Éditeur(s) : HAL CCSD Geological Society of America
Résumé : International audience
Because of its essential role in coupling climate and tectonics, denudation is a key parameter when constraining the history of Earth’s surface. This is particularly true at the Pliocene-Pleistocene transition, and the potential impact of the onset of Quaternary glaciations remains strongly debated. In the present study, we measured in situ cosmogenic 10Be within continuous late Cenozoic sedimentary sections that had already been dated using magnetostratigraphy. The new data were obtained from four sedimentary basins in the northern and southern Tianshan range (Central Asia). We first thoroughly discuss how in situ cosmogenic 10Be concentrations can be corrected for radioactive decay and for the contribution of postdepositional cosmogenic accumulation to derive the paleo–denudation rates. Our analysis shows that, in the four sedimentary records, the potential bias remains low enough to consider the derived denudation rates reliable. The four records, although likely influenced by local particularities due to lithological heterogeneity and local tectonics, display similar trends of continuously increasing denudation between ca. 9 Ma and the present. These rates have remained relatively high but steady since 4 Ma, ∼1.5 m.y. before the onset of the Quaternary glacial cycles. Though the rejuvenation of the Tianshan range since 11 Ma may explain most of the progressive increase (×5) in denudation, our data suggest that the Quaternary glaciations had only a limited impact on denudation in the Tianshan. Our data, however, indicate an increase in the spatial and high-frequency variability (<1 m.y.) of the denudation rates between 3 and 1 Ma. This may correspond to a transient readjustment of the landscape in response to the onset of Quaternary glacial cycles.
ISSN: 0016-7606

hal-01685766
https://hal.archives-ouvertes.fr/hal-01685766
DOI : 10.1130/B31475.1

Éditeur(s) : Amer Geophysical Union
Résumé : The Algerian margin has originated from the opening of the Algerian basin about 25-30 Ma ago. The central margin provides evidence for large-scale normal faults of Oligo-Miocene age, whereas transcurrent tectonics characterizes the western margin. A set of NW-SE oriented dextral transform faults was active during basin opening and divided the 600 km long central margin into segments of similar to 120-150 km. The upper Miocene, Plio-Quaternary, and present-day tectonic setting is, however, compressional and supports the occurrence of a margin inversion, a process still poorly documented worldwide. We show that the central Algerian margin represents a rare example of inverted margin, where the process of subduction inception is particularly well expressed and helps understand how extensional and transtensive structures are involved in margin shortening. Using multibeam bathymetry and multichannel seismic reflection sections from the MAR-ADJA 2003 and 2005 cruises, we evidence Pliocene-Pleistocene shortening with contrasting styles along the margin between west (Khayr Al Din bank) and east (Boumerdes-Dellys margin) of Algiers. Pre-Miocene structures such as basement highs and transform faults appear to control changes of the deformation pattern along this part of the margin, resulting in different widths, geometries, and relative positions of folds and faults. Plio-Quaternary and active blind thrust faults do not reuse Oligo-Miocene normal and transform faults during inversion, but instead grow within the continental margin (as testified for instance by the 21 May 2003 M-w 6.8 Boumerdes-Zemmouri earthquake), at the foot of the continental slope and at the northern sides of basement highs interpreted as stretched continental blocks of the rifted margin. The inherited structures of the margin appear, therefore, to determine this deformation pattern and ultimately the earthquake and tsunami sizes offshore. The complex geometry of the fault system along the Algerian margin suggests a process of initiation of subduction in its central and eastern parts.
Tectonics (0278-7407) (Amer Geophysical Union), 2010-03 , Vol. 29 , N. TC2008 , P. 1-22

Droits : 2010 American Geophysical Union
http://archimer.ifremer.fr/doc/00008/11883/9286.pdf
http://archimer.ifremer.fr/doc/00008/11883/9287.pdf
DOI:10.1029/2009TC002547
http://archimer.ifremer.fr/doc/00008/11883/

