Contribution au Dosage de l'Argon dans L'Echantillon de Glauconite GL-O     

C. CASSIGNOL  B. DAVID  P.Y. GILLOT 《Geostandards and Geoanalytical Research》1977,1(2):105-106

Une série de mesures a été effeotuée sur le matériel de référence Glauconite GL-O (grains) afin de définir sa teneur en Argon 40 radiogénique. Les résultats obtenus rendent compte d'une bonne homogénéité, l'éscort-type relatif étant inférieur à 0.5 % pour 9 mesures.  相似文献   

The Biotite Isograd and the Lower Greenschist Facies in the Dalradian Rocks of Scotland   总被引：1，自引：0，他引：1  

MATHER  JOHN DAVID 《Journal of Petrology》1970,11(2):253-275

Analyses of a series of coexisting minerals and their host rocks,from the Aberfoyle area, indicate that previously proposed biotite-formingreactions are inadequate to account for the appearance of biotitein the Dalradian greywackes and pelites. Initially biotite isformed as a product of the breakdown of the assemblage chlorite+microcline+phengiticmuscovite in greywackes of suitable bulk composition. With increasein grade the stability field of the biotite-bearing assemblageis enlarged through the reduction in the amount of celadonitesubstitution that can be tolerated by the white micas. The stabilityfield increases so that it includes progressively more aluminousrocks. The sequence of biotile-forming reactions is used to definethree zones of increasing metamorphic grade in the Dalradiangreywackes and pelites. The interrelationships of the assemblagesdeveloped in these zones are considered in detail. The assemblagesdeveloped in the Green Beds are explained on the assumptionthat the fugacity of CO₂ is a third intensive variable.  相似文献   

Wildfires and seasonal aridity recorded in Late Cretaceous strata from south-eastern Arizona, USA     

DAVID B. FINKELSTEIN  LISA M. PRATT  TARA M. CURTIN†  SIMON C. BRASSELL 《Sedimentology》2005,52(3):587-599

Lithostratigraphic and organic chemostratigraphic studies of fluvial/lacustrine sediments in the Late Cretaceous Fort Crittenden Formation in south-eastern Arizona USA, reveal changes in palaeoclimate and tectonics as well as associated fluctuations in lake level. The lower Fort Crittenden is dominated by marginal wetland to deep-water lake deposits, whereas the upper Fort Crittenden is characterized by wetland to deltaic deposits. Abundance of polycyclic aromatic hydrocarbons (PAH) and reflectance of fusinite substantiate the impact of wildfires within the watershed. Organic geochemical evidence of wildfires is linked with sedimentological indicators of seasonal aridity suggesting that wildfires were common occurrences. Sedimentological evidence for seasonal aridity includes mottles and pseudoslickensides on ped structures within wetland mudstones. Distinct variations in PAH assemblages, characterized by the number of aromatic rings, indicate that there were variations in the intensities of wildfires, assuming no variations in the types of fuel. Fusinite reflectance values are consistent with combustion temperatures from 470 to 550 °C observed in modern wildfires.  相似文献   

Influence of waves and horseshoe crab spawning on beach morphology and sediment grain-size characteristics on a sandy estuarine beach   总被引：2，自引：0，他引：2  

NANCY L. JACKSON  KARL F. NORDSTROM  DAVID R. SMITH 《Sedimentology》2005,52(5):1097-1108

