New results on the stratigraphy and structure of the Rhodesian Lomagundides     

Dr. W. B. G. Jacobsen 《International Journal of Earth Sciences》1968,58(2):908-929

Results obtained during detailed geological investigations in the Silverside area of the Lomagundi District, Rhodesia, call for certain changes in the stratigraphical sequence of the late Precambrian Lomagundi System. They confirm in principle a new sequence, established by J. B. E.Jacobsen (1962). A basal tillite is followed by a series of carbonatic rocks, partly of stromatolitic nature, which is overlain by an arenaceous series of great thickness. The system rests unconformably on volcanic rocks, for which the retention of the term Deweras System is proposed in contrast to the recently established term Deweras Series as lowermost portion of the Lomagundi System. The System is covered unconformably by much younger sediments, for which the term, Hunyani System is suggested. These sediments were so far included in the Lomagundi System. A correlation between the Lomagundi System and systems of similar age in Zambia and Katanga by J. B. E.Jacobsen (1962) is quoted.Nappe structures, which were observed for the first time in the Lomagundi Folded Belt at the Alaska Mine (J. B. E.Jacobsen, 1962 and 1964), govern the structural pattern at Silverside as a consequence of intense asymmetrical folding. They are deformed by the later phases of this folding period. Subsequent cross warping in an ENE-WSW direction created shallow anti- and synformes. The thrust planes are marked by intense brecciation, silicification and invasion of hydrothermal quartz and copper mineralisation. The latter has produced sporadic, rootless, semi-allochthonous copper occurrences, which occur either as relics of mineralised thrust breccias or as steep ore bodies, formed by the descent of solutions from the breccia into fractured and loosened up structures underneath. The solutions have probably ascended along the root zones of the major thrusts to the West of the area and proceeded along the thrust planes.

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Zusammenfassung Ergebnisse geologischer Detailaufnahmen in der Umgebung der Silverside-Kupfergrube im Lomagundi-Distrikt Rhodesiens machen einige Änderungen in der stratigraphischen Abfolge der spätkambrischen rhodesischen Lomagundi-Formation erforderlich. Sie bestätigen im wesentlichen eine von J. B. E.Jacobsen (1962) aufgestellte Schichtenfolge. Ein basaler Tillit wird von einer Reihe karbonatischer Gesteine von gelegentlich stromatolitischer Natur überlagert. Dieser untere Teil der Formation wird von einem mächtigen Paket sandiger Gesteine bedeckt. Die Formation ruht diskordant auf vulkanischen Gesteinen, für welche die Beibehaltung des älteren Namens Deweras-Formation vorgeschlagen wird (im Gegensatz zum neuerdings erschaffenen Begriff Deweras-Stufe der basalen Lomagundi-Formation). Mit großer zeitlicher und räumlicher Diskordanz liegen auf der Lomagundi-Formation jüngere Sedimente, für die der Name Hunyani-Formation vorgeschlagen wird. Diese Sedimente wurden bisher der Lomagundi-Formation zugerechnet. Ein stratigrapbischer Vergleich zwischen der Lomagundi-Formation und Formationen ähnlichen Alters in Zambia, Katanga und Süd-West-Afrika durch J. B. E.Jacobsen ist wiedergegeben.Deckenüberschiebungen, die in den Lomagundiden zum ersten Male durch J. B. E.Jacobsen (1962 und 1964) von der Alaska-Grube beschrieben wurden, beherrschen das strukturelle Bild in der Silverside-Gegend. Sie haben sich als Folge intensiver, asymmetrischer Faltung in NNE-SSW entwickelt. Ausklingende Phasen der Faltung haben die Decken noch mit erfaßt. Eine viel spätere Querwellung in ENE-WSW schuf eine Verbiegung des älteren Faltensystems in flache Becken und Schwellen. Die Schubflächen der Decken sind durch intensive Brekzienbildung, Verkieselung, wie auch durch Einwanderung von hydrothermalen quarz- und kupferhaltigen Lösungen gekennzeichnet. Diese haben sporadisch wurzellose, semi-allochthone Kupfervorkommen hinterlassen, die sich entweder deszendent durch Auffüllung steiler, aufgelockerter, stark zerbrochener Sattelachsen gebildet haben oder als Reste mineralisierter Dislokationsbrekzien auftreten. Der Ursprung der mineralisierenden Lösungen ist entlang den Deckenwurzelzonen und Überschiebungsbahnen weiter im W zu vermuten.

