The carbon dioxide review     

William C. Clark 《Climatic change》1983,5(1):3-5

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Sterane distribution of solid bitumen pyrolyzates. Changes with biodegradation of crude oil in the Ouachita Mountains,Oklahoma     

Joseph A Curiale  William E. Harrison  Garmon Smith 《Geochimica et cosmochimica acta》1983,47(3):517-523

Solid bitumens (grahamite and impsonite) of southeastern Oklahoma have been shown to originate from near-surface alteration of crude oil (Curiale, 1981; Curiale and Harrison, 1981). Pyrolysis of these solids has been employed to compare the sterane distribution of geographically proximate oils to that of the bitumens. The ratio of rearranged to regular steranes is higher in the pyrolyzates than in the oils, a finding consistent with a bitumen origin due to biodegradation of oil. The remaining presence of steranes, particularly regular steranes, in the bitumens suggests that sterane occlusion may have occurred prior to or during the alteration process, thus removing tetracyclic compounds from the influence of microbial attack. These data suggest that pyrolysis-$\text{GC}\text{MS}$ offers a viable approach to correlation problems involving solid bitumens.  相似文献   

Geotechnical properties of lower trench inner-slope sediments     

L.E. Shephard  William R. Bryant 《Tectonophysics》1983,99(2-4)

Geotechnical property analyses on sediments recovered by DSDP drilling within select convergent margins were integrated to determine the variability in these properties along the trench inner-slope and to delineate the effects of convergence on these properties. Consolidation states range from very underconsolidated to highly overconsolidated, with preconsolidation pressures exceeding 46,000 kPa in Quaternary sediments. Underconsolidated sediments are attributed to:

1. (1) high sedimentation rates.

2. (2) low sediment permeability relative to the length of the drainage path; (3) laterally applied stresses; and (4) induced pore water pressures resulting from the subduction of pelagic sediments with high water content. Factors contributing to the state of overconsolidation include: (1) tectonically induced overpressures; (2) removal of overburden by mass movement processes.

3. (3) low sediment accumulation rates.

4. (4) age.

Vertical gradients of index properties also vary greatly with the maximum gradient associated with overconsolidated sediments. Values of porosity generally exceed 30% at all margins studied, suggesting this porosity represents the minimum attainable solely by the effects of convergence.Geotechnical property results and site-specific parameters suggest two end members should be considered in the general geotechnical property model for convergent margin sediments. Clastic dominated margins form the basis for the initial geotechnical property model. These margins are characterized by thick trench sediment sequences which are folded and faulted and become progressively more deformed upslope. Convergence rates are low, and no well-developed faults or hrst and graben structures are evident on the downbending oceanic plate. Highly overconsolidated sediments and index property values which change rapidly with depth result from the slow progressive deformation of trench and lower slope sediments. Examples of clastic-dominated margins include the Nankai Trough, Aleutian Trench, and Washington continental margin.Pelagic-dominated margins have significantly different geotechnical properties and site-specific parameters. These margins are characterized by thin clastic trench sediment sequences overlying pelagic sediments on a rapidly converging oceanic plate. Well-developed faults and/or hrst and graben structures are evident on the downbending oceanic plate. Sediment deformation along the trench and lower slope appears limited. These sediments are underconsolidated and index property values change gradually but often irregularly with depth. Japan Trench and Middle America Trench-Guatemala margins are considered pelagic-dominated. Middle America Trench-Mexico appears to represent an intermediate case having characteristics of both margin types.  相似文献   

Structural features of the bonin arc: Implications for its tectonic history     

William L. Bandy  Thomas W.C. Hilde   《Tectonophysics》1983,99(2-4)

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Nucleation on perthite-perthite boundaries and exsolution mechanisms in alkali feldspars     

William L. Brown  Ian Parsons 《Physics and Chemistry of Minerals》1983,10(2):55-61

