ABSTRACT
Workers in a number of closed lake basins in tropical Africa have described lacustrine formations which have been cited as evidence for a major wet period between 30 000 and 20 000 BP. The validity of this phase has always been open to question, because the chronological framework relies too heavily on carbonate dates. This paper presents new stratigraphic and palynological evidence from the Aberdare Plateau, Kenya, indicating that there was an important forest period prior to the last glacial maximum, which culminated after 24 000 BP. A review of the most reliable lacustrine chronologies suggests that the greatest extent of lakes occurred between 25 000 and 22 000 BP. This wet phase was most marked between the equator and about 22°N. It was not experienced in the equatorial lakes, but is clearly evident in deep sea cores which record long-term fluctuations in the discharge of the Niger and the Nile. We attribute the lake expansion to a combination of lower temperatures, slightly increased precipitation and possibly increased cloud cover and runoff.
