Paleoenvironnements du bassin Nord-Tanganyika (Zaire, Burundi, Tanzanie) au cours des 13 derniers mille ans: Apport de la palynologie

Abstract

Detailed palynological data recorded from two cores of lake Tanganyika (Rumonge and Nyanza-Lac basins) document the botanical, climatic and hydrological history of this basin from 13,000 B.P. Rich and well diversified microflora show an important climatic change during the Late Pleistocene-Holocene transition. Prior to 12,000 B.P., the extension of montane communities at lower altitude than their modern range, suggests cool climatic conditions. Between 12,000 and 10,000 B.P., soudano-zambezian and zambezian woodlands (Miombo) expand around the lake, reaching their maximum of development and diversity between 10,000 and ca. 2500 B.P. This change is related both to an increase in temperatures and to a higher rainfall than before. The humid phase between 10,000 and 2500 B.P. is interrupted by a distinct episode interpreted as a local hydrological event concerning the North-Tanganyika basin. Indeed, the composition of the microflora would suggest a sudden and temporary overflow of Lake Kivu via the Rusizi river, later than 6000 B.P. and prior to 2500 B.P. After 2500 B.P., a deterioration of the arboreal cover is detected, related to the progressive establishment of the modern climatic conditions.