Tectonic and climatic control on evolution of rift lakes in the Central Kenya Rift, East Africa
Tectonic and climatic control on evolution of rift lakes in the Central Kenya Rift, East Africa
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DOI：
10.1016/j.quascirev.2009.07.008
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发表时间：
2009-12-01
影响因子：
4
通讯作者：
Duehnforth, M.
中科院分区：
文献类型：
--
作者：
Bergner, A. G. N.;Strecker, M. R.;Duehnforth, M.
肯尼亚裂谷中部邻近的纳库鲁-埃尔门蒂塔和奈瓦沙湖盆的长期历史表明，构造和气候效应对裂谷湖演化和不同沉积环境的形成具有相对重要性。尽管肯尼亚中部裂谷的现代气候条件与这些盆地非常相似，但由于受构造控制的盆地几何形状、集水区大小和河流演变的差异，今天的纳库鲁湖、埃尔门泰塔湖和奈瓦沙湖的水文和水化学截然不同。在这项研究中，我们使用了18个(14)C和(40)Ar/(39)Ar测年的河湖相沉积剖面，揭示了湖盆在构造和气候影响下的时空演化。基于硅藻化石组合和地质野外填图，我们重建了这些盆地记录的古气候和生态趋势。我们的研究表明，在过去的100万年里，这两个湖泊盆地的水体都有增加碱度和收缩的趋势。正在进行的湖盆火山构造分割，以及上游排水网络的重组，导致水文状况与邻近的碱性和淡水条件形成反差。在过去的极端潮湿时期，例如全新世早期气候最佳时期，湖泊水位很高，所有盆地都向淡水系统演化。在干旱时期，这些湖泊中的一些恢复到碱性状态，而另一些则保持淡水特征。我们的结果对于在构造活动区利用和解释湖泊沉积物作为气候档案具有重要意义，并强调了从构造与气候强迫机制方面去卷积湖泊记录的必要性。(C)2009爱思唯尔有限公司。保留所有权利。
The long-term histories of the neighboring Nakuru-Elmenteita and Naivasha lake basins in the Central Kenya Rift illustrate the relative importance of tectonic versus climatic effects on rift-lake evolution and the formation of disparate sedimentary environments. Although modem climate conditions in the Central Kenya Rift are very similar for these basins, hydrology and hydrochemistry of present-day lakes Nakuru, Elmenteita and Naivasha contrast dramatically due to tectonically controlled differences in basin geometries, catchment size, and fluvial processes. In this study, we use eighteen (14)C and (40)Ar/(39)Ar dated fluvio-lacustrine sedimentary sections to unravel the spatiotemporal evolution of the lake basins in response to tectonic and climatic influences. We reconstruct paleoclimatic and ecological trends recorded in these basins based on fossil diatom assemblages and geologic field mapping. Our study shows a tendency towards increasing alkalinity and shrinkage of water bodies in both lake basins during the last million years. Ongoing volcano-tectonic segmentation of the lake basins, as well as reorganization of upstream drainage networks have led to contrasting hydrologic regimes with adjacent alkaline and freshwater conditions. During extreme wet periods in the past, such as during the early Holocene climate optimum, lake levels were high and all basins evolved toward freshwater systems. During drier periods some of these lakes revert back to alkaline conditions, while others maintain freshwater characteristics. Our results have important implications for the use and interpretation of lake sediment as climate archives in tectonically active regions and emphasize the need to deconvolve lacustrine records with respect to tectonics versus climatic forcing mechanisms. (C) 2009 Elsevier Ltd. All rights reserved.