Morphosedimentological record and human settlements as indicators of West-African Late Holocene climate variations in the littoral zone of the Iwik peninsula (Banc d’Arguin – Mauritania)

Abstract

Abstract The geomorphological, sedimentological and archaeological studies of coastal features in the Iwik-Aouatil area show two categories of coastal sedimentary units: very extensive sand flats and linear relief features covered by a thin veneer of anthropogenic Anadara senilis shell-middens. These units provide an opportunity to discuss the return to arid conditions in western Sahara during the Late Holocene, when climate changes induced the alternating occurrence of more or less dry episodes, from around 5 ka until today. These constructions reflect the global climate change within the general framework known for the region. Two different processes occurred: (1) constant deposition of wide sand-flats and (2) construction of sedimentary ridges at specific moments. These processes demonstrate the existence of (1) constant sand discharge during the whole period as sand availability is not a limiting factor and (2) a substantially increased sand influx during the 4.2-3.2 ka episode. Because of sea-level stability in the Banc d’Arguin area during the Late Holocene, the variability of morphogenetic agents is considered to be the likely cause of fluctuations, influencing sand input rate and implying that either sand was delivered in greater abundance (aridity crisis and stronger winds) or littoral drift was more powerful (stronger waves and more frequent storms in the northern part of the Atlantic ocean), or both simultaneously. The action of these two driving forces in the depositional processes observed in the Iwik-Aouatil coastal plain is evaluated with respect to the occurrence of episodes of rapid climate changes (RCCs) and North Atlantic Oscillation (NAO) changes. A climate pattern combining episodes of RCC and NAO positive (NAO+) index during the 4.5-3.2 ka period is convenient for both sand supply, which accelerates the southwestward migration of barchan’s lines, and sand transportation, which improves the efficiency of the littoral drift.