Éditeur(s) : HAL CCSD
Résumé : International audience
This paper shows how the notion of “local site of a question” helps the teacher to get into this question in order to teach it. We discuss the relationship between the description of what has to be deeply known to answer the difficulties or the obstacles which arise for the pupils during the study of a question, and what Shulman, and his successors, model under the name of pedagogical content knowledge. A survey, conducted among current French teachers, shows how they are powerless when facing the difficulties of their pupils and a study of some old teaching books shows how this problem was addressed in former teaching practices. Based on these results, we open the discussion of the training of the teachers.
L’article montre l’usage possible de la notion de « site local d’une question » dans le travail du professeur se préparant à enseigner cette question. On discute à cette occasion les proximités entre la description de ce qu’il y a à savoir profondément, pour répondre aux difficultés ou obstacles que rencontreront les élèves au cours de l’étude d’une question, et ce que Shulman et ses successeurs modélisent sous le terme de « pedagogical content knowledge ». Une enquête auprès de professeurs actuels montre comment ils sont démunis face aux difficultés des élèves, et une enquête dans des ouvrages d’enseignement anciens montre comment le problème soulevé a été traité en pratique par l’enseignement traditionnel. L’article discute alors le problème de la formation que les professeurs seraient en droit d’attendre.
Education & Didactique

hal-01530862
https://hal.univ-antilles.fr/hal-01530862

Éditeur(s) : Elsevier
Résumé : During the Fanindien 2006 cruise of R/V 'Beautemps-Beaupre', high resolution multibeam bathymetry, sub-bottom profiling and sediment coring was carried out along the East African margin, offshore Tanzania and Mozambique (Indian Ocean). The newly acquired data reveal the presence of a giant deep-sea valley (the Tanzania channel) that is more than 10 km wide at 4000 m water depth, along the continental rise. The valley remains similar to 70 m deep and 7 km wide at 800 km from the Tanzania coast. Morphological comparison with worldwide submarine channels show that the Tanzania channel is one of the largest known submarine valleys. This discovery brings new light on development of submarine valleys that drain sediments originated from the East African Rift System (EARS) highlands (i.e. the Tanzania channel and its neighbor Zambezi channel located similar to 1000 km southward). Both of the systems have a morphology markedly different to the classical sinuous, V-shaped channels located at similar latitudes (e.g. the Zaire or Amazon channels). Their submarine drainage system consists of a downslope converging tributary canyons joining a central trunk channel in the continental rise. The presence of such giant deep-sea drainage systems is probably linked to a strong structural control on the sediment pathway, associated to a massive sediment transfer towards the Indian Ocean in relation with the tectonic activity of the East African Rift System (i.e. the uplift periods trough mid-Miocene and Plio-Pleistocene times) and its interplay with the East African equatorial climate changes.
Marine Geology (0025-3227) (Elsevier), 2008-12 , Vol. 255 , N. 3-4 , P. 179-185

Droits : 2008 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/00324/43491/42958.pdf
DOI:10.1016/j.margeo.2008.09.002
http://archimer.ifremer.fr/doc/00324/43491/

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
A new genus and species of deep-sea eelpout (Zoarcidae), Barbapellis pterygalces, is herein described from a single adult female specimen carrying eggs and measuring 204 mm in total length. It was collected on the eastern Antarctic continental slope, off Terre Ad,lie, at ca. 1,200 m depth, on muddy bottom. Barbapellis is placed in the subfamily Gymnelinae and can be distinguished from all other genera by morphological characters unusual in zoarcids as well as by molecular barcoding. The genus is characterized by the presence of a complex system of cephalic skin crests and flaps, especially well developed around the mouth. A new terminology is proposed for the eleven crests and sevenfolds described. The skin folds may be used for foraging on muddy sea bottoms. The genus is also characterized by large, flexible, and highly palmate pectoral fins. The designation of the new genus is discussed.
ISSN: 0722-4060

hal-01544913
https://hal.archives-ouvertes.fr/hal-01544913
DOI : 10.1007/s00300-011-1057-3

Éditeur(s) : HAL CCSD Cambridge University Press (CUP)
Résumé : We present detailed biostratigraphy based on conodonts and palaeoenvironmental trends deduced from microfacies and conodont abundance through the Famennian (Late Devonian) at Col des Tribes (Montagne Noire, France). The succession is characterized by micritic limestones deposited in settings oscillating between mid to outer ramp. Facies contain poor fauna, widely dominated by nektonic organisms. This section is complete and one of the most conodont-rich for the Famennian of the north Gondwana-related area. The Upper Kellwasser event (Frasnian–Famennian boundary) and the Hangenberg (Devonian–Carboniferous boundary) have been lithologically identified. They are characterized by decimetre-thick black dysoxic to anoxic argillaceous sediments. The Condroz and annulata events, although not materialized by lithological changes, have been positioned due to the precise stratigraphy. The first event occurred during the deposition of condensed ferruginous facies (griotte limestones) and the second event during the deposition of micrites barren of benthic fauna. The combination of information from both facies and conodont biofacies changes allows a general sea-level curve through the entire Famennian for north Gondwana to be proposed for the first time. At Col des Tribes, the general trend is a slight deepening upwards from triangularis to trachytera zones, then a pronounced shallowing-upwards trend from upper trachytera to praesulcata zones. This curve correlates with the well-known reference curve from Euramerica concerning the late Famennian (trachytera to praesulcata Zones). There are some discrepancies in minor cycles which can be explained by tectonical phenomena at the onset of the edification of the Variscan belt in Europe.
ISSN: 0016-7568

hal-01115222
https://hal.archives-ouvertes.fr/hal-01115222
DOI : 10.1017/S0016756813000927

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
New outcrops in the Sinis peninsula (Sardinia, Italy) allow a detailed description of the Messinian erosion surface. The correlation between outcrops, industrial seismic data and data collected offshore Oristano from a recent cruise permits reconstruction of the geometry of this surface from presently emerged interfluves to the deep canyons offshore, with: - onshore: an eroded karstic plateau presently cropping out over a 20 km × 5 km area. Well-preserved karst structures occur locally and can form several metres high reliefs. The southernmost edge of the plateau is limited by a cliff. The karstic plateau and the cliff are sealed by transgressive deposits of Pliocene age; - offshore, an interfluve zone with a mostly flat and low-angle dipping plateau, westward dissected by paleovalleys which were identified down to a depth of 2000 m. In the Oristano Gulf, Messinian paleovalleys were also identified. The Capo San Marco paleocliff was probably located on the edge of a canyon. Onshore, only one major erosion surface was identified, located at the top the Messinian sequence. Offshore, this surface extends down to the abyssal plain. The surface was emplaced above deposits related to the Terminal Carbonate Complex. This indicates that the marginal evaporites are older than the major drawdown of the Mediterranean sea-level. The major drawdown is related to the deposition of the deep evaporites.
ISSN: 0037-0738

hal-00407864
https://hal.archives-ouvertes.fr/hal-00407864
DOI : 10.1016/j.sedgeo.2008.06.005

