59 research outputs found
Open field study of some Zea mays hybrids, lipid compounds and fumonisins accumulation
Lipid molecules are increasingly recognized as signals exchanged by organisms interacting in pathogenic and/or symbiotic ways. Some classes of lipids actively determine the fate of the interactions. Host cuticle/cell wall/membrane components such as sphingolipids and oxylipins may contribute to determining the fate of hostâpathogen interactions. In the present field study, we considered the relationship between specific sphingolipids and oxylipins of different hybrids of Zea mays and fumonisin by F. verticillioides, sampling ears at different growth stages from early dough to fully ripe. The amount of total and free fumonisin differed significantly between hybrids and increased significantly with maize ripening. Oxylipins and phytoceramides changed significantly within the hybrids and decreased with kernel maturation, starting from physiological maturity. Although the correlation between fumonisin accumulation and plant lipid profile is certain, the data collected so far cannot define a cause-effect relationship but open up new perspectives. Therefore, the questionââDoes fumonisin alter plant lipidome or does plant lipidome modulate fumonisin accumulation?ââis still open
Post Rift Evolution of the Indian Margin of Southern Africa
International audienceThe objective of this study is to discuss the evolution of the South African Plateau along the Indian margin ofSouthern Africa. Since the classical works of A. du Toit and L.C. King and the improvement of thermochronologicalmethods and numerical models, the question of the uplift of South African Plateau was highly debatedwith numerous scenarios: early Cretaceous at time of rifting (Van der Beek et al., J.Geophys.Res., 2002), lateCretaceous (Braun et al., Solid Earth, 2014), late Cenozoic (Burke & Gunnell, Geol.Soc.of America, 2008).Limited attention has been paid on the constraints provided by the offshore stratigraphic record of the surroundingmargins. The objective of our study is to integrate onshore and offshore data (seismic profiles andindustrial wells) to (1) analyse the infill of the whole margin (21S to 31S) from its hinterland to the distal deepwater basin, (2) to constrain and quantify the vertical movements. We discuss the impact on accommodation andsediments partitioning, and their significance on South African Plateau uplift history.1. Sedimentary basins of the Indian margin of Southern Africa are related to the break-up of Gondwanaduring late Jurassic, resulting in rifts and flexural basins. First marine incursions started during early Cretaceoustimes (oldest marine outcropping sediments are of Barremian age 128 Ma). The region developed as a normalcontinental shelf at the Aptian-Albian transition (113 Ma).2. The Cretaceous geological history of the basins is characterized by differential uplift and subsidence of thebasement, controlled by structures inherited from break up. As example, major early Cretaceous depocenters of themargin are located on the north of Save-Limpopo uplift (Forster, Paleogography, Paleoclimatology, Paleoecology,1975) showing an eastward drainage pattern, maybe related to a proto Limpopo drainage. Those observationssuggest that the escarpment bordering the Bushveld depression is an old relief inherited from early Cretaceous.3. Two major uplift events occur during upper Cretaceous along the Kwazulu-Maputaland margin (25.5S to31S). During late Cenomanian (95 Ma) and during late Cretaceous (71-66 Ma). Both events are coeval with amajor tilting and erosion of the upstream part of the margin, river incision and the growth of basin floor fans.4. At first order, the margin shows a retrogradational trend up to a major flooding during mid Eocene time (54Ma), dominated by carbonate sedimentation. A widespread tilt of the margin occur during early Miocene (18Ma) times leading to progradational geometries and the actual high elevation topography of the margin.These results suggest that the South African plateau results from a polyphased uplift history. Most of therelief is inherited from three uplift of the margin, during the continental break-up, during late Cenomanian andduring late Cretaceous. The actual high elevation topography was acquired during a widespread tilting of themargin during late Cenozoic