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Résumé Dans les environs de la mine Silverside au Département Lomagundi, Rhodésie, les résultats des investigations géologiques détaillées demandent certaines modifications à l'égard de la succession stratigraphique du Système de Lomagundi du Précambrien supérieur. En essentiel, ils confirment une succession des gîtes, rangée par J. B. E.Jacobsen (1962). Sur un tillite basale il se trouve une série de roches carbonatiques qui sont parfois stromatolitiques. Cette partie d'en bas du système est couverte d'un paquet énorme de roches sablonneux. Le système pose en contact discordant sur des roches volcaniques, pour lesquelles la conservation du premier terme « Système de Deweras » est proposée (contrairement au terme récemment créé pour la partie inférieure du Système de Lomagundi: «Série de Deweras»). Par un considerable discordance temporelle et régionale il y a sur le système de Lomagundi des sédiments plus jeunes, pour lesquels le terme « Système d'Hunyani » est proposé. Jusqu'à présent ces sédiments étaient attribués au Système de Lomagundi. C'était J. B. E.Jacobsen, qui a comparé la stratigraphie du Système de Lomagundi avec des formations d'un âge analogue en Zambia, Katanga et l'Afrique Sud Ouest.Des structures des nappes tout d'abord décrites par J. B. E.Jacobsen (en 1962 et en 1964), gouvernent le dessin structurel aux environs de Silverside. Leur développement résulte d'un plissement intense et asymétrique de NNE à SSW. Les dernières phases de ce plissement ont déformé les nappes préexistantes. Une déformation ondulatoire transversale plûtard (de ENE à WSW) a produit des bassins et des rides secondaires. Les plans du transport des nappes sont marqués par une brêche tectonique énorme, par une silicification et par une invasion des solutions hydrothermales de quartz et de cuivre. Ces solutions ont effectué sporadiquement des depôts détachés et sémi-allochthones de cuivre qui sont formés par des solutions déscendantes et par un remplissage des structures anticlinales éscarpées, ou bien sont trouvés en quilté des réliques des brêches tectoniques minéralisées. L'origine des solutions minéralisantes se trouve probablement le long des zones d'origine des nappes et des plans de transport vers l'ouest de la région.

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The use of broad-band prior covariance for inverse palaeoclimate estimation   总被引：1，自引：0，他引：1  

Delia Zemira &#;erban  Bo Holm Jacobsen 《Geophysical Journal International》2001,147(1):29-40

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The Vendian record of Sr and C isotopic variations in seawater: Implications for tectonics and paleoclimate   总被引：26，自引：0，他引：26  

Alan J. Kaufman  Stein B. Jacobsen  Andrew H. Knoll 《Earth and Planetary Science Letters》1993,120(3-4):409-430

New Sr and C isotopic data, both obtained on the same samples of marine carbonates, provide a relatively detailed record of isotopic variation in seawater through the latest Proterozoic and allow, for the first time, direct correlation of these isotopic changes in the Vendian ( 540–610 Ma). The strong isotope variations determined in this study record significant environmental and tectonic changes. Together with a fairly poorly constrained Nd isotopic record, the Sr and C isotopic records can be used to constrain rates of erosion, hydrothermal alteration and organic C burial. Further, comparison of these records with those of the Cenozoic permit investigation of the general relationship between global tectonics and continental glaciation. In particular, results of this study show a very large change in the ⁸⁷Sr/⁸⁶Sr of marine carbonates from low pre-Vendian ( > 610 Ma) values ( 0.7066) to high Middle Cambrian values ( 0.7090). This change is greater in magnitude than the significant increase in seawater ⁸⁷Sr/⁸⁶Sr through the Cenozoic. Both changes are attributed to high erosion rates associated with continent-continent collisions (Pan-African and Himalayan-Tibetan). In the latest Proterozoic these high erosion rates, probably coupled with high organic productivity and anoxic bottom-water conditions, contributed to a significant increase in the burial rate of organic C. Ice ages mark both the Neoproterozoic and Cenozoic, but different stratigraphic relationships between the Sr isotopic increase and continental glaciation indicate that uplift-driven models proposed to explain Cenozoic climatic change cannot account for the latest Proterozoic ice ages.  相似文献   

