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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 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 detailLes invertébrés des carrières souterraines de craie de la Montagne Saint-Pierre (Province de Liège, Belgique). Note préliminaire
Dethier, Michel; Willems, Luc ULg

in Notes Fauniques de Gembloux (2005), 57

During the 1930’s, Leruth collected 145 species in the underground chalk quarries at the Montagne Saint-Pierre. None was troglobitic. To evaluate the biological interest of the sites and the faunal drift ... [more ▼]

During the 1930’s, Leruth collected 145 species in the underground chalk quarries at the Montagne Saint-Pierre. None was troglobitic. To evaluate the biological interest of the sites and the faunal drift 70 years after, we have undertaken in 2004 a new faunistic survey. [less ▲]

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See detailOpal-a Speleothems of Wei-Assipu-Tepui, Roraima Province, Brazil
Urbani, Franco; Compère, Philippe ULg; Willems, Luc ULg

in Boletín de la Sociedad Venezolana de Espeleología (2005), 39

Bol. Soc. Venezolana Espel. v.39 Caracas dic. 2005 ®download el artículo en el formato PDF Como citar este artículo Opal-a Speleothems of Wei-Assipu-Tepui, Roraima Province, Brazil Franco Urbani1 ... [more ▼]

Bol. Soc. Venezolana Espel. v.39 Caracas dic. 2005 ®download el artículo en el formato PDF Como citar este artículo Opal-a Speleothems of Wei-Assipu-Tepui, Roraima Province, Brazil Franco Urbani1, Phillipe Compère2 & Luc Willems2 1Universidad Central de Venezuela. Fac. Ingeniería. Escuela de Geología. Lab. de Geología y Geoquímica. Caracas 1053 y Sociedad Venezolana de Espeleología. Apartado 47028. Caracas 1041A. urbani@cantv.net 2Université de Liège, Laboratoire de Morphologie Ultrastructurale, Département des sciences et gestion de l'environnement, allée de la Chimie, 3, B-4000 Liège 1,Belgium. 3University of Liège. Laboratoire de Pétrologie Sédimentaire, Département de Géologie, B20, B-4000 Liege, Belgium.Lucwillems65@versateladsl.be ABSTRACT Coralloid-shaped speleothems samples were collected from a small cave in a mountain of the Roraima massif, Brazil. They were mineralogically identified as opal-A and show two concentric growth zones: A massive light colored inner one, and a darker outer zone with a spongy texture. On the surface the presence of some filaments probably of algae suggest biomineralisation. Chemically the outer zone shows impurities with high values of Cl and P. The leaching of bird nest guano may be the source of P. The two zones were probably formed in two different climatic conditions, the outer one in the current wet and vegetated period, and the inner zone during a former drier period. [less ▲]

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See detailChalk karsts – Saint-Pierre Mountain – Basse-Meuse (Belgium)
Willems, Luc ULg; Rodet, Joël; Masséi, Nicolas et al

Poster (2004, May)

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See detailCarste em Quartzito de Região de Diamantina : Gruta do Salitre e Parque Estadual do Rio Preto, Minas Gerais
Willems, Luc ULg; Rodet, J.; Pouclet, A. et al

Poster (2004)

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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 detailPhénomènes karstiques en roches silicatées non carbonatées. Cas des grès, des micaschistes, des gneiss et des granites en Afrique sahélienne et équatoriale
Willems, Luc ULg

Doctoral thesis (2000)

Cette recherche comprend six parties : 1. Un inventaire des karsts ou des phénomènes assimilés aux karsts en roches non carbonatées silicatées - grès, quartzites, granites, gneiss et schistes. Cet ... [more ▼]

