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  • Abu El-Enen, M.M., et al. (författare)
  • P–T path and timing of crustal thickening during amalgamation of East and West Gondwana: A case study from the Hafafit Metamorphic Complex, Eastern Desert of Egypt.
  • 2016
  • Ingår i: Lithos. - 0024-4937 .- 1872-6143. ; 263, s. 213-238
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The southeastern sector of the Hafafit Metamorphic Complex, southern Eastern Desert of Egypt comprises infrastructural orthogneisses of tonalite and syenogranite parentage, amphibolites, and a volcano-sedimentary association. These are overthrust by an obducted suprastructural ophiolite nappes via the Nugrus thrust. The protolith of the biotite–hornblende-gneisses was formed during island-arc accretion, while that of the garnet–biotite gneisses were formed in a within-plate regime, consistent with a transition to a post-collisional setting. The volcano-sedimentary association comprises interbedded and intercalated highly foliated metapelitic schists, metabasites, and leucocratic gneisses, deposited in a back-arc basin. The metapelites and the leucocratic gneisses originated from immature Fe-shales and arkoses derived from intermediate-mafic and acidic igneous rocks, respectively, via weak chemical weathering in a tectonically active island arc terrane. The intercalated amphibolites were derived from tholeiitic basalts generated in a back-arc setting.</p><p>The volcano-sedimentary association was metamorphosed under upper-amphibolite facies conditions with pressures of 9–13 kbar and temperatures of 570–675 °C, as derived from conventional geothermobarometry and pseudosection calculation. A steep, tight clockwise P–T path is constrained and a geothermal gradient around 20 °C/km is estimated for the peak metamorphism. We assume that deformation and metamorphism are due to crustal thickening during the collision of East and West Gondwana, where peak metamorphism took place in the middle to lower crust at 33 km average crustal depth. This was followed by a subsequent quasi-isothermal decompression due to rapid exhumation during wrench tectonics. Sinistral transcurrent shearing with extensional denudation resulted in vertical ductile thinning that was accompanied by heat input from magmatism, as indicated by a higher geothermal gradient during retrograde metamorphism and exhumation of the complex.</p><p>U–Pb data from magmatic zircons yields protolith ages of 731 ± 3 Ma for the biotite–hornblende gneisses and 646 ± 12 Ma for the garnet–biotite gneisses. Conforming to field evidence, our geochronology data point to a depositional age of the volcano-sedimentary cover at around 650 Ma. The age of metamorphism is constrained by a low Th/U ratio of a zircon grain crystallized at an age of 597 ± 6 Ma.</p>
  • ACOSTA HOSPITALECHE, Carolina, et al. (författare)
  • Historical perspective of Otto Nordenskjöld´s Antarctic fossil penguin collection and Carl Wiman’s contribution
  • 2017
  • Ingår i: Polar Record. - Cambridge. - 0032-2474 .- 1475-3057. ; 53:4, s. 364-375
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The early explorer and scientist Otto Nordenskjöld, leader of the Swedish South Polar Expedition of 1901–1903, was the first to collect Antarctic penguin fossils. The site is situated in the northeastern region of Seymour Island and constitutes one of the most important localities in the study of fossilised penguins. The task of describing these specimens together with fossilised whale remains was given to Professor Carl Wiman (1867–1944) at Uppsala University, Sweden. Although the paradigm for the systematic study of penguins has changed considerably over recent years, Wiman's contributions are still remarkable. His establishment of grouping by size as a basis for classification was a novel approach that allowed them to deal with an unexpectedly high morphological diversity and limited knowledge of penguin skeletal anatomy. In the past, it was useful to provide a basic framework for the group that today could be used as ‘taxon free’ categories. First, it was important to define new species, and then to establish a classification based on size and robustness. This laid the foundation for the first attempts to use morphometric parameters for the classification of isolated penguin bones. The Nordenskjöld materials constitute an invaluable collection for comparative purposes, and every year researchers from different countries visit this collection.</p>
  • Adam, B., et al. (författare)
  • N2-fixation, ammonium release, and N-transfer to the microbial and classical food web within a plankton community.