REE in the Great Whale River estuary, northwest Quebec   总被引：1，自引：0，他引：1  

Steven J. Goldstein  Stein B. Jacobsen 《Earth and Planetary Science Letters》1988,88(3-4)

We report rare earth element (REE) concentrations of a longitudinal profile within the estuary of the Great Whale River in northwest Quebec and in Hudson Bay. All of the measured REE have concentrations less than those predicted by conservative mixing of seawater and river water, demonstrating removal of the REE from solution. REE removal is rapid, occurring primarily at salinities less than 2‰. Removal of the REE is greatest for the light REE, and ranges from about 7% for the light REE to no more than 40% for the heavy REE. Fe removal is essentially complete at low salinity. The shape of the Fe and REE vs. salinity profiles is not consistent with a simple model of destabilization and coagulation of iron and REE-bearing colloidal material. A linear relationship between the activity of free ion REE³⁺ and pH is consistent with a simple ion-exchange model for REE removal.Surface and subsurface samples of Hudson Bay seawater are characterized by high REE concentrations and high La/Yb relative to average seawater. The subsurface sample has a Nd concentration of 100 pmol/kg and an ε_Nd of −29.3 ± 0.3. These characteristics are consistent with the high REE concentration, high La/Yb, and low ε_Nd of river inputs into Hudson Bay. These results indicate that rivers draining the Canadian Shield are a major source of non-radiogenic Nd and REE to the Atlantic Ocean. We estimate that outflow of water from Hudson Bay to the Labrador Sea could supply ≈ 30% of the non-radiogenic Nd in North Atlantic Deep Water.  相似文献   

POLAR 5—an electron accelerator experiment within an aurora. 2. Scattering of an artificially produced electron beam in the atmosphere     

B.N. Maehlum  B. Grandal  T.A. Jacobsen  J. Trøim 《Planetary and Space Science》1980,28(3):279-289

The interaction between an artificially produced narrow beam of electrons and the upper atmosphere has been studied by the POLAR 5 electron accelerator “mother”-“daughter” rocket. It is shown how the beam develops a “halo” of scattered electrons and how the low energy electron population in this “halo” is produced partly during the ionization process (at low altitudes), partly by a “wave-plasma” interaction which accelerates the ionospheric background electrons.  相似文献   

Gottfried Konecny:The photogrammetric and remote sensing trend setter     

Karsten Jacobsen 《地球空间信息科学学报》2021,24(1):13-21

PREFACE There are various publications on the 90th birthday of Gottfried Konecny.His involvement in the International Society for Photogrammetry and Remote Sensing(ISPRS)is particularly described by others.Here,his forward-oriented impulses in research and development at the former Institute for Photogrammetry and Engineering Survey of the(Technical)University of Hannover,today Institute for Photogrammetry and Geoinformation,Leibniz University Hannover,and some of his activities supporting developing and other countries by given short-term courses are highlighted.Gottfried Konecny was always one of the first in pushing new technologies.With the analytical plotter AP/C-3,he introduced analytical photogrammetry in Germany.Based on his experience with this not really operational version,he induced the company Zeiss to develop the first really operational analytical plotter Planicomp,which resulted in the end of analog photogrammetric devices and their limitations.At the invitation of Gilbert Hobrough,a mainly hardware-based image correlator was developed for the AP/C-3 in Hannover which anticipated many of today's applications.Gottfried Konecny initiated remote sensing in Germany.Based on his proposal with the Metric Camera Flight on Spacelab,the then highest resolution civil stereoscopic space images available were generated.Despite limited computer performance at his institute,a digital stereo plotter was developed,using hardware components from the cooperating Swedish company Context Vision,long before digital stereo workstations with increased and affordable computer capacity were possible.Also,in the area of GIS,he too,pushed development in collaboration with companies and administrations.Shortly before the end of his time as head of the institute,and more so after he became emeritus professor,he started a series of educational workshops,particularly in developing countries,but also other countries,to support the development of photogram-metry,remote sensing and GIS.He promoted the use of space imagery for mapping to improve the situation of poorly updated topographic maps.  相似文献   

