Éditeur(s) : HAL CCSD Coastal Education and Research Foundation
Résumé : The south part nearshore zone of the Gulf of Lions coast (Mediterranean Sea) is characterized by a double crescentic sandbar system. During the winter 2007, a campaign of intensive hydrodynamical measurements (current profiles) was realized. During this campaign, based mainly on ADCPs, the maximal recorded wave height was 1.5 m. Four events were observed; two of those had northern incidence, one with southern incidence and a last one with frontal incidence. This paper proposes 3D hydrodynamical circulation maps over this microtidal bar system. The currents described reveals rip, bed-return and longshore currents strongly influenced by the wind-waves forcing and the bathymetry. At the apex of the oblique incidence events, the longshore component is the most important. The breaker zone is only located over the inner bar. During storm waning conditions, the cross-shore currents appear over the trough of the outer bar. The hydrodynamic circulation is then compared with other observations made in the literature.
ISSN: 0749-0208
Szczecin, Poland

hal-00767593
https://hal.archives-ouvertes.fr/hal-00767593

Éditeur(s) : HAL CCSD Cambridge University Press (CUP)
Résumé : International audience
The Ben Zireg anticline NW of Bechar yields the currently most-important Frasnian succession on the northern margin of the Algerian Sahara. It represents 26.5 m of calcilutites which are attributed to the middle–late Frasnian. As the early Frasnian is not represented, the succession rests conformably on undifferentiated, probably late Givetian, substrate. Fine-scaled conodont biostratigraphy reveals a continuous sequence of Montagne Noire Zones 5–13, superseded by the earliest Famennian Lower triangularis Zone. The deposits are organized into 15 sedimentary cycles that are initially condensed and become dilated upwards. Conodont biofacies indicate an overall deepening towards the top of the section with an episode of slight shallowing at the MN11/12 transition marked by an increase of ancyrodellids, which is also seen in the Marhouma section of the Ougarta region (SW Algeria). Homogeneous calcareous microfacies with only a few shaly intercalations determine a predominantly oxygenated depositional environment on an outer platform, submarine rise or ramp setting. This is also indicated by relatively low sedimentation rates which are similar in selected sections from the Tafilalt platform, and contrast with those from the Marhouma trough and the Maider basin. Unlike other Frasnian successions south of the Atlas Fault, but similar to the Moroccan Meseta, the Upper Kellwasser horizon is clearly discriminated at Ben Zireg by an outstanding occurrence of black shales on top of the oxygenated latest Frasnian deposits.
ISSN: 0016-7568

hal-01217151
https://hal.archives-ouvertes.fr/hal-01217151
DOI : 10.1017/S0016756814000715

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
The strike-slip faults of north Tibet accommodate part of the Cenozoic convergence between India and Asia. Along the Karakax valley south of Yecheng and near the Xidatan trough south of Golmud, the active traces of the Altyn-Tagh and Kunlun faults follow narrow belts of metamorphic rocks. The deformation recorded in those mylonites is sinistral strike-slip. Rb/Sr and 40Ar/39Ar ages of deformation from syntectonic fabrics formed at 350–400°C 120 Ma. Argon loss suggests that deformation was associated to a 250–300°C thermal pulse that lasted 5–20 Ma after the onset of movement. Unroofing occurred much later, around 25 Ma when sudden cooling suggests a component of thrusting or more likely normal faulting. The Cretaceous shear may be related to collision between the Qiantang and the Lhasa blocks. The Karakax and Xidatan shear zones may have formed a unique, continuous boundary in the Cretaceous, which was later reused by the Tertiary strike-slip faults, leading to potentially calculable offsets along the Altyn-Tagh fault.
ISSN: 2169-9313

hal-00197562
https://hal.archives-ouvertes.fr/hal-00197562
https://hal.archives-ouvertes.fr/hal-00197562/document
https://hal.archives-ouvertes.fr/hal-00197562/file/Arnaud_JGR000904_def.pdf
DOI : 10.1029/2001JB000904

