Insertion socioprofessionnelle des sortants de la formation agricole non formelle sur le marché de l’emploi au Burkina Faso et importance accordée à la production céréalière : cas des sortants du centre de promotion rurale de Goundi

L'étude combine les méthodes qualitative et qualitative à travers l’utilisation du questionnaire et du canevas d’entrevue. Elle s’appuie sur un cadre conceptuel élaboré à partir de revue de littérature et de concepts clefs tels que : le capital social, le capital humain, l’identité personnelle, l’identité professionnelle et la socialisation, Les résultats déterminent le profil d’un céréalier indiquant son attachement aux valeurs professionnelles liées au transfert de ses connaissances, à la modernisation de l’exploitation, à la recherche de l’amélioration du rendement et à l’utilisation d’outils modernes.

El Fòrum a una escola rural : una experiencia intercicles. 'El Fórum en una escuela rural : una experiencia interciclos'.

Resumen de la revista en catalán

Geological features of Permian ophiolite in the Jiaomuri area, Qiangtang, Tibet, and its tectonic significance

During the regional geological mapping of the 1∶250000 Mayigangri Sheet, a very complete ophiolite was discovered in the Jiaomuri area, which consists of radiolarian chert, pillow basalt, gabbro, diabase and metaperidotite. This ophiolite is the most intact and complete one in the central Qiangtang area.

Geochemical Study of the Itabirite Iron Ores of the Alegria Mine - Quadrilátero Ferrífero, Minas Gerais, Brazil

The iron ores of Alegria mine are composed of itabirites enclosing minor bodies of high-grade ores. The itabirites are classified according to mineralogical composition in five types: martite-rich, goethite-rich, specularite-rich, magnetite-rich and anphibolite-rich ores. The hematites are martite-rich, magnetite-rich, specularite-rich and more rarely, amphibolite-rich. Other classification criteria of the ores are based on the physical properties and the degree of compaction. As such, the itabirites and hematites can be classified as hard, friable and soft types. The mineralogical/textural evolution of the ores is linked to the pressure and temperature conditions that accompanied the tectonic processes in anphibolite facies and the different degrees of subsequent surficial weathering processes. Petrographic and microstructural studies indicate that the magnetite and amphibole bearing itabirites represent the parent rocks that created the other itabirites and that the specularite itabirites and the hard martite types are related to silica dissolution and redeposition in zones of high and low strain. Most of itabirites ores correspond to chert oxide facies banded iron formation, except the goethite and amphibole bearing itabirite that resemble a silicate or oxide-silicate facies with minor carbonate impurities. The great mass and pods of soft martite itabirites are probably shaley oxide facies BIFs with little volcanic contribution. Trace element contents of the Alegria's itabirites show strong dissimilarities with BIFs associated with volcanism (Algoma type), but closely ressemble to the Lake Superior type, with high content in Cr, Co and low V, Ni, Cu and Zn. Although the absolute contents of REE present in the Alegria's itabirites are, in general very low, the pattern when normalised by NASC is similar to the great majority of the Archean and Paleoproterozoic BIFs elsewhere in the world, and characterised by positive Eu anomaly.

Modelo de campo de gás não convencional do tipo indireto: caso Elsinore, Oeste do Texas, EUA

Pós-graduação em Geologia Regional - IGCE

Paleoambiente e diagênese da formação Itaituba, carbonífero da bacia do Amazonas, com base em testemunho de sondagem, região de Uruará, Pará

