In-situ Gesteinsspannungen und Mechanismen der Kluftöffnung

Zusammenfassung Die Orientierung von post-orogenen Klüften in proterozoischen Sedimentgesteinen des Elliot Lake-Gebietes, Canada, läßt sich mit der meßbaren Gesteinsentspannung in Bohrlöchern in Beziehung bringen. Steile lokale und regionale Kluftscharen ohne Bewegungsspuren streichen in Richtung der elastischen Hauptentformungsachse, also in Richtung der größten in-situ-Kompressionsspannung.Die Klüfte lassen sich deshalb wahrscheinlich als Extensionsfugen erklären, und zwar als Resultat der Wechselwirkung zwischen Oberflächenabtrag des Gesteins und remanenter tektonischer Gesteinsspannung. Der vorgeschlagene Mechanismus sollte auch zum Verständnis von spät-orogenen (ac)-Klüften in gefaltetem Deckgebirge und oberflächenparallelen Klüften in massigen Gesteinen beitragen.

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Orientation of post-orogenic joints in Proterozoic sedimentary rocks of the Elliot Lake area (Canada) seems to be directly related to elastic-strain-recovery as measured in boreholes. Steep local and regional joint sets without displacement are parallel with the axis of maximum elastic-strain-recovery (i. e. the direction of the major principal in situ stress component). Consequently these joints are interpreted as extension joints forming as a result of the interaction between natural (or artificial) erosion of the rock mass and its remanent tectonic stresses. The proposed mechanism should also help to understand late-orogenic (ac)-joints in folded cover rocks and exfoliation joints in otherwise unjointed rocks.

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Résumé L'orientation des diaclases post-tectoniques dans des roches sédimentaires protérozoïques de la région du Lac d'Elliot, Canada, peut être mise en relation avec les tensions élastiques des roches telles qu'on peut les mesurer dans les trous de forage. Les systèmes de diaclases redressées, locales et régionales, sans traces de mouvement, sont dirigés parallèlement aux axes principaux de la déformation élastique, c'est-à-dire à la direction de la plus grande compression in situ mesurée par le changement de forme d'un trou de sonde. Par conséquent, les diaclases s'expliquent vraisemblablement comme joints d'extension, et en fait comme le résultat de l'action réciproque entre des tensions tectoniques rémanentes et l'érosion en surface. Le mécanisme proposé explique aussi les diaclase (ac) tardives dans les couvertures plissées et l'exfoliation parallèle à la surface dans les roches massives.

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- Elliot Lake, , . , in situ. , , , , , . - .

     

Lake Kivu: structure,chemistry and biology of an East African rift lake

Geophysical, geochemical and biological data are integrated to unravel the origin and evolution of an unusual rift lake. The northern basin of Lake Kivu contains about 0.5 km of sediments which overlie a basement believed to be crystalline rocks of Precambrian age. Volcanic rocks at the northern end of the lake have created large magnetic anomalies of up to 300. Heat flow varies from 0.4 to 4 hfu. The extreme variability may be due in part to sedimentation or recent changes in the temperature of the bottom water. Sharp boundaries in the vertical temperature and salinity structure of the water across the lake can best be explained as separate convecting layers. Such convecting cells are the result of the increase in both temperature and salinity with depth.Concentrations of the major dissolved gases in the deep water, CO₂ and CH₄, approach saturation but do not exceed it at any depth. The salts are supplied mainly by hydrothermal discharges at the bottom of the lake which we calculate to have a salinity of 4 which is about 60% higher than the salinity of the bottom water. The annual discharge at the present time is about 0.5 km³. Zinc anomalies in the water are explained by the accumulation of sphalerite-containing globules at certain depths.Stratigraphic correlation of sediments is possible across the entire lake, based on physical, geochemical and paleontological criteria. Sedimentation rates are of the order of 30 cm/1000 years implying a Pliocene age for the deepest part of the lake. Periods of hydrothermal activities and heightened volcanism, as recorded in the sediments, appear to have coincided with pluvial times.Enrichment of the surface waters of Lake Kivu by nutrients has led to explosive speciation in the diatom genusNitzschia. Several new types of methane oxidizing and-producing bacteria were isolated. Bacterial degradation of recent plankton appears insufficient to explain the amount of methane in the lake, and some of it is derived diagenetically.