A transmission electron microscope study of intracrystalline boundaries between two perthites of markedly different composition in composite crystals, one a tenary mesoperthite (Or₂₆Ab₅₂An₂₂, initially a homogeneous potassian monalbite) the other a more potassic cryptoperthite (Or₆₁Ab₃₃An₆, initially a homogeneous sodian sanidine), shows that the two perthites are in nearly parallel intergrowth. Most boundaries examined were of (hkO) type; (010) boundaries are straight, whereas other (hkO) boundaries are curved or stepped. Exsolution occurred first in the potassian monalbite (mesoperthite) and was unaffected by the boundary. Subsequent exsolution in the sodian sanidine (cryptoperthite) was affected by the boundary, but for up to only a few micrometers. Exsolution occurred by heterogeneous nucleation and growth of oligoclase on and from the intracrystalline boundary. At almost the same time the rest of the volume of sanidine exsolved by spinodal decomposition. 1–2 μm from the boundary in the intervening K-rich matrix of the sodian sanidine, further exsolution occurred by homogeneous nucleation. Time — temperature — transition curves for continuous cooling have been devised to account for the unusual complexity of the exsolution texture. Except in such exceptional circumstances as the example studied, the initial exsolution in high-temperature alkali feldspars of intermediate composition, unlike other minerals, probably does not occur by nucleation, but only by spinodal decomposition.  相似文献   

<Superscript>40</Superscript>Ar/<Superscript>39</Superscript>Ar dating of the eruptive history of Mount Erebus,Antarctica: volcano evolution     

Richard?P.?EsserEmail author  Philip?R.?Kyle  William?C.?McIntosh 《Bulletin of Volcanology》2004,66(8):671-686

Mt. Erebus, a 3,794-meter-high active polygenetic stratovolcano, is composed of voluminous anorthoclase-phyric tephriphonolite and phonolite lavas overlying unknown volumes of poorly exposed, less differentiated lavas. The older basanite to phonotephrite lavas crop out on Fang Ridge, an eroded remnant of a proto-Erebus volcano and at other isolated locations on the flanks of the Mt. Erebus edifice. Anorthoclase feldspars in the phonolitic lavas are large (~10 cm), abundant (~30–40%) and contain numerous melt inclusions. Although excess argon is known to exist within the melt inclusions, rigorous sample preparation was used to remove the majority of the contaminant. Twenty-five sample sites were dated by the ⁴⁰Ar/³⁹Ar method (using 20 anorthoclase, 5 plagioclase and 9 groundmass concentrates) to examine the eruptive history of the volcano. Cape Barne, the oldest site, is 1,311±16 ka and represents the first of three stages of eruptive activity on the Mt. Erebus edifice. It shows a transition from sub-aqueous to sub-aerial volcanism that may mark the initiation of proto-Erebus eruptive activity. It is inferred that a further ~300 ky of basanitic/phonotephritic volcanism built a low, broad platform shield volcano. Cessation of the shield-building phase is marked by eruptions at Fang Ridge at ~1,000 ka. The termination of proto-Erebus eruptive activity is marked by the stratigraphically highest flow at Fang Ridge (758±20 ka). Younger lavas (~550–250 ka) on a modern-Erebus edifice are characterized by phonotephrites, tephriphonolites and trachytes. Plagioclase-phyric phonotephrite from coastal and flank flows yield ages between 531±38 and 368±18 ka. The initiation of anorthoclase tephriphonolite occurred in the southwest sector of the volcano at and around Turks Head (243±10 ka). A short pulse of effusive activity marked by crustal contamination occurred ~160 ka as indicated by at least two trachytic flows (157±6 and 166±10 ka). Most anorthoclase-phyric lavas, characteristic of Mt. Erebus, are less than 250 ka. All Mt. Erebus flows between about 250 and 90 ka are anorthoclase tephriphonolite in composition.Editorial responsibility: J. Donelly-Nolan  相似文献   

Trace element signature and U–Pb geochronology of eclogite-facies zircon,Bergen Arcs,Caledonides of W Norway     

Bernard?BingenEmail author  H?kon?Austrheim  Martin?J.?Whitehouse  William?J.?Davis 《Contributions to Mineralogy and Petrology》2004,147(6):671-683

