Late Cenozoic fluvial dynamics of the River Tana, Kenya, an uplift dominated record
Veldkamp, A. ; Buis, E. ; Wijbrans, J.R. ; Olago, D.O. ; Boshoven, E.H. ; Maree, M. ; Berg van Saparoea, R.M. van den - \ 2007
Quaternary Science Reviews 26 (2007)22-24. - ISSN 0277-3791 - p. 2897 - 2912.
african climate-change - east-africa - terrace stratigraphy - quaternary volcanism - environmental-change - mount kenya - rift - geochronology - history - lahars
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.
Late cenozoic landscape development and its tectonic implications for the guadalhorce valley near alora (southern Spain)
Schoorl, J.M. ; Veldkamp, A. - \ 2003
Geomorphology 50 (2003). - ISSN 0169-555X - p. 43 - 57.
landschap - tektoniek - spanje - geomorfologie - zeespiegelschommelingen - kaenozoïcum - geomorphology - landscape - tectonics - spain - sea level fluctuations - kenozoic - se spain - betic cordilleras - terrace stratigraphy - level changes - sorbas basin - late miocene - evolution - uplift - pliopleistocene - chronology
Landscape evolution is the result of a variety of geomorphological processes and their controls in time. In southern Spain tectonics, climate and sea-level fluctuations have been some of the main variables controlling long-term (Late Cenozoic) landscape evolution. In the Guadalhorce valley, Malaga, geomorphological reconstructions can be undertaken using sedimentary evidence from marine and fluvial deposits as well as erosional evidence such as terrain form and longitudinal profile analysis. Data are obtained and analysed from the Upper Miocene to present. These allow reconstructions which add information and constraints to the uplift history and landscape development of the area. Main sedimentation phases are the Late Tortonian, Early Pliocene and Pleistocene. Important erosional hiatus are found for the Middle Miocene, Messinian and Late Pliocene to Early Pleistocene. These phases of erosion and sedimentation resulted in a relative large and elongated Tortonian marine valley filled with complex sedimentary structures. Next, a prolonged stage of erosion of these deposits and incision of the major valley system took place during the Messinian. In the Pliocene, a short palaeo-Guadalhorce, in a narrow and much smaller valley existed. This valley was partly filled with marine sediments and prograding fan delta complexes. During the Pleistocene, a wider and larger incising river system resulted in rearrangements of the drainage network. Evaluating the uplift history of the area, we found that rates of tectonic activity were higher during the Tortonian-Messinian and Upper Pleistocene, while tectonic activity was lower during the Pliocene. Relative uplift rates for the study area range for the Messinian between 160 and 276 in Ma(-1), for the Pliocene between 10 and 15 in Ma and for the Pleistocene between 40 and 100 in Ma(-1) (C) 2002 Elsevier Science B.V All rights reserved.
Reconstructing late quaternary fluvial process controls in the upper aller valley (north Germany) by means of numerical modeling
Veldkamp, A. ; Berg, M. van den; Dijke, J.J. van; Berg van Saparoea, R.M. van den - \ 2002
Netherlands journal of geosciences 81 (2002)3-4. - ISSN 0016-7746 - p. 375 - 388.
geomorfologie - kwartaire afzettingen - tektoniek - terrassen - dalen - simulatiemodellen - geologische sedimentatie - duitsland - rivieren - geomorphology - rivers - geological sedimentation - quaternary deposits - tectonics - terraces - valleys - simulation models - germany - terrace stratigraphy - maas record - europe - uplift - system
The morpho-genetic evolution of the upper Aller valley (Weser basin, North Germany) was reconstructed using geological and geomorphologic data integrated within a numerical process model framework (FLUVER-2). The current relief was shaped by Pre-Elsterian fluvial processes, Elsterian and Saalian ice sheets, followed by Weichselian fluvial processes. Structural analysis based on subsurface data and morphological interpretations were used to reconstruct uplift/subsidence rates. A detailed analysis led to the hypothesis that we are dealing with either a NNW-SSE or a WSW-ENE oriented compression leading to uplift in the upper Aller valley. It is also hypothesised that the NNW-SSE compression might have caused strike-slip deformation leading to differential block movement and tilt.Two different uplift rate scenarios were reconstructed and used as a variable parameter in numerical modelling scenarios simulating the Late Quaternary longitudinal dynamics of the Aller. Each different scenario was run for 150.000 years and calibrated to the actual setting. The resulting model settings were consequently evaluated for their plausibility and validity. Subsequently, regional semi-3D simulations of valley development were made to test the two tectonic stress hypotheses. Differential tectonic uplift and regional tilt seems to have played an important role in shaping the current valley morphology in the upper Aller. Unfortunately, due to the uncertainties involved, we were unable to discriminate between the two postulated tectonic stress scenarios.