Plate kinematics: The Americas,East Africa,and the rest of the world

Euler vectors (relative angular velocity vectors) have been determined for twelve major plates by global inversion of carefully selected sea-floor spreading rates, transform fault trends, and earthquake slip vectors. The rate information comes from marine magnetic anomalies less than 5 m.y. old, so the motions are valid for post-Miocene times. Plate motions in a mean hotspot frame of reference have also been determined, and statistical confidence limits for all the Euler vectors estimated. Among the consequences of the global motion model is the conclusion that fast-spreading ridges (separation rates greater than 3 cm/yr) have plate motion nearly perpendicular to the strike of the ridge and magnetic anomalies. Four more slowly separating ridges have an average obliquity of spreading of almost 20°.For several plate boundaries, results that differ from previous studies are in agreement with geological evidence. The North and South American plates converge slowly about a pole east of the Antilles and near the Mid-Atlantic Ridge. The results for Africa versus Somalia imply slow east-west extension on the East African Rift Valleys. The pole for motion of Eurasia relative to North America is located near Sakhalin, in accordance with evidence from Siberia and Sakhalin.     

Characterisation of the hydrogeology of the Augustus River catchment,Western Australia

Understanding the hydrogeology of weathered rock catchments is integral for the management of various problems related to increased salinity within the many towns of Western Australia. This paper presents the results of site characterisation investigations aimed at improving the overall understanding of the hydrogeology of the southern portion of the Augustus River catchment, an example of a weathered rock catchment. Site data have highlighted the presence of both porous media aquifers within the weathered profile and fractured rock aquifers within the basement rocks. Geophysical airborne surveys and other drilling data have identified a large number of dolerite dykes which crosscut the site. Fractured quartz veins have been found along the margins of these dolerite dykes. Detailed groundwater-level measurements and barometric efficiency estimates indicate that these dolerite dykes and fractured quartz veins are affecting groundwater flow directions, promoting a strong hydraulic connection between all aquifers, and also influencing recharge mechanisms. The hydrogeological significance of the dolerite dykes and fractured quartz veins has been assessed using a combination of high-frequency groundwater-level measurements (30-min sampling interval), rainfall measurements (5-min sampling interval) and barometric pressure fluctuations (30-min sampling interval). A conceptual model was developed for describing various hydrogeological features of the study area. The model indicates that fractured quartz veins along the margins of dolerite dykes are an important component of the hydrogeology of the weathered rock catchments.

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Resumen Entender la hidrogeología de cuencas con rocas meteorizadas es esencial para gestionar diversos problemas relacionados con el incremento de salinidad en muchas ciudades de Australia Occidental. Este artículo presenta los resultados obtenidos en la caracterización de varios emplazamientos con el fin de mejorar el conocimiento general de la hidrogeología en la zona sur de la cuenca del Río Augustus, que sirve como ejemplo de cuenca en rocas meteorizadas. Los datos de campo resaltan la presencia tanto de medios acuíferos porosos dentro del perfil meteorizado como de acuíferos en rocas fracturadas dentro de la roca fresca. Los registros geofísicos aéreos y datos de las perforaciones han identificado un gran número de diques de dolerita que intersectan el emplazamiento. Se ha hallado venas de cuarzo fracturado a lo largo de los márgenes de los diques de dolerita. Medidas detalladas del nivel piezométrico y estimaciones de la eficiencia barométrica indican que los diques de dolerita y las venas de cuarzo fracturado afectan las direcciones del flujo de las aguas subterráneas, originando una fuerte conexión hidráulica entre todos los acuíferos e influenciando también a los mecanismos de recarga. Se ha establecido la importancia hidrogeológica de los diques de dolerita y de las venas de cuarzo fracturado mediante una combinación de medidas muy frecuentes del nivel piezométrico (cada 30 min), de la precipitación (cada 5 min) y de las fluctuaciones de la presión barométrica (cada 30 min). Se ha desarrollado un modelo conceptual para describir varias características hidrogeológicas del área de estudio. El modelo indica que las venas de cuarzo fracturado en los márgenes de los diques de dolerita constituyen un componente importante de la hidrogeología de cuencas con rocas meteorizadas.