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Deep-seated gravitational spreading (DSGS) affects the slopes of formerly glaciated mountain ridges. On Mars, DSGS has played a key role in shaping the landforms of the giant Valles Marineris troughs. Though less spectacular, DSGS is common in terrestrial orogens, where understanding its mechanics is critical in the light of the ongoing climate change because it is a potential source of catastrophic landslides in deglaciated valleys. We conducted parametric numerical studies in order to identify important factors responsible for DSGS initiation. DSGS models are computed using an elastoviscoplastic finite element code. Using ADELI's software, we reproduce topographic ridge spreading under the effect of valley unloading. Two types of spreading topographic ridges are investigated, homogeneous or with horizontal rheological layering. We find that gravitational instabilities are enhanced by high slopes, which increase gravitational stress, and low friction and cohesion, which decrease yield stress. In the unlayered ridge, instability is triggered by glacial unloading with plastic strain concentration inside the ridge and at the base of the high slopes. Vertical fractures develop in the upper part of the slope, potentially leading to fault scarps. Ridge homogeneity promotes a deformation mode controlled by uphill-facing normal faulting and basal bulging. In the second case, the ridge encompasses horizontal geological discontinuities that induce rock mass anisotropy. Discontinuity located at the base of the slope accumulates plastic strain, leading to the formation of a sliding plane evolving into a landslide. The presence of a weak layer at ridge base therefore promotes another slope deformation mode ending up with catastrophic failure. Mechanical conditions and slope height being equal, these conclusions can probably be extrapolated to Earth. Compared with Mars, DSGS on Earth is inhibited because terrestrial topographic gradients are lower than in Valles Marineris, an effect counterbalanced by increased gravitational stress, where the intensity of deformation is enhanced because of the Earth gravity potential.
ISSN: 0169-555X

hal-01420007
https://hal.archives-ouvertes.fr/hal-01420007
DOI : 10.1016/j.geomorph.2016.06.011

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Cold seeps, located on sea floors and frequently fueled with methane, have been much studied for the formation of carbonate nodules, crusts or masses resulting from the activity og communities of anaerobic bacteria. In this paper, we examine the impact of cold seepage on their caging sediments, as far as their geochemical composition and microfaunal content are concerned. To this end, two fossil cold seeps of the Jurassic Beauvoisin site (Vocontian Trough, SE-France) are studied, focusing on the redox-sensitive and/or sulfide-forming trace metals. We observe that: 1) the carbonate edifices of the cold seeps are enriched in specific elements, namely, Sr, Mo As and Sb, compared to their caging marlstones, and 2) the benthic foraminifer populations were present close to the edifices. The Sr enrichment is ascribed to a contamination of the seeping fluids at the contact with underlying evaporites; the Mo-As-Sb enrichment may have several, non-exclusive, origins. We retain two scenarios; in the first one, the enrichment is due to the ascending fluids that could collect these elements when passing through thick shaly formations; in the second scenario, Mo, As and Sb were supplied to the sites of carbonate precipitation together with Fe- and Mn-oxy-hydroxides (the so-called particulate shuttle process). We favor the second scenario (possibly coupled to the first one) because the rather uncommon Mo-As-Sb association is also observed for reducing sediments deposited under the influence of Fe-Mn-shuttling.
ISSN: 0009-2541

hal-00806655
https://hal.archives-ouvertes.fr/hal-00806655
DOI : 10.1016/j.chemgeo.2012.12.012

