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Origin and evolution of silcretes
Kohoutová, Iveta ; Zachariáš, Jiří (advisor) ; Adamovič, Jiří (referee)
Summary: Silcretes are rocks with high content of SiO2 (usually more than 90 wt. %) formed by mobilization of SiO2 during weathering processes. Silcretes formed near the Earth's surface by soil weathering in warm and humid climate are termed as pedogenic silcretes. Another type of silcrete is groundwater silcrete, whose origin is usually associated with the groundwater table and depths of 5-50 m below the surface and arid to semi-arid climate. The third type of silcretes is associated with evaporites. Its genesis is complicated; as well it is difficult to date this silicification. There are four types of silcrete textures: GS-, F-, M-, C- textures; the most common is the F-texture. In the Czech Republic silcretes are more known under the term "sluňáky" or "quartzite". Indeed, in every country where they occur, have their own specific name. Silcretes are essentially composed of SiO2, minor constituents represent heavy minerals and/or feldspar. Cement is mostly α-quartz, chalcedony and opal. Average thickness of silcretes is 1-3 m, rarely 5 meters. Main source of SiO2 is chemical weathering of silicate minerals or quartz dust grains carried by wind and deposited on natural barriers, like blades of grass. There are two models of silcrete formation: lateral and vertical transport model SiO2. Sedimentary...
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Karstification of carbonato-silicate rocks: review of literature and leaching experiments
Vojtíšek, Jan ; Bruthans, Jiří (advisor) ; Kůrková, Iva (referee)
The process of karstification doesn't occur only in easily soluble rock, such as limestone and evaporites, but also occurs in other rocks such as quartzites or siliciclastic rocks with carbonate cement. The "ghost rock" karstification is, unlike the classical karstification, two- step process, where the soluble component are dissolved first and subsequently the insoluble components are eroded and flushed away. These processes also occur in the Czech Republic, for example in the Bohemian Cretaceous Basin (BCB). Practical part of this thesis consists of leaching experiments of samples from BCB. Leaching in hydrochloric acid is an accelerated simulation of natural processes of dissolution by acidic solutions. Leaching of the samples in acid led to the decrease of sample strength, sometimes to their desintegration. The samples are probabbly prone to the evolution of karst conduits. Leaching experiments showed that the carbonate content is an important but not the only driving factor in the karstification process.
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Karstification of carbonato-silicate rocks: review of literature and leaching experiments
Vojtíšek, Jan ; Bruthans, Jiří (advisor) ; Kůrková, Iva (referee)
The process of karstification doesn't occur only in easily soluble rock, such as limestone and evaporites, but also occurs in other rocks such as quartzites or siliciclastic rocks with carbonate cement. The "ghost rock" karstification is, unlike the classical karstification, two- step process, where the soluble component are dissolved first and subsequently the insoluble components are eroded and flushed away. These processes also occur in the Czech Republic, for example in the Bohemian Cretaceous Basin (BCB). Practical part of this thesis consists of leaching experiments of samples from BCB. Leaching in hydrochloric acid is an accelerated simulation of natural processes of dissolution by acidic solutions. Leaching of the samples in acid led to the decrease of sample strength, sometimes to their desintegration. The samples are probabbly prone to the evolution of karst conduits. Leaching experiments showed that the carbonate content is an important but not the only driving factor in the karstification process.
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Origin and evolution of silcretes
Kohoutová, Iveta ; Zachariáš, Jiří (advisor) ; Adamovič, Jiří (referee)
Summary: Silcretes are rocks with high content of SiO2 (usually more than 90 wt. %) formed by mobilization of SiO2 during weathering processes. Silcretes formed near the Earth's surface by soil weathering in warm and humid climate are termed as pedogenic silcretes. Another type of silcrete is groundwater silcrete, whose origin is usually associated with the groundwater table and depths of 5-50 m below the surface and arid to semi-arid climate. The third type of silcretes is associated with evaporites. Its genesis is complicated; as well it is difficult to date this silicification. There are four types of silcrete textures: GS-, F-, M-, C- textures; the most common is the F-texture. In the Czech Republic silcretes are more known under the term "sluňáky" or "quartzite". Indeed, in every country where they occur, have their own specific name. Silcretes are essentially composed of SiO2, minor constituents represent heavy minerals and/or feldspar. Cement is mostly α-quartz, chalcedony and opal. Average thickness of silcretes is 1-3 m, rarely 5 meters. Main source of SiO2 is chemical weathering of silicate minerals or quartz dust grains carried by wind and deposited on natural barriers, like blades of grass. There are two models of silcrete formation: lateral and vertical transport model SiO2. Sedimentary...
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