Diatom, Pollen, and Chemical Evidence of Postglacial Climatic Change at Big Lake, South-Central British Columbia, Canada     

Joseph R. Bennett  Brian F. Cumming  Peter R. Leavitt  Marian Chiu  John P. Smol  Julian Szeicz   《Quaternary Research》2001,55(3):332

Postglacial climatic conditions were inferred from cores taken from Big Lake in southern British Columbia. Low concentrations of nonarboreal pollen and pigments near the base of the core suggest that initial conditions were cool. Increases in both aquatic and terrestrial production suggest warmer and moister conditions until 8500 cal yr B.P. Hyposaline diatom assemblages, increases in nonarboreal pollen, and increased concentrations of pigments suggest the onset of arid conditions from 8500 to 7500 cal yr B.P. Slightly less arid conditions are inferred from 7500 until 6660 cal yr B.P. based on the diatoms, small increases and greater variability in biogenic silica and pigments, and higher percentages of arboreal pollen. At 6600 cal yr B.P., changes in diatoms, pigments, biogenic silica, and organic matter suggest that Big Lake became fresh, deep, and eutrophic until 3600 cal yr B.P., when water levels and nutrients decreased slightly. Our paleoclimatic inferences are similar to pollen-based studies until 6600 cal yr B.P. However, unlike these studies, our multiple lines of evidence from Big Lake imply large changes in effective moisture since 6000 cal yr B.P.  相似文献   

The influence of tectonic plates on mantle convection patterns, temperature and heat flow   总被引：1，自引：0，他引：1  

Julian P. Lowman  Scott D. King  Carl W. Gable 《Geophysical Journal International》2001,146(3):619-636

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Uncertainty assessment in river flow projections for Ethiopia’s Upper Awash Basin using multiple GCMs and hydrological models     

Wilson C. H. Chan  Julian R. Thompson  Richard G. Taylor  Alistair E. Nay  Tenalem Ayenew  Alan M. MacDonald 《水文科学杂志》2020,65(10):1720-1737

ABSTRACT

Uncertainty in climate change impacts on river discharge in the Upper Awash Basin, Ethiopia, is assessed using five MIKE SHE hydrological models, six CMIP5 general circulation models (GCMs) and two representative concentration pathways (RCP) scenarios for the period 2071–2100. Hydrological models vary in their spatial distribution and process representations of unsaturated and saturated zones. Very good performance is achieved for 1975–1999 (NSE: 0.65–0.8; r: 0.79–0.93). GCM-related uncertainty dominates variability in projections of high and mean discharges (mean: –34% to +55% for RCP4.5, – 2% to +195% for RCP8.5). Although GCMs dominate uncertainty in projected low flows, inter-hydrological model uncertainty is considerable (RCP4.5: –60% to +228%, RCP8.5: –86% to +337%). Analysis of variance uncertainty attribution reveals that GCM-related uncertainty occupies, on average, 68% of total uncertainty for median and high flows and hydrological models no more than 1%. For low flows, hydrological model uncertainty occupies, on average, 18% of total uncertainty; GCM-related uncertainty remains substantial (average: 28%).  相似文献   

Progressive niedriggradige Metamorphose glaukonitführender Horizonte in den helvetischen Alpen der Ostschweiz     

Martin Frey  Johannes C. Hunziker  Peter Roggwiller  Conrad Schindler 《Contributions to Mineralogy and Petrology》1973,39(3):185-218

Glauconite-bearing formations of Cretaceous and Tertiary age in the Helvetic zone of the Glarus Alps have been investigated by microscopic, X-ray, wet chemical, electron microprobe, Mössbauer spectroscopic, and K-Ar dating methods. 3 different metamorphic zones with increasing grade can be distinguished (Fig. 3). Original, unmetamorphosed sediments containing glauconite-calcite-quartz±chlorite comprise zone I. The glauconite is very rich in potassium (8–9 wt.%) and the chlorite is Fe-rich. In zone II green stilpnomelane forms by the reaction: glauconite±chlorite + quartz = stilpnomelane + k-feldspar + H₂O + O₂. The green stilpnomelane contains as much as ten times the amount of K found in brown stilpnomelane, which is believed to be a weathering feature. In zone III biotite appears by the reaction: chlorite + k-feldspar = biotite + stilpnomelane + quartz + H₂O. Riebeckite is a possible additional phase in all three zones. Generally, zones I–III are arranged nearly parallel to the Alpine border with metamorphic grade increasing to the south. In the Glarnisch Massif, however, the transition from zone I to zone II is clearly controlled by the overburden of the nappe pile (Fig. 6). The beginning of zone II also seems to coincide with the middle of the anchizone, as defined by illite-crystallinity measurements in adjoining marly shales and slates; this corresponds approximately to the transition from the zeolite facies to the prehnitepumpellyite facies.K-Ar-ages on glauconites regularly decrease when approaching the zone I/II-transition. Field evidence and combined K-Ar age determinations on glauconites, stilpnomelanes and riebeckites point to a peak of the metamorphism during Lower to Middle Oligocene, shortly after the main orogenic phase in this part of the Helvetic Alps.