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Zusammenfassung Geophysikalische, geochemische und biologische Daten werden vorgelegt und miteinander in Beziehung gebracht, um einen besseren Einblick in Entstehung und Evolution eines ungewöhnlichen Sees zu gewinnen. Das nördliche Becken des Kivu-Sees enthält Sedimente von etwa 0,5 km Mächtigkeit, die dem präkambrischen kristallinen Grundgebirge überlagert sind. Die im Norden des Sees vorliegenden vulkanischen Gesteine erklären die hohen magnetischen Anomalien, die bis zu 300 betragen. Der Wärmefluß schwankt zwischen 0,4 und 4 cal/cm²/sec. Diese Schwankungsbreite erklärt sich zum Teil aus den Sedimentationsverhältnissen oder den lokalen Temperaturveränderungen im Tiefenwasser. Scharfe Grenzflächen in der vertikalen Temperatur- und Salinitätsstruktur des Wassers über den Gesamtsee sind das Ergebnis von Konvektion, die zu übereinanderliegenden Konvektionszellen führt, in denen jeweils Temperatur und Salinität konstant sind. Die Bildung, Anzahl und Stabilität solcher Zellen hängt von dem Verhältnis der durch Temperatur und Salzgehalt hervorgerufenen Dichteveränderungen ab.Die Konzentrationen der im Tiefenwasser gelösten Gase, d. h. von Kohlendioxyd und Methan, liegen für alle Tiefen unterhalb der Löslichkeit. Die vorliegenden Salze entstammen weitgehend hydrothermalen Lösungen, die dem Seeboden entweichen und deren Salinität etwa 4 beträgt; der Vergleichswert für das Tiefenwasser beträgt 2,5 Diese hydrothermalen Ausschüttungen haben eine Größe von etwa 0,5 km³ pro Jahr, was etwa ein Tausendstel des Gesamtseevolumens ausmacht. Zinkanomalien im Wasser sind ebenfalls hydrothermal bedingt.Physikalische, geochemische und paläontologische Indikatoren erlauben eine stratigraphische Korrelation aller Sedimentkerne. Die Sedimentationsraten liegen bei 30 cm/ 1000 Jahren, und ein pliozänes Alter errechnet sich daraus für das tiefe nördliche Becken. Perioden hydrothermaler Aktivitäten und verstärkter vulkanischer Tätigkeit, die sich in den Sedimenten nachweisen lassen, scheinen mit Pluvialzeiten zu koinzidieren.Die Anreicherung der Oberflächenwässer vom Kivusee durch Mineralstoffe führte zu einer explosionsartigen Spezisierung in der GattungNitzschia. Verschiedene neue Arten von Methan-oxidierenden und -produzierenden Bakterien wurden isoliert. Das Auftreten von Methan ist zum Teil bakteriell und zum Teil diagenetisch bedingt.