Éditeur(s) : HAL CCSD Oxford University Press (OUP): Policy B - Oxford Open Option A Oxford University Press (OUP)
Résumé : International audience
Peridotite xenoliths exhumed by Quaternary alkaline magmatism in the Tahalgha district, southern Hoggar, represent fragments of the subcontinental lithospheric mantle beneath the boundary between the two major structural domains of the Tuareg Shield: the ‘Polycyclic Central Hoggar’ to the east and the ‘Western Hoggar’, or ‘Pharusian Belt’, to the west. Samples were collected from volcanic centres located on both sides of a major lithospheric shear zone at 4°35' separating these two domains. Although showing substantial variations in their deformation microstructures, equilibrium temperatures and modal and chemical compositions, the studied samples do not display any systematic changes of these features across the 4°35' fault. The observed variations rather record small-scale heterogeneities distributed throughout the study area and reflecting the widespread occurrence of vein conduits and metasomatized wall-rocks related to trans-lithospheric melt circulation during the Cenozoic. These features include partial annealing of pre-existing deformation microstructures, post-deformation metasomatic reactions, and trace-element enrichment, coupled with heating from 750–900°C (low-temperature lherzolites) to 900–1150°C (intermediate-T lherzolites and high-T harzburgites and wehrlites). Trace-element modelling confirms that the range of rare earth element (REE) variations observed in the Tahalgha clinopyroxenes may be accounted for by reactive porous flow involving a single stage of basaltic melt infiltration into a light REE (LREE)-depleted protolith. Whole-rock compositions record the final entrapment of disequilibrium metasomatic melts upon thermal relaxation of the veins–wall-rock system. The striking correlations between equilibrium temperatures and trace-element enrichment favor a scenario in which the high-temperature peridotites record advective heat transport along melt conduits, whereas the intermediate- and low-temperature lherzolites reflect conductive heating of the host Mechanical Boundary Layer. This indicates that the lithosphere did not reach thermal equilibrium, suggesting that the inferred heating event was transient and was rapidly erased by thermal relaxation down to the relatively low-temperature present-day geotherm. The low-T (<900°C) deformed lherzolites (porphyroclastic to equigranular) are characterized by only incipient annealing and LREE-depleted clinopyroxene compositions. They were only weakly affected by the Cenozoic events and could represent relatively well-preserved samples from rejuvenated Pan-African lithosphere. Extensive lithospheric rejuvenation occurred either regionally during the Pan-African orogeny, as a result of lithospheric delamination or thermomechanical erosion after thickening, or more locally along the meridional shear zones. The low-T Tahalgha lherzolites are comparable with lherzolites from Etang de Lherz, southern France, interpreted as lithospheric mantle rejuvenated by melt-induced refertilization during a late stage of the Variscan orogeny.
ISSN: 0022-3530

hal-01107410
https://hal.archives-ouvertes.fr/hal-01107410
DOI : 10.1093/petrology/egu056

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Tyrrhenian Sea is usually interpreted to be a Neogene back-arc basin that opened by continental rifting and oceanic spreading caused by the eastward migration of the Apennine subduction system during Miocene and Pliocene times. Rifting of the southern Tyrrhenian Sea started first along the Eastern Sardinian margin during the middle to late Miocene times, including the Messinian. The "METYSS" project aims at better constraining the relationships between crustal tectonics, salt tectonics and sedimentation from Messinian times to present-day. The "METYSS 1" cruise (2009) allowed to acquire about 1200 km of HR seismic-reflection profiles along the Eastern Sardinian margin, Western Tyrrhenian Sea. This data set clearly illustrates that this area has been highly dissected during the rifting stage by N-S trending normal faults delineating ridges and basins, as previously described. The Messinian seismic markers (UU and MU) locally display fan-shaped stratal geometries, but the mechanism responsible for such geometries, salt tectonics or rifting, has yet to be carefully deciphered. We also mapped the spatial distribution of the mobile salt. The highly variable thickness of the small confined salt basins may be related to the initial pre-Messinian basin geometry, to the fact that salt deposition was syn-rift or to salt movement. Southeastward, salt tectonics is vigorous in unconfined basins and appears to have started early during the UU deposition. More surprisingly, our data demonstrate that some of the major faults have been significantly reactivated during the post-rift period, up to late Quaternary time, as shown by bathymetric scarps and associated debris flows. Moreover, some of this post-rift deformation can be evidenced within the Plio-Quaternary sequence by a regional unconformity. The post-Miocene deformation style varies greatly between different areas of the margin, and can also be strongly influenced by the presence or absence of mobile Messinian salt.
ISSN: 0040-1951

hal-00996665
https://hal.archives-ouvertes.fr/hal-00996665
DOI : 10.1016/j.tecto.2013.12.015

Éditeur(s) : Gauthier-Villars
Résumé : The Middle America Trench off Guatemala was transected by 24-channel seismic-reflection surveys, seismic-refraction surveys, and drilling with the Glomar Challanger . The drilling was doneat three sites on the oceanic Cocos plate and four sites on the Caribbean plate. These plates converge at about 10 cm/yr as indicated by global plate reconstruction. On the oceanic Cocos plate a basal chalk sequence of lower and middle Miocene age is overlain by a thin interval of abyssal clay. In contrast is the Cretaceous to lower Miocene claystone sequence recovered only at a site 3 km landward of the trench axis where drilling penetrated the hemipelagic slope deposits. A large amount of sediment along with ocean crust has been subducted during the present (Miocene to Quaternary) episode of subduction, and parts of the continental framework may have been subducted as well. No current tectonic model satisfactorily explains the surprising occurrence of Cretaceous to Miocene claystone at the foot of the continent.
Oceanologica Acta, Special issue (0399-1784) (Gauthier-Villars), 1981

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00245/35671/34179.pdf
http://archimer.ifremer.fr/doc/00245/35671/

