Nested intrashelf platform clinoforms—Evidence of shelf platform growth exemplified by Lower Cretaceous strata in the Barents Sea

Two nested clinoform set types of different scales and steepness are mapped and analysed from high-resolution seismic data. Restoration of post-depositional faulting reveals a persistent pattern of small-scale, high-angle clinoforms contained within platform-scale, low-angle clinothems, showing a combined overall progradational depositional system. The large clinoforms lack a well-defined platform edge, and show a gradual increase in dip from topset to foreset. A consistent recurring stratal pattern is evident from the architecture, and is considered a result of interplay between relative sea-level change and autocyclic switching of sediment delivery focal points that brought sediment to the platform edge. This un-interrupted succession records how intra-shelf platforms prograde. Quantitative clinoform analysis may assist in determining the most influential depositional factors. Post-depositional uplift and erosion requires restoration with re-burial to maximum burial depth. Backstripping, decompaction and isostatic correction was performed assuming a range of lithologic compositions, as no wells test the lithology. Nearby wells penetrate strata basinward of the clinoforms, proving mudstone content above 50%, which in turn guide restoration values. Typical restored platform heights are 250–300 m, with correspondingly sized platform-scale clinoform heights. Typical large-scale clinoform foreset dip values are 1.3°–2.4°. Small-scale clinothems are typically 100 m thick, with restored foreset dip angles at 4.4° - > 10°. The results suggest that intrashelf platform growth occurs in pulses interrupted by draping of strata over its clinoform profile. The resultant architecture comprises small-scale clinoforms nested within platform-scale clinothems.     

The holocenic evolution of a stretch of an eastern italian alpine valley

The morphological evolution of a stretch of an alpine valley located in the Eastern Italian Alps is described. This has been conditioned by a great alluvial fan that was formed as a consequence of interconnected events, deriving from large rockfalls which occurred in the late glacial period at the head of the Missiaga–Bordina valley, on the left side of the Agordo basin. The aggradation of the alluvial fan blocked the Cordevole valley south of the Agordo basin and produced a lake that is documented by lacustrine sediments. Age determination by ¹⁴C techniques on wood remnants found in these sediments fixes the life of the lake at between approximately 5880 and 5300 years BP . This represents, indirectly, the age of the main phase of the development of the fan. After the building up of the alluvial fan, an erosional phase began, leading to the formation of the present landscape. A series of illustrations depicts the sequence of the fan's development.     

Fundamental energy and closed space

The existence of the universal quantization law E=n ε E =any energy; n = an integer, ε = the fundamental energy ∼ħ c/R with ħ = the reduced Planck constant, c = the speed of light, R = the curvature radius of the closed cosmological space) is advocated and discussed. A possible connection between ε and the mass of elementary particles is pointed out.     

Maximal mass and size of celestial bodies born from superstrings

The generalized Buchdahl inequality in the presence of a positive cosmological constant gives rise to a constraint on the mass density of celestial bodies. We find that such a constraint implies an upper bound on the mass and radius of spherical celestial bodies born from macroscopic superstrings. We obtain a maximal mass of about 10¹⁵ solar masses and a maximal radius of about 80 million light years, not far from the observed mass and size of the largest structures in the universe, viz. the superclusters of galaxies.     

A simplified model for estimating field‐scale surface runoff hydrographs

The problem of obtaining field‐scale surface response to rainfall events is complicated by the spatial variability of infiltration characteristics of the soil and rainfall. In this paper, we develop and test a simplified model for generating surface runoff over fields with spatial variation in both rainfall rate and saturated hydraulic conductivities. The model is able to represent the effects of local variation in infiltration, as well as the run‐on effect that controls infiltration of excess water from saturated upstream areas. The effective rainfall excess is routed to the slope outlet using a simplified solution of the kinematic wave approximation. Model results are compared to averaged hydrographs from numerically‐intensive Monte–Carlo simulations for observed and design rainfall events and soil patterns that are typical of Central Italy. The simplified model is found to yield satisfactory results at a relatively small computational expense. A proposal to include a simple channel routing scheme is also presented as a prelude to extend this conceptualization to watershed scales. Copyright © 2006 John Wiley & Sons, Ltd.     