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The active collision zone around Taiwan orogen receives a variety of sedimentary inputs, including terrigenous flux from Taiwan and Chinese rivers, oceanic currents and atmospheric dust. In order to determine the present-day respective contributions of these different sources, we analysed the Pb and Sr isotopic compositions of late Quaternary sediments accumulated offshore east Taiwan. Samples from the Taiwan Coastal Range (andesites, sandstones, conglomerate and Peinan River terraces and suspended loads) have also been analysed to constrain the mean Taiwan isotopic signature. Mixing lines between the different sources of material indicate that the core located in the Okinawa Trough represents a mixture of about 60% of Taiwan, 30% of Chinese Loess and 10% of Yangtze River contributions. The southernmost core, located close to Luzon Are, is influenced by Taiwan (60%) and volcanic material (40%). The Sr and Pb isotopic compositions of samples cored in the Manila Trench and in the Huatung Basin are strongly influenced by the Taiwan signature, while the Ryukyu Trench core samples point to significant but variable contributions of Chinese Loess and Yangtze River. This work also reports Zn isotopic variations in the silicate fraction of these marine core samples. The overall variation in Zn isotopic compositions (expressed as 666 Zn) is greater than 0.3 per mil (parts per thousand) for an analytical precision of +/- 0.05 parts per thousand. The Zn isotopic signal for most of the marine core samples is similar to the literature data measured on sedimentary material, except for the Manila Trench core samples and the older sample from the Huatung Basin: they present values heavier by 0.2-0.3 parts per thousand, close to those obtained on all Taiwan rocks and Peinan River particulates. These results show: 1- the particular characteristics of Taiwan Zn isotopic compositions on a large scale; and: 2- the possible use of Zn isotopes as a tracer of material sources.
ISSN: 0009-2541

hal-00412214
https://hal.archives-ouvertes.fr/hal-00412214
DOI : 10.1016/j.chemgeo.2007.10.024

Éditeur(s) : HAL CCSD Linnean Society of London
Résumé : International audience
Although migratory pelagic fishes generally exhibit little geographic differentiation across oceans, as expected from their life-history (broadcast spawning, pelagic larval life, swimming ability of adults) and the assumed homogeneity of the pelagic habitat, exceptions to the rule deserve scrutiny. One such exception is the narrow-barred Spanish mackerel (Scomberomorus commerson), where strong genetic heterogeneity at the regional scale has been previously reported. We investigated the genetic composition of S. commerson across the Indo-West Pacific range using control-region sequences (including previously published datasets), cytochrome-b gene partial sequences, and eight microsatellite loci, to further explore its phylogeographic structure. All haplotypes sampled from the Indo-Malay-Papua archipelago (IMPA) and the southwestern Pacific coalesced into a clade (Clade II) that was deeply separated (14.5% nucleotide divergence) from a clade grouping all haplotypes from the Persian Gulf and Oman Sea (Clade I). Such a high level of genetic divergence suggested the occurrence of two sister-species. Further phylogeographic partition was evident between the western IMPA and the regions sampled east and south of it, i.e. northern Australia, West Papua, and the Coral Sea. Strong allele-frequency differences were found between local populations in the southwestern Pacific, both at the mitochondrial locus (ΦST=0.282-0.609) and at microsatellite loci (^θ=0.202-0.313). Clade II consisted of four deeply divergent subclades (9.0-11.8% nucleotide divergence for the control region; 0.3-2.5% divergence at the cytochrome b locus). Mitochondrial sub-clades within Clade II generally had narrow geographic distribution, demonstrating further genetic isolation. However, one particular haplogroup within Clade II was present throughout the central Indo-West Pacific; that haplogroup was found to be sister-group to an haplogroup restricted to West Papua and the Coral Sea, yielding evidence of recent secondary westward colonization. Such a complex structure is in sharp contrast with the generally weak phylogeographic patterns uncovered to date in other widely distributed, large pelagic fishes with pelagic eggs and larvae. We hypothesize that in S. commerson and possibly other Scomberomorus species, philopatric migration may play a role in maintaining the geographic isolation of populations by annihilating the potential consequences of passive dispersal.
ISSN: 0024-4066

ird-00759711
http://hal.ird.fr/ird-00759711
http://hal.ird.fr/ird-00759711v2/document
http://hal.ird.fr/ird-00759711/file/FauvelotBorsa_Scomberomorus%20commerson%20p%20HAL.pdf

Résumé : The MEDECO Leg 2 cruise followed the MEDECO Leg 1 cruise that had crossed the Mediterranean Sea from the west to the east to study benthic communities of the Var canyon, deep corals found on the Calabrian Margin and cold seep ecosystems of the Mediterranean Ridge. The main objective of the MEDECO Leg 2 cruise was to study and compare, using a multidisciplinary approach, the structure and dynamics of deep-sea ecosystems at various active cold seep sites from the Nile deep sea fan and the Calabrian Arc, in the Eastern Mediterranean sea. During MEDECO Legs 1 & 2, a multiscale strategy was promoted to integrate (1) a high resolution cartography of geological structures (km2 scale), (2) a detailed mapping, including video imagery, of smaller-scale areas (scale 100 to 300 m2), (3) the physical, chemical and sedimentary characteristics of the habitat (multiscale), (4) the structure and functioning of faunal communities, including microbes, in terms of composition, diversity and biomass (multiscale), (5) small scale studies of interactions between organisms and their environment (scale < m2), (6) detailed ecophysiological studies at the organism scale on invertebrates. The use of the ROV “Victor 6000” and of various equipments for in situ and ex situ observations and measurements has helped reaching our objectives. The MEDECO cruise represented the key-Mediterranean cruise of the HERMES project “Hotspot Ecosystem Research on the Margins of European Seas” (P.I. P. Weaver, NOC-Southampton). The cruise was organized to follow the objectives of the HERMES program to better understand the functioning of deep ecosystems of the continental margins aiming at obtaining: (1) the description and quantification of the natural drivers (geological, hydrological, chemical factors) that control the distribution of ecosystems on margins; (2) the characterization and quantification of biodiversity, from bacteria to megafauna, as well as the knowledge of ecosystem functioning; (3) the study of ecosystems dynamics including the biology/physiology of key-species. Specific objectives. Colonization experiments conducted in the frame of two European programs, Diwoo and Chemeco, have given the opportunity to recover the fauna installed in the devices deployed during the Bionil cruise (2006) and to deploy new ones at the same site located in the pockmark area of the central province of Nile deep sea fan.