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We present new Sr-Nd-Pb isotope data of the western Alpujárride metamorphic basement and the pre-Miocene Flysch sediments of the Betic Cordillera (southern Spain). Nd model ages are consistent with an increasing detrital input from the Alborán domain to the Flysch Trough in the western Mediterranean during the late Oligocene. The Alpujárride metamorphic crustal rocks derived from Archean-Paleoproterozoic terranes located along the northern margin of Gondwana in the Neoproterozoic. The heterogeneous isotopic signatures of the Alpujárride units indicate that they have different sedimentary protoliths and underwent contrasted Variscan and pre-Variscan tectono-magmatic evolutions. Melts/fluids derived from the western Alpujárride gneisses contaminated the mantle source of the Ronda high-Mg pyroxenite dykes, implying that the Alpujárride lower crust underthrusted the subcontinental lithospheric mantle of the Alborán domain generating subduction-like magmatism in the late Oligocene. The western Alpujárride upper crust is involved in the Neogene volcanism of the Alborán Sea basin, but only contaminated some LREE-enriched calc-alkaline lavas erupted along the continental margins. On the other hand, tholeiitic lavas in the center of the basin show no isotopic evidence of crustal assimilation. This indicates that most of the crust in the central Alborán Sea accreted by Miocene tholeiitic magmatism and that Alpujárride lower crust is absent and likely foundered close to the continental margins of the basin.
ISSN: 0024-4937

hal-01526912
https://hal.archives-ouvertes.fr/hal-01526912
DOI : 10.1016/j.lithos.2016.10.003

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
An active seismic experiment has been conducted across the southern Ryukyu margin east of Taiwan over the whole trench-arc-backarc system in May 2009. Twenty-four ocean bottom seismometers (OBS) were deployed from the Ryukyu trench to the southern Okinawa trough over the Ryukyu arc and forearc. Wide angle seismic data were recorded by the OBS array while coincident reflection seismic data were acquired using a 6 km long streamer and a 6600 cubic inch seismic airgun array. Results from tomographic inversion of 21091 travel time picks along this line allowed us to image crustal structures of the Ryukyu margin down to a depth of 25 km. The transect has been designed to provide a better seismic velocity structure of the subduction zone in a highly deformed area that has produced an M8 earthquake in 1920. The line crosses a seismic cluster of earthquakes which source mechanisms are still poorly understood. The subducting oceanic crust of the Huatung Basin is about 5-6 km thick. The underlying mantle exhibits low seismic velocities around 7.8 km/s suggesting some hydrothermal alterations or alteration of the upper mantle through faults generated by the flexure of the subducting plate as it enters the subduction. Low velocities, up to 4.5 km/s, associated with the accretionary wedge are well imaged from the trench back to the Nanao forearc. A major result concerns the abrupt termination of the buttress at the rear of the accretionary wedge. Despite the low resolution of the tomographic inversion near the subduction interface, several lines of evidence supporting the presence of a low velocity zone beneath the toe of the forearc buttress could be established. The Moho beneath the Ryukyu non-volcanic arc is located at a depth around 25 km depth.
ISSN: 0040-1951

hal-00795573
https://hal.archives-ouvertes.fr/hal-00795573
DOI : 10.1016/j.tecto.2011.10.010

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

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

Éditeur(s) : North-Holland Publishing Company
Résumé : The Rift Valley between 36° 42'N and 36° 55'N in the Atlantic Ocean is 31 km wide, with half-widths of 12 and 19 km for the western and eastern sides respectively. Both outer edges of the Rift Valley stand about 1500 m above an Inner Floor where very fresh pillow lavas occur. The Inner Floor probably includes the locus of new crust ; and its bordering slopes, which are particularly well-defined on the western side, limit to less than about 2.5 km the width of the zone over which new crust may have evolved with little or no vertical displacement. The width of the locus of new crust may be less than 0.5 km between 36° 45'N and 36° 47'N, where the deepest slopes of the Rift Valley walls nearly merge. Near 36° 50'N, the Inner Floor accommodates an approximately 1 km wide, 4 km long Central High, with a height of up to 250 m. In this area, the locus of new crust may also occupy a very narrow zone ; it may lie either along the Central High or along a trough flanking the Central High. The magnetic anomaly pattern indicates that, since the beginning of the Brunhes epoch (6.9 X 10(5) yr B.P.), the eastern limb has grown approximately twice as fast as the western limb. Using extrapolated spreading rates, the ages of the outer edges of the Rift Valley are 1.3 and 1.7 m.y. for the eastern and western sides respectively. Comparison with data for the Rift Valley in other parts of the ocean further suggests that the residence time of new crust in the Rift Valley is about 1.5 m.y. Uplift of crust from the Inner Floor, which may be dominated by lithospheric thickening, may thus be primarily a function of age. [NOT CONTROLLED OCR]
Earth and Planetary Science Letters (North-Holland Publishing Company), 1974 , Vol. 22 , P. 29-43

