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Enviroscan Ukrainian Institute of Speleology and Karstology


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Community news

Speleology in Kazakhstan

Shakalov on 04 Jul, 2018
Hello everyone!   I pleased to invite you to the official site of Central Asian Karstic-Speleological commission ("Kaspeko")   There, we regularly publish reports about our expeditions, articles and reports on speleotopics, lecture course for instructors, photos etc. ...

New publications on hypogene speleogenesis

Klimchouk on 26 Mar, 2012
Dear Colleagues, This is to draw your attention to several recent publications added to KarstBase, relevant to hypogenic karst/speleogenesis: Corrosion of limestone tablets in sulfidic ground-water: measurements and speleogenetic implications Galdenzi,

The deepest terrestrial animal

Klimchouk on 23 Feb, 2012
A recent publication of Spanish researchers describes the biology of Krubera Cave, including the deepest terrestrial animal ever found: Jordana, Rafael; Baquero, Enrique; Reboleira, Sofía and Sendra, Alberto. ...

Caves - landscapes without light

akop on 05 Feb, 2012
Exhibition dedicated to caves is taking place in the Vienna Natural History Museum   The exhibition at the Natural History Museum presents the surprising variety of caves and cave formations such as stalactites and various crystals. ...

Did you know?

That prismatic compass is a compass with a prism attached so that the compass card can be read at the same time as the compass is directed into the line of sight to a distance point [25].?

Checkout all 2699 terms in the KarstBase Glossary of Karst and Cave Terms


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Featured articles from Cave & Karst Science Journals
Chemistry and Karst, White, William B.
See all featured articles
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 hollow (Keyword) returned 39 results for the whole karstbase:
Showing 16 to 30 of 39
Environmental problems caused by gypsum karst and salt karst in Great Britain., 2001,
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Cooper A. H.
In Great Britain, gypsum karst is widespread in the Late Permian (Zechstein) gypsum of north-eastern England. Here and offshore, a well-developed palaeokarst with large breccia pipes was formed by dissolution of the underlying Permian gypsum. Farther south, around Ripon, the same rocks are still being dissolved, forming an actively evolving phreatic gypsum-maze cave system. This is indicated by the presence of numerous active subsidence hollows and sulphate-rich springs. In the English Midlands, gypsum karst is locally developed in the Triassic deposits south of Derby and Nottingham. Where gypsum is present, its fast rate of dissolution and the collapse of overlying strata lead to difficult civil-engineering and construction conditions; these can be further aggravated by water abstraction. Salt (halite) occurs within British Permian and Triassic strata, and has a long history of exploitation. The main salt fields are in central England and the coastal areas of northwest and northeast England. In central England, saline springs indicate that rapid, active dissolution occurs that can cause subsidence problems. In the past, subsidence was aggravated by shallow mining and the uncontrolled extraction of vast amounts of brine. This has now almost stopped, but there is a legacy of unstable buried salt karst, formed by both natural and induced dissolution. The buried salt karst occurs at depths ranging from about 40 m to 130 m; above these depths, the overlying strata are foundered and brecciated. In the salt areas, construction and development are hampered by both abandoned mines and by natural or induced brine runs, with their associated unstable ground.

Middle Pleistocene Karst Evolution in the State of Qatar, Arabian Gulf, 2002,
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Sadiq, A. M. , Nasir, S. J.
Karst is widespread on the peninsula of Qatar in the Arabian Gulf, including depressions, sinkholes, caves, and solution hollows. More than 9700 large and small depressions, and several exposed sinkholes and caves are known. Field and air-photo studies indicate that the depressions, sinkholes, and caves of Qatar are genetically related, sinkholes representing an early phase in the development of depressions. Karst is concentrated mainly within the limestone, dolomite, gypsum, and anhydrite horizons of the Eocene Rus and Dammam Formations. Most karst features in Qatar show NE-SW and NW-SE orientations, similar to the joint and fracture systems. This observation indicates that rock type and the presence of joints and fractures played a major role in the development of karst in Qatar. Cylindrical, bottle-shaped, compound, and bowl-shaped morphotype karst pits were identified. These forms represent a genetic sequence in which the bowl-shaped pits evolved through a series of cylindrical and bottle-shaped compound intermediate stages. Most karst of central Qatar was formed due to extensive subsurface dissolution of carbonate and sulfate deposits under Middle Pleistocene wet climatic conditions and consequent subsidence. Joint-flow drainage may account for differential dissolution resulting in the formation of a pitted karst terrain in the northern part of Qatar.