Droits : 2008 Insu, Cnrs, Locean
http://archimer.ifremer.fr/doc/00134/24550/22583.pdf
http://archimer.ifremer.fr/doc/00134/24550/

Éditeur(s) : Elsevier
Résumé : The long-term BIOZAIRE multidisciplinary deep-sea environmental program on the West Equatorial African margin organized in partnership between Ifremer and TOTAL aimed at characterizing the benthic community structure in relation with physical and chemical processes in a region of oil and gas interest. The morphology of the deep Congo submarine channel and the sedimentological structures of the deep-sea fan were established during the geological ZAIANGO project and helped to select study sites ranging from 350 to 4800 m water depth inside or near the channel and away from its influence. Ifremer conducted eight deep-sea cruises on board research vessels between 2000 and 2005. Standardized methods of sampling together with new technologies such as the ROV Victor 6000 and its associated instrumentation were used to investigate this poorly known continental margin. In addition to the study of sedimentary environments more or less influenced by turbidity events, the discovery of one of the largest cold seeps near the Congo channel and deep coral reefs extends our knowledge of the different habitats of this margin. This paper presents the background, objectives and major results of the BIOZAIRE Program. It highlights the work achieved in the 16 papers in this special issue. This synthesis paper describes the knowledge acquired at a regional and local scale of the Equatorial East Atlantic margin, and tackles new interdisciplinary questions to be answered in the various domains of physics, chemistry, taxonomy and ecology to better understand the deep-sea environment in the Gulf of Guinea.
Deep Sea Research Part II: Topical Studies in Oceanography (0967-0645) (Elsevier), 2009-11 , Vol. 56 , N. 23 , P. 2156-2168

Droits : 2009 Elsevier Ltd All rights reserved.
http://archimer.ifremer.fr/doc/2009/publication-7349.pdf
DOI:10.1016/j.dsr2.2009.04.015
http://archimer.ifremer.fr/doc/00000/7349/

Éditeur(s) : Elsevier
Résumé : During the Fanindien 2006 cruise of R/V 'Beautemps-Beaupre', high resolution multibeam bathymetry, sub-bottom profiling and sediment coring was carried out along the East African margin, offshore Tanzania and Mozambique (Indian Ocean). The newly acquired data reveal the presence of a giant deep-sea valley (the Tanzania channel) that is more than 10 km wide at 4000 m water depth, along the continental rise. The valley remains similar to 70 m deep and 7 km wide at 800 km from the Tanzania coast. Morphological comparison with worldwide submarine channels show that the Tanzania channel is one of the largest known submarine valleys. This discovery brings new light on development of submarine valleys that drain sediments originated from the East African Rift System (EARS) highlands (i.e. the Tanzania channel and its neighbor Zambezi channel located similar to 1000 km southward). Both of the systems have a morphology markedly different to the classical sinuous, V-shaped channels located at similar latitudes (e.g. the Zaire or Amazon channels). Their submarine drainage system consists of a downslope converging tributary canyons joining a central trunk channel in the continental rise. The presence of such giant deep-sea drainage systems is probably linked to a strong structural control on the sediment pathway, associated to a massive sediment transfer towards the Indian Ocean in relation with the tectonic activity of the East African Rift System (i.e. the uplift periods trough mid-Miocene and Plio-Pleistocene times) and its interplay with the East African equatorial climate changes. (C) 2008 Elsevier B.V. All rights reserved.
Marine Geology (0025-3227) (Elsevier), 2008-12 , Vol. 255 , N. 3-4 , P. 179-185

Droits : 2008 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/2008/publication-6855.pdf
DOI:10.1016/j.margeo.2008.09.002

Éditeur(s) : Pergamon-elsevier Science Ltd
Résumé : The late Quaternary has experienced large glacial/interglacial climatic variations and related 10's to 100 meters high-amplitude sea level fluctuations at Milankovich frequencies from 10's to 100 kyr during which carbonate platform tops have been exposed and re-flooded in many occasions. This study focuses on the accumulation of calci-turbidites, the aragonite onset/sharp increase in fine sediments and their timing in deep basins adjacent to carbonate platforms. A particular emphasis is developed on the occurrence of the first gravity flow event and aragonite onset/sharp increase and their linkage to the initial re-flooding of the platform tops during deglaciations. Three basins adjacent to isolated platforms in the Bahamas, the Northern Nicaragua Rise, and the Gulf of Papua, were selected to represent pure carbonate versus mixed systems, in quiescent versus tectonically active settings, and various carbonate bank top morphologies, ranging from atoll to relatively deeply and narrowly flooded flat top banks. In spite of these differences, each record illustrates a clear relationship between the timing of platform top re-flooding and initiation of significant carbonate export by gravity flows and low-density plumes into the surrounding basins. The concept of "re-flooding window" is introduced to characterize the prolific period of time during which bank and atoll-tops are flooded enough to produce large export of bank-derived aragonite and of calci-turbidites in adjacent basins. According to our datasets, the main re-flooding windows have occurred mainly on the last part of the sea level rise at each glacial termination (T), those periods being marked by some of the highest rates of sea level rise. The analysis of a long-piston core from the earthquakes-prone Walton Basin (Northern Nicaragua Rise) demonstrates that sea level, not seismic activities, played a major role as trigger mechanism for the initiation of gravity flows since the last four glacial/interglacial transitions, and supports the existence of an extra glacial termination during the early portion of the transition from MIS 7.4 to MIS 7.3 (TIIIA). (C) 2010 Elsevier Ltd. All rights reserved.
Quaternary Science Reviews (0277-3791) (Pergamon-elsevier Science Ltd), 2010-08 , Vol. 29 , N. 17-18 , P. 2010-2026