Éditeur(s) : Elsevier
Résumé : The Okinawa Trough is a natural laboratory for the study of later Quaternary land-ocean interaction and paleoenvironmental changes. In this study we reconstruct the evolution of clay mineral assemblages in Core DGKS9604 retrieved from the central Okinawa Trough. Illite dominates the clay mineral compositions, with average contents above 60%. Clay mineral evolution since 28 ka is closely related to changes in sediment provenance and paleoenvironment. Sea level rise and the strength of the Kuroshio Current control the dispersal and deposition of clays on the East China Sea shelf and in the Okinawa Trough, and thus, determine the clay mineral compositions in the core sediments. During the late last glacial period (28.0-14.0 ka), the paleo-Changjiang River mouth was situated at the shelf edge close to the central Okinawa Trough and thus, together with the outer shelf, supplied large volumes of terrigenous sediments directly into the trough. From 14.0 to 8.4 ka influence from the Changjiang decreased while the mid-outer shelf of the East China Sea became the dominant sediment source to the central Okinawa Trough as sea level rose and the Changjiang river mouth migrated west. Strong sediment reworking and erosion at the shelf edge at 15-13 ka significantly increased the lateral transport of fine-grained shelf sediments to the central Okinawa Trough. Since ca. 8.4 ka clays from Taiwan have dominated the sediment flux to the site, coinciding with the re-entry of the Kuroshio Current into the trough. The increasing influence of the Changjiang-sourced sediments since 1.5 ka was probably related to the weakening of the Kuroshio Current and/or a higher river flux. (C) 2010 Elsevier B.V. All rights reserved.
Palaeogeography, Palaeoclimatology, Palaeoecology (0031-0182) (Elsevier), 2010-03 , Vol. 288 , N. 1-4 , P. 108-117

Droits : 2010 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/00002/11367/7977.pdf
DOI:10.1016/j.palaeo.2010.01.040
http://archimer.ifremer.fr/doc/00002/11367/

Éditeur(s) : HAL CCSD Universidad Complutense de Madrid
Résumé : Based on new seismological and recent faulting data, we analyze five main sectors in the western part of the Betic Cordillera from an active tectonic perspective: i. The northwestern frontal sector of the cordillera, including the Morón de la Frontera area, with shallow (< 15 km depth) seismogenic active NE-SW reverse and strike-slip faults that do not reach the surface. ii. The Teba area, in the External Zones, which is deformed by sparse N-S to NW-SE normal faults with associated wedges of Quaternary sediments and active strike-slip faults at intermediate crustal levels. iii. The Ronda Basin, representing the major Late Miocene intramontane basin of the western Betic Cordillera, is mainly deformed by NNE-SSW and WNW-ESE folds and locally by NW-SE normal faults. iv. The internal part of the orogen, which is characterized by shallow (<40 km) and intermediate (40 to 120 km depth) seismicity beneath Málaga and the Alborán Sea, ENE-WSW folding, relief uplift, river incision and scarce active faults with surface expression. v. The Spanish Atlantic coast, which coincides with the western end of the Betic orogen, where Pliocene to Quaternary shallowmarine sedimentary rocks are deformed by meso-scale NW-SE oriented normal faults and few ENE-WSW reverse faults. These data support the recent tectonic activity of the western Betic Cordillera determined by the NW-SE Eurasian-African convergence with variable features from the mountain front, characterized by shallow deformations, up to the Internal Zones that mainly undergo uplift and intermediate seismicity.
ISSN: 1698-6180

hal-00750359
https://hal.archives-ouvertes.fr/hal-00750359
DOI : 10.5209/rev_JIGE.2012.v38.n1.39211

Éditeur(s) : Gauthier-Villars
Résumé : Calcareous nannofossil assemblages of the family Noelaerhabdaceae have been studied in sediments of seventeen Quaternary cores raised from various climatic areas of the Atlantic and Pacific oceans. These sections display a regular, hiatus-free sedimentation for the last 500000 years. They have been dated using oxygen-isotopic measurements, variations of calcium carbonate content, variations of total nannofossil abundance, thorium measurements and volcanic ash horizons. Coccoliths of the genus Gephyrocapsa have been placed in three distinct taxonomic groups, based on morphological criteria inferred from light-microscope observations. Their acmes, as well as the acme of Emiliania huxleyi, are considered as stratigraphic markers. These markers characterize most of the last thirteen glacial-interglacial climatic stages, as well as some climatic events of lower magnitude (8.5 and 6.5). Most of these markers have global stratigraphic significance: acme of ''closed'' Gephyrocapsa during stages 13,11 and 9, and during event 8.5; acme of ''small'' Gephyrocapsa during stage 7 and event 6.5; acme of ''open'' Gephyrocapsa at top of event 6.5, and during stages 5 and 3; acme of E. huxleyi during stages 3 and 1. Others are only valid south of the southernmost latitude reached by the North-Atlantic polar front during the Quaternary: acme of ''closed'' Gephyrocapsa during stage 12; acme of ''small'' Gepkyrocapsa in early and middle stage 5; acme of E. huxleyi during stage 2. Others are only valid south of 20-degrees-S: acme of ''small'' Gephyrocapsa at the 10/9 stage boundary; acme of ''open'' Gephyrocapsa during stage 6.
Oceanologica Acta (0399-1784) (Gauthier-Villars), 1993 , Vol. 16 , N. 4 , P. 349-362

