Éditeur(s) : Société Géologique de France
Résumé : Numerous data obtained during recent marine geophysical surveys have been compiled together in order to present the structural framework of Niger Delta and adjacent areas. Seismic reflection results show that the delta slope is characterized by intense diapiric deformations and that the overall structure of the delta is fairly comparable to the structures of the Gulf Coast province margin or of Angolan margin. Seismics as well as gravity and magnetic measurements indicate the existence in the vicinity of the Niger delta of two oceanic trends apparently related to an early phase of opening of the South Atlantic. Both trends can tentatively be correlated on land with the major structures known in the southern and northern Benue trough. A comparion between the whole area (Niger Delta and Benue trough) and another intracratonic chain-the Pyrenees mountains - is briefly discussed. [NOT CONTROLLED OCR]
J. Min. Geol. (Société Géologique de France), 1976 , Vol. 13 , N. 1 , P. 12-28

Droits : Société Géologique de France
http://archimer.ifremer.fr/doc/1976/publication-5171.pdf
http://archimer.ifremer.fr/doc/00000/5171/

Éditeur(s) : HAL CCSD Elsevier
Résumé : The seismic characteristics of focused fluid-related features such as pockmarks and carbonate build-ups on the Nigerian continental slope have been investigated using complementary seismic data sets (reprocessed 3D exploration data and 2D Very High Resolution hull-mounted and near-bottom seismic data) coupled with the results of previous studies (sedimentological, geotechnical and geochemical analyses).The results show different types of fluid-related features within the hemipelagic phase of long duration (∼1 Myr) Turbidite/Hemipelagic cycles. They are the product of the disturbance of the hosting sediments following two main distinct processes: (1) no or low sediment deposition caused by fluid escape associated with seafloor settlement (benthic fauna, carbonate precipitation, gas hydrate formation) and (2) post-depositional erosion, caused either by fluid release (dewatering from underlying features such as channels and upward migration from a deep source) or by collapse (destabilisation of gas hydrates). The temporal evolution reveals a decrease in fluid flow during the hemipelagic deposition as witnessed by the decrease in methanogenic activity and by gas hydrate destabilisation. The spatial distribution of fluid-related features seems to be controlled by the type of fault (small fault or structural lineament).
ISSN: 0264-8172

hal-01685513
https://hal.archives-ouvertes.fr/hal-01685513
DOI : 10.1016/j.marpetgeo.2017.10.004

Éditeur(s) : Public Library Science
Résumé : Like hydrothermal vents along oceanic ridges, cold seeps are patchy and isolated ecosystems along continental margins, extending from bathyal to abyssal depths. The Atlantic Equatorial Belt (AEB), from the Gulf of Mexico to the Gulf of Guinea, was one focus of the Census of Marine Life ChEss (Chemosynthetic Ecosystems) program to study biogeography of seep and vent fauna. We present a review and analysis of collections from five seep regions along the AEB: the Gulf of Mexico where extensive faunal sampling has been conducted from 400 to 3300m, the Barbados accretionary prism, the Blake ridge diapir, and in the Eastern Atlantic from the Congo and Gabon margins and the recently explored Nigeria margin. Of the 72 taxa identified at the species level, a total of 9 species or species complexes are identified as amphi-Atlantic. Similarity analyses based on both Bray Curtis and Hellinger distances among 9 faunal collections, and principal component analysis based on presence/absence of megafauna species at these sites, suggest that within the AEB seep megafauna community structure is influenced primarily by depth rather than by geographic distance. Depth segregation is observed between 1000 and 2000m, with the middle slope sites either grouped with those deeper than 2000m or with the shallower sites. The highest level of community similarity was found between the seeps of the Florida escarpment and Congo margin. In the western Atlantic, the highest degree of similarity is observed between the shallowest sites of the Barbados prism and of the Louisiana slope. The high number of amphi-atlantic cold-seep species that do not cluster according to biogeographic regions, and the importance of depth in structuring AEB cold-seep communities are the major conclusions of this study. The hydrothermal vent sites along the Mid Atlantic Ridge (MAR) did not appear as "stepping stones" for dispersal of the AEB seep fauna, however, the south MAR and off axis regions should be further explored to more fully test this hypothesis.
Plos One (1932-6203) (Public Library Science), 2010-08 , Vol. 5 , N. 8 , P. 1-11