Mthodes et lments de cartographie dun palokarst. Lexemple de la Carrire du Clypot (Hainaut, Belgique), 2002,
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Quinif Yves, Quinif Gilles
Palaeokarsts have been often considered like geological objects different from the present karst systems, which can be explored partially by speleological ways. But it is obvious that their genesis have not been different from the genesis of the neogene karst systems, in same environmental conditions. The study of palaeokarsts has a great importance for the comparison with present systems. Moreover, they conserve continental sediments which generally disappear, but with possibility of dating by marine trangressive series which cover the palaeokarsts or by absolute dating like K-Ar or Ar-Ar on glauconite or ferriferous illite. We present here an interesting example of palaeokarstic features in a quarry where the works permit to map those features. This map constitutes the basis for future studies; it has shown different types of morphological features and deposits, their geometrical relations and their genetic links. We have (i) ghosts-rocks and pseudo-endokarsts, which result from the alteration in situ of the host-rock with formation of residual alterite. Those features organise like linear channels along tectonic fractures. Some channels can joint together in great pockets. At the summit of the limestone formation, (ii) palaeo-clints develop under the transgressive cover where we find pebbles and sands. Finally, (iii) endokarstic galleries can come from an autonomous hollowing (classical karst) or from old ghost-rocks, which become partially empty by a new hydrological activity.

