Contrasting flooding histories of Mississippian carbonate platforms revealed by marine alteration effects in palaeosols   总被引：1，自引：0，他引：1  

V. PAUL WRIGHT‡  SIMON D. VANSTONE  JAMES D. MARSHALL† 《Sedimentology》1997,44(5):825-842

Palaeosols associated with exposure surfaces in Mississippian platform carbonate sequences in Britain invariably show evidence for later alteration by sea water. These alteration effects can be attributed to flooding of the emergent platforms during transgressions that terminated exposure surface development. A study of 230 palaeosol profiles representing 60 stratigraphic levels has revealed a two fold division of these marine hydromorphic effects. Palaeosols in ramp sequences (Chadian-Arundian stages) are capped by ferroan dolomite horizons with carbonized rootlets, pyrite and thin coals. The ferroan dolomites exhibit δ¹³C and δ¹⁸O values indicative of formation in brackish waters. These are interpreted as coastal marshes that developed landward of a transgressive shoreline. Younger Asbian-Brigantian palaeosols lack these dolomites but have been extensively pyritised. The pyrite also developed through marine hydromorphic alteration but flooding was relatively instantaneous over the flat topped platforms. These differences in flooding history reflect both different platform configuration and more rapid transgressions during the Asbian-Brigantian, likely a result of glacio-eustatic effects. Flooding characteristics of the Asbian-Brigantian platforms differ from those associated with late Cainozoic examples, apparently because complete platform rims were not developed. Similar mineralogical alteration effects are likely to be common in other platform sequences in the geological record, but have not been documented.  相似文献   

MEDJUGORJE: FINDING PEACE AT THE HEART OF CONFLICT     

JAMES M. JURKOVICH  WILBERT M. GESLER 《Geographical review》1997,87(4):447-467

ABSTRACT. Pilgrims to the Bosnian town of Medjugorje find peace at the heart of several conflicts that involve ethnic, religious, and political tensions; the natural and the supernatural; rural and urban lifestyles; the role of the Catholic Church; the sacred and the profane; and the Virgin Mary's messages. Peace within this place is found by creating community, the Other, ritual, and myth.  相似文献   

Cross-stratified calcarenites from New Zealand: subaqueous dunes in a cool-water, Oligo-Miocene seaway   总被引：2，自引：0，他引：2  

ALEXIS S. ANASTAS  ROBERT W. DALRYMPLE  NOEL P. JAMES  CAMPBELL S. NELSON† 《Sedimentology》1997,44(5):869-891

Cross-bedded, cool-water, bioclastic limestones of the Te Kuiti Group on the North Island of New Zealand are composed primarily of bryozoans, echinoderms, and benthic foraminifers. Their prominent, large-scale, unidirectional cross-stratification is interpreted as produced by migrating subaqueous dunes on the floor of a 50–100 km wide, north-east-trending seaway in water depths of 40–60 m. These dunes are thought to have developed in response to strong, seaway-parallel, tidal currents combined with a north-east-directed, set-up or oceanic current. Cross-stratification is organized into four hierarchical levels: (1) cross-lamination; (2) first-order sets; (3) second-order sets; and (4) cross-stratified successions. The levels are based on increasing degrees of internal complexity. Distinct attributes such as internal organization, cross-set thickness, foreset shape, and lower bounding-surface shape are used to describe and interpret the cross-stratification. All these attributes are here integrated in a new and expanded classification of unidirectional cross-stratification that emphasizes flow and bedform dynamics rather than overall set shape. Individual cross-stratified successions are interpreted to have formed by dunes with varying sinuosity, superposition, and flow history, under conditions of different current strength but constant sediment production. Horizontally bedded successions are the result of robust, active dune fields that grew during times of vigorous sediment transport. Formset successions were produced from large compound dunes and are the expression of languid and decaying dune fields that developed during times of decreasing sediment transport. These decaying dunes were gradually smothered by continuously and locally produced bioclastic sediment. Formset cross-stratified successions are most likely to develop in carbonates, where the sediment is produced in place, than in terrigenous clastics where the sediment is imported.  相似文献   

A middle Proterozoic palaeokarst unconformity and associated sedimentary rocks, Elu Basin, northwest Canada     

