The Sahara experienced several humid episodes during the late Quaternary, associated with the development of vast fluvial networks and enhanced freshwater delivery to the surrounding ocean margins. In particular, marine sediment records off Western Sahara indicate deposition of river-borne material at those times, implying sustained fluvial discharges along the West African margin. Today, however, no major river exists in this area; therefore, the origin of these sediments remains unclear. Here, using orbital radar satellite imagery, we present geomorphological data that reveal the existence of a large buried paleodrainage network on the Mauritanian coast. On the basis of evidence from the literature, we propose that reactivation of this major paleoriver during past humid periods contributed to the delivery of sediments to the Tropical Atlantic margin. This finding provides new insights for the interpretation of terrigenous sediment records off Western Africa, with important implications for our understanding of the paleohydrological history of the Sahara.
The reconstruction of pre-depositional cooking treatments used by prehistoric coastal populations for processing aquatic faunal resources is often difficult in archaeological shell midden assemblages. Besides limiting our knowledge of various social, cultural, economic and technological aspects of shell midden formation, unknown pre-depositional cooking techniques can also introduce large errors in palaeoclimate reconstructions as they can considerably alter the geochemical proxy signatures in calcareous skeletal structures such as bivalve shells or fish otoliths. Based on experimental and archaeological data, we show that carbonate clumped-isotope thermometry can be used to detect and reconstruct prehistoric processing methods in skeletal aragonite from archaeological shell midden assemblages. Given the temperature-dependent re-equilibration of clumped isotopes in aragonitic carbonates, this allows specific processing, cooking or trash dispersal strategies such as boiling, roasting, or burning to be differentiated. Besides permitting the detailed reconstruction of cultural or technological aspects of shell midden formation, this also allows erroneous palaeoclimate reconstructions to be avoided as all aragonitic shells subjected to pre-historic cooking methods show a clear alteration of their initial oxygen isotopic composition.
At the end of the Neolithic Era, during the third millennium BCE, there were fewer humid periods, and the sub-Saharan and Sahelian zones from the Atlantic to Lake Chad assumed their current geographical form. Since then, the climate has continued undergoing major variations. The succession of climatic episodes, humid or dry, is pointed out along with the episodes' complex interactions. These variations are placed in parallel to cultural phases of evolution in archaeology and history. Climate-related events have always had heavy consequences on the peopling of this vast region, often subject to extreme natural conditions. The relative synchronism between the principal cultural trends from west to east across the Sahel seems to have often been subject to swings in the climate and the resulting environmental changes.Résumé La fin du Néolithique, au cours du III e millenaire BP, a correspondu à l'affaiblissement des périodes humides et à la mise en place de la géographie actuelle dans la zone sud-saharienne et sahélienne, qui s'etend de l'Atlantique au lac Tchad. Depuis cette époque le climat a cependant continué à beaucoup varier. La succession des differents épisodes climatiques, phases humides ou phases arides-et leurs interactions complexes-est precisée. Ces faits climatiques sont mis en parallèle avec l'évolution archéologique et historique des differentes phases culturelles. Dans cette immense region, souvent à la limite des conditions naturelles extrêmes, les évènements climatiques ont toujours eu des conséquences très importantes sur l'évolution des peuplements humains. Le relativement bon synchronisme des principaux changements culturels, d'ouest en est à travers la bande sahélienne, paraît avoir été fréquemment Afr Archaeol Rev (2015) 32:179-232 contrôlé par le rôle directeur des changements climatiques majeurs et des variations environnementales qui en ont resulté.
Dhar Néma, easternmost of the Tichitt escarpment chain, was neglected by archaeologists throughout the twentieth century. However, since 2000, two separate archaeological teams have conducted survey and test excavation work in the region. This article presents the final research results of one of these teams. Two sites in particular are closely examined: the settlement mound of Djiganyai with stratified intermittent occupation between c. 2000 and 800 cal. BC, and the multi-component site of Bou Khzama II, featuring structural elements, inhumations, and large scale iron-smelting remains. It is argued that Dhar Néma, although an ecologically favourable zone, was politically peripheral to the central Tichitt-Walata polity and comparatively sparsely settled. A period of relative regional abandonment, or widespread shifts in settlement, between 1400 and 1100 cal. BC is also noted. Regardless, a range of Pre-Tichitt and Tichitt Tradition settlements are documented for the region, including evidence for millet agriculture equivalent in age to that of the Dhar Tichitt region. It is suggested that the origins of Tichitt agriculture must now be sought in the third millennium BC. Concerning more recent periods, putative new data for first millennium BC iron metallurgy in the Dhar Néma region are presented and their technical aspects analysed. Finally, a revised hypothesis for the role of incoming Berber populations in the denouement of the Tichitt Tradition is considered, with cultural syncretism rather than replacement advocated.Le Dhar Néma, à l'extrêmité est de la falaise de Tichitt-Walata a été négligé par les archéologues pendant tout le XX e siècle. Cependant, depuis 2000, deux équipes archéologiques différentes ont conduit des prospections et des travaux de fouille dans la region. Cet article présente le résultat final d'une des deux équipes. Deux sites ont été plus particulièrement étudiés: la butte d'habitat de Djiganyai, avec une occupation intermittente-en stratigraphie Á entre 2000 et 800 cal BC; le site complexe, fréquemment réoccupé, de Bou Khzama II, qui présente des structures d'habitat, des inhumations et un vaste espace où les restes de métallurgie du fer abondent. On y constate que le Dhar Néma, bien que situé dans une zone écologiquement favorable, est dans un position périphérique par rapport au centre de gravité politique de la culture de Tichitt, établie sur les dhars Tichitt et Walata. Le peuplement y est aussi moins dense. On note également une période de relatif abandon de la region, ou d'importants changements dans le peuplement, entre 1400 et 1100 cal BC. Cependant, la succession des groupes humains, de la culture Pré-Tichitt à la culture classique de Tichitt, est bien visible dans la region. La chronologie de la culture du mil y est la même que dans la zone du Dhar Tichitt. L'article suggère que les origines de l'agriculture dans la region doivent se situer au 3 e millénaire BC. En ce qui concerne les périodes plus récentes, de nouvelles dates indiquent que la métallurgie du fer, dont les aspect...
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