High-resolution morpho-sedimentary and paleoenvironmental evolution of Wadi Akka (Drâa Basin, Morocco) from Late Pleistocene to Holocene.

Abstract

The fluvial evolution of southern Morocco during the Late Quaternary, particularly in non-Mediterranean basins such as the Wadi Akka, a tributary of the Drâa, remains poorly documented. This study presents the first chronostratigraphic framework for the Wadi Akka formations, based on a high-resolution reconstruction of fluvial dynamics and paleoenvironmental changes since the end of the last interglacial period. The analysis follows a multiproxy approach, combining geomorphological, sedimentological, and geochemical data, and is supported by 13 radiocarbon and four optically stimulated luminescence (OSL) ages. Nine main stratigraphic units reveal alternating phases of aggradation, pedosedimentary stability, and incision, associated with climatic fluctuations from Marine Isotope Stage (MIS) 5b (~82 ka) to the late Holocene. During MIS 3 (~40 ka cal BP), a low-energy hydromorphic environment prevailed, marked by fine sedimenta-tion and soil development under relatively humid conditions. The early African Humid Period (11.400-9.700 cal BP) is characterized by fluvio-lacustrine settings, peat layers, and tufa deposits, indicating stable, wet environments. Conversely, arid phases are marked by signifi-cant incision and sedimentary hiatuses, particularly between 9.500-8.500 and after 6.000 cal BP. Alluviation phases are also dated to around 7.200 and 656-579 cal BP. The presence of tuf deposits and travertine dams indicates peaks in humidity, especially during the beginning of Little Ice Age. Finally, comparison with other regional archives has allowed for the reconstruction of Upper Pleistocene and Holocene paleoenvironmental conditions at both regional and supra-regional scales, highlighting the correspondence between phases recorded in the Akka Plain and broader climatic events in the region.