A Formação Itaituba de idade carbonífera representa a sedimentação carbonática de depósitos transgressivos do Grupo Tapajós da Bacia do Amazonas. A sucessão Itaituba é interpretada como depósitos de planície de maré mista, constituídos de calcários fossilíferos, dolomitos finos, arenitos finos a grossos e subordinadamente siltitos avermelhados, evaporitos e folhelhos negros. A análise de fácies e microfácies do testemunho de sondagem da região de Uruará, Estado do Pará, permitiu individualizar dezenove fácies agrupadas em cinco associações: planície de maré (AF1), canal de maré (AF2), laguna (AF3), barra bioclástica (AF4) e plataforma externa (AF5). AF1 é composta por arenito fino com rip-up clasts e gretas de contração, marga com grãos de quartzo e feldspato, dolomudstone laminado com grãos terrígenos e dolomito fino silicificado, com intercalação de argilito com grãos de quartzo disseminados, dolomitizado e localmente com sílica microcristalina. AF2 consiste em arenito médio a grosso com estratificação cruzada acanalada, recoberta por filmes pelíticos nos foresets, arenito muito fino a fino com acamamento wavy, siltito laminado com falhas sinsedimentares e acamamento convoluto. AF3 é constituída de siltito vermelho maciço, mudstone com fósseis, floatstone com braquiópodes e pirita disseminada e mudstone maciço com frequentes grãos de quartzo. AF4 e AF5 exibem abundantes bioclastos representados por espinhos e fragmentos de equinodermas, conchas, fragmentos e espinhos de braquiópodes, ostracodes, foraminíferos, algas vermelhas e conchas de bivalves. AF4 é formada por grainstone oolítico fossilífero e grainstone com terrígenos principalmente grãos de quartzo monocristalino e AF5 se compõe de wackestone fossilífero, wackestone com terrígenos e mudstone maciço com grãos de quartzo monocristalino. Subarcósios (AF1), arcósios (AF2) e arcósios líticos (AF2) são os tipos de arenitos da sucessão Itaituba e apresentam como principais constituintes grãos de quartzo monocristalino e policristalino, K-feldspato, plagioclásio, pirita, muscovita detrítica, fragmento de rocha pelítica, metamórfica e chert e raros bioclastos. O cimento é de calcita espática não ferrosa, óxido/hidróxido de ferro e sobrecrescimento de sílica. A porosidade é intergranular, móldica e às vezes alongada, sem permeabilidade perfazendo até 11% da rocha. Os processos diagenéticos dos arenitos são compactação física, sobrecrescimento de sílica, cimentação de calcita, formação de matriz diagenética, compactação química, substituição de grãos, autigênese de pirita, formação de óxido/hidróxido de ferro e alteração do plagioclásio. Os processos diagenéticos dos carbonatos são: micritização, neomorfismo, colomitização, fraturamento, compactação química, cimentação de calcita, dissolução secundária e autigênese de minerais. A sucessão da Formação Itaituba representa um sistema de laguna/planície de maré ligada a uma plataforma marinha carbonática. Planícies de maré desenvolveram-se nas margens das lagunas e eram periodicamente supridas por influxos de terrígenos finos (silte) que inibiam a precipitação carbonática. Barras bioclásticas eram cortadas por canais de maré (inlet) que conectavam a laguna com a plataforma rasa rica em organismos bentônicos.

Petrographic approach to the study of organic microfossils from the Irati Subgroup (Permian, Parana Basin, Brazil)

Early diagenetic chert, infrequently exploited in Phanerozoic micropaleontology, was examined for organic-walled microfossils in petrographic thin sections of silicified dolostones from diverse levels and localities of the Assistencia Formation (Permian, Parana Basin) in the state of Sao Paulo, Brazil. In contrast to previous palynological studies of this formation, the use of thin sections allowed direct observation in three dimensions of common palynomorphs, as well as benthic microbial mats preserved in situ in various stages of their life cycles and degradation. As in palynological residues from the more wellknown shale of this formation, the chert contains wind-dispersed pollen grains and phytoclasts derived from terrestrial sources and planktonic cryptarchs (unornamented coccoidal unicellular or colonial palynomorphs). However, only in the chert is it possible to see much more delicate microfossils, such as abundant cyanobacteria of the in situ benthic microbiota as well as chlorophycean microalgae of the microphytoplankton. Post-depositional processes affecting the formation have destroyed all but the most resistant organic remains in the other lithologies, such that only rare, degraded pollen grains are seen in the unsilicified dolostone of the formation, and in the shale the vast majority of microfossils have been compacted to flattened disks. On the other hand, early silicification not only preserved organic remains at an incipient stage of decomposition but also impeded significant further degradation due to compaction, recrystallization, and oxidation. Thus, the petrographic study of such chert can complement traditional palynological investigations in Phanerozoic rocks by furnishing hitherto unavailable information, especially with regard to benthic organic microfossils and fragile organic-walled phytoplankton normally absent from organic residues. (C) 2011 Elsevier Ltd. All rights reserved.

