Stochastic analysis of complex lithological successions

It is difficult to develop stochastic models for complex lithological sequences that are typically associated with intertidal-supratidal depositional environments. A sequence from the Upper Silurian Leopold Formation on eastern Somerset Island is used to demonstrate that a combination of cluster analysis, Markov Chain analysis, and substitutability analysis can give considerable insight into the nature of such complex successions. The high variability of this sequence was created by a combination of (a) variation in the depositional environment, (b) variation in the degree of dolomitization, (c) variation in the clastic influx, (d) random highenergy (possibly storm associated events) and (e) random breaks in the succession of depositional environments.     

Precision size-frequency distributions of craters for 12 selected areas of the lunar surface

Total crater populations in Lunar Orbiter photographs have been counted and measured for 12 selected areas of the lunar surface using precision techniques. Details of the counting procedure are described. Incremental and cumulative frequencies per km² (and their logarithms) are presented in graphical as well as tabular form for general use by other investigators. The data include 333,404 craters in areas totaling 10,833.3 km².     

THE EFFECT OF SOCIAL HETEROGENEITY WITHIN URBAN TRAVEL CORRIDORS ON THE TRAVEL BEHAVIOR OF RESIDENTS

Results from behavioral investigations of urban travel indicate the importance of privacy as a personal construct that significantly affects the manner in which individuals traverse North American urban transportation networks. With an expectation of encountering social heterogeneity in travel, the privacy aspect becomes all the more important to the traveling public. It is hypothesized in this paper that social heterogeneity within urban travel corridors significantly reduces patronage of public transportation by residents of these corridors. A causal analysis of bus patronage in travel corridors of Columbus, Ohio, Louisville, Kentucky, Syracuse, New York, and Hartford, Connecticut results in the acceptance of the hypothesized relationship, and it points out a critical question that must be addressed if public transportation is to meet the desires of consumers of travel services.     

Hydrodynamical winds from two-temperature plasma in X-ray binaries

Hydrodynamical winds from a spherical two-temperature plasma surrounding a compact object are constructed. The mass-loss rate is computed as a function of electron temperature, optical depth and luminosity of the sphere, the values of which can be constrained by the fitting of the spectral energy distributions for known X-ray binary systems. The sensitive dependence of the mass-loss rate with these parameters leads to the identification of two distinct regions in the parameter space separating wind-dominated from non-wind-dominated systems. A critical optical depth ( τ _c) is defined as a function of luminosity and electron temperature, which differentiates these two regions. Systems with optical depths significantly smaller than τ _c are wind-dominated.
The results are applied to black hole candidate X-ray binary systems in the hard spectral state (Cyg X-1, GX 339−4 and Nova Muscae), and it is found that the inferred optical depth ( τ ) is similar to τ _c, suggesting that they are wind-regulated systems. On the other hand, for X-ray binary systems containing a neutron star (e.g., Cyg X-2) τ is much larger than τ _c indicating the absence of significant hydrodynamical winds.     

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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Bolide impacts, acid rain, and biospheric traumas at the Cretaceous-Tertiary boundary

Large projectiles impacting the Earth will cause severe shock heating and chemical reprocessing of the Earth's atmosphere. This occurs during atmospheric entry and, more importantly, as a result of the supersonic plume ejected on impact. In particular, very large amounts of nitric oxide would result from the impact of the putative Cretaceous-Tertiary bolide(s). We present models of the shock chemistry, the conversion of NO to NO₂ and thence to nitrous and nitric acids, and the global dispersion of the NO₂ and acids. Two plausible projectiles are considered: an ice-rich long-period comet and a much smaller rock-metal asteroid. The comet produces semi-global atmospheric NO₂ mixing ratios of 0.1% while the asteroid produces these high mixing ratios only in the immediate region of the impact. The comet produces concentrated nitrous and nitric acid rain with apH ≈ 0–1.5 globally. The asteroid produces rain with apH ≈ 0–1 near the impact and≈ 4–5 globally. Immediate environmental effects of these nitrogen species include inhibition of photosynthesis due to extinction of solar radiation by NO₂, foliage damage due to exposure to NO₂ and HNO₃, toxicosis resulting from massive mobilization of soil trace metals, and respiratory damage due to exposure to NO₂. The acid rain decreases the pH of the oceanic mixed layer affecting the stability of calcite with important implications for the survival of calcareous-shelled organisms and for exhalation of CO₂ from the mixed layer to the atmosphere. Longer-term environmental effects perhaps≈ 1000years in duration include a global warming due to the sudden CO₂ injection and the simultaneous extinction of the ocean micro-organisms which normally help remove CO₂ from the atmosphere-mixed layer system. Havens for survival include carbonate-buffered lakes and burrows. This acid rain theory therefore serves to explain the peculiar selectivity of the extinctions seen at the Cretaceous-Tertiary boundary. The first few years of acid rain will lead to massive weathering rates of continental soils characterized by large ratios of the relatively insoluble metals (e.g. Be²⁺, Al³⁺, Hg²⁺, Cu⁺, Fe²⁺, Fe³⁺, Tl³⁺, Pb²⁺, Cd²⁺, Mn²⁺, Sr²⁺) to the more soluble metals (Ca²⁺, Mg²⁺) which should have left a clear signal in the fossils of neritic organisms and in unperturbed neritic sediments near river deltas if such sediments still exist for the Cretaceous-Tertiary time frame.     