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Résumé Comprendre lhydrogéologie des bassins en roches altérées est essentiel pour la gestion de différents problèmes liés à laugmentation de la salinité dans de nombreuses villes dAustralie occidentale. Cet article présente les résultats détudes de caractérisation de sites conduites pour améliorer la compréhension de lhydrogéologie de la partie sud du bassin de la rivière Augustus, exemple de bassin en roches altérées. Les données concernant le site ont mis en évidence la présence simultanée daquifères poreux dans le profil daltération et daquifères de roches fracturées dans le socle. Des campagnes de géophysique aéroportée et dautres données de forages ont identifié de très nombreux dykes de dolérite traversant le site. Des veines de quartz fracturées ont été trouvées aux marges de ces dykes de dolérite. Des mesures détaillées de niveau des nappes et des estimations des effets barométriques indiquent que ces dykes de dolérite et les veines de quartz fracturées affectent les directions découlement souterrain, favorisant une forte connexion hydraulique entre tous ces aquifères, et influençant également les mécanismes de recharge. La signification hydrogéologique des dykes de dolérite et des veines de quartz fracturées a été analysée en combinant des mesures à haute fréquence du niveau des nappes (toutes les 30 min), de la pluie (toutes les 5 min) et des variations de la pression barométrique (toutes les 30 min). Un modèle conceptuel a été établi pour décrire les différents phénomènes hydrogéologiques de la région étudiée. Ce modèle indique que les veines de quartz aux marges des dykes de dolérite sont une importante composante de lhydrogéologie des bassins en roches altérées.

     

Experimental calibration of lake-sediment spectral reflectance to chlorophyll a concentrations: methodology and paleolimnological validation

Chlorophyll a preserved in lake sediments reflects, in part, past primary production. This study assesses the spectral properties of sedimentary chlorophyll a using visible-near infrared reflectance (VNIR) spectroscopy, with the objective of establishing a new, non-destructive paleolimnological proxy. Reflectance spectra were determined from a dilution series (n = 10) involving incremental additions of pulverized modern algae to a lake sediment matrix of low organic content. This enabled an assessment of the development of sediment reflectance spectra in relation to different sediment chlorophyll a concentrations, and subsequent regression of spectral features against measured concentrations of chlorophyll a and derivatives obtained by high performance liquid chromatography (HPLC). The experiment demonstrates that ubiquitous troughs in sediment reflectance near 675 nm are attributable to chlorophyll a and derivative compounds. A significant correlation (r ² = 0.98, P < 0.01) was obtained between the area of the reflectance trough in the 650–700 nm interval and summed concentrations of chlorophyll a, all derivative isomers, and degradational pheopigments. A simple linear inference model derived from this experiment was applied to a down-core sequence of VNIR spectra from a productive prairie lake (Alberta, Canada), where it produced inferred sediment chlorophyll a concentrations in concordance with HPLC measurements. Although a larger training set is desirable to further refine the inference model, the analyses reported here demonstrate that reflectance spectroscopy provides a rapid, semi-quantitative method for assessing the chlorophyll a content of lake sediments.     

Lithospheric controls on the formation of provinces hosting giant orogenic gold deposits

Ages of giant gold systems (>500 t gold) cluster within well-defined periods of lithospheric growth at continental margins, and it is the orogen-scale processes during these mainly Late Archaean, Palaeoproterozoic and Phanerozoic times that ultimately determine gold endowment of a province in an orogen. A critical factor for giant orogenic gold provinces appears to be thickness of the subcontinental lithospheric mantle (SCLM) beneath a province at the time of gold mineralisation, as giant gold deposits are much more likely to develop in orogens with subducted oceanic or thin continental lithosphere. A proxy for the latter is a short pre-mineralisation crustal history such that thick SCLM was not developed before gold deposition. In constrast, orogens with protracted pre-mineralisation crustal histories are more likely to be characterised by a thick SCLM that is difficult to delaminate, and hence, such provinces will normally be poorly endowed. The nature of the lithosphere also influences the intrinsic gold concentrations of potential source rocks, with back-arc basalts, transitional basalts and basanites enriched in gold relative to other rock sequences. Thus, segments of orogens with thin lithosphere may enjoy the conjunction of giant-scale fluid flux through gold-enriched sequences. Although the nature of the lithosphere plays the crucial role in dictating which orogenic gold provinces will contain one or more giant deposits, the precise siting of those giants depends on the critical conjunction of a number of province-scale factors. Such features control plumbing systems, traps and seals in tectonically and lithospherically suitable terranes within orogens.     

On a Non-local Parameterisation for Shear Turbulence and the Uniqueness of its Solutions

A non-local parameterisation of shear turbulence is proposed, which includes a dimensionless multiplicative constant as the sole tunable parameter. Analytical and numerical solutions in the case of plane Couette flow exhibit sheared velocity profiles with logarithmic behaviour near the boundaries, and the classical logarithmic flow profile is reproduced for a semi-infinite domain. We also prove that the families of analytical solutions obtained are locally unique: if the velocity is a strictly-increasing function of the distance from the boundary, a small perturbation of the velocity profile must be of the same functional form as the basic flow.     

Observations of the Sunyaev–Zel''dovich effect at high angular resolution towards the galaxy clusters A665, A2163 and CL0016+16

We report on the first observation of the Sunyaev–Zel'dovich (SZ) effect, a distortion of the Cosmic Microwave Background radiation (CMB) by hot electrons in clusters of galaxies, with the Diabolo experiment at the IRAM 30 m telescope. Diabolo is a dual-channel 0.1 K bolometer photometer dedicated to the observation of CMB anisotropies at 2.1 and 1.2 mm. A significant brightness decrement in the 2.1 mm channel is detected in the direction of three clusters (Abell 665, Abell 2163 and CL0016+16). With a 30 arcsec beam and 3 arcmin beamthrow, this is the highest angular resolution observation to date of the SZ effect. Interleaving integrations on targets and on nearby blank fields have been performed in order to check and correct for systematic effects. Gas masses can be directly inferred from these observations.     

