Abstract
AbstractMountainous depocentres are often the single available archives in intracontinental areas. As such, the investigation of their sedimentary dynamics is the only way to reconstruct palaeoenvironmental evolution in these peculiar regions. Here, the basin‐scale sedimentary dynamics of the Agadir‐Tissint Feija (i.e. feija is the local name for lowlands) are discussed together with new palaeoenvironmental information on the late Quaternary in the north‐western Sahara margin. The succession consists of up to ca 40 m thick fluvio‐lacustrine deposits subdivided into three depositional sequences (S1–S3) that were deposited between ca 75 ka and ca 10 ka. S1 and S2 reflect the evolution of a palaeolake intercalated by carbonate‐rich palustrine to alluvial plain environments, while S3 shows the transition to an entirely clastic alluvial plain environment. The three sequences are genetically associated with three pulses of tufa buildups at the outlet of the depocentre. Each pulse of tufa buildup is attributed to wet conditions, while each interruption is associated with drier conditions. The wet–dry alternation at the origin of S1 fits with summer insolation fluctuation suggesting that precession parameters may have paced long‐term climate variability in the area. Superimposed on wet–dry cycles, submillennial‐scale (750–900 year) shorter‐term lake fluctuations are identified in S1 and S2; their origins may be related to North Atlantic Oscillation mechanisms. Furthermore, the sudden increase in clastic sediment supply in S3 evidences a change in sediment production in the catchment area attributed to lower temperatures established during the last glacial period. Finally, this newly identified continental archive is unique at the northern Sahara margin; it enables reconstructions of the local and regional hydrological conditions during the last glacial cycle. Even if a more systematic investigation of palaeoclimate forcing is still necessary, the Agadir‐Tissint Feija will potentially bring important information to understand past and anticipate future regional climate change.
Highlights
Northwest Africa constitutes a transitional climatic zone influenced by Atlantic, Western Mediterranean and Saharan air masses (Kuhlmann, Meggers, Freudenthal, & Wefer, 2004; Tierney, Pausata, & deMenocal, 2017; Zielhofer et al, 2017)
Continental late Quaternary sedimentation in northwest Africa took place predominantly in mountainous domains in foreland depressions, which are rarely utilized at their full potential as archives of palaeoenvironmental changes
Two basin-scale transects summarize the basin-scale architecture of the depocentre and four reconstructed depositional systems illustrate the successive palaeoenvironments
Summary
Northwest Africa constitutes a transitional climatic zone influenced by Atlantic, Western Mediterranean and Saharan air masses (Kuhlmann, Meggers, Freudenthal, & Wefer, 2004; Tierney, Pausata, & deMenocal, 2017; Zielhofer et al, 2017). Between the southern front of the Anti-Atlas and the escarpment of the Jbel Bani, these rivers leave narrow valleys and feed extensive 15–50 km wide lowlands locally called ‘Feijas’ (Figure 1a,b) These feijas originated from differential erosion of clay-d ominated Middle Cambrian and Lower Ordovician rocks and more resistant sandstone-dominated and limestone-dominated Lower Cambrian and Upper Ordovician rocks (Michard, 1976). Five different feijas associated with five different rivers are recognized along the southern flank of the Anti-A tlas (Thorp et al, 2002; Figure 1a) They corresponded to important Late Quaternary depocentres (Andres, 1977; Dijon, 1976; Thorp et al, 2002; Weisrock, 2003) consisting of alternating fluvial and lacustrine sediments. This gorge constitutes the modern outlet of the system (Figure 1c)
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