Controls of mud mound formation: The Early Devonian Kess-Kess carbonates of the Hamar Laghdad,Antiatlas, Morocco

The origin and development of Early Devonian (late Pragian to late Zlichovian; predominantly uppermost Zlichovian as indicated by conodont faunas) mud mounds of the Hamar Laghdad area in the eastern Antiatlas, Morocco, are controlled by extrinsic and intrinsic factors. Extrinsic factors include the existence of a paleohigh (Lochkovian volcaniclastics), unidirectional currents and repeated storm events as well as sea level fluctuations. Intrinsic, biologically induced factors are the preferred growth of organisms on the top and the flanks of the mounds because of more favourable ecological conditions, and a rapid synsedimentary lithification of the steep mound flanks by interskeletal cementation of auloporid tabulate corals.The mounds developed in an epicontinental basin below the wave base but within the range of storms.The formation of the mounds started within the uppermost part of the bedded crinoid facies of the Kess-Kess Formation with the hydrological accumulation of a bioclastic pile. This elevation became settled by crinoids and high-diverse tabulate corals producing bioclastic sediment. Binding activities of the organisms were missing, calcareous algae and stromatoporoids are completely absent. Baffling by thamnoporid tabulate corals might have occurred locally but was not important for the development of the mounds.Steep slopes to the north and less steep slopes to the south may be the result of north-northwest to south-southeast trending currents, derived from orientation patterns of orthocone nautiloids in the uppermost beds of the Kess-Kess Formation.A synsedimentary cementation of the flanks, possibly triggered by submarine interskeletal cementation of patchily distributed auloporid colonies, protected the bioclastic sediment against redistribution by frequent storms (indicated by densely spaced eventstone intervals and partly also by the common »Stromatactis«-like structures within the mound facies).Accumulation of more parautochthonous bioclastic sediment within the mounds as compared to the intermound area, therefore, is caused by a selfsustaining system of hydrologic piling of sediment triggered by storms, preferred settlement of organisms upon these piles, producing bioclastic sediment and coeval biocementation of the growing mound flanks.This model differs from existing mud mound models in the lack or only minor significance of binding and baffling, in the lack of mound facies sequences and in the greater importance of extrinsic control factors.

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Zusammenfassung Die Bildung der unterdevonischen Mud Mounds (oberes Prag bis Zlichov; nach Conodonten-Faunen überwiegend Grenzbereich Zlichov/Daleje) im Hamar Laghdad im östlichen Antiatlas (Marokko) wurde durch exogene und biologische Faktoren kontrolliert: Exogene Faktoren umfassen die Existenz eines im Zeitbereich Lochkov bis unteres Prag gebildeten Hochgebietes (Vulkanschwelle), die Auswirkungen von Meeresspiegelschwankungen sowie die Existenz von gerichteten Bodenströmungen und von häufig auftretenden Großstürmen. Biologisch induzierte Faktoren sind das bevorzugte Wachstum sessiler Organismen (Crinoiden, tabulate Korallen) am Top und am Hang der Mounds und die durch die synsedimentäre Zementation von Auloporiden-Kolonien ausgelöste rasche Lithifizierung der steilen Mound-Flanken.Die Mounds entstanden unterhalb der Wellenbasis, aber oberhalb der Sturmwellenbasis. Die Mound-Bildung begann im obersten Abschnitt der Kess-Kess-Formation mit der durch Stürme verstärkten Anhäufung von bioklastischem Sediment. Die derart entstandenen flachen Hügelstrukturen wurden durch Crinoiden und tabulate Korallen (Auloporiden, Favositiden/Thamnoporen) besiedelt, die neues bioklastisches Sediment lieferten. Sedimentbindende Organismen wie Kalkalgen oder Stromatoporen fehlen. Die Rolle der tabulaten Korallen als Sedimentfänger war gering (Thamnoporen).NNW-SSE gerichtete Strömungen (abgeleitet aus der Einregelung von orthoconen Nautiloideen) dürften für die Ausbildung von steilen Nord- und weniger steilen Südflanken der Mounds verantwortlich gewesen sein.Die synsedimentäre Biozementation schützte die wachsenden Mounds gegen Zerstörung durch die in relativ kurzen Abständen auftretenden Stürme, deren Wirkung durch eng aufeinanderfolgende Eventstone-Lagen und durch Stromatactis-ähnliche Hohlraumstrukturen angezeigt wird.Die Mound-Bildung entspricht daher einem sich selbst verstärkenden System, bestehend aus einer durch Stürme induzierten Sedimentanhäufung auf einer Tiefschwelle, bevorzugter Besiedlung der derart gebildeten lokalen Kalksand- und Schlammbänke durch bioklastisches Sediment liefernde Crinoiden und tabulate Korallen und gleichzeitiger rascher Zementation der Mound-Flanken.Das Modell unterscheidet sich von üblichen Mud Mound Modellen durch die geringe bis fehlende Bedeutung der Sedimentbildung durch sedimentbindende oder sedimentfangende Organismen, durch das Fehlen von deutlichen Fazies-Folgen innerhalb der Mounds und durch die größere Rolle von exogenen Steuerungsfaktoren.