Bilan "Source to Sink" Ă lâĂ©chelle dâun continent - LâAfrique : Dynamique du manteau et routage sĂ©dimentaire
International audienceA source to sink approach was performed at the scale of a continent â Africa - in the frame of the TopoAfrica project, with three main objectives (1) the characterization of the relative importance of deformation (uplift) and climate (precipitation) (2) the quantification of the deformation, its nature and causes, (3) the effect of those deformations on the past African topography and on the sediment routing system. We mainly focused on Western, Central and Austral Africa, characterized by anorogenic relief (plains and plateaus) record of long (several 100 km) to very long (several 1000 km) wavelength deformations, respectively of lithospheric and mantle origin. The sink measurement was based on the seismic stratigraphic analysis of numerous regional seismic lines (from the upstream part of the margin to the abyssal plain) merge of industrial and academic data, calibrated in ages and lithologies on reevaluated wells to get the best possible ages. Volumes measured between successive time-lines, were compacted for a comparison with solid eroded volumes.The source study was performed using dated stepped planation surfaces (etchplains and pediplains) - key morphological features of Africa - mappable at catchments-scale. During Late Paleocene to Middle Eocene times, Africa experienced a very hot and very humid climate leading to the formation of an African-scale weathering surface (etchplain) known as the African Surface. This surface today deformed and preserved as large plains, domes or plateaus, can be used as (1) a marker of the very long wavelength deformations and (2) a reference level to measure eroded volumes since 40 Ma. Some other younger planation surfaces were also mapped of (1) Early Oligocene and (2) Late Miocene ages.(1) Deformation (uplift) is the dominant control of the sediment budget. Climate (precipitation) changes only enhance or inhibit a deformation-controlled flux.(2) The sources of clastic sediments are or closed marginal bulges or far field domes due to mantle dynamics with by-pass (transfer zones) along long-lasting polygenic surfaces located in
Mouvements verticaux post-rift des margesindiennes dâAfrique australe
National audienceLâobjectif de cette Ă©tude est de discuter de la mise en place duPlateau Sud-Africain en amont des marges transformantes IndiennesdâAfrique Australe. Depuis le dĂ©veloppement des mĂ©thodesthermochronologiques et des modĂšles numĂ©riques, la cinĂ©tique etles mĂ©canismes de mise en place du Plateau Sud-Africain est trĂšsdĂ©battue.- Les modĂšles thermochronologiques et numĂ©riques dâĂ©rosion(e.g. Van der Beek et al., J.Geophys.Res., 2002) suggĂšrent quâilsâagirait dâun relief ancien, hĂ©ritĂ© de la phase de rift au CrĂ©tacĂ©infĂ©rieur.- Les donnĂ©es thermochronologiques (e.g. Brown et al.,J.Geophys.Res., 2002) mettent en Ă©vidence une phasedâexhumation rapides au CrĂ©tacĂ© (110 - 90 Ma) qui concordeavec une accĂ©lĂ©ration des flux silicoclastiques dans les bassinssĂ©dimentaires Ă mer (e.g. Braun et al., Solid Earth, 2014).- Les Ă©tudes gĂ©omorphologiques des surfaces dâaplanissementprĂ©servĂ©es Ă terre, lâinterprĂštent comme un relief hĂ©ritĂ© de surrectionssuccessives (e.g. King, Univ.NatalPress, 1982) avecune phase majeure de dĂ©formation au CĂ©nozoĂŻque (~30 Ma) rattachĂ©eĂ la mise en place dĂŽme Est-Africain (Burke & Gunnell,Geol.Soc.of America, 2008).Peu dâattention a Ă©tĂ© portĂ©e aux bassins cĂŽtiers qui bordent cePlateau. Lâobjectif ici est (1) de rĂ©aliser une analyse stratigraphiquedu remplissage sĂ©dimentaire des marges indiennesdâAfrique Australe (21S to 31S) en intĂ©grant des observationsde terrains et des donnĂ©es de subsurface (forages et sismique 2D); (2) de contraindre et quantifier les mouvements verticaux qui affectentcette marge ; (3) de discuter lâimpact de ces dĂ©formationssur la morphologie de la marge (accomodation, partitionnementsĂ©dimentaire entre le plateau continental et le bassin profond)et de leurs implications sur la mise en place du Plateau Sud-Africain.