Late Quaternary megaturbidites of the Indus Fan: Origin and stratigraphic significance
The Indus sedimentary basin forms one of the largest "source-to-sink" systems of the Quaternary and extends over 106 km2 offshore. It is characterized by a complex tectonic setting marked by the Himalayan active orogenic belt in the source area, and the active strike-slip India-Arabia plate boundary (Owen Fracture Zone; OFZ) in its distal reaches. This paper focuses on a Late Quaternary channel-levee system from the Indus Fan captured by the recent opening of the 20°N pull-apart basin, located at 850 km off the present-day Indus Delta, along the OFZ. In this area the channel-mouth deposits consist of a set of up to 23 m thick megaturbidites trapped in the basin. These deposits form "ponded" lobe deposits in a tectonically-active confined basin. Age determination from radiocarbon dating and extrapolation of local deformation rates show that the older deposits observed on the seismic profiles are up to 358 ka BP old (MIS 10). The origin of these Late Quaternary deposits are investigated in the context of the Indus "source-to-sink" system and their significance is placed in a sequence stratigraphic framework. Integration of the stratigraphic architecture of the 20°N Basin megaturbidites with previous work in the area suggests that the Indus Fan evolved from a delta-fed turbidite system with several active canyons and channel-levee during the forced regressive conditions of the last falling stage of sea-level (122-25 ka BP), to a point source turbidite system during the sea-level lowstand (Last Glacial Maximum) and early transgressive stages (25-12 ka BP). This work sheds new light on the recent evolution of the Indus sedimentary system and illustrates the importance of the delta/river evolution during the fall of sea-level (e.g., incised valley formation) on the timing of sedimentary transfer and sediment distribution at the basin-scale.
(Marine Geology. vol. 336, n° 0025-3227, pp. 10-23, 01/02/2013)
UWA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, iSTeP, UPMC, CNRS, LGENS, INSU - CNRS, CNRS, ENS-PSL, PSL, SHOM, LDO, INSU - CNRS, UBO EPE, CNRS
A mesocosm study of fate and effects of CuO nanoparticles on endobenthic species (Scrobicularia plana, Hediste diversicolor)
The fate and effects of CuO nanoparticles (CuO NPs) were examined in endobenthic species (Scrobicularia plana, Hediste diversicolor), under environmentally realistic conditions in outdoor mesocosms (exposure to Cu at 10 μg L−1 in particulate (CuO NPs) or soluble salt (CuNO3) forms) for 21 days. Labile Cu was determined in water and sediment by using diffusive gradient in thin films. No labile Cu being detected from CuO NPs; the observed effects in invertebrates exposed to CuO NPs were mainly attributed to the toxicity of nanoparticulate rather than dissolved Cu toxicity. Bioaccumulation of CuO NPs was observed in both species. Biomarkers were examined at different levels of biological organization: biochemical markers of defense and damage, biomarkers of genotoxicity (comet assay), and behavioral biomarkers (feeding and burrowing). Behavioral biomarkers, antioxidant defenses (catalase, glutathion S-transferase, metallothionein), and genotoxicity are the most sensitive tools to highlight the effect of soluble or nanoparticulate metal forms. Concerning other biomarkers of defense (superoxide dismutase, lactate dehydrogenase, laccase) and damage (thiobarbituric acid reactive substances, acetylcholinesterase, acid phosphatase), no significant effects were detected. This experiment shows the suitability of mesocosms for studying the environmental effects of nanoparticles.