Oilfield waters and sandstone diagenesis

The evolution of the organic geochemistry and carbonate alkalinity of oilfield waters is apparently regular and predictable; this evolution can be typified by five generalizations (1) at or near 80°C there appears to be an exponential rise in the concentration of organic acid anions; (2) the maximum concentration of organic acid anions occurs over approximately the 80–100°C temperature interval; (3) the highest concentrations of difunctional acid anions are associated with the other organic species maxima; (4) difunctional acid anions are the first to be decarboxylated, typically at temperatures of 100–110°C; (5) with increasing temperature (110–130°C) monofunctional acid anions begin to become decarboxylated, resulting in a fluid alkalinity dominated by bicarbonate. Dissolution experiments using artificial and natural oilfield waters demonstrate that mono- and difunctional carboxylic acid anions and hydroxybenzoic acid anions (present in both oilfield waters and the aqueous phase of hydrous pyrolysates) are capable of greatly enhancing Al, Si, Fe and Ca concentrations in solutions from dissolution of minerals by organometallic complexation. This enhancement of mineral solubility has been called upon to explain aluminosilicate dissolution porosity which is quantitatively important in many subsurface reservoirs; certainly, no other viable mechanism has been proposed to explain aluminum transport in the subsurface. When integrated into basin models, the regular evolution of organic and carbonate alkalinity in oilfield waters and the changing mineral stabilities that accompany that evolution help explain commonly observed diagenetic sequences in clastic systems.     

The kinematics of gouge deformation

The methods and first results of a new approach to examining fault gouge are described. Samples of undisturbed fault gouge from the exhumed Lopez fault zone in the San Gabriel Mountains, California were impregnated with low viscosity epoxy resin and sectioned to produce microscope slides. The slides were photographed using optical and electron microscopy with magnifications ranging in factors of 2 from 12.5 to 1600. At all scales, the particles appeared angular with planar faces, suggesting tensile failure. No shear zones were discernable. The particle size distribution was studied. At each magnification the particles were sorted by diameter into four classes, differing in mean diameter by factors of 2. The numbers in each class were then scaled by the characteristic class dimension. The process revealed a remarkable degree of self-similarity. Over the range examined, the fractal dimension was within 5% of 2.60.On the basis of the observations, a new model for the mechanical processes that generate gouge is offered. It is argued that self-similarity results from repeated tensile splitting of grains. Unlike earlier models that consider splitting probability to be either independent of particle size or due to the preexisting distribution of defects, we propose that failure probability depends largely on the relative size of nearest neighbors. If nearest neighbors of the same size are preferentially broken, any initial distribution of particles will tend toward a self-similar distribution having a fractal dimension of 2.58.The model allows us to outline a procedure whereby the observed comminution in a fault zone can be related to the shear strain that the zone has accommodated and propose a theoretical frequency magnitude relation for the seismic energy emitted by the fracture process.     

A wind-profile index for canopy flow

Canopy wind profiles can often be represented by an exponential function. The associated attenuation index,a, is found to be proportional to [(Flexibility)(Leaf Area)(Density)]^1/3. Leastsquare values of the index have been calculated for wind profiles in about a dozen natural and artificial canopies which included oats, wheat, corn, rice, sunflowers, larch trees, citrus trees, Xmas trees, plastic strips, wooden pegs and bushel baskets. It is found that canopy flow is a function of canopy density, element flexibility, and height and that the behaviour of artificial canopy elements is compatible with that of natural vegetation. The same calculations also show that the attenuation coefficient: (a) is not a universal constant, (b) is however, rather limited in range (-0.3 to 3.0), (c) varies with stage of growth, and (d) increases as density and flexibility increase. A compilation ofa-values for several canopies reveals that lowa-values correspond to sparsely arrayed rigid elements while higha-values correspond to densely arrayed and flexible elements. Finally, lowa-values appear to be relatively independent of wind speed, while higha-values tend to increase as wind speeds increase.