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Abstract: A major outcome from studying the sedimentary archives of the Timiris Canyon off Mauritania is that climate shifts in the Saharan hinterland not only influenced offshore pelagic sedimentation processes, but also controlled turbidite activity in the canyon system. Sediment supply to the slope, predominantly by eolian dust and remobilised eolian sands, was greatest during hyperarid glacial and deglacial periods and, due to overall increased Trade wind strengths, upwelling induced pelagic productivity attained highest magnitudes. Turbidite activity in the Timiris Canyon responded rapidly to these shifts in the surrounding sedimentary regime on the continental slope. During high-glacial and early deglacial times, the tributary gullies on the uppermost slope were rapidly and repetitively filled, subsequently turbidity currents were released and large turbulent flows passed through the lower Timiris Canyon, leading to overspill sequences on its levees. In addition to this scenario, partial flooding of the exposed outer shelf during successive sea-level rises in MIS 3 may have caused re-mobilization of huge aeolian dune fields, that had expanded close to the shelf edge during glacial exposure. During the Holocene, no turbidite activity is recorded in the Lower Timiris Canyon, whereas a core from a widened area in the Upper Timiris Canyon reveals an interesting climate controlled 900-year cyclicity of carbonate- and mud-turbidite events throughout the Holocene. [ABSTRACT FROM AUTHOR]

Abstract: Sediment records from continental shelves and slopes might provide paleoenvironmental information in the highest temporal resolution but are often hampered due to strong erosional and reworking processes. Here, we present a Holocene sedimentary record from an exceptional shelf mud belt depocenter off northern Mauritania, compared to a second sediment core located inside a large canyon system at the adjacent continental slope. Both records are of outstandingly continuous and highest temporal resolution (9a/cm) and are investigated by sedimentological and geochemical methods. A series of sharply defined, recurrent dust peaks is preserved in the shelf archive. Each event has lasted for a single decade only and seems to coincide with an individual turbidite bed in the canyon. A joint mechanism should, thus, be responsible for both of these deposits and we suggest a regional atmospheric trigger. Only short-lasting Trade wind strengthening would cause such pronounced aridity over western Saharan Africa. The effect would be massive dust export to shelf and slope. Recently developed high resolution aridity and humidity records from western Africa support the existence of these events over the Holocene and identify them as being controlled by the Atlantic system as far south as 19°N. [Copyright &y& Elsevier]

Abstract: Large-scale mass wasting is an important sedimentary process along the northwest African margin, and is related to high sediment accumulation rates under an ocean margin upwelling regime. Although the margin is generally arid with limited fluvial input, additional sediment supply comes from wind-borne Saharan dust. Recent mapping of the margin off Mauritania has revealed a major sediment slide, here called the Mauritania Slide Complex, as it comprises elements of true sliding as well as more mobile distal debris flow. Seismic data image stacked slide deposits separated by undisturbed stratified sediments indicating that undisturbed sediment accumulation was interrupted by several phases of slope failure. A series of stepped headwalls, 25–100m high, represents the source area of the youngest slide event, which most likely occurred as retrogressive type of failure. The area of seafloor affected by this mass movement is ∼30,000km2, while the deposit volume is ∼600km3. The uppermost debrite unit, which has been 14C dated at 10.5–10.9ka, forms a broad tongue extending down to the lower slope. This debrite comprises a vertical succession of three different layers of matrix types, with a predominantly outer shelf source at the base and pelagite-dominated composition at the top. The complete sequence of three layers was deposited at a mid slope position, whereas only the upper layers reached the lower slope. A thick pile of sediments with outer shelf/upper slope derived biogenic and terrigenous debris-rich sediments at the base and hemipelagic sediments on top failed at an upper to mid slope location and disintegrated into a layered debris flow on its down-slope journey. [Copyright &y& Elsevier]

Seafloor mapping of the Mauritania margin by multibeam bathymetry as well as shallow and high-resolution seismics in combination with core data has revealed a wide variety of seafloor features, which are primarily generated by turbidity currents and landslides. The largest observed features in the study area are two submarine slides, which both have affected over 30,000 km2 of seafloor. The Cap Blanc Slide is not considered to be a significant geohazard at the present day as it has a minimum age of 165 ka and shows no evidence of recent reactivation. In contrast, the complex Mauritania Slide Complex is characterized by a retrogressive failure style and has an age of only 10.5-10.9 cal. ka B.P.We found no indication for recent reactivation of this slide, but more data are needed to assess the present seafloor stability in this area. Turbidity current activity on the margin is evidenced by numerous gullies, canyons and channels. The largest of these is the >450 km-long meandering Cap Timiris Canyon.During the present Holocene sea-level highstand, however, terrigenous sediment supply to the modern outer shelf has been restricted and most of the conduits are therefore thought to be largely inactive, at least in terms of large sand-rich flows. [ABSTRACT FROM AUTHOR]