Al–Mg and Pb–Pb systematics of Allende CAIs: Canonical solar initial Al/Al ratio reinstated     

Benjamin Jacobsen  Qing-zhu Yin  Frederic Moynier  Yuri Amelin  Alexander N. Krot  Kazuhide Nagashima  Ian D. Hutcheon  Herbert Palme 《Earth and Planetary Science Letters》2008,272(1-2):353-364

The precise knowledge of the initial ²⁶Al/²⁷Al ratio [(²⁶Al/²⁷Al)₀] is crucial if we are to use the very first solid objects formed in our Solar System, calcium–aluminum-rich inclusions (CAIs) as the “time zero” age-anchor and guide future work with other short-lived radio-chronometers in the early Solar System, as well as determining the inventory of heat budgets from radioactivities for early planetary differentiation. New high-precision multi-collector inductively-coupled plasma mass spectrometry (MC-ICP-MS) measurements of ²⁷Al/²⁴Mg ratios and Mg-isotopic compositions of nine whole-rock CAIs (six mineralogically characterized fragments and three micro-drilled inclusions) from the CV carbonaceous chondrite, Allende yield a well-defined ²⁶Al–²⁶Mg fossil isochron with an (²⁶Al/²⁷Al)₀ of (5.23 ± 0.13) × 10^− 5. Internal mineral isochrons obtained for three of these CAIs (A44A, AJEF, and A43) are consistent with the whole-rock CAI isochron. The mineral isochron of AJEF with (²⁶Al/²⁷Al)₀ = (4.96 ± 0.25) × 10^− 5, anchored to our precisely determined absolute ²⁰⁷Pb–²⁰⁶Pb age of 4567.60 ± 0.36 Ma for the same mineral separates, reinstate the “canonical” (²⁶Al/²⁷Al)₀ of 5 × 10^− 5 for the early Solar System. The uncertainty in (²⁶Al/²⁷Al)₀ corresponds to a maximum time span of ± 20 Ka (thousand years), suggesting that the Allende CAI formation events were culminated within this time span. Although all Allende CAIs studied experienced multistage formation history, including melting and evaporation in the solar nebula and post-crystallization alteration likely on the asteroidal parent body, the ²⁶Al–²⁶Mg and U–Pb-isotopic systematics of the mineral separates and bulk CAIs behaved largely as closed-system since their formation. Our data do not support the “supra-canonical” ²⁶Al/²⁷Al ratio of individual minerals or their mixtures in CV CAIs, suggesting that the supra-canonical ²⁶Al/²⁷Al ratio in the CV CAIs may have resulted from post-crystallization inter-mineral redistribution of Mg isotopes within an individual inclusion. This redistribution must be volumetrically minor in order to satisfy the mass balance of the precisely defined bulk CAI and bulk mineral data obtained by MC-ICP-MS.The radiogenic ²⁰⁸Pb/²⁰⁶Pb ratio obtained as a by-product from the Pb–Pb age dating is used to estimate time-integrated ²³²Th/²³⁸U ratio (κ value) of CAIs. Limited κ variations among the minerals within a single CAI, contrasted by much larger variations among the bulk CAIs, suggest Th/U fractionation occurred prior to crystallization of igneous CAIs. If interpreted as primordial heterogeneity, the κ value can be used to calculate the mean age of the interstellar dust from which the CAIs condensed.  相似文献   

Determining flow patterns and emplacement dynamics from tsunami deposits with no visible sedimentary structure          下载免费PDF全文

Claire Kain  Patrick Wassmer  James Goff  Catherine Chagué‐Goff  Christopher Gomez  Deidre Hart  Daniela Fierro  Geraldine Jacobsen  Atun Zawadzki 《地球表面变化过程与地形》2017,42(5):763-780

