Maribo—A new CM fall from Denmark     

Henning HAACK  Thomas GRAU  Addi BISCHOFF  Marian HORSTMANN  John WASSON  Anton SØRENSEN  Matthias LAUBENSTEIN  Ulrich OTT  Herbert PALME  Marko GELLISSEN  Richard C. GREENWOOD  Victoria K. PEARSON  Ian A. FRANCHI  Zelimir GABELICA  Philippe SCHMITT‐KOPPLIN 《Meteoritics & planetary science》2012,47(1):30-50

Abstract– Maribo is a new Danish CM chondrite, which fell on January 17, 2009, at 19:08:28 CET. The fall was observed by many eye witnesses and recorded by a surveillance camera, an all sky camera, a few seismic stations, and by meteor radar observatories in Germany. A single fragment of Maribo with a dry weight of 25.8 g was found on March 4, 2009. The coarse‐grained components in Maribo include chondrules, fine‐grained olivine aggregates, large isolated lithic clasts, metals, and mineral fragments (often olivine), and rare Ca,Al‐rich inclusions. The components are typically rimmed by fine‐grained dust mantles. The matrix includes abundant dust rimmed fragments of tochilinite with a layered, fishbone‐like texture, tochilinite–cronstedtite intergrowths, sulfides, metals, and carbonates often intergrown with tochilinite. The oxygen isotopic composition: (δ¹⁷O = ?1.27‰; δ¹⁸O = 4.96‰; Δ¹⁷O = ?3.85‰) plots at the edge of the CM field, close to the CCAM line. The very low Δ¹⁷O and the presence of unaltered components suggest that Maribo is among the least altered CM chondrites. The bulk chemistry of Maribo is typical of CM chondrites. Trapped noble gases are similar in abundance and isotopic composition to other CM chondrites, stepwise heating data indicating the presence of gas components hosted by presolar diamond and silicon carbide. The organics in Maribo include components also seen in Murchison as well as nitrogen‐rich components unique to Maribo.  相似文献   

The perils of taxonomic inconsistency in quantitative palaeoecology: experiments with testate amoeba data     

RICHARD J. PAYNE  MARIUSZ LAMENTOWICZ  EDWARD A. D. MITCHELL 《Boreas: An International Journal of Quaternary Research》2011,40(1):15-27

Payne, R. J., Lamentowicz, M. & Mitchell, E. A. D. 2010: The perils of taxonomic inconsistency in quantitative palaeoecology: experiments with testate amoeba data. Boreas, 10.1111/j.1502‐3885.2010.00174.x. ISSN 0300‐9483. A fundamental requirement of quantitative palaeoecology is consistent taxonomy between a modern training set and palaeoecological data. In this study we assess the possible consequences of violation of this requirement by simulating taxonomic errors in testate amoeba data. Combinations of easily confused taxa were selected, and data manipulated to reflect confusion of these taxa; transfer functions based on unmodified data were then applied to these modified data sets. Initially these experiments were carried out one error at a time using four modern training sets; subsequently, multiple errors were separately simulated both in four modern training sets and in four palaeoecological data sets. Some plausible taxonomic confusions caused major biases in reconstructed values. In the case of two palaeoecological data sets, a single consistent taxonomic error was capable of changing the pattern of environmental reconstruction beyond all recognition, totally removing any real palaeoenvironmental signal. The issue of taxonomic consistency is one that many researchers would rather ignore; our results show that the consequences of this may ultimately be severe.  相似文献   

Continental/Cordilleran ice interactions: a dominant cause of westward super-elevation of the last glacial maximum continental ice limit in southwestern Alberta, Canada     

EDWARD C. LITTLE  LIONEL E. JACKSON Jr.  THOMAS S. JAMES  STEPHEN R. HICOCK  ELIZABETH R. LEBOE 《Boreas: An International Journal of Quaternary Research》2001,30(1):43-52

In southwestern Alberta, Canada, a westward-rising last-glacial-maximum continental ice limit has been identified. This limit is defined by the upper elevation of Canadian Shield erratics deposited by last-glacial-maximum continental ice along the flanks of prominent ridges and buttes within the region. The interpolation between ice-limit data points has produced two distinct slope profiles: 2.9 m/km to the east, and 4.2 m/km to the west of Mokowan Butte. Three hypotheses are proposed to explain this westward rise of the last-glacial-maximum continental ice limit: (1) regional tectonic uplift, (2) glacio-isostatic uplift, and (3) continental ice-flow convergence due to topographic obstacles and interaction with montane ice. Inferred long-term rates of tectonic uplift and glacio-isostatic modelling show that these two mechanisms account for less than 25% of the observed absolute elevation increase of the limit between the Del Bonita uplands and Cloudy Ridge in southwestern Alberta. The remaining rise in elevation of the continental ice-sheet margin in this region is thought to result from continental ice-flow convergence due to the combined effects of the regional topography and interaction with montane glaciers to the west. The steeper rise in the former continental ice surface west of Mokowan Butte can be explained by the topographic obstruction and interaction with montane glaciers in the area of the Rocky Mountain front.  相似文献   