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Résumé Des données géophysiques, géochimiques et biologiques sont présentées et collationnées pour donner une vue meilleure sur l'origine et l'évolution d'un lac particulier de la «Rift valley». La baie septentrionale du lac Kivu contient environ 500 mètres de sédiments qui recouvrent le socle cristallin d'âge précambrien. Des épanchements volcaniques au Nord du lac expliquent les fortes anomalies magnétiques qui atteignent 300. Les valeurs du flux thermique varient entre 0.4 et 4 cal/cm²/sec. Cette importante variation s'explique en partie par la sédimentation ou par des changements locaux de la température de l'eau de fond. Des surfaces-limites brusques dans la structure verticale de la répartition de la température et de la salinité de l'eau dans l'étendue du lac sont dûs à la convection; celle-ci conduit à la superposition de cellules de convection dans lesquelles la température et la salinité sont constantes. La formation, le nombre et la stabilité de telles cellules dépendent du rapport des variations de densité dues à la température et à la teneur en sels.Les concentrations des gaz dissouts dans l'eau profonde, en l'occurrence CO₂ et CH₄, sont, à toute profondeur, inférieures à la saturation. Les sels minéraux proviennent surtout de solutions hydrothermales qui émanent du fond du lac, et dont la salinité est voisine de 4; la valeur comparative pour l'eau profonde est de 2,5. L'apport annuel de ces sources est de l'ordre de 0,5 km³, soit 1/1000 du volume total du lac. Les teneurs anormales en Zn sont dues également à ce caractère hydrothermal.Des données physiques, géochemiques et paléontologiques permettent la corrélation stratigraphique des sédiments. Les vitesses de sédimentation sont de l'ordre de 30 cm/1000 ans, donnant ainsi un âge pliocène pour la partie profonde de la baie septentrionale. Les périodes d'activité hydrothermale et de renforcement de la vulcanicité qui se manifestent dans les sédiments, semblent coïncider avec les périodes pluviales.L'enrichissement des eaux de surface du lac Kivu en substances minérales a entraîné un développement explosif des diatomées, en particulier du genreNitzchia. Différentes espèces nouvelles de bactéries oxydant et produisant CH₄ ont été isolées. La présence de méthane est due en partie à la destruction du plancton par les bactéries et en partie à une transformation diagénétique.

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, , . Kivu 0,5 , . , 300 . 0,4 4 (²) . , . . , , , . , . . _{2 4} . , 4%. 2,5%. 0,5 ³, , 1/1000 . ., . 30 /1000 , . . . , , , . Kivu Nitzschia. , . , — .

     

On the electrical conductivity of air inside buildings

Summary Simultaneous measurements of the electrical conductivity of air inside and outside of buildings have been performed with continuously recording electronic instruments of high sensitivity and short time constant. It appears that the electrical conductivity, a measure of the natural ionization of air, is one atmospheric-electric parameter that can manifest itself inside occupied buildings without appreciable difference in physical character from outside values.The probable importance of these experimental results for the field of bioclimatology is pointed out and the possibility is discussed that the electrical conductivity of air might be one of the searched—for parameters in associating physiological phenomena with weather changes.

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Zusammenfassung Gleichzeitige Messungen der luftelektrischen Leitfähigkeit im Freien und innerhalb von Gebäuden wurden mit kontinuierlich registrierenden Röhreninstrumenten von großer Empfindlichkeit und kurzer Zeitkonstante durchgeführt. Es wurde gefunden, daß die Leitfähigkeit als Maß der natürlichen Luftionisierung eine luftelektrische Größe darstellt, die ohne wesentliche physikalische Beeinflussung in bewohnte Gebäude einzudringen vermag.Die mögliche Bedeutung dieser experimentellen Ergebnisse für das Gebiet der Bioklimatologie wird angedeutet und die Wahrscheinlichkeit diskutiert, daß die luftelektrische Leitfähigkeit einen der noch unbestimmten Faktoren des Zusammenhanges physiologischer Erscheinungen mit Wetterveränderungen darstellen könnte.

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Résumé Des instruments électroniques à enregistrement continu de haute fidelité et ayant une constante de courte durée ont permis de prendre des mesures simultanées de la conductivité électrique de l'air à l'intérieur et à l'extérieur de bâtiments. Il semble que la conductivité électrique, mesure de l'ionisation naturelle de l'air, soit un paramètre de l'électricité atmosphérique qui peut se manifester à l'intérieur de bâtiments habités sans différence appréciable de caractéristiques physiques avec celles des valeurs extérieures.L'importance probable de ces résultats expérimentaux dans le champ de la bioclimatologie est indiquée, et la possibilité que la conductivité atmosphérique puisse être un des paramètres recherchés dans l'association des phénomènes physiologiques avec des changements du temps est étudiée.

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With 1 Figure.

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Publication No. 25 of the Institute of Geophysics, University of California at Los Angeles. The research reported in this paper has been sponsored in part by the Geophysics Research Directorate of the Air Force Cambridge Research Center, Air Research and Development Command, under Contract No. AF 19(122)-254.     

