National Repository of Grey Literature 18 records found  1 - 10next  jump to record: Search took 0.01 seconds. 
Magnetic record of conretions
Smrčinová, Lucie ; Kletetschka, Günther (advisor) ; Adamovič, Jiří (referee)
Abstact The submitted bachelor thesis is focusing on the analysis of emergence of the concretion samples, which were discovered in recent years on the location of Jurassic Navajo Sandstone in Utah, and simultaneously their comparison with concretions found during exploration of Mars on the place Meridiani Planum. The major objective of this study is to compare the condition of origin and to search possible similarities. Terestrical concretions of iron oxid maintain diagenetical record of interaction between underground water flow and sandy material. Based on the input parametres, observed here, numerical and laboratory simulations were performed, leading to explanation of an image about growth of these spherules. Important factors during precipitation of nodules is concentation, flux and time. The experiment with reactions of ferrous sulfate, iron nitrate and potassium hydroxid shows the process of precipitation and maturation of hydrated iron around nucleation center of cencretion. Comparison laboratory results, numerical simulations and found samples helps to understanding to emergence of iron concretionson Mars in a certain chemical and hydrological environment. The importance of this contribution is, that on the basis of knowledge research about concretions, their both magnetical and geochemical...
15th International Ichnofabric Workshop : program, abstracts, Field Guidebook
Kočová Veselská, Martina ; Adamovič, Jiří ; Kernhoff, M. ; Rifl, M. ; Šamánek, J. ; Mikuláš, Radek
Radek Mikuláš convened the 15th International Ichnofabric Workshop to Prague (April 27th – May 5th, 2019). Thirty-two specialists from over the world presented recent contributions from the mainstream branch of ichnology, e.g., ichnofabrics of terrestrial systems. Special discussion block was devoted to the use of computed tomography in the study of Ichnofabric. Three days (five days for participants of the post-workshop excursion) for the workshop were devoted to field excursions. Thereby, most of the localities known only through publications have been seen and evaluated directly to the world top ichnologists.
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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...
Cave formation initiated by dissolution of carbonate cement in qartzose sandstones
Adamovič, Jiří ; Mikuláš, Radek ; Navrátil, Tomáš ; Mertlík, J.
Besides cavities of irregular shape, European sandstones also feature symmetrical cavities of spherical, ellipsoidal or teardrop shapes. Most of them are tens of centimetres across but some reach as much as 2–3 m in diameter and may coalesce into large caves tens of metres in length. Their origin has not been clearly explained yet. Based on the field comparison between such cavities in quartzose sandstones and incompletely developed cavities in carbonate-cemented sandstones, it can be demonstrated that the symmetrical cavities form by carbonate dissolution within the limits of former carbonate concretions. The diagnostic features of post-concretionary cavities include their circular or elliptical cross-section, a uniform orientation of their long axes across the region, and the presence of a set of parallel vertical joints or grooves/ribs on their inner walls. In some sandstone areas (e.g., Petite Suisse area in Luxembourg, Kokořín area in the Czech Republic), a wide variety of transitional forms can be found between the cavities and concretions forming positive relief on a vertical cliff face, depending on the position of the carbonate dissolution front in the present landscape.

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2 Adamovič, Ján
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