Secondary-ion mass spectrometry (SIMS) U–Pb and trace element data are reported for zircon to address the controversial geochronology of eclogite-facies metamorphism in the Lindås nappe, Bergen Arcs, Caledonides of W Norway. Caledonian eclogite-facies overprint in the nappe was controlled by fracturing and introduction of fluid in the Proterozoic—Sveconorwegian—granulite-facies meta-anorthosite-norite protolith. Zircon grains in one massive eclogite display a core–rim structure. Sveconorwegian cores have trace element signatures identical with those of zircon in the granulite protolith, i.e. 0.31Th/U0.89, heavy rare earth element (HREE) enrichment, and negative Eu anomaly. Weakly-zoned to euhedral oscillatory-zoned Caledonian rims are characterized by Th/U0.13, low LREE content (minimum normalized abundance for Pr or Nd), variable enrichment in HREE, and no Eu anomaly. A decrease of REE towards the outermost rim, especially HREE, is documented. This signature reflects co-precipitation of zircon with garnet and clinozoisite in a feldspar-absent assemblage, and consequently links zircon to the eclogite-facies overprint. The rims provide a mean ²⁰⁶Pb/²³⁸U crystallization age of 423±4 Ma. This age reflects eclogite-forming reactions and fluid–rock interaction. This age indicates that eclogite-facies overprint in the Lindås nappe took place at the onset of the Scandian (Silurian) collision between Laurentia and Baltica.  相似文献   

The potential listing of Acropora species under the US Endangered Species Act     

Precht WF  Robbart ML  Aronson RB 《Marine pollution bulletin》2004,49(7-8):534-536

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Inputs of dissolved and particulate 226Ra to lakes and implications for 210Pb dating recent sediments   总被引：8，自引：6，他引：2  

Mark Brenner  Claire L. Schelske  William F. Kenney 《Journal of Paleolimnology》2004,32(1):53-66

Gamma spectroscopy was used to measure radioisotope (²¹⁰Pb, ²²⁶Ra, ¹³⁷Cs) activities in sediment cores from 20 lakes and a wetland in Florida, USA. Nine profiles display relatively low (<5 dpm g^–1) and constant ²²⁶Ra activities, whereas 12 show high (>5 dpm g^–1) and variable ²²⁶Ra activities. In the latter group, most display up-core increases in activity. Upper sediments from two lakes (Round and Rowell) possess very high (>20 dpm g^–1) ²²⁶Ra activities that exceed total ²¹⁰Pb activities, clearly illustrating disequlibrium between ²²⁶Ra and supported ²¹⁰Pb. Supported ²¹⁰Pb activity is generally thought to come from in situ, ²²⁶Ra-containing detrital mineral particles, and is typically assumed to be in secular equilibrium with ²²⁶Ra activity. Since 1966, Round Lake has been augmented hydrologically with ²²⁶Ra-rich (6.2 dpm L^–1) groundwater pumped from the local deep aquifer. Adsorption of dissolved ²²⁶Ra to recent Round Lake sediments probably accounts for the high measured ²²⁶Ra activities and the pronounced disequilibrium between ²²⁶Ra and supported ²¹⁰Pb in topmost deposits. We suspect that many Florida waterbodies receive some ²²⁶Ra-rich runoff and seepage from groundwater pumped for irrigation, residential use, industrial applications, and mining. This may account for up-core increases in ²²⁶Ra activity measured in sediment cores from some Florida lakes. Significant groundwater pumping began within the last century, and there has been insufficient time for supported ²¹⁰Pb to come into equilibrium with adsorbed ²²⁶Ra in uppermost deposits. Input of ²²⁶Ra-rich groundwater to lakes may occur in any geographic region where local bedrock contains ²³⁸U and its daughters. When dissolved ²²⁶Ra adsorbs to recent sediments, it complicates accurate estimation of supported ²¹⁰Pb activity, and confounds calculation of unsupported ²¹⁰Pb activity that is used in dating models.  相似文献   

Capture zone,travel time,and solute-transport predictions using inverse modeling and different geological models   总被引：2，自引：1，他引：1  

William?G.?HarrarEmail author  Torben?Obel?Sonnenborg  Hans?J?rgen?Henriksen 《Hydrogeology Journal》2003,11(5):536-548