Existence of karsts into silicated non-carbonated crystalline rocks in Sahelian and Equatorial Africa, hydrogeological implications, 2002,
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Willems Luc, Pouclet Andre, Vicat Jean Paul,
Various cavities studied in western Niger and South Cameroon show the existence of important karstic phenomena into metagabbros and gneisses. These large-sized caves 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. Introduction. - Since a few decades, several karst-like morphologies are described in non-carbonated rocks (sandstones, quartzites, schistes, gneisses...) [Wray, 1997 ; Vicat and Willems, 1998 ; Willems, 2000]. The cave of Guessedoundou in West Niger seems to be due to a large dissolution of metagabbros. The cave of Mfoula, South Cameroon, attests for the same process in gneisses. This forms proof that big holes may exist deeper in the substratum even of non-carbonated silicate rocks. Their size and number could mainly influence the landscape and the hydrogeology, especially in the Sahelian areas. Guessedoundou, a cave into metagabbros in West Niger. - The site of Guessedoundou is located 70 km south-west of Niamey (fig. 1). The cave is opened at the top of a small hill, inside in NNE-SSW elongated pit (fig. 2 ; pl. I A). The hole, 3 to 4 m deep and 20 m large, has vertical walls and contains numerous sub-metric angular blocks. A cave, a few meters deep, comes out the south wall. Bedrocks consist of metagabbros of the Makalondi greenstone belt, a belt of the Palaeoproterozoic Birimian Formations of the West Africa craton [Pouclet et al., 1990]. The rock has a common granular texture with plagioclases, partly converted in albite and clinozoisite, and pyroxenes pseudomorphosed in actinote and chlorite. It is rather fairly altered. Chemical composition is mafic and poorly alkaline (tabl. I). A weak E-W schistosity generated with the epizonal thermometamorphism. The site depression was created along a N010o shear zone where rocks suffered important fracturation and fluid transfers, as shown by its silification and ferruginisation. The absence of human activity traces and the disposition of the angular blocks attest that the pit is natural and was due to the collapse of the roof of a vast cavity whose current cave is only the residual prolongation. To the vertical walls of the depression and at the cave entry, pluridecimetric hemispheric hollows are observed (pl. I B). Smooth morphology and position of these hollows sheltered within the depression dismiss the assumptions of formation by mechanical erosion. In return, these features are typical shape of dissolution processes observed into limestone karstic caves. That kind of process must be invoked to explain the opening of the Guessedoundou cave, in the total lack of desagregation materials. Dissolution of metagabbro occurred during hydrous transfer, which was probably guided by numerous fractures of the shear zone. Additional observations have been done in the Sirba Valley, where similar metabasite rocks constitute the substratum, with sudden sinking of doline-like depressions and evidence of deep cavities by core logging [Willems et al., 1993, 1996]. It is concluded that karstic phenomena may exist even in silica-aluminous rocks of crystalline terrains, such as the greenstones of a Precambrian craton. Mfoula a cave into gneisses in South Cameroon. - The cave of Mfoula is located 80 km north-east of Yaounde (fig. 3). It is the second largest cave of Cameroon, more than 5,000 m3, with a large opening in the lower flank of a deep valley (pl. I C). The cavity is about 60 m long, 30 m large and 5 to 12 m high (fig. 4; pl. I D). It is hollowed in orthogneisses belonging to the Pan-African Yaounde nappe. Rocks exhibit subhorizontal foliation in two superposed lithological facies: the lower part is made of amphibole- and garnet-bearing layered gneisses, and the upper part, of more massive granulitic gneisses. Average composition is silico-aluminous and moderately alkaline (tabl. I). The cave is made of different chambers separated by sub-cylindrical pillars. The ceiling of the main chamber, 6 m in diameter, is dome-shaped with a smooth surface (D, fig. 4). The walls have also a smooth aspect decorated with many hemispherical hollows. The floor is flat according to the rock foliation. They are very few rock debris and detrital fragments and no traces of mechanical erosion and transport. The general inner morphology is amazingly similar to that of a limestone cave. The only way to generate such a cavity is to dissolve the rock by water transfer. To test the effect of the dissolution process, we analysed a clayey residual sampled in an horizontal fracture of the floor (tabl. I). Alteration begins by plagioclases in producing clay minerals and in disagregating the rock. However, there is no more clay and sand material. That means all the silicate minerals must have been eliminated. Dissolution of silicates is a known process in sandstone and quartzite caves. It may work as well in gneisses. To fasten the chemical action, we may consider an additional microbial chemolitotrophe activity. The activity of bacteria colonies is known in various rocks and depths, mainly in the aquifer [Sinclair and Ghiorse, 1989 ; Stevens and McKinley, 1995]. The formation of the Mfoula cave is summarized as follow (fig. 5). Meteoric water is drained down along sub-vertical fractures and then along horizontal discontinuities of the foliation, particularly in case of lithological variations. Chemical and biological dissolution is working. Lateral transfers linked to the aquifer oscillations caused widening of the caves. Dissolved products are transported by the vertical drains. Regressive erosion of the valley, linked to the epeirogenic upwelling due to the volcano-tectonic activity of the Cameroon Line, makes the cavities come into sight at the valley flanks. Discussion and conclusion. - The two examples of the Guessedoundou and Mfoula caves evidence the reality of the karsts in non-carbonated silicated rocks. The karst term is used to design >> any features of the classical karst morphology (caves, dolines, lapies...) where dissolution plays the main genetical action >> [Willems, 2000]. Our observations indicate that (i) the karst genesis may have occurred into any kind of rocks, and (ii) the cave formation is not directly dependent of the present climate. These facts have major consequences to hydrogeological investigations, especially for water supply in Sahelian and sub-desertic countries. Some measurements of water transfer speed across either sedimentary pelitic strata of the Continental terminal or igneous rocks of the substratum in West Niger [Esteves and Lenoir, 1996 ; Ousmane et al., 1984] proved that supplying of aquifers in these silico-aluminous rocks may be as fast as in a karstic limestone. That means the West Niger substratum is highly invaded by a karstic net and may hidden a lot of discontinuous aquifers. The existence of this karst system can be easily shown by morphological observations, the same that are done in karstic limestone regions (abnormally suspended dry valleys, collapses, dolines...). Clearly, this must be the guide for any search of water, even in desertic areas where limestones are absent