Droits : North-Holland Publishing Company, Amsterdam
http://archimer.ifremer.fr/doc/1974/publication-5159.pdf
http://archimer.ifremer.fr/doc/00000/5159/

Éditeur(s) : HAL CCSD
Résumé : The effects of climate change on extreme events are difficult to assess because extremes present large variability and consequently, it is difficult to identify significant trends in relation to the lack of instrumental long time series. Here we present a record of these extreme storm events in the French Mediterrannean coast over the past 7000 years based on a long sediment core from lagoonal environment in Gulf of Lions. Using a high resolution multiproxies approach on core associating grain size, faunal to reconstruct Mid to Late Holocene history of backbarrier deposits in relation to landfalling activity. Even if change in lagoon geomorphological setting over the Holocene does not allow to compare storm events in terms of intensity trough time, we have recorded six periods of increase in storm activity at 6200, 5500, 4400, 3200, 1500 yr cal B.P. and over the LIA (450 and 100 yr cal B.P.). These evidences of changes in coastal hydrodynamic, inversely correlated to periods of aridification in Western Mediterranean region, are in phase with those observed over the North Atlantic and correspond to Holocene cooling events. This increase in storm activity during Holocene cold events over Mediterranean region was probably due to thermal gradient increase leading to enhanced lower tropospheric baroclinicity over a large Central Atlantic-European domain. This study demonstrates that temperatures in North Atlantic region influence the severe storm activity and therefore the Mediterranean climate at Holocene timescale.
Les effets du changement climatique sur les événements extrêmes sont difficiles à estimer car ces phénomènes présentent une large variabilité, et par conséquent il est délicat d'identifier des tendances significatives compte tenu de l'absence de longues séries de données instrumentales. Dans cette étude, nous présentons un enregistrement de ces tempêtes extrêmes sur la côte Méditerranéenne française au cours des 7000 dernières années à partir de carottes sédimentaires prélevées dans un système lagunaire du Golfe du Lion. L'utilisation d'une approche multi-traceur à haute résolution avec des analyses granulométriques, faunistiques, géochimiques (XRF), en minéraux argileux associées à des données chronologiques de radiocarbone et de 210Pb, 137Cs ; nous a permis de reconstruire l'histoire, au cours de l'Holocène, des dépôts lagunaires en relation avec l'activité des tempêtes. Bien que les paramètres morphologiques de cet environnement lagunaire aient changé durant l'Holocène, ne permettant pas de comparer ces événements au cours du temps en terme d'intensité, nous enregistrons six périodes d'augmentation de l'activité des tempêtes datées à 6200, 5500, 4400, 3200, 1500 an cal B.P. et durant le Petit Age Glaciaire (de 450 à 100 an cal B.P.). Ces changements de l'activité hydrodynamique côtière, en antiphase avec les périodes d'aridifications en Méditerranée de l'Ouest, sont corrélées avec celles observées dans le bassin Nord Atlantique et correspondent aux événements de refroidissement Holocène. L'augmentation de l'activité des tempêtes dans la cette région de la Méditerranée durant les périodes froides, associée à une diminution des températures au pôle Nord, est probablement liée à l'augmentation du gradient thermique qui, par interaction barocline, favorise les cycles d'évolution des tempêtes dans toute l'Europe et la Méditerranée de l'Ouest. Cette étude démontre ainsi que la température dans la région Nord Atlantique influence l'activité des tempêtes extrêmes et donc du climat Méditerranéen à l'échelle de l'Holocène.
https://tel.archives-ouvertes.fr/tel-00437757

