References of "Pouclet, André"
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See detailProblème des karsts en roches silicatées... lacunes d’observation et paradigme du karst
Willems, Luc ULg; Ek, Camille ULg; Rodet, Joël et al

Conference (2009, December 05)

Depuis le développement de la karstologie, la grande majorité des cavités prospectées l'ont été dans les roches carbonatées ou apparentées, réputées fort solubles. Partant de ce principe, les autres ... [more ▼]

Depuis le développement de la karstologie, la grande majorité des cavités prospectées l'ont été dans les roches carbonatées ou apparentées, réputées fort solubles. Partant de ce principe, les autres lithologies n'ont été à ce jour que partiellement investiguées puisque réputées peu ou pas solubles. Pourtant, depuis plusieurs siècles, des grottes et autres formes apparentées sont mentionnées notamment dans des grès, des granites ou les quartzites. Très rapidement, elles ont été catégorisées comme pseudokarst en se basant sur deux principes, le premier, la convergence de forme, le second, les processus physico-chimiques qui présideraient à leur formation seraient différents de ceux rencontrés dans les calcaires. L'évolution des recherches et des techniques de ces vingt dernières années ouvre de nouvelles perspectives sur une réalité karstique commune qui transcenderait les lithologies tant carbonatées que non carbonatées. Peu à peu, elle oblige les chercheurs à se repositionner quant à la notion de karst. [less ▲]

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See detailAbordagem geomorfológica da bacia do rio Peruaçu e implicações geoarqueológicas
Rodet, Joël; Rodet, Jacqueline; Willems, Luc ULg et al

in Arquivos do Museu de História Natural (2009), 19(1), 75-103

The Rio Peruaçu Basin is the object of a geomorphological redifinition starting from a multi-field approach carried out for over ten years. Based on the works of the Minas Gerais archaeologists and ... [more ▼]

The Rio Peruaçu Basin is the object of a geomorphological redifinition starting from a multi-field approach carried out for over ten years. Based on the works of the Minas Gerais archaeologists and speleologists, this study defines four geomorphological compartments from the springs to the juction with the Sao Francisco river,namely: the zone of the upper valley, the zone of the geological transition, the zone of the karstic canyon and the zone of the alluvial plain. The main stages of the geomorphological evolution of the system were released and make it possible to define the space distribution of the mineral resources potentially usable by the prehistoric groups, and also to work out a typology of the raw material deposits. This approach contributes to the definition of the perception of the space by the first human settlements. [less ▲]

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See detailKarsts in sandstones and quartzites of Minas Gerais, Brazil
Willems, Luc ULg; Rodet, Joël; Pouclet, André et al

in Cadernos do Laboratorio Xeolóxico de Laxe (2008), 33

The state of Minas Gerais (Brazil) is characterized by significant karst regions, which develop <br /><br />in both sandstone and quartzite terrains and display complex suites of underground and ... [more ▼]

The state of Minas Gerais (Brazil) is characterized by significant karst regions, which develop <br /><br />in both sandstone and quartzite terrains and display complex suites of underground and surfaceforms. In the Espinhaço Ridge, Central Minas Gerais, several caves of up to a few hundred metres long, occur in the surroundings of the town of Diamantina. Some of these caves, such as Salitre actually consist of swallow-holes. Other horizontal caves are characterized by corrosion forms generated in the phreatic zone. In some places, such as in the Rio Preto area, these phreatic forms are overprinted by ceiling tubes, suggesting a polyphase karst evolution, prior to the draining in the cave. Remains of paths, with circular cross section up to one metre in diameter, can be found through residual tower-like surface landforms widely present in the landscapes. Their dissection is due to a generalised karstification in the area, resulting in closed canyons, megakarrens and kamenitzas. In Southern Minas Gerais, close to the Mantiqueira Ridge, the caves of the Ibitipoca state park can reach more than 2 km in length. These caves are associated with a very large hanging geological syncline. Several of these caves contain active streams, which flow for hundreds of metres before disappearing in sand-choked passages. Keyhole cross sections characterize steeply descending passages in these caves, indicatinga chan ge from slow phreatic flow towards a faster vadose flow responsible for the vertical incision of the passage. Such change is probably related to base level lowering and/or to turn in the direction of the water flow. Several generations of wall-pockets, from a few centimetres to over a metre long, occur into the caves. These features are good indicators of the initial phase of speleogenesis, generating the initial conduits by their coalescence. This mechanism is also responsible for cut-off meanders. In the area, the main river flows along the syncline axis and cuts through a rock barrier, generating a tunnel-like passage. This cave drains, through resurgences in its walls, part of the water that flows in other caves located in the flank of the syncline. [less ▲]