Environmental problems caused by gypsum karst and salt karst in Great Britain, 2002,
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Cooper Ah,
In Great Britain, gypsum karst is widespread in the Late Permian (Zechstein) gypsum of north-eastern England. Here and offshore, a well-developed palaeokarst with large breccia pipes was formed by dissolution of the underlying Permian gypsum. Farther south, around Ripon, the same rocks are still being dissolved, forming an actively evolving phreatic gypsum-maze cave system. This is indicated by the presence of numerous active subsidence hollows and sulphate-rich springs. In the English Midlands, gypsum karst is locally developed in the Triassic deposits south of Derby and Nottingham. Where gypsum is present, its fast rate of dissolution and the collapse of overlying strata lead to difficult civil-engineering and construction conditions; these can be further aggravated by water abstraction. Salt (halite) occurs within British Permian and Triassic strata, and has a long history of exploitation. The main salt fields are in central England and the coastal areas of northwest and northeast England. In central England, saline springs indicate that rapid, active dissolution occurs that can cause subsidence problems. In the past, subsidence was aggravated by shallow mining and the uncontrolled extraction of vast amounts of brine. This has now almost stopped, but there is a legacy of unstable buried salt karst, formed by both natural and induced dissolution. The buried salt karst occurs at depths ranging from about 40 m to 130 in; above these depths, the overlying strata are foundered and brecciated. In the salt areas, construction and development are hampered by both abandoned mines and by natural or induced brine runs, with their associated unstable ground

Elments de rflexion sur la morphogense des plateaux de Vaucluse (France) : les apports du karst superficiel, 2003,
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Depambour Christophe, Guendon Jeanlouis
ABOUT THE GENESIS OF VAUCLUSE PLATEAUX: THE LESSONS FROM KARSTIC LANDFORMS - The study of the principal forms of the surface karst gives a first diagram of evolution of the plates of Vaucluse. Paleo-surfaces now perched and/or deformed are witnesses old major phases of flattening, in regional matter, undoubtedly of ante-Miocene age. The whole of intermediate surfaces (850 m) seems to cut the Miocene deposits (Burdigalian) of the ditch of Aurel-Sault. It thus reveals a major phase of post-miocene flattening. These surfaces of karstic flattening were to be in relation to the vastpo1jes of the sectors of Saint-Christol and the ditch of Sault. Their genesis, dependent on dysfunction of the endokarstic drainage, could be related to the Pliocene transgression. Canyon of Nesque, structuring elements major landscape, present, on both sides Rocher du Cire, two distinct parts, having own morphologies. The downstream part, wide open, would have grown hollow by headwater erosion from a karstic steephead perhaps since the end of Miocene. The narrow upstream part would have incised itself, after capture of the polje of Sault, undoubtedly at the time of the cold phases of the Quaternary one.

Sulfate Cavity Filling in the Lower Werra Anhydrite (Zechstein, Permian), Zdrada Area, Northern Poland: Evidence for Early Diagenetic Evaporite Paleokarst Formed Under Sedimentary Cover, 2003,
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Hryniv Sofiya P. , Peryt Tadeusz Marek,
Paleokarst developed in sulfate deposits is common, and it is usually formed along the contact with the overlying permeable rocks or it is due to near-surface dissolution of bedded evaporites. In the Lower Werra Anhydrite (Zechstein) of northern Poland the paleokarst cavities are usually filled by bluish semitransparent anhydrite and more rarely by celestite, polyhalite, halite, and carbonate. In small cavities (a few centimeters across), a rim of rod-like anhydrite crystals arranged in narrow bundles occurs, and the inner part of the cavity is filled with a mosaic aggregate of short prismatic crystals of anhydrite and celestite as well as coarse irregular anhydrite. Celestite crystals and fan-shaped aggregates as well as spherulites of anhydrite are rare. In bigger cavities (some ten centimeters across), multiple zones of fibrous anhydrite are arranged in different directions in the middle part of the cavity fill. The innermost parts of large karst cavities remain hollow in some cases, with the cavity walls encrusted by coarse, well-developed crystals of anhydrite and celestite. The karst cavities in the Lower Werra Anhydrite developed in the subsurface by dissolution of CaSO4 strata in halite-rich intervals due to gypsum dehydration water. During gypsum dehydration, dissolution of that halite would have increased the sodium chloride content of the solution and thus the solubility of calcium sulfate. Dissolved calcium sulfate was removed from a leaching zone by diffusion and/or downward flow in interstitial space, and the minerals in karst cavities precipitated from the same solutions as those solutions became oversaturated because of decreases in NaCl concentration over time. This study suggests that karst in sulfate deposits can develop in the subsurface and without uplift and/or near-surface conditions