Droits : © 2010 Olu et al.
http://archimer.ifremer.fr/doc/00011/12207/8975.pdf
DOI:10.1371/journal.pone.0011967
http://archimer.ifremer.fr/doc/00011/12207/

Résumé : La taxonomie des huîtres est longtemps restée basée sur des critères morphologiques tel que la coquille et les organes internes ou sur la répartition géographique. Ces critères se révèlent aujourd'hui peut fiable du fait de la grande plasticité des caractères morphologiques des huîtres en fonction des conditions environnementales, et du transport d'espèce par l'ostréiculture ou accidentellement. La biologie moléculaire et en particulier les marqueurs génétiques sont des outils très utiles pour différencier les espèces. La phylogéographie des huîtres creuses de l'Atlantique Sud a ainsi été étudié grâce à différentes méthodes d'observation du polymorphisme de l'ADN. Ces techniques ont dans un premier temps été appliquées à des fragments mitochondriaux (16S) pui à des fragments nucléaires (ITS). La PCR6RFLP a été utilisée d'une part sur les fragments 16S pour déterminer les haplotypes de 5 nouvelles populations du genre Crassostrea provenant du Sénégal, du Nigeria et du Brésil. Il a été ainsi possible d'identifier une nouvelle population de Crassostrea gasar en Amérique du Sud. Nous nous sommes ensuite intéressés aux polymorphisme pouvant exister entre les différentes populations de C. gasar de part et d'autre de l'Atlantique. Pour cela des fragments nucléaires ITS, à priori plus polymorphes que les fragments mitochondriaux 16S ont été étudiés. Différentes mises au point ont été réalisées afin de révéler un éventuel polymorphisme entre les populations. Toutes les informations recueuillies tendent vers cette hypothèse sans toutefois pouvoir la confirmer. La présence d'une zone de sympatrie entre les espèces C. gasar en Amérique du Sud poste la question de son introduction, soit par l'homme soit accidentellement. Des études complèmenaires sont indispensables, par un échantillonnage plus large, pour évaluer l'étendue de la présence des espèces de part et d'autre de l'océan. Il est également nécessaire de continuer la mise au point sur les marqueurs nucléaires afin de confirmer le polymorphisme suspecté entre les populations C. gasar d'Afrique et d'Amérique. La publication récente d'un article séparant les espèces C. brasiliana et C. rhizophorae pose également la question de la position de C. brasiliana par rapport aux deux espèces que nous avons étudié.

Droits : 2000 Univ. La Rochelle
http://archimer.ifremer.fr/doc/00033/14409/11706.pdf
http://archimer.ifremer.fr/doc/00033/14409/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The N-S oriented Raghane shear zone (8 degrees 30') delineates the western boundary of the Saharan metacraton and is, with the 4 degrees 50' shear zone, the most important shear zone in the Tuareg shield. It can be followed on 1000 km in the basement from southern Air, Niger to NE Hoggar, Algeria. Large subhorizontal movements have occurred during the Pan-African orogeny and several groups of granitoids intruded during the Neoproterozoic. We report U-Pb zircon datings (laser ICP-MS) showing that three magmatic suites of granitoids emplaced close to the Raghane shear zone at c. 790 Ma, c. 590 and c. 550 Ma. A comprehensive and detailed (158 sites, more than 1000 cores) magnetic fabric study was performed on 8 plutons belonging to the three magmatic suites and distributed on 200 km along the Raghane shear zone. The main minerals in all the target plutons do not show visible preferential magmatic orientation except in narrow shear zones. The AMS study shows that all plutons have a magnetic lineation and foliation compatible with the deformed zones that are zones deformed lately in post-solidus conditions. These structures are related to the nearby mega-shear zones, the Raghane shear zone for most of them. The old c. 793 Ma Touffok granite preserved locally its original structures. The magnetic structures of the c. 593 Ma Ohergehem pluton, intruded in the Aouzegueur terrane, are related to thrust structures generated by the Raghane shear zone while it is not the case of the contemporaneous plutons in the Assode-Issalane terrane whose structures are only related to the subvertical shear zones. Finally, the c. 550 Ma granite group has magnetic structure related to the N-S oriented Raghane shear zone and its associated NNE-SSW structures when close to them, but NW-SE oriented when further. These NW-SE oriented structures appear to be characteristic of the late Neoproterozoic evolution of the Saharan metacraton and are in relation to the convergence with the Murzuq craton. This evolution reflects the rheological contrast existing along the Raghane shear zone marking the western boundary of the Saharan metacraton.
ISSN: 0040-1951

hal-00429354
https://hal.archives-ouvertes.fr/hal-00429354
DOI : 10.1016/j.tecto.2009.04.022