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See detailKarsts des craies et calcarénites de la Montagne Saint-Pierre (Basse Meuse liégeoise)
Willems, Luc ULg; Rodet, Joël; Ek, Camille ULg et al

in Bulletin des Chercheurs de la Wallonie (2007), XLVI

The “Montagne Saint-Pierre” (Sint Pietersberg) is a separate part of the Hesbaye plateau, isolated between the lower valleys of the Geer and the Meuse rivers. It is exploited by a big open-air quarry and ... [more ▼]

The “Montagne Saint-Pierre” (Sint Pietersberg) is a separate part of the Hesbaye plateau, isolated between the lower valleys of the Geer and the Meuse rivers. It is exploited by a big open-air quarry and by numerous underground quarries developing galleries on hundreds of kilometers long. Excavated in Cretaceous chalk and calcarenite, these artificial networks allow an exceptional 3-D observation of karsts inside a very porous and permeable rock, less favourable to a concentrated solution. The most numerous of them are “organ pipes” or “earth pipes”. They are vertical tubular solution pipes that may exceed 60 m in depth. Sponge networks and subhorizontal caves occur, without any visible connection with fracturation. Finally, downwards to at least 20 m below the alluvial plain of the Meuse river, pluridecametric nodes of weathered chalk are found. By their size and rounded morphology, the nodes resemble to the natural caves occurring in the calcarenite and intersected by the underground quarries. All the studied karsts allow us to propose a scenario for the genesis of a polyphase karst system. Independently of surface conditions, caves are generated deeply in the phreatic zone (endokarsts). During the downcutting of theMeuse valley, and related to the fluvial terraces, solution pipes (input karsts) are generated. Due to the valley incision and to the lowering of the aquifer,theses solution pipes progress downward and cut the endokarsts. A concentrated water circulation takes place. In the dewatered upper part of the system, caves cut by solution pipes are rapidly filled by superficial deposits. The high porosity of the calcarenite makes it comparable to a sponge. The rock absorbs quickly the out-flows coming from the surface and causes a rapid deposit of the fine particles transported inside horizontal passages. The sealing of these conduits allows their conservation inside a very crumbly rock. [less ▲]

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See detailPolyphase karst system in Cretaceous chalk and calcarenite of the Belgian-Dutch border
Willems, Luc ULg; Rodet, Joël; Fournier, Matthieu et al

in Zeitschrift für Geomorphologie (2007), 51(3), 361-376

Along the Belgian-Dutch border, underground and surface quarries dug in Cretaceous calcarenite and chalk intersect many karst features as well as deep large nodes of weathered rock. Their observation ... [more ▼]

Along the Belgian-Dutch border, underground and surface quarries dug in Cretaceous calcarenite and chalk intersect many karst features as well as deep large nodes of weathered rock. Their observation allows the reconstruction of the genesis of an original karst system resulting from the merging of initially independent endokarsts and exokarsts. Deep weathering has developed within the Cretaceous formations, creating nodes of weathered chalk and closed cavities. These phenomena are expanded over time and can form interconnected voids. Near the surface, solution pipes are generated under the coarsest deposits of a fluvial terrace capping the Cretaceous formations. These pipes develop vertically and may be related to the progressive lowering of the water table in connection with the incision of the Meuse valley. Some of these phenomena cut up the older endokarsts and organize complex systems of out-flow within the chalk. [less ▲]

