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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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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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