Éditeur(s) : The American Association of Petroleum Geologlists
Résumé : The west African continental margin between Abidjan (Ivory Coast) and Walvis Boy (Southwcst Africa) was surveyed in 1971 by the R/V Jean Charcot. Fiftyeight seismic-reflection (flexotir source), bathymetric (3.5 and 12 kc), gravimetric, and magnetic profiles were obtained. The seaward limit of an evaporitic zone outlined during the survey is at the boundary between continental slope and continental rise. Variation of depth of this limit as a function of latitude shows the presence of a large offset at 11°S which seems to be related to an east-east-southeast line of magnetic seamounts cutting into the continental slope. The Annobon-Cameroun volcanic axis separates the salt zones of the Nigerian basin and Congo-Angola basin. The northern limit of Salt deposition in the Congo-Angola basin is marked near 1°N by a strong southwest-northeast magnetic trend. On the south it extends to necr 14°s. The Walvis Ridge, located farther south, does not seem to have an effect on evaporite deposition. [NOT CONTROLLED OCR]
The American Association of Petroleum Geologlists Bulletin (The American Association of Petroleum Geologlists), 1973 , Vol. 57 , N. 9 , P. 1658-1671

Droits : The American Association of Petroleum Geologlists
http://archimer.ifremer.fr/doc/1973/publication-5123.pdf
http://archimer.ifremer.fr/doc/00000/5123/

Éditeur(s) : ISTPM
Résumé : The Atlantic and Mediterranean members of the scorpaenidae family have always triggered numerous discussions about their reciprocious congenialities. Back in the (recent) days when the number of species known on the French coasts was still fairly low, the belonging of one species to such or such genus, as Helicolenus (Sebastes) dactylopterus DELAROCHE or Scorpaena maderensis Cuvier and Valenciennes, has been the subject of numerous articles of which the authors' conclusions might differ from one another, and even today light is still far from being shed on those topics. The difficulties met in the determination of scorpaenidae: similar general appearance, subtle differences, impossibility of comparing the samples with the types, incomplete or misinterpreted descriptions, have lead scientists to make hasty determinations resulting in: an even more complicated synonymy and incorrect data about the biogeography of the species. Thereby, the rockfish named Scorpaena rubellio by JORDAN and GUNN (I) is considered as a synonymous of S. maderensis Cuvier Valenciennes by J. R. NORMAN (2), and of S. porcus Linné by H. W. FOWLER (3). Likewise, the dispersion area of S. scrofa in Guinea, Niger and Sainte-Hélène, is caused by its confusion with other species such as S. stephanica, S. angolensis and S. scrofina. (unverified OCR)
Les représentants de la famille des Scorpénidés dans l'Atlantique et la Méditerranée ont toujours donné lieu à de nombreuses discussions au sujet de leurs affinités réciproques. A l'époque encore récente où le nombre des espèces connues des côtes de France était encore très réduit, la place dans tel ou tel genre d'espèces telles que Helicolenus (Sebastes) dactylopterus DELAROCHE ou Scorpaena maderensis Cuvier et Valenciennes, par exemple, ont provoqué des séries d'articles où les conclusions des auteurs successifs n'étaient pas toujours concordantes, et aujourd'hui encore la lumière est loin d'être faite sur bien des points. Les difficultés que l'on rencontre dans la détermination des Scorpénidés : grande ressemblance générale, différences parfois difficiles à saisir, impossibilité de comparer les échantillons d'étude aux types, obligation de se contenter de descriptions incomplètes .ou mal interprétées, ont trop souvent entraîné les chercheurs à des déterminations trop hâtives ayant comme résultats : de compliquer la synonymie et de fausser plus ou moins complètement les données acquises sur la biogéographie d'une espèce. C'est ainsi que la Scorpène appelée Scorpaena rubellio par JORDAN et GUNN (Il est considérée comme synonyme de S. maderensis Cuvier Valenciennes par J. R. NORMAN (2), et de S. porcus Linné par H. W. FOWLER (3). De même l'extension de l'aire de dispersion de S. scrofa en Guinée, au Niger et à Sainte-Hélène, est due à des confusions avec des espèces différentes telles que S. stephanica, S. angolensis et S. scrofina. (OCR non contrôlé)
Revue des Travaux de l'Institut des Pêches Maritimes (0035-2276) (ISTPM), 1943 , Vol. 13 , N. 1-4

