Climatic changes,magnetic intensity variations and fluctuations of the eccentricity of the earth's orbit during the past 2,000,000 years and a mechanism which may be responsible for the relationship — A discussion     

Alan D. Chave  Charles R. Denham 《Earth and Planetary Science Letters》1979,44(1):150-152

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The age,origin, and volcanological significance of the Y-5 ash layer in the Mediterranean     

Robert Thunell  Alan Federman  Stephen Sparks  Douglas Williams 《Quaternary Research》1979,12(2):241-253

The Y-5 ash is the most widespread layer in deep-sea sediments from the eastern Mediterranean. This ash layer was previously correlated with the Citara-Serrara tuff on Ischia Island and dated at approximately 25,000 yr B.P. New data on the glass chemistry of the Y-5 ash and pyroclastic deposits from the Neopolitan volcanic province suggest that the layer is correlative with the large-volume Campanian ignimbrite and not with the deposit from Ischia Island. The volume of the Y-5 ash is approximately 65 km³ which is comparable in magnitude to the volume of the Campanian ignimbrite. An interpolated age of approximately 38,000 yr B.P. is estimated based on sedimentation rates derived from δ¹⁸O stratigraphy. There is a discrepancy between this estimate and previously reported radiocarbon ages which range from 24,000 to 35,000 yr B.P. We propose that the “Campanian tuff ash layer” should be adopted as the full stratigraphic name for the Y-5 ash. The deep-sea ash layer is divisible into two units in proximal localities, probably correlating with two major phases of the eruption: plinian and ignimbrite.  相似文献   

Toward a comprehensive theory of climatic change     

Alan D. Hecht  John Imbrie 《Quaternary Research》1979,12(1):2-5

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Garnet growth in a metapelite from the Moinian rocks of Northern Sutherland,Scotland     

Carol A. Finlay  Alan Kerr 《Contributions to Mineralogy and Petrology》1979,71(2):185-191

Compositional profiles of a series of garnets, extracted from a pelitic schist occurring in the Moinian rocks of Northern Sutherland, have been established. The profiles are complex and do not conform to a simple fractionation model. A model to explain them is suggested.  相似文献   

Diagenesis of Cretaceous sandstones of the Kootenay Formation at Elk Valley (southeastern British Columbia) and Mt Allan (southwestern Alberta)     

Ian Hutcheon  Alan Oldershaw  Edward D. Ghent 《Geochimica et cosmochimica acta》1980,44(10):1425-1435

Vitrinite reflectance data for two sections of the Kootenay Formation are different, but increase with depth. Illite crystallinities (XRD) are irregular with depth but detailed S.E.M. examination shows that crystal size and morphology increase with depth.At Elk Valley (low reflectance) S.E.M. examination shows kaolinite + dolomite as the authigenic assemblage. At Mt Allan (45 km north, higher reflectance) kaolinite disappears at 265 m and chlorite + calcite appears implying the equilibrium 5 CaMg(CO₃)₂ + Al₂Si₂O₅(OH)₄ + SiO₂ + H₂OagMg₅Al₂Si₃O₁₀(OH)₈ + 5CaCO₃ + 5CO₂. (1)Equilibrium (1) involves CO₂ and H₂O which form an immiscible fluid at diagenetic conditions. Thermochemical data, activity coefficients for the fluid mixture (Margules solution model), and fugacity coefficients allow the position of intersection of the miscibility surface and equilibria similar to (1) to be calculated. Maximum temperatures (180–250°C) in water-rich fluids are in accord with geothermal gradients of 33°C/km and temperatures from vitrinite reflectance (220°C). It is suggested that produced CO₂ may be responsible for the development of secondary porosity during deep burial.  相似文献   

Comment on “The Fossil Coleoptera of the Two Creeks Forest Bed, Wisconsin”, by Alan V. Morgan and Anne Morgan     

Edward B. Evenson  Donald F. Eschman  William R. Farrand  Louis J. Maher  David M. Mickelson  Alan V. Morgan  Anne Morgan   《Quaternary Research》1980,14(3):377-378

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Generators in atmospheric electricity     

J. Alan Chalmers 《Pure and Applied Geophysics》1964,57(1):189-192

Summary The definition of a generator in atmospheric electricity is considered, and various phenomena are discussed as to whether they can be described as generators.  相似文献   

The Mordor Complex: A highly differentiated potassic intrusion with kimberlitic affinities in central Australia   总被引：2，自引：0，他引：2  

Alan P. Langworthy  Lance P. Black 《Contributions to Mineralogy and Petrology》1978,67(1):51-62

The Mordor Complex in central Australia consists of a suite of highly fractionated potassic rocks. Syenite and monzonite are intruded by phlogopite shonkinite and melamonzonite, which are in turn intruded by numerous plug-like bodies of phlogopiterich periodotite and pyroxenite, and by pegmatite dykes, and carbonate-rich breccia.The consanguinity of the suite, cumulate texture of the ultramafic rocks, enrichment of the Complex in large-ion-lithophile (LIL) elements, mineral equilibrium data, and mineral and whole-rock Rb-Sr isochron data, indicate that the rocks were produced by fractional crystallization from an ultrapotassic mafic magma in an intermediate-level magma chamber. Magma genesis possibly involved modification during uprise of potassic partial melt derived from phlogopite-bearing atypical upper mantle source rock. Evidence for regional compositional heterogeneity in the upper mantle is discussed.  相似文献   

Guest editorial     

Alan D. Hecht 《Climatic change》1977,1(2):107-108

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The relationship between major element chemistry and tectonic environment of basic and intermediate volcanic rocks   总被引：2，自引：0，他引：2  

T.H. Pearce  B.E. Gorman  T.C. Birkett 《Earth and Planetary Science Letters》1977,36(1):121-132

This work reports the preliminary results of a study of the relationship between tectonic environment and major element chemistry of volcanic rocks. Using a file of 8400 analyses of rocks of varying ages and geographic distribution it has been found that a simple ternary plot of MgOFeO(total)Al₂O₃ may be used to distinguish five tectonic environments: ocean ridge and floor, ocean island, continental, orogenic, and spreading center island. Subalkaline “basaltic-andesites” (51–56% SiO₂ calculated anhydrous) are used in this study. Alkaline rocks do not generally show the simple patterns of tholeiitic or subalkaline rocks. The ocean island suite is bimodal with one mode tholeiitic and the other alkaline. A bimodal age/chemistry relationship in the continental suite is tentatively related to different conditions during and after active breaking up of continents (rifting and drifting stages).Most of the Archean rocks in our file generally do not fall in the orogenic field. It is unlikely that modern island arc models can be generally applied to Archean greenstone belts. Locally, however, there may be Archean rocks analogous in some respect to modern calc-alkali rocks.  相似文献