Place and people: spatializing degrees of bonding and bridging social capital in Lisbon (Portugal)

GeoJournal - Broad academic interest in measuring social relationships within an urban context has grown over recent decades. Significant research attention is focused on where social synergies...     

Modeling and Fitting of Three-Dimensional Mineral Microstructures by Multinary Random Fields

Mathematical Geosciences - Modeling a mineral microstructure accurately in three dimensions can render realistic mineralogical patterns which can be used for three-dimensional processing...     

Plio-Pleistocene mammals from Mille-Logya,Ethiopia, and the post-Hadar faunal change

We describe the non-primate mammalian fauna from the late Pliocene to earliest Pleistocene deposits of Mille-Logya in the Lower Awash Valley, Ethiopia, dated to c. 2.9–2.4 Ma, and divided into three successive units: Gafura, Seraitu, and Uraitele. We identify 41 mammalian taxa (including rodents), the most diverse group being the Bovidae, with 17 taxa. While the Gafura assemblage still resembles those from the earlier Hadar Formation, the younger Seraitu assemblage documents a major turnover. While there is little change in the species present across this interval, the relative abundances of various taxa change dramatically, with suids being largely replaced by open-country bovids (Alcelaphini and Antilopini). We interpret this faunal change as reflective of an environmental shift, contemporaneous with the replacement of Australopithecus afarensis by Homo in the area.     

Spatial Variation in the Optical Properties of Dissolved Organic Matter (DOM) in Lakes on the Canadian Precambrian Shield and Links to Watershed Characteristics

In the present study, we explored the use of various optical parameters to detect differences in the composition of the dissolved organic matter (DOM) in a set of lakes that are all located on the Canadian Precambrian Shield, but within which Cu and Ni speciation predictions were previously shown to diverge from measured values in some lakes but not in others. Water samples were collected with in situ diffusion samplers in 2007 (N = 18 lakes) and 2008 (N = 8 lakes). Significant differences in DOM quality were identified between the sampling regions (Rouyn-Noranda, Québec and Sudbury, Ontario) and among lakes, based on dissolved organic carbon concentrations ([DOC]), specific UV absorbance (SUVA₂₅₄), fluorescence indices (FI), and excitation–emission matrix (EEM) fluorescence measurements. Parallel factor analysis (PARAFAC) of the EEM spectra revealed four components, two of which (C3, oxidized quinone fluorophore of allochthonous origin, and C4, tryptophan-like protein fluorescence of autochthonous origin) showed the greatest inter-regional variation. The inter-lake differences in DOM quality were consistent with the regional watershed characteristics as determined from satellite imagery (e.g., watershed-to-lake surface area ratios and relative percentages of surface water, rock outcrops vegetative cover and urban development). Source apportionment plots, built upon PARAFAC components ratios calculated for our lakes, were used to discriminate among DOM sources and to compare them to sources identified in the literature. These results have implications for other areas of research, such as quantifying lake-to-lake variations in the influence of organic matter on the speciation of trace elements in natural aquatic environments.     

Carbonation and melting reactions in the system CaO–MgO–SiO2–CO2 at mantle pressures with geophysical and petrological applications