Droits : 2010 Elsevier Ltd All rights reserved.
http://archimer.ifremer.fr/doc/00012/12298/9095.pdf
DOI:10.1016/j.quascirev.2010.04.016
http://archimer.ifremer.fr/doc/00012/12298/

Éditeur(s) : HAL CCSD
Résumé : Satellite and in situ chlorophyll concentration data collected as part of VALidation HYperspectral of a BIOgeochemical model (ValHyBio), a PNTS-sponsored project dedicated to satellite ocean-colour imaging of the Southwest Pacific, are analyzed to describe chlorophyll variability in the Coral Sea, a vast oligotrophic region characterized by a deep chlorophyll maximum and blue waters of high transparency. Average chlorophyll concentrations estimated from MODIS-Aqua are very low (<0.2 mg m-3) except in the vicinity of main islands and coral reefs, where enrichment may occur due to upwelling or internal waves that bring nutrients to the euphotic zone from the deep part of the water column. During the summer season, blooms of cyanobacteria (Trichodesmium) develop in the surface waters and may form large slicks. The nitrogen fixed by these slicks is a potential source of new nitrogen later assimilated by picoplankton and the marine food chain. Coastal areas exhibit higher chlorophyll concentrations because of nutrient input from the land, as observed in 2008 around New Caledonia. In lagoon areas, the sea colour is influenced by turbidity and bathymetry, and the MODIS OC3 algorithm is inadequate, with a systematic overestimation of chlorophyll concentration in the New Caledonia lagoon. Improved bio-optical algorithms are needed for those turbid and shallow waters, to allow not only a better description of chlorophyll variability, but also evaluation of chlorophyll simulations by recently developed biogeochemical models.
of the 12th International Coral Reef Symposium, 18E
CAIRNS, Australia

hal-00746470
https://hal.archives-ouvertes.fr/hal-00746470
https://hal.archives-ouvertes.fr/hal-00746470/document

Éditeur(s) : HAL CCSD
Résumé : The Deep Basin of the Gulf of Mexico (DBGM) extends over eastern Mexico, the southeastern part of the United States, west of the Atlantic Ocean. This study, based on the interpretation and integration of seismic profiles, exploration wells and outcrop studies, focus on the deep part of the Gulf of Mexico, where bathymetry varies from 200 to 3750 m, thus comprising both the continental slope and the abyssal plain. The first part of this thesis focus on the description of the sedimentary infill of the western part of the Gulf of Mexico, in the Veracruz State, and to its geodynamic controls. The geodynamic evolution of the Deep Basin of the Gulf of Mexico (DBGM) begins during the Triassic-Jurassic with the break-up and the opening of a continental rift, in the southern part of the North American lithospheric plate. This opening induced a relative movement of the Yucatan Block towards the southeast. This intra-continental rifting episode was followed by a stage of post-rift thermal subsidence in the basins of the continental margin in the west, coeval with oceanic accretion in the DBGM. The thermal subsidence of the margin was subsequently modified by the Laramian orogeny, which impacted strongly the overall architecture of the margin as well as its litho-stratigraphic evolution, inducing the deposition of siliciclastic deposits in various morphotectonic provinces: i.e., near the tectonic front of the Sierra Madre Oriental (SMO), within the adjacent Chicontepec foreland basin, over the Tuxpan Platform (Golden Lane), across the continental slope and up to the deep abyssal plain, these two last morphotectonic provinces belonging to the DBGM. During the Early Paleogene, the effects of the thermal subsidence of the passive margin were stressed by the tectonic load of the Laramian orogen (i.e., the Sierra Madre Oriental, SMO), thus allowing the development of a foreland basin flexural. In this geodynamic framework, the main sedimentary transfers developed from the tectonic front "SMO" in the west, towards the DBGM in the east, the main source for clastic sediments being linked to the erosion of the "SMO" mountains. During the Paleocene and the Early Eocene, the architecture of the silici-clastic syn-tectonic sediments deposited in submarine fans was characterized by sliding, turbidites with A and B Bouma facies, as well as levees and channels. After the stop of the flexural subsidence, the thermal subsidence of the passive margin resumed during the Late Eocene, the Oligocene and the Neogene, allowing the development of a new sedimentary prism, prograding eastwards toward the DBGM. This sedimentary infill was again made up of levees-channels, sand bars and delta systems. During the Neogene, an extensional system with listric faults and roll-over features developed across the slope of the DBGM, due to an active detachment developing within overpressured Eocene-Oligocene clays. This gravitational gliding of Neogene series accounted also for the development of compressional features at the toe of the slope. Approximately 60% of the Miocene siliciclastic sediments have been trapped in growth strata and slope basins associated with this complex gravitational system, ranging from river-delta features towards gravity slides associated with slump facies. The second part of this thesis aims at a quantification of these various processes, including the construction of balanced cross sections, forward Thrustpack kinematic modelling coupling the development of a basal detachment, lithospheric flexure, erosion and sedimentation, as well as subsequent stratigraphic modelling with the Dionisos software, the later aiming at predicting the sand versus clay ratios in Neogene siliciclastic deposits of the DBGM and its surroundings.
Le bassin profond du Golfe du Mexique (BPMG) est localisé à l'est du Mexique, au sud-est des États-Unis et à l'ouest de l'Océan Atlantique. Cette étude de la partie profonde du Golfe du Mexique est basée sur l'intégration de données de sismique, de forages pétroliers et d'études de terrain; elle comprend toute la pente continentale et la plaine abyssale, avec une bathymétrie qui varie de 200 à 3750 m. La première partie de cette thèse est consacrée à la description du remplissage sédimentaire de la bordure occidentale du Golfe du Mexique, dans le secteur de Veracruz, en liaison avec son évolution géodynamique. L'évolution géodynamique du BPMG commence au Trias-Jurassique avec la rupture et la propagation d'un rift continental, dans le secteur sud de la plaque nord américaine. Cette ouverture et le déplacement relatif vers le sud-est du bloc crustal du Yucatan sont à l'origine du BPGM. Cette géodynamique de rift continental est suivie d'une étape post-rift accompagnée de l'océanisation du bassin. Les bassins de la marge passive ont poursuivi leur évolution sous l'effet de la subsidence thermique à l'ouest du Golfe du Mexique, tandis que de la croûte océanique se formait dans le BPGM. Cette subsidence thermique de la marge a ensuite été perturbée par l'orogénèse Laramienne, qui a remodelé l'architecture stratigraphique silico-clastique des dépôts du Tertiaire entre les éléments morphotectoniques suivants: lefront tectonique de la Sierra Madre Orientale (SMO), le bassin d'avant-pays Chicontepec, la Plateforme de Tuxpan-Faja de Oro, la pente continentale et la plaine abyssale, ces deux dernières provinces morphotectoniques appartenant au BPGM. Pendant le Paléogèneinférieur, les effets de la subsidence thermique de la marge passive ont été accentués par la charge tectonique de l'orogénèse laramienne (SMO), permettant ainsi le développement d'un bassin flexural d'avant-pays. Au cours de cette étape, les principaux transferts sédimentaires se sont effectués du front tectonique "SMO" vers le BPGM. La source principale de sédiments clastiques est liée à l'érosion de la chaîne de montagnes "SMO". Pendant le Paléocène et l'Éocène inférieur, l'architecture des premiers sédiments silico-clastiques syn-tectoniques déposés dans des éventails sous-marins sont caractérisés par des figures de glissement, des faciès turbiditiques A et B de Bouma, des chenaux-levées. Après l'arrêt de la subsidence flexurale, la subsidence thermique de la marge passive s'est poursuivie pendant l'Éocène supérieur, l'Oligocène et le Néogène, permettant le développement d'un nouveau prisme sédimentaire progradant. Les remplissages sédimentaires sont encore constitués de chenaux et de levées, avec des barres de sable associées à des systèmes deltaïques sur la plateforme. Pendant le Néogène, un système de failles listriques s'est développé sur la pente du BPGM, au-dessus d'une surface de décollement située, dans la région d'étude, dans les argiles de l'Éocène-Oligocène. Ce système de failles de croissance a piégé plus de 60% des sédiments silico-clastiques du Miocène. Ce remplissage sédimentaire évolue latéralement de faciès fluviaux deltaïques vers des faciès de pente affectés de glissements gravitaires et associés à des turbidites. La deuxième partie de cette thèse est consacrée à une approche quantitative basée sur des modélisations structurales (coupes équilibrées et modélisations cinématiques directes avec Thrustpack, couplant décollement gravitaire, flexure lithosphérique, érosion et sédimentation), puis sédimentaires (prise en compte des transferts de matériel clastique depuis la partie émergée de la chaîne jusqu'au bassin profond, à l'aide du logiciel Dionisos, afin de mieux comprendre les processus de piégeage des sédiments grossiers dans les structures de croissance et les bassins perchés de la marge.
https://tel.archives-ouvertes.fr/tel-00435120