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00099/21061/18687.pdf
http://archimer.ifremer.fr/doc/00099/21061/

Éditeur(s) : HAL CCSD
Résumé : The present study addresses the question of increasing need in water supply. One line of research consists in investigating karst aquifers that represent significant water supplies for the areas around the Mediterranean. This work aims at developing a methodology of predictive evaluation of karst distribution and karst thickness within the carbonate massifs. It is based on the study of the Tethysian carbonate platform from the area of Montpellier, South of France. This area underwent a polyphased, complex, tectonic evolution, involving successive karst forming events. The approach is based on the relationships between eustacy and geodynamics, on one hand, and base-level variation recorded within palaeokarsts, on the other hand. Sedimentary fill of palaeokarsts allows to identify distinct karstification phases and sometimes to date them. It is a marker of base-level variations, which we attempt to quantify, that is responsible for karst formation and karst filling and sealing. For three palaeokarsts of regional extent, we analyze : karst sedimentary-fill, the distribution along upstream-downstream profile, the vertical extension of palaeokarsts, indicative of the base-level lowering. - The " Bauxite palaeokarst " results from the two-stage evolution of the " Isthme Durancien " : i) Bauxitic weathering of the Neocomian cover over the southern Massif Central , related to an inversion during Barremian ; ii) ≥1600 m uplift and exhumation during Aptian-Albian, inducing erosion of alterites, upstream, and deposition of detrital bauxites, downstream. - The " Early Paleocene palaeokarsts with marine sedimentary-fill " indicate base level variations of more than 350m in the upstream area. It is suggested here that such base-level variations, exceeding eustacy and recorded in tabular undeformed series, result from desiccation-flooding events in an endoreic silled basin. - The " Miocene palaeokarst with Cevennes-sourced sediment-fill " records a Serravalian-Tortonian base-level drop, depicted by canyon incision in the hinterland of the Gulf of Lion Margin. Uplift values of ≥ 400m upstream, about 250m in an intermediate area and 10's of m downstream, are measured. The present 3D geometry and distribution of carbonate massifs (exposed and covered) are modeled in the study area, from the Cevennes to the Mediterranean. The 3D geological model integrates seismic reflection, borehole and gravimetric data. Tectonic restoration of a N-S section, extracted from the 3D model, allows to reconstruct paleo-base-levels with respect with the carbonate massifs, at different stages of deformation and successive phases of karstification. The 3D paleo-flows through carbonates across the study area, are thus constrained, especially during the Messinian desiccation stage. Application of the results to hydrogeology leads to the following : - Uplift of upstream hinterland (Cretaceous, Miocene) produces large amplitude karsts, but they do not make significant reservoirs. - Karstification responsible for the development of important and deep karst reservoirs is related to desiccation of endoreic basins (early Paleocene and Messinian). - Theses two events have produced two main deep karst reservoirs, with a gravimetric signature : (1) Upstream of Montpellier Thrust, between Pic St Loup, Les Matelles Fault and Hérault Basin, a deep karsts developed over 900m thickness in the Malm limestone, during Paleocene. (2) Downstream (south) of Montpellier Thrust, the coastal karsts extend offshore over more than 10km, they are sealed by a thick Miocene to Quaternary cover, and they result from the Messinian event.
Cette étude s'inscrit dans un contexte de demande croissante en ressources en eau, conduisant à mieux contraindre et estimer la distribution des aquifères karstifiés qui représentent une ressource importante, notamment sur le pourtour méditerranéen. Le but de ce travail est d'élaborer une méthode prédictive de la distribution de la karstification et de l'épaisseur de massifs carbonatés karstifiés, notamment pour les karsts profonds. La méthodologie est développée à partir de l'étude des karsts de la plateforme carbonatée téthysienne du Languedoc montpelliérain; région qui a subi une histoire tectonique complexe et polyphasée, entrainant des phases de karstification successives. Elle est basée sur la compréhension des relations entre eustatisme, géodynamique et niveau de base, enregistrées par les paléokarsts de la région. Le remplissage sédimentaire des paléokarsts permet d'identifier les épisodes de karstification et de les dater ; c'est un marqueur des variations -que l'on cherche à quantifier- du niveau de base local responsable de la formation et du comblement des karsts. On analyse 3 paléokarsts d'extension régionale dont on peut étudier : le remplissage karstique, la distribution le long de profils amont-aval et l'extension verticale indicatrice de l'amplitude de l'abaissement du niveau de base dont il est issu. On en déduit les causes géodynamiques à l'origine de leur formation: - Le " paléokarst des bauxites " à remplissage caractéristique, résulte de l'évolution en 2 phases de " l'Isthme Durancien " : altération bauxitique de la couverture néocomienne sur le sud du Massif Central, liée à une inversion au Barrémien, suivi d'une surrection ≥ 1600m à l'Aptien-Albien, causant l'érosion des altérites en amont et le dépôt des bauxites détritiques en aval. - Le " paléokarst à remplissage marin paléocène inférieur " indique des variations du niveau de base local ≥350m dans la zone amont sud-cévenole. On propose que ces variations de niveau de base d'amplitude très supérieures aux variations eustatiques et dans une zone faiblement déformée, résultent d'assèchements et d'ennoiements d'un bassin endoréique à seuil. - Le " paléokarst à remplissage détritique d'origine cévenole ", enregistre la chute du niveau de base au Serravalien-Tortonien, qui se traduit par l'incision de canyons dans l'arrière-pays de la marge du Golfe du Lion. On détermine une surrection de plus de 400 mètres à l'amont, près de 250m dans les blocs faillés intermédiaires et quelques dizaines de mètres dans la zone avale. En parallèle, on établit la géométrie et la distribution actuelles des massifs carbonatés dans la zone d'étude (y compris sous couverture), en construisant un modèle géologique 3D, des Cévennes à la Méditerranée. On intègre les données de sismique réflexion, de forages et les données gravimétriques. La restauration tectonique séquentielle d'une coupe Nord-Sud extraite du modèle géologique permet d'appréhender la position des paléo-niveaux de base par rapport aux massifs carbonatés, pour chaque époque de karstification. On déduit l'organisation 3D des paléo-écoulements à travers la géométrie complexe des massifs carbonatés languedociens, notamment pendant l'évènement messinien. En terme d'évaluation de la ressource en eau, on déduit que: - Les surrections de l'arrière-pays (Crétacé " moyen ", Miocène) produisent des karsts de grande amplitude, mais ne constituent pas de réservoirs significatifs. - La karstification à l'origine de réservoirs exploitables importants et profonds est créée par l'assèchement de bassins endoréiques, qui ont affecté la région au Paléocène inférieur et au Messinien . - Ces deux évènements sont à l'origine de deux principaux réservoirs karstiques profonds qui ont une signature gravimétrique : (1) En amont du chevauchement de Montpellier, entre le Pic Saint Loup, la faille des Matelles et le bassin de l'Hérault, le karst profond se développe sur une épaisseur atteignant 900m, et est attribuée à l'événement du Paléocène. (2) Au Sud du chevauchement de Montpellier les karsts côtiers s'étendent jusqu'à plus de 10 km au large, scellés par une épaisse couverture Miocène et Plio-Quaternaire, et résultent de l'événement Messinien.
https://tel.archives-ouvertes.fr/tel-00936257