Bowen's petrogenetic grid was based initially on a series of decarbonation reactions in the system CaO-MgO-SiO₂-CO₂ with starting assemblages including calcite, dolomite, magnesite and quartz, and products including enstatite, forsterite, diopside and wollastonite. We review the positions of 14 decarbonation reactions, experimentally determined or estimated, extending the grid to mantle pressures to evaluate the effect of CO₂ on model mantle peridotite composed of forsterite(Fo)+orthopyroxene(Opx)+clinopyroxene(Cpx). Each reaction terminates at an invariant point involving a liquid, CO₂, carbonates, and silicates. The fusion curves for the mantle mineral assemblages in the presence of excess CO₂ also terminate at these invariant points. The points are connected by a series of reactions involving liquidus relationships among the carbonates and mantle silicates, at temperatures lower (1,100–1,300° C) than the silicate-CO₂ melting reactions (1,400–1,600° C). Review of experimental data in the bounding ternary systems together with preliminary data for the system CaO-MgO-SiO₂-CO₂ permits construction of a partly schematic framework for decarbonation and melting reactions at upper mantle pressures. The key to several problems in the peridotite-CO₂ subsystem is the intersection of a subsolidus carbonation reaction with a melting reaction at an invariant point near 24 kb and 1,200°C. There is an intricate series of reactions between 25 kb and 35 kb involving changes in silicate and carbonate phase fields on the CO₂-saturated liquidus surfaces. Conclusions include the following: (1) Peridotite Fo+Opx+Cpx can be carbonated with increasing pressure, or decreasing temperature, to yield Fo+Opx+Cpx+Cd (Cd=calcic dolomite), Fo+Opx+Cd, Fo+Opx+Cm (Cm=calcic magnesite), and finally Qz+Cm. (2) Free CO₂ cannot exist in subsolidus mantle peridotite with normal temperature distributions; it is stored as carbonate, Cd. (3) The CO₂ bubbles in peridotite nodules do not represent free CO₂ in mantle peridotite along normal geotherms. (4) CO₂ is as effective as H₂O in causing incipient melting, our preferred explanation for the low-velocity zone. (5) Fusion of peridotite with CO₂ at depths shallower than 80 km produces basic magmas, becoming more SiO₂-undersaturated with depth. (6) The solubility of CO₂ in mantle magmas is less than about 5 wt% at depths to 80 km, increasing abruptly to about 40 wt% at 80 km and deeper. (7) Deeper than 80 km, the first liquids produced are carbonatitic, changing towards kimberlitic and eventually, at considerably higher temperatures, to basic magmas. (8) Kimberlite and carbonatite magmas rising from the asthenosphere must evolve CO₂ at depths 100-80 km, which contributes to their explosive emplacement. (9) Fractional crystallization of CO₂-bearing SiO₂-undersaturated basic magmas at most pressures can yield residual kimberlite and carbonatite magmas.     

Alkaline ultramafic lamprophyres and associated carbonatite dykes from the Kalix area,northern Sweden

Alkahne ultramafic lamprophyres and associated carbonatite dykes form north-south trending dyke swarms. The lamprophyres are sub-divided into micaceous, picritic and breccia varieties. Carbonatites sensu stricto (beforsites) occur very subordinate.The dykes of the Kalix area show great similarities to petrographically related rocks from other Scandinavian occurrences (Sokli, Alnö and Fen). Major differences are found in their tectonic setting (regularly striking dyke swarms) and the REE-pattern (distinctly negative cerium anomalies).The following petrogenetic model is advanced for the Kalix dykes: (1) partial melting of upper mantle material, (2) Intrusion into a crustal magma chamber, fractional crystallization, (3) Interactions between crystallized material and the volatile phase (light REE depletion, oxidation of cerium), (4) Intrusion in fracture zones under horizontal tension.

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Zusammenfassung Alkalin-ultrabasiscbe Lamprophyre und begleitende KarbonatitgÄnge bilden nordsüdlidi streichende GangschwÄrme. Die Lamprophyre zeigen gewisse Ähnlichkeiten zu alnöitischen und kimberlitischen Gesteinen; sie wurden unterteilt in glimmerreiche und pikritische Lamprophyre sowie Brekzien. Karbonatite im engeren Sinn treten nur sehr untergeordnet auf; sie sind als Beforsite charakterisiert.Die Ganggesteine des Kalix-Gebiets weisen gro\e Ähnlichkeiten mit petrographiscb verwandten Gesteinen von anderen skandinavischen Vorkommen (Sokli, Alnö und Fen) auf. GrundsÄtzliche Unterschiede finden sich vor allem im tektonischen Auftreten (ziemlich konstant streichende GangschwÄrme) und im Verteilungsmuster der seltenen Erden (deutlich negative Cer-Anomalien).Die Bildung der Kalix-GÄnge wird folgenderweise erklÄrt: (1) Partielle Aufschmelzung des oberen Mantels, (2) Intrusion der Schmelze in eine krustale Magmakammer, gefolgt von fraktionierter Kristallisation, (3) Reaktion zwischen vorzugsweise kristallisiertem Material und der volatilen Phase (Entarmung an leichten seltenen Erden, Oxidation des Cers), (4) Intrusion in Bruchzonen, die horizonteller Dehnung ausgesetzt sind.

