Géomorphologie, stratigraphie, géochronologie et oscillations glacio-eustatiques dans le domaine de la basse terrasse côtière, à l'embouchure de l'assif Tamraght (Baie de Tarhazout, Agadir, Maroc) pendant le MIS 5 et le MIS 4

At the Assif (=wadi) Tamraght mouth, a lower coastal terrace extends between the foot of a main dead cliff situated at ca. +8 m and the Ocean. This terrace contains evidences of the sea-level fluctuations that occured during MIS 5 and MIS 4. Evidences of two datable distinct marine stratigraphic units are found under +8 m, corresponding at two successive and transgressive glacio-eustatic oscillations: 1) (U1): at "Baie sud" site, left bank, between 0 and ca. +3 m, 150 m north-west of the dead cliff, a prograding basal gravel overlies the brief part of an ancient buried low-cliff; this lag deposit is overcomed by a MISS 5.3 marine sand (U/Th and IRSL dates); (U1) is found also on the right bank of the wadi under +1.50 m, 600 m off the main dead cliff; 2)(U2) on both banks also: "Cap 3" site, right bank, at +1.50 m, ca. 600 m NW of the dead cliff, and "Petit Cap", left bank, between +1 and + 3 m, ca. 300 m off the main dead cliff. (U2) consists of sandy marine sediments at Cap 3 and pebbly ones at Petit Cap, all of MISS 5.1 age. (U2) culminates at +4/+6 m with fine bioturbated aeolian sands right bank and pebbly berms left bank. Then, mainly on the right bank of the wadi, two others stratigraphic units, of continental deposits, occured: 3) (U3), more or less thick MIS 4 well stratified aeolian sands. 4) (U4), heterometric polygenic colluvial deposits, with mainly red-brown sands and silts, calcretes and sparse lithic tools. During the sea-level rises (MISS 5.3 and MISS 5.1), the morphogenic role of the wadi was restricted to episodic supply to marine sedimentation. Oceanic surf was responsible of marine abrasion surfaces and correlative cliffs; coastal currents built pebbly barriers and beaches. At the beginning of MIS 4, sandy coastal dunes were built by strong NW winds and drive the wadi mouth off to the south. Dunes represent the most part of the stratigraphic substratum below the lower terrace, their crest being truncated by a late MIS 4 colluvial glacis.