A record of the upper Cochiti polarity transition from the Southern Hemisphere (FIJI)

We sampled the upper Cochiti polarity transition recorded in the Suva Marl in Fiji (18° S, 178° E). The Suva Marl accumulated at an average rate of 83.2 m/m.y. and provides a unique opportunity to address the question of whether present-day overprints bias the transition records. Fiji has undergone a 30° counterclockwise rotation since the deposition of the Suva Marl and hence a present day overprint onto the transitions would bias the VGPs toward the east of the site. Replicate transition records yield VGPs over both Asia and the Americas. Progressive demagnetization reveals a normal polarity overprint which was acquired prior to the rotation of Fiji, and therefore does not produce an easterly bias to the transition data even after correction for the rotation. We collected an oriented block sample across a portion of the transitional interval in the upper Cochiti reversal. Subsampling of this block into 1.0 cm thick wafers cut parallel to bedding provides considerably greater detail during the transition. These detailed data suggest that the oscillatory movement of the VGPs in these sections may be a result of the averaging caused by standard, detailed minicoring and not by the sediments or the remanence acquisition process.     

An interpolation method taking into account inequality constraints: I. Methodology

Several kinds of data can provide information about a variable measured on a one- or two-dimensional space; at some points, the value is known to be equal to a certain number. At other points, the only information may be that the variable is greater or smaller than a given value. The theory of splines provides interpolating functions that can take into account both equality and inequality data. These interpolating functions are presented. The parallel between splines and kriging is reviewed, using the formalism of dual kriging. Coefficients of dual kriging can be obtained directly by minimizing a quadratic form. By adding some inequality constraints to this minimization, an interpolating function may be calculated which takes into account inequality data and is more general than a spline. The method is illustrated by some simple one-dimensional examples.Work performed at Sohio Petroleum Company     

Multivariate Monitoring with GPS Observations and Auxillary Multisensor Data

In a multisensor measurement or monitorin environment, p variables are measured simultaneously. The measured data are correlated and can be monitored to identify special causes of variation in order to establish control and to obtain reference samples to use as a basis in determining the control limits for future observations. One common method is to construct a multivariate control chart based on Hotelling's T² statistic. When the monitoring process is at the start-up stage, F and chi-square distributions are used to construct the necessary control limits. An example from a seven-day GPS data sample measured concurrently with the accelerometer response, wind velocity and temperature illustrates that this technique can improve the interpretation of GPS results. Moreover, the computational complexity is reduced through a reduction in the data dimensionality. ? 2002 Wiley Periodicals, Inc.     

Hyperspectral core logging for fire reconstruction studies

Lacustrine sediments contain a wide range of proxies that enable paleoenvironmental reconstructions. For instance, charcoal can be used to document past fire regime changes. In order to analyse high-temporal- and spatial-resolution records, however, it is necessary to develop fast, low-cost and high-stratigraphic-resolution methods. We developed a new paleo-fire proxy by studying a lacustrine core from the Esterel Massif, SE France, an area affected by two recent fire events, in AD 1987 and 2003. For this purpose, we searched for charcoal deposited and preserved in the lake sediments by combining a number of complementary methods, including: classic macrocharcoal tallying, scanning spectrophotometry, scanning hyperspectral imaging and high pressure liquid chromatography analyses. Macrocharcoal quantification is efficient, but time-consuming, and only provides intermediate-resolution data (cm scale). Spectrophotometry, used classically to quantify colour, is very fast, provides high-resolution data (4 mm) and is non-destructive (core preservation). Hyperspectral data have the same advantages as spectrophotometry, but offer higher spatial resolution (64-µm pixel size) and higher spectral resolution (6 nm) for core logging applications. The main result of this research is based on hyperspectral analysis at very high stratigraphic resolution using the I-band index. This index usually measures reflectance values at [660, 670 nm] corresponding to the trough in red reflectance produced by Chlorophyll a and its diagenetic products. This [660, 670 nm] reflectance trough, however, is also affected by the presence of altered organic matter and decreases with altered organic matter such as charcoal particles. Charcoal effect on the reflectance of Chlorophyll a and its diagenetic products is identified on first derivative spectra by a characteristic pattern around 675 nm, which is also in agreement with the Chlorophyll a concentrations measured by high-pressure liquid chromatography and charcoal particles. The I-band index is hence suitable for detecting burned organic matter, by quantifying the dilution of the chlorophyll signal by the charcoal signal. Thus, this adaptation of the I-band index can be applied in fire reconstruction studies.