Fluvio‐lacustrine sedimentation in the Agadir‐Tissint Feija (Anti‐Atlas, Morocco): A promising palaeoclimate archive for the last glacial cycle in northwest Africa
Résumé
Mountainous 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.
Domaines
Stratigraphie
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