tel-00435120
https://tel.archives-ouvertes.fr/tel-00435120
https://tel.archives-ouvertes.fr/tel-00435120/document
https://tel.archives-ouvertes.fr/tel-00435120/file/thesealzaga.pdf

Éditeur(s) : HAL CCSD
Résumé : Sand intrusions (or injectites) are most often the product of post-depositional remobilization of sand leading to its injection into the surrounding rocks. While injectites were recognized for the first time nearly 200 years ago, their emplacement process has been studied for a couple of decades only, since the concepts of deep sea depositional environments have allowed us to better understand their emplacement processes. However, these processes are still relatively poorly understood. Our approach is based on the study of injectites in the Lower Congo Basin from seismic and well data, which we compare to a fossil system in the SE France basin. We have shown that: (1) In buried turbidite channel systems draping deposits on the channel flanks and terraces of channels have the same geophysical signature as 'wing-like' injectites. Finally, the only criterion for identifying seismic injectites is the presence of bedding-discordant seismic reflections, and in the best case the associated uplift of the overlying seismic reflectors. (2) Seismic-scale conical and saucer-shaped sand injectites have been identified in the Lower Congo Basin. The remobilization is likely due to overpressuring induced by the buoyancy effect of hydrocarbons trapped in the margins of a lobe buried underneath 160 m of sediment, followed by the sudden injection of fluidized sand associated with fault reactivation of faults (with a possible role of nearby salt diapirs). (3) A network of injectites (dykes, sills/wings and laccoliths) was formed in the Vocontian basin during the late Albian and/or early Cenomanian, from a lower-middle Albian turbidite channel. The emplacement is probably due to the early compartmentalization of the channel during its burial and the increase of the sedimentation rate generating overpressure; and the subsequent large influx of deep fluids triggering injection. The injection of sand was polyphased: a first episode formed the sills and another emplaced the dykes. Sills/wings and dykes propagated about 2 km laterally away from the parent sand body and about 200 m up to the surface, revealing a much more extended lateral than vertical reach, contrary to the classically accepted idea from the interpretation of seismic data. (4) The emplacement of this large network of injectites was governed by hydrofracturing. Therefore, its morphology is dependent on the host rock heterogeneity (isotropy, fractures), the paleo-stress orientation (ó3 = NW-SE) and the burial depth of the source (300-600 m) at the time of injection. The study of this fossil network allows us to define the relationship between morphology of the injected network and stress state at the time of injection. This relationship can be extrapolated to constrain the morphology of subsurface networks beyond seismicvisibility. (5) Sands injected into low permeability lithologies bear evidence to a major event of fluid escape in the studied basin, but also channeled fluids long after their formation. In this way, injectites both attest to specific episodes of fluid migration in sedimentary basins and contribute to long-lived re-routing of migrating fluids once emplaced. The injection of sand is associated with the sudden escape of fluids, probably resulting from a significant tectonic and/or sedimentary event; in addition, the architecture of injectite networks is governed by the local paleo-stress and heterogeneity in the host rock. Consequently, characterizing injectite networks is an important step in understanding the plumbing systems of continental margins, i.e. the post-depositional evolution of sedimentary basins.
Les intrusions sableuses (ou injectites) sont le plus souvent le produit de la remobilisation post-dépositionnelle des sédiments et de l'injection du sable dans les roches environnantes. Bien que reconnues pour la première fois il y a près de 200 ans, elles ne sont réellement étudiées que depuis quelques dizaines d'années, depuis que les concepts sur les environnements de dépôt dans les domaines marins profonds nous permettent de mieux comprendre les processus de mise en place. Cependant, ces processus restent encore aujourd'hui relativement mal compris. Notre approche repose sur l'étude d'injectites dans le bassin du Bas-Congo a partir de données de sismique et de puits que nous comparerons a un système fossile dans le bassin du SE de la France. Nous avons montre que : (1) Dans des systèmes de chenaux turbiditiques enfouis, les dépôts de drapage sur les marges et terrasses de chenaux présentent la même signature géophysique que les injectites de type "wing". Finalement, le seul critère sismique d'identification des injectites est la présence de réflexions sismiques sécantes vis-a-vis de la stratigraphie associée dans le meilleur des cas au soulèvement des réflecteurs sismiques sus-jacents. (2) Des injectites d'échelle sismique en forme de cône et d'assiette ont été identifiées dans le bassin du Bas-Congo. La remobilisation résulte probablement des pressions anormales induites par l'effet de flottabilité des hydrocarbures piégés dans les marges d'un lobe enfoui sous 160 m de sédiment, puis de l'injection soudaine du sable fluidise associée a la réactivation de failles (possible rôle des diapirs de sel a proximité). (3) Un réseau d'injectites (dykes, sills/wings et laccolites) s'est formé dans le bassin Vocontien entre la fin de l'Albien supérieur et/ou le début du Cénomanien, depuis un chenal turbiditique de l'Albien inférieur-moyen. La mise en place résulte probablement de la compartimentalisation précoce du chenal au cours de son enfouissement et de l'augmentation du taux de sédimentation générant la surpression et de l'apport ulterieur d'importante quantité de fluides profonds déclenchant l'injection. L'injection du sable a été polyphasée : une première injection a formé des sills et une suivante des dykes. Les sills/wings et les dykes se sont propagés latéralement au chenal source sur environ 2 km et vers la surface sur environ 200 m, mettant en évidence une forte remobilisation latérale plutôt que verticale, contrairement a l'idée classiquement admise a partir de l'interprétation des données sismiques. (4) La formation de ce large réseau d'injectites a été gouvernée par des mécanismes d'hydrofracturation. Par conséquent, sa morphologie a été dépendante des hétérogenéités de la roche hôte (milieu isotrope, fracture), des directions de paléo-contraintes (ƒÐ3 = NWSE) et de la profondeur d'enfouissement de la source (300-600 m) au moment de l'injection. L'étude de ce réseau fossile permet de définir les relations entre morphologie du réseau injecté et état de contraintes au moment de l'injection. Cette relation peut être extrapolée de façon à contraindre la morphologie des réseaux de subsurface au-delà de la visibilité sismique. (5) Les sables injectés dans des lithologies de faible perméabilité témoignent d'un épisode d'échappement de fluide important dans les bassins étudiés mais ont aussi guide les fluides longtemps après leur formation. Les injectites contribuent ainsi a l'initiation épisodique et la pérennisation de migrations de fluides dans les bassins sedimentaires. Le processus d'injection est associé a l'échappement brutal de fluides, résultant vraisemblablement d'un évènement tectonique et/ou sédimentaire important, et l'architecture des réseaux d'injectites est gouverné par les paléo-contraintes locales et les hétérogénéités de la roche hôte. Par conséquent, la caractérisation des réseaux d'injectites est une étape importante dans la compréhension de la plomberie des marges, c'est-a-dire l'évolution post-dépôt des bassins sédimentaires.
https://tel.archives-ouvertes.fr/tel-01011486