The Rock of Gibraltar     

EDWARD P. F. ROSE  M. S. ROSENBAUM 《Geology Today》1991,7(3):95-101

Most people have heard of the Rock of Gibraltar, yet few know anything of its geology. Recent studies now interpret the Rock as a partly overturned mass of Jurassic limestone, thrust into position during continent-continent collision by about 15–20 million years ago, and shaped largely by shoreline processes active during Pleistocene tectonic uplift. The Rock's geology has implications for currently developing interpretations of the geological evolution of the western Mediterranean region and for the fast-growing development of Gibraltar's urban environment.  相似文献   

Origin of stratified basal ice in outlet glaciers of Vatnajökull and Öræfajökull,Iceland     

GRAHAME J. LARSON  DANIEL E. LAWSON  EDWARD B. EVENSON  ÓSKAR KNUDSEN  RICHARD B. ALLEY  MANTHA S. PHANIKUMAR 《Boreas: An International Journal of Quaternary Research》2010,39(3):457-470

Larson, G.J., Lawson, D.E., Evenson, E.B., Knudsen, Ó., Alley, R.B. & Phanikumar, M.S. 2010: Origin of stratified basal ice in outlet glaciers of Vatnajökull and Öræfajökull, Iceland. Boreas, Vol. 39, pp. 457–470. 10.1111/j.1502‐3885.2009.00134.x. ISSN 0300‐9483. During the period 2000–2005, we collected samples of englacial ice, vent water, frazil/anchor ice and stratified basal ice from warm‐based outlet glaciers of Vatnajökull and Öræfajökull, Iceland, and analysed them for ³H, ¹⁸O and D. Results of ³H analyses show that the stratified basal ice contains ³H from atmospheric thermonuclear testing and is younger than the englacial ice. Results of the ¹⁸O and D analyses show that frazil/anchor and stratified basal ice are both enriched by an average of 2.4‰ in ¹⁸O and 11‰ in D relative to vent water. These values are consistent with fractionation during partial freezing of supercooled subglacial water in an open system, one in which the remaining water is continuously removed and replenished by water of similar composition. The isotopic data and field observations do not support either a regelation or a thermal ad‐freeze‐on origin for the stratified basal ice.  相似文献   

Morphology and evolution of bars in a wandering gravel-bed river; lower Fraser river, British Columbia, Canada   总被引：2，自引：0，他引：2  

STEPHEN P. RICE  MICHAEL CHURCH§  COLIN L. WOOLDRIDGE†  EDWARD J. HICKIN‡ 《Sedimentology》2009,56(3):709-736

A hierarchical typology for the channels and bars within aggradational wandering gravel-bed rivers is developed from an examination of a 50 km reach of lower Fraser River, British Columbia, Canada. Unit bars, built by stacking of gravelly bedload sheets, are the key dynamic element of the sediment transfer system, linking sediment transport during individual freshets to the creation, development and remoulding of compound bar platforms that have either a lateral or medial style. Primary and secondary unit bars are identified, respectively, as those that deliver sediment to compound bars from the principal channel and those that redistribute sediment across the compound bar via seasonal anabranches and smaller channels. The record of bar accretion evident in ground-penetrating radar sequences is consistent with the long-term development of bar complexes derived from historical aerial photographs. For two compound bars, inter-annual changes associated with individual sediment transport episodes are measured using detailed topographic surveys and longer-term changes are quantified using sediment budgets derived for individual bars from periodic channel surveys. Annual sediment turnover on the bars is comparable with the bed material transfer rate along the channel, indicating that relatively little bed material bypasses the bars. Bar construction and change are accomplished mainly by lateral accretion as the river has limited capacity to raise bed load onto higher surfaces. Styles of accretion and erosion and, therefore, the major bar form morphologies on Fraser River are familiar and consistent with those in gravelly braided channels but the wandering style does exhibit some distinctive features. For example, 65-year histories reveal the potential for long sequences of uninterrupted accretion in relatively stable wandering rivers that are unlikely in braided rivers.  相似文献   