(Environmental Science and Technology. vol. 47, n° 0013-936X, pp. 1620-1628, 01/02/2013)
MMS, UM, UN UFR ST, UN, UFR SPB, UN, LIENSs, INSU - CNRS, ULR, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, BE, IFREMER, ECOMERS, UNS, CNRS, UniCA, NHM, MMS UCO, UCO, UNAM
A three-year time series of mineral dust deposits on the West African margin: Sedimentological and geochemical signatures and implications for interpretation of marine paleo-dust records
Mineral dust deposits in the Northeastern Tropical Atlantic Ocean (NETAO) are an important contribution for reconstructing paleoenvironments and paleoclimates of West Africa. However, the interpretation of the changes in the sedimentological and geochemical characteristics of the dust deposits recorded in the marine sediments from the NETAO remains incomplete. In order to improve our understanding of dust proxies, in particular its mineralogical and geochemical provenance tracers, present-day dust deposition has been monitored at Mbour (∼80 km south of Dakar) on the Senegalese margin. Here we report a multi-proxy investigation of a unique three-year continuous time series of mineral dust deposits collected at a weekly (or better) temporal resolution over the March 2006–March 2009 period. Mass deposition flux and mean modal grain size display marked but reverse seasonal features, with higher flux during the winter/spring seasons and coarser grain size mode in summer when flux is minimal, reflecting contrasting transport patterns throughout the year. Similarly, clay mineralogy, the illite/kaolinite ratio in particular, shows seasonal fluctuations, manifesting the latitudinal displacement of the contributing domains of provenance in response to the seasonal migration of the ITCZ position and the associated wind systems. Our three-year record also reveals the occurrence of major deposition events superimposed on the seasonal pattern, generally during the winter/spring dry seasons and most frequently during the month of March. Our study shows that these major events, which contribute a large fraction of the total annual deposition flux, all originate from the western Sahara–Sahel (a major area of emission in the region beside the Bodele Depression, stretching from the Mauritanian and Western Saharan coasts to the Hoggar Mountains). Combined with air mass tri-dimensional back-trajectories and satellite images, the mineralogical and Sr–Nd isotopic compositions of these large dust events enable us to identify several mineralogically and geochemically distinct provenance sectors within this vast western area. Unlike the background dust deposits, the 87Sr/86Sr and the εNd isotopic signatures of the major dry events closely match that of the NETAO Late Holocene sediments, supporting the hypothesis that these events account for most of the aeolian terrigenous supply reaching the ocean floor. Although this database needs to be expanded, our results already provide useful constraints for the interpretation of the dust proxies' variations in marine sedimentary archives off Mauritania/Senegal in terms of changes in wind regimes and aridity over West Africa.
(Earth and Planetary Science Letters. vol. 364, n° 0012-821X, pp. 145-156, 01/02/2013)
LOG, INSU - CNRS, ULCO, CNRS, IRD [Ile-de-France], CNRS, MPIC, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IMAGO, IRD
Limited Consequences of Seagrass Decline on Benthic Macrofauna and Associated Biotic Indicators
Marine phanerogams are ecosystem engineers, as their presence induces major environmental changes that impact on the benthic fauna. Consequently, modifications to the structure of benthic communities would be expected to be associated with seagrass decline. Since 2005, Zostera noltii seagrass beds in Arcachon Bay (France), the largest in Europe, have undergone a severe decline. Twelve stations distributed throughout the lagoon were sampled in 2002, and all were found to be densely planted at that time. Subsequently, the same stations were revisited in 2010 and seagrass cover had drastically decreased by that time. Based on benthic macrofauna, multidimensional scaling (MDS) analysis identified four groups. Years were separated. In 2002, two groups were distinct in relation to the water body, since in 2010 separation between the two other groups was related to seagrass occurrence. When looking at community structure and dominant species there were moderate differences within and between years, independent of seagrass decline. Seagrass loss did not drastically modify the species composition as they were preserved in the remaining seagrass patches. However, there was a drop in macrofauna abundance in unvegetated muddy compared with abundance in the remaining seagrass areas. Epifauna was particularly affected by seagrass decline. Among biotic indicators based on macrofauna, multivariate indicator MISS (Macrobenthic Index in Sheltered Systems) was in agreement with the similarity of macrofauna structure among groups, while other tested indicators performed badly in relation to seagrass occurrence. However, no index detected seagrass loss, highlighting the necessity of maintaining a separate survey on seagrass cover.
