Clay mineral‐organic matter relationships in the early solar system     

Victoria K. Pearson  Mark A. Sephton  Anton T. Kearsley  Philip A. Bland  Ian A. Franchi  Iain Gilmour 《Meteoritics & planetary science》2002,37(12):1829-1833

Abstract— As the solar system formed, it inherited and perpetuated a rich organic chemistry, the molecular products of which are preserved in ancient extraterrestrial objects such as carbonaceous chondrites. These organic‐rich meteorites provide a valuable and tangible record of the chemical steps taken towards the origin of life in the early solar system. Chondritic organic matter is present in the inorganic meteorite matrix which, in the CM and CI chondrites, contains evidence of alteration by liquid water on the parent asteroid. An unanswered and fundamental question is to what extent did the organic matter and inorganic products of aqueous alteration interact or display interdependence? We have used an organic labelling technique to reveal that the meteoritic organic matter is strongly associated with clay minerals. This association suggests that clay minerals may have had an important trapping and possibly catalytic role in chemical evolution in the early solar system prior to the origin of life on the early Earth.  相似文献   

Calcium isotope fractionation in modern scleractinian corals     

Florian Böhm  Nikolaus Gussone  Anton Eisenhauer  Stéphanie Reynaud 《Geochimica et cosmochimica acta》2006,70(17):4452-4462

The ⁴⁴Ca/⁴⁰Ca ratios of cultured (Acropora sp.) and open ocean (Pavona clavus, Porites sp.) tropical reef corals are positively correlated with growth temperature. The slope of the temperature-fractionation relation is similar to inorganic aragonite precipitates. However, δ^44/40Ca of the coral aragonite is offset from inorganic and sclerosponge aragonite by about +0.5‰. This offset can neither be explained by the very fast, biologically controlled calcification of scleractinian corals, nor as a consequence of calcification from a partly closed volume of fluid. As corals actively transport calcium through several cell layers to the site of calcification, the most likely explanation for the offset is a biologically induced fractionation. Our results indicate a limited use of Ca isotopes in scleractinian corals as temperature proxy.  相似文献   

Some observational results on moustaches     

Anton Bruzek 《Solar physics》1972,26(1):94-107

The results of new observations of moustaches in H filtergrams and in H spectra are presented and their relations to photospheric and chromospheric phenomena are studied. The main findings and conclusions are: (1) previous results on basic data (size, brightness, lifetime, etc.) are essentially confirmed; (2) limb observations located the moustaches at the base of the structured H chromosphere, just above the level of the emission of H±1 Å. At the disk moustaches are, in general, covered by absorbing and slightly Doppler-shifted chromospheric elements which determine the H core in the moustache spectrum. However, absorption-free moustaches with an H emission core revealing a pure (true) moustache spectrum have also been found; (3) moustaches have been found to coincide with continuous facular granules; it is suggested that they are an extension of facular granules into the chromosphere rather than a low-level flare-like phenomenon.Mitteilung aus dem Fraunhofer Institut, No. 114.  相似文献   

Variability of African farming systems from phenological analysis of NDVI time series     

Anton Vrieling  Kirsten M. de Beurs  Molly E. Brown 《Climatic change》2011,109(3-4):455-477

Food security exists when people have access to sufficient, safe and nutritious food at all times to meet their dietary needs. The natural resource base is one of the many factors affecting food security. Its variability and decline creates problems for local food production. In this study we characterize for sub-Saharan Africa vegetation phenology and assess variability and trends of phenological indicators based on NDVI time series from 1982 to 2006. We focus on cumulated NDVI over the season (cumNDVI) which is a proxy for net primary productivity. Results are aggregated at the level of major farming systems, while determining also spatial variability within farming systems. High temporal variability of cumNDVI occurs in semiarid and subhumid regions. The results show a large area of positive cumNDVI trends between Senegal and South Sudan. These correspond to positive CRU rainfall trends found and relate to recovery after the 1980??s droughts. We find significant negative cumNDVI trends near the south-coast of West Africa (Guinea coast) and in Tanzania. For each farming system, causes of change and variability are discussed based on available literature (Appendix A). Although food security comprises more than the local natural resource base, our results can perform an input for food security analysis by identifying zones of high variability or downward trends. Farming systems are found to be a useful level of analysis. Diversity and trends found within farming system boundaries underline that farming systems are dynamic.  相似文献   

Mineralogy and petrogenesis of a Ba–Ti–Zr-rich peralkaline dyke from Šebkovice (Czech Republic): Recognition of the most lamproitic Variscan intrusion     

