Meteoritic material at five large impact craters     

Herbert Palme  Marie-Josée Janssens  H. Takahashi  Edward Anders  Jan Hertogen 《Geochimica et cosmochimica acta》1978,42(3):313-323

Sixteen crater samples were analyzed by radiochemical neutron activation analysis for Ge, Ir, Ni, Os, Pd and Re. Two impact melt rock samples from Clearwater East (22 km) showed strong, uniform enrichments in all elements except Ge, corresponding to 7.4% C1 chondrite material. Interelement ratios suggest that the meteorite was a C1 (or C2) chondrite, not an iron, stony iron, or chondrite of another type. An Ivory Coast tektite (related to the 10 km Bosumtwi crater) was enriched in Ir + Os and Ni to about 0.04 and 1.6% of C1 chondrite levels, but in the absence of data on country rocks, the meteorite cannot yet be characterized.Impact melt rock samples from Clearwater West (32km), Manicouagan (70km), and Mistastin (28 km) showed no detectable meteoritic component. Upper limits, as Cl chondrite equivalent, were Os ≤ 2 × 10^?3% (~0.01 ppb), Ni ≤ 2 × 10^?1% (~20ppm). Possible causes are high impact velocity and/or a chemically inconspicuous meteorite (achondrite, Ir,Os-poor iron or stony iron). However, a more likely reason is that some fraction of the impact melt remains meteorite-free, especially at craters with central peaks.Clearwater East is the first terrestrial impact crater found to be associated with a stony meteorite. Apparently the consistent absence of stony projectiles at small craters (< 1 km diameter) reflects their destruction in the atmosphere, as proposed by Öpik.  相似文献   

Meteoritic and non-meteoritic trace elements in Luna 16 samples     

J.C. Laul  R. GanapathyJohn W. Morgan  Edward Anders 《Earth and Planetary Science Letters》1972

Two Luna 16 soils have been analyzed for Ag, Au, Bi, Br, Cd, Co, Cs, Cu, Ga, Ge, In, Ur, Ni, Rb, Re, Sb, Se, Te, Tl, and Zn. A meteoritic component similar to that in Apollo 11 and 12 soils seems to be present, corresponding to ∼1.5 to 2% Cl chondrites or equivalent. It probably consists largely of micrometeorites. Three elements show strong enrichments compared to Apollo 11 and 12 soils: Cd (5× to 200×), Ag (5× to 10×), and Bi (3×). Presumably these elements were brought in by Cd-Ag-Bi rich material, similar to that in Unit VI of Apollo core 12028.  相似文献   

Eutrophication in a Small Stream in Central Sweden   总被引：1，自引：0，他引：1  

Dr Doc Nils Brink  Anders Widell 《Aquatic Sciences - Research Across Boundaries》1967,29(2):333-360

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Epiphytic Diatoms along Environmental Gradients in Western European Shallow Lakes          下载免费PDF全文

Saúl Blanco  Cristina Cejudo‐Figueiras  Irene Álvarez‐Blanco  Ellen van Donk  Elisabeth M. Gross  Lars‐Anders Hansson  Erik Jeppesen  Timo Kairesalo  Brian Moss  Tiina Nõges  Eloy Bécares 《洁净——土壤、空气、水》2014,42(3):229-235

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Female ornaments signal own and offspring quality in a sex‐role‐reversed fish with extreme male parental care          下载免费PDF全文

Mário A. B. Cunha  Anders Berglund  Nuno M. Monteiro 《Marine Ecology》2017,38(5)

Although female ornaments have been described in many taxa, the full spectrum of information conveyed by such traits together with the potential male fitness benefits are far from fully understood. Here, we used a sex‐role‐reversed species, the black‐striped pipefish, Syngnathus abaster, where females are the ornamented sex and intensively compete for mates who present an extreme form of paternal care (male pregnancy). We investigated what information is conveyed by female traits and if males are using it during mate choice. We further assessed which traits would reflect offspring quality at birth. We found that although body length generally portrays information on female reproductive potential (gonadosomatic index and oocyte diameter), it does so indirectly. Different aspects of the female traits, such as stripe width and trunk broadness, were found to be better direct indicators. When size is kept constant, males prefer females with wider stripes. Moreover, stripe coloration was found to reflect offspring quality as darker‐striped females produced larger newborns. Our observations suggest that in a species with exclusive paternal care, independently from the male's direct investment in reproduction, female contribution decisively impacts male fitness. Thus, at least in sex‐role‐reversed species such as the black striped pipefish, female ornaments can be selected in an analogous way to those of males in species with conventional sex roles (i.e. by mate choice).  相似文献   

