Éditeur(s) : Université de Brest
Résumé : The channel-lobe transition zone has been studied in two turbiditic systems: the Amazon channel-mouth lobe complex at the termination of the last eight channel-levee systems and the Neochannel termination, the last active channel of the Petit-Rhone turbidite system. - In the two cases, the internal geometry and stacking pattern of the deposits show a significant control of the configuration (size and shape) of the receiving basins, their morphology (gradients and subtle gradient changes), and their degree of confinement. - The Amazon and Petit-Rhone systems, with lobes built after the Last Glacial Maximum and the ensuing sea-level rise, evidence the major impact of external forcings (climatic events and eustatic variations) that induce variations in sediment fluxes delivered to the deep basin and therefore exert a control on channel-mouth lobes construction. The channel-mouth lobes of the Amazon and Petit-Rhone systems, even if they are located at great distances from the river mouths, at the termination of the turbidite systems and in areas characterised by subtle morphological variations, are both constrained by combined internal (accommodation and compensation) and external factors (post-glacial deconnection between the fluvial system and the deep basin).
La zone de transition chenal-levées/lobes a été étudiée dans 2 systèmes turbiditiques : le complexe de lobes à la terminaison des 8 derniers chenaux de l'éventail de l'Amazone et la terminaison du Néochenal, dernier chenal de l'éventail du Petit-Rhône. - Dans les deux cas, l'agencement des dépôts et leur évolution dans l'espace et le temps révèlent un fort contrôle de la configuration des réceptacles (taille et forme), de la morphologie des fonds (pentes et taux de changement des pentes) et du degré de confinement. - Les systèmes de l'Amazone et du Petit-Rhône, dont les lobes se sont construits à partir du Dernier Maximum Glaciaire et lors de la remontée du niveau marin qui a suivi, ont en outre permis de souligner l'impact majeur, sur la mise en place des lobes terminaux, de certains forçages externes (événements climatiques et variations eustatiques), qui déterminent les variations des flux sédimentaires arrivant au bassin. Ainsi, bien que situés à des distances considérables des sources fluviatiles et dans des zones distales où les variations de relief sont très ténues, les lobes terminaux de ces deux grands systèmes turbiditiques se sont révélés contraints à la fois par des processus internes (processus de compensation) et par des processus externes (déconnexion post-glaciaire du fleuve et du bassin).

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/2008/these-6796.pdf
http://archimer.ifremer.fr/doc/00000/6796/