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Résumé Les mud mounds de la région de Hamar Laghdad (Anti-Atlas oriental, Maroc), s'étendent du Praguien supérieur au Zlichovien supérieur, avec prédominance au Zlichovien tardif d'après les faunes à conodontes. Leur origine et leur développement sont régis par des facteurs externes et internes. Les facteurs externes comprennent: l'existence du Lochkovien au Praguien inférieur d'un paléorelief d'origine volcanique, la présence de courants de fond orientés, l'occurrence de tempêtes répétées ainsi que des fluctuations du niveau de la mer. Les facteurs internes, d'origine biologique, sont: la croissance des organismes qui, en raison des conditions écologiques plus favorables, s'effectue de préférence sur le sommet et les flancs des mounds, ainsi qu'une lithification rapide synsédimentaire sur les flancs raides due à la cimentation par des coraux tabulés auloporides.Les mounds se sont développés dans un bassin épicontinental à une profondeur inférieure à la base des vagues, mais atteinte par l'agitation des tempêtes.La formation des mounds a commencé dans la partie supérieure de la Formation de Kess-Kess, avec l'accumulation par les tempêtes d'un sédiment bioclastique. Les légers bombements ainsi engendrés ont été alors occupés par des crinoïdes et divers coraux tabulés qui ont engendré de nouveaux sédiments bioclastiques. Les organismes susceptibles de fixer les sédiments, comme les algues ou les stromatopores, font défaut. Le rôle des tabulés comme capteurs de sédiments était subordonné.La présence de pentes raides sur les flancs nord et plus modérées sur les flancs sud est attribuée à des courants de tempête, dirigés du NNW au SSE, dont témoignent l'orientation de Nautiloïdes orthocones dans les couches supérieures de la Formation de Kess-Kess.Les mud-mounds en voie de croissance ont été protégés de la destruction par les tempêtes répétées grâce à une biocimentation synsédimentaire, dont témoignent des niveaux serrés d'eventstone ainsi que les structures fréquentes de type «Stromatactis».De la sorte, l'accumulation préférentielle de sédiments bioclastiques sur les mounds, par rapport aux aires voisines, résulte d'un système auto-entretenu, comportant l'accumulation par l'action de tempêtes de sédiments en amas surbaissés, l'occupation préférentielle de ces reliefs par des organismes producteurs de bioclastites et la cimentation concomitante des flancs des mounds en formation. Ce modèle se distingue de ceux qui sont habituellement proposés par l'absence d'organismes fixateurs de sédiments, par l'absence de séquences de faciès dans les mounds et par le rôle important joué par les facteurs externes.

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Detemination of the ring current radii from cosmic ray neutron monitor data for the 17 December 1971 magnetic storm

Variations of the cosmic ray cut-off rigidities have been observed at mid latitudes during the magnetic storm period 16–18 December 1971. In the present paper the cut-off changes over Europe are determined on an hourly basis from the registrations of 10 European neutron monitor stations. As a first order approximation it is assumed that the observed cut-off variations originate from a spherical current sheet concentric with the Earth and with a current density proportional to the cosine of the geomagnetic latitude. Applying results obtained by Treiman (1953), the radii of the current sphere can then be deduced from the dependences of the relative cut-off rigidity variations on geomagnetic latitude. The sphere is found to be located between 4 and 6 Earth radii during the main phase of the magnetic storm on 17 December 1971. A comparison of these results with in situ measurements carried out in the equatorial plane by Explorer 45 shows good agreement.     