The role of epikarst in the morphogenesis of the karstic forms, especially hollow forms in Greece, 2004,
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Papadopoulouvrynioti, Kyriaki

The role of epikarst in the morphogenesis of the subcutaneous karren and the karstic hollow forms is different. Cavernous karren and subcutaneous kluftkarren, are covered with terra rossa and show the activity of water. They are developed in the epikarstic zone due to the diffused corrosion on the joints through a capillary aquifer, situated in the high vadose zone. The rounded tops and the cavities of those subcutaneous karren are formed due to the continuous and uniform corrosion, acting by soil moisture in the high part of the epikarstic zone. Karstic hollowforms are developed in carbonate layers only, and also on the contact of karstified and non-karstified but easily erodable rocks. In this case, a lot of material is produced for the formation of soils that fill these landforms. Uvalas and poljes usually develop in sites of old valleys or tectonic depressions through the process of widening of the joints in the subcutaneous zone and the lowering of the latter zone. Simultaneously there occurs the gradual impermeability of the zone and the reinforcement of the lateral corrosion. These forms are mostly formed above the piezometric level. The poljes - periodical lakes are created due to the development when they temporary reach epikarstic water table.


The karst periodical lakes of Upper Pivka, Slovenia, 2004,
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Ravbar Nataš, A, Š, Ebela Stanka

At dry season the Pivka river appears between Prestranek and Rakitnik while near Zagorje the underground karst waters are about ten meters below the valley bottom of periodical Pivka river. High waters pour over the surface and fill stream valley of the Pivka river, which runs continually from Zagorje to the ponor of Postojnska jama. When the level of the underground water increases, also shallow karst hollows - uvalas are flooded and changed into more than 15 periodical karst lakes.


Empirical study of conduit radial cross-section determination and representation methods on cavernous limestone porosity characterization, 2006,
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Sasowsky I. D. , Bishop M. R.
Radial cross sections are constructed during cave mapping in order to illustrate karst groundwater conduit (cave passage) morphology. These sections can also be employed in studies of porosity distribution and paleohydrology. Cave surveyors usually estimate left, right, up, and down (LRUD) distances from a survey station to the conduit wall, and these four values are used to construct the radial cross section, and occasionally integrated along the length of the passage to determine cave volume. This study evaluates the potential errors caused by LRUD estimation, as well as the effects of differing geometric approximations of passage shape. Passage dimensions at 18 stations of diverse size and morphology in Scott Hollow Cave, West Virginia were first estimated for LRUD and then precisely surveyed using a laser rangefinder taking 16 radial measurements. Results show that, depending upon the purpose of a survey, a reasonable approximation of passage shape might be made with fewer (four or eight) measurements. In cases where only four lengths are determined, approximation of the passage as an ellipse or rectangle provides a more accurate morphology and area than if portrayed as a quadrilateral. In the former case, average area errors were on the order of 10%, as opposed to -45% in the latter. Surveyor estimates of LRUD give an average overestimate of 27%. Length errors compound, however, when areas are calculated. This results in an average cross-section area error (as quadrilateral) of 57% when using estimates instead of measurements. This may be problematic for such analyses as calculation of fluid storage volumes or paleodischarges.