Orbital evolution studies of planet-crossing asteroids

Numerical integrations of 26 orbits of planet-crossing astetoids of Apollo-Amor type have been performed, in a solar system model including the perturbations by the planets from Venus to Neptune. The 15:th order RADAU integrator (Everhart, 1985) has been used. Orbits for the asteroids 433 Eros, 887 Alinda, 1036 Ganymed, 1221 Amor, 1580 Betulia, 1627 Ivar, 1685 Toro, 1862 Apollo, 1863 Antinous, 1864 Daedalus, 1865 Cerberus, 1915 Quetzalcoatl and 1916 Boreas have been integrated over 100 000 years forward in time and for 1866 Sisyphus, 2102 Tantalus, 2201 Oljato, 2329 Orthos, 3360 1981 VA, 3552 1983 SA, 1981 EJ30, 1985 PA, 1985 WA, 1986 DA 1986 JK and 1986 RA a period of about 33 000 years has been covered. The orbital evolutions of these asteroids are discussed. This work is part of a larger study of the long-term orbital evolution of planet-crossing asteroids and will be continued within the project SPACEGUARD (Milani et al., 1987).     

Effects of lava flows on lunar crater populations

It is shown that endogenic lava flow processes can be identified by their characteristic effects on lunar crater size distributions without necessarily being able to recognise individual flows on the photographs studied. The thickness of lava flows or a series of flows can be estimated from these crater size distribution characteristics. The lava flow histories of the Apollo landing sites 11, 12 and 15 are discussed in detail. The thicknesses of the most recent (3–3.4 × 10⁹ years ago) flows there and of the youngest flows in an area in south-west Mare Imbrium (3 × 10⁹ years) are found to range between 30 and 60 m. The subsequent flow episodes at the landing sites showing up in the crater size distributions can be related to differences in the radiometric ages of the respective lunar rocks.     

Deep structure and kinematics of the Northern Calcareous Alps (TRANSALP Profile)

The Northern Calcareous Alps (NCA) of southern Bavaria and northern Tyrol constitute a carbonate-dominated polyphase fold-thrust wedge; together with its Grauwacken Zone Basement, it is the northernmost part of the far-travelled Upper Austroalpine thrust complex of the Eastern Alps. The present geometry developed in several kinematic stages. Jurassic extensional faults that affected large parts of the NCA and their basement originated when the main part of the NCA was still located southeast of the Central Alpine Ötztal-Silvretta complex. These faults and related facies transitions influenced the later style of detachment of the NCA thrust sheets. Mid to Late Cretaceous detachment, thrust-sheet stacking and motion over the Central Alpine complex are registered in clastic deposits of syntectonic basins. The latest Cretaceous to Cenozoic NNE- to N-directed motion of the NCA towards Europe in front of the Central Alpine complex created another set of significant contraction structures, which at depth overprinted all previous structures. During Cretaceous to Cenozoic deformation, the NCA experienced about 80 km of shortening, i.e., about 73% along the TRANSALP Profile. The European basement and autochthonous Mesozoic cover beneath the allochthonous NCA thrust sheets and flysch complexes seem to have remained relatively undeformed.     

Paleoenvironmental evolution of the Paratethys in the Slovenian Basin during the Late Paleogene

Several sections from the uppermost Eocene and Oligocene of northern Slovenia have been investigated with respect to sedimentary facies, foraminiferal assemblages, stable isotopes, carbonate microfacies, and palynology. The main objective was to reconstruct the paleoenvironmental history of the Paleogene Paratethys in this region of the eastern Alpine realm. The sediments exhibit a transgressive succession beginning with conglomerates, sandstones, and mudstones of fluvial and lacustrine origin followed by carbonates and muddy marls indicating marine conditions. The foraminiferal faunal changes from brackish to shallow marine to deeper marine assemblages and the distribution of the palynofloras corroborate the sedimentological results. Microfacies analysis of the limestones shows a wide variation of shallow water, generally mud-rich facies dominated by coralline algae, foraminifera, and corals. Microfaunas adapted to low-oxygen conditions indicate temporal sluggish bottom-water circulation which can be associated with high fresh-water fluxes. These results are discussed as reflecting both the global sea-level rise during the Early Oligocene and the regional tectonic and climatic evolution.     