Éditeur(s) : HAL CCSD
Résumé : The Franceville Basin (2.1 Ga) in southeastern Gabon, hosts a black shale series well preserved (FB Formation) which represents an exceptional example of unmetamorphised Paleoproterozoic sediment strata. This basin includes the protore of one of the largest Mn-oxide laterite ore worldwide, mined by Eramet-Comilog. The aim of this this work is to determine formation conditions of this protore and to characterize the global sedimentary evolution of the FB Formation which include the protore. This 75 m thick protore is constituted of Mn carbonate-rich black shales which represent a potential ore deposit for the future. It was drilled, on the Bangombé plateau, during a recent campaign of 24 boreholes with an average depth of 125 m.Through multidisciplinary study on these cores and key outcrops of the basin, this work focuses on : i) the depositional environment of the Mn-protore and FB Formation ; ii) the processes of formation of the Mn-carbonates at 2.1 Ga and iii) the architecture and distribution of Mn-rich levels of the protore on the Bangombé Plateau.A detailed sedimentological and petrological study allowed us to redefine the division of the FB into nine units, named U1 to U9 from the base to the top. These units show a fine upward cycle up to U5 and a reverse coarse loop until U9. This division leads to a new interpretation to propose an evolution from a shoreface depositional environment controlled by deltaic currents (U1) to an offshore depositional environment with anoxic conditions (U2). In this basin, a system of submarine fan is developed, feeding a network of sand injections (injectites) covering the Bangombé plateau (70 km²) and with a thickness of 150 m affecting U4 to U7, including the Mn-protore. The protore depositional environment formed below the wave base limit (U4, U5 and U6) in a starved basin, controlled by biochemical sedimentation allowed the formation of Mn-carbonates. The end of starved basin, would allow the re-opening of the detrital input into the offshore basin (U7). This basin is then filled by storm bar deposits intersected by deltaic sub-aquatic channels (U8). The U9 unit corresponds to a quiet lagoon environment, allowing the multicellular organism development for the first time on the planet.A geochemical study allowed the characterization of the depositional environment of Mn-carbonates as an anoxic to sub-oxic and alkaline environment. For the first time, we showed that the manganese carbonates, present as bacteriomorph forms, are precipitated from the seawater by the mediated photosynthetic cyanobacterial activity, which allows CO2 / HCO3 depression of the environment and a local increase of pH. The cyanobacterial activity is controlled by the absence of bottom currents, which increase the detrital input. This would stop the activity of the cyanobacteria and thus would lead to the decrease of the Mn-concentration along the protore.Finally, well-log and a sequential correlation analyses allowed us to detail spatial and timing repartition of FB Formation deposit, controlled by a tectono-sedimentary model. We propose two- tectono-sedimentary phases. A first syn-tectonic phase (U1 to U3) controls the depocentres and sedimentation gaps. Turbidite coarse deposits are located in the most subsident part, clay deposits rather on the slope and carbonates on shoals. A second post-tectonic phase (U4 to U7) allows isopach deposits. The Mn-protore formed during the post-tectonic phase. However, it shows a variable thickness due to subsidence to the north of the Bangombé plateau. So, on the Bangombé plateau, Mn-contents increase towards the south, whereas the protore thickness increases towards the NNE. Moreover sand injectites decrease Mn-content in the eastern part of the Bangombé plateau and impact on the economic evaluation of the Mn-carbonates. Currently, the protore is structured by post-sedimentary faults, which lead to a non-continuity of the high Mn levels on the Bangombé plateau.
Le Bassin de Franceville situé au SE du Gabon présente une série de black shales (Formation FB) d'âge Paléoprotérozoïque (2,1 Ga) surmontant les grès de la Formation FA. Ce bassin peu déformé et non métamorphique représente une archive exceptionnelle des processus de dépôt de cette période de l’histoire de la Terre où la vie commence à se développer. En particulier, la Formation FB contient le protore d'un gisement mondial d'oxydes de manganèse exploité par la société Eramet-Comilog. L’objectif de ce travail est de préciser les conditions de formation de ce protore et de le replacer dans l’histoire du remplissage du bassin. Ce protore d'une épaisseur moyenne de 75 m est constitué de carbonates de manganèse ; il a fait l'objet d'une récente campagne de 24 forages carottés d'une profondeur moyenne de 125 m sur le plateau de Bangombé.A travers une approche pluridisciplinaire comprenant l'étude de ces forages et des affleurements clefs du bassin, ce travail porte sur la caractérisation i) de l'environnement de dépôt du protore et des séries qui l'encadrent (du toit du FA au toit du FB) ; ii) du mode de formation des carbonates de Mn à 2,1 Ga et iii) de l'architecture et de la répartition des hautes teneurs en Mn du protore qui représente un gisement potentiel du futur.L’étude pétro-sédimentaire détaillée a permis de distinguer neuf unités (U1 à U9) au sein de la Formation FB organisées suivant un cycle rétrogradant jusqu’à U5 puis progradant jusqu’à U9. Ce découpage montre une évolution du milieu de dépôt depuis un domaine de shoreface contrôlé par des courants deltaïques (U1) évoluant vers des dépôts d’offshore restreint (U2). Ce bassin enregistre ensuite un système de chenaux-levées turbiditiques (U3) qui alimentent un réseau d'injectites reconnu sur l’ensemble du Pl. de Bangombé et qui traverse 150 m de série (U4 à U7) en affectant le protore et ainsi les teneurs en Mn. L'environnement de dépôt du protore (U5 et U6) marque l’isolement du bassin qui devient affamé et contrôlé par une sédimentation biochimique à l’origine du dépôt des carbonates de Mn. L'Unité 7 correspond à la réouverture des apports détritiques en domaine d'offshore supérieur puis en domaine de shoreface dominé par des dépôts de tempêtes et de chenaux sous-aquatiques deltaïques (U8), et enfin lagunaire (U9) dans lequel apparaissent les premiers métazoaires de l’histoire de la planète, suivant une séquence régressive.Une étude géochimique a permis de préciser les conditions de dépôt du protore qui se forme en milieu alcalin anoxique à sub-oxique. Dans ce milieu, nous montrons pour la première fois une précipitation directe des carbonates de Mn sous forme bactériomorphe induite par l'activité photosynthétique des cyanobactéries qui consomment le CO2/HCO3 et conduisent à une augmentation du pH favorable à la formation des carbonates de Mn. L'activité cyanobactérienne est conditionnée par l’absence de courants de fond qui augmentent la turbidité du milieu et stoppent cette dernière.Les corrélations diagraphiques et séquentielles permettent de préciser la répartition spatiale et temporelle du FB permettant ainsi de replacer le protore dans l’histoire tectono-sédimentaire du bassin. Une première phase syn-tectonique (U1 à U3) contrôle l’épaisseur et la mise en place de dépôts turbiditiques dans les parties subsidentes, de dépôts argileux sur les pentes et de dépôt de carbonates sur les hauts-fonds. La seconde phase post tectonique (U4 à U7) permet la mise en place de dépôts relativement isopaques, bien que le protore enregistre une subsidence plus importante au nord du Pl. de Bangombé. On observe ainsi, sur le Plateau de Bangombé, des teneurs en Mn qui augmentent vers le sud alors que l’épaisseur du protore augmente vers le NNE. Postérieurement au dépôt du FB, le protore est structuré par des failles qui le compartimentent en touches de piano limitant ainsi sa continuité sur le Plateau de Bangombé.
https://hal.archives-ouvertes.fr/tel-01621460

tel-01621460
https://hal.archives-ouvertes.fr/tel-01621460
https://hal.archives-ouvertes.fr/tel-01621460/document
https://hal.archives-ouvertes.fr/tel-01621460/file/these_Dubois2017-MnGabon.pdf

