Late Quaternary climatic events and sea-level changes recorded by turbidite activity, Dakar Canyon, NW Africa

The relationship of sea-level changes and short-term climatic changes with turbidite deposition is poorly documented, although the mechanisms of gravity-driven sediment transport in submarine canyons during sea-level changes have been reported from many regions. This study focuses on the activity of the Dakar Canyon off southern Senegal in response to major glacial/interglacial sea-level shifts and variability in the NW-African continental climate. The sedimentary record from the canyon allows us to determine the timing of turbidite events and, on the basis of XRF-scanning element data, we have identified the climate signal at a sub-millennial time scale from the surrounding hemipelagic sediments. Over the late Quaternary the highest frequency in turbidite activity in the Dakar Canyon is confined to major climatic terminations when remobilisation of sediments from the shelf was triggered by the eustatic sea-level rise. However, episodic turbidite events coincide with the timing of Heinrich events in the North Atlantic. During these times continental climate has changed rapidly, with evidence for higher dust supply over NW Africa which has fed turbidity currents. Increased aridity and enhanced wind strength in the southern Saharan–Sahelian zone may have provided a source for this dust

New constraints on oceanographic vs. seismic control on submarine landslide initiation: a geotechnical approach off Uruguay and northern Argentina

Submarine landslides are common along the Uruguayan and Argentinean continental margin, but size, type and frequency of events differ significantly between distinct settings. Previous studies have proposed sedimentary and oceanographic processes as factors controlling slope instability, but also episodic earthquakes have been postulated as possible triggers. However, quantitative geotechnical slope stability evaluations for this region and, for that matter, elsewhere in the South Atlantic realm are lacking. This study quantitatively assesses continental slope stability for various scenarios including overpressure and earthquake activity, based on sedimentological and geotechnical analyses on three up to 36 m long cores collected on the Uruguayan slope, characterized by muddy contourite deposits and a locus of landslides (up to 2 km3), and in a canyon-dominated area on the northern Argentinean slope characterized by sandy contourite deposits. The results of shear and consolidation tests reveal that these distinct lithologies govern different stability conditions and failure modes. The slope sectors are stable under present-day conditions (factor of safety >5), implying that additional triggers would be required to initiate failure. In the canyon area, current-induced oversteepening of weaker sandy contourite deposits would account for frequent, small-scale slope instabilities. By contrast, static vs. seismic slope stability calculations reveal that a peak ground acceleration of at least 2 m/s2 would be required to cause failure of mechanically stronger muddy contourite deposits. This implies that, also along the western South Atlantic passive margin, submarine landslides on open gentle slopes require episodic large earthquakes as ultimate trigger, as previously postulated for other, northern hemisphere passive margins

Evolution of a high-latitude sediment drift inside a glacially-carved trough based on high-resolution seismic stratigraphy (Kveithola, NW Barents Sea)

Published version, source at http://doi.org/10.1016/j.quascirev.2016.02.007. License CC BY-NC-ND 4.0.Kveithola is a glacially-carved, E-W trending trough located in the NW Barents Sea, an epicontinental shelf sea of the Arctic Ocean located off northern Norway and Russia. A set of confined sediment drifts (the “Kveithola Drift”) is located in the inner part of the trough. In general, drift deposits are commonly characterized by high lateral continuity, restricted occurrence of hiatuses and relatively high accumulation rates, and thus represent excellent repositories of paleo-environmental information. We provide for the first time a detailed morphological and seismostratigraphic insight into this sediment drift, which is further supported by some preliminary lithological and sedimentological analyses. The complex morphology of the drift, imaged by combining all available multibeam data, includes a main and a minor drift body, two drift lenses in the outer part of the trough, more or less connected drift patches in the innermost part and small perched sediment patches in a structurally-controlled channel to the north. The seismic (PARASOUND) data show that the main and minor drift bodies are mainly well-stratified, characterized by sub-parallel reflections of moderate to high amplitude and good lateral continuity. The reflectors show an abrupt pinch-out on the northern edge where a distinct moat is present, and a gradual tapering to the south. Internally we identify the base of the drift and four internal horizons, which we correlate throughout the drift. Two units display high amplitude reflectors, marked lensoidal character and restricted lateral extent, suggesting the occurrence of more energetic sedimentary conditions. Facies typical for contourite deposition are found in the sediment cores, with strongly bioturbated sediments and abundant silty/sandy mottles that contain shell fragments. These characteristics, along with the morphological and seismic information, suggest a strong control by a bottom current flowing along the moat on the northern edge of the drift. Though both Atlantic and Arctic waters are known to enter the trough, from the west and the north respectively, brine-enriched shelf water (BSW) produced during winter and flowing westward in the moat, is suggested to be responsible for the genesis of the Kveithola Drift. The formation of BSW is inferred to have started around 13 cal ka BP, the onset of drift deposition, suggesting that conditions leading to atmospheric cooling of the surface waters and/or the presence of coastal polynyas and wind or floating ice shelves have persisted on the western Barents Shelf since that time. The units inferred to have been deposited under more energetic sedimentary conditions (tentatively dated to the Younger Dryas and to 8.9–8.2 cal ka BP) are suggestive of stronger BSW formation. In general, we infer that variations in the bottom current regime were mainly related to BSW formation due to atmospheric changes. They could also have been a response to successive episodes of grounded and sea ice retreat that allowed for a first limited, later open shelf current, which progressively established on the western Barents Sea shelf