Six regional-scale flow models are compared to gain insight into how different representations of hydraulic-conductivity distributions affect model calibration and predictions. Deterministic geological models were used to define hydraulic-conductivity distributions in two steady-state flow models that were calibrated to heads and baseflow estimates using inverse techniques. Optimized hydraulic-conductivity estimates from the two models were used to calculate layer and model mean hydraulic-conductivity values. Despite differences in the two geological models, inverse calibration produced mean hydraulic-conductivity values for the entire model domain that are quite similar. The layer and model mean hydraulic-conductivity values were used to generate four additional flow models and forward runs were performed. All of the models adequately simulate the observed heads and total baseflow. The six flow models were used to predict the steady-state impact of a proposed well field, and the flow solutions were used in simulating particle tracking and solute transport. Results of the predictive simulations show that, for this example, simple models of heterogeneity produce capture zones similar to more complex models, but with very different travel times and breakthroughs. Inverse modeling combined with different geological models can provide a measure of capture zone and breakthrough reliability.

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Resumen Se compara seis modelos de flujo a escala regional para conocer cómo afecta a la calibración y a la predicción del modelo diversas representaciones de la distribución de la conductividad hidráulica. Se ha utilizado modelos geológicos deterministas para definir las distribuciones de la conductividad hidráulica en dos modelos de flujo permanente, calibrados mediante técnicas inversas con niveles piezométricos y estimaciones del flujo de base. Se ha adoptado estimaciones optimizadas de la conductividad hidráulica de los dos modelos para calcular las cotas de las capas y sus conductividades hidráulicas medias. A pesar de las diferencias entre ambos modelos geológicos, con la calibración inversa se obtiene valores similares de conductividad hidráulica en todo el dominio. Estos valores de las capas y de las conductividades hidráulicas medias han servido para generar cuatro modelos adicionales de flujo y realizar predicciones. Todos los modelos simulan de forma adecuada los niveles observados y los caudales de base. Los seis modelos han sido aplicados a la predicción del impacto estacionario de un campo de pozos, y las soluciones del flujo permiten simular el transporte de partículas y de solutos. Los resultados de estas predicciones muestran que, para este ejemplo, los modelos sencillos de la heterogeneidad dan lugar a zonas de captura similares a las generadas por modelos más complejos, pero aparecen grandes diferencias en los tiempos de tránsito y en las curvas de llegada. Una combinación de modelación inversa y de modelos geológicos diferentes puede proporcionar una medida de la fiabilidad de la zona de captura y de las curvas de llegada.

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Résumé Six modèles d'écoulement à l'échelle régionale sont comparés afin d'avoir un aperçu de la manière dont les différentes représentations de la distribution de la conductivité hydraulique affectent la calibration et les prédictions de modèles. Des modèles géologiques déterministes ont été utilisés pour définir les distributions de la conductivité hydraulique dans deux modèles d'écoulement en régime permanent qui ont été calibrés avec des estimations des charges et des écoulements de base faites par des techniques inverses. Les estimations optimisées de la conductivité hydraulique de ces deux modèles ont servi à calculer les valeurs de conductivité hydraulique moyenne des couches et du modèle. Malgré des différences entre les deux modèles géologiques, la calibration inverse a donné des valeurs de conductivité hydraulique moyenne pour le domaine complet du modèle qui sont complètement semblables. Les valeurs de la conductivité moyenne des couches et du modèle ont été utilisées pour générer quatre modèles d'écoulement supplémentaires et des traitements ont été effectués. Tous les modèles simulent correctement les charges observées et l'écoulement de base total. Les six modèles ont servi à prédire l'impact en régime permanent d'un champ captant projeté et les solutions d'écoulement ont été utilisées dans une simulation par suivi de particules et de transport de soluté. Les résultats de simulations prédictives montrent que, pour cet exemple, de simples modèles d'hétérogénéité fournissent des zones de capture semblables aux modèles plus complexes, mais pour des temps de parcours et des restitutions très différents. Une modélisation inverse combinée à différents modèles géologiques peut assurer une mesure de la zone de capture et une fiabilité de la restitution.

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