Éditeur(s) : HAL CCSD
Résumé : The Neogene geodynamics evolution of the south-Alboran realm in western Mediterranean has been clarified, based on sedimentological and chronostratigraphical studies. This work focuses on three main themes of research, the first is to establish the moments for the opening and closing of the North Rifian Corridor by studying two Neogene basins of the southern edge of the Alboran sea. The second, aims to understand the behavior of these two basins face a major event in the history of the Mediterranean: The Messinian Salinity Crisis. Finally, the third theme aims to understand the modalities Post-MSC reflooding in the southern part of the Alboran realm.The late Miocene evolution of the North Rifian Corridor is clarified on the basis of chronostratigraphic studies of the Neogene Boudinar and Arbaa Taourirt basins (northeastern Morocco). The marine sediments deposited in the Boudinar basin between the early Tortonian and the late early Messinian (10 Ma to 6.1 Ma) and in the late Tortonian-earliest Messinian interval in the Arbaa Taourirt basin. Palaeoenvironmental data record a major drowning in association with extensive tectonics in the Boudinar basin during the early Messinian at ~7.2 Ma. At the same time, prograding conglomerates and sandstones developed over the late Tortonian marls in the Arbaa Taourirt basin. During the late-early Messinian, a shallowing trend occurred in the Boudinar basin. Thus, the North Rifian Corridor opened at ~7.2 Ma ensuring Atlantic-Mediterranean connections, then was progressively restricted during the late-early Messinian and totally closed at ~6.1 Ma. New sedimentological and paleontological studies of the late Messinian-early Pliocene deposits in the Boudinar basin provide new information on the Messinian Salinity Crisis (« MSC ») and the Zanclean reflooding in the Alboran sea. The Messinian erosional surface « MES » is of late Messinian age and was emplaced in subaerial settings. It is polygenic, its original geometry is locally preserved and was re-shaped by the Pliocene transgressive surface. Above the « MES », the Boudinar basin infill is characterized by a wide variety of facies from continental settings to lower offshore conditions. Two major sets are recognized: a latest Messinian-Zanclean set that constitutes a transgressive-regressive megasequence interrupted at the top by a tectonic unconformity, and an Plio-Quaternary regressive set. During the late Messinian Zanclean interval, four successive depositional models were documented. They record major changes in palaeoflow and paleogeography related to base-level fluctuations. No Gilbert-type delta has ben identified at Boudinar. the beginning of base-level rise is marked by normal regressions and by the formation of several lacs and fan-delta complexes on the margins of the basin in the late Messinian and befor the marine reefloding in the early Zanclean. The marine reflooding of the basin appears later, with a transgressive surface of ravinment and a thick package of transgressive deposits. These transgressive deposits onlap over all previous deposits. The major part of the basin infill did not issue from an inner landward position (south of the basin) but from the northwestern side of the basin, i.e. near the Mediterranean. Sediments were subsequently reworked by storms and transported by longshore-drift towards the south. a maximum flooding surface is found several tens of metres above the « MES ». This fiding is consistent with a progressive and not a catastrophic early Zanclean flooding of the westernMediterranean after the Mediterranean base-level fall.
Sur la base d’études sédimentologiques et chronostratigraphiques dans les bassins de Boudinar et d’Arbaa Taourirt (Rif oriental, Maroc), l’évolution géodynamique néogène du domaine sud-Alboran en Méditerranée occidentale a été clarifiée. Ce travail est axé sur trois grandes thématiques de recherche. La première vise à l’établissement d’un cadre chronostratigraphique pour l’ouverture et la fermeture du Couloir Nord Rifain, par l’étude de deux bassins nèogènes de la bordure sud de la mer d’Alboran. La deuxième, vise à comprendre le comportement de ces deux bassins face à un événement majeur de l’histoire de la Mediterranée : la Crise de salinité messinienne. Finalement, la troisième vise à comprendre les modalités de remise en eau de la Méditerranée après la Crise : le reenoiement pliocène. L'évolution du Couloir Nord Rifain au Miocène supérieur est clarifiée sur la base des études chronostratigraphiques des bassins néogènes de Boudinar et d'Arbaa Taourirt (Maroc Nord oriental). Les sédiments marins miocènes se sont déposés entre le Tortonien inférieur et le Messinien inférieur (10 à 6.1 Ma) dans le bassin de Boudinar et entre le Tortonien supérieur et le Messinien inférieur dans le bassin d'Arbaa Taourirt. Les données paléoenvironnementales enregistrent un ennoyage important du bassin de Boudinar en relation avec une tectonique extensive pendant le Messinien inférieur (~7.2 Ma). En même temps, des conglomérats et de grès progradants se sont développés au-dessus des marnes tortoniennes dans le bassin d’Arbaa Taourirt. Le bassin de Boudinar a subi un désapprofondissement au Messinien inférieur. Ces résultats indiquent que le Couloir Nord Rifain s’est ouvert à ~7.2 Ma assurant les communications entre l’Atlantique et la Méditerranée, puis a subi une restriction progressive pendant le Messinien inférieur avant d’être totalement fermé à ~6.1 Ma.De nouvelles études sédimentologiques et paléontologiques des dépôts Messinien supérieur-Pliocène inférieur dans le bassin de Boudinar fournissent des informations sur la Crise de salinité messinienne (« MSC ») et le réennoiement zancléen dans la Mer d'Alboran. L’un des marqueurs majeurs de la Crise est identifié : la surface d’érosion messinienne « MES ». Elle est d'âge Messinien supérieur et a été mise en place dans des conditions subaériennes. Sa géométrie originale n’est préservée que localement et a été remodelée par la surface transgressive du Pliocène inférieur. Au dessus de la « MES » le remplissage sédimentaire du bassin de Boudinar est caractérisé par une grande variété de faciès allant des conditions de dépôts continentales jusqu’à des conditions d’offshore inférieur. Deux ensembles majeurs sont reconnus : un ensemble messinien terminal-zancléen qui constitue une mégaséquence transgressive-regressive, interrompue au sommet par une discordance tectonique, et un ensemble plio-quaternaire regressif. Durant l’intervalle Messinien terminal-Zancléen, quatre modèles de dépôts successifs ont été documentés enregistrant des changements majeurs de paléocourants et de paléogéographies, liés aux fluctuations de niveau de base. Nous n’avons pas identifié de Gilbert delta à Boudinar. La remontée du niveau de base est marquée par une régression normale et par le développement des lacs et de complexes de fan-deltas sur les marges du bassin pendant le Messinien supérieur, avant l’inondation marine au Zancléen basal. Le réennoiement marin du bassin apparait plus tard avec une surface de transgression ravinante et par d’épais dépôts transgressifs, en onlap sur tous les dépôts précédents. La majeure partie du remplissage sédimentaire du bassin n’est pas reçue des reliefs de la bordure sud du bassin, mais du côté Nord-Ouset au bord de la Méditerranée. Les sédiments sont alors remaniés par les tempêtes et transportés vers le sud par la dérive littorale. Une surface d’inondation maximale a été identifiée à plusieurs dizaines de mètres au-dessus de la « MES ». Ceci suggère un ennoiement progressif et non catastrophique, après la chute du niveau de base méditerranéen.
https://tel.archives-ouvertes.fr/tel-01473572

