Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
6446895 | Quaternary Science Reviews | 2007 | 16 Pages |
Abstract
The Late Cenozoic development of the River Tana in Kenya has been reconstructed for its central reach near its confluence with the River Mutonga, which drains the Mount Kenya region. Age control for this system has been provided by K-Ar and Ar-Ar dating. Between 3.21 and 2.65 Ma a major updoming occurred, in relation to the formation of the Kenyan rift valley. The tilting related to this doming has been reconstructed from lava flows that preserve former river gradients. Linear projection of these trends to the current rift valley rim suggests a net updoming of the eastern Gregory Rift valley by at least â¼1 km during 3.21-2.65 Ma. In contrast, since 2.65 Ma the Tana system has been mainly subject to relatively minor epeirogenic uplift. Changing climatic conditions combined with continuing uplift yielded a typical staircase of strath terraces with at least 10 distinct levels. A more detailed reconstruction of the incision rates since 215 ka has been made, by correlating mineralogically fingerprinted volcaniclastic Tana deposits with dated tephras in a lake record. These volcaniclastic sediments were deposited during glacial periods, contemporaneous with lahars. The reconstructed incision rates for the three youngest terraces are â¼0.1-0.2 mm aâ1, thus considerably faster than the overall average rate of valley incision since the Mid-Pliocene, of 0.06 mm aâ1. A plausible uplift history has been reconstructed using the estimated ages of the Tana terraces and marine terraces on the Indian Ocean coastline. The result suggests an increase in the rate of incision by the River Tana at â¼0.9 Ma, an observation typical in most European river terrace staircases. The reconstructed Late Quaternary development of Tana valley indicates that a similar Quaternary uplift mechanism has operated in both Europe and East Kenya, suggesting a globally applicable process.
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Geology
Authors
A. Veldkamp, E. Buis, J.R. Wijbrans, D.O. Olago, E.H. Boshoven, M. Marée, R.M. van den Berg van Saparoea,