Droits : Ifremer
http://archimer.ifremer.fr/doc/1943/publication-3420.pdf
http://archimer.ifremer.fr/doc/00000/3420/

Éditeur(s) : HAL CCSD Elsevier
Résumé : This paper is the first presentation of a project called GHYRAF (Gravity and Hydrology in Africa) devoted to the detailed comparison between models and multidisciplinary observations (ground and satellite gravity, geodesy, hydrology, meteorology) of the variations of water storage in Africa from the Sahara and part to the monsoon equatorial part. We describe the various actions planned in this project. We first detail the actions planned in gravimetry which consist in two main surface gravity experiments: on the one hand the periodic repetition of absolute gravity measurements along a north-south monsoonal gradient of rainfall in West Africa, going from Tamanrasset (20 mm/year) in southern Algeria to Djougou (1200 mm/year) in central Benin; on the other hand the continuous measurements at Djougou (Benin) with a superconducting gravimeter to monitor with a higher sampling rate the gravity changes related to an extreme hydrological cycle. Another section describes the actions planned in GPS which will maintain and develop the present-day existing network in West Africa. The third type of actions deals with hydrology and we review the three sites that will be investigated in this joint hydrogeophysics project namely Wankama (near Niamey) and Bagara (near Diffa) in the Niger Sahelian zone and Nalohou (near Djougou) in the Benin monsoon zone. We also address the question of the ground truth of satellite-derived missions: in this context the GHYRAF project will lead to test the hydrology models by comparison both with in situ and satellite data such as GRACE, as well as to an important increase of our knowledge of the seasonal water cycle in Africa. We finally present preliminary results in GPS based on the analysis of the vertical motion of the Djougou site. The resulting absolute gravity changes related to the 2008 monsoon are finally given.
ISSN: 0264-3707

hal-00475660
https://hal.archives-ouvertes.fr/hal-00475660
DOI : 10.1016/j.jog.2009.09.014

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Intraplate deformation is most often linked to major stress applied on plate margins. When such intraplate events are accompanied by magmatism, the use of several dating methods integrated within a multidisciplinary approach can bring constraints on the age, nature and source mobilized for generating the magma and in turn on the nature of the intraplate deformation. This study focuses on the large gabbro Arrikine sill (35 km in extension) emplaced within the Silurian sediments of the western margin of the Murzuq cratonic basin in southeastern Algeria. Its emplacement is dated during the early Devonian (415-400 Ma) through the determination of a reliable paleomagnetic pole by comparison with the Gondwana Apparent Polar Wander Path (APWP). This age can be correlated with deep phreatic eruptions before Pragian time thought to be at the origin of sand injections and associated circular structures in Algeria and Libya. For the sill, the K–Ar age of 325.6 ± 7.7 Ma is related to a K-rich aplitic phase that has K-enriched by more than 20% the Devonian gabbro. Laser-ICP-MS U–Pb method dates only inherited zircons mostly at c. 2030 Ma with additional ages at c. 2700 Ma and younger ones in the 766-598 Ma age range. The Arrikine sill is a high-Ti alkaline gabbro having the geochemical composition of a hawaiite akin to several intraplate continental and oceanic provinces, including the contemporaneous Aïr ring complexes province in Niger, but also to the Mauna Loa volcano in Hawaii. This peculiar composition akin to that of the contemporaneous Aïr province is in agreement with a lower Devonian age for the Arrikine sill.The lower Devonian Arrikine sill emplacement is related to a “Caledonian” transtensive reactivation of the western metacratonic boundary of the Murzuq craton. This event also generated in the Saharan platform the so-called “Caledonian unconformity” of regional extension, the Aïr ring complexes and magmatic rocks that produced sand injections. It could be related to rifting of the Hun terranes that occurred at the plate margin to the north (Stampfli and Borel, 2002, Blackey, 2008 and references therein). The mid-Carboniferous (c. 326 Ma) reactivation corresponds to Variscan compression on NW Africa generating aplitic fluids, but also to the major “Hercynian unconformity” of regional extension. The generation of the Arrikine magma is attributed to partial melting through adiabatic pressure release of uprising asthenosphere along tectonically reactivated mega-shear zones, here bordering the relictual Murzuq craton enclosed in the Saharan metacraton.
ISSN: 0899-5362