Heiltraditionen und Biodiversität: Die traditionelle Medizin der Baatombu Nordbenins

Im Zentrum der vorliegenden Untersuchung steht die Nutzung von Medizinalpflanzen vor dem Hintergrund einer zurückgehenden Phytodiversität in Nordbenin. Die Dissertation ba-siert auf ethnologischen Forschungen, die in das interdisziplinäre Forschungsprojekt BIOTA (Biodiversity Monitoring Transect Analysis in Africa) eingebunden sind. Das BIOTA-Projekt untersucht die Wirkung menschlichen Handelns (insbesondere Nutzung) auf die Biodiversi-tät und versucht aus diesen Erkenntnissen Maßnahmen zum Erhalt der biologischen Vielfalt abzuleiten. Die vorliegende Studie basiert auf einem 13-monatigen Feldforschungsaufenthalt im Zeitraum von April 2004 bis August 2006 in der nordbeninischen Gemeinde Ouassa-Pehunco. Meine Informanten sind überwiegend traditionelle Heiler, mit denen ich standardi-sierte und offene Interviews durchführte, deren Behandlungsverfahren und Heilzeremonien ich teilnehmend beobachtete sowie dokumentierte und auf deren Initiative hin ich mich bei dem Aufbau eines Medizinalpflanzengartens einbrachte (cf. Kap. 1). In diesem Forschungsfeld situiere ich mich mit der Frage nach dem Einfluss einer verän-derten Pflanzenvielfalt auf die traditionelle medizinische Versorgung der Baatombu Nordbe-nins. Die Beantwortung dieser Frage erfolgt in mehreren Schritten. 1. Die Phytodiversität nimmt, wie von naturwissenschaftlicher Seite bestätigt, in der Region ab. 2. Lokale Heilkun-dige nehmen diesen Rückgang an verfügbaren Heilpflanzen ebenso wahr. 3. Die Abnahme der Pflanzenbestände führen die Heiler vor allem auf den Baumwollanbau und die demogra-fischen Entwicklungen der Region zurück - dies entspricht ebenfalls den Auffassungen von Naturwissenschaftlern, die eine Verdichtung der landwirtschaftlichen Bodennutzung fest-stellten. 4. Heilkundige und Heilpflanzenverkäuferinnen vermerken eine zunehmende Nach-frage nach lokaler Pflanzenmedizin aufgrund der steigenden Bevölkerungszahlen. 5. Die pflanzenbasierte Gesundheitsversorgung der lokalen Bevölkerung ist jedoch relativ gesi-chert, da die Heiler sich alternativ wirkender Medizinalpflanzen bedienen, ihre Therapiefor-men der veränderten Lage anpassen (z.B. geringere Dosierungen) und sie regelmäßig genutz-te Pflanzen im Medizinalpflanzengarten Guson wieder anpflanzen. Ein wichtiger Aspekt der Arbeit ist, dass die Heilpraktiken der Baatombu nicht allein auf naturheilkundlichem Erfahrungswissen beruhen, sondern in magisch-religiöse Vorstellungen eingebettet sind (cf. Kap. 2). Demzufolge untersuche ich die lokalen Krankheits- und Ge-sundheitsvorstellungen und die symbolischen Klassifikationen von Heilpflanzen und Krank-heiten (cf. Kap. 3). Ich stellte fest, dass nach Auffassung von Heilkundigen soziokulturelle Faktoren wie der Zeitpunkt und der Ort einer Sammlung sowie entsprechende Ernte-Rituale die medizinische Wirksamkeit von Pflanzen maßgeblich bedingen (cf. Kap. 5). Die Umwelt-klassifikation der Heiler (Landschafts- und Vegetationstypen) richtet sich demzufolge nach dem medizinischen Wert, den sie einer Heilpflanze zuschreiben (cf. Kap.4). Basierend auf diesen Erkenntnissen wurde von einigen engagierten Heilern und mit Un-terstützung von BIOTA, der GTZ und der Deutschen Botschaft der Medizinalpflanzengarten Guson eingerichtet, der eine Antwort auf die regionale Ressourcenverknappung darstellt und in seiner Anlage dem lokalen ökologischen und heilkundlichen Wissen der Heiler entspricht (cf. Kap. 6). Den Anwendungsbezug der Forschung nutzten die Heiler, um sich als Interes-sensgemeinschaft für den Erhalt der benötigten pflanzlichen Ressourcen einzusetzen.

