Search for purines and pyrimidines in the Murchison meteorite     

W. van der Velden  Alan W. Schwartz 《Geochimica et cosmochimica acta》1977,41(7):961-968

A 1 g interior sample of the Murchison CII meteorite was examined for the presence of purines and pyrimidines by dual-column, ion-exclusion chromatography and ultraviolet spectroscopy. Xanthine, not previously reported in meteorites, was found to be the major purine liberated by extraction with formic acid, with a concentration corresponding to 2.3 μg/g of meteorite. Guanine (0.1 ppm) and hypoxanthine (0.04 ppm) were also tentatively identified. The presence of adenine could not be confirmed. No pyrimidines were detected at concentrations higher than the background level (0.01 ppm) in water, formic acid or strong acid extracts. Silylation of the water extract, however, resulted in the appearance of 4-hydroxypyrimidine, 4-hydroxy-2-methylpyrimidine and 4-hydroxy-6-methylpyrimidine. These compounds are-though to be formed during the silylation procedure from contaminants present in the reagent.  相似文献   

Comment on the paper “Systematic variation in chemistry and Nd-Sr isotopes across a Caledonian calc-alkaline volcanic arc: Implications for source materials”, by M.F. Thirlwall     

O. van Breemen  B.J. Bluck 《Earth and Planetary Science Letters》1983,65(1):206-207

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The Clogging of Shallow Discharge Wells in the Netherlands River Region   总被引：1，自引：0，他引：1  

C.G.E.M. van  Beek W. F. Kooper 《Ground water》1980,18(6):578-586

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Thermochemical remanent magnetization in Jurassic silicic volcanics from Nevada,U.S.A.     

J.W. Geissman  R. Van der Voo 《Earth and Planetary Science Letters》1980,48(2):385-396

Characteristic magnetizations from Middle Jurassic dacitic to andesitic subaerial volcanics (the Fulstone and Artesia Formations) in the Buckskin Mountain Range, western central Basin and Range Province, are well-grouped, generally display univectorial decays to the origin in demagnetization and have hematite blocking temperatures restricted almost entirely to above 620°C. Petrographic, rock magnetic and electron microprobe investigations confirm that nearly pure hematite is the essential magnetic phase (up to about 10 vol. %) occurring as a replacement of coarse titaniferous magnetite phenocrysts and fine groundmass particles, as a secondary alteration product of ferromagnesian phenocrysts and as a mobilized phase filling cracks and other open spaces. The presence of antipodal directions in each flow unit and in interbedded volcanoclastic units (some having retained magnetite as a major magnetic phase) and magnetite-dominated remanences in time-equivalent intrusives cutting the flows indicates that the volcanics acquired their hematite remanence, a faithful record of the geomagnetic field, in high-temperature, deuteric oxidation during and following their emplacement, not during a later thermal event such as regional metamorphism. The remanence is probably a thermochemical remanent magnetization, although part may be of thermoremanent origin.  相似文献   

Sulfate-Reducing Bacteria in Ground Water from Clogging and Nonclogging Shallow Wells in the Netherlands River Region     

C.G.E.M. van  Beek D. van der  Kooij 《Ground water》1982,20(3):298-302

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Paleomagnetic and rock magnetic results from the Twin Creek Formation (Middle Jurassic), Wyoming     

Chad McCabe  Rob Van der Voo  Bruce H. Wilkinson 《Earth and Planetary Science Letters》1982,60(1):140-146

A magnetization which passes the fold test has been observed in 73 limestone samples (10 sites) from the Middle Jurassic Twin Creek Formation. The pole calculated from the site mean poles is located at 68.4°N, 145.0°E (K = 31.8,A₉₅ = 8.7°). This pole lies in a segment of the North American apparent polar wander (APW) path for which there are only a few reliable poles in the literature. The results corroborate earlier studies which conclude that the Jurassic segment of the APW path does not include the present north pole. However, the position of the Twin Creek pole suggests that significantly more APW took place prior to the late Jurassic than previous studies indicated.  相似文献   

Theoretical organic geochemistry. I. The thermodynamic stability of several cholestane isomers calculated by molecular mechanics     

Ger van Graas  Jan M.A. Baas  B. van de Graaf  J.W. de Leeuw 《Geochimica et cosmochimica acta》1982,46(11):2399-2402

The thermodynamic stabilities of thirteen cholestane isomers have been computed using molecular mechanics. The calculated composition of a mixture of these isomers at thermodynamic equilibrium is in agreement with the composition of a cholestane isomerate. From the calculated stabilities the extent to which isomerisation reactions can proceed during maturation can be predicted. The GLC retention order on non-polar phases of 20R/S isomeric pairs has been estimated from the preferred geometries of the molecules which are also obtained by molecular mechanics.  相似文献   

Stratigraphy,pollen analysis,and paleoclimatic interpretation of Pulbeena Swamp,northwestern Tasmania     

E.A. Colhoun  G. van de Geer  W.G. Mook 《Quaternary Research》1982,18(1):108-126

Sedimentary, palynologic, and ¹⁴C analysis of 480 cm of freshwater marl and swamp-peat deposits, formed under the influence of fluctuating artesian springs, provides a paleoenvironmental and paleoclimatic record of approximately 65,000 yr for northwestern Tasmania.The Holocene (Pollen Zone 1, 11,000-0 yr B.P.) climate was warm and moist, and forest vegetation was dominant throughout the area. During the later part of the last glacial stage (Pollen Zone 2, 35,000–11,000 yr B.P.) the climate was generally drier, and grassy open environments were widespread. The driest part of this period occurred between 25,000 to 11,000 yr B.P., when temperatures in western Tasmania were markedly reduced during the last major phase of glaciation. Prior to 35,000 yr B.P. (Pollen Zones 3–9) a long “interstadial complex” dating to the middle of the last glacial stage is recognized. During this period the climate was generally moist, and forest and scrub communities were more important than during the later part of the last glacial stage, except during Pollen Zone 5 when high Gramineae plus Compositae values suggest drier conditions. High Gramineae and Compositae values also occur in Pollen Zone 10 at the base of the diagram. They suggest that a phase of drier and cooler climatic conditions occurred during the early part of the last glacial stage.  相似文献   

Instrumental Neutron Activation Analysis Of 37 Geochemical Reference Samples     

H.A. van der  SLOOT J. ZONDERHUIS 《Geostandards and Geoanalytical Research》1979,3(2):185-193

37 geochemical reference samples, issued mostly by the U.S. Geological Survey and the "Centre de Recherches Pétrographiques et Géochi-miques", have been analysed for more than twenty trace elements using instrumental neutron activation technique. The results are compared with published data; in most oases, the agreement is good.  相似文献   

Investigations of the 500 mb level in relation to the general circulation. III. Conversions of kinetic energy between meridional and zonal transient eddies and the mean zonal motion     

W. van Dijk 《Meteorology and Atmospheric Physics》1978,27(3-4):402-402

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