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 syngenetic karst is 1. karst developed contemporaneously with the lithification of the formation, as in eolian calcarenite where lithification and karstification of dune sands may proceed simultaneously [10]. 2. karst landforms that developed upon young, porous carbonate rocks, such as aeolianites, as they underwent lithification [9]. synonyms: (french.) karst syngenetique; (german.) syngenetischer karst; (greek.) synegeticon karst; (italian.) carsismo singenetico; (spanish.) karst singenetico; (turkish.) esturumlu karst; (yugoslavian.) singenetski krs (kras).?

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

What is Karstbase?



Browse Speleogenesis Issues:

KarstBase a bibliography database in karst and cave science.

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;
See all featured articles from other geoscience journals

Search in KarstBase

Your search for volcanism (Keyword) returned 25 results for the whole karstbase:
Showing 1 to 15 of 25
Prsentation des principales cavites du Causse de Laissac-Sverac (Aveyron), 1990, Rigal, C.
PRESENTATION OF THE MAIN CAVES OF THE CAUSSE OF LAISSAC-SEVERAC (AVEYRON, FRANCE) - The causse of Laissac-Severac is situated between "Grands Causses" and "Causse of Sauveterre" (Aveyron), in limestones and dolomites of Lias and Middle Jurassic. This speleological area presents two kinds of karst systems: losses and resurgences at the contact of the crystalline massif (Levezou) on the south part (Clos del Pous = 3km), and caves with numerous sumps under the Causse of Severac on the north part (plateau with large depressions (Tantayrou = 3.1km). These caves are post-Miocene because of the dated volcanism; they cut an eogene paleokarst, which is characterised by ferralitic paleosoils (ferruginous sandstone called "Siderolithique") from the alteration of crystalline massif.

Les karsts dans le Jurassique ardchois, 1992, Marchand, Th.
ARDECHE KARSTS IN THE JURASSIC LIMESTONES - The southern part of the department of the Ardeche consists of numerous karstic zones. In these places, there are several caves, some of which are well-known: The Sauvas-Cocalieres cave, St Marcels cave... But speleological and scientific studies have mainly focused on the Cretaceous karst. The Ardche gorges cut through this area. The Jurassic karsts although lesser known deserve to be studied in depth for their hydrogeological and geomorphologic interest. The surface landforms show evidence of the intense karstification, but it is deep down underground that these phenomena are most impressive. Four elements characterise the originality of these plateaus: the very strong amplitude of outflows in relation to the structure, the active grinding and the neotectonic affect most of the caves, the importance of the fillings which are sometimes allochtonous and the probable age of the caves. In most cases, investigating them means using subterranean diving techniques.

Origin of Eocene-covered karst bauxites of the Transdanubian Central Range (Hungary); evidence for early Eocene volcanism, 1992, Dunkl I,

Observations sur le karst de Bardas Blancas-Malarge (Andes de Mendoza, Argentine), 1995, Mikkan, R. A.
The karst of Bardas Blancas, situated south of Mendoza province, deve-lops in Jurassic and Cretaceous limes-tones. The continental and semi-arid climate (300 mm/year) is characterized by temperate summers and cold winters. The periglacial processes are actives. The relief presents a semi-karstic morphology: structural landforms ("Schichttreppenkarst" with cuestas) and afew dolines, swallow-holes and pavements. The Los Brujas cave, about 1 000 m long, shows a labyrinthic network (3 siaged levels) with phreatic passages. The impor-tant gypsum speleothems (crusts, flowers) in the lower level and the calcite-opale speleothems indicate an hydrothermal speleogenesis (dissolution by sulfuric acid and gypsum deposit). The actual and active tectogenesis of this region (uphft, hydrothermalism, volcanism) plays an important part in the geomorphological evolution.

Platform carbonates of the Upper Triassic Dachstein Limestone in Naszaly Hill have been karstified extensively over the past 200 million years. They provide an excellent example of polyphase karstic diagenesis that is probably typical of many subaerially exposed carbonate sequences. Seven karstic phases are recognized in the area, each of which include polyphase karstic events. The first karst phase was associated with the Lofer cycles. Meteoric waters caused dissolution; enlarged fractures and cavities were filled by marine and/or vadose silts and cement. The second karst phase was caused by local tectonic movements. Bedding-plane-controlled phreatic caves were formed, and filled by silts. The third karst phase lasted from the end of the Triassic to the Eocene. This was a regional, multiphase karstic event related to younger composite unconformities. Bauxitic fill is the most characteristic product of this phase. The karst terrain reached its mature or senile stage with very little porosity. Narrow veins and floating rafts of white calcite marks karst phase 4, which resulted from hydrothermal activity associated with Palaeogene magmatism. The early Rupelian phase of Alpine uplift caused large-scale rejuvenation of the former karst terrain (karst phase 5). Subsequently Naszaly Hill was buried as an area of juvenile karst with significant porosity. A second period of hydrothermal activity in the area (karst phase 6) was induced by Miocene volcanism, which resulted in wide, pale green calcite veins. Finally karst phase 7 was of tectonic origin. Following the most recent, Miocene uplift of the Naszaly Hill, the carbonates have again become the site of vadose karst development

