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See detailKarl Marx, Œuvres, IV, Politique I
Durand, Pascal ULg

in Avancées (1995)

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See detailDe Karmelietenkerk in Gent, Dendrochronologische analyse van de dakconstructie boven tweede beuk
Hoffsummer, Patrick ULg; Houbrechts, David

in Stadsarcheologie (1995), 18(2),

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See detailKarst dans les évaporites : marqueur efficace des événements récents. L’exemple du Mont Sédom (Israel)
Hallot, Eric ULg

in Bulletin de la Société Géographique de Liège (1999), 37

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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 detailKarst et hydrologie
Petit, François ULg

Book (1999)

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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 detailKarst in het krijt van Limburg en ombeving
Lagrou, David; Dusart; Willems, Luc ULg

Poster (2008)

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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 detailLe karst
Ek, Camille ULg; Schyns, Jean-Christophe; Ozer, André ULg

in Direction générale de l'aménagement du territoire, du logement et du patrimoine (Ed.) Les risques majeurs en Région wallonne (2006)

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See detailKarstification souterraine en milieu saturé
Briffoz, Albert; Ek, Camille ULg; Gewelt, Michel

in Annales de la Société Géologique de Belgique (1985), 108

In order to explain the development of caves, considering the slowness of water circulations into the fissures of the limestone, only a chemical action i.e. corrosion can be called upon in most cases ... [more ▼]

In order to explain the development of caves, considering the slowness of water circulations into the fissures of the limestone, only a chemical action i.e. corrosion can be called upon in most cases. However, as saturation is rapidly reached, we consider, in order to extend the dissolution action of underground water, the possibility of dissolution in a saturated environment. [less ▲]

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See detailKarsts dans les gneiss - alvéoles géantes et micro-alvéoles dans la région de Milagres, état de Bahia, Brésil
Rodet, Joël; Willems, Luc ULg; Auler, Augusto

Conference (2009, December 05)

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See detailKarsts des calcarénites de la carrière du Romont (Eben – Belgique)
Willems, Luc ULg; Rodet, Joël

in Bulletin des Chercheurs de la Wallonie (2010), (hors-série n°3), 119-134

Th e quarry of Romont (Eben/Bassenge, near the Belgian-Dutch border) intersects many endo and exokarsts developing essentially in coarse chalk (calcarenites) of the Maastricht Formation (Upper Cretaceous ... [more ▼]

Th e quarry of Romont (Eben/Bassenge, near the Belgian-Dutch border) intersects many endo and exokarsts developing essentially in coarse chalk (calcarenites) of the Maastricht Formation (Upper Cretaceous). It is an appropriate place to study deep and superficial karstification in highly porous rocks. Th e porosity partially inhibits the further development of closed caves (endokarsts) aft er they dewatered. Caves are later fi lled-up by collapsing or when they are cut by solution pipes (exokarsts), and thus partially sealed and preserved in a soft lithology. Th ese solution pipes are generated under river gravels and can go tens of meters deep through calcarenites. [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 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 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 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 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 in sandstones and quatrzites of Minas Gerais, Brazil
Willems, Luc ULg; Rodet, J.; Pouclet, A. et al

Poster (2007)

Detailed reference viewed: 21 (1 ULg)