Lukáš Krmíček  Jan Cempírek  Aleš Havlín  Antonín Přichystal  Stanislav Houzar  Michaela Krmíčková  Petr Gadas 《Lithos》2011,121(1-4):74-86

A peralkaline, ultrapotassic dyke found at ?ebkovice (T?ebí? district, western Moravia) is a mineralogically extreme member of a dyke swarm occurring along the south-eastern border of the Moldanubian Region of the Bohemian Massif. The dyke shows a simple zoning, with a very fine-grained marginal zone grading into a medium-grained central zone. It has a primary mineral assemblage of microcline and potassic amphiboles, with accessory apatite and altered phlogopite. The microcline exhibits an unusual red luminescence colour and pronounced substitution of Fe³⁺ for Al, with measured contents of Fe₂O₃ up to 8.5 wt.% (0.31 apfu Fe³⁺). Amphiboles have very high K (up to 0.99 apfu) and Si contents; their compositions follow an alkaline fractionation trend from potassic-richterite to potassic-magnesio-arfvedsonite, characterized by an increase of Na/K and a decrease of Ca, Mg, Fe²⁺ and Ti via heterovalent substitutions ^[B]Ca + ^[C](Mg,Fe²⁺) → ^[B]Na + ^[C]Fe³⁺ and Ti + Mg → 2Fe³⁺. The most evolved apatite is significantly enriched in SrO (up to 9.7 wt.%; 0.49 apfu Sr). The core of the dyke and late veinlets contain unique late- to post-magmatic Ba–Ti–Zr-bearing mineral assemblages of baotite, henrymeyerite, titanite, rutile, benitoite and bazirite. Anhedral baotite fills interstices distributed inhomogeneously in the dyke centre; it is locally replaced by a Ba-bearing titanite + henrymeyerite + rutile + quartz assemblage. Henrymeyerite (the second record in a lamproite) shows variable Fe/Ti ratios and represents a solid solution of the hepta- and hexatitanate components. Euhedral crystals of benitoite and bazirite are enclosed in the late-stage quartz–titanite–apatite veinlets in the fine-grained margin of the intrusion. In terms of a mineralogical–genetic classification, the ?ebkovice dyke can be considered as a new high-silica (~ 57 wt.% SiO₂) variety of lamproite (variety ?ebkovice), and represents a unique expression of post-collisional potassic magmatism on the south-eastern border of the Bohemian Massif. The peralkaline dykes from this area show mineralogical and geochemical features similar to those of silica-rich orogenic lamproites emplaced at destructive plate margins. In terms of the modern classification of lamproites, the ?ebkovice dyke is the first lamproite recognised in the Variscan orogenic belt.  相似文献   

GSD‐1G and MPI‐DING Reference Glasses for In Situ and Bulk Isotopic Determination     

Klaus Peter Jochum  Steven A. Wilson  Wafa Abouchami  Marghaleray Amini  Jérome Chmeleff  Anton Eisenhauer  Ernst Hegner  Linda M. Iaccheri  Bruno Kieffer  Joachim Krause  William F. McDonough  Regina Mertz‐Kraus  Ingrid Raczek  Roberta L. Rudnick  Denis Scholz  Grit Steinhoefel  Brigitte Stoll  Andreas Stracke  Sonia Tonarini  Dominique Weis  Ulrike Weis  Jon D. Woodhead 《Geostandards and Geoanalytical Research》2011,35(2):193-226

This paper contains the results of an extensive isotopic study of United States Geological Survey GSD‐1G and MPI‐DING reference glasses. Thirteen different laboratories were involved using high‐precision bulk (TIMS, MC‐ICP‐MS) and microanalytical (LA‐MC‐ICP‐MS, LA‐ICP‐MS) techniques. Detailed studies were performed to demonstrate the large‐scale and small‐scale homogeneity of the reference glasses. Together with previously published isotopic data from ten other laboratories, preliminary reference and information values as well as their uncertainties at the 95% confidence level were determined for H, O, Li, B, Si, Ca, Sr, Nd, Hf, Pb, Th and U isotopes using the recommendations of the International Association of Geoanalysts for certification of reference materials. Our results indicate that GSD‐1G and the MPI‐DING glasses are suitable reference materials for microanalytical and bulk analytical purposes.  相似文献   