tel-00437757
https://tel.archives-ouvertes.fr/tel-00437757
https://tel.archives-ouvertes.fr/tel-00437757/document
https://tel.archives-ouvertes.fr/tel-00437757/file/Sabatier_these.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : We present new analytical data from lavas and associated rocks dredged and/or drilled from the South Fiji Basin, Northland Plateau, Colville Ridge and Havre Trough. These results provide much-needed ground truth about the geology, age and tectonic evolution of the Cenozoic submarine ridges and basins between the active intraoceanic Tonga–Kermadec arc, and rifted continental borderlands of New Zealand, the Norfolk Ridge and New Caledonia. Key results from this study include: (1) Ar–Ar dates on Minerva Abyssal Plain oceanic crust suggest that the ages of magnetic anomalies in the South Fiji Basin have been overestimated by earlier workers; (2) subduction-related lavas are widespread across the region, are not presently organised into arc-like chains, and cluster in the age range 22–18 Ma (Early Miocene); (3) the oldest subduction-related lavas occur in the western part of the region (32–26 Ma: Norfolk and Three Kings Ridge); (4) shoshonites, interpreted as rifted arc lavas, were erupted in a narrow 20–21 Ma interval over a wide area. Put together, these results indicate high magmatic flux and large and rapid horizontal tectonic translations and basin opening from 18–23 Ma in the region immediately north of New Zealand. We explain the Miocene tectonomagmatic development of the region by a model of rapid rollback of a single, east-facing Pacific arc–trench system that became established after Northland Allochthon emplacement. Critical testing of this, versus other, tectonic models must await drilling and dating of thus-far unsampled Kupe Abyssal Plain crust.
ISSN: 0025-3227

hal-00405803
https://hal.archives-ouvertes.fr/hal-00405803
DOI : 10.1016/j.margeo.2006.10.033

Éditeur(s) : Elsevier Science Bv
Résumé : In this study, the Capbreton canyon head, just off the coast, is investigated using high-resolution multibeam bathymetry datasets, sediment samples and numerical modeling. The HR bathymetry analysis reveals a morphological connection between the longshore trough and the head of the canyon. The analysis of recent sediment samples shows a clear correlation between the sediment of the canyon head and that of the nearshore. Hydrodynamic modeling (a coupled wave-flow model) shows that for high-energy waves, the rotational nature of surf-zone circulation reverses and wave-induced currents have the potential to transport large quantities of nearshore sands toward the canyon head. All these arguments support the assumption that the canyon head captures a part of the sand transported by longshore drift. Over the 15 years of observation (1998–2013), time-lapse bathymetry shows that the floor of the canyon head and one lateral gully network experienced significant morphological reworking. In terms of hazards, despite this strong activity, the position of the canyon head and the profile of its longitudinal slope remained stable and appears as a comforting factor. However, the activity of unusual lateral erosions needs to be monitored.
Marine Geology (0025-3227) (Elsevier Science Bv), 2014-05 , Vol. 351 , P. 1-12

Droits : 2014 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/00180/29118/27524.pdf
DOI:10.1016/j.margeo2014.03.001
http://archimer.ifremer.fr/doc/00180/29118/

Éditeur(s) : American Geophysical Union
Résumé : The Fairway Ridge is a buried continental structure that separates the Fairway Basin from the New Caledonia Basin. The proposed Cretaceous age of the Fairway Basin has remained highly hypothetical to date. Deep offshore petroleum exploration wells revealed well-dated Mesozoic carbonaceous sedimentary rocks in the Taranaki Basin at the southern end of the Aotea Basin. In this paper we use geophysical data to confirm the continuity of the 2000 km long Fairway-Aotea Basin connecting New Caledonia to New Zealand and prove its early Late Cretaceous age. Analysis of seismic reflection profiles together with newly compiled gravity and magnetic maps reveals Late Cretaceous NE–SW trending lineaments projecting northeastward from major Tasman Sea fracture zones and the Bellona Trough, which demonstrate that the opening of the Fairway-Aotea Basin predates the opening of the Tasman Sea. This result combined with observations of the Mesozoic regional geology suggests that the Lord Howe, Fairway, and Norfolk ridges are part of a remnant late Early Cretaceous continental arc, which was fragmented into three pieces by the late Early to early Late Cretaceous. This event might be contemporaneous with a plate motion change between the Gondwana and Pacific plates and/or the arrival of the Hikurangi plateau in the subduction zone around 105 Ma, which caused the cessation of subduction along this plate boundary. We interpret either of those two events as being possible trigger events for the post–Early Cretaceous fragmentation of the eastern Gondwana margin in a slab retreat process.
Geochemistry Geophysics Geosystems - G3 (1525-2027) (American Geophysical Union), 2009-12 , Vol. 10 , N. 12 , P. 1-24