(Estuaries and Coasts. vol. 36, n° 1559-2723, pp. 795-807, 29/01/2013)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Étude de la contamination de la côte libanaise par les hydrocarbures aromatiques polycycliques (HAPs) et les éléments traces métalliques (ETMs) : archives sédimentaires et biomonitoring suite à une marée noire
Ce projet de recherche porte sur l’étude de la contamination de la côte libanaise par les composés organiques (HAP, DDE) et par les éléments-trace métalliques (Hg, Pb principalement). Les travaux sur les compartiments sédimentaires et biologiques de la côte libanaise constituent deux parties aux problématiques et aux approches distinctes autour desquelles s’articule cette thèse. Dans la première partie, l’analyse d’une carotte sédimentaire datée prélevée sur le plateau continental du Sud du Liban a permis de reconstituer l’historique de contamination dans le bassin Levantin. Les analyses de contaminants dans les sédiments de la carotte C1 combinés à la datation aux 210Pb et 137Cs ont permis d’obtenir un enregistrement fiable des variations du dépôt de mercure, de plomb et de HAP sur le plateau continental libanais, dans le bassin Levantin. Bien que les concentrations et les flux soient relativement faibles, une augmentation en deux phases des concentrations est bien mise en évidence par le profil sédimentaire de C1. Le charbon est identifié comme source principale de Pb, de Hg et de HAP dans le bassin Levantin entre la moitié du 19ème siècle et la moitié du 20ème siècle. Les résultats des ratios isotopiques du Pb et des ratios diagnostiques de HAP appuient ce constat. Les archives sédimentaires dans la carotte C1 fournissent un signal du dépôt de contaminants à l’échelle globale probablement lié aux sources d’émissions atmosphériques en provenance d’Europe Centrale et de l’Est. Dans la seconde partie, une étude de la contamination par les HAP du littoral libanais est menée suite à la marée noire résultant du conflit armé israélo-libanais en 2006. Une approche de biomonitoring sur trois ans utilisant l’espèce de moules invasives Brachidontes variabilis a été développée. Les résultats indiquent une décroissance progressive des concentrations de HAP dans l’écosystème intertidal du littoral libanais. La contamination par les HAP du fioul en zone subtidale en 2007 est nettement plus faible. Cependant la signature des HAP dans les tissus de moules prélevées trois ans après la marée noire indique toujours la présence des composés du fioul de Jiyeh. La contamination est particulièrement persistante dans certaines zones fortement touchées par la nappe de fioul en 2006. Il apparaît que l’état initial pré-marée noire n’a pas été atteint, même trois ans après la marée noire de Jiyeh. L’examen détaillé de l’évolution spatiale et temporelle de la contamination par les HAP de l’environnement intertidal est présenté dans ce volet de notre étude.
(25/01/2013)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Live (Stained) Benthic Foraminifera Off Walvis Bay, Namibia: A Deep-Sea Ecosystem under the Influence of Bottom Nepheloid Layers
(Journal of Foraminiferal Research. vol. 43, n° 0096-1191, pp. 55-71, 22/01/2013)
BIAF, UA, LPG-ANGERS, LPG, UA, UN UFR ST, UN, INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, LPG, UA, UN UFR ST, UN, INSU - CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Nearshore Dynamics of Tsunami-like Undular Bores using a Fully Nonlinear Boussinesq Model.
When tsunami wave fronts reach the shore, they can evolve into a large range of bore types, from undular non-breaking bore to purely breaking bore. It is the complex competition between non-linearities, dispersive effects and energy dissipation which will govern their transformations, making the prediction of their evolution a challenging task for numerical models. In this paper we investigate the ability of a fully nonlinear Boussinesq model, SURF-WB, to predict bore dynamics in a large range of Froude numbers. The model is first applied to the formation of undular bores, and compared with laboratory data. Its ability to predict the different bore shapes is then investigated. Finally, the effects of the bore transformation on wave run-up over a sloping beach are considered.