Droits : http://hal.archives-ouvertes.fr/licences/copyright/
tel-01473572
https://tel.archives-ouvertes.fr/tel-01473572
https://tel.archives-ouvertes.fr/tel-01473572/document
https://tel.archives-ouvertes.fr/tel-01473572/file/Th%C3%A8se-achalhi.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 : 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 Blackwell Publishing
Résumé : International audience
Differentiating between forced regressive deposits from deglacial periods inhigh latitude domains and forced regressive deposits from the onset of glacialperiods in low latitude domains is fundamental for the accurate interpretationof glacial cycles within the geological record and then for thereconstruction of palaeogeography and palaeo-climate. A forced regressivedeglacial sequence is documented from the Lake Saint-Jean basin (Quebec,Canada). In this area, the Late Pleistocene to Holocene sediments haverecorded the Laurentide ice sheet retreat accompanied by the invasion ofmarine waters (Laflamme Gulf) from ca 129 cal kyr BP. Subsequently, fluviodeltaicand coastal prograding wedges were deposited; they followed thebase-level fall due to glacio-isostatic rebound. This succession, representinga transition from glacial to post-glacial periods within a previously glaciatedarea, was investigated through recent mapping, preserved landforms, faciesanalysis, and new optical stimulated luminescence and radiocarbon dates.Three basin-scale geological sections share a common lower part made ofisolated ice-contact fan deposits overlying bedrock. Throughout the entirebasin, ice-contact fans are capped by glacimarine muds. Above, fluvial andcoastal prograding systems were deposited and evolved through four steps:(i) deltaic systems progressively increased in width; (ii) coastal influence onsedimentation increased; (iii) hydrographic drainage systems became moreorganised; and (iv) deltas graded from steep (Gilbert delta) to low-angle foresets(mouth-bar delta). Deposited during the base-level fall from glacioisostaticrebound, the complete succession has been designated as a singlefalling stage system tract referred to as a deglacial falling stage system tract.It is representative of a deglaciation sequence in areas previously covered byice during glacial periods (i.e. medium to high latitude domains). Diagnosticcriteria are provided to identify such a deglacial falling stage system tract inthe geological record, which may aid identification of previously unknownglacial cycles.
ISSN: 1469-3496

insu-01184731
https://hal-insu.archives-ouvertes.fr/insu-01184731
DOI : 10.1111/sed.12196

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Sedimentary rocks and detrital minerals sample large areas of the continental crust, and they are increasingly seen as a reliable archive for its global evolution. This study presents two approaches to model the growth of the continental crust through the sedimentary archive. The first builds on the variations in U-Pb, Hf and O isotopes in global databases of detrital zircons. We show that uncertainty in the Hf isotope composition of the mantle reservoir from which new crust separated, in the 176Lu/177Hf ratio of that new crust, and in the contribution in the databases of zircons that experienced ancient Pb loss(es), adds some uncertainty to the individual Hf model ages, but not to the overall shape of the calculated continental growth curves. The second approach is based on the variation of Nd isotopes in 645 worldwide fine-grained continental sedimentary rocks with different deposition ages, which requires a correction of the bias induced by preferential erosion of younger rocks through an erosion parameter referred to as K. This dimensionless parameter relates the proportions of younger to older source rocks in the sediment, to the proportions of younger to older source rocks present in the crust from which the sediment was derived. We suggest that a Hadean/Archaean value of K = 1 (i.e., no preferential erosion), and that post-Archaean values of K = 4–6, may be reasonable for the global Earth system. Models built on the detrital zircon and the fine-grained sediment records independently suggest that at least 65% of the present volume of continental crust was established by 3 Ga. The continental crust has been generated continuously, but with a marked decrease in the growth rate at ~ 3 Ga. The period from > 4 Ga to ~ 3 Ga is characterised by relatively high net rates of continental growth (2.9–3.4 km3 yr− 1 on average), which are similar to the rates at which new crust is generated (and destroyed) at the present time. Net growth rates are much lower since 3 Ga (0.6–0.9 km3 yr− 1 on average), which can be attributed to higher rates of destruction of continental crust. The change in slope in the continental growth curve at ~ 3 Ga is taken to indicate a global change in the way bulk crust was generated and preserved, and this change has been linked to the onset of subduction-driven plate tectonics. At least 100% of the present volume of the continental crust has been destroyed and recycled back into the mantle since ~ 3 Ga, and this time marks a transition in the average composition of new continental crust. Continental crust generated before 3 Ga was on average mafic, dense, relatively thin (< 20 km) and therefore different from the calc-alkaline andesitic crust that dominates the continental record today. Continental crust that formed after 3 Ga gradually became more intermediate in composition, buoyant and thicker. The increase in crustal thickness is accompanied by increasing rates of crustal reworking and increasing input of sediment to the ocean. These changes may have been accommodated by a change in lithospheric strength at around 3 Ga, as it became strong enough to support high-relief crust. This time period therefore indicates when significant volumes of continental crust started to become emergent and were available for erosion and weathering, thus impacting on the composition of the atmosphere and the oceans.
ISSN: 0037-0738

hal-01622696
https://hal.archives-ouvertes.fr/hal-01622696
DOI : 10.1016/j.sedgeo.2017.06.001

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Tapajós Domain in the Amazonian Craton comprises hundreds of gold occurrences mainly hosted by Paleoproterozoic granitic rocks, whose geotectonic evolution and deformation style are poorly understood. The Tocantinzinho granite hosts a large amount of gold, forming the largest gold deposit known in the Tapajós Domain. The Tocantinzinho area is formed by plutonic rocks cut by subvolcanic rocks shallowly emplaced and constrained by NW-SE strike-slip faults, probably in a transtensive site. The magmatism started with the emplacement of huge granodiorite that presently formed the basement country rocks (2007–1997Ma), it was followed by the Tocantinzinho granite magmatism (1989–1979 Ma), and the coeval to late andesite emplacement. Petrological and textural evidence suggest the complex and synchronous occurrence of tectonics and few magmatic events expressed by the emplacement of successive granite, aplite, pegmatite, andesite, and dacite. The magmatic event finished with the cooling of this set of rocks below c. 320 °C, at c. 1950 Ma. The cooling rates vary from c. 3.6–14.7°C/Ma, with an average of 7.5°C/Ma, indicating no important vertical exhumations. The elongated geometry of the Tocantinzinho granite and related rocks, features of solid-state deformation within granites and syntectonic deformation of some andesite dikes imply the existence of wrench type tectonic control. The I-type signature of these rocks, their high-K calc-alkaline and metaluminous to peraluminous affinities combined with the tectonic style indicate a post-collisional tectonic setting. Based on geochemical and structural constrains, the rocks from the Tocantinzinho area are interpreted as a part of the Creporizão Suite and probably represent the first expressions of this syn-to late-tectonic magmatism in the region. A continuous and progressive process of magmatic emplacement controlled by tectonics will be proposed and discussed in conclusion.
ISSN: 0895-9811

hal-01526936
https://hal.archives-ouvertes.fr/hal-01526936
DOI : 10.1016/j.jsames.2017.02.003

