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Roman Aubrecht - One of the best experts on this subject based on the ideXlab platform.
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reply to the comment on sandstone caves on venezuelan tepuis return to Pseudokarst
Geomorphology, 2013Co-Authors: Roman Aubrecht, Tomas Lanczos, M Gregor, Jan Schlogl, B Smida, P Liscak, Ch Brewercarias, L VlcekAbstract:Abstract In Aubrecht et al. (2011) we brought new data showing that the arenitic caves in the Venezuelan tepuis did not necessarily originate through quartz cement dissolution (‘arenization’) but the main portion of the caves originated because of poor lithification prior to erosion. An additional important process is lateritization which is responsible for at least 30% of the caves' volume. Sauro et al. (2012) in their comment support the ‘arenization’ theory (quartz cement dissolution) and provide several arguments against some points of our research. Their main objections and arguments relate to the following topics: 1) the validity of the arenization theory, 2) the origin and importance of the ‘finger-flow’ pillars, 3) the importance of the Schmidt hammer measurements and, 4) metamorphism of the Mataui Formation. In our reply we present further documentation that: 1) The quartz cement dissolution theory of cave evolution was far less documented petrographically than the new theory presented by us. Although the presence of quartz dissolution is evident, there is no current evidence that it is widespread or that it plays a trigger role. Many of the presented examples of corrosion on quartz grains could have been caused by local alkalization. In addition, the hydrogeochemical data presented in the comment to support the ‘arenization’ theory do not in fact contradict our speleogenetic interpretations. 2) ‘Finger-flow’ pillars are speleogenetic indicators and not speleogenetic factors. Their absence in some caves provides no evidence against our theory. 3) Schmidt hammer measurements only objectivize the data on contrasting hardness in the Mataui Formation beds. They do not say anything about the origin of this difference. 4) The arguments of Sauro et al. (2012) involve the metamorphic overprint of the Mataui Formation shown by the presence of pyrophyllite and quartz mobilizations. Because quartz mobilization also occurs in hypergenic conditions, it may be neglected as a metamorphic indicator. Pyrophyllite is mentioned as a metamorphic indicator in the literature (anchizone to epizone) but it does not explain why there is still a vast quantity of kaolinite that did not undergo this reaction in the soft arenitic beds. There is an evidence that pyrophyllite may originate at lower temperatures. Some phases of the alumino-silicate mineral phases existing at atmospheric pressure and 25 °C temperature show that H 4 SiO 4 concentration is a critical factor in kaolinite/pyrophyllite transition. An increase in this concentration can theoretically cause transformation of kaolinite to pyrophyllite without increased temperature or pressure.
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sandstone caves on venezuelan tepuis return to Pseudokarst
Geomorphology, 2011Co-Authors: Roman Aubrecht, Tomas Lanczos, M Gregor, Jan Schlogl, B Smida, P Liscak, Ch Brewercarias, L VlcekAbstract:Abstract Venezuelan table mountains (tepuis) host the largest arenite caves in the world. The most frequently used explanation of their origin so far was the “arenization” theory, involving dissolution of quartz cement around the sand grains and subsequent removing of the released grains by water. New research in the two largest arenite cave systems – Churi-Tepui System in Chimanta Massif and Ojos de Cristal System in Roraima Tepui showed that quartz dissolution plays only a minor role in their speleogenesis. Arenites forming the tepuis are not only quartzites but they display a wide range of lithification and breakdown, including also loose sands and sandstones. Speleogenetic processes are mostly concentrated on the beds of unlithified sands which escaped from diagenesis by being sealed by the surrounding perfectly lithified quartzites. Only the so-called “finger-flow” pillars testify to confined diagenetic fluids which flowed in narrow channels, leaving the surrounding arenite uncemented. Another factor which influenced the cave-forming processes by about 30% was lateritization. It affects beds formed of arkosic sandstones and greywackes which show strong dissolution of micas, feldspars and clay minerals, turning then to laterite (“Barro Rojo”). The main prerequisite to rank caves among karst phenomena is dissolution. As the dissolution of silicate minerals other than quartz appears to play not only a volumetrically important role but even a trigger role, these arenitic caves may be ranked as karst.
Jorge Morales - One of the best experts on this subject based on the ideXlab platform.