tel-01011486
https://tel.archives-ouvertes.fr/tel-01011486
https://tel.archives-ouvertes.fr/tel-01011486/document
https://tel.archives-ouvertes.fr/tel-01011486/file/These_Monnier_2013_banalisee.pdf

Éditeur(s) : HAL CCSD
Résumé : This work focus on the characterization of the source and dynamic of compactional fluids during sedimentary burial, through two complementary examples of late orogenic oil‐field half‐grabens: The exhumed Lodève Permian Basin and a deep buried Jurassic basin in the North Viking Graben (North Sea).Constituting the main part of the thesis, a multi‐disciplinary approach was conducted in the Lodève Basin where Ba‐F‐Cu‐Pb polymetallic mineralized systems are trapped into synrift faults and paleokarsts in the carbonate basement at the hinge point of the rollover. The source, timing and P/T conditions of fluid migration were deduced from the analysis of the microfabric, the fluid inclusions microthermometry, and the isotopic (Sr, S, O, H) and Rare Earth Element (REE) signature. Results are then crossed with a structural and thermal modeling that consolidates the sequence and dynamics of fluid during burial.A similar approach was conducted in the North Viking Graben where fluid markers are restricted to 3D seismic and well core data. Comparable Ba‐Pb‐Zn veins are reported in basin margin, plugging one of the most important siliciclastic hydrocarbon reservoir in the substratum. This analysis provides additional constraints on basinal fluid behavior and allows us to propose a global dynamic model for various compositions of fluids and reservoirs.We conclude to a polyphase fluid sequence history including:(a) In the carbonate basement of the Lodève Basin, karstic paleocanyon incisions and associated cavities coupled to synrift fault, act as major drain for fluids. These structures are early affected by hypogen‐sulfuric karstification in response to the interaction between bacterial oxidation of sulfides entrapped within Lower Permian blackshales and the basement oxidizing aquifer.(b) Disequilibrium compaction initiates overpressure‐driven basinal fluid migration towards basin margins, characterized by temperatures around 150‐180°C and salinities between 9 et 18wt%eq.NaCl. Isotopic (Sr, S, O) and REE analyses reveal that Ba‐M+‐rich mineralizing fluids derived mainly from buried blackshales diagenesis. External fluids coming from the lower crust are also identified that play a key role in fluorite precipitation by the leaching of late hercynian granites (mean temperature of 250°C and salinity > 20wt%eq.NaCl).(c) During the synrift period, fluid overpressure is responsible for the periodic reactivation of fault plane according to seismic‐valve process, bedded‐control shearing and hydraulic brecciation at the basement‐seal interface. These mechanisms induce cyclic polymetallic mineralization by the mixing between in‐situ formation water and deep ascending basinal fluids.(d) Thermogenic fluids expulsion starts with last basinal fluids during late burial stage. Hydrocarbons thus migrate along the same regional pathways up to the rollover crest, where they are partly rerouted by the previous mineralized baffle.(e) In the Lodève basin, post‐rift exhumation of the margins led to the remobilization of synrift deposits by subaerial biochemical processes at the sulfate‐methane transition. The latter results from the interaction between the still active hydrocarbon dysmigration with a playa lake sulfate‐rich aquifer. Secondary low‐temperature barite fronts precipitate then within basement meteoric karsts.In addition to the « source to sink » model of basinal fluids, this work provides new insights on the early plugging of hydrocarbon reservoirs and for the metallogenesis of Mississippi Valley‐Type deposits.
Ce travail porte sur la caractérisation de la source et de la dynamique des fluides de bassin au cours de leur chargement à travers deux exemples complémentaires de demi‐grabens tardi‐orogéniques pétroliers : Le Bassin Permien de Lodève, aujourd’hui à l’affleurement et un bassin jurassique enfouis dans le North Viking Graben (Mer du Nord).Le coeur de la thèse concerne le Bassin de Lodève où, à partir d’une approche pluridisciplinaire intégrée, nous avons caractérisé l’architecture des minéralisations (Ba, F, Cu, Pb) piégées dans un réseau paléokarstique alimenté par les failles syn‐rift, dans le substratum carbonaté à l’apex du roll‐over. La source, le calendrier et les conditions de migration des fluides ont été approchés à partir de l’analyse de la micro‐fabrique, la microthermométrie sur inclusions fluides, les analyses isotopiques (Sr, S, O, H) et de Terres Rares. Les résultats analytiques ont été enfin croisés avec un modèle thermique et structural du bassin qui conforte la séquence et la dynamique du système fluide en cours d’enfouissement.Une démarche similaire, mais plus limitée, a été conduite dans le bassin