Variation of stable silicon isotopes: Analytical developments and applications in Precambrian geochemistry

Die vorliegende Dissertation behandelt die Gesamtgesteinsanalyse stabiler Siliziumisotope mit Hilfe einer „Multi Collector-ICP-MS“. Die Analysen fanden in Kooperation mit dem „Royal Museum for Central Africa“ in Belgien statt. Einer der Schwerpunkte des ersten Kapitels ist die erstmalige Analyse des δ30Si –Wertes an einem konventionellen Nu PlasmaTM „Multi-Collector ICP-MS“ Instrument, durch die Eliminierung der den 30Si “peak” überlagernden 14N16O Interferenz. Die Analyse von δ30Si wurde durch technische Modifikationen der Anlage erreicht, welche eine höherer Massenauflösung ermöglichten. Die sorgsame Charakterisierung eines adäquaten Referenzmaterials ist unabdingbar für die Abschätzung der Genauigkeit einer Messung. Die Bestimmung der „U.S. Geological Survey“ Referenzmaterialien bildet den zweiten Schwerpunkt dieses Kapitales. Die Analyse zweier hawaiianischer Standards (BHVO-1 and BHVO-2), belegt die präzise und genaue δ30Si Bestimmung und bietet Vergleichsdaten als Qualitätskontrolle für andere Labore. Das zweite Kapitel befasst sich mit kombinierter Silizium-/Sauerstoffisotope zur Untersuchung der Entstehung der Silizifizierung vulkanischer Gesteine des „Barberton Greenstone Belt“, Südafrika. Im Gegensatz zu heute, war die Silizifizierung der Oberflächennahen Schichten, einschließlich der „Chert“ Bildung, weitverbreitete Prozesse am präkambrischen Ozeanboden. Diese Horizonte sind Zeugen einer extremen Siliziummobilisierung in der Frühzeit der Erde. Dieses Kapitel behandelt die Analyse von Silizium- und Sauerstoffisotopen an drei unterschiedlichen Gesteinsprofilen mit unterschiedlich stark silizifizierten Basalten und überlagernden geschichteten „Cherts“ der 3.54, 3.45 und 3.33 Mill. Jr. alten Theespruit, Kromberg und Hooggenoeg Formationen. Siliziumisotope, Sauerstoffisotope und die SiO2-Gehalte demonstrieren in allen drei Gesteinsprofilen eine positive Korrelation mit dem Silizifizierungsgrad, jedoch mit unterschiedlichen Steigungen der δ30Si-δ18O-Verhältnisse. Meerwasser wird als Quelle des Siliziums für den Silizifizierungsprozess betrachtet. Berechnungen haben gezeigt, dass eine klassische Wasser-Gestein Wechselwirkung die Siliziumisotopenvariation nicht beeinflussen kann, da die Konzentration von Si im Meerwasser zu gering ist (49 ppm). Die Daten stimmen mit einer Zwei-Endglieder-Komponentenmischung überein, mit Basalt und „Chert“ als jeweilige Endglieder. Unsere gegenwärtigen Daten an den „Cherts“ bestätigen einen Anstieg der Isotopenzusammensetzung über der Zeit. Mögliche Faktoren, die für unterschiedliche Steigungen der δ30Si-δ18O Verhältnisse verantwortlich sein könnten sind Veränderungen in der Meerwasserisotopie, der Wassertemperatur oder sekundäre Alterationseffekte. Das letzte Kapitel beinhaltet potentielle Variationen in der Quellregion archaischer Granitoide: die Si-Isotopen Perspektive. Natriumhaltige Tonalit-Trondhjemit-Granodiorit (TTG) Intrusiva repräsentieren große Anteile der archaischen Kruste. Im Gegensatz dazu ist die heutige Kruste kaliumhaltiger (GMS-Gruppe: Granit-Monzonite-Syenite). Prozesse, die zu dem Wechsel von natriumhaltiger zu kaliumhaltiger Kruste führten sind die Thematik diesen Kapitels. Siliziumisotopenmessungen wurden hier kombiniert mit Haupt- und Spurenelementanalysen an unterschiedlichen Generationen der 3.55 bis 3.10 Mill. Yr. alten TTG und GMS Intrusiva aus dem Arbeitsgebiet. Die δ30Si-Werte in den unterschiedlichen Plutonit Generationen zeigen einen leichten Anstieg der Isotopie mit der Zeit, wobei natriumhaltige Intrusiva die niedrigste Si-Isotopenzusammensetzung aufweisen. Der leichte Anstieg in der Siliziumisotopenzusammensetzung über die Zeit könnte auf unterschiedliche Temperaturbedingungen in der Quellregion der Granitoide hinweisen. Die Entstehung von Na-reichen, leichten d30Si Granitoiden würde demnach bei höheren Temperaturen erfolgen. Die Ähnlichkeit der δ30Si-Werte in archaischen K-reichen Plutoniten und phanerozoischen K-reichen Plutoniten wird ebenfalls deutlich.