  • 2016
  • Ingår i: The ISME Journal. - 1751-7362 .- 1751-7370. ; 19, s. 450-459
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>We investigated the role of N<sub>2</sub>-fixation by the colony-forming cyanobacterium, <em>Aphanizomenon</em> spp., for the plankton community and N-budget of the N-limited Baltic Sea during summer by using stable isotope tracers combined with novel secondary ion mass spectrometry, conventional mass spectrometry and nutrient analysis. When incubated with <sup>15</sup>N<sub>2</sub>, <em>Aphanizomenon</em> spp. showed a strong <sup>15</sup>N-enrichment implying substantial <sup>15</sup>N<sub>2</sub>-fixation. Intriguingly, <em>Aphanizomenon</em> did not assimilate tracers of <sup>15</sup>NH<sub>4</sub><sup>+</sup> from the surrounding water. These findings are in line with model calculations that confirmed a negligible N-source by diffusion-limited NH<sub>4</sub><sup>+</sup> fluxes to <em>Aphanizomenon</em> colonies at low bulk concentrations (&lt;250 nm) as compared with N<sub>2</sub>-fixation within colonies. No N<sub>2</sub>-fixation was detected in autotrophic microorganisms &lt;5 μm, which relied on NH<sub>4</sub><sup>+</sup> uptake from the surrounding water. <em>Aphanizomenon</em> released about 50% of its newly fixed N<sub>2</sub> as NH<sub>4</sub><sup>+</sup>. However, NH<sub>4</sub><sup>+</sup> did not accumulate in the water but was transferred to heterotrophic and autotrophic microorganisms as well as to diatoms (<em>Chaetoceros</em> sp.) and copepods with a turnover time of ~5 h. We provide direct quantitative evidence that colony-forming <em>Aphanizomenon</em> releases about half of its recently fixed N<sub>2</sub> as NH<sub>4</sub><sup>+</sup>, which is transferred to the prokaryotic and eukaryotic plankton forming the basis of the food web in the plankton community. Transfer of newly fixed nitrogen to diatoms and copepods furthermore implies a fast export to shallow sediments via fast-sinking fecal pellets and aggregates. Hence, N<sub>2</sub>-fixing colony-forming cyanobacteria can have profound impact on ecosystem productivity and biogeochemical processes at shorter time scales (hours to days) than previously thought.</p>
  • Adrian, Brent, et al. (författare)
  • New Miocene Carnivora (Mammalia) from Moruorot and Kalodirr, Kenya
  • 2018
  • Ingår i: Palaeontologia Electronica. - 1935-3952 .- 1094-8074. ; 21
  • Tidskriftsartikel (refereegranskat)abstract
    • <p> We describe new carnivoran fossils from Kalodirr and Moruorot, two late Early</p><p>Miocene sites in the Lothidok Formation of West Turkana, Kenya. The fossils include a</p><p>new species of viverrid, <em>Kichechia savagei</em>  sp. nov., a new genus and species of felid,</p><p><em>Katifelis nightingalei</em>  gen. et sp. nov., and an unidentified musteloid. We also report</p><p>new records of the amphicyonid <em>Cynelos macrodon</em>. These new fossils increase the</p><p>known diversity of African Early Miocene carnivorans and highlight regional differences</p><p>in Africa.</p>
  • Alerstam, Thomas, et al. (författare)
  • Flight speeds among bird species : allometric and phylogenetic effects.
  • 2007
  • Ingår i: PLoS biology. - 1544-9173 .- 1545-7885. ; 5:8, s. e197
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Flight speed is expected to increase with mass and wing loading among flying animals and aircraft for fundamental aerodynamic reasons. Assuming geometrical and dynamical similarity, cruising flight speed is predicted to vary as (body mass)(1/6) and (wing loading)(1/2) among bird species. To test these scaling rules and the general importance of mass and wing loading for bird flight speeds, we used tracking radar to measure flapping flight speeds of individuals or flocks of migrating birds visually identified to species as well as their altitude and winds at the altitudes where the birds were flying. Equivalent airspeeds (airspeeds corrected to sea level air density, Ue) of 138 species, ranging 0.01-10 kg in mass, were analysed in relation to biometry and phylogeny. Scaling exponents in relation to mass and wing loading were significantly smaller than predicted (about 0.12 and 0.32, respectively, with similar results for analyses based on species and independent phylogenetic contrasts). These low scaling exponents may be the result of evolutionary restrictions on bird flight-speed range, counteracting too slow flight speeds among species with low wing loading and too fast speeds among species with high wing loading. This compression of speed range is partly attained through geometric differences, with aspect ratio showing a positive relationship with body mass and wing loading, but additional factors are required to fully explain the small scaling exponent of Ue in relation to wing loading. Furthermore, mass and wing loading accounted for only a limited proportion of the variation in Ue. Phylogeny was a powerful factor, in combination with wing loading, to account for the variation in Ue. These results demonstrate that functional flight adaptations and constraints associated with different evolutionary lineages have an important influence on cruising flapping flight speed that goes beyond the general aerodynamic scaling effects of mass and wing loading.</p>
  • Ali, K.A., et al. (författare)
  • Single zircon Hf-O isotope constraints on the origin of A-type granites from the Jabal Al-Hassir ring complex, Saudi Arabia.
  • 2015
  • Ingår i: Precambrian Research. - 0301-9268 .- 1872-7433. ; 256, s. 131-147
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The Jabal Al-Hassir ring complex in the southern Arabian Shield is an alkaline granite complex comprising an inner core of biotite granite that outwardly becomes a porphyritic sodic-calcic amphibole (ferrobarroisite–katophorite) granite. A combined study of mineral chemistry and single zircon Hf–O zircon isotope analyses was carried out to infer the magma sources of the Neoproterozoic post-collisional A-type granitoids in Saudi Arabia. The granitic rocks show high positive initial ɛHf(<em>t</em>) values of +7.0 to +10.3 and δ<sup>18</sup>O values of +5.8‰ to +7.4‰ that are consistent with melting of a juvenile crustal protolith that was formed during the Neoproterozoic assembly of the Arabian-Nubian Shield (ANS). Crustal-model ages (Hf-<em>t</em><sub>NC</sub>) of 0.71–0.94 Ga indicate minor contribution from an older continental crust in the formation of the Jabal Al-Hassir granitic rocks (crystallization age = 620 ±3 Ma), but any such component is likely to be Neoproterozoic in age. Temperature and oxygen fugacity (ƒO<sub>2</sub>) estimates suggested that the Jabal Al-Hassir A-type granite magma was generated at high temperature (820–1050 °C) and low ƒO<sub>2</sub>. Geochemical characteristics (e.g., low ƒO<sub>2</sub>), geochronological data, and Hf and O isotope compositions, indicate that the magmas of the Neoproterozoic A-type granites of the Jabal Al-Hassir ring complex were likely generated by crustal partial melting of a juvenile Neoproterozoic lower crustal tholeiitic rocks, following collision between East and West Gondwana in the final stages of the evolution of the Arabian Shield.</p>
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