tel-00936257
https://tel.archives-ouvertes.fr/tel-00936257
https://tel.archives-ouvertes.fr/tel-00936257/document
https://tel.archives-ouvertes.fr/tel-00936257/file/thA_se_husson_couleurs.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Mosha and North Tehran faults correspond to the nearest seismic sources for the northern part of the Tehran megacity. The present-day structural relationships and the kinematics of these two faults, especially at their junction in Lavasanat region, is still a matter of debate. In this paper, we present the results of a morphotectonic analysis (aerial photos and field investigations) within the central part of the Mosha and eastern part of the North Tehran faults between the Mosha valley and Tehran City. Our investigations show that, generally, the traces of activity do not follow the older traces corresponding to previous long-term dip-slip thrusting movements. The recent faulting mainly occurs on new traces trending E-W to ENE-WSW affecting Quaternary features (streams, ridges, risers, and young glacial markers) and cutting straight through the topography. Often defining en-echelon patterns (right- and left-stepping), these new traces correspond to steep faults with either north- or south-dipping directions, along which clear evidences for left-lateral strike-slip motion are found. At their junction zone, the two sinistral faults display a left-stepping en-echelon pattern defining a positive flower structure system clearly visible near Ira village. Further west, the left-lateral strike-slip motion is transferred along the ENE-WSW trending Niavaran fault and other faults. The cumulative offsets associated with this left-lateral deformation is small compared with the topography associated with the previous Late Tertiary thrusting motion, showing that it corresponds to a recent change of kinematics.
ISSN: 0040-1951

hal-00617778
https://hal.archives-ouvertes.fr/hal-00617778
DOI : 10.1016/j.tecto.2010.09.013