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See detailKarsts des craies et calcarénites de la Montagne Saint-Pierre (Basse Meuse liégeoise)
Willems, Luc; Rodet, Joël; Ek, Camille ULg et al

in Bulletin de la Société Royale Belge d'Etudes Géologiques et Archéologiques (2007), XLVI

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See detailPolyphased karst systems in sandstones and quartzites of Minas Gerais, Brazil
Willems, Luc ULg; Rodet, Joël; Pouclet, André et al

in Proceeding 14th UIS Congress, Athens-Kalamos, 23-28 august 2005, Abstract Book : 71. (2005)

The state of Minas Gerais (Brazil) exhibits several major karst areas located in sandstone and quartzite terrains, that display a complex suite of underground and surface karstic forms. In the Espinhaço ... [more ▼]

The state of Minas Gerais (Brazil) exhibits several major karst areas located in sandstone and quartzite terrains, that display a complex suite of underground and surface karstic forms. In the Espinhaço Ridge, central Minas Gerais, several caves, up to a few hundred metres long, occur in the surroundings of the town of Diamantina. Some of these caves, such as Salitre, represent swallow-holes and show dome pits. Other horizontal caves are characterized by corrosion forms generated into the phreatic zone. In some places, such as in the Rio Preto area, these phreatic forms have been overprinted by ceiling tubes, suggesting a polyphase karst evolution, prior to the draining of the cave. Relicts of passages, with circular cross section up to a metre in diametre, can be found amidst the residual tower-like surface landforms, which constitute a typical scenery in the landscape. Their dissection is due to a generalised karstification in the area, resulting in closed canyons, megakarrens and kamenitzas. In southern Minas Gerais, close to the Mantiqueira Ridge, the caves of the state park of Ibitipoca can extent 2 km in length. These caves are associated with a very large hanging geological syncline. Several of these caves contain active streams, that flow for hundreds of metres before disappearing in sand-choked passages. Keyhole cross sections characterize steeply descending passages in these caves, indicating a change from slow phreatic flow towards a faster vadose flow responsible for the vertical incision of the passage. Such change is probably related to base level lowering and/or to turn in the direction of the water flow. Several generations of wall-pockets, from a few centimetres to over a metre long, occur into the caves. These features are good indicators of the initial phase of speleogenesis, generating the initial conduits by their coalescence. This mechanism is also responsible for cut-off meanders. The main river in the area, which flows along the syncline axis, cuts through a rock barrier, generating a tunnel-like passage. This cave drains, through resurgences in its walls, part of the water that flows in other caves located in the flank of the syncline. The non-carbonate karst features observed in the state of Minas Gerais demonstrate the complex organisation of polyphase karst systems due to the linkage of underground and surface forms not previously connected. As in carbonate areas, these systems may play an important hydrological role. [less ▲]

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See detailKarsts en roches non carbonatées - l'exemple des quartzites et des itabérites de Minas Gerais, Brésil
Willems, Luc ULg; Rodet, Joël; Auler, Augusto et al

in Rodet, Joël (Ed.) Actes des Journées Européennes de l'AFK 2003 (2003)

The state of Minas Gérais, Brazil, contains numerous karsts booth inside carbonated and non carbonated rocks. Différent caves are found in quartzite and Itaberite formations (Banded Iron formation). The ... [more ▼]

The state of Minas Gérais, Brazil, contains numerous karsts booth inside carbonated and non carbonated rocks. Différent caves are found in quartzite and Itaberite formations (Banded Iron formation). The term karst is used in the meaning of "any features of the classical karst morphology (caves, sink-holes, lapies...) where dissolution plays the main genetically action and this in any kind of rocks". In some areas, lapiaz and kamenitza affect wide landscapes (area of Diamantina, Natural Parc of Rio Preto). Several caves are found and some of these are several kilomeetres long (grutta do Bromelias, Natural Parc of Ibitipoca). Inside caves, we found numerous forms like dissolution alveoli, spelothems, .... Many times, the cave sides and solutional forms are covered by crust which solidify a very crumbly quartzite. Différent morphologies show an primary solutional stage of the rocks before a physical erosional stage which destroy the earliest forms (piping, river érosion, collapsing). [less ▲]