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Die Autoren danken Herrn Prof. E. Niggli für das fördernde Interesse an dieser Arbeit, die Überlassung der Probe EN 8999 sowie die kritische Durchsicht des Manuskriptes. Für wertvolle Diskussionen und Hinweise danken wir den Prof. E. Jäger, R. Herb und P. M. Orville sowie Dr. W. D. Brückner und Dr. N. Clauer. M.F. möchte Herrn E. Weber herzlich für die Einführung auf der Mikrosonde danken. Herrn Prof. Th. Hügi danken wir für die Benützung des geochemischen Labors, Herrn Prof. H. Schwander für einige Na-Bestimmungen auf der Basler Mikrosonde und Herrn Dr. F. Hofmann für die Bestimmung der C-Gehalte. Den Herren Theo Küpfer und J. Fuhrimann verdanken wir verschiedene Laborarbeiten. Diese Arbeit wurde durch die folgenden Stipendien des Schweizerischen Nationalfonds zur Förderung der wissenschaftlichen Forschung unterstützt: Nr. 5358.2 an M.F., Nr. 2.367.70 an J.H. sowie Nr. 2598 an P.R. Die Durchführung der Mikrosondenanalysen wurden zudem möglich dank eines Studienaufenthaltes von M. F. an der Yale Universität, New Haven, Connecticut, wofür dieser Autor der Forschungskommission der Universität Bern zu großem Dank verpflichtet ist.  相似文献   

Aragonite crystallization from strained calcite at reduced pressures and its bearing on aragonite in low-grade metamorphism     

Robert C. Newton  Julian R. Goldsmith  Joseph V. Smith 《Contributions to Mineralogy and Petrology》1969,22(4):335-348

Aragonite, the dense form of CaCO₃, grew hydrothermally at 100–300° C and dry at 300–400° C at very low pressures from calcite strained by grinding. Nearly complete inversion to aragonite occurred in some runs with Ca-Mg chloride solutions at 0–2.4 kb and 100–200° C on strained calcite having a (10¯14) reflection with a half-width of 0.48° 2 Cu K. A little aragonite grew dry at one atm. from the ground calcite at 300–400° C in a few hrs. Simultaneous shear during recrystallization of calcite in a rotating squeezer resulted in significant aragonite at 300–400° C several kb. below the stability field. No inversion occurred in any ground calcite when previously annealed in CO₂ at 500° C for a few hrs. Thermochemical data show that at least 200 cal/mole of strain energy can be produced in calcite by mild deformation. This much stored energy would lower the pressure requirements of aragonite, relative to the strained calcite by more than 3 kb, and our observation that aragonite growth was faster than strain recovery of calcite indicates that aragonite can grow in nature at reduced pressures from strained calcite.Some experiments were also carried out on highly magnesian calcites with the thought that aragonite might also form at the expense of this metastable material. No aragonite was produced, but the possibility that this mechanism could be operative in nature cannot be discounted.The microtexture of aragonitic deformed marbles from NW Washington (prehnite-pumpellyite facies rocks, courtesy of J. A. Vance) as well as electron probe microanalysis of these rocks indicates that aragonite selectively replaced highly strained calcite. The calcite-aragonite transition is thus a questionable indicator of high-pressure in certain metamorphic rocks.  相似文献   

Charles Franklin Brooks     

V. Conrad 《Meteorology and Atmospheric Physics》1958,11(1):136-137

Ohne Zusammenfassung

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Charles Franklin Brooks

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小波变换及其在影像表示中的应用和其方向选择性算法的改进     

邵巨良  李德仁 《武汉大学学报(信息科学版)》1993,(2)