Modelling the seismic response of a 2-storey URM benchmark case study: comparison among different equivalent frame models

Bulletin of Earthquake Engineering - The paper presents the comparison of the results of non-linear static analyses performed with different software based on the equivalent frame (EF) modelling...     

Geological,petrochemical and metallogenic characteristics of the Costa Rican gold belt: Contribution to new explorations

The Costa Rican Gold Belt is located in the northwestern part of Costa Rica. The geology of this region is characterized by tectonically juxtaposed volcanic-sedimentary and igneous rock units of Tertiary age.Mineralization within the Gold Belt consists of: 1) veins and fissure fillings of epithermal type which bear gold, silver and base metals; 2) disseminated mineralization of complex sulphides (Au, Ag, Pb, Zn); 3) disseminated specks of native gold; 4) eluvial Au rich lateritic soils.Hydrothermal circulation, induced by the emplacement of epizonal plutons, together with continuous and intense pervasive tectonism has been responsible for the epithermal gold-silver mineralization occurring within the Aguacate volcanic series. Contamination and assimilation of andesitic and »shoshonitic« rocks by uprising granitic magmas generated, in association with hydrothermal phenomena, composite environments for gold deposits.Calc-alkaline rocks of the Costa Rican Gold Belt appear to be enriched in incompatible elements of low ionic potential (particularly Ba). For a similar silica concentration, there is a general increase in Y, Ni, and Zr from Miocene to Pliocene rocks. K/Rb and Rb/Sr ratios increase from older to younger suites as well.On the basis of trace element distribution it is suspected that the Guacimal intrusive rocks may represent a marginal suite comparable to those of the New Guinea Mobile Belt. This would imply that the Precambrian-Paleozoic igneous and metamorphic basement, present in northern Nicaragua, might extend further south.Four different magmatic events have been recognized and correlated with regional geodynamic conditions: Eocene-Oligocene calc-alkaline and »shoshonitic« volcanism (plate convergence and subduction), Middle-Early Miocene to Late Miocene calc-alkalic magmatism (compression and uplift), Early Pliocene alkalic magmatism (E-W trending rift), Middle-Late Pliocene calc-alkaline magmatism (crustal extension followed by compression and uplift).Correlation between tectonic events, magmatism and mineralization suggests that metal enrichment may have some relation to different stress regimes associated with active subduction.

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Zusammenfassung Der goldführende Gürtel von Costa Rica befindet sich in dem nordwestlichen Teil des Landes. Die Geologie dieses Gebietes ist durch tektonisch aneinandergelagerte vulkaisch-sedimentäre und magmatische Gesteine des Tertiärs gekennzeichnet.Die Mineralisierungen in dem goldführenden Gürtel bestehen aus: 1) quarzführenden Gängen epithermaler Art, die Gold, Silber, Zink und Blei enthalten 2) Mineralisierungen mit komplexen Sulfiden (Au, Ag, Pb, Zn) 3) punktförmige Einschlüsse von gediegenem Gold 4) eluvialem, Aureichem, lateritischem Boden.Der durch das Eindringen von epizonalen Plutonen bedingte hydrothermale Umlauf, zusammen mit einer intensiven, ununterbrochenen durchgreifenden tektonischen Tätigkeit ist für die Au-Ag epithermalen Mineralisierungen in der vulkanischen Reihe von Aguacate verantwortlich. Die Kontamination und die Assimilation von andesitischen und »shoshonitischen« Gesteinen durch die aufdringenden Granitmagmen hat, in Verbindung mit hydrothermalen Erscheinungen, verschiedene Typen von Goldmineralisierungen erzeugt.Die kalkalkalischen Gesteine des goldführenden Gürtels von Costa Rica sind anscheinend an inkopatiblen Elementen mit niedrigem Ionenpotential (insbesondere Ba) angereichert. Bei vergleichbaren Kieselsäurekonzentrationen begegnet man eine allgemeine und allmähliche Zunahme an Y, Ni und Zr in den jüngsten Gesteinen, wenn man diese mit den Miozän-Gesteinen vergleicht. Au\erdem ist eine Zunahme der K/Rb und Rb/Sr Verhältnisse zu verzeichnen.Aufgrund der Verteilung der Spurenelemente vermutet man, da\ die Intrusivgesteine von Guacimal eine Gesamtheit von marginalen Plutonen darstellen, die mit denen der mobilen Kordillere (mobile belt) in Neuguinea vergleichbar sind. Dies würde bedeuten, da\ das magmatisch-metamorphe Fundament aus dem Präkambrium-Paläozoikum, das im nördlichen Teil von Nicaragua vorhanden ist, sich nach Süden ausdehen könnte.Vier unterschiedliche Magmaerzeugnisse sind ermittelt worden: kalkalkalischer und »shoshonitischer« Vulkanismus des Späteozäns-Oligozäns (Plattenkonvergenz und Subduktion); kalkalkalischer Miozän-Magmatismus (Kompression und Aufwölbung); alkalischer Magmatismus des Frühpliozäns (Entstehung des Valle Central Senkungsgrabens, mit E-W Streichen); Kalkalkali-Magmatismus des Mittel-Spätpliozäns (Krustenausdehnung und anschlie\ende Kompression und Aufwölbung).Die Beziehung zwischen den tektonischen Ereignissen, dem Magmatismus und den Mineralisierungen lä\t vermuten, da\ die Metallanreicherung der Kruste auf veränderliche Stre\bedingungen in Verbindung mit aktiver Subduktion zurückzuführen sein könnte.

