Climate and sea level induced turbidite activity in a canyon system offshore the hyperarid Western Sahara (Mauritania): The Timiris Canyon

摘要

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.