Éditeur(s) : HAL CCSD Wiley
Résumé :
How Quaternary climatic and geological disturbances influenced the composition of Neotropical forests is hotly debated. Rain fall and temperature changes during and/or immediately after the Last Glacial Maximum (LGM) are thought to have strongly affected the geographical distribution and local abundance of tree species. The paucity of the fossil records in Neotropical forests prevents a direct reconstruction of such processes. To describe community-level historical trends in forest composition, we turned therefore to inferential methods based on the reconstruction of past demographic changes. In particular, we modelled the history of rainforests in the Eastern Guiana Shield over a time scale of several thousand generations, through the application of Approximate Bayesian Computation (ABC) and Maximum Likelihood (ML) methods to diversity data at nuclear and chloroplast loci in eight species or subspecies of rainforest trees. Depending on the species and on the method applied, we detected population contraction, expansion or stability, with a general trend in favour of stability or expansion, with changes presumably having occurred during or after the LGM. These findings suggest that Guiana Shield rain forests have globally persisted, while expanding, through the Quaternary, but that different species have experienced different demographic events, with a trend towards the increase in frequency of light-demanding, disturbance-associated species.
ISSN: 0962-1083

hal-01512150
https://hal.archives-ouvertes.fr/hal-01512150
https://hal.archives-ouvertes.fr/hal-01512150/document
https://hal.archives-ouvertes.fr/hal-01512150/file/Barthe_et_al-_%7B0B6A8C5E-DDFF-4C4E-822C-4E7BC22A6C9B%7D.pdf
DOI : 10.1111/mec.13949

Éditeur(s) : HAL CCSD
Résumé : We present high-resolution bulk sedimentary δ 15N data from the southern edge of the present-day oxygen minimum zone of the eastern South Pacific. The record is interpreted as representing changes in water column nitrogen removal during the last 70,000 years. We found significant fluctuations in the isotopic signal that suggest major reorganizations of the oxygen minimum zone at millennial timescales. These fluctuations were not related to other millennial-scale changes like the Northern Hemisphere's Dansgaard-Oeschger climate swings or local changes in primary productivity, so appear to be dictated by the Southern Hemisphere's climate rhythm. This is preliminarily corroborated by an overall agreement between our δ 15N data and the sedimentary proxy of ice sheet dynamics in Patagonia, which is in turn correlated with surface water properties at the midlatitude subduction region of the eastern South Pacific intermediate waters. Finally, potential implications on late Quaternary changes in atmospheric CO2 concentrations are discussed.
Paleoceanography / PALEOECEANOGRAPHY

hal-00407260
https://hal.archives-ouvertes.fr/hal-00407260
DOI : 10.1029/2006PA001308

Éditeur(s) : Amer Geophysical Union
Résumé : The origin of the Algerian margin remains one of the key questions still discussed in the Western Mediterranean sea, due to the imprecise nature and kinematics of the associated basin during the Neogene. For the first time, the deep structure of the Maghrebian margin was explored during the SPIRAL seismic survey. In this work, we present a N-S transect off Tipaza (west of Algiers), a place where the margin broadens due to a topographic high (Khayr-al-Din Bank). New deep penetration seismic profiles allow us to image the sedimentary sequence in the Algerian basin and the crustal structure at the continent-ocean boundary. Modeling of the wide-angle data shows thinning of the basement, from more than 15km in the continental upper margin to only 5–6km of oceanic-type basement in the Algerian basin, and reveals a very narrow or absent transitional zone. Analysis of the deep structure of the margin indicates features inherited from its complex evolution: (1) an oceanic-type crust in the deep basin, (2) similarities with margins formed in a transform-type setting, (3) a progressive deepening of the whole sedimentary cover, and the thickening of the Plio-Quaternary sediments at the margin foot, coeval with (4) a downward flexure of the basement in the basin. These features argue for a multiphased evolution of the margin, including (1) an early stage of rifting and/or spreading, (2) a late transcurrent episode related to the westward migration of the Alboran domain, and (3) a diffuse Plio-Quaternary compressional reactivation of the margin.
Journal Of Geophysical Research-solid Earth (0148-0027) (Amer Geophysical Union), 2013-08 , Vol. 118 , N. 8 , P. 3899-3916

Droits : 2013. American Geophysical Union. All Rights Reserved.
http://archimer.ifremer.fr/doc/00152/26333/24412.pdf
DOI:10.1002/jgrb.50318
http://archimer.ifremer.fr/doc/00152/26333/

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

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

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
Subduction of a narrow slab of oceanic lithosphere beneath a tightly curved orogenic arc requires the presence of at least one lithospheric scale tear fault. While the Calabrian subduction beneath southern Italy is considered to be the type example of this geodynamic setting, the geometry, kinematics and surface expression of the associated lateral, slab tear fault offshore eastern Sicily remain controversial. Results from a new marine geophysical survey conducted in the Ionian Sea, using high-resolution bathymetry and seismic profiling reveal active faulting at the seafloor within a 140 km long, two-branched fault system near Alfeo Seamount. The previously unidentified 60 km long NW trending North Alfeo Fault system shows primarily strike-slip kinematics as indicated by the morphology and steep-dipping transpressional and transtensional faults. Available earthquake focal mechanisms indicate dextral strike-slip motion along this fault segment. The 80 km long SSE trending South Alfeo fault system is expressed by one or two steeply dipping normal faults, bounding the western side of a 500+ m thick, 5 km wide, elongate, syntectonic Plio-Quaternary sedimentary basin. Both branches of the fault system are mechanically capable of generating magnitude 6–7 earthquakes like those that struck eastern Sicily in 1169, 1542, and 1693.
ISSN: 0278-7407

insu-01256887
https://hal-insu.archives-ouvertes.fr/insu-01256887
https://hal-insu.archives-ouvertes.fr/insu-01256887/document
https://hal-insu.archives-ouvertes.fr/insu-01256887/file/GutscherEtal_2015_Tectonics.pdf
DOI : 10.1002/2015TC003898