du North Viking Graben où l’accès aux marqueurs fluides est restreint aux données de sismique 3D et de carottes. Comme à Lodève, les minéralisations Ba‐Pb‐Zn colmatent un réservoir dans le substratum à l’apex du roll‐over. Elles se présentent sous forme de ciments dans des grès ou des fractures. Cette analyse apporte des contraintes complémentaires et permet de proposer un modèle dynamique général avec des variantes en fonction de la nature des fluides et des réservoirs.On retiendra donc la séquence fluide suivante :(a) Dans le cas du bassin de Lodève sur substratum carbonaté, les chemins préférentiels de drainage se développent dans des paléocanyons N‐S couplés à un réseau de fractures et d’endokarsts météoriques. Ces derniers sont élargis en début de rifting par la dissolution hypogène sulfurique produite par l’oxydation bactérienne des sulfates et des pyrites des blackshales, au contact de l’aquifère oxydant du Cambrien.(b) Le déséquilibre de compaction initie la migration des fluides interstitiels en surpression vers les marges avec des températures autour de 150‐180°C et des salinités entre 9 et 18wt%eq.NaCl. Les analyses isotopiques (Sr, S, O) révèlent que la majorité des fluides provient de l’altération diagénétique des blackshales riches en métaux. Des interactions sont également mises en évidence avec des fluides profonds (entre 240°C et 260°C ; salinités > à 20wt%eq.NaCl), qui lessivent les granites tardi‐hercyniens.(c) Pendant le syn‐rift, les conditions de surpression de fluide permettent la réactivation cyclique des failles, les décollements stratigraphiques et la formation de brèches hydrauliques, favorisant la mise en connexion avec les réservoirs superficiels à l’apex du rollover. Le modèle de Sibson ajusté aux fluides de bassins est alors le moteur de la migration verticale.(d) Les fluides thermogéniques commencent à être expulsés avec les derniers fluides de compaction au cours d’un stade plus évolué de l’enfouissement en empruntant les mêmes chemins jusqu’à l’apex du roll over. Ils sont alors partiellement freinés et déviés par les colmatages minéralisés antérieurs.(e) A Lodève, la continentalisation des minéralisations antérieures au cours de l’exhumation post‐rift conduit à leur remaniement partiel au niveau de la transition sulfate‐méthane induite par l’interaction entre une playa évaporitique et la dysmigration des hydrocarbures. Des barytines secondaires de basse température, déprimées en Sr sont alors précipitées de manière synsédimentaire dans des karsts météoriques du socle.Outre l’illustration d’un modèle complet (source to sink) de dynamique des fluides dans un bassin, ce travail apporte de nouvelles contraintes dans l’approche du colmatage des réservoirs à hydrocarbures sur les têtes de blocs basculés et sur la genèse des gîtes miniers de type Mississippi Valley‐Type.
https://hal.archives-ouvertes.fr/tel-01457583

tel-01457583
https://hal.archives-ouvertes.fr/tel-01457583
https://hal.archives-ouvertes.fr/tel-01457583/document
https://hal.archives-ouvertes.fr/tel-01457583/file/th%C3%A8seLaurent2015V2.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Almost all Red Sea deeps contain metal-rich sediments covered by brine pools. It is generally agreed that these metal-rich deposits precipitated from overlying metal-rich brines that originated from migrating hydrothermal fluids. No brine pool has ever been reported in Thetis Deep, inciting us to evaluate if such a brine layer ever occurred in the deep during the past. In order to address that questioning, a study combining mineralogical, geochemical (major-, minor-, rare-earth elements) and isotopic (Sr. Nd. Pb) approaches was completed on cored sediments and extracted interstitial waters from inside and outside the deep.;The sediments have an overall hydrothermal origin, as shown by the REE concentrations and patterns, metal contents, and Pb-Nd isotopic data, all pointing to a mantle signature. The intensity of the hydrothermal activity varied with time in the deep; the most intense episode resulting in an almost pure Fe-oxi-hydroxide layer. Varied chemical arguments, especially the Zr and REE data of the sediments, favor the fact that the whole sedimentation in Thetis Deep occurred in the absence of a stable, salt-rich and mineralized brine pool, and that no brine layer ever existed. This conclusion is supported by the constant Sr isotope composition of the sediment and its interstitial waters that are almost identical to that of the Red Sea seawater. The study also suggests that hydrothermal activity monitored fluid supplies that interacted differently with seawater in the different Red Sea deeps, resulting in an overall formation of metal-rich sediments, but along varied local conditions. (C) 2009 Elsevier B.V. All rights reserved.
ISSN: 0375-6742

hal-00475646
https://hal.archives-ouvertes.fr/hal-00475646
DOI : 10.1016/j.gexplo.2009.10.001