- La mise en place du Plateau Sud-Africain est une histoirepolyphasĂ©e avec trois phases de dĂ©formations majeures : A labase du Turonien (92 Ma), au CrĂ©tacĂ© supĂ©rieur (78-65 Ma), Ă la transition OligocĂšne-MiocĂšne (23 Ma). Lâessentiel du reliefest crĂ©Ă© pendant le CrĂ©tacĂ©, mais sa topographie est acquise auCĂ©nozoĂŻque.- Les bassins cĂŽtier enregistrent diffĂ©rents types de dĂ©formationsdes marges, e.g. (1) basculement de la marge associĂ© Ă un basculementdu bassin et la mise en place dâune discordance angulairedans le domaine amont ; (2) surrection horizontale de la margequi se traduit par une chute du niveau marin relatif, une reprise delâĂ©rosion continentale (incisons fluviatiles) en amont du bassin etla mise en place de prismes de bas-niveau dans le domaine aval.- Lâorigine de ces dĂ©formations est mal comprise, mais leurlongueur dâonde (Ă1000 km) suggĂšre une origine mantelliqueet/ou des dĂ©formations dâĂ©chelle continentale
GROWTH OF THE GREAT ESCARPMENT ACROSS THE INDIAN MARGIN OF SOUTH AFRICA: a couple stratigraphic-geomorphologicstudy
International audienceThe South African Plateau is formed by marginal bulges clustered around an intracontinental basin (the KalahariBasin) with a mean elevation between 1000 and 1400 m. On seaward side, marginal bulges form major escarpmentsthat can reach an elevation up to 3500 m in the Drakensberg area, boundering the high elevation continentfrom a dissected coastal region.The factors controlling escarpment evolution of those high-elevation passive margins are highly debated. On theone hand, geomorphic studies interpret escarpments in term of pulses of uplift and scarp retreat (King, The NatalMonocline, 1982; Partridge & Maud, S.Afr.J.Geol., 1987). On the other hand, thermochronological data andnumerical models of escarpment erosion (Gallagher & Brown, Phil.Trans.R.Soc.Lon., 1999; Van der Beek et al.,J.Geophys.Res., 2002) suggest that escarpments predate the breakup with a minimal escarpment retreat duringpost-rift margin evolution.To answer this question, we studied the Indian margin of South Africa (from Bushveld area to Port-Elizabeth)using sequence stratigraphy analysis of industrial seismic lines and wells. This study is coupled with an analysisof the adjacent landforms, constrained by dated sediments and weathering deposits.The first outcomes of our study are:1. A first uplift during Late Cenomanian (95-90 Ma) created an initial escarpment along the Indian coast.2. A second uplift occurred during the latest Cretaceous to earliest CenozoĂŻc with a sequential tilting andtruncations of the inner part of the margin followed by the incision of pediments on the seaward side of the initialescarpment,3. A third uplift that occurred during Late Eocene â Early Oligocene and Miocene with the incision of two newgenerations of pediments.These preliminary results suggest that the âGreat Escarpmentâ along the Indian coast of South Africa resultsfrom the stepping of at least four generations of pediments which record the polyphasic uplift history of theSouth African Plateau during the last 100 My
Post-Rift Vertical Movements Of The Southern African Margins - Implications For The South African Plateau Uplift