The effects of wave action and horseshoe crab spawning on the topography and grain-size characteristics on the foreshore of an estuarine sand beach in Delaware Bay, New Jersey, USA were evaluated using data collected over six consecutive high tides. Data were gathered inside and outside a 25 m long exclosure constructed to create a control area free of disturbance by crabs. The density of crabs in the swash zone outside the exclosure was 8·1 organisms m⁻². The maximum depth of sediment activation on the upper foreshore where spawning occurred was 0·103 m during periods characterized by low significant wave heights: < 0·08 m. This depth is greater than the depth of activation by waves alone during moderate significant wave heights of 0·16–0·18 m but less than the maximum depth (0·127 m) recorded when spawning occurred during periods of moderate wave heights. Spawning, combined with moderate wave heights, creates a concave upper foreshore that is similar to the type of profile change that occurs during storms, thus lowering the wave-energy threshold for morphological response. Spawning during low wave heights increases the mean grain size and sorting of surface sediments caused by the addition of gravel to the swash. Sedimentological differences are most pronounced on the upper foreshore, and data from this location may be most useful when using grain-size characteristics to interpret the effect of spawning in the sedimentary record. Depths of sediment reworking by horseshoe crabs can be greater than those by subsequent storm waves, so evidence of spawning can be preserved on non-eroding beaches. Greater depth of activation by horseshoe crab spawning than by waves alone, even during moderate-energy conditions, reveals the importance of crab burrowing in releasing eggs to the water column and making them available for shore birds.  相似文献   

Viscous Energy Dissipation and Strain Partitioning in Partially Molten Rocks   总被引：1，自引：0，他引：1  

HOLTZMAN  BENJAMIN K.; KOHLSTEDT  DAVID L.; MORGAN  JASON PHIPPS 《Journal of Petrology》2005,46(12):2569-2592

We develop a steady-state fluid-mechanical analysis describingthe effect of strain partitioning on viscous energy dissipation.As observed in experimental studies of shear deformation ofpartially molten rocks, strain partitions when melt segregatesbecause viscosity is reduced in regions of elevated melt fraction.The equations derived here are based on parameters measuredin experiments, describing the evolution of melt distributionand rheological properties. We find that the dissipation dependsstrongly on the configuration of the melt-rich network of shearzones, including the average angle, volume fraction of meltand amplification of strain rate in the melt-rich bands. Minimain energy dissipation as a function of band angle develop, correspondingto configurations of melt networks that minimize the differencein mean stress between the band and the non-band regions. Wepropose that the organization of band networks occurs by theinterplay between strain localization and viscosity variationsassociated with melt segregation. The band networks maintaina steady-state angle during shear by continuously pumping meltthrough the network. The development of strain partitioningin melt-rich networks will modify the energetics of meltingand melt transport by efficiently extracting melt and reducingeffective viscosity. KEY WORDS: melt transport; rheology; self-organization; strain localization; strain partitioning  相似文献   

A National Park Revisited Assessing Change in Recreational Use of Arthur's Pass National Park     

STEPHEN R. ESPINER  DAVID G. SIMMONS 《New Zealand geographer》1998,54(1):37-45

At a time of increasing visitation and activity diversification, the relationship between use and conservation of New Zealand's national parks is under scrutiny. During this period it is especially important that resource use is understood and monitored over time. Using a replicative format this paper documents the findings of two visitation studies undertaken in Arthur's Pass National Park fifteen years apart. The findings suggest that, despite some strong elements of stability, there are indications of considerable change in use patterns at this site. Data presented are acquiescent in supporting the thesis that Arthur's Pass National Park is undergoing a transition initially shaped by wider social and economic pressures and manifest at the Park by increasing use for commercial purposes, an intensification of use, and increasing numbers of visitors from overseas. While continued research into visitation trends is encouraged, the authors also advise that the challenge of replicative studies in natural resource settings should not be underestimated.  相似文献   

The Klippfisk Formation—a new lithostratigraphic unit of Lower Cretaceous platform carbonates on the Western Barents Shelf     

