification of significant dinoflagellate cyst events in ODP Hole 959D. The Late Cretaceous stage boundaries are mostly consistent with previous studies. However, the Maastrichtian/Danian boundary is placed much lower than previously recognized on the basis of the first occurrences of Carpatella cornuta and Damassadinium californicum. The base of the Selandian is recognized from the last occurrence of Cerodinium diebelii and the first occurrence of Adnatosphaeridium multispinosum. The base of the Thanetian is recognized from the first occurrence of Areoligera gippingensis. The rarity of the age-marker taxa is the main reason for different age determinations among studies of the same section.  相似文献   

Weather radar observations of the Hekla 2000 eruption cloud,Iceland     

C.?LacasseEmail author  S.?Karlsdóttir  G.?Larsen  H.?Soosalu  W.?I.?Rose  G.?G.?J.?Ernst 《Bulletin of Volcanology》2004,66(5):457-473

The Hekla eruption cloud on 26–27 February 2000 was the first volcanic cloud to be continuously and completely monitored advecting above Iceland, using the C-band weather radar near the Keflavík international airport. Real-time radar observations of the onset, advection, and waning of the eruption cloud were studied using time series of PPI (plan-position indicator) radar images, including VMI normal, Echotop, and Cappi level 2 displays. The reflectivity of the entire volcanic cloud ranges from 0 to >60 dBz. The eruption column above the vent is essentially characterised by VMI normal and Cappi level 2 values, >30 dBz, due to the dominant influence of lapilli and ash (tephra) on the overall reflected signal. The cloud generated by the column was advected downwind to the north-northeast. It is characterised by values between 0 and 30 dBz, and the persistence of these reflections likely result from continuing water condensation and freezing on ash particles. Echotop radar images of the eruption onset document a rapid ascent of the plume head with a mean velocity of ~30 to 50 m s^–1, before it reached an altitude of ~11–12 km. The evolution of the reflected cloud was studied from the area change in pixels of its highly reflected portions, >30 dBz, and tied to recorded volcanic tremor amplitudes. The synchronous initial variation of both radar and seismic signals documents the abrupt increase in tephra emission and magma discharge rate from 18:20 to 19:00 UTC on 26 February. From 19:00 the >45 dBz and 30–45 dBz portions of the reflected cloud decrease and disappear at about 7 and 10.5 h, respectively, after the eruption began, indicating the end of the decaying explosive phase. The advection and extent of the reflected eruption cloud were compared with eyewitness accounts of tephra fall onset and the measured mass of tephra deposited on the ground during the first 12 h. Differences in the deposit map and volcanic cloud radar map are due to the fact that the greater part of the deposit originates by fallout off the column margins and from the base of the cloud followed by advection of falling particle in lower level winds.Editorial responsibility: P. Mouginis-Mark  相似文献   

Sliding response of gravity dams including vertical seismic accelerations     

Constantin?ChristopoulosEmail author  Pierre?Léger  André?Filiatrault 《地震工程与工程振动(英文版)》2003,2(2):189-200

Seismic safety assessment of gravity dams has become a major concern in many regions of the world while the effects of vertical seismic accelerations on the response of structures remain poorly understood. This paper first investigates the effect of including vertical accelerations in the sliding response analysis of gravity dams subjected to a range of historical ground motion records separated in two groups according to their source-to-site distance. Analyses showed that the incidence of vertical accelerations on the sliding response of gravity dams is significantly higher for near-source records than for farsource records. The pseudo-static 30% load combination rule, commonly used in practice to account for the non-simultaneous occurrence of the peak horizontal and vertical accelerations, yielded good approximations of the minimum safety factors against sliding computed from time-history analyses. A method for empirically estimating the vertical response spectra based on horizontal spectra, accounting for the difference in frequency content and amplitudes between the two components is investigated. Results from analyses using spectrum compatible horizontal and vertical synthetic records also approximated well the sliding response of a gravity dam subjected to series of simultaneous horizontal and vertical historical earthquake records.  相似文献   

