431 research outputs found
Mise en évidence d'une péjoration climatique entre ca. 2 500 et 2 000 ans B.P. en Afrique tropicale humide
Essai sur le rôle de la zone tropicale dans les changements climatiques : l'exemple africain
Remarques sur quelques sites préhistoriques de la vallée du Nil (deuxième cataracte)
Maley Jean. Remarques sur quelques sites préhistoriques de la vallée du Nil (Deuxième Cataracte). In: Bulletin de la Société préhistorique française. Comptes rendus des séances mensuelles, tome 63, n°2, 1966. pp. 71-72
Essays on the ecology of the Guinea-Congo rain forest
This chapter sets out to give a historical overview of the African rain forest from its origins, towards the end of the Cretaceous period. The areas around the Gulf of Guinea, in particular from Ivory Coast to Nigeria and especially Cameroon, Gabon and Congo, appear to have been already occupied at this time by wet tropical forest formations mainly composed of Angiosperms which were then becoming established. In the course of the Tertiary period the combined effect of the equator being situated further north than now and the development of the Antarctic ice cap favoured the development of wet tropical conditions over a large part of North Africa which in turn led to the extension of tropical forest to various sites on the shores of the Tethys Sea. There were probably at this time common taxa and similar vegetation patterns stretching from the Gulf of Guinea to the Tethys Sea. Towards the end of the Tertiary, the equator reached its present position and the northern hemisphere ice caps appeared, and these phenomena resulted in the disappearance of the forest formations spread across the north of Africa, and the concentration of these formations near the equatorial zone around the Gulf of Guinea and in the Congo-Zaïre basin. From 800 000 years ago onwards the marked glacial variations at middle and high latitudes in both hemispheres, with a periodicity of about 100 000 years determined by the orbital variations of the earth around the sun, lowered temperatures in equatorial areas and brought arid climates at times of maximum glacial extension. The most arid periods resulted in the fragmentation of the forest cover, and the forest biotopes and their biodiversity were preserved in a series of refugia. The lowering of temperatures also resulted in the extension of montane flora to low altitudes, with migration of montane flora and fauna between main mountain ranges... (D'après résumé d'auteur
Les variations climatiques dans le bassin du Tchad durant le dernier millénaire : Essai d'interprétation climatique de l'Holocène africain
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