Caracterisation des marqueurs sedimentaires du ruissellement sur un massif saharien au Tardiglaciaire et a P Holocene inferieur (Termit, Niger oriental, Bassin du lac Tchad)

摘要

The Termit Massif is a meso-cenozoic uplifted block in the T￡n6r6 sand-sea. In the West-Termit endoreic depression, approximately 350m downwards, a 15,57 m core provided a record of the Lateglacial and early Holocene deposits. A sedimentological study of the coarse fraction (>400 um) was carried out: granulometry, morphoscopy, exoscopy, mineralogy. This study makes it possible to discuss the allochtonous/autochtonous features of the material. Five types of ferruginous particles were distinguished of which four were brought by run-off from the massif. The last type of ferruginous particles corresponds to synsedimentary or diagenetic ferruginous crusts in palustro-lacustrine deposits. Several types of quartz grains were also distinguished. Three of them which have a thin ferruginous crust were brought by run-off from the massif. The others have all the characteristics of the quartz grains worked by the wind. In this core a sandy level is thus deposited by the wind during arid conditions. Nevertheless, essentially, these wind-worked coarse grains are dispersed in sediments deposited by run-off. The sedimentological characteristics of these grains were acquired before their final deposit.