A small cave in a basalt dyke, Mt.Fuans, Victoria, Australia, 2006,
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Grimes Ken G.
A small but unusual cave has formed within a large dyke that intrudes a scoria cone at the summit of Mount Fyans, western Victoria. Draining of a still-liquid area, after most of the dyke had solidified, left an open cavity. Features within the cave mimic those of conventional lava caves, and suggest that the lava levels oscillated within the cave. Some smaller fingers of lava that intruded the scoria also have hollow, drained, cores. Includes: 7 figures, 6 refs

Continental France and Belgium during the early Cretaceous: paleoweatherings and paleolandforms, 2006,
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Thiry Medard, Quesnel Florence, Yans Johan, Wyns Robert, Vergari Anne, Theveniaut Herve, Simoncoincon Regine, Ricordel Caroline, Moreau Marie Gabrielle, Giot Denis, Dupuis Christian, Bruxelles Laurent, Barbarand
During the early Cretaceous, successive tectonic phases and several sea level falls resulted in the emersion of the main part of western Europe and the development of thick 'lateritic' weathering. This long period of continental evolution ended with the Upper Cretaceous transgressions. During this period, the exposed lands displayed a mosaic of diverse morphologies and weathered landscapes. Bauxites are the most spectacular paleoweathering features, known for long in southern France. Recently, new residual outcrops have been identified, trapped in the karstic depressions of the Grands Causses. Other bauxitic formations, containing gibbsite, have also been recognised, occurring with the Clay-with-Jurassic-cherts in the southeastern border of the Paris Basin. These bauxitic formations overlay Jurassic limestone and are buried beneath Upper Cretaceous marine deposits. The recognition of bauxites up north into the southern Paris Basin significantly widens the extension of the Lower Cretaceous bauxitic paleolandscapes. On the Hercynian basements thick kaolinitic weathering mantles occur. They have been classically ascribed to the Tertiary. The first datings of these in situ paleosoils, by means of paleomagnetism and/or radiogenic isotopes, record especially early Cretaceous ages. This is the case for the 'Siderolithic' formations on the edges of the French Massif Central, but also for the kaolinitic profiles in the Belgian Ardennes. In the Flanders, the Brabant basement is deeply kaolinised beneath the Upper Cretaceous cover. These paleosoils show polygenetic evolutions. The relief of these basement paleolandscapes may have been significant. There where probably high scarps (often of tectonic origin) reaching 200 m in elevation or beyond, as well as wide surfaces with inselbergs, as in the present day landscapes of tropical Africa and South America. On the Jurassic limestone platforms occur diverse kaolinitic and ferruginous weathering products. Around the Paris Basin they show various facies, ranging from kaolinitic saprolites to ferricretes. Due to the lack of sedimentary cover, the age of these ferruginous and kaolinitic weathering products has been debated for long, most often allocated to the Siderolithic sensu lato (Eocene-Oligocene). Recent datings by paleomagnetism have enabled to date them (Borne de Fer in eastern Paris Basin) back also to the early Cretaceous (130 {} 10 Ma). These wide limestone plateaus show karstified paleolandforms, such as vast closed and flat depressions broken by conical buttes, but also deep sinkholes in the higher areas of the plateaus and piedmonts. The depth of the karst hollows may be indicative of the range of relative paleoelevations. Dissolution holes display seldom contemporaneous karst fillings, thus implying that the karstland had not a thick weathering cover or that this cover had been stripped off before or by the late Cretaceous transgression. Nevertheless, some areas, especially above chert-bearing Jurassic limestone or marl, show weathering products trapped in the karst features or as a thick weathering mantle. In the Paris Basin, the Wealden gutter looked like a wide floodplain in which fluvio-deltaic sands and clays were deposited and on which paleosoils developed during times of non-deposition. The edges of the gutter were shaped as piedmonts linked up with the upstream basement areas. The rivers flowing down to the plain deposited lobes of coarse fluvial sands and conglomerates. The intensity of the weathering, the thickness of the profiles and their maturation are directly dependent on the duration of the emersion and the topographic location relative to the gutter. Near the axis of the gutter, where emersion was of limited duration, the paleoweathering features are restricted to rubefaction and argillization of the Lower Cretaceous marine formations. On the other hand, on the borders of the basin and on the Hercynian basement, where emersion was of longer duration, the weathering profiles are thicker and more intensively developed. The inventory of the Lower Cretaceous paleoweathering features shows the complexity of the continental history of this period. Moreover, the preserved weathering products are only a part of this long lasting period, all the aspects relative to erosion phases are still more difficult to prove and to quantify. In this domain, apatite fission tracks thermochronology (AFTT) can be helpful to estimate the order of magnitude of denudation. Residual testimonies and subsequent transgressions may enable to estimate relative elevations, but in return, we presently have no reliable tool to estimate absolute paleoelevations. In the work presented here, the inventory enabled to draw a continental paleogeographic map showing the nature of the weathering mantles and the paleolandscape features, just as paleoenvironments and paleobathymetry presently appear on marine paleogeographic maps. For the future, the challenge is to make progress in dating the paleoweathering profiles and especially in the resolution of these datings, in order to correlate precisely the continental records with the different events which trigger them (eustatism, climate, regional and global geodynamics). The final goal will be to build up a stratigraphic scale of the 'continental geodynamic and climatic events' in parallel with 'sequential stratigraphy' in the marine realm