On the accuracy of modified Stokes's integration in high-frequency gravimetric geoid determination     

P. Novák  P. Vaníc˘ek  M. Véronneau  S. Holmes  W. Featherstone 《Journal of Geodesy》2001,74(9):644-654

 Two numerical techniques are used in recent regional high-frequency geoid computations in Canada: discrete numerical integration and fast Fourier transform. These two techniques have been tested for their numerical accuracy using a synthetic gravity field. The synthetic field was generated by artificially extending the EGM96 spherical harmonic coefficients to degree 2160, which is commensurate with the regular 5^′ geographical grid used in Canada. This field was used to generate self-consistent sets of synthetic gravity anomalies and synthetic geoid heights with different degree variance spectra, which were used as control on the numerical geoid computation techniques. Both the discrete integration and the fast Fourier transform were applied within a 6^∘ spherical cap centered at each computation point. The effect of the gravity data outside the spherical cap was computed using the spheroidal Molodenskij approach. Comparisons of these geoid solutions with the synthetic geoid heights over western Canada indicate that the high-frequency geoid can be computed with an accuracy of approximately 1 cm using the modified Stokes technique, with discrete numerical integration giving a slightly, though not significantly, better result than fast Fourier transform. Received: 2 November 1999 / Accepted: 11 July 2000  相似文献   

Geomechanische Auswirkungen von Abtragungsvorgängen     

Univ.-Prof. Dr.-Ing. Dr. mont. h. c. Leopold Müller-Salzburg 《International Journal of Earth Sciences》1969,59(1):163-178

Zusammenfassung Durch Erosion verfrachtete Massen bedeuten nicht nur in den Sedimentationsräumen, sondern auch in den Gebieten der Abtragung einschneidende Belastungsänderungen. Geomechanisch betrachtet bringen sie keineswegs eine Entlastung des Materials im Sinne einer Spannungsminderung, sondern im Gegenteil Spannungsumlagerungen mit sich, welche nicht selten Überlastung des Materials bis zum Bruch bedeuten können. Die dabei ausgelösten Bewegungserscheinungen, Bruch- und Strukturbildungen, sind von weit höherer Größenordnung und reichen viel weiter und tiefer in die Umgebung des Bergleibes hinein als gemeinhin angenommen wird. Die Art ihrer Ausprägung hängt von dem im Krustenmaterial bereits vorhandenen Flächengefüge sowie von den in der Kruste herrschenden Spannungen ab, seien diese nun tektonischer Natur, Restspannungen aus tektonischen Vorgängen oder nur Eigengewichtsspannungen.Die solcherart durch Erosion einfacher Formen entstehenden Spannungsverteilungen, Bewegungen, Neuklüfte und Störungen können mittels der Finite-Element-Methode in einer jüngst vonMalina (1969) erweiterten Form derselben rechnerisch erfaßt werden, was an Beispielen vorgezeigt wird.

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The materials removed by erosion cause important changes of loading not only in the depositional areas but also in the regions of erosion. From the geomechanical point of view the changes in the erosional area will not have a simple unloading effect resulting in a decrease of stresses but will result in a reorientation of stresses which causes new stress concentrations, possibly even overstressing and fracturing of the material.The resulting displacements and fracture processes are far more important and reach farther and deeper into the surrounding rock masses than is commonly expected. Their development depends on the jointpatterns and stressfields already present in these rock masses, which can be of tectonic, residual tectonic or bodyforce origin.The reorientation of stressfields and resulting displacements and fracturing processes can be analysed mathematically by means of the Finite Element Method. For this purpose the Finite Element Method has been improved. Some examples are given.