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See detailKarsts en roches cristallines silicatées non carbonatées. Cas dans des gneiss : la grotte de Mfoula, Sud Cameroun
Willems, Luc ULg; Pouclet, André; Vicat, Jean-Paul

in Actes des Journées Européennes de l'AFK 2003 (2003)

Since the Seventies, a séries of phenomena developed in non carbonated silicated rocks question the traditional vision of karst. The term of karst is used in the meaning of "any feature of the classical ... [more ▼]

Since the Seventies, a séries of phenomena developed in non carbonated silicated rocks question the traditional vision of karst. The term of karst is used in the meaning of "any feature of the classical karst morphology (caves, sink-holes, lapiaz...) where dissolution plays the main genetic action and this in any kind of rocks". The cave of Guéssédoundou illustrâtes a karst in métagabbros. It opens at the top of a small hill, in a dépression twenty meters long and three to four meters deep. The walls of this dépression are subvertical and the bottom is partially occupied by angular pluridecimetric blocks. The cave is opened on several meters in the southern side of the dépression and is prolonged in the form of too narrow conduits to be explore. The bedrock is a metagabbro with fine grains, slightly weathered, crossed by decimetric quartzose veins. Gabbroïc texture is preserved, as well as part of magmatic plagioclases. The remainder is transformed into a mixture of white feldspar and clinozoisite. Pyroxene are pseudomorphosed in actinote and chlorite. The site dépression was created along a N 10° shear zone where rocks suffered important fracturation and fluid transfers, as shown by its silification and ferruginisation.. Moreover, a East-West schistosity, former to shearing, structures the gabbro. The présence of angular blocks of variable size and the absence of human activity trace on the site show that the dépression was formed naturally by collapse of the roof of a more vast cavity whose current cave would be the visible residual prolongation. The absence of flow traces and mechanical abrasion means that this cavity is due only to chemical érosion . At the cave entry and on the subvertical walls of the dépression were formed by alveoli a few centimètres to a few décimètres in diameter. Thèse alveoli of wall are known in other lithologies, in particular in limestones. The absence of salts within the rock draws aside a formation by sait weathering. The smooth aspect and non fractured walls of the cells cannot resuit from a corrosion to a fracturing node. The closed aspect of the dépression and the absence of flow trace eliminate the assumptions from formation by water swirls or eolisation. The genesis of the cave must be earlier to the installation of a weathering cover since the rock is little deteriorated and the alveoli are not developed on a quite particular level which would correspond to a précise pedogenic horizon. Only a generalized dissolution of the métagabbros, in relation to a slow solution circulation, being carried out with the favour of the fracturing plans of the shearing zone makes it possible to explain the formation of the alveoli. The inversion of relief results from a weaker érosion of the rocks made more résistant to this place by the quartz seam mainstay and by the ferruginisation along the shearing zone. In the other hand, the crushed rocks, become porous, drained the infiltrations of meteoric water, facilitating the dissolution processes. The study of the site of Guéssédoundou shows that karstic phenomena can also exist in silico-aluminous formations of crystalline rocks [less ▲]

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See detailKarsts en roches cristallines silicatées non carbonatées.. Cas dans les métagabbros : grotte de Guessédoundou, Niger occidental
Willems, Luc ULg; Pouclet, André; Vicat, Jean-Paul

in Rodet, Joël (Ed.) Actes des Journées Européennes de l'AFK 2003 (2003)

Since the Seventies, a séries of phenomena developed in non carbonated silicated rocks question the traditional vision of karst. The term of karst is used in the meaning of "any feature of the classical ... [more ▼]