MORTEN SMELROR  ATLE MØRK  ERIC MONTEIL  DAVID RUTLEDGE  HAN LEEREVELD 《Polar research》1998,17(2):181-202

A new Lower Cretceous lithostratigraphic unit of the Western Barents Shelf, named the Klippfisk Formation, is formally introduced. The formation represents a condensed carbonate succession deposited on platform areas and structural highs, where it consists of limestones and marls, often glauconitic. The limestones may have a nodular appearance, and fossil debris, which are dominated by Inoceramus prisms, may be abundant. The Klippfisk Formation is composed of two members: the Kutling Member defined herein from cores drilled on the Bjarmeland Platform, and the coeval Tordenskjoldberget Member described on Kong Karls Land. The base of the formation is defined by the abrupt decrease in gamma-ray intensity, where the dark shales of the underlying Hekkingen or Agardhfjellet formations are replaced by marls. It is often unconformable. The Klippfisk Formation is of Berriasian to Early Barremian age and appears to be time-transgressive over parts of the Western Barents Shelf (including Kong Karls Land). It passes laterally into the basinal Knurr Formation. On Kongsøya (Kong Karls Land) a thin shale unit, bounded by unconformities, earlier included in the Tordenskjoldberget Member, represents the northernmost extension of the overlying Kolje Formation in the Barents Shelf.  相似文献   

Embedding production rules in a GIS     

DAVID PULLAR 《Transactions in GIS》1997,2(3):257-265

A long-standing issue in GIS has been the need to provide support for more complex spatial models that have specialized Operations, but at the same time to take advantage of generic functionality provided by the GIS for visualizing, querying, and manipulating spatial features. Two approaches may be used to incorporate domain-specific knowledge in computer software, namely object-oriented programming and logic-based programming. Based upon a commonly used data model and object-oriented application framework available in modern GIS software, this paper explores integrating rules as a generic approach to building more meaningful spatial representations for land use and land control planning.  相似文献   

SOLAR ECLIPSE EFFECTS OBSERVED IN THE PLANETARY BOUNDARY LAYER OVER A DESERT     

F. D. EATON  J. R. HINES  W. H. HATCH  R. M. CIONCO  J. BYERS  D. GARVEY  DAVID R. MILLER 《Boundary-Layer Meteorology》1997,83(2):331-346

Boundary-layer meteorologicalmeasurements were made before, during, and after theMay 10, 1994 partial (94%) solar eclipse over thedesert at the Atmospheric Profiler Research Facilityat White Sands Missile Range, New Mexico, U.S.A. A largenumber of sensors were located in the middle of theTularosa Basin to measure mean and turbulentquantities and the refractive index structureparameter (Cn2). This event permitted a rareopportunity to measure, examine, and document theeffects upon the atmospheric boundary layer of asudden cut-off and subsequent turn-on of the sun'sradiant energy. At the peak of the eclipse, whichoccurred for more than three hours, all of the heatexchange parameters were affected, the turbulentprocesses were diminished, and the refractive indexstructure parameter decreased dramatically. A time-heightdisplay from the FM-CW radar shows a Kelvin–Helmholtzwave that developed during theeclipse. The results of several analyses arepresented to document and characterize the eclipse-modifiedboundary layer.  相似文献   

Submarine sedimentation on a developing Holocene fan delta   总被引：4，自引：0，他引：4  

DAVID B. PRIOR  BRIAN D. BORNHOLD 《Sedimentology》1989,36(6):1053-1076

The submarine morphology, sediments, and three-dimensional geometry of a developing fan delta are described using data from acoustic surveys, bottom sampling, and observations from a manned submersible. The fan system is being built in a British Columbian fjord (water depth 410 m) supplied with coarse-grained sediments from a fjord-side river. Construction of the subaqueous fan began about 10–12,000 yr BP and is ongoing. The system is analogous to part of one fault-uplift sedimentation cycle in ancient fan deltas. Initially, when offshore relief was at a maximum, acoustically chaotic sediment wedges were emplaced over fjord-bottom glaciomarine deposits. Subsequent aggradation/progradation resulted in moderately dipping sequences interrupted by local chaotic units. The present fan surface (average slope 13°) is divided into six zones arranged concentrically from the fan apex, on the basis of form, sediment and process interpretations. Continued subaqueous fan growth results from settling of river-derived sediments from suspension and downslope sediment dispersal by episodic gravity flows, apparently fed by underflows from the river.  相似文献