The ALOMAR Rayleigh/Mie/Raman lidar: objectives, configuration, and performance

We report on the development and current capabilities of the ALOMAR Rayleigh/Mie/Raman lidar. This instrument is one of the core instruments of the international ALOMAR facility, located near Andenes in Norway at 69°N and 16°E. The major task of the instrument is to perform advanced studies of the Arctic middle atmosphere over altitudes between about 15 to 90 km on a climatological basis. These studies address questions about the thermal structure of the Arctic middle atmosphere, the dynamical processes acting therein, and of aerosols in the form of stratospheric background aerosol, polar stratospheric clouds, noctilucent clouds, and injected aerosols of volcanic or anthropogenic origin. Furthermore, the lidar is meant to work together with other remote sensing instruments, both ground- and satellite-based, and with balloon- and rocket-borne instruments performing in situ observations. The instrument is basically a twin lidar, using two independent power lasers and two tiltable receiving telescopes. The power lasers are Nd:YAG lasers emitting at wavelengths 1064, 532, and 355 nm and producing 30 pulses per second each. The power lasers are highly stabilized in both their wavelengths and the directions of their laser beams. The laser beams are emitted into the atmosphere fully coaxial with the line-of-sight of the receiving telescopes. The latter use primary mirrors of 1.8 m diameter and are tiltable within 30° off zenith. Their fields-of-view have 180 rad angular diameter. Spectral separation, filtering, and detection of the received photons are made on an optical bench which carries, among a multitude of other optical components, three double Fabry-Perot interferometers (two for 532 and one for 355 nm) and one single Fabry-Perot interferometer (for 1064 nm). A number of separate detector channels also allow registration of photons which are produced by rotational-vibrational and rotational Raman scatter on N₂ and N₂+O₂ molecules, respectively. Currently, up to 36 detector channels simultaneously record the photons collected by the telescopes. The internal and external instrument operations are automated so that this very complex instrument can be operated by a single engineer. Currently the lidar is heavily used for measurements of temperature profiles, of cloud particle properties such as their altitude, particle densities and size distributions, and of stratospheric winds. Due to its very effective spectral and spatial filtering, the lidar has unique capabilities to work in full sunlight. Under these conditions it can measure temperatures up to 65 km altitude and determine particle size distributions of overhead noctilucent clouds. Due to its very high mechanical and optical stability, it can also employed efficiently under marginal weather conditions when data on the middle atmosphere can be collected only through small breaks in the tropospheric cloud layers.     

Climate change and North Sea storm surge extremes: an ensemble study of storm surge extremes expected in a changed climate projected by four different regional climate models

The coastal zones are facing the prospect of changing storm surge statistics due to anthropogenic climate change. In the present study, we examine these prospects for the North Sea based on numerical modelling. The main tool is the barotropic tide-surge model TRIMGEO (Tidal Residual and Intertidal Mudflat Model) to derive storm surge climate and extremes from atmospheric conditions. The analysis is carried out by using an ensemble of four 30-year atmospheric regional simulations under present-day and possible future-enhanced greenhouse gas conditions. The atmospheric regional simulations were prepared within the EU project PRUDENCE (Prediction of Regional scenarios and Uncertainties for Defining EuropeaN Climate change risks and Effects). The research strategy of PRUDENCE is to compare simulations of different regional models driven by the same global control and climate change simulations. These global conditions, representative for 1961–1990 and 2071–2100 were prepared by the Hadley Center based on the IPCC A2 SRES scenario. The results suggest that under future climatic conditions, storm surge extremes may increase along the North Sea coast towards the end of this century. Based on a comparison between the results of the different ensemble members as well as on the variability estimated from a high-resolution storm surge reconstruction of the recent decades it is found that this increase is significantly different from zero at the 95% confidence level for most of the North Sea coast. An exception represents the East coast of the UK which is not affected by this increase of storm surge extremes.