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Résumé Les masses transportées par érosion impliquent des transformations importantes relatives aux sollicitations non seulement dans les zones sédimentaires mais aussi dans les domaines érodés. Au point de vue géomécanique elles n'entraînent pas du tout une décharge des matériaux au sens d'une chute des contraintes, mais imposent au contraire une réorientation des contraintes qui peut souvent entraîner l'apparition d'une nouvelle sollicitation et aussi d'une surcharge pouvant conduire á la rupture. Les déplacements résultants, les formations de rupture, et les structurations prennent une ampleur considérable et se déploient sur des zones étendues et profondes au voisinage du massif dans des proportions nettement plus importantes que celles habituellement admises. La nature de leur développement dépend de la structure superficielle préexistant dans les matériaux de l'écorce terrestre mais aussi de l'état de contraintes, que ce soient des contraintes de nature tectonique, des contraintes résiduelles dues à des phénomènes tectoniques ou encore des contraintes dues au poids propre. - De telles répartitions des contraintes dues à l'érosion, les déplacements et les fracturations nouvelles peuvent être analysés par la méthode des éléments finis (perfectionnée pour cette application), ce qui est illustré par quelques exemples.

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Die geologischen Ergebnisse der Salzbohrungen im Talbecken von Bad Reichenhall     

W. Hofrat Dipl.-Ing. Dr. mont. h. c. Othmar Schauberger  Professor Dr. Heinrich Zankl 《International Journal of Earth Sciences》1976,65(1):558-579

Zusammenfassung Im Talkessel von Bad Reichenhall sind 9 Bohrungen zur Erkundung der Salzlagerstätte niedergebracht worden. Gemeinsam mit den Ergebnissen neuer Kartierungsarbeiten haben diese Bohrungen die Kenntnisse zur Geologie dieses Kalkalpenabschnittes wesentlich erweitert.Die Salzlagerstätte besteht aus einem steil nach Süden einfallenden, in sich isoklinal verfalteten linsenförmigen Körper; er ist über 1200 m unter die heutige Talsohle zu verfolgen, der gesamte Tiefgang ist noch unbekannt.Der Internbau wird durch eine intensive Verfaltung von Haselgebirge und Reichenhaller Kalken bzw. Dolomit geprägt. Unter dem im Süden auflagernden Hochjuvavikum des Lattengebirges läßt sich bis in 800 m Tiefe ein Schuppenbau von Haselgebirge und oberkretazischen bis alttertiären Schichten nachweisen.Eine Fortsetzung des Saalachwestbruches begrenzt das Salinar im Norden. Entlang dieser tektonischen Linie liegen einzelne Hallstätter Kalk-Komplexe, die tektonisch zum Liegenden der Lagerstätte zu rechnen sind.Das Haselgebirge besteht überwiegend aus Buntem Salztongebirge und Anhydritischem Grausalzgebirge; Übergänge zu dolomitischem Anhydrit sind zu beobachten. Ein Ablagerungsraum in der Nähe eines Beckenrandes oder auf einer Schwelle bietet sich an. Dafür spricht auch der sedimentäre Übergang von Haselgebirge in fossilführende Reichenhaller Kalke.Der Nachweis von Oberskyth in Reichenhaller Kalken sowie von Oberperm mittels Sporen im Haselgebirge lassen auf eine langanhaltende Salzbildung schließen.Vergleicht man das Haselgebirge mit anderen nordalpinen Salzkörpern, so bildet das Salinar von Bad Reichenhall einen eigenen Typus, der deutlich von den Vorkommen in Berchtesgaden/Hallein und von Altaussee/Ischl unterschieden ist.