Éditeur(s) : HAL CCSD
Résumé : International audience
Continental erosion and weathering destroy parts of the stratigraphic record. Analyses of the sedimentary filling of paleokarsts help completing the geological record of regions that have been submitted to post-depositional, long-term, continental evolution. Jurassic carbonate platform of Languedoc (South of France) has undergone several karstification phases from Cretaceous to Neogene. Later incision of canyons through the carbonate massifs allows to observe paleokarsts over 400m depth, within the massifs. Paleokarsts are partly filled with sediments. Some have yielded marine bioclasts (echinoderms, radiolars), foraminifera and nannofossils; others are composed of polygenic detrital sediments, including sources from the upstream Paleozoic basement (Cevennes). The age of the filling of successive paleokarsts can be constrained by structural relationships and by biostratigraphy. These findings suggests 1) the marine elements of the karstic filling relate to a Late Cretaceous to Early Paleocene interval, while 2) the Paleozoic basement-sourced-sediments were trapped in the karst during Miocene to Present. Karstic sediment containing Early Paleocene foraminifera and nannofossils are found in paleokarsts cavities distributed across the entire thickness of the carbonate massif (≥350m). This requires base-level lowering and associated karstification, followed by base-level rise and karst filling of at least 350 m amplitude, respectively. The time interval corresponding to the occurrence of foraminifera and nannofossils in karsts covers 10 Myrs ; surprisingly, no equivalent marine sediments are preserved on the surface. In addition, analyses of the different forams species suggests several (up to 3) distinct karstification and marine filling cycles. Finally, sedimentological facies analysis of the karst filling reveals the following succession of processes: low energy settling of mudstone, high energy reworking, transport and deposition of silts and sandstones within the karst system. Integration of geological, paleontological and sedimentological data, leads to a polyphase scenario in response to repeated base-level variations, more than 350m amplitude. Such an amplitude excludes eustacy, and the improbable repeated sequence of uplift and subsidence rules out tectonics, as driving forces for base-level change, respectively. We propose that the high-amplitude base-level changes results from a succession of desiccation-flooding events of an endorheic, silled, basin during Early Paleogene. The later detrital assemblage sourced in the Cevennes occurs on perched paleosurfaces and in karst cavities across the whole 350m-deep canyon walls. When found on paleosurfaces, they correspond to the south-flowing Early Miocene fluvial drainage, and can be correlated downstream with the marine, well dated, Early Miocene, sediments. When found within the karst cavities, they correspond to successive base-level surfaces connected to the progressive incision of the canyon. This canyon incision is coeval with a Late Miocene uplift of the hinterland.
24th International Karstological School "Classical karst" : Paleokarst
Postojna, Slovenia

hal-01306683
https://hal-brgm.archives-ouvertes.fr/hal-01306683
https://hal-brgm.archives-ouvertes.fr/hal-01306683/document
https://hal-brgm.archives-ouvertes.fr/hal-01306683/file/Abstract_IKS.pdf

Éditeur(s) : HAL CCSD Société géologique de France
Résumé : The Maguelone shore extends along the northern coast of the Gulf of Lions margin, West of the Rhone delta and East of some high gradient coastal streams that have been providing most of the elastic sediments to the Gulf of Lions margin since the early Miocene. This 10 km wide area comprises an onshore small coastal watershed (15 km long) in low-lying carbonate hills, kilometer wide marshes, sandy beach and shoreface featuring local low sedimentation. Deposit architecture in such a coastal zone records dynamics of incised valley fill under the influence of rivers and wave/current hydrodynamics in a microtidal environment during an eustatic cycle.;A detailed analysis of about 250 km of very high resolution seismic profiles, tens of cores and outcrops data revealed the evolution of the Maguelone coastal system from Late-Quaternary to present-day. It highlighted also dominant denudation processes in the upstream catchments associated to the formation of incised valley seaward during Quaternary. Combination of this inherited morphology together with hydrodynamics controlled the lagoonal environment evolution since the last transgression. In particular, the Maguelone shore is characterized by the formation of built-over-rias lagoonal systems and records an evolution from partially protected lagoon to isolated lagoon environment. These two stages of lagoon evolution correspond to distinct deposit environments. Correlation of fauna contents with deposit geometry improves lagoonal environment models.
EISSN: 1777-5817

hal-00486370
https://hal.archives-ouvertes.fr/hal-00486370
DOI : 10.2113/gssgfbull.181.2.211

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In order to better constrain the relationship between tectonics and sedimentation of the Eastern Sardinian Margin, from the Messinian to the present day (METYSS project), a lithostratigraphic study was carried out on the Late Neogene deposits along the Cedrino Valley (eastern Sardinia). The late Neogene evolution is documented from sedimentological and tectonic analysis, biostratigraphic dating, and by mapping and logging stratigraphic sections. Previous authors have differentiated an early Pliocene marine formation from an older continental formation, possibly Miocene, the entire system being covered by late Pliocene to Quaternary lava flows. Preliminary biostratigraphic data suggest the absence of the lowermost Pliocene, based on the absence of Globorotalia margaritae and the presence of Globorotalia puncticulata, implying a sediment age between 3.81 and 2.41 Ma. At the foot of the Fiuli cliff, some mud clasts include a coccolith microflora, Tortonian in age, suggesting reworking. The Pliocene marine deposits consist of a single filling sequence instead of a succession of superimposed sequences as we would expect during this period of time; the occurrences of terms rarely respect the usual transgressive-regressive succession. Contrasting bathymetric environments (fore-shore, pro-delta, shelf or upper slope) can be abruptly superimposed on top of the other, along few meter thick intervals. A rapidly flooded term is observed in several sites and indicates a spatial variability over only a few kilometers distance. Some deep water deposits are in the middle of the infilling Pliocene sequence, whereas shallower water deposits can be repeated along a vertical section, or even interrupted by emersion. These marked differences can express syn-, or possibly post-sedimentation tectonic uplifts. The 10–25° bed dips originated through local tectonic uplift. At Fiuli, the geometry of the bedding planes is indicative of tilting toward the west, in a direction opposite to the one observed at Onifai. These Pliocene series form a wide syncline with an approximately NNE–SSW axis. This morpho-structural behavior appears to be largely atypical of this East-Sardinian coastal area.
ISSN: 1040-6182

hal-01134707
https://hal.archives-ouvertes.fr/hal-01134707
DOI : 10.1016/j.quaint.2014.11.022