Evaluation of track stiffness with a vibrator for prediction of train-induced displacement on railway embankments     

Christoffer With  Anders Bodare 《Soil Dynamics and Earthquake Engineering》2009

A measuring car, the rolling stiffness measuring vehicle (RSMV), has been developed to investigate track conditions. The investigation described in this paper firstly attempts to understand whether the point flexibility of the track, i.e., the track-embankment-subsoil system, can be obtained by simultaneously measuring the force applied to an axle of the measuring car and the resulting acceleration response. Secondly, it attempts to determine the physical properties of the track by modelling it as a Bernoulli–Euler beam on a Kelvin foundation. The final part of the paper investigates the possibility of predicting displacements on a railway embankment based on the physical properties obtained after a train passage. Results from two sites in Sweden, Kumla and Kåhög, have been used. Investigations give encouraging results. However, as seen here, it can be difficult to analyse and obtain parameters if the resonance frequency of the system is low. The peak particle displacement of the ballast on the railway embankment was achieved with fair accuracy for both Kumla and Kåhög using the results from the accelerometer on the RSMV.  相似文献   

Post World War II orcharding creates present day DDT-problems in The Sørfjord (Western Norway) - A case study     

Anders Ruus  Norman W. Green  Carl Einar Amundsen  Jens Skei 《Marine pollution bulletin》2010,60(10):1856-1861

The Sørfjord has a long history of agriculture and industry, and environmental monitoring has been conducted for decades, comprising analyses of contaminants in mussel, fish and sediments. DDT was used as an insecticide in orchards surrounding the fjord between World War II and 1970. Since the early 1990s, elevated concentrations of DDT were found in mussels and fish. Unexpectedly, DDT-concentrations increased towards present day, despite the discontinuation of use. The highest concentrations in mussels (in 2006) corresponded to about two orders of magnitude higher than background. Analyses of sediment core sections also indicated increased input towards present day. Shifts in climatic parameters, as well as increased amounts of soil dissolved organic carbon following a decline in atmospheric sulphate deposition may have contributed to this phenomenon. We warrant the need for increased knowledge of the effects of alterations in variables acting regionally and globally on the disposition of contaminants in ecosystems.  相似文献   

A clast of Bali‐like oxidized CV material in the reduced CV chondrite breccia Vigarano     

Alexander N. KROT  Anders MEIBOM  Klaus KEIL 《Meteoritics & planetary science》2000,35(4):817-825

Abstract— The CV (Vigarano‐type) chondrites are a petrologically diverse group of meteorites that are divided into the reduced and the Bali‐like and Allende‐like oxidized subgroups largely based on secondary mineralogy (Weisberg et al., 1997; Krot et al., 1998b). Some chondrules and calcium‐aluminum‐rich inclusions (CAIs) in the reduced CV chondrite Vigarano show alteration features similar to those in Allende: metal is oxidized to magnetite; low‐Ca pyroxene, forsterite, and magnetite are rimmed and veined by ferrous olivine (Fs_40–50); and plagioclase mesostases and melilite are replaced by nepheline and sodalite (Sylvester et al., 1993; Kimura and Ikeda, 1996, 1997, 1998). Our petrographic observations indicate that Vigarano also contains individual chondrules, chondrule fragments, and lithic clasts of the Bali‐like oxidized CV materials. The largest lithic clast (about 1 times 2 cm in size) is composed of opaque matrix, type‐I chondrules (400–2000 μm in apparent diameter) surrounded by coarse‐grained and fine‐grained rims, and rare CAIs. The matrix‐chondrule ratio is about 1.1. Opaque nodules in chondrules in the clast consist of Cr‐poor and Cr‐rich magnetite, Ni‐ and Co‐rich metal, Ni‐poor and Ni‐rich sulfide; low‐Ni metal nodules occur only inside chondrule phenocrysts. Chromium‐poor magnetite is preferentially replaced by fayalite. Chondrule mesostases are replaced by phyllosilicates; low‐Ca pyroxene and olivine phenocrysts appear to be unaltered. Matrix in the clast consists of very fine‐grained (<1 μm) ferrous olivine, anhedral fayalite grains (Fa_80–100), rounded objects of porous Ca‐Fe‐rich pyroxenes (Fs_10–50Wo₅₀), Ni‐poor sulfide, Ni‐ and Co‐rich metal, and phyllosilicates; magnetite is rare. On the basis of the presence of the Bali‐like lithified chondritic clast—in addition to individual chondrules and CAIs of both Bali‐like and Allende‐like materials—in the reduced CV chondrite Vigarano, we infer that (1) all three types of materials were mixed during regolith gardening on the CV asteroidal body, and (2) the reduced and oxidized CV materials may have originated from a single, heterogeneously altered asteroid.  相似文献   