International audienceThe South African Plateau (SAP) is the worldâs largest non-orogenic plateau. It forms a large-scale topographic anomaly which rises from sea level to > 1000 m. Most mechanisms proposed to explain its elevation gain imply mantle processes. The age of the uplift and the different steps of relief growth are still debated. On one hand, a Late Cretaceous uplift is supported both by thermochronological studies and sedimentary flux quantifications. On the other hand, geomorphological studies suggest a Late Cenozoic uplift scenario (<30 Ma). However few attentions were paid to the evolution of the overall geomorphic system, from the upstream erosional system to the downstream depositional system. This study is based on two different approaches: - Onshore, on the mapping and chronology of all the macroforms (weathering surfaces, pediments and pediplains, incised rivers, wave-cut platforms) dated by intersection with the few preserved sediments and the volcanics. - Offshore, on a more classical dataset of seismic lines and petroleum wells, coupled with biostratigraphic revaluations (characterization and dating of vertical movements of the margins - sediment volume measurement). The main result of this study is that the SAP is an old Upper Cretaceous relief (90-70 Ma) reactivated during Oligocene (30-15 Ma) times
MASS TRANSFER BETWEEN THE SOUTH AFRICAN PLATEAU AND THE ADJACENT ATLANTIC MARGIN (NAMIBIA - SOUTH AFRICA) SINCE THE GONDWANA BREAK-UP
International audienceThe South African Plateau (SAP) forms a large - scale topographic anomaly (Ă1000 km)which rises from sea level to up to 3000 m elevation. Tomographic models suggest that thehigh elevated southern African topography is the expression of a surface upwelling caused byflows in the underlying mantle. However, documenting the surface uplift due to mantle flowsis a major challenge in geology. Here we link onshore landforms (planation surfaces, incisedvalleys) of the SAP to offshore sediment accumulation along the Atlantic margin (from 18°S to38°S), using numerous seismic reflexion profiles, well data and outcrops. We attempt to relatesource and sink analysis in order to solve some first order issues relative to the timing of theexhumation and the growth of the Southern African Plateau.Offshore, we calculate the solid sediment volumes history of the margin for the last 131Ma (i.e. late Hauterivian â today) based on Guillocheau et al. [1] approach. Volumes and accumulationrates were higher during the Upper Cretaceous (335 Ă103 km3 at 51.5 Ă103 km3/Mafrom 100 to 93.5 Ma, 790 Ă103 km3 at 63 Ă103 km3/Ma from 93.5 to 81 Ma, and 395 Ă103 km3 at26.3 Ă103 km3/Ma from 81 to 66 Ma). Volumes and accumulation rates were lower for the LowerCretaceous (73 Ă103 km3 at 4 Ă103 km3/Ma from 131 to 113 Ma, and 16 Ă103 km3 at 12.2 Ă103km3/Ma from 113 to 100 Ma) and the Cenozoic (67 Ă103 km3 at 1.6 Ă103 km3/Ma from 66 to 30Ma, and 92 Ă103 km3 at 6.5 Ă103 km3/Ma from 30 to 11 Ma, and 35 Ă103 km3 at 32 Ă103 km3/Ma).Onshore, four generations of landforms were recognised and dated by geometrical relationshipswith volcanism and sediments. The successive growth of these landforms are relatedto uplifts (Guillocheau et al. [2]).âą > 80 Ma: two generations of planation surfaces (at least). The oldest one forms thehighest reliefs of the study area, which are preserved as remnant plateaus (Etchplains). Its ageis not known. The younger, form a large - scale pediplain that could be related to the increaseof the sedimentary flux occurring during the Upper Cretaceous (i.e. 100 to 81 Ma), driven by aregional uplift.âą 80 - 75 to 70 - 65 Ma: large scale pediplain called the Bushmanland Surface. It canbe related to a strike flexure of the margin (i.e. seaward tilting) recognised offshore from 23°Sto 36°S. Most of the present-day relief was probably created by that time. This is supported bythe decrease of the sedimentary flux which suggests a reorganisation of the interior drainagepattern.âą 35 - 25 to 15 - 12 Ma: degradation by river incision of the Bushmanland Surface inresponse to a continental scale uplift (?) and/or change of the climate conditions.These results suggest that the Southern African plateau (SAP) results from a two phasesuplift history: (1) a widespread tilting of the margin during late Cretaceous, (2) continental scaledeformations during the Oligocene. Most of the relief is inherited from the Upper CretaceousReferences:[1] Guillocheau et al. (2012) Basin Res., 24(1), 3-30[2] Guillocheau et al. (2016) accepted Gondwana Res
SINK MEASUREMENT OF THE ZAMBEZI SYSTEM (DELTA TO DEEPSEAFAN): A RECORD OF THE EAST AFRICAN RIFT UPLIFT ANDASSOCIATED CLIMATE CHANGES