Water in Albitic Glasses   总被引：2，自引：1，他引：2  

SILVER  LYNN; STOLPER  EDWARD 《Journal of Petrology》1989,30(3):667-709

Infrared spectroscopy has been calibrated to provide a preciseand accurate method for determining the concentrations of molecularwater and hydroxyl groups in hydrous albitic glasses. At totalwater contents less than 4 wt.%, most of the water is dissolvedas hydroxyl groups; at higher total water contents, molecularwater becomes the dominant species. For total water contentsabove 4 wt.%, the amount of water dissolved as hydroxyl groupsis nearly constant at about 2 wt.% and additional water is incorporatedas molecular water. These trends in the concentrations of theH-bearing species are similar to those observed in other silicateglasses using infrared and NMR spectroscopies. The ratio ofmolecular water to hydroxyl groups at a given total water contentis independent of the pressure and only weakly dependent onthe temperature of equilibration. Molecular water and hydroxyl group concentrations in glassesprovide constraints on the dissolution mechanisms of water insilicate liquids. Several mixing models involving homogeneousequilibria of the form H₂O+O^2– = 2OH^– among meltspecies in albitic melts have been developed. These models canaccount for the measured species concentrations if the effectsof non-ideal behavior or mixing of polymerized units are included,or by allowing for several different anhydrous species. We used two thermodynamic models of hydrous albitic melts tocalculate phase equilibria. The first assumes that Henry's lawholds for molecular water in albitic liquids; i.e. that theactivity of molecular water in the melt is proportional to itsmole fraction as determined by infrared spectroscopy. The seconddescribes the speciation and thermodynamics of hydrous albiticmelts using the formalism of a strictly regular solution. Thesemodels can account reasonably well for the position of the vapor-saturatedsolidus of high albite and the pressure and temperature dependenceof the solubility of water in albitic melts. To the extent thatthese models are successful, our approach provides a directlink between measured species concentrations in hydrous albiticglasses and the macroscopic thermodyn amic properties of theNaAlSi₃O₈-H₂O system.  相似文献   

Sillimanite and Ilmenite from High-grade Metamorphic Rocks of Antarctica and Other Areas   总被引：1，自引：0，他引：1  

GREW  EDWARD S. 《Journal of Petrology》1980,21(1):39-68

Sillimanite from a variety of high-grade metamorphic rocks containsfrom 0.13 to 1.82 weight per cent Fe₂O₃ and less than 0.1 weightper cent TiO₂. The iron is trivalent and substitutes for Alonly. Ilmenite associated with the sillimanite contains no morethan 0.4 weight per cent Al₂O₃, SiO₂, CaO, and MnO; and MgOdoes not exceed 1.6 weight per cent. It ranges in compositionfrom Ilm₉₉Hem₁ to Ilm₈₅Hem₁₅. A least squares fit of precision unit cell data on 10 analyzedsillimanites gives the following cell dimensions for iron-freesillimanite: a = 7.4830 Á, b = 7.6708 Á, c = 5.7694Á and V = 331.15 Á³. The projected increase incell volume with substitution of 10 mole per cent Fe₂SiO₃ is1.66 per cent. A regular increase in the Fe₂O₃ content of sillimanite withincreasing Fe₂O₃ content of associated ilmenite in 15 of 21samples analyzed suggests that sillimanite and ilmenite crystallizedin equilibrium in the 15 samples. The compositions of the tensillimanite-ilmenite pairs analyzed by the author fit the followingempirical curve (sol;(X_Fe2O3)Il = 1.110 x 10^–3. This regularincrease in Fe₂O₃ contents fits a model of Fe³⁺ substitutionfor Al on two independent sites in sillimanite and a coupledsubstitution of for Fe²⁺ Ti on two sites in ilmenite. Sillimaniteand ilmenite are behaving as ideal solutions over the compositionalrange 0 < X_Fe2SIO3 < 0.013 in sillimanite and 0 < X_Fe2O3< 0.15 in ilmenite. Equations have been derived for expressing the variation inFe₂O₃ content of sillimanite associated with quartz and ilmeniteor hematite as a function of pressure, temperature, and Fe₂O₃content of the oxide minerals. For example, the Fe₂O₃ contentof a sillimanite with 1.5 mole per cent Fe₂SiO₃ coexisting withTi-free hematite is calculated to decrease 11 per cent witha 5 kb increase in pressure. The rate of increase with temperatureof the Fe₂O₃ content of sillimanite is greater in hematite-bearingassemblages than in ilmenite-bearing assemblages.  相似文献   

The silicate inclusions of the Ocotillo IAB iron meteorite     

EDWARD J. OLSEN  JAMES SCHWADE 《Meteoritics & planetary science》1998,33(1):153-155

Abstract— The Ocotillo IAB iron meteorite contains small silicate inclusions consisting of olivine, low-Ca pyroxene, chromian diopside, plagioclase, magnesiochromite, apatite, troilite and metal. The ferromagnesian silicates have a small range of Fe/(Fe + Mg) ratios that are not due to zoning. These phases appear to be not well equilibrated. The FeO content of magnesiochromite is lower than values normally seen in silicate assemblages in IAB iron meteorites. The minerals in Ocotillo are generally like silicate assemblages in other IAB meteorites, covering similar composition ranges and exhibiting a metamorphic (granoblastic) texture. An estimate was made of the bulk composition of Ocotillo silicate inclusions. The bulk composition is close to that of ordinary chondrites with the exception of a deficiency in CaO that might be due to a sampling problem associated with the method used to estimate the bulk composition.  相似文献   

TRENDS IN ORGANOCHLORINE AND RADIONUCLIDE CONCENTRATIONS IN THE UPPER RIO GRANDE BASED ON SEDIMENT CORE ANALYSES FROM ELEPHANT BUTTE RESERVOIR,NEW MEXICO     

P. C. VAN METRE  B. J. MAHLER  EDWARD CALLENDER 《国际泥沙研究》1998,(4)

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