SHANE M. PELECHATY  NOEL P. JAMES  CHARLES KERANS  JOHN P. GROTZINGER 《Sedimentology》1991,38(5):775-797

A major palaeokarst erosion surface is developed within the middle Proterozoic Elu Basin, northwestern Canada. This palaeokarst is named the sub-Kanuyak unconformity and truncates the Parry Bay Formation, a sequence of shallow-marine dolostones that were deposited within a north-facing carbonate platform under a semi-arid climate. The sub-Kanuyak unconformity exhibits up to 90 m of local relief, and also formed under semi-arid conditions when Parry Bay dolostones were subaerially exposed during a relative sea-level drop of about 180 m. Caves and various karren developed within the meteoric vadose and phreatic zones. Their geometry, size and orientation were largely controlled by northwest- and northeast-trending antecedent joints, bedding, and lithology. Near-surface caves later collapsed forming valleys, and intervening towers or walls, and plains. Minor terra rossa formed on top of highs. Karstification was most pronounced in southern parts of Bathurst Inlet but decreased northward, probably reflecting varying lengths of exposure time along a north-dipping slope. The Kanuyak Formation is up to 65 m thick, and partially covers the underlying palaeokarst. It consists of six lithofacies: (i) breccia formed during collapse of caves, as reworked collapse breccia and regolith; (ii) conglomerate representing gravel-dominated braided-fluvial deposits; (iii) sandstone deposited as braided-fluvial and storm-dominated lacustrine deposits; (iv) interbedded sandstone, siltstone and mudstone of sheet flood origin; (v) dolostones formed from dolocretes and quiet-water lacustrine deposits; and (vi) red-beds representing intertidal-marine mudflat deposits. Rivers flowed toward the northwest and northeast within karst valleys and caves; lakes were also situated within valleys; marine mudflat sediments completely cover the palaeokarst to the north. A regional correlation of the sub-Kanuyak unconformity with the intra-Greenhorn Lakes disconformity within the Coppermine homocline suggests that similar styles of karstification occurred over an extensive region. The Elu Basin palaeokarst, however, was developed more landward, and was exposed for a longer period of time than the Coppermine homocline palaeokarst.  相似文献   

Origin of Mafic Enclaves in the Dinkey Creek Pluton, Central Sierra Nevada Batholith, California   总被引：4，自引：1，他引：4  

DORAIS  MICHAEL J.; WHITNEY  JAMES A.; RODEN  MICHAEL F. 《Journal of Petrology》1990,31(4):853-881

Two types of mafic enclaves occur in the Dinkey Creek pluton:ubiquitous microgranular enclaves, and rare gabbroic enclaves.Common petrographic features of the microgranular enclaves are:(1) fine grain-size, (2) abundant acicular apatite, and (3)plagioclase zoned from bytownitic cores to andesine-labradoriterims, with sharp boundaries between these main zones. Subordinateoscillatory variations are commonly superimposed on both coresand rims. It has been found by secondary ion mass spectrometrythat the rims are identical in major and trace element compositionto plagioclase in the tonalite, which suggests crystallizationfrom the same or similar magmas. The gabbroic enclaves are composedpredominantly of hornblende (50–85%) and appear to bemagmatic segregations. The microgranular enclaves and host rocks display two convergingtrends on silica variation diagrams for Fe₂O₃, TiO₂, Al₂O₃,Zn, and Zr. The dominant trend is defined by small microgranularenclaves, by samples from a large (20 m?30 m) microgranularenclave, and by the Dinkey Creek tonalites and granodiorites.The subordinate trend covers tholeiltic dikes and tonalitich and converges with the Dinkey Creek host rocks at 61 wt.%SiO₂ Alkali and alkaline earth elements exhibit greater variabilitythan the above constituents and appear to be either enrichedor depleted as required for equilibrium with the host rocks.Low CaO and Sr concentrations in small enclaves (<30 cm)apparently reflect a lower modal abundance of calcic plagioclaseand more sericitization of this feldspar as compared with theplagioclase of the large microgranular enclave. The large enclaveis also richer in MgO than the small enclaves. With the exceptionof the alkali elements, the major element compositions of themicrogranular enclaves approach high-Al basaltic to andesiticcom positions. In one analyzed microgranular enclave, low La/Cerelative to chondrites and more abundant HREE than in othermicrogranular samples suggest that it may also contain minorcumulus hornblende. The petrographic and whole-rock geochemical relations, and theplagioclase compositions in the microgranular enclaves and theirhost rocks, indicate that the microgranular enclaves representmixtures of quenched basalts and Dinkey Creek tonalites. Itappears that dikes of high-alumina basalt were intruded intothe lower, tonalitic portions of the Dinkey Creek pluton, wherethey were partially quenched along an interface with overlyingtonalitic magma. Large portions of residual liquid in the partiallyquenched basalts permitted mixing with the overlying magma toform a hybrid zone. This zone was then disaggregated, yieldingthe enclaves, and they were dispersed throughout the upper partof the Dinkey Creek magma chamber. Subsequent crystallizationof tonalitic melt within the enclaves produced the zoned plagioclaseand re-equilibrated hornblende and biotite in the enclaves tothe Dinkey Creek magmatic conditions. Scouring disrupted hornblende-richmagmatic segregations and produced the gabbroic enclaves.  相似文献   