International audienceThe Zambezi deltaic system is one of the largest in Africa after the Niger, the Congo and the Nile. Thispassive margin-scale delta is characterized by a topographically and tectonically segmented depositionalprofile studied in the frame of the project PAMELAPassive Margin Exploration Laboratoriesfounded byTOTAL and IFREMER): (1) an upstream 10 km thick deltaic wedge with no gravitary tectonics, (2) theAngoche pounded deep depositional area and (3) the Zambezi deep-sea fan, bounded fromm the Angoche areby a major contouritic drift.The sink measurement was based on the seismic stratigraphic analysis of numerous regional seismiclines (from the upstream part of the margin to the abyssal plain) merge of industrial and academic data,calibrated in ages and lithologies on reevaluated wells to get the best possible ages. Volumes measuredbetween successive time-lines, were compacted for a comparison with solid eroded volumes. Uncertaintieswere calculated (including ages, time-depth conversion law, porosities...) using the VolumeEstimator software.Four main periods of sediments delivery were identified: (1) 94-66 Ma (Turonian-Maastrichtian) firstsilicilastic imput, (2) 66-34 Ma (Paleocene-Eocene) â very low siliciclastic supply, (3) 34-5.5 Ma (Oligocene-Miocene) â second input of siliciclastic sediments and 5.5-0 Ma (Plio-Pleistocene) â sharp increase of thesediment supply.These changes correspond to major deformation and/or climate changes. The reconstruction of theclimate (precipitation) evolution was based on a palynological study along wells of the Zambezi Delta andsummarized as follows: 100 to 90 Masemi-arid, 90 Ma (base Coniacian)sharp increase to very humidconditions up to 40 Ma, 40-30 Ma and 15-11 Ma dryer periods, 30-20 Ma and 11-7 Ma very humid conditionsagain.(1) The 94-66 Ma first siliciclastic sediments supply can be related to the uplift of the South AfricanPlateau and the erosion of the Bushveld reentrant. This can be enhanced after 90 by the sharp increase of thehumidity.(2) The 66-34 Ma period of low siliciclasctic supply is both a period of tectonic stability, very humidconditions and then of intense weathering with carbonate platforms.(3) The 34 Ma second increase of siliciclastic sediments results from an African-scale upliftrelated tomantle dynamics â onset of a mechanical erosion of the Eocene weathering profiles.(4) The sharp increase of sediment supply around 5.5 Ma result from more local processes. They are nomajor climate changes with an amplitude higher than the other Neogene variations. This even is related to amajor change of the drainage pattern of the Zambezi River at time of the initiation of the Malawi Rift
Degradation of aflatoxins by means of laccases from trametes versicolor: An in silico insight
Mycotoxins are secondary metabolites of fungi that contaminate food and feed, and are involved in a series of foodborne illnesses and disorders in humans and animals. The mitigation of mycotoxin content via enzymatic degradation is a strategy to ensure safer food and feed, and to addresstheforthcomingissuesinviewoftheglobaltradeandsustainability. Nevertheless, the search for active enzymes is still challenging and time-consuming. The in silico analysis may strongly support the research by providing the evidence-based hierarchization of enzymes for a rational designofmoreeffectiveexperimentaltrials. ThepresentworkdealtwiththedegradationofaïŹatoxin B1 andM1 bylaccaseenzymesfromTrametesversicolor. Theenzymesâsubstrateinteractionforvarious enzymeisoformswasinvestigatedthrough3Dmolecularmodelingtechniques. Structuraldifferences among the isoforms have been pinpointed, which may cause different patterns of interaction between aïŹatoxin B1 and M1. The possible formation of different products of degradation can be argued accordingly. Moreover, the laccase gamma isoform was identiïŹed as the most suitable for protein engineering aimed at ameliorating the substrate speciïŹcity. Overall, 3D modeling proved to be an effective analytical tool to assess the enzymeâsubstrate interaction and provided a solid foothold for supporting the search of degrading enzyme at the early stag