Volcanostratigraphic Controls on the Occurrence of Massive Sulfide (VMS) Deposits in the Semail Ophiolite, Oman

The Semail ophiolite in Oman is capped by up to 2 km of basaltic-andesitic lavas that host copper-dominant, Cyprus-type, volcanogenic massive sulfide (VMS) deposits. This study identifies multiple volcanostratigraphic horizons on which the deposits are situated, based on characterization of footwall and hanging-wall lavas from 16 deposits or deposit clusters. Comparison of field and petrographic features, compositions of igneous clinopyroxenes, and whole-rock geochemical signatures permits classification of the lavas within a modified version of the established regional volcanostratigraphy. Four extrusive units host deposits: Geotimes (earliest), Lasail, Alley, and Boninitic Alley (latest). The latter was previously known only at few localities, but this study reveals its regional extent and significance as a host for VMS deposits. The Geotimes and Lasail units represent Late Cretaceous, ocean spreading ridge and related off-axis volcanic environments, respectively. The Alley and Boninitic Alley units represent younger, subduction-related volcanism prior to Coniacian-Santonian obduction of the ophiolite. Our results show that VMS deposits occur on or near the Geotimes/Lasail and Geotimes/Alley contacts as well as entirely within the Geotimes, Lasail, Alley, and Boninitic Alley units. Highest Cu grades tend to occur in deposits lying on or within the Geotimes, whereas highest Au grades occur in deposits within the Boninitic Alley. In contrast to earlier studies, we conclude that essentially every horizon marking a hiatus in lava deposition in the Semail ophiolite, i.e., contacts between the four major eruptive units, and umbers and sedimentary chert layers within the units, has exploration potential for Cu-Au VMS deposits.

Investigation of diagenesis in sediment core CRP-1 from the Ross Sea, Antarctica

A diagenetic study was carried out on the cored Miocene section in CRP-1 by thin-section, X-ray diffraction, scanning electron microscope, electron microprobe and stable isotopic analysis. Carbonate (calcite, siderite) microconcretions occur locally within intergranular pores and open fractures, and some sands are cemented by microcrystalline calcite. Calcite cement at 115.12 mbsf (metres below sea floor) and possibly microconcretionary calcite at 44.62 mbsf record infiltration of meteoric waters into the section, consistent with sequence stratigraphic evidence for multiple glacial advances over the CRP-1 drillsite. Diagenetic carbonates incorporated carbon derived from both organic matter and marine carbonate. Carbon isotope data are consistent with microconcretion formation at shallow depths. Sandstones are poorly compacted and, despite containing a large component of chemically unstable grains, are virtually unaltered. Preservation of the chemically unstable grain component reflects the cold climate depositional setting and shallow maximum burial depths.

Geochemical composition of the Trincheira Complex in the southwestern Amazon craton, Brazil