Charophytes from the warm springs of Svalbard     

Anders Langangen 《Polar research》2000,19(2):143-153

Two of Svalbard' Trollkjeldane (Troll Springs) have a luxuriant vegetation of charophytes. This article is based on material collected in the Trollkjeldane by Sissel Aarvik, of the Office of the Sysselmann (Governor) of Svalbard, on 28 August 1992 and 16 August 1993. Chara canescens is described, based on living material. The Svalbard specimens have been named Chara canescens f. spitsbergensis comb. nov., which is synonymous with Chara aspera f. spitsbergensis Nordstedt. An imperfect charophyte is described here as a new subspecies of C. canescens: Chara canescens subsp. hoelii, named after Adolf Hoel, who first collected specimens of this subspecies. It is believed that this subspecies originates from Chara canescens, presumably by a genetic reorganization or a mutation of the species. A new subspecies is justified because of the ecorticate internodes, the incomplete or lacking cortex of the branchlets, the occurrence of accessory branchlets and the special bulbils found in this taxon. These are interpreted as characteristics with positive selective value in the special environment of the spring, where asexual reproduction by bulbils presumably has the same selective value as the parthenogenic reproduction by oospores in Chara canescens f. spitsber- gensis.
In a growth experiment, the best growth of C. canescens f. spits- bergensis from the springs was obtained in water with relatively low salt content.
Growing tourism in Svalbard threatens to the springs; more active protection must be evaluated. There is also an urgent need to survey the springs in more detail.  相似文献   

Denudation and uplift history of the Jameson Land basin, East Greenland—constrained from maturity and apatite fission track data     

Anders Mathiesen  Torben Bidstrup  Flemming G. Christiansen 《Global and Planetary Change》2000,24(3-4)

The Jameson Land basin in East Greenland comprises a well exposed succession of Upper Paleozoic–Mesozoic sediments. During Middle Devonian–Early Permian rifting, 13 km of continental clastics were deposited. In latest Paleozoic to Mesozoic times, 4 km of sediments accumulated during regional subsidence. In the Early Paleocene, during North Atlantic break-up, the basin was covered by a thick volcanic pile. Subsequently, uplift and erosion took place over the whole region. The volcanic cover was completely removed from Jameson Land and erosion cut deeply into the underlying sediments. To assess the exploration potential of Jameson Land, a basin modelling study with 21 1D pseudo-wells was carried out based on all seismic and surface data available. In addition to the calculation of hydrocarbon generation in space and time, the basin modelling provided an opportunity to study the magnitude and timing of uplift and erosion. Basin modelling constrained by apatite fission track data has made it possible to determine a consistent uplift and erosion history of the area. Tectonic backstripping based on a simple Airy type isostatic model has been used to separate the tectonic uplift from the actual uplift. The combined basin modelling and backstripping study has led to the following conclusions: (1) the thickness of the Cretaceous succession varied from 1.3 km in the south to 0.3 km in the north; (2) the volcanic rocks formed a wedge with a thickness of >2 km in the south thinning to <0.1 km in the north; (3) the subsequent erosion of 2–3 km is in response to tectonic uplift with a magnitude of 1 km, and the calculated tectonic uplift shows increasing values to the north. The erosion rate generally accelerated from Late Paleocene up to the present time.  相似文献