Cambios históricos en el aporte terrígeno de la cuenca del Río de la Plata sobre la plataforma interna Uruguaya

El Río de la Plata (RdlP) presenta significativas variaciones naturales (hidrodinámicas y oceanográficas) asociadas a diferentes condiciones climáticas. El propósito de este trabajo es inferir los cambios de aportes continentales de sedimentos y su relación con las variaciones hidrológicas del Río de la Plata, a través del análisis de proxies sedimentológicos y geoquímicos en testigos de sedimentos de la plataforma interna uruguaya que registran los últimos 100 años, aproximadamente. A partir de ladatación por 210Pb de dos testigos de sedimentos (GeoB 13813-4 y BAR1) se reconstruyó la geocronología del ambiente, y se relacionó con datos de las forzantes climáticas Pacific Decadal Oscillation, El Niño/La Niña Southern Oscillation, Atlantic MultidecadalOscillation, y las anomalías hidrológicas de los ríos Paraná y Uruguay. Los valores máspositivos y estables del Southern Oscillation Index, los cuales corresponden a fases La Niña,se observan en el periodo correspondiente entre 1910-1970, respecto al resto de la serie,donde se aprecia una mayor variabilidad y una tendencia hacia valores más negativos(eventos El Niño). Se hicieron dendrogramas (clustering) jerárquicos para ambos testigos. Para el testigo GeoB 13813-4, se utilizó la relación Ca/Ti y la granulometría, mientras que para BAR1 se recurrió a variables granulométricas y la tasa de sedimentación. El mayoraporte continental hacia la región de la plataforma adyacente al Río de la Plata registrado a partir del año 1970, podría ser el factor principal de los agrupamientos observados en los clusters para ambos testigos. Las agrupaciones mostraron una diferenciación en la década de 1970 lo que estaría asociado al aumento de los caudales de los ríos Paraná y Uruguay, durante las últimas tres décadas del siglo XX. Por otra parte se observa que la granulometría del testigo BAR1 presentó un mayor tamaño de grano y más variabilidad que en el caso del testigo GeoB 13813-4. También se determinó una mayor acumulación de sedimentos a través del tiempo en el cinturón de barro del Río de la Plata (plataforma continental adyacente), comparado con aquel registrado en la Barra del Indio (límite entre zona intermedia y externa del estuario). Estas diferencias podrían estar relacionadas con la influencia del Río de la Plata la cual genera un ambiente altamente dinámico sobre la Barra del Indio y un ambiente más estable sobre el cinturón de barro en la plataforma continental.Fil: Marrero, Analía. Universidad de la República. Facultad de Ciencias; UruguayFil: Tudurí, Adriana. Universidad de la República. Facultad de Ciencias; UruguayFil: Perez, Laura. Universidad de la República. Facultad de Ciencias; UruguayFil: Cuña Rodriguez, Carolina Celeste. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Muniz, Pablo. Universidad de la República. Facultad de Ciencias; UruguayFil: Lopes Figueira, Rubens C.. Instituto Oceanografico; BrasilFil: Michcelovitch de Mahiques, Michel. Instituto Oceanografico; BrasilFil: Alves de Lima Ferreira, Paulo. Instituto Oceanografico; BrasilFil: Pittauerová, Daniela. Center For Marine Environmental Sciences, Marum; AlemaniaFil: Hanebuth, Till. Center For Marine Environmental Sciences, Marum; AlemaniaFil: Garcia Rodriguez, Felipe. Universidad de la República. Facultad de Ciencias; Urugua