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A new understanding of the geology of the Reichenhall valley has recently evolved as a result of the examination of samples from 9 drill holes combined with new mapping in the area.Salt is found dipping steeply to the south in a lense shaped body displaying isoclinal folding. Drill holes (maximum of 1200 m depth) found no trace of the base of the salt.Intensive folding of the Reichenhall limestone and dolomite with the Haselgebirge characterizes the internal structure of the main salt body. Underneath the overlying tectonic unit in the south infolding of Upper Cretaceous and Lower Tertiary was traced to 800 m depth within the Haselgebirge.The northern boundary of the salt body is marked by an eastern continuation of the Saalach fault. Along this tectonic boundary one finds isolated blocks of Hallstatt limestone which are located tectonically below the Haselgebirge.The Haselgebirge is made up mainly of Buntes Salztongebirge and Anhydritisches Grausalzgebirge. Transition of the salt rocks into dolomitic anhydrite can be observed. The Haselgebirge can also be found interfingering with fossiliferous Reichenhall limestone. These transitions indicate that the despositional environment was probably proximal to a basin rim or on top of a topographic high.Evidence for a very long period of salt formation is indicated by Upper Permian spores in the Haselgebirge and Upper Scythean fossils in the Reichenhall limestone.Evidence presented above emphasizes the unique character of the Haselgebirge of Reichenhall compared to the other well known deposits of Berchtesgaden/Hallein and those of Altaussee/Ischl.

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Résumé Dans le cirque de Bad Reichenhall on été installées 9 sondes servant à l'exploration du marais salan. En accord avec les résultats de la nouvelle cartographie, ces sondes ont permis d'élargir la connaissance géologique de la région des Alpes calcaires.Le marais salan consiste en un massif isoclinal, tombant à pic vers le sud, constitué lui-même de plis ayant la forme de lentilles. On peut le suivre aujourd'hui jusqu'à 1200 m au dessous du fond de la vallée; la profondeur exacte n'étant pas encore connue.La constitution interne est caractérisée par un pli intensif de Haselgebirge et des calcaires de Reichenhall, voire de dolomites.Sous la couche supérieure du Hochjuvavikum des Lattengebirge dans le sud, jusqu'à une profondeur de 800 m, une formation d'écailles laisse témoigner avec le Haselgebirge, de couches crétacées supérieures et tertiaires inférieures.Une continuité de la faille de la Saalach limite, au nord, le marais salan. Le long de cette ligne tectonique, se trouve les complexes du Hallstatt isolé, que l'on peut compter tectoniquement sur la muraille du marais.Le Haselgebirge se compose surtout des «Buntem Salztongebirge» et des «Anhydritischem Grausalzgebirge»; on peut observer les transitions aux anhydrites dolomitiques. A proximité du bord du bassin, ou sur le seuil, s'offre un emplacement de sédimentation. La transition sédimentaire du Haselgebirge dans les calcaires du Reichenhall, contenant des fossiles, le prouve.Le témoignage du Skythien supérieur dans les calcaires du Reichenhall, ainsi que du Permien supérieur à l'aide des spores de Haselgebirge, permettent de conclure à une génèse du sel très longue.Si l'on compare aujourd'hui le Haselgebirge avec d'autres massifs salés du nord des Alpes, on se représente ces marais salans de Bad Reichenhall d'un type spécifique, clairement différencié des gisements des Berchtesgaden/Hallein et Altaussee/Ischl.

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Lo?c Cahierre 《Journal of Geodesy》1955,29(2):20

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Late cretaceous volcanogenic flysch and diabase-chert formations in the Yugoslav Inner Dinarides     