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Resumen La Cintura Aurífera de Costa Rica está localizada en el sector norte-occidental del país y está caracterizada por unidades volcano-sedimentarias e igneas de edad terciaria en yuxtaposición tectónica.Las mineralizaciones dentro de la Cintura Aurífera están representadas por: 1) vetas cuarzo-auríferas y relleno de fisuras de origen epitermal asociadas con plata y metales básicos; 2) mineralizaciones diseminadas de sulfuros complejos (Au, Ag, Pb, Zn); 3) laminillas diseminadas de oro nativo; 4) suelos lateríticos eluviales ricos en oro.Se asigna como responsable de las mineralizaciones epitermales oro-plata de la Serie Volcanica de Aguacate, al tectonismo intenso y continuado, así como a la circulación hidrotermal inducida por el emplazamiento de plutones y »stocks« en condiciones epitermales. La contaminación y asimilación de rocas andesiticas y »shoshoniticas« por parte de magmas graniticos ascendentes generó, en asociación con fenomenos hidrotermales, un ambiente de campo aurífero compuesto.Las rocas calco-alcalinas de la Cintura Aurífera de Costa Rica muestran un elevado contenido de elementos incompatibles (en particular Ba). Por contenidos de SiO₂ similares, se evidencia un enrequecimiento general en Y, Ni, Zr desde las rocas del Mioceno a las rocas del Plioceno. Paralelamente se registra un aumento de las relaciones K/Rb y Rb/Sr.En particular se suspecha, por medio de la distribución de los elementos en traza, que las rocas intrusivas de Guacimal puedan representar un »grupo« de plutones marginales comparables con aquellos de la »Mobile Belt« de Nueva Guinea. Lo que indicaria la posible extensión al Sur del basamento igneo y metamórfico de edad Precambrica-Paleozoica presente en el norte de Nicaragua.Se reconocen quatro eventos magmaticos asociados con las condiciones geodinamicas regionales: vulcanismo calco-alcalino de edad Eoceno-Oligoceno (en condiciones de convergencia y subducción de placas), magmatismo calcoalcalino del Mioceno Medio y Temprano hasta Mioceno Tardio (en condiciones de compresión crostal y levantamiento), vulcanismo alcalino del Mioceno Temprano (Rift prevalente E-W), magmatismo calco-alcalino del Plioceno Medio-Tardfo (en condiciones de extensión crostal seguida por compressión y levantamiento).Las correlaciones entre condiciones geodinámicas, magmatismo y mineralizaciones, sugieren que el enriquecimiento en metales esta vinculado con los diferentes regimenes de deformación asociados con procesos de subducción activa.

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