Mineralogy of stalactites formed by subaerial weathering of natrocarbonatite hornitos at Oldoinyo Lengai, Tanzania, 2006,
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Mitchell R. H. ,
Stalactites formed by the chemical weathering of natrocarbonatite lava decorate the roofs of hollow inactive hornitos at Oldoinyo Lengai, Tanzania. The stalactites are composed principally of trona with lesser and very variable amounts of nahcolite, (NaHCO3), thermonatrite (Na2CO3.H2O), aphthitalite [(K,Na)3Na(SO4)2], kogarkoite [Na3(SO4)F], schairerite [Na21(SO4)7F6Cl], halite and sylvite. Stalactites are considered to form by the evaporation of Ca-free highly alkaline brines seeping from the altered lavas which form the roofs of the hornitos. The principal subaerial weathering products of natrocarbonatite, i.e. pirsonnite, gaylussite, shortite and calcite are not found in the stalactites and are retained in the altered lavas of the homito roof. Fluorine required for the formation of kogarkoite and schairerite is derived from the decomposition of fluorite at high pH (>10). Sulphur is derived from the decomposition of gregoryite

A small cave in a basalt dyke, Mt. Fyans, Victoria, Australia, 2006,
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Grimes, Ken G.

A small but unusual cave has formed within a large dyke that intrudes a scoria cone at the summit of Mount Fyans, western Victoria. Draining of a still-liquid area, after most of the dyke had solidified, left an open cavity. Features within the cave mimic those of conventional lava caves, and suggest that the lava levels oscillated within the cave. Some smaller fingers of lava that intruded the scoria also have hollow, drained, cores.


Etude de la karstification partir des donnes de forages : le cas des Monts de Tlemcen (Algrie), 2007,
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Bensaoula Fouzia
STUDY OF KARSTIFICATION FROM BOREHOLE DATA. THE CASE OF THE TLEMCEN MOUNTAINS. The Tlemcen mountains are the second largest carbonate massif in the north-west of Algeria, after the one of the Saida mountains. It is a large horst structure trending NE-SW, composed mainly of Upper Jurassic and Lower Cretaceous formations. The aquifers within it constitute the main water resource of the area. They are tapped by more than 160 boreholes, which constitute a great tool for studying the karst, especially its phreatic part. In the holes made by conventional drills, the total loss of drilling mud indicate karstification. The registration of the altitude of those losses permit to recognize the fissured and karstified levels. Three different aspects of karstifications were observed: an important fracturation, seen by complete loss of drilling mud during the drilling, important caves, observed by the free fall of drilling tools, and caves filled by karstic sediments, found thanks to diagraphies and the study of material brought up by the drilling. A statistical analysis of these data permitted to evidence the following elements: The dolomitic facies is much more dominant than the limestone facies; The frequency of incidences slowly decreases with depth; The fracturation is most important in the first 120 to 130 m below the top of the karstified formations, although it does not disappear at depth. In the breakdown zone of Tlemcen, situated in the northern piedmont part of the Tlemcen mountain, 26 boreholes permitted to draw an isopach map of the thickness of the karstic cover as well as the top of the karstified formation. This one shows two hollow zones below 100 m depth in the SW and NE parts. The top of the jurassic carbonates shows a very irregular surface which might correspond to a karstic paleorelief that was drowned by the Miocene transgression. Finally, the last map shows a karstified surface that can possibly be connected to a pseudo-paleo-piezometric surface.

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