Incised valleys on the Algarve inner shelf, northern Gulf of Cadiz margin: stratigraphic architecture and controlling factors in a low fluvial supply setting

A network of cross-shelf paleovalleys has been recognized over the paleo-inner shelf off the Gila & SIM;o-Almargem Estuary, a small fluvial drainage system that presently receives minor sediment supply in the eastern Algarve shelf, northern margin of the Gulf of Cadiz (SW Iberian Peninsula). This study is aimed at determining the driving controls that triggered substantially different paleohydrological conditions and sedimentary dynamics of ancient fluvial systems in this margin. We focus on evidences of secondary controls on valley genesis and evolution, superimposed to primary glacio-eustatic control such as antecedent geology, low fluvial supply and changing hydrodynamic regimes. The architecture and spatial distribution of these paleovalleys were interpreted based on a grid of seismic profiles with different resolutions. Likewise, a sediment core obtained in a distal position of the paleovalley system provided information about sedimentary processes during the most recent stage of valley infilling. The chronostratigraphic framework was constructed based on regional seismic horizons defined in previous studies and complemented with two AMS 14C dates obtained from bivalve shells.The inner shelf paleovalley system is composed of several incised valley features which exhibit a remarkable similar internal architecture. These inner valley features exhibit two major incision phases (from oldest to youngest; IP 2 and IP 1) that are thought to constitute a simple paleovalley system formed during the last glacial cycle. The origins of the incision are considered to be different. The older one is related to fluvial incision during the sea-level fall leading into the Last Glacial Maximum, whereas the recent one is interpreted as the result of tidal scour during the postglacial transgression. Their corresponding infillings are interpreted, respectively, as estuarine bay-fill deposits and estuary-mouth sands. Overlying the paleovalley infilling, a distinctive reflective unit is in agreement with the generation of coastal barriers and related depositional systems.The formation of the paleo-inner-shelf paleovalley system was strongly conditioned by antecedent geology, which strongly limited the generation of wide incised valleys and determined the amount of incision landward of a well-defined break of slope. Its postglacial infilling was mainly estuarine in nature, likely involving the development of a dendritic system, with numerous barriers interrupted by tidal inlets and channels in a mixed estuarine system with low fluvial supply.Research projects CGL2011-30302-C02-02 and PID2021-125489OB-I00, supported by Spanish Ministries of Economy and Competitiveness and Science and Innovation. LA/P/0069/2020info:eu-repo/semantics/publishedVersio

Dropstones in the Mar del Plata Canyon Area (SW Atlantic): Evidence for Provenance, Transport, Distribution, and Oceanographic Implications