Since the Seventies, a séries of phenomena developed in non carbonated silicated rocks question the traditional vision of karst. The term of karst is used in the meaning of "any feature of the classical karst morphology (caves, sink-holes, lapiaz...) where dissolution plays the main genetic action and this in any kind of rocks". The cave of Guéssédoundou illustrâtes a karst in métagabbros. It opens at the top of a small hill, in a dépression twenty meters long and three to four meters deep. The walls of this dépression are subvertical and the bottom is partially occupied by angular pluridecimetric blocks. The cave is opened on several meters in the southern side of the dépression and is prolonged in the form of too narrow conduits to be explore. The bedrock is a metagabbro with fine grains, slightly weathered, crossed by decimetric quartzose veins. Gabbroïc texture is preserved, as well as part of magmatic plagioclases. The remainder is transformed into a mixture of white feldspar and clinozoisite. Pyroxene are pseudomorphosed in actinote and chlorite. The site dépression was created along a N 10° shear zone where rocks suffered important fracturation and fluid transfers, as shown by its silification and ferruginisation.. Moreover, a East-West schistosity, former to shearing, structures the gabbro. The présence of angular blocks of variable size and the absence of human activity trace on the site show that the dépression was formed naturally by collapse of the roof of a more vast cavity whose current cave would be the visible residual prolongation. The absence of flow traces and mechanical abrasion means that this cavity is due only to chemical érosion . At the cave entry and on the subvertical walls of the dépression were formed by alveoli a few centimètres to a few décimètres in diameter. Thèse alveoli of wall are known in other lithologies, in particular in limestones. The absence of salts within the rock draws aside a formation by sait weathering. The smooth aspect and non fractured walls of the cells cannot resuit from a corrosion to a fracturing node. The closed aspect of the dépression and the absence of flow trace eliminate the assumptions from formation by water swirls or eolisation. The genesis of the cave must be earlier to the installation of a weathering cover since the rock is little deteriorated and the alveoli are not developed on a quite particular level which would correspond to a précise pedogenic horizon. Only a generalized dissolution of the métagabbros, in relation to a slow solution circulation, being carried out with the favour of the fracturing plans of the shearing zone makes it possible to explain the formation of the alveoli. The inversion of relief results from a weaker érosion of the rocks made more résistant to this place by the quartz seam mainstay and by the ferruginisation along the shearing zone. In the other hand, the crushed rocks, become porous, drained the infiltrations of meteoric water, facilitating the dissolution processes. The study of the site of Guéssédoundou shows that karstic phenomena can also exist in silico-aluminous formations of crystalline rocks. [less ▲]

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See detailKarst in granitic rocks, South Cameroon: cave genesis and silica and taranakite speleothems
Willems, Luc ULg; Compère, Philippe ULg; Hatert, Frédéric ULg et al

in Terra Nova (2002), 14(5), 355-362

A cave in granitic rocks was studied in Mezesse, South Cameroon. Coralloid speleothems, draperies and dissolution traces on the cave walls attest to its truly karstic nature. The speleothems consist of ... [more ▼]

A cave in granitic rocks was studied in Mezesse, South Cameroon. Coralloid speleothems, draperies and dissolution traces on the cave walls attest to its truly karstic nature. The speleothems consist of microlayers of opal and taranakite (K,NH4)Al-3(PO4)(3)(OH).9H(2)O. They indicate a significant mobilization of silica, Al and K from granite during the formation of the cave. Identification of silicified bacteria in the speleothems layers suggests a possible role of these micro-organisms in silica deposition. The presence of taranakite and of silicified organic remains within the speleothems lead to a better understanding of the genesis of the cave. [less ▲]

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See detailExistence de karsts en roches cristallines silicatées non carbonatées en Afrique sahélienne et équatoriale, implications hydrogéologiques
Willems, Luc ULg; Pouclet, André; Vicat, Jean-Paul

in Bulletin de la Société Géologique de France (2002), 173(4), 337-345

Various cavities studied in western Niger and South Cameroon show the existence of important karstic phenomena into metagabbros and gneisses. These large-sized eaves resulted from generalized dissolution ... [more ▼]