Éditeur(s) : HAL CCSD Société géologique de France
Résumé : International audience
The central part of the Gulf of Lions shoreline is characterized by many coastal wetlands that resulted from the interaction between a process of shoreline regularization by migrations of littoral barriers and a slow filling of the back-barrier areas by the riverine and marine inputs. Analyses of Late-Holocene deposits with a very high-resolution multi-proxy study of two sediment cores, allow us to reconstruct the evolution of this coastal system. Two main Holocene sediment units are identified overlying a Pliocene carbonate continental formation. The lower unit consists of sandy and pebbly marine sediments deposited around 7800 B.P., during the final stand of the last sea level rise. Just above, the upper unit displays lagoonal grey clay silts with shells and some intercalated layers of silty sands related to paleostorm events. The age model was established from radiocarbon dating, for the oldest part of the core. Over the last century, sedimentation rates were calculated using the CFCS Pb-210 model, together with Cs-137 data. Radiocarbon data show an increase in he accumulation rate from the base to the top of cores. Marine sand units related to the last transgressive deposit allow to refine the curve of Holocene post-glacial sea level rise. Sedimentological and faunal analyses associated with chronological data provide a means for reconstructing the Late-Holocene paleoenvironments along this part of the coast and suggest that the final closure of the coastal lagoon by the sandy barrier occurred at around 730 +/- 120 yr cal B.P. The beginning of this closure, together with the progradation of the coastal plain, could be responsible for the decline in economic activity of the Lattara harbour during the Roman period.
La partie centrale du littoral du golfe du Lion est caractérisée par de nombreuses lagunes qui résultent de l'interaction entre un processus de régularisation du trait de côte par migration de barrières littorales et d'un lent remplissage des zones situées en arrière des barrières par des apports continentaux et marins. Les analyses des dépôts tardi-holocènes avec une étude multi-traceurs à très haute résolution de deux carottes sédimentaires nous permettent de reconstruire l'évolution de ce système côtier. Deux unités sédimentaires holocènes sont identifiées recouvrant une formation pliocène carbonatée. L'unité inférieure est constituée de sables et de galets d'origine marine déposés vers 7800 B.P., durant les stades ultimes de la dernière remontée marine. Audessus, l'unité supérieure montre des dépôts d'argile et de silt gris coquilliers d'origine lagunaire, dans lesquels sont intercalés des niveaux de sable silteux révélant la présence d'événements de tempêtes. Le modèle d'âge est établi à partir de dates radiocarbones pour les parties les plus anciennes des archives sédimentaires, tandis que pour le dernier siècle, les taux de sédimentation sont calculés en utilisant le modèle CFCS pour le 210Pb, associé aux données de 137Cs. Les données 14C montrent une augmentation du taux d'accumulation depuis la base jusqu'en surface des carottes. Les unités de sables marins liées aux dépôts de la dernière transgression marine permettent de préciser la courbe post-glaciaire de remontée du niveau marin. Les analyses sédimentologiques et faunistiques associées aux données chronologiques fournissent une méthode permettant de reconstituer les paléoenvironnements littoraux tardi-holocènes dans la zone d'étude et suggèrent que la fermeture finale de ces lagunes par le cordon sableux survient autour de 730 ± 120 ans cal B.P. Le début de cette fermeture, associée à la une progradation deltaïque, pourrait être responsable du déclin des activités économiques du port de Lattara durant la période Romaine.
EISSN: 1777-5817

halshs-00740923
https://halshs.archives-ouvertes.fr/halshs-00740923
DOI : 10.2113/gssgfbull.181.1.27

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) : HAL CCSD Elsevier
Résumé : International audience
The dating of alluvial landforms by cosmogenic nuclides requires distinguishing the pre-deposition inheritance from the post-deposition history of the clasts in the studied marker. Moreover, estimating catchment-scale erosion rates from the concentrations of cosmogenic nuclides in active alluvia requires a good knowledge of the local/regional relationships between rock exhumation and transport through space and time. This is still poorly known for timescales of tens of thousand years. In order to document the evolution of clast exhumation and transport rates through time, we analyze in situ 10Be concentrations in boulders and cobbles from hillslopes to outlet of an arid mountainous catchment located in Gobi-Altay, Mongolia, strongly affected by global climatic changes during the Pleistocene-Holocene period. Samples were collected on bedrock, abandoned alluvial deposits, active colluvia and alluvia. Our results show a large 10Be scattering in the active river bed, consistent with a low and discontinuous catchment erosion rate dominated by mass wasting and fluvial incision. On the contrary, pre-exposure signal within abandoned terraces is much more homogeneous, consistent with climatic pulses responsible of strong erosional events on hillslopes and rapid fluvial transport. These results show that exhumation/transport processes at the catchment scale vary in style and intensity through time as a consequence of climatic oscillations. The occurrence of abrupt climatic changes during short periods of time recorded by 10Be concentrations in abandoned alluvia raise questions about the temporal applicability of catchment erosion rates derived from cosmogenic nuclide concentrations measured in sediments of active rivers. On the other hand, strong and short erosion events limit and homogenize the pre-exposure 10Be signal in associated deposits like debris-flows, making them particularly suitable markers for dating in active tectonic and paleoclimatic studies.
ISSN: 0169-555X

hal-00626702
https://hal.archives-ouvertes.fr/hal-00626702
https://hal.archives-ouvertes.fr/hal-00626702/document
https://hal.archives-ouvertes.fr/hal-00626702/file/GEOMOR-2485R1_corrected.pdf
DOI : 10.1016/j.geomorph.2011.07.023

