Late Pleistocene colluvial deposits in central Tanzania; erosional response to climatic change?

Abstract

Two major colluvial deposits have been identified on the slopes of the Irangi Hills in north central Tanzania. The oldest of these occurs in shallow depressions on the pediment slopes. The time of deposition has been dated by the use of optical stimulated luminescence (OSL) dating techniques to Late Pleistocene. The OSL dates were 14,700 ± 1600, 14,200 ± 1500, and 11,400 ± 1300 years. In Late Pleistocene time the climate changed from dry to wet conditions throughout much of the tropics and this time period is frequently reported as a period characterised by enhanced soil erosion. It is likely that the older colluvial unit in the Irangi Hills was formed as a result of climatic change when rainfall increased ahead of a vegetation change and thereby provided conditions favourable for soil erosion. The younger colluvial unit yielded deposition ages of 400–600 years and is part of a number of successive erosion and deposition periods during the last millenium, probably as a result of anthropogenic impact on the landscape.

Key Words:

• Soil erosion
• colluvial deposits
• climatic change
• Late Pleistocene
• Holocene
• Tanzania
• East Africa