Droits : 2009 American Geophysical Union
http://archimer.ifremer.fr/doc/2009/publication-7322.pdf
DOI:10.1029/2009GC002612
http://archimer.ifremer.fr/doc/00000/7322/

Éditeur(s) : Amer Geophysical Union
Résumé : Since Last Glacial Maximum (23-19 ka), Earth climate warming and deglaciation occurred in two major steps (Bolling-Allerod and Preboreal), interrupted by a short cooling interval referred to as the Younger Dryas (12.5-11.5 ka B. P.). In this study, three cores (MV-33, MV-66, and MD-40) collected in the central part of Pandora Trough (Gulf of Papua) have been analyzed, and they reveal a detailed sedimentary pattern at millennial timescale. Siliciclastic turbidites disappeared during the Bolling-Allerod and Preboreal intervals to systematically reoccur during the Younger Dryas interval. Subsequent to the final disappearance of the siliciclastic turbidites a calciturbidite occurred during meltwater pulse 1B. The Holocene interval was characterized by a lack of siliciclastic turbidites, relatively high carbonate content, and fine bank-derived aragonitic sediment. The observed millennial timescale sedimentary variability can be explained by sea level fluctuations. During the Last Glacial Maximum, siliciclastic turbidites were numerous when the lowstand coastal system was located along the modern shelf edge. Although they did not occur during the intervals of maximum flooding of the shelf (during meltwater pulses 1A and 1B), siliciclastic turbidites reappear briefly during the Younger Dryas, an interval when sea level rise slowed, stopped, or perhaps even fell. The timing of the calciturbidite coincides with the first reflooding of Eastern Fields Reef, an atoll that remained exposed for most of the glacial stages.
Journal Of Geophysical Research-earth Surface (0148-0227) (Amer Geophysical Union), 2008-03-29 , Vol. 113 , N. F01S19 , P. 1-15

Droits : Copyright 2008 by the American Geophysical Union.
http://archimer.ifremer.fr/doc/00079/19014/16592.pdf
DOI:10.1029/2006JF000649
http://archimer.ifremer.fr/doc/00079/19014/

Éditeur(s) : Texas A & M University, Ocean Drilling Program, College Station, TX, United States (USA)
Résumé : This chapter presents major oxide and trace element determinations of igneous whole-rock compositions from sites drilled during Leg 60 and electron microprobe mineral and glass analyses of samples from Sites 454 and 458. Interarc basin basalts from the Mariana Trough (Sites 454 and 456) are similar in all respects to depleted mid-ocean ridge basalts. Basaltic andesites and andesites from Site 458 (Mariana fore-arc region) are more depleted than mid-ocean ridge basalts and show different geochemical behavior for Zr-, Hf, and Ti when compared on an extended Coryell- Masuda plot. [NOT CONTROLLED OCR]
Initial Reports of the Deep Sea Drilling Project (Texas A & M University, Ocean Drilling Program, College Station, TX, United States (USA)), 1981 , Vol. 60 , P. 657-677

Droits : Texas A & M University, Ocean Drilling Program, College Station, TX, United States (USA)
http://archimer.ifremer.fr/doc/1981/publication-5308.pdf
http://archimer.ifremer.fr/doc/00000/5308/