小波理论是研究多分辨率信号处理的理论,目前被公认为有前途的新理论。金字塔结构的影像处理、影像理解,现代GIS处理多比例尺的要求以及地形、场论中的逼近均需有关这一理论的支持。本文利用小波变换分解原始影像以实现影像的小波表示,并发展为任意方向的小波变换、逆变换,利用它检测航片中建筑物及其阴影的公共边缘。这种表示方式可为某些影像特征或识别目标提供较为经济的分辨率,该表示方式使影像中具有一定层次的结构更易于发现和利用。实验结果证明了此方法是有效的。  相似文献   

A study to explain the emission of nitric oxide from a marsh soil   总被引：1，自引：0，他引：1  

Armin Remde  Jörg Ludwig  Franz X. Meixner  Ralf Conrad 《Journal of Atmospheric Chemistry》1993,17(3):249-275

In the period 18–21 September 1989, soil NO emission was studied at Halvergate Marshes, Norfolk (U.K.) within the framework of the BIATEX-LOVENOX joint field experiment. Using a dynamic chamber technique, 186 measurements at four plots were performed showing a net NO flux of 7.2–14.6×10^–12 kgN m^–2 s^–1. Soil samples from a soil profile (1.0 m) at a representative site and from the uppermost layer (0.1 m) of each of the four plots were sent to the laboratory for (a) detailed physical and chemical soil analysis, (b) determination of NO production rates, NO uptake rate constants, and NO compensation mixing ratios, and (c) characterization of the microbial processes involved. A diffusive model (Galbally and Johansson, 1989) was applied to the laboratory results to infer NO fluxes of the individual soil samples. When we compared these fluxes with those measured in the field, we found agreement within a factor 2–4. Furthermore, laboratory studies showed, that NO was produced and consumed only in the upper soil layer (0–0.1 m depth) and that the NO production and consumption activities observed in the Halvergate marsh soil were most probably due to the anaerobic metabolism of denitrifying bacteria operating in anaerobic microniches within the generally aerobic soil.  相似文献   

Microscopic feather fractures in the faulting process     

R.E. Conrad II  M. Friedman 《Tectonophysics》1976,33(1-2)

The nature and development of microscopic feather fractures (mff) are investigated in experimentally deformed intact and precut cylinders of room-dry Tennessee and Coconino Sandstone. All specimens are deformed at 25° C, and at a shortening rate of 10⁻⁴ sec⁻¹ ; the intact ones are at confining pressures from 0.5 to 2.5 kbar; and the precut specimens at 1.0 and 1.5 kbar. Mff occur in grains adjacent to induced shear fractures or faults; they are wedge-shaped and die out within one or two grain diameters from the fault; and they make acute angles with the fault such that arrows directed into the apices of these angles on either side of the fault define its sense of shear. Occurrence of mff only after slip on precut surfaces clearly demonstrates that they form as a result of shear displacement. The average angle between the mff and fault is 10° greater than that between the load axis and the fault, and it increases with increasing confining pressure in initially intact specimens. Data suggest that the abundance of mff (mean number per grain) increases with increasing normal stress across the fault and with displacement. The wedgeshaped character of many mff and their consistent orientation at 10° to the load axis are distinguishing characteristics. Mff are shown to be parallel to the local maximum compressive stress and thus are extension microfractures. They are not to be confused with precursive micro fractures developed prior to macroscopic fracture, nor to Riedel shears developed during faulting.  相似文献   

Magma mixing in the Aleutian arc: evidence from cognate inclusions and composite xenoliths     

Walter K. Conrad  Suzanne M. Kay  Robert W. Kay 《Journal of Volcanology and Geothermal Research》1983,18(1-4)

The complexity of igneous processes in the Aleutian calc-alkaline magma series can be inferred from study of xenolithic fragments. Composite xenoliths and cognate inclusions provide direct evidence for magma—magma and wall-rock—magma mixing processes. Using distributions of Cr in clinopyroxene, compositional endmembers involved in mixing are identified within the xenoliths. The basaltic mixing endmember is more mafic than calc-alkaline lavas in the arc. Magma mixing and wall-rock assimilation within calc-alkaline basaltic to andesitic magmas is identified in phenocrystic assemblages as well as in xenoliths, and appears to be a widespread phenomenon in Aleutian calc-alkaline magmas.  相似文献