Éditeur(s) : HAL CCSD
Résumé : La grotte d'Angel, datée du Pléistocène moyen et de la base du Pléistocène supérieur, a livré un important matériel lithique et faunistique, et présente un intérêt exceptionnel dans la Péninsule Ibérique. Vu son importance, et dans le cadre d'un programme de recherche européen (N°IDPH/ER/05), une étude pluridisciplinaire a été réalisée sur le remplissage sédimentologique et les vestiges archéologiques. Nous présentons dans cet article les résultats de l'étude des propriétés magnétiques du remplissage de la grot- te. Cette approche a révélé la présence de deux unités magnétostratigraphiques. L'unité stratigraphique inférieure se caractérise par une forte concentration en grains magnétiques, parmi lesquels un fort pour- centage en grains superparamagnétiques (SP). Les minéraux magnétiques sont d'origine secondaire, de petite taille, de nature douce et dominés par la magnétite et la maghémite. Ces derniers ont subi une évo- lution géochimique post-dépositionnelle importante (forte pédogenèse). Au contraire, dans l'unité supé- rieure, les valeurs des différents paramètres magnétiques sont faibles et les minéraux magnétiques sont d'origine détritique et se caractérisent par une force coercitive élevée, conforme à la présence d'hématite. The Angel cave, dated between the middle to the base of the Upper Pleistocene, contains important lithic and faunal material, and is of exceptional interest in the Iberian Peninsula. Because of its importance, and in the framework of an European research project (N°IDPH/ER/05), a multidisciplinary study including palaeomagnetism, was undertaken on the sedimentary deposit and the archaeological material. The study of the magnetic properties of the cave sediments reveals the presence of two magnetostratigraphic units. The lower stratigraphic unit is characterized by an important concentration of magnetic grains with a con- siderable percentage of superparamagnetic grains (SP). The magnetic minerals are of secondary origin, fine grained, magnetically soft and dominated by magnetite and maghemite. The latter have undergone an important post-depositional geochemical evolution (marked pedogenesis). On the contrary, the upper unit is characterized by weaker magnetic parameters and the magnetic minerals are harder, of detrital origin, dominated by hematite
ESTUDIOS GEOLOGICOS-MADRID

hal-00903622
https://hal.archives-ouvertes.fr/hal-00903622
DOI : 10.3989/egeol.40946.222

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
The stratigraphy of the last deglaciation sequence is investigated in Lake Saint-Jean (Québec Province, Canada) based on 300 km of echo-sounder two dimensional seismic profiles. The sedimentary archive of this basin is documented from the Late Pleistocene Laurentidian ice-front recession to the present-day situation. Ten seismic units have been identified that reflect spatio-temporal variations in depositional processes characterizing different periods of the Saint-Jean basin evolution. During the postglacial marine flooding, a high deposition rate of mud settling, from proglacial glacimarine and then prodeltaic plumes in the Laflamme Gulf, produced an extensive, up to 50 m thick mud sheet draping the isostatically depressed marine basin floor. Subsequently, a closing of the water body due to glacio-isostatic rebound occurred at 8.5 cal. ka BP, drastically modifying the hydrodynamics. Hyperpycnal flows appeared because fresh lake water replaced dense marine water. River sediments were transferred towards the deeper part of the lake into river-related sediment drifts and confined lobes. The closing of the water body is also marked by the onset of a wind-driven internal circulation associating coastal hydrodynamics and bottom currents with sedimentary features including shoreface deposits, sediment drifts and a prograding shelf-type body. The fingerprints of a forced regression are well expressed by mouth-bar systems and by the shoreface-shelf system, the latter unexpected in such a lacustrine setting. In both cases, a regressive surface of lacustrine erosion (RSLE) has been identified, separating sandy mouth-bar from glaciomarine to prodeltaic muds, and sandy shoreface wedges from the heterolithic shelf-type body, respectively. The Lake Saint-Jean record is an example of a regressive succession driven by a glacio-isostatic rebound and showing the transition from late-glacial to post-glacial depositional systems.
ISSN: 0300-9483

hal-00984683
https://hal.archives-ouvertes.fr/hal-00984683
DOI : 10.1111/bor.12039

Éditeur(s) : HAL CCSD Geological Society of London
Résumé : Permo-Triassic rift basins offer important hydrocarbon targets along the Atlantic margins. Their fill is dominated by continental red beds, comprising braided fluvial, alluvial fan, aeolian, floodplain and lacustrine facies. These relatively lightly explored basins span both the Atlantic and Tethyan domains and developed above a complex basement with inherited structural fabrics. Sparse data in offshore regions constrain understanding of depositional geometries and sedimentary architecture, further impeded by their deep burial beneath younger strata, combined with the effects of later deformation during continental breakup. This paper provides results from a multidisciplinary analysis of basins along the Atlantic margin. Regional seismic and well data, combined with geochemical provenance analysis from the European North Atlantic margins, are integrated with detailed outcrop studies in Morocco and Nova Scotia. The research provides new insights into regional basin tectonostratigraphic evolution, sediment fill, and reservoir distribution, architecture and quality at a range of scales. Regional seismic profiles, supported by key well data, indicate the presence of post-orogenic collapse basins, focused narrow rifts and low-magnitude multiple extensional depocentres. Significantly, Permo-Triassic basin geometries are different and more varied than the overlying Jurassic and younger basins. Provenance analysis using Pb isotopic composition of detrital K-feldspar yields new and robust controls on the sediment dispersal patterns of Triassic sandstones in the NE Atlantic margin. The evolving sedimentary architecture is characterized by detailed sedimentological studies of key outcrops of age equivalent Permian-Triassic rifts in Morocco and Nova Scotia. The interplay of tectonics and climate is observed to influence sedimentation, which has significant implications for reservoir distribution in analogue basins. New digital outcrop techniques are providing improved reservoir models, and identification of key marker horizons and sequence boundaries offers a potential subsurface correlation tool. Future work will address source and seal distribution within the potentially petroliferous basins.
Petroleum Geology: From Mature Basins to New Frontiers Proceedings of the 7th Petroleum Geology Conf