Žarko Ž. Jovanovíc 《Sedimentary Geology》1973,9(2):117-147

In the Turonian and Maastrichtian, the “Diabase-chert Formation” and the “Volcanogenic flysch” were formed as two specific rock series, due to the synchronous basic volcanism of the Drenica area in Kosovo (Yugoslavia). Comparison with other localities of the Inner Dinarides has proved that, regardless of their different stratigraphic position, each of these two formations exhibits in individual localities great lithological and structural similarities. Both formations are associated with large tectonic zones with ophiolitic occurrences which extend from the Alps through the Yugoslav Inner Dinarides, northern and northeastern Greece, part of Turkey (Asia Minor) and further southeast.The Diabase-chert Formation is a lateral facies of Turnonian limestone. It is represented by a characteristic regime of a specific geochemical character, brought about by synchronous basic volcanism, and by the introduction of volcanogenic components — these factors are responsible for great lithological diversity and very rapid lateral and vertical changes. A certain consistency in the lithological composition is only noticable in the closing horizons of this formation at its transition into limestone sediments.The volcanogenic flysch was formed as a result of subvolcanic activity synchronous with flysch sedimentation whereby semi-consolidated flysch sediments acquired certain volcanogenic-sedimentary characteristics. The most intensively disturbed parts around submarine flows of diabase have been recognized as the “zone of highly disturbed flysch”. The zone is conformably overlain by the stratified cherty-clayey zone. This continues into the “zone of ball sandstone”, and ends with the “zone of normal flysch”. Their newly acquired characteristics resulting from synchronous basic volcanism distinguish them clearly from normal flysch and make them a special type of flysch — the volcanogenic flysch.  相似文献   

Radioactivity in sediments and gross alpha–beta activities in surface water of Fırtına River, Turkey     

B. Kücükömeroglu  A. Kurnaz  R. Keser  F. Korkmaz  N. T. Okumusoglu  G. Karahan  C. Sen  U. Cevik 《Environmental Geology》2008,55(7):1483-1491

The concentrations and distribution of natural and artificial radionuclides in sediment and water samples collected from Fırtına River in the Eastern Black Sea region of Turkey were investigated with an aim of evaluating the environmental radioactivity and radiation hazard. Natural gross α and gross β activities were determined for 21 different water samples, and the activity concentrations were obtained for ²²⁶Ra, ²¹⁴Pb, ²¹⁴Bi, ²²⁸Ac, ²⁰⁸Tl, ⁴⁰K and ¹³⁷Cs in 20 different sediment samples. The obtained results showed that natural gross α and gross β activity concentrations in water samples range from 12.4 ± 3.4 to 66.2 ± 9.2 mBq l⁻¹ and from 27.9 ± 3.3 to 133.3 ± 4.1 mBq l⁻¹, respectively. The mean activity concentrations were 32.6 ± 3.8 mBq l⁻¹ for gross α and 69.9 ± 4.4 mBq l⁻¹ for gross β. Generally, the gross β activities were higher than the corresponding gross α activities. The average concentrations of ²³⁸U and ²³²Th daughter products vary from 11 to 167 Bq kg⁻¹ and from 16 to 107 Bq kg⁻¹, respectively. The concentrations of ⁴⁰K and ¹³⁷Cs vary from 51 to 1,605 Bq kg⁻¹ and from 0.8 to 42 Bq kg⁻¹, respectively. Sediment characterization was also investigated using grain size, thin section and XRD analysis.  相似文献   

Modeling the attenuated total reflectance infrared (ATR-FTIR) spectrum of apatite     

Julie Aufort  Loïc Ségalen  Christel Gervais  Christian Brouder  Etienne Balan 《Physics and Chemistry of Minerals》2016,43(9):615-626

Attenuated total reflectance (ATR) infrared spectra were measured on a synthetic and a natural fluorapatite sample. A modeling approach based on the computation of the Fresnel reflection coefficient between the ATR crystal and the powder sample was used to analyze the line shape of the spectra. The dielectric properties of the samples were related to those of pure fluorapatite using an effective medium approach, based on Maxwell–Garnett and Bruggeman models. The Bruggeman effective medium model leads to a very good agreement with the experimental data recorded on the synthetic fluorapatite sample. The poorer agreement observed on the natural sample suggests a more significant heterogeneity of the sample at a characteristic length scale larger than the mid-infrared characteristic wavelength, i.e., about 10 micrometers. The results demonstrate the prominent role of macroscopic electrostatic effects over fine details of the microscopic structure in determining the line shape of strong ATR bands.  相似文献