Various cavities studied in western Niger and South Cameroon show the existence of important karstic phenomena into metagabbros and gneisses. These large-sized eaves resulted from generalized dissolution of silicate formations in spite of their low solubility. Karstification is produced by deep hydrous transfer along lithological discontinuities and fracture net works. The existence of such caves has major implications in geomorphology, under either Sahelian and Equatorial climate, and in hydrogeology and water supply, particularly in the Sahel area. [less ▲]

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See detailPhénomènes karstiques fossiles et actuels au sein des formations métamorphiques silico-alumineuses de la nappe pan-africaine de Yaoundé (Sud-Cameroun)
Vicat, Jean-Paul; Mvondoc, Henri; Willems, Luc ULg et al

in Comptes Rendus de l'Académie des Sciences. Série II, Mécanique, Physique, Chimie, Sciences de l'Univers, Sciences de la Terre (2002), 334

Fossil and present-time karstic phenomena in silico-aluminous metamorphic formations of the Pan-African nappe of Yaoundé (South-Cameroon). Numerous karstic features have been recognised in the non ... [more ▼]

Fossil and present-time karstic phenomena in silico-aluminous metamorphic formations of the Pan-African nappe of Yaoundé (South-Cameroon). Numerous karstic features have been recognised in the non-carbonaceous micaschists and gneisses of the Yaoundé Pan-African nappe, south of Cameroon. It is shown that their formation was controlled by the structural features of the rocks. The wells and the pipes in the bedrock outcrops point out a current karstification process, resulting from the plagioclase dissolution by the acid rain waters. Hill wall alveoli and caves, of pre-Miocene age, are exhumed features that were done by dissolution in the aquiferous underground. [less ▲]

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See detailKarst dans les micaschistes d'Akok Bekoé - Sud Cameroun
Willems, Luc ULg; Vicat, Jean-Paul; Pouclet, André

in Bulletin de la Société Géographique de Liège (1999), 37(2), 5-18

50 km south of Yaoundé, karst phenomena are developed in micaschists. A network of fractures dependent in thrusting area guided formation of caves, conduits and other morphologies comparable with those ... [more ▼]

50 km south of Yaoundé, karst phenomena are developed in micaschists. A network of fractures dependent in thrusting area guided formation of caves, conduits and other morphologies comparable with those found in the karst limestones. The presence of a spring and the proximity of the Nyong river suggest that a chemical erosion within an aquifer is at the origin of most of forms. The position of certain conduits and tafonis dismisses the assumption of a genesis within a weathering mantle. [less ▲]

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See detailPhénomènes pseudo-kartiques et karstiques dans la couverture latéritique et le substratum plutono-métamorphique du Sud du Cameroun
Vicat, Jean-Paul; Willems, Luc ULg; Pouclet, André

in Géosciences au Cameroun - collection Geocam (1998), 1

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See detailKarst non carbonaté au Cameroun méridional. L'exemple des grottes de Mfoula
Willems, Luc ULg; Pouclet, André; Vicat, Jean-Paul

in Würzburger Geographische Arbeiten (1997), 89

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See detailPhénomènes karstiques dans les roches plutoniques et métamorphiques du sud Cameroun
Vicat, Jean-Paul; Lips, Bernard; Pouclet, André et al

in Karstologia (1997), 29

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See detailPhénomènes karstiques en milieux non carbonatés. Etudes de cavités et problématique de leur développement au Niger Occidental
Willems, Luc ULg; Pouclet, André; Lenoir, François et al

in Zeitschrift für Geomorphologie (1996)

The study of several caves in siliceous formations belonging to the Precambrian basement and its Cenozoic sedimentary cover brings to the fore the importante of an underground drainage network in relation ... [more ▼]

The study of several caves in siliceous formations belonging to the Precambrian basement and its Cenozoic sedimentary cover brings to the fore the importante of an underground drainage network in relation with crustal fracturation. This network guides the waler transfer from the land surface to the depth and generates géomorphologic phenomena similar to those in calcareous areas. The study of caves in a siliceous environmemts shows the importance of solution phenomena in their formation and also in that of West Niger landscapes. Therfore, a general model of topographic evolution îs proposed. [less ▲]

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