The nature of water in chalcedony and opal-C from brazilian agate geodes

The water species (H₂O_(SiOH) and H₂O_(mol)) of length-fast chalcedony and opal-C in Brazilian agates were studied with thermoanalytical, chemical and infrared absorption methods. Specific surfaces were measured with the BET nitrogen adsorption method and the specific densities were determined. Chalcedony and opal-C have fully hydrated crystal surfaces at the open porosity. They contain additional water at inner surfaces, which are closed micropores in the case of opal-C and regions of accumulated defects (e.g. twinlamellae boundaries) in chalcedony. All surfaces are covered with silanole groups, hydrogen-bonded to molecular water. Additional hydroxyl groups, weakly hydrogen bonded to the structural framework within the crystallites, are located at structural point defects. Wall-lining chalcedony ranges from translucent gray to milky white bands corresponding with decreasing total water content, the H₂O_(SiOH)/H₂O_(mol)-ratio, BET-surfaces and increasing density. The H₂O_(SiOH)/H₂O_(mol)-ratio is sensitive to subsequent hydrothermal treatment and indicates a low temperature formation of chalcedony.     

Coccolithen-Diagenese in Malm-Kalken (Solnhofen/Frankenalb,Oberalm/Salzburg)

Zusammenfassung Rasterelektronenmikroskopische Untersuchungen der Solnhofener Plattenkalke (Lagunensediment) und der Oberalmer Kalke (bathyale Sedimente) zeigen weitgehend ähnliche diagenetische Veränderungen der Coccolithen-Morphologie. Die Vielfalt der während der Sedimentation, am Meersboden und im Sediment möglichen Lösungs- und Abscheidungsvorgänge (siehe Abb. 1) erscheinen in den beiden, aus unterschiedlichen paläogeographischen Bereichen stammenden Malm-Kalken homogenisiert.

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According to Stereoscan Electron Microscope Studies of the Upper Jurassic (Tithonian) Solnhofen limestone (Southern Franconia) and of the Oberalm limestone (Northern Calcareous Alps) similar diagenetic criteria can be recognized in the alterations of the coccolith morphology. In contrast to the various solution- and precipitation patterns formed during the sedimentation of the ultraplancton, on the sea-floor or in the sediment (see fig. 1) no differentiation can be made with regard to the submicroscopic criteria caused by diagenetic processes in different environments (Solnhofen: subtidal lagoon with alternating hypersaline conditions with growth of blue-green-algal mats and normal marine water conditions with the sedimentation of ultraplancton. — Oberalm: bathyal basin with strongly burrowed soft bottoms and common sedimentation of ultraplancton).

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Résumé Les études par S.E.M. des calcaires en minces bancs de Solenhofen (sédiment lagunaire) et des calcaires d'Oberalm (sédiment bathyal) montrent des transformations diagénétiques sensiblement les mÊmes dans la morphologie des coccolithes. La multiplicité des processus de dissolution et de précipitation pouvant intervenir au cours de la sédimentation sur le fond de la mer et dans le sédiment, apparaissent comme s'homogénéisant dans ces deux calcaires du Mahn provenant de domaines paléogéographiques différents.

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Berichtigung

Ohne Zusammenfassung     

Die Grösse der Globalstrahlung verschieden orientierter Flächen

Zusammenfassung Mit einem Solarimeter Moll-Gorczynski wurden in Locarno-Monti die Wärmemengen gemessen, die von Sonne+Himmel auf die fünf Seiten eines nach Süden gerichteten, senkrecht stehenden Einheitswürfels eingestrahlt werden. Unter Hinzuziehung von Messungen der Intensität der direkten Sonnenstrahlung konnte auch an heiteren Tagen der Anteil der Himmelsstrahlung bestimmt werden. Es zeigte sich zudem, dass die Strahlung der verschiedenen Flächen zu jener der Horizontalen in einem bestimmten, mit der Jahreszeit wechselnden, Verhältnis steht. Mit Hilfe dieser Verhältniszahlen lassen sich langjährige Registrierungen der Globalstrahlung der horizontalen Fläche auf andere Flächen umrechnen. Schliesslich wurde noch der Strahlungsgenuss der Flächen des Würfels für bedeckte Tage ermittelt.

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Summary By means of a solarimeter Moll-Gorczynski the quantities of heat were measured at Locarno-Monti which radiated from the sun and sky upon the five sides of unity cube facing South and standing vertically. By adding the measurements of the intensity of direct sun radiation it was possible on bright days also to determine the proportion by sky radiation. Furthermore it was revealed that the radiation for the various planes moves in a definite proportion, varying in accordance with the season, to that for the horizontal plane. With the help of these proportional figures, registrations over many years of global radiation for the horizontal plane can be converted into those for other planes. Finally, the radiation of the surfaces of the cube on cloudy days was determined.

