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

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

Sedimentology and geochemistry of sediments from the Sunda Shelf

The Sunda Shelf represents one of the largest tropical shelf areas in the world. Its broad extension, the very low gradient, and the tectonical stability offer excellent conditions for a reconstruction of the exposure and flooding history during the last glacial cycle. A high fluvial input dominated this siliciclastic deposystem over long time intervals. The proximal part of the transect of the research cruise Sonne-115 covers the riverine structures of the ancient North Sunda River ('Molengraaff' River) from -70 to -126 m modern water depth. The aim of the study presented here was to analyse the stratigraphic architecture of the Sunda Shelf during the last 50 kyr, to develop a high-resolution sea-level curve, as well as to reconstruct the flooding history of this part of the world. The facies types examined in 36 sediment cores were classified by sedimentological and geochemical methods. 80 AMS-14C datings and additional fractionation measurement led to a high-resolution age determination. A shallow-seismic survey along and crosswise to the transect illustrated large- to medium-scale sediment structures. Eleven facies types were identified and related to the paleo-shoreline. They extend from terrestrial and coastline deposits to full-marine environments and were classified into five groups along the transect, which contain distinct local facies successions. The sea-level rise from 21 to 11 cal. kyr BP was determined by dating of plant remnants from the intertidal zone, following the retrograde migrating paleo-coastline. During lowstand, sea-level dropped at about -120 m. A conspicuous phase of the subsequent rise between 14.6 and 14.3 cal. kyr BP corresponding to meltwater pulse 1A was documented the first time and indicated as much as 16 m. In response to the sea-level changes during the last 50 kyr, characteristic processes formed the deposits and changed drastically several times until the terrigenous supply starved at about 11 kyr BP. Most remarkable were incised valley fills, which preserved deposits of the transgressive phase. A sequence-stratigraphic interpretation classified the deposits into three systems tracts and indicates, that three major factors controlled the depositional history: sediment input, physiography, and sea-level fluctuations. The specific modification of these factors in comparison to the general model was related to the asymmetry of the sea-level fall and rise and the extreme morphological conditions on the Sunda Shelf. Nevertheless, hiatuses of several thousand years and massive erosion activity were almost always predominantly affecting and strongly reducing the original sediment thickness

Report and first results of the POSEIDON Cruise P342 GALIOMAR, Vigo-Lisboa (Portugal), August 19th - September 06th, 2006. Distribution Pattern, Residence Times and Export of Sediments on the Pleistocene/Holocene Galician Shelf (NW Iberian Peninsula)

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