We document the first-known Mesoproterozoic ophiolite from the southwestern part of the Amazon craton, corresponding to the Trincheira Complex of Calymmian age, and propose a tectonic model that explains many previously enigmatic features of the Precambrian history of this key craton, and discuss its role in the reconstruction of the Columbia supercontinent. The complex comprises extrusive rocks (fine-grained amphibolites derived from massive and pillowed basalts), mafic-ultramafic intrusive rocks, chert, banded iron formation (BIFs), pelites, psammitic and a smaller proportion of calc-silicate rocks. This sequence was deformed, metasomatized and metamorphosed during the development of the Alto Guaporé Belt, a Mesoproterozoic accretionary orogen. The rocks were deformed by a single tectonic event, which included isoclinal folding and metamorphism of the granulite-amphibolite facies. Layered magmatic structures were preserved in areas of low strain, including amygdaloidal and cumulate structures. Metamorphism was pervasive and reached temperatures of 780-853°C in mafic granulites and 680-720°C in amphibolites under an overall pressure of 6.8 kbar. The geochemical composition of the extrusive and intrusive rocks indicates that all noncumulus mafic-ultramafic rocks are tholeiitic basalts. The mafic-ultramafic rocks display moderately to strongly fractionation of light rare earth elements (LREE), near-flat heavy rare earth elements (HREE) patterns and moderate to strong negative high field strength elements (HFSE) anomalies (especially Nb), a geochemical signature typical of subduction zones. The lowest units of mafic granulites and porphyroblastic amphibolites in the Trincheira ophiolite are similar to the modern mid-ocean ridge basalt (MORB), although they locally display small Ta, Ti and Nb negative anomalies, indicating a small subduction influence. This behavior changes to an island arc tholeiites (IAT) signature in the upper units of fine-grained amphibolites and amphibole rich-amphibolites, characterized by progressive depletion in the incompatible elements and more pronounced negative Ta and Nb anomalies, as well as common Ti and Zr negative anomalies. Tectono-magmatic variation diagrams and chondrite-normalized REE and primitive mantle normalized patterns suggest a back-arc to intra-oceanic island arc tectonic regime for the eruption of these rocks. Therefore, the Trincheira ophiolite appears to have originated in an intraoceanic supra-subduction setting composed of an arc-back-arc system. Accordingly, the Trincheira Complex is a record of oceanic crust relics obducted during the collision of the Amazon craton and the Paraguá block during the Middle Mesoproterozoic. Thus, the recognition of the Trincheira ophiolite and suture significantly changes views on the evolution of the southern margin of the Amazon craton, and how it can influence the global tectonics and the reconstruction of the continents.

Abundance and preservation of radiolarian faunas of ODP Hole 122-761B (Table 1)

Sites 759 through 764 were drilled during Ocean Drilling Program Leg 122 on the Exmouth and Wombat plateaus off northwest Australia, eastern Indian Ocean. Radiolarian recovery was generally poor due to unsuitable lithofacies. A few Quaternary radiolarian faunas were recovered from most of the sites. Rare and poorly preserved Oligocene and Eocene radiolarian faunas were recovered from Holes 760A, 761B, 761C, and 762B. Poorly preserved Cretaceous radiolarians occur in samples from Holes 761B, 762C, 763B, and 763C. Chert intervals from Cores 122-761B-28X, 122-761C-5R, and 122-761C-6R contain moderately well-preserved Cretaceous radiolarian faunas (upper Albian, mid- to upper Cenomanian, and mid-Albian, respectively). Rare fragments of Upper Triassic radiolarians were recovered from sections in Holes 759B, 760B, and 764A. The only well-preserved pre-Quaternary radiolarians are in lower and upper Paleocene faunas (Bekoma campechensis Zone) recovered from Site 761, Sections 122-761B-16X-1 to 122-761C-19X-CC. The composition of these faunas differs somewhat from that of isolated coeval Paleocene faunas from Deep Sea Drilling Project sites in the Atlantic, Gulf of Mexico, tropical Pacific, eastern Indian Ocean, and near Spain and North Africa, as well as from several on-land sites in North America, Cuba, and the USSR.

(Table 1) Distribution of ichthyolith subtypes at DSDP Hole 62-464

At Site 464, a 308-meter-deep hole was drilled on the Hess Rise (39°51.64'N, 173°53.33'E; water depth 4637 m). The upper strata consist of siliceous clay and oozes of Pleistocene, Pliocene, and possibly latest Miocene ages (36 m) and the lower strata are Albian chert, chalk, and marlstone (219 m). The middle part of the stratigraphic section is pelagic brown clay (53 m) which is essentially barren of microfossils except for ichthyoliths. At the base of this middle unit in Core 10 is a recrystallized Cretaceous radiolarian assemblage and an impoverished late Miocene nannofossil assemblage. Fifteen samples from Cores 6 through 10 in the middle unit and three samples from the overlying siliceous clay were examined for ichthyoliths.