In the absence of eyewitness reports or clear sedimentary structures, it can be difficult to interpret tsunami deposits or reconstruct tsunami inundation patterns. The emplacement dynamics of two historical tsunami deposits were investigated at seven transects in Okains Bay, New Zealand, using a combined geospatial, geomagnetic and sedimentological approach. The tsunami deposits are present as layers of sand and silt intercalated between soils and become finer and thinner with distance inland. The deposits are attributed to the 1960 and possibly the 1868 tsunamis, based on radiometric dating and correlation with historical records. Measurements of Magnetic Fabric (MF: Anisotropy of Magnetic Susceptibility) and particle size were used to reconstruct the evolution of flow dynamics laterally and vertically. A combination of statistical methods, including spatial autocorrelation testing, Spearman's rank order correlation, Principal Component Analysis (PCA) and K‐means cluster analysis, was applied to examine relationships between MF parameters and sediment texture, and infer depositional hydrodynamics. Flow patterns deduced from MF show the estuary channel acted as a conduit for inundation, with flow commonly aligned sub‐perpendicular to the estuary bed. MF and sediment data suggest deposition occurred from settling during laminar flow. Evidence of both uprush and backwash deposition, as well as wave reflection from infrastructure, was found. Statistical analysis of data showed significant relationships between grain size parameters and MF parameters associated with flow speed and magnetic fabric type. PCA and cluster analysis differentiated samples into two primary hydrodynamic groups: (1) samples deposited from laminar flow; and (2) samples deposited close to the limit of inundation, which includes samples deposited further inland, those affected by flow convergence, and those in the upper part of tsunami deposits. This approach has potential as a tool for reconstructing hydrodynamic conditions for palaeotsunamis and by combining spatial and statistical analyses, large‐scale investigations can be more easily performed. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Temperature increase and respiratory performance of macroinvertebrates with different tolerances to organic pollution     

Lennie Rotvit  Dean Jacobsen 《Limnologica》2013,43(6):510-515

Respiration rates (mg O₂ g^?1 AFDW h^?1) of Leuctra hippopus, Sericostoma personatum, Helodes minuta, Gammarus pulex and Asellus aquaticus were studied across an oxygen gradient at 2.8 and 6.3 °C, corresponding to an expected 3.5 °C increase in Danish winter stream temperature. Species were selected from the Danish Stream Fauna Index (DSFI), representing an expected hierarchy of tolerance towards water quality degradation. We expected that low-ranking, tolerant species (i.e. indicators of bad water quality) would have the capacity to regulate their oxygen uptake relatively independently of oxygen availability (oxy-regulators) and high-ranking, sensitive species (i.e. indicators of good water quality) would be less able to do so (oxy-conformers). For all species respiration rate was higher (although non-significantly) at 6.3 °C. The species’ oxy-regulatory capacity did not consistently reflect their DSFI ranking. As expected, and in accordance with its DSFI ranking, A. aquaticus had the highest oxy-regulatory capacity with the ability to regulate O₂ uptake until an oxygen saturation of only 20%, which did not change with increasing temperature, emphasizing the robustness of A. aquaticus towards changes in the environment. S. personatum, H. minuta and G. pulex revealed no oxy-regulatory capacity. In contrast, the plecopteran L. hippopus did display an unexpected oxy-regulatory capacity. Though an increase in temperature changed L. hippopus’ capacity to oxy-regulate (the critical limit increased from 32.5 to 43.5% oxygen), respiration rates did not change significantly in spite of the temperature increase. This result contradicts the general belief that stoneflies, because of their affinity to well oxygenated habitats, are conformers. Our findings call for further studies on the respiratory conformer–regulator concept and its role as an eco-physiological trait for bio-assessment.  相似文献   

Nogle midtsjællandske kanalplaner fra begyndelsen af det 19. århundrede     

Dr. N. H. Jacobsen 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):33-44

Jacobsen, N. H., 1973: Nogle midtsjællandske kanalplaner fra begyndelsen af det 19. århundrede. Geografisk Tidsskrift 72, s. 33–44. København, September 30, 1973.

Based on archives studies, canal-projects on Sjælland are described. The plans were submitted a. 1800 in order to facilitate military transports and improve the supplies of food and fuel to Copenhagen.  相似文献