MOUVEMENTS VERTICAUX ET BILANS SEDIMENTAIRES DE MADAGASCAR AUCENOZOĂQUE : ETUDE COUPLEE GEOMORPHOLOGIE/STRATIGRAPHIE SISMIQUE
National audienceLâobjectif de ce projet est de comprendre la surrection dâun continent de petite taille, lâĂźle deMadagascar et les bilans dâĂ©rosion associĂ©s. Il sâinscrit dans le cadre du projet PAssive MarginExploration LAboratory (PAMELA â thĂšse cofinancĂ©e par TOTAL-IFREMER), dans lequel noussouhaitons comprendre lâĂ©volution dâune marge dans son intĂ©gralitĂ© terre-mer au travers de lâanalysedes formes du relief Ă Madagascar et de lâĂ©tude stratigraphique des bassins sĂ©dimentaires cĂŽtiers deMorondava et Majunga (Madagascar). En effet, les formes du relief rĂ©sultent dâune histoiregĂ©ologique associant des mouvements verticaux de plus ou moins grande longueur dâonde Ă des processusdâĂ©rosion, de transport et dâaltĂ©ration, eux-mĂȘmes intimement liĂ©s au climat.Madagascar est une Ăźle, constituĂ©e dâun haut plateau central culminant entre 1200 et 1800mdâaltitude en moyenne et qui sâĂ©tend du nord au sud sur prĂšs de 1600km. Il est limitĂ© Ă lâEst par unescarpement cĂŽtier majeur, alors que vers lâOuest, la transition avec la plaine cĂŽtiĂšre est marquĂ©e par lasuccession de surfaces dâaplanissement (etchplain : surfaces plus ou moins altĂ©rĂ©es et pĂ©diments).Lâessentiel des produits dâĂ©rosion de cette surrection sont prĂ©servĂ©s dans deux marges passives, le bassinde Morondava, Ă lâOuest limitĂ© par la ride de Davie et se dĂ©versant lui-mĂȘme dans la plaine sousmarinedu ZambĂšze (ocĂ©an mozambicain), et au Nord, le bassin de Majunga connectĂ© avec la marge sudde lâocĂ©an Somalie.LâĂ©tude gĂ©omorphologique se fonde sur la cartographie des diffĂ©rentes surfaces dâaplanissementĂ©tagĂ©es, qui traduisent des chutes successives du niveau de base, du fait de la surrection. Cettecartographie est Ă©tablie dâaprĂšs lâĂ©tude des MNT Ă 30 et 90m (SRTM), et Ă des observations deterrain, couplĂ©e Ă des profils topographiques. Concernant les marges, seuls les puits clĂ©s du bassin deMorondava ont Ă©tĂ© analysĂ©s pour lâinstant.(1) Les puits offshore montrent une succession de 3 pĂ©riodes. Une pĂ©riode volcano-clastique (trappsde Madagascar au CrĂ©tacĂ© supĂ©rieur), suivie dâune gigantesque plate-forme carbonatĂ©e sans apportsterrigĂšnes, du PalĂ©ocĂšne au MiocĂšne moyen. Le retour de la sĂ©dimentation clastique est observĂ© Ă partir du MiocĂšne moyen cependant contemporaine de quelques plates-formes carbonatĂ©es.(2) Des hauts plateaux centraux Ă la plaine cĂŽtiĂšre, 5 surfaces ont Ă©tĂ© identifiĂ©es. La premiĂšre et plushaute donc est une surface dâaltĂ©ration bauxitique, suivie de 4 surfaces pĂ©dimentaires.(3) Lâintersection de ces surfaces avec le volcanisme, abondant et bien datĂ© (K/Ar sur roche totale)Ă Madagascar, et avec les sĂ©ries sĂ©dimentaires des bassins cĂŽtiers, permet de contraindre lâĂąge desmouvements verticaux. Tous ces reliefs sont postĂ©rieurs Ă lâOligocĂšne supĂ©rieur.(4) La surface la plus ancienne a subit une dĂ©formation importante et apparait particuliĂšrement âbombĂ©e â dans le paysage malgache, confĂ©rant Ă lâĂźle une forme en dĂŽme caractĂ©ristique.(5) LâEocĂšne dans le bassin de Morondava est caractĂ©risĂ© par des dĂ©pĂŽts carbonatĂ©s trĂšs Ă©tendus, du sudde lâile jusquâau centre du bassin, au niveau de la Tsiribihina. Ils culminent Ă prĂšs de 900m au Nordestde TulĂ©ar, ce qui traduit, aux corrections eustatiques prĂšs, des mouvements verticaux dâune ampleurde 900m au minimum.Les donnĂ©es gĂ©omorphologiques montrent que la surrection dĂ©bute donc au MiocĂšne, ce qui esten accord avec les donnĂ©es de puits qui montrent que les premiers dĂ©pĂŽts clastiques nâarrivent pasavant le MiocĂšne moyen, sous rĂ©serve dâune meilleure datation. Madagascar est le rĂ©sultat dâunedĂ©formation de type â dĂŽme â qui nâest pas sans rappeler celle des dĂŽmes Ă©thiopiens et est-africains(Kenyans), qui sont eux, plus anciens
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