Éditeur(s) : Gauthier-Villars
Résumé : The paper summarizes the biostratigraphic results of eighteen dives of the French submersible Cyana at the Mazagan Escarpment (CYAMAZ cruise), based on calcareous nannoplankton and foraminifera. This paper is restricted to the study of the Early Cretaceous to Quaternary post-platform series. Most of the stratigraphical data are based on the determination of calcareous nannofossils (P. Cepek) which, however, are mostly poorly preserved and of rare occurrence. From the 170 studied subsamples 49 are barren of calcareous samples are listed according to the species epithets, separated for the Cretaceous and Tertiary. The biostratigraphy based on foraminifera and the microfacies was studied in thin-section (H. hagn). Foraminiferal microfaunas of Late Cretaceous, Paleocene, Eocene-Oligocene and Quaternary age are described and shown in Plates.
Oceanologica Acta, Special issue (0399-1784) (Gauthier-Villars), 1985

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00247/35827/34337.pdf
http://archimer.ifremer.fr/doc/00247/35827/

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
[1] Zircons and monazites from 6 samples of the North Ayilari dextral shear zone (NAsz), part of the Karakorum fault zone (KFZ), have been dated with the U-Th-Pb method, using both ID-TIMS and SIMS techniques. The ages reveal (1) inheritance from several events spanning a long period between the late Archean and the Jurassic; (2) an Eocene-Oligocene magmatic event (similar to 35-32 Ma); (3) an Oligo-Miocene magmatic event (similar to 25-22 Ma), at least partly synkinematic to the right-lateral deformation; and (4) a period of metamorphism metasomatism (similar to 22-14 Ma) interpreted as thermal and fluid advection in the shear zone. The Labhar Kangri granite located similar to 375 km farther Southeast along the KFZ is dated at 21.1 +/- 0.3 Ma. Such occurrence of several Oligo-Miocene granites along the KFZ, some of which show evidence for synkinematic emplacement, suggests that the fault zone played an important role in the genesis and /or collection of crustal melts. We discuss several scenarios for the onset and propagation of the KFZ, and offset estimates based on the main sutures zones. Our preferred scenario is an Oligo-Miocene initiation of the fault close to the NA range, and propagation along most of its length prior to similar to 19 Ma. In its southern half, the averaged long-term fault-rate of the KFZ is greater than 8 to 10 mm/a, in good agreement with some shorter-term estimates based on the Indus river course, or Quaternary moraines and geodesy. Our results show the KFZ cannot be considered as a small transient fault but played a major role in the collision history.
ISSN: 0278-7407

hal-00412570
https://hal.archives-ouvertes.fr/hal-00412570
DOI : 10.1029/2007TC002184

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
We carried out morphotectonic studies along the left-lateral strike-slip Bogd Fault, the principal structure involved in the Gobi-Altay earthquake of 1957 December 4 (published magnitudes range from 7.8 to 8.3). The Bogd Fault is 260 km long and can be subdivided into five main geometric segments, based on variation in strike direction. West to East these segments are, respectively: the West Ih Bogd (WIB), The North Ih Bogd (NIB), the West Ih Bogd (WIB), the West Baga Bogd (WBB) and the East Baga Bogd (EBB) segments. Morphological analysis of offset streams, ridges and alluvial fans-particularly well preserved in the arid environment of the Gobi region-allows evaluation of late Quaternary slip rates along the different faults segments. In this paper, we measure slip rates over the past 200 ka at four sites distributed across the three western segments of the Bogd Fault. Our results show that the left-lateral slip rate is similar to 1 mm yr(-1) along the WIB and EIB segments and similar to 0.5 mm yr(-1) along the NIB segment. These variations are consistent with the restraining bend geometry of the Bogd Fault.;Our study also provides additional estimates of the horizontal offset associated with the 1957 earthquake along the western part of the Bogd rupture, complementing previously published studies. We show that the mean horizontal offset associated with the 1957 earthquake decreases progressively from 5.2 m in the west to 2.0 m in the east, reflecting the progressive change of kinematic style from pure left-lateral strike-slip faulting to left-lateral-reverse faulting. Along the three western segments, we measure cumulative displacements that are multiples of the 1957 coseismic offset, which may be consistent with a characteristic slip. Moreover, using these data, we re-estimate the moment magnitude of the Gobi-Altay earthquake at M-w 7.78-7.95.;Combining our slip rate estimates and the slip distribution per event we also determined a mean recurrence interval of similar to 2500-5200 yr for past earthquakes along the different segments of the western Bogd Fault. This suggests that the three western segments of the Bogd Fault and the Gurvan Bulag thrust fault (a reverse fault bounding the southern side of the Ih Bogd range that ruptured during the 1957 earthquake) have similar average recurrence times, and therefore may have ruptured together in previous earthquakes as they did in 1957. These results suggest that the western part of the Bogd Fault system, including the Gurvan Bulag thrust fault, usually behaves in a 'characteristic earthquake' mode.
ISSN: 0956-540X

hal-00639467
https://hal.archives-ouvertes.fr/hal-00639467
https://hal.archives-ouvertes.fr/hal-00639467v2/document
https://hal.archives-ouvertes.fr/hal-00639467/file/rizzaGJI2011.pdf
DOI : 10.1111/j.1365-246X.2011.05075.x

