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  • 1
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    Salt-induced crestal faults control the formation of Quaternary tunnel valleys in the southern North Sea (2021)
    Details
    Publication Date: 2021-10-29
    Description: Tunnel valleys are major features of glaciated margins and they enable meltwater expulsion from underneath a thick ice cover. Their formation is related to the erosion of subglacial sediments by overpressured meltwater and direct glacial erosion. Yet, the impact of pre-existing structures on their formation and morphology remains poorly known. High-quality 3D seismic data allowed the mapping of a large tunnel valley that eroded underlying preglacial delta deposits in the southern North Sea. The valley follows the N–S strike of crestal faults related to a Zechstein salt wall. A change in downstream tunnel valley orientation towards the SE accompanies a change in the strike direction of salt-induced faults. Fault offsets indicate important activity of crestal faults during the deposition of preglacial deltaic sediments. We propose that crestal faults facilitated tunnel valley erosion by acting as high-permeability pathways and allowing subglacial meltwater to reach low-permeability sediments in the underlying Neogene deltaic sequences, ultimately resulting in meltwater overpressure build-up and tunnel valley excavation. Active faults probably also weakened the near-surface sediment to allow a more efficient erosion of the glacial substrate. This control of substrate structures on tunnel valley morphology is considered as a primary factor in subglacial drainage pattern development in the study area.
    Keywords: 551 ; southern North Sea ; Quarternary ; tunnel valley formation ; salt-induced faults
    Language: English
    Type: map
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    CITATION GEO-LEO
  • 2
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    The Agadir Slide offshore NW Africa: Morphology, emplacement dynamics, and potential contribution to the Moroccan Turbidite System (2018)
    Elsevier
    In:  Earth and Planetary Science Letters, 498 . pp. 436-449.
    Details
    Publication Date: 2021-02-08
    Description: A newly identified large-scale submarine landslide on the NW African margin (Agadir Slide) is investigated in terms of its morphology, internal architecture, timing, and emplacement processes using high-resolution multibeam bathymetry data, 2D seismic profiles, and gravity cores. The Agadir Slide is located south of the Agadir Canyon at a water depth ranging from 500 m to 3,500 m, showing an estimated affected area of approximately 5,500 km2. The analysis of the Agadir Slide's complex morphology reveals the presence of two headwall areas and two slide fairways (the Western and Central slide fairways). Volume calculations indicate that ∼340 km3 of sediment were accumulated downslope along the slide fairways (∼270 km3) and inside the Agadir Canyon (∼70 km3). Stratigraphic correlations based on five gravity cores indicate an emplacement age of 142±1 ka for the Agadir Slide. However, its emplacement dynamics suggest that the slide was developed in two distinct, successive stages. The presence of two weak layers (glide planes) is a major preconditioning factor for the occurrence of slope instability in the study area, and local seismicity related to fault activity and halokinesis likely triggered the Agadir Slide. Importantly, the Agadir Slide neither disintegrated into sediment blocks nor was transformed into turbidity currents. The emplacement timing of the Agadir Slide does not correlate with any turbidites cored downslope across the Moroccan Turbidite System.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.epsl.2018.07.005
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Morphology and sediment dynamics of upper headwall area of the Sahara Slide Complex, NW Africa (2015)
    In:  [Poster] In: 7. International Symposium Submarine Mass Movements and Their Consequences, 01.-05.11.2015, Wellington, New Zealand .
    Details
    Publication Date: 2016-09-26
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Poster
  • 4
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    Morphology, age and sediment dynamics of the upper headwall of the Sahara Slide Complex, Northwest Africa: Evidence for a large Late Holocene failure (2017)
    Elsevier
    In:  Marine Geology, 393 . pp. 109-123.