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Résumé Des lamprophyres alcalins ultrabasiques accompagnés de carbonatites forment des essaims de dykes de direction nord-sud. Les lamprophyres se subdivisent en variétés micacée, picritique ainsi que brÊchique. Les carbonatites sensu stricto sont rares et sont plutÔ des beforsites.Les dykes de la région de Kalix présentent de grandes similitudes avec des roches pétrographiquement apparentées d'autres localités Scandinaves (Sokli, Alnö et Fen). Les différences essentielles sont dues à leur situation tectonique (essaims de dykes de direction régulière) ainsi qu'à la distribution des Terres Rares (anomalie négative distincte de cérium).Le modèle pétrogénétique suivant est proposé pour les dykes de Kalix: (1) fusion partielle de matériau du manteau supérieur, (2) intrusion dans une chambre magmatique de l'écorce et cristallisation fractionnée, (3) interaction entre le material déjà cristallisé et la phase volatile (appauvrissement des éléments légers des Terres Rares, oxydation du cérium), (4) intrusion le long de zones de fracture dans des conditions d'extension horizontale.

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Mineralogy of sedimentary formations in the western North Atlantic Ocean: Preliminary results

Six sedimentary formations, and two separate members recently were described byJansa, et al. (1979) from the western North Atlantic Ocean basin. We have investigated the mineralogical composition of these lithostratigraphic units by qualitative X-ray diffraction analyses of about five hundred samples from DSDP Sites 105, 106, 386, 387, and 391. The sedimentary section studied, from bottom to top, consists of: argillaceous limestones (Cat Gap Formation); limestones (Blake-Bahama Formation); claystones and shales (Hatteras Formation); zeolitic claystones (Plantagenet Formation); nannofossil marls (Crescent Peaks Member); siliceous oozes, clays, and cherts (Bermuda Rise Formation), and hemipelagic muds (Blake Ridge Formation) that locally contain redeposited shallow-water carbonates (Great Abaco Member). The section ranges in age from Oxfordian at the base to Quaternary at the sea-floor.Most of the formations and members described byJansa, et al. (1979) have a characteristic mineralogical composition. Thus it is possible to recognize boundaries between formations and members by changes in mineral components, although these changes range from sharp to transitional. Within the same formation local differences in mineral spectra between sites can be explained by changing distance from terrigenous sources, lateral changes in surface paleoproductivity, and varying diagenetic conditions.