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Riassunto A Locarno-Monti furono misurate con un solarimetro Moll-Gorczynski, le quantità di energia calorica, irradiate da sole+cielo sulle cinque facce di un cubo, unitario, disposto perpendicolarmente e orientato verso sud. Considerando misure della intensità della radiazione solare diretta si potè calcolare la parte della radiazione del cielo anche per giorni sereni. Inoltre si trovò che la radiazione per le diverse superfici sta a quella della superficie orizzontale in un determinato rapporto, variabile con le stagioni. Con l'aiuto di tali rapporti si può calcolare dalla registrazione pluriannuale della radiazione globale sulla superficie orizzontale, quella per altre superfici. Da ultimo fu determinata anche la quantità di radiazione ricevuta dalle superfici del cubo in giorni coperti.

     

Gravitational drainage systems in urban areas: case study (Galaţi town, Romania)

The water leakage in the urban areas causes a continuous rise in the water table, with harmful effects. An experimental drainage system, based on horizontal well technology, was designed and implemented in a populated area. Groundwater flow modeling was used to assess the hydrodynamic efficiency of the system through drain conductance parameter estimation.     

Temporali e precipitazioni temporalesche al margine meridionale delle Alpi

Riassunto Per il periodo 1936–1950 vengono comunicati il numero medio annuo dei giorni con temporali (udito almeno un tuono) e la statistica dei periodi di giorni successivi con temporali, secondo la loro lunghezza, per 8 stazioni poste pressapoco su di una sezione da sud a nord attraverso le Alpi, con estremi Milano e Zurigo. Per Locarno-Monti, periodo 1936–1953, sono confrontate le precipitazioni dei giorni con temporali con la quantità totale. Per il semestre aprile-settembre del quinquennio 1949–1953, le precipitazioni di Locarno-Monti dei giorni con temporali vengono suddivise secondo i tre tipi di temporali: frontali, di Südstau e locali, tenendo conto che nello stesso giorno ad ore diverse possono verificarsi temporali di diverso tipo, e paragonate fra loro.

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Zusammenfassung Von acht Stationen, die ungefähr auf der Linie Mailand-Zürich liegen, wurden für die Periode 1936–1950 die mittlere Anzahl der Tage mit Gewittern und Andauer aufeinanderfolgender Gewittertage berechnet. Des weiteren wurde für die Station Locarno-Monti (1936–1953) der Anteil der Niederschlagsmenge an Gewittertagen an der Gesamtmenge ermittelt und für die Periode 1949–1953 von April bis September die Niederschlagsmenge an den Tagen untersucht, an denen Front-, Südstauoder Lokalgewitter vorkamen. Auch die Fälle, an denen am gleichen Tag verschiedene Gewitterarten auftraten, wurden berücksichtigt.

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Comunicazione presentata alla II Assemblea Generale della Società Italiana di Geofisica e Meteorologia, Genova, 23–25 Aprile 1954.     

A Methodology for the Definition of Geotechnical Mine Sectors Based on Multivariate Cluster Analysis

This paper offers a new method for the definition of geotechnical sectors in open pit mines based on multivariate cluster analysis. A geological-geotechnical data set of a manganese open pit mine was used to demonstrate the methodology. The data set consists of a survey of geological and geotechnical parameters of the rock mass, measured directly in several points of the mine, structured initially in twenty-eight variables. After the preprocessing of the data set, the clustering technique was applied using the k-Prototype algorithm. The squared Euclidean distance was used to quantify the proximity between numerical variables, and the Jaccard's coefficient of similarity was used to quantify the proximity between the nominal variables. The different cluster results obtained were validated by the multivariate analysis of variance. The identification of cluster structures was achieved by plotting them on the mine map for spatial visualization and definition of geotechnical sectors. These sectors are spatially contiguous and relatively homogeneous regarding their geological–geotechnical properties, indicated by a high density of points of the same group. It was possible to observe a great adherence of the proposed sectors to the mine geology, demonstrating the practical representativeness of the clustering results and the proposed sectors.

     

Ionization of the earth’s atmosphere by solar and galactic cosmic rays

A brief review of the research of atmospheric effects of cosmic rays is presented. Numerical models are discussed, that are capable to compute the cosmic ray induced ionization at a given location and time. Intercomparison of the models, as well as comparison with fragmentary direct measurements of the atmospheric ionization, validates their applicability for the entire atmosphere and the whole range of the solar activity level variations. The effect of sporadic solar energetic particle events is shown to be limited on the global scale, even for the most severe event, but can be very strong locally in polar regions, affecting the physical-chemical properties of the upper atmosphere, especially at high altitudes. Thus, a new methodology is presented to study cosmic ray induced ionization of the atmosphere in full detail using realistic numerical models calibrated to direct observations.