hal-00590618
https://hal.archives-ouvertes.fr/hal-00590618

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Brecciated and fractured peridotites with a carbonate matrix, referred to as ophicalcites, are common features of mantle rocks exhumed in passive margins and mid-oceanic ridges. Ophicalcites have been found in close association with massive peridotites, which form the numerous ultramafic bodies scattered along the North Pyrenean Zone (NPZ), on the northern flank of the Pyrenean belt. We present the first field, textural and stable isotopic characterization of these rocks. Our observations show that Pyrenean ophicalcites belong to three main types: (1) a wide variety of breccias composed of sorted or unsorted millimeter- to meter-sized clasts of fresh or oxidized ultramafic material, in a fine-grained calcitic matrix; (2) calcitic veins penetrating into fractured serpentine and fresh peridotite; and (3) pervasive substitution of serpentine minerals by calcite. Stable isotopic analyses (O, C) have been conducted on the carbonate matrix, veins and clasts of samples from 12 Pyrenean ultramafic bodies. We show that the Pyrenean ophicalcites are the product of three distinct genetic processes: (1) pervasive ophicalcite resulting from relatively deep and hot hydrothermal activity; (2) ophicalcites in veins resulting from tectonic fracturing and cooler hydrothermal activity; and (3) polymictic breccias resulting from sedimentary processes occurring after the exposure of subcontinental mantle as portions of the floor of basins which opened during the mid-Cretaceous. We highlight a major difference between the eastern and western Pyrenean ophicalcites belonging, respectively, to the sedimentary and to the hydrothermal types. Our data set points to a possible origin of the sedimentary ophicalcites in continental endorheic basins, but a post-depositional evolution by circulation of metamorphic fluids or an origin from relatively warm marine waters cannot be ruled out. Finally, we discuss the significance of such discrepancy in the characteristics of the NPZ ophicalcites in the frame of the variable exhumation history of the peridotites all along the Pyrenean realm.
ISSN: 1437-3254

insu-00944405
https://hal-insu.archives-ouvertes.fr/insu-00944405
https://hal-insu.archives-ouvertes.fr/insu-00944405/document
https://hal-insu.archives-ouvertes.fr/insu-00944405/file/clerc-etal-IJES-Review.pdf
DOI : 10.1007/s00531-013-0927-z

Éditeur(s) : HAL CCSD
Résumé : International audience
Two opposing visions of the Aegean backarc tectonics implicitly contain contrasting images of the rheological behaviour of the lihosphere, supported by different sets of observations. The propagation of the NAF and extension in the Corinth Rift suggest a strongly localising rheology whereas the formation of MCC in the Cyclades and the Rhodope suggests instead a more viscous behaviour. This paradox was the seminal question addressed by the ANR-EGEO programme (2007-2010) that leads to the following conclusions: (1) The exhumation of the Cycladic MCC's is accommodated by the N-dipping North Cycladic Detachment System (NCDS) that partly reworks the Vardar suture and at the base by a series of thrusts, including the basal contact of the Cycladic Blueschists (CBS) over the Cycladic Basement (CB). The activity of LANF is due to the reactivation of pre-existing discontinuities such as thrusts or earlier detachments and much less to the interaction with granitic plutons. (2) Exhumation in the Cyclades has proceeded in two stages: (a) Eocene syn-orogenic exhumation within the subduction lower/upperplate interface while the post-orogenic Rhodope MCC formed further north, (b) Oligo-Miocene post-orogenic extension in an MCC mode coeval with syn-orogenic exhumation in Crete and the Peloponnese. (3) Both stages were associated with slab retreat, as early as the Eocene with an acceleration at 30-35 Ma. (4) The localisation of the presently active steeply-dipping normal faults on the southern margin of the Corinth Rift may have been preceded by a partial reworking of thrusts and syn-orogenic detachments by shallow-dipping decollements. (5) The localisation of the NAF in the Marmara Sea region and the Northern Aegean Sea is now accurately dated between 5.3 and 5 Ma Ma using the erosion and deposition surfaces that mark the Messinian salinity Crisis and nannofossils ages. (6) The formation of MCCs in the Cyclades resulted in the draining of the low viscosity lower crust from the northern Aegean Sea and led to an easier coupling between upper mantle and upper crust, easing the localisation and propagation of the NAF. (7) A comparison between crustal and mantle finite strain suggests that mantle flow due to slab retreat controls the stretching of the crust. Our model involves progressive slab retreat and mantle flow below the overriding plate inducing the observed succession of tectonic episodes with a progressive localisation of extension due to several slab tearing events. There is no paradox in the tectonic history and rheological behaviour of the Aegean lithosphere but an evolution of the kinematic boundary conditions due to slab deformation at depth.
American Geophysical Union
San Francisco, United States

insu-00860518
https://hal-insu.archives-ouvertes.fr/insu-00860518
BIBCODE : 2010AGUFM.T13G..04J

Éditeur(s) : HAL CCSD Geological Society of America
Résumé : International audience
The post-rift denudation history of high-elevation divergent continental margins is central to deciphering source-to-sink systems across such margins and to unraveling their topographic evolution. We performed 40Ar-39Ar dating of supergene K-Mn oxides from supergene manganese ore deposits in order to constrain the age of in situ formed laterites on both the lowland and highland sides of the Western Ghats Escarpment of Peninsular India. Documentation of laterites as old as 53 Ma on the highland and 47 Ma at the foot of the escarpment shows that the escarpment stabilized before 47 Ma (possibly 60 Ma). The topographic setting of the dated weathering mantles also constrains denudation of the lowland and the highland since ca. 50 Ma to maximums of 5 m/m.y. and 15 m/m.y., respectively. Our results challenge denudation rates derived from apatite fission track thermochronology by documenting the topography and relief longevity of the southwest Indian margin and its hinterland. The results preclude large-magnitude uplift of Peninsular India after the Eocene, and more generally argue against late Neogene uplift and topographic rejuvenation of continental shields.
ISSN: 0091-7613

hal-01306559
https://hal.archives-ouvertes.fr/hal-01306559
DOI : 10.1130/G37303.1