    Details
    Publication Date: 2020-02-06
    Description: Highlights • The upper headwall region of Sahara Slide is mapped for the first time. • The upper headwall region comprises multiple slope failures. • Slope failure occurred on pronounced glide planes at different stratigraphic levels. • Failure is young (~ 2 ka) contradicting the hypotheses of a relatively stable continental margin at present. • This young age requires a reassessment of slope instability and associated risks off NW Africa. Abstract The Sahara Slide Complex in Northwest Africa is a giant submarine landslide with an estimated run-out length of ~ 900 km. We present newly acquired high-resolution multibeam bathymetry, sidescan sonar, and sub-bottom profiler data to investigate the seafloor morphology, sediment dynamics and the timing of formation of the upper headwall area of the Sahara Slide Complex. The data reveal a ~ 35 km-wide upper headwall opening towards the northwest with multiple slide scarps, glide planes, plateaus, lobes, slide blocks and slide debris. The slide scarps in the study area are formed by retrogressive failure events, which resulted in two types of mass movements, translational sliding and spreading. Three different glide planes (GP I, II, and III) can be distinguished approximately 100 m, 50 m and 20 m below the seafloor. These glide planes are widespread and suggest failure along pronounced, continuous weak layers. Our new data suggest an age of only about 2 ka for the failure of the upper headwall area, a date much younger than derived for the landslide deposits on the lower reaches of the Sahara Slide Complex, which are dated at 50–60 ka. The young age of the failure contradicts the postulate of a stable slope off Northwest Africa during times of relative stable sea-level highstands. Such an observation suggests that submarine-landslide risk along the continental margin of Northwest Africa should be reassessed based on a robust dating of proximal and distal slope failures.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1016/j.margeo.2016.11.013
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Faulting of salt-withdrawal basins during early halokinesis: Effects on the Paleogene Rio Doce Canyon system (Espírito Santo Basin, Brazil) (2009)
    (AAPG) American Association of Petroleum Geologists
    In:  AAPG Bulletin, 93 (5). pp. 617-652.
    Details
    Publication Date: 2021-01-08
    Description: Three-dimensional seismic-reflection data are used in the analysis of submarine channel systems in the Espírito Santo Basin, Brazil. The exceptional quality of the studied data set allows the detailed documentation of the geometry, regional distribution, and statistical parameters of salt-related normal faults, and their effect on the Rio Doce Canyon system (RDCS). On the Espírito Santo continental slope, normal faulting was triggered during early halokinesis (stage A] but barely controlled the initial evolution of the RDCS, which incised the continental slope axially within a salt-withdrawal basin. However, in a second stage (stage B), crestal or radial faults controlled erosion over growing salt structures, whereas synclinal and channel-margin fault sets dissected overbank strata to the RDCS. In the later part of stage B, channel sinuosity decreased sharply in response to fault activity and associated sea-floor desta-bilization. Vertical propagation of blind faults was triggered in a third stage (stage C), in association with crestal collapse of buried salt anticlines and regional diapirism, but synclinal and channel-margin faults did not propagate vertically above a regional unconformity marking the base of stage C strata. Statistical analyses of observed fault sets demonstrate that synclinal faults are in average 2.3 times longer than the crestal or radial types but record 60% of the throw (average 83 m [272 ft]] experienced by the latter. In addition, the fault sets are shown to have contributed to local cannibalization of the sea floor, vertical stacking of channel-fill strata, and structural and deposi-tional compartmentalization of potential reservoir successions. As a result, channel systems show marked differences in mean values for sinuosity, height, and width in relation to five main phases of channel development. The structural setting in the study area differs from productive areas offshore Espirito Santo (e.g., Golfinho field), west Africa, and Gulf of Mexico, revealing in distal parts of the Brazilian margin the existence of local controls on submarine channel architecture and structural compartmentalization prior to the main stages of diapirism.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1306/02030908105
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Large-scale scours formed by supercritical turbidity currents along the full length of a submarine canyon, northeast South China Sea (2020)
    Elsevier
    Details
    Publication Date: 2023-02-08