hal-01306637
https://hal.archives-ouvertes.fr/hal-01306637
DOI : 10.1016/j.jafrearsci.2015.11.019

Résumé : L'espèce Ludwigia leptocarpa (Onagracées) présente dans le paysage antillais est méconnue par la population locale. Pourtant, au Nigéria, ses feuilles sont préconisées pour traiter les rhumatismes, la dysenterie et pour leurs vertus laxative et vermifuge. L'absence de données phytochimiques sur cette plante justifie le choix de notre étude. Un criblage phytochimique réalisé sur les extraits bmts de feuilles, de fruits et de tiges a mis en évidence la présence de terpénoïdes dans les extraits hexane et dichlorométhane et des acides phénoliques et flavonoïdes dans les extraits méthanol et eau. L'évaluation du potentiel biologique des extraits apolaires des feuilles a révélé des activités antibiotique (E. coli et S. aureus) et anti-inflammatoire intéressantes. Les extraits plus polaires présentent des potentiels antioxydant, antibiotique (E. coli et S. aureus), antifongique (c. albicans et C. tropica/is), et antiviral (HSV-l) significatifs. L'étude des fractions volatiles de feuilles, de tiges et des parties aériennes par microextraction en phase solide a conduit à l'identification de 54 composés. Les analyses GC/MS menées sur les extraits apolaires de feuilles et de fruits ont mis en évidence la présence d'acides gras, de triterpènes et de stéroïdes. Le fractionnement et la purification des extraits polaires de feuilles ont mené à l'isolation et l'identification de 8 composés phénoliques parmi lesquels 1 acide polyhydroxylé, 3 acides phénoliques, 2 flavonoïdes et 2 tanins galliques. L'apport de nouvelles données scientifiques sur 1. leptocarpa contribue à la valorisation de cette matière végétale locale et laisse entrevoir des perspectives de recherche et d'application
Ludwigia Leptocarpa species (Onagraceae) is present in Caribean landscape, it remains unknown by French West Indies population. However, in Nigeria the leaves are recommended to treat rheumatism, dysentery and as laxative or deworming. The lack of data phytochemical on this plant justifies our study choice. A phytochemical screening carried out on crude extracts from leaves, fruits and stems highlighted terpenoids presence in hexane and dichloromethane crude extracts and phenolic compounds (phenolic acids and flavonoids) in methanol and water cmde extracts. The biological potentials evaluation of apolar extracts showed interesting antibiotic (E. coli and S. aureus) and inflammatory activities. Polar extracts present antioxidant, antibiotic (E. coli and S. aureus), antifungal (C albicans and C tropicalis), and viral (HSV-l) potential. Volatile fraction study of lcave, stems and aerial parts by Solid Phase MicroExtraction (SPME) 100 to theidentification of 54 compounds. GCIMS analysis conducted on leaves and fruits apolar extracts underlined the presence of fatty acid, triterpenes and steroids. Leaves polar extract fractionnation and purification resulted to isolation and identification of 8 phenolic componuds including 1 polyhydroxylated acid, 3 phenolic acids, 2 flavonoids and 2 gallic tannins. The addition of new scientific data on L. /eptocarpa contributes to the enhancement of this local plant rnaterial and suggests many opportunities for research and application

http://www.theses.fr/2013AGUY0676/document

Éditeur(s) : Paris : Société de Géographie
Siècle(s) traité(s) : 19
Droits : Domaine public
Provenance : Collectivité territoriale de Guyane. Bibliothèque Alexandre-Franconie
Permalien : http://www.manioc.org/patrimon/FRA11060
FRA11060