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Featured articles from Cave & Karst Science Journals
Characterization of minothems at Libiola (NW Italy): morphological, mineralogical, and geochemical study, Carbone Cristina; Dinelli Enrico; De Waele Jo
Chemistry and Karst, White, William B.
The karst paradigm: changes, trends and perspectives, Klimchouk, Alexander
Long-term erosion rate measurements in gypsum caves of Sorbas (SE Spain) by the Micro-Erosion Meter method, Sanna, Laura; De Waele, Jo; Calaforra, José Maria; Forti, Paolo
The use of damaged speleothems and in situ fault displacement monitoring to characterise active tectonic structures: an example from Zapadni Cave, Czech Republic , Briestensky, Milos; Stemberk, Josef; Rowberry, Matt D.;
Featured articles from other Geoscience Journals
Karst environment, Culver D.C.
Mushroom Speleothems: Stromatolites That Formed in the Absence of Phototrophs, Bontognali, Tomaso R.R.; D’Angeli Ilenia M.; Tisato, Nicola; Vasconcelos, Crisogono; Bernasconi, Stefano M.; Gonzales, Esteban R. G.; De Waele, Jo
Calculating flux to predict future cave radon concentrations, Rowberry, Matt; Marti, Xavi; Frontera, Carlos; Van De Wiel, Marco; Briestensky, Milos
Microbial mediation of complex subterranean mineral structures, Tirato, Nicola; Torriano, Stefano F.F;, Monteux, Sylvain; Sauro, Francesco; De Waele, Jo; Lavagna, Maria Luisa; D’Angeli, Ilenia Maria; Chailloux, Daniel; Renda, Michel; Eglinton, Timothy I.; Bontognali, Tomaso Renzo Rezio
Evidence of a plate-wide tectonic pressure pulse provided by extensometric monitoring in the Balkan Mountains (Bulgaria), Briestensky, Milos; Rowberry, Matt; Stemberk, Josef; Stefanov, Petar; Vozar, Jozef; Sebela, Stanka; Petro, Lubomir; Bella, Pavel; Gaal, Ludovit; Ormukov, Cholponbek;
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Your search for venezuela (Keyword) returned 27 results for the whole karstbase:
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Minor weathering forms on the Roraima Quartzite in the Carrao River Basin of Southeastern Venezuela have the appearance of the karren that form on limestone surfaces in karst terrains. Climatological and chemical evidence indicates that these forms were generated by a solutional mechanism and that this area thus exhibits a minor karst topography on quartzite.
The invertebrate faunas of four caves in northern Venezuela were studied. Three were dry and one was a wet cave; but guano provided the base of the food chain in all four caves. The faunas in each were strikingly different. Of 24 non-accidental species of arthropods, all were judged to be troglophiles. All were scavengers except for 5 predators, one ectoparasite, and one parasitoid.
QUARTZITE PLATEAUX OF THE RORAIMA FORMATION (GRAN SABANA - VENEZUELA) - The high sandstone-quartzite plateaux of the Roraima period situated in the Gran Sabana region of south-east Venezuela have some specific macro- and micro-geomorphological characteristics. On one hand, this Precambrian sedimentary cover includes some spectacular relief consisting of high structural plateaux affected by major anticlines, synclines, and monoclines, partly dismantled by erosion. On the other hand, and on a smaller scale, pseudo-karst have developed on the surface (karren) and at depth (caves, shafts). Several hypotheses are put forward in an attempt to explain the genesis of this pseudo-karst.
MORPHOGENESIS OF CAVES AND LANDFORMS IN THE PRECAMBRIAN QUARTZITE OF RORAIMA GROUP (VENEZUELA) - This paper describes caves and landforms developed in the Precambrian quartzite of the Roraima Group (1600-1800 My) in the Gran Sabana of Venezuela (cf. Pouyllau and Seurin, in Karstologia, 1985, n° 5). High plateaus (Tepuys) are remnants of old erosional surfaces of Secondary-Tertiary age. The weathering of quartzite is produced in fissures by means of the dissolution of the intergranular siliceous cement. Depressions, fields of blocks and small towers, deep fissures characterise the edges of tepuys. Underground passages could be formed by dissolution, arenisation and piping from the fractures which dissect the tepuys. The part of hydrothermalism in speleogenesis is not proved.
Ironstone is any chemical sedimentary rock with > 15% Fe. An iron formation is a stratigraphic unit which is composed largely of ironstone. The solutes which have precipitated to become ironstone have dissolved from the Earth's surface, from the upper crust, e.g. the basaltic layer of oceanic crust, or from deeper within the Earth. Genetic modellers generally choose between surficial weathering, e.g. soil formation, and hydrothermal fluids which have convected through the upper kilometre of oceanic crust. Most genetic modellers attribute cherty laminated iron formations to hydrothermal convection and noncherty oolitic iron formations to surficial weathering. However, both types of iron formations are attributable to the exhalation of fluids from a source region too deep for convection of seawater. Evidence for a deep source of ferriferous fluids comes from a comparison of ancient ironstone with modern ferriferous sediment in coastal Venezuela. A deep-source origin for ironstone has wide-ranging implications for the origins of other chemical sedimentary ores, e.g. phosphorite, manganostone, bedded magnesite, sedimentary uranium ore, various karst-filling ores, and even petroleum. Preliminary study of a modern oolitic iron deposit described herein suggests that the source of iron and silica to iron formations may have been even deeper than envisioned within most hydrothermal convection models
During the expedition Tepuy 93'. six caves were explored in the precambrian quartzites of Roraima Group, in the Auyan-tepui massif. One of this caves reaches the depth of 370 m and a development of almost 3 km; its name is "Sima Auyan-tepui Noroeste" and it is currently the deepest cave in the world discovered in siliceous rocks The geological and morphological study of this cave has underlined again the importance of deep solutional weathering, along the network of fractures for the formation of caves in siliceous rocks. The different formation stages of the big superficial shafts, called "simas" were observed in some vertical collapse caves explored during the expedition, while galleries with phreatic forms were observed in the deep network of caves. All these deep forms involve karst processes of solution at least in the initial stage.
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