The Petrogenetic Significance of Interstratified High- and Low-Ti Basalts in Central Nicaragua   总被引：3，自引：0，他引：3  

WALKER  JAMES A.; CARR  MICHAEL J.; FEIGENSON  MARK D.; KALAMARIDES  RUTH I. 《Journal of Petrology》1990,31(5):1141-1164

Basalts erupted from recent volcanoes in central Nicaragua canbe divided into distinct high-and low-Ti suites. Low-Ti basaltshave higher concentrations of LILE and LREE than high-Ti basalts.In addition, low-Ti basalts have obviously higher Ba/La, La/Sm,and ⁸⁷Sr/⁸⁶Sr, and lower Ti/Zr, than high-Ti basalts. In contrast,there are no mineralogical or petrographic differences betweenthe two suites. The differences between the high-and low-Ti basalts of centralNicaragua are inherited from their source regions. The primarymagmas of both are generated in the mantle wedge. However, low-Tiprimary magmas come from parts of the wedge which bear a strongsubduction zone signature, including that of subducted pelagicsediment. On the other hand, the primary magmas of the high-Tibasalts are generated in parts of the wedge relatively freeof subduction zone influence. Subducted pelagic sediment can therefore be a key source componentat active continental margins as well as at island arcs. Pelagicsediment could also be responsible for subtle high-field-strengthelement fractionations within subduction zone magmas. The mantlewedge beneath Nicaragua, which is variably modified by the subductingplate, is relatively enriched suboceanic mantle.  相似文献   

A local ensemble Kalman filter for atmospheric data assimilation   总被引：6，自引：0，他引：6  

EDWARD OTT  BRIAN R. HUNT  ISTVAN SZUNYOGH  ALEKSEY V. ZIMIN  ERIC J. KOSTELICH  MATTEO CORAZZA  EUGENIA KALNAY  D. J. PATIL  JAMES A. YORKE 《地球，A辑:动力气象学与海洋学》2004,56(5):415-428

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Comparative assessment of water use and environmental implications of coal slurry pipelines / Evaluation comparative de l'utilisation de l'eau et des implications pour l'environnement des pipelines de bouillie de charbon     

RICHARD N. PALMER  IVAN C. JAMES II  ROBERT M. HIRSCH 《水文科学杂志》2013,58(4):455-469

Abstract

One of the most talked about issues with respect to development, transportation, and conversion of the energy resources of the Western United States is the water requirement and its consequent impacts upon the ambience of that part of the country. In conjunction with other studies conducted by the US Geological Survey of water use in the conversion and transportation of the West's coal, an analysis of water use and environmental implications of coal slurry pipeline transport is presented.

Simulations of a hypothetical slurry pipeline of 1000 mile length transporting 12.5 million tons per year indicate that pipeline costs and energy requirements are quite sensitive to the coal-to-water ratio. For realistic water prices, the optimal ratio will not vary far from the 50/50 ratio by weight. In comparison to other methods of energy conversion and transport, coal slurry pipelines utilize about a third of the amount of water required for coal gasification, and about a fifth of the amount required for onsite electrical generation.

An analysis of net energy output from operating alternative energy transportation systems for the assumed conditions indicates that both slurry pipeline and rail shipment require approximately 4.5 per cent of the potential electrical energy output of the coal transported and high-voltage, direct-current transportation requires approximately 6.5 per cent. The environmental impacts of the different transport options are so substantially different that a common basis for comparison does not exist.  相似文献   

A review of numerical simulation of hydrothermal systems / Examen de la simulation numérique des systèmes hydrothermiques     

JAMES W. MERCER  CHARLES R. FAUST 《水文科学杂志》2013,58(3):335-343

Abstract

Many advances in simulating single and two-phase fluid flow and heat transport in porous media have recently been made in conjunction with geothermal energy research. These numerical models reproduce system thermal and pressure behaviour and can be used for heat-transport problems other than those associated with geothermal energy development, such as high-level radioactive waste disposal and heat-storage projects. Although these models are general, additional research is necessary before they can be applied to certain site-specific problems that are concerned with additional processes, such as mass transport and flow in fractured media.  相似文献   

LOS LAVADORES: DISCOVERING PLACE IN THE ANDES     

CASEY D. ALLEN 《Geographical review》2012,102(3):364-371

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