The Paris CM chondrite: Secondary minerals and asteroidal processing     

Yves Marrocchi  Matthieu Gounelle  Ingrid Blanchard  Florent Caste  Anton T. Kearsley 《Meteoritics & planetary science》2014,49(7):1232-1249

We report a petrographic and mineralogical survey of Paris, a new CM chondrite considered to be the least‐altered CM identified so far (Hewins et al. 2014 ). Compared to other CMs, Paris exhibits (1) a higher concentration of Fe‐Ni metal beads, with nickel contents in the range 4.1–8.1 wt%; (2) the systematic presence of thin lamellae and tiny blebs of pentlandite in pyrrhotite grains; and (3) ubiquitous tochilinite/cronstedtite associations with higher FeO/SiO₂ and S/SiO₂ ratios. In addition, Paris shows the highest concentration of trapped ³⁶Ar reported so far for a CM chondrite (Hewins et al. 2014 ). In combination with the findings of previous studies, our data confirm the reliability of (1) the alteration sequence based on the chemical composition of tochilinite/cronstedtite associations to quantify the fluid alteration processes and (2) the use of Cr content variability in type II ferroan chondrule olivine as a proxy of thermal metamorphism. In contrast, the scales based on (1) the Fe³⁺ content of serpentine in the matrix to estimate the degree of aqueous alteration and (2) the chemical composition of Fe‐Ni metal beads for quantifying the intensity of the thermal metamorphism are not supported by the characteristics of Paris. It also appears that the amount of trapped ³⁶Ar is a sensitive indicator of the secondary alteration modifications experienced by chondrites, for both aqueous alteration and thermal metamorphism. Considering Paris, our data suggest that this chondrite should be classified as type 2.7 as it suffered limited but significant fluid alteration and only mild thermal metamorphism. These results point out that two separated scales should be used to quantify the degree of the respective role of aqueous alteration and thermal metamorphism in establishing the characteristics of CM chondrites.  相似文献   

Effect of Pinus radiata plantations on water balance in Chile     

Anton Huber  Andrés Iroumé  James Bathurst 《水文研究》2008,22(1):142-148

The effect of Pinus radiata (D. Don) plantations on water resources at different Chilean sites located between 33 and 40 south was determined. Incoming precipitation, canopy interception loss, evapotranspiration, net evapotranspiration (transpiration and evaporation from the soil), percolation and soil water content were measured in each site, where Pinus radiata plantations were 12 to 17 years old and between 700 and 830 trees ha^?1 dense. The results were compared with those obtained from areas covered with perennial grasses and shrubs at the same sites. The pine canopies intercepted on average 36–40% of the annual rainfall at all sites where rainfall was less then 1200 mm, while only 15% of the mean rainfall was intercepted in the southernmost and rainy (2081 mm year^?1) site. Annual net evapotranspiration increased from south to north from 32% of the incoming precipitation for the southernmost site to 55% for the one located at the lower latitude. In this northernmost site almost the entire incoming precipitation was evapotranspired. Annual percolation registered its minimum value in the northern site (5% of incoming precipitation) and its maxima in the southern one (53%). The values of net evapotranspiration and percolation were regulated by the pluviometric regime and the soil moisture retention capacity in each site. Compared with the shrub or grass covers, sites under Pinus radiata plantations registered higher water consumption by evapotranspiration and reduced percolation. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Ethnicity and Geography     

Anton Gosar 《GeoJournal》1993,31(3):303-201

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Runoff and peak flow responses to timber harvest and forest age in southern Chile     

Andrs Iroum  Octavio Mayen  Anton Huber 《水文研究》2006,20(1):37-50

Runoff and peak flows in three experimental catchments with different forest conditions were analysed in a rainy temperate climate in southern Chile. The hydrological effects of clearcutting a Pinus radiata plantation covering 79·4% of the La Reina catchment were studied by analysing runoff and peak flows in the pre‐ and post‐harvesting periods. Mean annual runoff increased 110% after timber harvesting. Clearcutting generated a 32% mean increase in peak flows. Peak flow and runoff were examined in two adjacent catchments with different forest conditions. The older plantation in Los Ulmos 1 increasingly consumed more water than the younger plantation established at Los Ulmos 2, whereas differences in peak flows between these two catchments were not significant. Runoff and peak flows comparisons not only reflected changes in forest cover, but also the effect of rainfall characteristics during the study periods and the basins' morphologies. Comparisons between pre‐ and post‐harvesting peak discharges must be undertaken with caution, because a previous analysis at La Reina using a partial set of data overestimated changes in peak flows after timber harvesting. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献