Late Holocene morphodynamics in the littoral zone of the Iwik Peninsula area (Banc d'Arguin — Mauritania)

Abstract

In the littoral zone of the Banc d'Arguin both littoral sedimentary units and man-made deposits (shell-middens) abound. They were formed during the Late Holocene after the final onset of the post-glacial transgression. Here, a geo-archaeological approach is used to study them. The geomorphological and sedimentological characteristics of the coastal features define two distinct coastal sedimentary units in the Iwik–Aouatil zone between an ancient shoreline which formed on the Tafaritian substratum ca 6.7–5.7 cal. ka BP and the present one: (i) very extensive sand flats and (ii) linear relief features, both covered by a thin veneer of anthropogenic Anadara senilis shell-middens. They developed under a stable sea-level regime. The sand flats expanded at variable rates throughout the period. The linear relief features represent beach barriers and coastal dunes which can be dated archaeologically thanks to the superimposed shell-middens, supplemented by 14C dating. Two series of linear sedimentary units are identified. First, a complex north–south system of dunes and hook-ended sand barriers developed from 4.8 to 4.1 cal. ka BP and, secondly, two regular and linear beach barriers developed between 3.7 and 3.3 cal. ka BP. Their morphological characteristics suggest that they were generated through littoral drift processes. Directional changes observed between the first and the second groups demonstrate that the wave refraction pattern was dramatically modified after the closure of the strait between the former Iwik Island and the land. A comparison with the nearby Jerf el Oustani coastal area in the Late Holocene shows that both sites shared similarities in depositional patterns but also differences in the chronology of the sedimentary units. Processes involved in the development of the linear units are indicative of the enhancement of both sand influx and longshore drift due to climatic change.