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pattern of sedimentary infilling of fossil mammal traps formed in Pseudokarst at cerro de los batallones madrid basin central spain
Sedimentology, 2013Co-Authors: J P Calvo, Manuel Pozo, Pablo G Silva, Jorge MoralesAbstract:Fossil mammal sites of late Miocene age (ca 9 Ma) occur in hourglass-shaped, non-interconnected cavities up to 15 m deep, hosted in mudstone (mostly sepiolite), chert and carbonate bedrock in Cerro de los Batallones. This paper provides a model for the sedimentary infilling of the cavities, which functioned as traps for vertebrate faunas and contain one of the richest and best preserved Neogene mammal assemblages of the Iberian Peninsula. Generation of the mammal-bearing cavities started with the solution of underlying evaporites, which resulted in fissures that were subsequently enlarged by subsurface piping, a process rarely preserved in the ancient sedimentary record. The system of subterranean cavities evolved into a Pseudokarst landscape, resulting in doline-like shafts reaching the ancient land surface. The sedimentary infilling of the cavities comprises both clastic and carbonate lithofacies that were investigated by outcrop observation, standard and scanning electron microscope petrography, mineralogical analysis, and stable isotope geochemistry. Gravel and breccia talus deposits, clast and mud-supported gravel, pebbly sandstone and mudstone are common detrital infill deposits mostly derived by overflow erosion of bedrock. The deposits containing the mammal bones are marls, and occur both in subsurface cavities and doline-like depressions. In the underground cavities, marlstone was mainly of clastic origin and accumulated in ponds scattered over the floor of the cavity. In contrast, marlstone deposits in the surface dolines formed mostly as a result of biochemical carbonate deposition in small shallow lakes subjected to fluctuation of the water level. The δ18O and δ13C carbonate values indicate different origins for the two kinds of marls. During the final phases of pipe infill the doline marlstone sealed the mammal sites, usually off-lapping the adjacent bedrock.
L Vlcek - One of the best experts on this subject based on the ideXlab platform.
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reply to the comment on sandstone caves on venezuelan tepuis return to Pseudokarst
Geomorphology, 2013Co-Authors: Roman Aubrecht, Tomas Lanczos, M Gregor, Jan Schlogl, B Smida, P Liscak, Ch Brewercarias, L VlcekAbstract:Abstract In Aubrecht et al. (2011) we brought new data showing that the arenitic caves in the Venezuelan tepuis did not necessarily originate through quartz cement dissolution (‘arenization’) but the main portion of the caves originated because of poor lithification prior to erosion. An additional important process is lateritization which is responsible for at least 30% of the caves' volume. Sauro et al. (2012) in their comment support the ‘arenization’ theory (quartz cement dissolution) and provide several arguments against some points of our research. Their main objections and arguments relate to the following topics: 1) the validity of the arenization theory, 2) the origin and importance of the ‘finger-flow’ pillars, 3) the importance of the Schmidt hammer measurements and, 4) metamorphism of the Mataui Formation. In our reply we present further documentation that: 1) The quartz cement dissolution theory of cave evolution was far less documented petrographically than the new theory presented by us. Although the presence of quartz dissolution is evident, there is no current evidence that it is widespread or that it plays a trigger role. Many of the presented examples of corrosion on quartz grains could have been caused by local alkalization. In addition, the hydrogeochemical data presented in the comment to support the ‘arenization’ theory do not in fact contradict our speleogenetic interpretations. 2) ‘Finger-flow’ pillars are speleogenetic indicators and not speleogenetic factors. Their absence in some caves provides no evidence against our theory. 3) Schmidt hammer measurements only objectivize the data on contrasting hardness in the Mataui Formation beds. They do not say anything about the origin of this difference. 4) The arguments of Sauro et al. (2012) involve the metamorphic overprint of the Mataui Formation shown by the presence of pyrophyllite and quartz mobilizations. Because quartz mobilization also occurs in hypergenic conditions, it may be neglected as a metamorphic indicator. Pyrophyllite is mentioned as a metamorphic indicator in the literature (anchizone to epizone) but it does not explain why there is still a vast quantity of kaolinite that did not undergo this reaction in the soft arenitic beds. There is an evidence that pyrophyllite may originate at lower temperatures. Some phases of the alumino-silicate mineral phases existing at atmospheric pressure and 25 °C temperature show that H 4 SiO 4 concentration is a critical factor in kaolinite/pyrophyllite transition. An increase in this concentration can theoretically cause transformation of kaolinite to pyrophyllite without increased temperature or pressure.
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sandstone caves on venezuelan tepuis return to Pseudokarst
Geomorphology, 2011Co-Authors: Roman Aubrecht, Tomas Lanczos, M Gregor, Jan Schlogl, B Smida, P Liscak, Ch Brewercarias, L VlcekAbstract:Abstract Venezuelan table mountains (tepuis) host the largest arenite caves in the world. The most frequently used explanation of their origin so far was the “arenization” theory, involving dissolution of quartz cement around the sand grains and subsequent removing of the released grains by water. New research in the two largest arenite cave systems – Churi-Tepui System in Chimanta Massif and Ojos de Cristal System in Roraima Tepui showed that quartz dissolution plays only a minor role in their speleogenesis. Arenites forming the tepuis are not only quartzites but they display a wide range of lithification and breakdown, including also loose sands and sandstones. Speleogenetic processes are mostly concentrated on the beds of unlithified sands which escaped from diagenesis by being sealed by the surrounding perfectly lithified quartzites. Only the so-called “finger-flow” pillars testify to confined diagenetic fluids which flowed in narrow channels, leaving the surrounding arenite uncemented. Another factor which influenced the cave-forming processes by about 30% was lateritization. It affects beds formed of arkosic sandstones and greywackes which show strong dissolution of micas, feldspars and clay minerals, turning then to laterite (“Barro Rojo”). The main prerequisite to rank caves among karst phenomena is dissolution. As the dissolution of silicate minerals other than quartz appears to play not only a volumetrically important role but even a trigger role, these arenitic caves may be ranked as karst.