Cette recherche comprend six parties : 1. Un inventaire des karsts ou des phénomènes assimilés aux karsts en roches non carbonatées silicatées - grès, quartzites, granites, gneiss et schistes. Cet inventaire s’appuie sur plusieurs centaines de références bibliographiques. Pour chacune des lithologies, une synthèse des différents processus génétiques proposés par les différents auteurs est réalisée. 2. Un état de la connaissance sur la solubilité de la silice, de l’aluminium et du fer. Cette partie intègre notamment les avancées bio géochimiques réalisées depuis les années 80. Cette partie de la thèse reprend différentes études montrant : • que la silice, l’aluminium et le fer peuvent se retrouver dans des domaines de solubilité identiques notamment en présence d’acides organiques ou inorganiques ; • que ces acides augmentent de façon considérable la solubilité des éléments ; • que ces acides peuvent être générés par des bactéries en milieu anaérobie ; • que ces bactéries peuvent se trouver en grand nombre à grande profondeur dans les roches et dans des milieux anaérobies (les complexes organométalliques solubles peuvent donc voyager sur de grandes distances et non être rapidement détruits comme c’est le cas en surface). L’hypothèse d’une dissolution généralisée de roches silicatées non carbonatées peut donc être envisagée au regard des modèles classiquement proposés pour expliquer la karstification des massifs. 3 & 4. Une étude de différentes formes de surface ou souterraines trouvées dans les formations gréseuses et les métagabbros du Niger occidental ainsi que dans les granites, les gneiss et les micaschistes du Cameroun méridional. Une analyse morphologique détaillée des grottes et autres conduits liée aux données hydrogéologiques, tectoniques et pétrographiques des différents sites est à la base des interprétations génétiques. 5. Une étude de concrétions et enduits siliceux trouvés dans des cavités du Niger et du Cameroun. L’analyse par microscope électronique à balayage, par diffractogramme des rayons X et par mapping compositionnel élémentaire, a été menée afin de préciser les conditions physico-chimiques dans lesquelles certaines cavités ont été générées. Ainsi, pour une des cavités ouvertes dans les granites, les analyses ont montré le rôle probable des bactéries dans la mise en place des karsts. 8. Une synthèse sur la problématique des karsts en roches non carbonatées et sur les conditions de leur développement. Les conclusions principales de la thèse sont : • l’importance de l’érosion chimique dans la genèse des différentes formes souterraines étudiées avec des phénomènes d’érosion mécanique tardifs (tout comme ce qui se passe dans les calcaires) ; • la mise en place d’une karstification initiale à grande profondeur, indépendamment des conditions de surface, peut être en relation avec la faune bactérienne découverte ces dernières décennies à grande profondeur. Si, à l’heure actuelle, de nombreux chercheurs envisagent la karstification à partir d’une altération progressant de la surface vers la profondeur, cette vision des choses peut être en partie erronée. La vitesse d’altération des processus de surface dans des lithologies carbonatées doit entraîner une modification également rapide des formes issues de la profondeur (élargissement des entrées supérieures,...) et masquer l’histoire ancienne de ces morphologies. • la nécessité d’envisager certaines lithologies et leur potentialité en eau sous l’angle de massifs karstifiés. Les nombreux karsts trouvés au Niger occidental et oriental influencent incontestablement l’évolution géomorphologique des paysages tant dans le développement des réseaux hydrographiques que dans la dissection des plateaux. Les lithologies gréseuses sont fort abondantes dans tout le Sahel et ont une structuration similaire à celle de la région de Niamey. On peut donc envisager qu’une grande partie du Sahel est karstifiée. [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 detailLes karsts siliceux d'Afrique
Vicat, Jean-Paul; Willems, Luc ULg

in Géosciences au Cameroun @ collection Géocam (1998), 1

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See detailSpéléothèmes des karsts siliceux du Niger et du Cameroun
Willems, Luc ULg; Compère, Philippe ULg; Sponholz, Barbara et al

in Géosciences au Cameroun & collection Géocam (1998), 1

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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 detailStudy of siliceous karst genesis in Eastern Niger. Microscopy and analysis of speleothems
Willems, Luc ULg; Compère, Philippe ULg; Sponholz, Barbara

in Zeitschrift für Geomorphologie (1998), 42(2), 129-142

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