A variety of gravel- to cobble-sized rocks, recovered from the Mar del Plata (MdP) Canyon area (Western South Atlantic at 38°S) and interpreted as ice-rafted debris, represent the first evidence that large icebergs have floated in the Falkland (Malvinas) Current from the southern polar high latitudes far northward. Detailed petrographic analyses identified the Antarctic Peninsula, sub-Antarctic islands in the Scotia Sea, and Tierra del Fuego as plausible source areas. The drift process could have started as early as at the beginning of the last deglaciation, according to an age obtained from a cold-water coral fragment associated with one of the dropstones. At the end of the Last Glacial Maximum, large icebergs have been supplied to the Antarctic Circumpolar Current, captured by those ocean current branches that circumvent the Falkland (Malvinas) Islands and entered the Argentine Margin. When the iceberg fleets approached the Brazil-Falkland (Malvinas) Confluence Zone with its steep latitudinal temperature gradient, the icebergs got oceanographically trapped and melted off rapidly. The sediment load sinking down to the seafloor formed a dropstone blanket particularly where the MdP Canyon had incised into the continental slope. Here, mass-flow processes, induced by local slope instability, and along-slope sediment resorting, due to the erosional effects of strong and persistent contouritic bottom currents, favored local enrichment in dropstones in the form of a loose, coarse sediment drape inside morphological depressions. The bottom current velocity would be locally strong enough to rework this sediment, leaving coarse rafted debris as a lag deposit.Fil: Bozzano, Graziella. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Cerredo, Maria Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Remesal, Marcela Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Steinmann, L.. Universitat Bremen; AlemaniaFil: Hanebuth, Till J.J.. Coastal Carolina University; Estados UnidosFil: Schwenk, T.. Universitat Bremen; AlemaniaFil: Baqués, Michele. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; Argentina. Ministerio de Defensa. Armada Argentina. Dirección Gral. de Investigación y Desarrollo de la Ara. Dirección de Investigación de la Armada; ArgentinaFil: Hebbeln, Dierk. Universitat Bremen; AlemaniaFil: Spoltore, Daniela Veronica. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Silvestri, Ornella. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; Argentina. Universidad de Buenos Aires; ArgentinaFil: Acevedo, Rogelio Daniel. Universidad Nacional de Tierra del Fuego, Antártida e Islas del Atlántico Sur. Instituto de Ciencias Polares, Ambientales y Recursos Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Spiess, V.. Universitat Bremen; AlemaniaFil: Violante, Roberto Antonio. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; ArgentinaFil: Kasten, Sabine. Universitat Bremen; Alemania. Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research; Alemani

Cambios históricos en el aporte terrígeno de la Cuenca del Río de la Plata sobre la plataforma interna uruguaya.

El Río de la Plata (RdlP) presenta significativas variaciones naturales (hidro- dinámicas y oceanográficas) asociadas a diferentes condiciones climáticas. El propósito de este trabajo es inferir los cambios de aportes continentales de sedimentos y su relación con las variaciones hidrológicas del Río de la Plata, a través del análisis de proxies sedimentológicos y geoquímicos en testigos de sedimentos de la plataforma interna uruguaya que registran los últimos 100 años, aproximadamente. A partir de la datación por 210Pb de dos testigos de sedimentos (GeoB 13813-4 y BAR1) se reconstruyó la geocronología del ambiente, y se relacionó con datos de las forzantes climáticas Pacific decadal oscillation, El Niño/La Niña southern oscillation, Atlantic Multidecadal oscillation, y las anomalías hidrológicas de los ríos Paraná y Uruguay. Los valores más positivos y estables del southern oscillation index, los cuales corresponden a fases La Niña, se observan en el periodo correspondiente entre 1910-1970, respecto al resto de la serie, donde se aprecia una mayor variabilidad y una tendencia hacia valores más negativos (eventos El Niño). Se hicieron dendrogramas (clustering) jerárquicos para ambos testigos. Para el testigo GeoB 13813-4, se utilizó la relación Ca/Ti y la granulometría, mientras que para BAR1 se recurrió a variables granulométricas y la tasa de sedimentación. El mayor aporte continental hacia la región de la plataforma adyacente al Río de la Plata registrado a partir del año 1970, podría ser el factor principal de los agrupamientos observados en los clusters para ambos testigos. Las agrupaciones mostraron una diferenciación en la década de 1970, lo que estaría asociado al aumento de los caudales de los ríos Paraná y Uruguay, durante las últimas tres décadas del siglo XX. Por otra parte se observa que la granulometría del testigo BAR1 presentó un mayor tamaño de grano y más variabilidad que en el caso del testigo GeoB 13813-4. También se determinó una mayor acumulación de sedimentos a través del tiempo en el cinturón de barro del Río de la Plata (plataforma continental adyacente), comparado con aquel registrado en la Barra del Indio (límite entre zona intermedia y externa del estuario). Estas diferencias podrían estar relacionadas con la influencia del Río de la Plata, el cual genera un ambiente altamente dinámico sobre la Barra del Indio y un ambiente más estable sobre el cinturón de barro en la plataforma continental