排序方式： 共有25条查询结果，搜索用时 46 毫秒
11.
Berengere Mougel Frederic Moynier Christian Koeberl Daniel Wielandt Martin Bizzarro 《Meteoritics & planetary science》2019,54(10):2592-2599
The existence of mass‐independent chromium isotope variability of nucleosynthetic origin in meteorites and their components provides a means to investigate potential genetic relationship between meteorites and planetary bodies. Moreover, chromium abundances are depleted in most surficial terrestrial rocks relative to chondrites such that Cr isotopes are a powerful tool to detect the contribution of various types of extra‐terrestrial material in terrestrial impactites. This approach can thus be used to constrain the nature of the bolide resulting in breccia and melt rocks in terrestrial impact structures. Here, we report the Cr isotope composition of impact rocks from the ~0.57 Ma Lonar crater (India), which is the best‐preserved impact structure excavated in basaltic target rocks. Results confirm the presence of a chondritic component in several bulk rock samples of up to 3%. The impactor that created the Lonar crater had a composition that was most likely similar to that of carbonaceous chondrites, possibly a CM‐type chondrite. 相似文献
12.
Crust and upper mantle structure of the Bohemian Massif from the dispersion of seismic surface waves
Summary The phase velocity dispersion of Rayleigh waves for the Moxa-Vienna (MOX-VIE) and Moxa-Kaperské Hory (MOX-KHC) profiles, and of both Rayleigh and Love waves for the Kaperské Hory-Ksi (KHC-KSP) profile have been measured and inverted into models of shearwave velocity vs. depth. The three paths cross, respectively, the central part of the Bohemian Massif, its western margin, and the Bohemian Pluton and Cretaceous. For the MOX-VIE profile mean and lower crustal shear wave velocities of 3.7 and 3.9 km/s, respectively, a mean Moho depth of 34 km, and no existence of a low-velocity layer in the lower crust were found. The model obtained for the MOX-KHC profile is characterized by a slightly lower velocity in the lower crust (3.8 km/s), by a slightly lower Moho depth (32 km), and by the appearance of a weak low-velocity channel between 55 and 140 km. The crustal section of the final model for the KHC-KSP profile agrees well with the KHKS82 model derived by Novotný from results of DSS along international profile VII. Our final Rayleigh-wave model has significantly lower shear-wave velocities down to 215 km in the mantle. A systematic difference of 0.18 km/s between the average velocities of Rayleigh and Love waves has been revealed for the depth range from 30 to 215 km. Since almost no contamination of the fundamental Love mode with higher modes has been observed, and since the investigated structure hardly contains an unresolved system of thin, alternately low- and high-velocity layers, the cause of the difference is evidently polarization anisotropy of the upper mantle beneath the Bohemian Massif. It is recommended that the discussed investigations should be supplemented with data from the fan of KSP-GRF (Gräfenberg Array, Germany) paths and from the KHC-BRG (Berggiesshübel, Germany) profile. 相似文献
13.
14.
Pure and Applied Geophysics - 相似文献
15.
Biogeography, Substrate Preference, and Feeding Types of North Adriatic Intertidal Collembola 总被引：1，自引：0，他引：1
Erhard Christian 《Marine Ecology》1989,10(1):79-93
Abstract. A survey of North Adriatic intertidal Collembola is given, including the first records of Friesea acuminata, Archisotoma interstitialis, Entomobrya dollfusi , and Pseudosinella hauseri. Granulometric and biococnological analyses of culittoral loose sediments allowed determination of the animals' substrate preference. The limitation to cuhaline habitats is tested by comparison with mixohaline shores nearby. Life-form typology is applied to elucidate the largely unknown relations of intertidal Collembola to the sediment surface or superficial strata. The different modes of nutrition are distinguished by mouthparts and by gut content analyses. 相似文献
16.