Éditeur(s) : HAL CCSD Elsevier
Résumé : We have integrated the relatively unknown distal domains of the Lower Congo basin, where the main depocenters of the Congo submarine fan are located, with the better-constrained successions on the shelf and upper slope, through the analysis of thousands of km of 2D seismic reflection profiles off-shore the Congo-Angola passive margin. The basin architecture is depicted by two ca. 800-km-long regional cross sections through the northern (Congo) and southern (Angola) margin. A large unit deposited basinward of the Aptian salt limit is likely to be the abyssal-plain equivalent of the upper-Cretaceous carbonate shelf that characterized the first post-rift deposits in West-equatorial African margins. A latest-Turonian shelf-deepening event is recorded in the abyssal plain as a long period (Coniacian-Eocene) of condensed sedimentation and basin starvation. The onset of the giant Tertiary Congo deep-sea fan in early Oligocene following this event reactivates the abyssal plain as the main depocenter of the basin. The time-space partitioning of sedimentation within the deep-sea fan results from the interplay among increasing sediment supply, margin uplift, rise of the Angola salt ridge, and canyon incision throughout the Neogene. Oligocene-early Miocene turbidite sedimentation occurs mainly in NW-SE grabens and ponded inter-diapir basins on the southern margin (Angola). Seaward tilting of the margin and downslope salt withdrawal activates the up-building of the Angola escarpment, which leads to a northward (Congo) shift of the transfer zones during late Miocene. Around the Miocene-Pliocene boundary, the incision of the Congo submarine canyon confines the turbidite flows and drives a general basinward progradation of the submarine fan into the abyssal plain The slope deposition is dominated by fine-grained hemipelagic deposits ever since. Results from this work contribute to better understand the signature in the ultra-deep deposits of processes acting on the continental margin as well as the basin-wide sediment redistribution in areas of high river input.
ISSN: 0040-1951

hal-00424533
https://hal.archives-ouvertes.fr/hal-00424533
DOI : 10.1016/j.tecto.2008.04.009

Éditeur(s) : Elsevier Science Bv
Résumé : Recent oceanographic surveys revealed the existence of five volcaniclastic deep-sea fans off La Reunion Island. The Cilaos fan is a large volcaniclastic submarine fan, connected to rivers that episodically experience torrential floods through a narrow and steep shelf-slope system. New piston cores presented in this study together with echosounder profiles give new insight into the evolution, of this extensive and sand-rich turbidite system. The Cilaos fan extends over 15,000 km(2) on an abyssal plain and is compartmentalized by topographic highs. Located southwest of the island, the sedimentary system consists of a canyon area and a deep sea fan divided into a proximal and a distal fan. The proximal fan is characterized by its wide extent and coarse-grained turbidites. The distal fan is characterized by elongated structures and fine-grained turbidites. A detailed morphological study of the fan which includes the analysis of swath bathymetry, backscatter, echosounder, and piston core data shows that the Cilaos fan is a complex volcaniclastic deep-sea fan, highly influenced by preexisting seafloor irregularities. The canyons and the slope area show a complex and evolving sediment feeding system with a direct sediment input by the river and irregular sediment supply by submarine landslide. Three main construction stages are identified for this system: (1) an old incision phase of the channels forming wide turbidites extending over the entire distal fan; (2) a period of no or low activity characterized by a thick layer of hemipelagic mud; and (3) a local reactivation of the channel in the proximal fan. Each stage seems to be linked to a different sediment source with a progressively increasing contribution of hemipelagic sediment and mud in younger stages. (C) 2011 Elsevier B.V. All rights reserved.
Marine Geology (0025-3227) (Elsevier Science Bv), 2011-10 , Vol. 288 , N. 1-4 , P. 1-17

Droits : 2011 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/00056/16704/14203.pdf
DOI:10.1016/j.margeo.2011.06.011
http://archimer.ifremer.fr/doc/00056/16704/

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
Cold seeps have recently been discovered in the Nile deep-sea fan (Eastern Mediterranean), and data regarding associated fauna are still scarce. In this study, two bivalve species associated with carbonate crusts and reduced sediment are identified based on sequence analysis of their 18S and 28S rRNAencoding genes, and associated bacterial symbioses are investigated using 16S rRNA gene sequencing and microscopy-based approaches. The specimens are closely related to Myrtea spinifera and Thyasira flexuosa, two species previously documented at various depths from other regions but not yet reported from the Eastern Mediterranean. Both species harbour abundant gammaproteobacterial endosymbionts in specialized gill epithelial cells. The Myrtea-associated bacterium is closely related to lucinid symbionts from both deep-sea and coastal species, whereas the Thyasira-associated bacterium is closely related to the symbiont of a T. flexuosa from coastal waters off the U.K. An epsilonproteobacterial sequence has also been identified in Thyasira which could correspond to a helicoid-shaped morphotype observed by electron microscopy, but this was not confirmed using fluorescent in situ hybridization. Virus-like particles were observed within some symbionts in Thyasira, mostly in bacteriocytes localized close to the ciliated zone of the gill filament. Overall, results indicate that very close relatives of shallow species M. spinifera and T. flexuosa occur at cold seeps in the Eastern Mediterranean and harbour chemoautotrophic symbioses similar to those found in their coastal relatives.
ISSN: 0173-9565

hal-00743765
https://hal.univ-antilles.fr/hal-00743765
DOI : 10.1111/j.1439-0485.2010.00413.x

Résumé : Herbácea o sufruticosa perenne de hasta 1 m de alto, de olor fétido. Hojas alternas, oblongas a elípticas, agudas a acuminadas en el ápice, generalmente glabras. Espigas de hasta 40 cm, pubérulas; flores perfectas, subsésiles, apétalas. Aquenio de alrededor de 8 mm de largo, cuneado, estriado, con seis cerdas terminales reflexas; semilla solitaria, linear.
Plante herbacée ou suffrutescente pérenne pouvant atteindre 1 m de haut, d&rsquo;odeur fétide. Feuilles alternes, oblongues à elliptiques, aiguës à acuminées à la pointe, généralement glabres. Epis pouvant atteindre 40 cm, pubérulents; fleurs parfaites, subsessiles, sans pétales. Akène d&rsquo;environ 8 mm de long, cunéiforme, strié, avec 6 soies terminales courbées vers l';arrière; graine solitaire, linéaire.
A weedy, deeply rooted, subherbaceous perennial 60-150 cm. high with the strong smell of garlic when broken. Leaves spirally arranged, simple, entire, oblong to elliptic, acute to acuminate at the tip, 20 x 7 cm. usually glabrous; Inflorescence a spikes up to 40 cm. long with minute hairs; 4 white perianth, becoming green in fruit; fruit an achene 6-8 mm long, flattened against the rachis of the inflorescence, developing two sharpely pointed, deflex bristles at the tip.
Originaria de América tropical, cultivada y naturalizada en regiones tropicales.
Originaire d’;Amérique tropicale, cultivée et naturalisée dans les régions tropicales.
Native to tropical America, cultivated and naturalized in tropical regions.

http://www.tramil.net/fototeca/plant273