Late Cenozoic fluvial dynamics of the River Tana, Kenya, an uplift dominated record

A. Veldkamp, E. Buis, J.R. Wijbrans, D.O. Olago, E.H. Boshoven, M. Maree, R.M. van den Berg van Saparoea

Research output: Contribution to journalArticleAcademicpeer-review

38 Citations (Scopus)

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 similar to 1 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 similar to 0.1-0.2 mm a(-1), thus considerably faster than the overall average rate of valley incision since the Mid-Pliocene, of 0.06 mm a(-1). 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 similar to 0.9 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. (c) 2007 Elsevier Ltd. All rights reserved.
Original languageEnglish
Pages (from-to)2897-2912
JournalQuaternary Science Reviews
Volume26
Issue number22-24
DOIs
Publication statusPublished - 2007

Keywords

  • african climate-change
  • east-africa
  • terrace stratigraphy
  • quaternary volcanism
  • environmental-change
  • mount kenya
  • rift
  • geochronology
  • history
  • lahars

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