The different coagulation‐flocculation behavior of iron(III) and aluminum(III) to coagulate silica particle suspension with four coagulants — FeCl3, Fe2(SO4)3, AlCl3, and in our laboratory produced polyaluminum chloride PACl‐2.0 — was investigated through studying particle property changes and coagulation efficiency, for example, variations in zeta potential of particles, particle number, average particle diameter, particle size distribution, and residual turbidity of the supernatant water. Influences of flocculation intensity and pH value on the coagulation‐flocculation process were also studied. The results suggest that, under the test conditions, among these four coagulants FeCl3 possesses an obviously stronger ability to form larger flocs and to remove turbidity, on the other hand, PACl‐2.0 obviously showed a better charge neutralization ability. 相似文献
17.
Schuster Roman Habler Gerlinde Schafler Erhard Abart Rainer 《Mineralogy and Petrology》2020,114(2):105-118
Mineralogy and Petrology - Polycrystalline calcite was deformed to high strain at room-temperature and confining pressures of 1–4 GPa using high-pressure torsion. The high confining... 相似文献
18.
19.
20.
Prof. Dr. Dr.-Ing. Hans D. Pflug Dr. Erhard Reitz 《International Journal of Earth Sciences》1988,77(2):417-427
Zusammenfassung Aus dem Proterozoikum der Zeitspanne 1400–1000 M.J. war bisher noch kein Vorkommen von eukaryotischem Phytoplankton bekannt. Unsere neuen Funde aus der Belt-Serie von Idaho und Montana gehören in dieses Intervall und füllen damit eine Kenntnislücke. Die identifizierten Mikrobiota passen gut ins bisher bekannte Bild der früh-riphäischen Algenwelt. Charakteristisch für die Vertreter ist eine einfache Morphologie, ein kleines Formenangebot, eine geringe Individuen-Zahl und ein seltenes Vorkommen, das überdies auf bestimmte Lebensräume der Schelfe beschränkt ist. Offenbar war das eukaryotische Phytoplankton zu dieser Zeit noch im langen Anfangsstadium einer Entwicklung, die dem Fossilbefund zufolge bereits vor mehr als 2000 M.J. begonnen haben mu\. Aber erst vor ca. 850 Millionen Jahren setzte eine stärkere Entwicklung zu neuen Formen ein, die dann schrittweise die urtümliche Cyanobakterien-Welt ablösten.
On the evolution of the eukaryotic phytoplankton in the Riphean — New evidence from the Beltian Serie of North America
No occurrences of eukaryotic phytoplankton were hitherto known during the time span from 1400–1000 M.Y. of the Proterozoic. Our findings from the Beltian Series of Idaho and Montana belong to this interval and thus fill a gap in our knowledge. The identified microbiota agree well with those from the early Riphean. They are characterized by simple morphologies, a limited variety of forms, a low number of individuals and a rare occurrence restricted to a few environments. The findings suggest, that the eukaryotic plankton of that time was still in its long initial stage of evolution which, according to present evidence, must have begun prior to 2000 M.Y. It was only later than 850 million years ago, that the diversification proceeded more rapidly. The new developments gradually replaced the ancient world of cyanobacteria.
Résumé La présence de phytoplancton eucaryotique n'était pas connue jusqu'à présent pendant la période allant de 1400 à 1000 Ma, au ProtérozoÏque. Nos nouvelles découvertes dans le domaine de la Série Belt de l'Idaho et du Montana se rapportent à ce laps de temps et comblent ainsi une lacune de nos connaissances. Les microbiota identifiés correspondent bien à l'image que l'on se fait des algues du pré-Riphéen connues jusqu'à présent. Ses représentants se caractérisent par une morphologie simple, une variété de formes limitée, un nombre réduit d'individus et une occurence rare, réduite à un petit nombre de milieux. Visiblement, le phytoplancton eucaryotique était encore à cette époque dans la longue phase initiale de son développement qui, d'après les fossiles trouvés, doit avoir commencé il y a plus de 2000 Ma. Ce n'est qu'à moins de 850 Ma que des formes nouvelles se sont diversifiées de faÇon importante et ont remplacé graduellement le monde des cyanobactéries d'origine.
1,4 1,0 . . . : , , , . , , , , 2,0 . 850 , .相似文献