J P Calvo - One of the best experts on this subject based on the ideXlab platform.
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pattern of sedimentary infilling of fossil mammal traps formed in Pseudokarst at cerro de los batallones madrid basin central spain
Sedimentology, 2013Co-Authors: J P Calvo, Manuel Pozo, Pablo G Silva, Jorge MoralesAbstract:Fossil mammal sites of late Miocene age (ca 9 Ma) occur in hourglass-shaped, non-interconnected cavities up to 15 m deep, hosted in mudstone (mostly sepiolite), chert and carbonate bedrock in Cerro de los Batallones. This paper provides a model for the sedimentary infilling of the cavities, which functioned as traps for vertebrate faunas and contain one of the richest and best preserved Neogene mammal assemblages of the Iberian Peninsula. Generation of the mammal-bearing cavities started with the solution of underlying evaporites, which resulted in fissures that were subsequently enlarged by subsurface piping, a process rarely preserved in the ancient sedimentary record. The system of subterranean cavities evolved into a Pseudokarst landscape, resulting in doline-like shafts reaching the ancient land surface. The sedimentary infilling of the cavities comprises both clastic and carbonate lithofacies that were investigated by outcrop observation, standard and scanning electron microscope petrography, mineralogical analysis, and stable isotope geochemistry. Gravel and breccia talus deposits, clast and mud-supported gravel, pebbly sandstone and mudstone are common detrital infill deposits mostly derived by overflow erosion of bedrock. The deposits containing the mammal bones are marls, and occur both in subsurface cavities and doline-like depressions. In the underground cavities, marlstone was mainly of clastic origin and accumulated in ponds scattered over the floor of the cavity. In contrast, marlstone deposits in the surface dolines formed mostly as a result of biochemical carbonate deposition in small shallow lakes subjected to fluctuation of the water level. The δ18O and δ13C carbonate values indicate different origins for the two kinds of marls. During the final phases of pipe infill the doline marlstone sealed the mammal sites, usually off-lapping the adjacent bedrock.
Manuel Pozo - One of the best experts on this subject based on the ideXlab platform.
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pattern of sedimentary infilling of fossil mammal traps formed in Pseudokarst at cerro de los batallones madrid basin central spain
Sedimentology, 2013Co-Authors: J P Calvo, Manuel Pozo, Pablo G Silva, Jorge MoralesAbstract:Fossil mammal sites of late Miocene age (ca 9 Ma) occur in hourglass-shaped, non-interconnected cavities up to 15 m deep, hosted in mudstone (mostly sepiolite), chert and carbonate bedrock in Cerro de los Batallones. This paper provides a model for the sedimentary infilling of the cavities, which functioned as traps for vertebrate faunas and contain one of the richest and best preserved Neogene mammal assemblages of the Iberian Peninsula. Generation of the mammal-bearing cavities started with the solution of underlying evaporites, which resulted in fissures that were subsequently enlarged by subsurface piping, a process rarely preserved in the ancient sedimentary record. The system of subterranean cavities evolved into a Pseudokarst landscape, resulting in doline-like shafts reaching the ancient land surface. The sedimentary infilling of the cavities comprises both clastic and carbonate lithofacies that were investigated by outcrop observation, standard and scanning electron microscope petrography, mineralogical analysis, and stable isotope geochemistry. Gravel and breccia talus deposits, clast and mud-supported gravel, pebbly sandstone and mudstone are common detrital infill deposits mostly derived by overflow erosion of bedrock. The deposits containing the mammal bones are marls, and occur both in subsurface cavities and doline-like depressions. In the underground cavities, marlstone was mainly of clastic origin and accumulated in ponds scattered over the floor of the cavity. In contrast, marlstone deposits in the surface dolines formed mostly as a result of biochemical carbonate deposition in small shallow lakes subjected to fluctuation of the water level. The δ18O and δ13C carbonate values indicate different origins for the two kinds of marls. During the final phases of pipe infill the doline marlstone sealed the mammal sites, usually off-lapping the adjacent bedrock.