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Zusammenfassung Sechs sedimentäre Formations und zwei dazugehörige Members wurden vor kurzem durchJansa, et al. (1979) aus dem Ozeanboden des westlichen Nordatlantik beschrieben. Wir haben die Mineralzusammensetzung dieser lithostratigraphischen Einheiten anhand von etwa 500 qualitativen röntgenographischen Analysen untersucht; die Proben dazu entstammen den DSDP-Bohrungen 105, 106, 386, 387 und 391. Vom Liegenden zum Hangenden lassen sich folgende Einheiten unterscheiden: Tonige Kalksteine (Cat Gap Formation); Kalksteine (Blake-Bahama Formation); Tonsteine und shales (Hatteras Formation); Zeolithische Tonsteine (Plantagenet Formation); Nannofossil-Mergel (Crescent Peaks Member); Kieselige Schlamme, Tone und Hornsteine (Bermuda Rise Formation) und Hemipelagische Schlamme (Blake Ridge Formation), die lokal umgelagerte Flachwasser-Karbonate (Great Abaco Member) enthalten. Das Gesamtprofil reicht altersmäßig von Oxfordium an der Basis bis zum Quartär.Die meisten der vonJansa, et al. (1979) beschriebenen Formations und Members haben eine charakteristische Mineralzusammensetzung; es ist daher möglich, Grenzen sowohl zwischen Formations als auch zwischen Formations und Members anhand ihrer Mineralkomponenten zu erkennen; der entsprechende Wechsel kann scharf sein oder fließende Übergänge aufweisen. Lokale Unterschiede in den Mineralspektren einer Formation zwischen einzelnen Bohrpunkten lassen sich auf wechselnde Entfernungen vom Liefergebiet bzw. unterschiedliche Liefergebiete selbst, auf laterale Wechsel in der oberflächennahen Paläo-Produktivität und/oder auf unterschiedliche diagenetische Bedingungen zurückführen.

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Résumé Six »formations« sédimentaires ainsi que deux »members« séparés ont été ré cemment décrits parJansa, et al. (1979) dans la partie nordouest du bassin de l'océan Atlantique. Nous avons étudié, d'un point de vue qualitatif, la composition minéralogique de ces unités lithostratigraphiques à partir de l'analyse diffractométrique d'environ 500 échantillons provenant des sites DSDP 105, 106, 386, 387 et 391. Les sections sédimentaires examinées comprennent de bas en haut: Des calcaires argileux (Cat Gap Formation); des calcaires (Blake-Bahama Formation); des argilites et des argiles schisteuses (Hatteras Formation); des argilites zéolitiques (Plantagenet Formation); de la marne aux nannofossiles (Crescent Peaks Member); des boues silicieuses, des argiles et du silex (Bermuda Rise Formation), ainsi que des boues hémipélagiques (Blake Ridge Formation) qui contiennent par endroits des carbonates resédimentaires provenant d'un milieu peu profond (Great Abaco Member). Leur âge s'échelonne de l'Oxfordien à la base jusqu'au Quaternaire au fond océanique.La plupart des »formations« et des »members« décrits parJansa, et al. (1979) ont une composition minéralogique caractéristique. Il est donc possible de reconnaître les limites entre des »formations« et des »members« à partir des changements de la composition minéralogique, bien que ces changements varient du net au transitoire. Dans une même formation on peut expliquer les différences locales des spectres minéraux entre les sites, par la variation de distance des sources terrigènes, des changements latéraux de la paléoproductivité de surface et des conditions diagénétiques variables.

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Effects of continuous chlorination on spat of the American oyster (Crassostrea virginica)

Newly settled spat of the American oyster (Crassostrea virginica) exhibited reduced survival and growth when exposed to chronic chlorination (as Na-OCl). Spat exposed to nominal concentrations of 0.250 and 0.500 mg per 1 chlorine-produced oxidant (CPO) had only 20% survival after 12 weeks, compared to 64% survival in controls. Spat growth was retarded by nominal concentrations as low as 0.125 mg per I CPO. Shell height of control oysters increased 103% after 12 weeks, while spat exposed to 0.125 mg per I CPO grew 39% and spat exposed to 0.250 mg per I CPO had no net growth. Surviving spat exposed to 0.500 mg per I CPO showed an apparent growth increase of 160%, due mainly to heavy mortality among smaller-sized spat. The numbers of spat (whether surviving or not) that showed any growth over the 12-week exposure period decreased with increasing chlorine concentration. Larger spat were found to be more resistant than smaller spat to increased chlorination. The mechanism of growth inhibition in spat (mantle retraction and cessation of feeding) appeared to be similar to that found in adult oysters exposed to chlorine.