(Journal of Coastal Research. vol. SI64, n° 0749-0208, pp. 603-607, 15/01/2013)
I3M, UM2, UM, CNRS, IMT, UT Capitole, Comue de Toulouse, INSA Toulouse, INSA, Comue de Toulouse, UT2J, Comue de Toulouse, UT3, Comue de Toulouse, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, DMA, ENS-PSL, PSL, CNRS
Longshore sediment flux hindcast: spatio-temporal variability along the SW Atlantic coast of France
The Aquitanian coast (SW France) is exposed to high-energy waves, and subject to an overall shoreline erosion of 1 to 3 m/year. Engineering practices in this area requires the knowledge of longshore sediment fluxes. The reference values of direction and variability have been estimated 33 years ago with data available at that time. More recent estimations have been done on limited area and time span. The present study aims at: (1) updating and discussing the longshore sediment flux on this coast, (2) comparing the longshore drift spatial variability with measured shoreline evolution, (3) analyzing the interannual variability, in comparison with NAO indexes. Using a recent wave hindcast spanning the period 1958–2001, and the Kamphuis (1991) formula, the obtained gradients in longshore drift appear roughly consistent with the shoreline evolution and previous estimations of residual sediment fluxes. However, the estimated northward oriented fluxes are smaller in the present study than in the 33 year old reference study. The analysis shows a strong interannual variability, slightly smaller than the longshore variability. The interannual variability is not uniform along the coast. The northern section seems to be correlated with NAO indexes. Further analyses are required to better understand the temporal variability of the longshore sediment fluxes.
(Journal of Coastal Research. vol. 165, n° 0749-0208, pp. 1785-1790, 03/01/2013)
BRGM, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CSIRO
Extreme winter storm versus Summer storm: morphological impact on a sandy beach
(Journal of Coastal Research. vol. 65, n° 0749-0208, pp. 648 - 653, 02/01/2013)
LPG, UA, UN UFR ST, UN, INSU - CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Run-out distance and erosion of debris-flows in the Nile deep-sea fan system: Evidence from lithofacies and micro-palaeontological analyses
Debrites with different volumes, depositional periods and setting are observed in the Nile deep-sea fan system. Here we present debrites from four late Quaternary environments: (i) within the Rosetta submarine channel at 1700 m; (ii) within small basins created by salt tectonics in the Eastern Province at 1300 m; (iii) on the open slope outside of channels at 2600 m; and (iv) in the distal part of the fan fringe beyond channel terminations at 3050 m water depth. The debrites comprise mud clasts in a generally ungraded muddy sand matrix. They are relatively thin (20-150 cm) in fan fringe, in channel and salt-tectonic basin settings, and somewhat thicker (>8 m) in the open slope setting. Benthic foraminiferal assemblages and variation in the planktonic/benthic foraminiferal ratios are considered as a useful tool for tentatively evaluating the origin of sediment in these debris flows and estimation of their run-out distance. Similar microfaunal contents of clast/matrix combinations document that the debrites in the Rosetta channel and salt-tectonic basin were locally sourced. The debrite from the open slope travelled farther (up to 150 km). Three separate debrites in a fan fringe core were deposited by debris flows that originated over 200 km away in water depths shallower than 1000 m. These far-travelled debris flows appear to have eroded remarkably little sediment as they travelled for ∼200 km across low (0.8-1.2°) gradient seafloor. This lack of erosion is attributed to hydroplaning or increasing pore-fluid pressure at the base of debris flows. This study confirms that remarkably mobile debris flows can travel long distances to produce thin debrites in the distal fringes of submarine fans.
(Marine and Petroleum Geology. vol. 39, n° 0264-8172, pp. 102-123, 01/01/2013)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, GEOAZUR 6526, IRD, UPMC, UNS, INSU - CNRS, UniCA, CNRS, ISMAR, ISMAR, CNR