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : Coastal Quaternary deposits of western Oranie show typical soft-sediment deformations including sedimentary dykes, sand volcanoes, sismoslumps, thixotropic bowls, thixotropic wedges, diapir-like structures, and faults grading. Field observations indicate that these deformations exist at several levels of the studied deposits along the west Oranian coast. This study demonstrated that these structures are earthquakes-related, by analysis of potential trigger sources. Several arguments demonstrate the seismic origin: the depositional environment rich in water that located in an active tectonic region, the thixotropic nature of deformations and their large vertical and horizontal diffusion in the Quaternary series consistent with a seismic recurrence. This allows characterizing these Quaternary soft-sediment deformations as seismites that were triggered by earthquakes.
ISSN: 1383-4649

hal-01560975
https://hal.archives-ouvertes.fr/hal-01560975
DOI : 10.1007/s10950-016-9616-2

Éditeur(s) : HAL CCSD
Résumé : International audience
The « METYSS » cruise was carried out in June 2009 onboard the R/V « Téthys II » along the eastern Sardinian and south-eastern Corsican margins, western Tyrrhenian Sea, in order to better constrain the potential links between deformation related to either crustal tectonics or salt tectonics and sediment accumulation, especially during the Messinian and Plio-Quaternary times. We acquired 15 high-resolution seismic reflection profiles (about 1200 km in cumulative length) along the south-eastern Corsican margin, immediately north of the Bonifacio Strait and along the upper and middle parts of the eastern Sardinian margin, from the continental slope to the Cornaglia Terrace. The Tyrrhenian Sea is considered as a Neogene back-arc basin that opened during continental rifting and oceanic spreading related to the eastward migration of the Apennine subduction system from Tortonian to Pliocene times (Jolivet et al., 2006). Rifting of the Tyrrhenian Sea started first along the Eastern Sardinian margin during the Tortonian-Messinian times and therefore the series of that age should be considered as syn-rift sediments (Sartori et al., 2004). The « METYSS » seismic profiles clearly illustrate that this part of the Tyrrhenian was highly segmented during the rifting stage by N-S trending normal faults delineating ridges (e.g., Baronie Ridge) and basins (e.g., Sardinian Basin and Cornaglia Terrace), as previously described for example by Thommeret (1999) and Sartori et al. (2004). The Messinian sedimentary units and especially the « Upper Unit » (UU, Lofi et al., this congress, corresponding to the « Upper Evaporites » in the previous literature) are, without any doubt, of syn-rift age, as they display a fan-shaped stratal geometry. The Mobile Unit (MU, Lofi et al., this congress), i.e. the Messinian halite, is clearly imaged in the study area and its spatial repartition can be outlined. The highly-variable thickness of the confined salt basins could be due to the initial basin geometry (i.e. before the Messinian salinity Crisis) or to the syn-rift character of the deposition. Southeastward of the study area, in the vicinity of the Cornaglia Seamount, salt tectonics appears surprisingly vigorous. More surprisingly, several normal faults seem to have remained active in recent times, if not even at present time. Fault slip has been recorded by bathymetric scarps and associated footwall debris flows interfingered within the Plio-Quaternary sequence, even though the eastern Sardinian margin is usually considered to be passive now. Moreover, some amount of tectonic inversion is visible on some normal faults that show contractional or transpressional components of late slip. In addition, this “post-rift” deformation can be illustrated within the Plio-Quaternary sequence by a regional unconformity. Consequently, numerous mass-transport deposits and channel-levees systems observed in the Plio-Quaternary cover could be partly controlled by tectonic activity. These very preliminary results require further investigations in order to better decipher the role of crustal tectonics and salt tectonics, salt-related structures being very efficient markers to discriminate between the respective contribution of gravity-driven, salt tectonics and deep-seated, crustal tectonics (Gaullier et al., 2010). Finally, we aim to precisely determine the relative vertical movements (tilting, subsidence, magmatism. . . ) and geodynamical history of the different segments of the area since 6 Ma.
Geophysical Research Abstracts
Vienne, Austria

hal-00537828
https://hal-brgm.archives-ouvertes.fr/hal-00537828
https://hal-brgm.archives-ouvertes.fr/hal-00537828/document
https://hal-brgm.archives-ouvertes.fr/hal-00537828/file/EGU2010-15469_ref6821.pdf