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Geochemical evolution of closed-basin lakes : general model and application to lakes Qinghai and Turkana

Yan, J. P. and Hinderer, Matthias and Einsele, G. (2002):
Geochemical evolution of closed-basin lakes : general model and application to lakes Qinghai and Turkana.
In: Sedimentary geology, pp. 105-122, 148, [Article]

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Abstract

In contrast to most previous models for the evolution of closed-basin lakes, we present an integrated model which considers various water budget patterns, clay regradation, SO4 reduction and subbottom leakage in addition to the classical equilibrium approach of mineral precipitation. The model was applied to Lakes Qinghai and Turkana, which significantly differ in the lithologies of their drainage areas but are representative of the carbonate-rich sedimentary rock province of the Tibet–Qinghai Plateau and the silicate rock province of Eastern Africa. Both lakes are now topographically closed, but to some degree hydrologically open (subbottom leakage). Major results of the mode calculations show that: the lithology controls the ultimate brine which is of Na–(K)–Cl-type for Qinghai Lake and of Na–HCO3–Cl-type for Lake Turkana. SO4 reduction delays the onset of sulfatic mineral precipitation and favours the formation of Na–carbonates such as trona at the expense of calcite. Clay mineral regradation plays an important role before the saturation of sulfatic or chlorine minerals is reached. In particular, magnesite formation may be in competition with Mg-bearing clay minerals. Finally, simulations with various hydrological scenarios have shown that the modern hydrochemistry of both lakes cannot be reproduced by simply evaporating inflow water, but reflects long-term accumulation and evolution of solutes by continuous inflow over several thousand years. The diversity of lake water composition within a uniform lithological province can thus be largely ascribed to varying hydrological conditions.

Item Type: Article
Erschienen: 2002
Creators: Yan, J. P. and Hinderer, Matthias and Einsele, G.
Title: Geochemical evolution of closed-basin lakes : general model and application to lakes Qinghai and Turkana
Language: English
Abstract:

In contrast to most previous models for the evolution of closed-basin lakes, we present an integrated model which considers various water budget patterns, clay regradation, SO4 reduction and subbottom leakage in addition to the classical equilibrium approach of mineral precipitation. The model was applied to Lakes Qinghai and Turkana, which significantly differ in the lithologies of their drainage areas but are representative of the carbonate-rich sedimentary rock province of the Tibet–Qinghai Plateau and the silicate rock province of Eastern Africa. Both lakes are now topographically closed, but to some degree hydrologically open (subbottom leakage). Major results of the mode calculations show that: the lithology controls the ultimate brine which is of Na–(K)–Cl-type for Qinghai Lake and of Na–HCO3–Cl-type for Lake Turkana. SO4 reduction delays the onset of sulfatic mineral precipitation and favours the formation of Na–carbonates such as trona at the expense of calcite. Clay mineral regradation plays an important role before the saturation of sulfatic or chlorine minerals is reached. In particular, magnesite formation may be in competition with Mg-bearing clay minerals. Finally, simulations with various hydrological scenarios have shown that the modern hydrochemistry of both lakes cannot be reproduced by simply evaporating inflow water, but reflects long-term accumulation and evolution of solutes by continuous inflow over several thousand years. The diversity of lake water composition within a uniform lithological province can thus be largely ascribed to varying hydrological conditions.

Journal or Publication Title: Sedimentary geology
Volume: 148
Divisions: 11 Department of Materials and Earth Sciences
11 Department of Materials and Earth Sciences > Earth Science
11 Department of Materials and Earth Sciences > Earth Science > Applied Sedimentary Geology
Date Deposited: 17 Jun 2015 06:56
License: [undefiniert]
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