    Description: High-resolution multibeam bathymetric and seismic data enables a detailed morphological investigation of a submarine canyon (West Penghu Canyon) on the northeastern South China Sea margin, where twenty-three (23) scours are observed along the canyon thalweg. These scours form narrow topographic depressions in plan view and show asymmetrical morphologies in cross-section. The identified scours can be further divided into two groups (Types A and B) based on their sizes and relative locations. They are separated by a slope break at a water depth of ~2850 m. Type A scours (S1-S18) occur upslope from the slope break, whereas Type B scours (S19-S23) lie downslope from this same break. The scours are interpreted as net-erosional cyclic steps associated with turbidity currents flowing through the West Penghu Canyon; the currents that form Type A scours reflect higher V, Q, and Δel compared to the currents forming Type B scours. A change in slope gradient and loss of lateral confinement are proposed to control the change from Type A to Type B scours. Furthermore, Coriolis force influences the flow direction of turbidity currents, leading to the preferential development and larger incision depths of scours towards the southwestern flank of the West Penghu Canyon. Our results contribute to a better understanding on the origin of scours in submarine canyons across the world.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Widespread hydrothermal vents and associated volcanism record prolonged Cenozoic magmatism in the South China Sea (2021)
    GSA (Geological Society of America)
    Details
    Publication Date: 2024-02-07
    Description: The continental margin of the northern South China Sea is considered to be a magma-poor rifted margin. This work uses new seismic, bathymetric, gravity, and magnetic data to reveal how extensively magmatic processes have reshaped the latter continental margin. Widespread hydrothermal vent complexes and magmatic edifices such as volcanoes, igneous sills, lava flows, and associated domes are confirmed in the broader area of the northern South China Sea. Newly identified hydrothermal vents have crater- and mound-shaped surface expressions, and occur chiefly above igneous sills and volcanic edifices. Detailed stratigraphic analyses of volcanoes and hydrothermal vents suggest that magmatic activity took place in discrete phases between the early Miocene and the Quaternary. Importantly, the occurrence of hydrothermal vents close to the present seafloor, when accompanied by shallow igneous sills, suggest that fluid seepage is still active, well after main phases of volcanism previously documented in the literature. After combining geophysical and geochemical data, this study postulates that the extensive post-rift magmatism in the northern South China Sea is linked to the effect of a mantle plume over a long time interval. We propose that prolonged magmatism resulted in contact metamorphism in carbon-rich sediments, producing large amounts of hydrothermal fluid along the northern South China Sea. Similar processes are expected in parts of magma-poor margins in association with CO2/CH4 and heat flow release into sea water and underlying strata.
    Type: Article , PeerReviewed
    Format: text
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Origin, evolution and significance of giant buried sediment mounds near the Sahara Slide Complex, North‐west African margin (2024)
    IAS (International Association of Sedimentologists) | Wiley
    Details
    Publication Date: 2024-03-01
    Description: Mixed turbidite–contourite depositional systems result from interactions between down‐slope turbidity currents and along‐slope bottom currents, comprising excellent records of past oceanographic currents. Modern and ancient systems have been widely documented along the continental margins of the Atlantic Ocean. Yet, few examples have so far been identified on the North‐west African continental margin, limiting understanding of the sedimentary and palaeoceanographic evolution in this area. This work uses two‐dimensional seismic reflection profiles to report, for the first time, the presence of three giant sediment mounds beneath the headwall region of the Sahara Slide Complex. The sediment mounds are elongated and separated by two broad canyons, showing a north‐west/south‐east orientation that is roughly perpendicular to the continental margin. These mounds are 24 to 37 km long and 12 to 17 km wide, reaching a maximum height of ca 1000 m. Numerous slide scarps are observed within and along the flanks of the mounds, hinting at the occurrence of submarine landslides during their development. Based on their geometries, external shapes, internal seismic architecture and stratigraphic stacking patterns, it is proposed that these sediment mounds comprise down‐slope elongated mounded drifts formed in a mixed turbidite–contourite system during four evolutionary stages: onset, growth, maintenance and burial. The significance of this work is that it demonstrates the gradual transition from a turbidite system to a full mixed turbidite–contourite system to be associated, in the study area, with the establishment of strong ocean currents along north‐west Africa.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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