Terrestrial hot-spring Co-rich Mn mineralization in the Pliocene-Quaternary Calatrava Region (central Spain), 1997, Crespo A, Lunar R,
Central Spain hosts a series of high-Co (up to 1.7% Co) Mn mineralizations displaying a variety of morphologies: spring aprons and feeders, pisolitic beds, wad beds and tufa-like replacements of plants and plant debris. The Mn mineralogy consist of cryptomelane, lithiophorite, birnessite and todorokite. The spring apron deposits formed in close proximity to Pliocene volcanic rocks (alkaline basaltic lava flows and pyroclastics) belonging to the so-called Calatrava Volcanic Field. The spring aprons are found along or near to normal faults bounding small basins and topographic highs. Mn tufa-like deposits are found near to the spring sources, while both pisolitic and wad beds are clearly distal facies occuring well within the Pliocene basins. The two latter are interbedded with clastic lacustrine and fluvial sediments. Collectively, these deposits contain a complex suite of Mn-(Co) mineralization ranging from proximal, hot-spring-type Mn facies, grading into more distant sedimentary, stratabound mineralization. Volcanism, basin formation and Mn deposition took place within a failed rift environment which triggered hydrothermal activity and Mn-(Co) deposition as proximal (near to the volcanic axes) and distal (of sedimentary affinities, within the basins) facies

The Dachstein paleosurface and the Augenstein Formation in the Northern Calcareous Alps - a mosaic stone in the geomorphological evolution of the Eastern Alps, 2001, Frisch W, Kuhlemann J, Dunkl I, Szekely B,
The central and eastern areas of the Northern Calcareous Alps (NCA) are characterized by remnants of the Dachstein paleosurface, which formed in Late Eocene (?) to Early Oligocene time and is preserved with limited modification on elevated karst plateaus. In Oligocene time, the Dachstein paleosurface subsided and was sealed by the Augenstein Formation, a terrestrial succession of conglomerates and sandstones, which are only preserved in small remnants on the plateaus, some in an autochthonous position. Thermochronological data suggest a maximum thickness of the Augenstein Formation of >1.3 km, possibly >2 km. The age of the Augenstein Formation is constrained by the overall geological situation as Early Oligocene to earliest Miocene. Fission track age data support an Early Oligocene age of the basal parts of the formation. The source area of the Augenstein Formation consisted predominantly of weakly metamorphic Paleozoic terrains (Greywacke Zone and equivalents) as well as the Late Carboniferous to Scythian siliciclastic base of the NCA to the south of the depositional area. To the west, the Augenstein Formation interfingered with the Tertiary deposits of the Inntal. Sedimentation of the Augenstein Formation was terminated in Early Miocene time in the course of the orogenic collapse of the Eastern Alps. The Augenstein sediments were eroded and redeposited in the foreland Molasse zone. From Pannonian times (similar to 10 Ma) on, the NCA and the denuded Dachstein surface experienced uplift in several pulses. The Dachstein paleosurface has been preserved in areas, in which thick limestone sequences allowed subsurface erosion by cave formation and thus prevented major surface erosion

Miocene phreatomagmatic volcanism at Tihany (Pannonian Basin, Hungary), 2001, Nemeth K. , Martin U. , Harangi S. ,
A late Miocene (7.56 Ma) maar volcanic complex (Tihany Maar Volcanic Complex - TMVC) is preserved in the Pannonian Basin and is part of the Bakony-Balaton Highland Volcanic Field. Base surge and fallout deposits were formed around maars by phreatomagmatic explosions, caused by interactions between water-saturated sediments and alkali basalt magma carrying peridotite Iherzolite xenoliths as well as pyroxene and olivine megacrysts. Subsequently, nested maars functioned as a sediment trap where deposition built up Gilbert-type delta sequences. At the onset of eruption, magma began to interact with a moderate amount of groundwater in the water-saturated sand. As eruption continued phreatomagmatic blasts excavated downward into limestones, providing access to abundant karst water and deeper to sandstones and schist both providing large amount of fracture-filling water, At the surface, this 'wet' eruption led to the emplacement of massive tuff breccias by fall, surge, mudflow and gravity flow deposition. The nature of the TMVC maar eruptions and their deposits appears to depend on the hydrological condition of the karst and/or fracture-filling aquifer, which varies seasonally with rainfall and spring runoff. The West and East Maar volcanoes of TMVC are interpreted to represent low water input from the karst and/or fracture-filling aquifer ('summer vent'), whereas the East Maar is interpreted to have formed when abundant karst and/or fracture-filling water was available ('spring vent'). (C) 2001 Elsevier Science B.V. All rights reserved

Les karsts de Nouvelle-Zlande, 2002, Salomon, Jeannol
Karsts of New-Zealand - New-Zealand presents numerous karsts developed as well in ancient rocks (Palaeozoic) as in recent ones (Oligocene). The stretching in latitude of the land, the high vegetal biodiversity and the strong rainfalls explain the importance of the karst development and the variety of the morphologies. Endokarsts are well developed, but many are still to explore. The polygonal karst of the King Country (North Island) in one hand, and the karsts of the Marble Mountains (South Island) in another one, are the most interesting. The possibilities of crossing of numerous datings (dendrochronology, speleothems, volcanism, etc.) and the location of these karsts in the south hemisphere provide to these last exceptional paleo-environmental recording systems.

Karst processes from the beginning to the end: How can they be dated?, 2003, Bosk, B

Determining the beginning and the end of the life of a karst system is a substantial problem. In contrast to most of living systems development of a karst system can be „frozen“ and then rejuvenated several times (polycyclic and polygenetic nature). The principal problems may include precise definition of the beginning of karstification (e.g. inception in speleogenesis) and the manner of preservation of the products of karstification. Karst evolution is particularly dependent upon the time available for process evolution and on the geographical and geological conditions of the exposure of the rock. The longer the time, the higher the hydraulic gradient
and the larger the amount of solvent water entering the karst system, the more evolved is the karst. In general, stratigraphic discontinuities, i.e. intervals of nondeposition (disconformities and unconformities), directly influence the intensity and extent of karstification. The higher the order of discontinuity under study, the greater will be the problems of dating processes and events. The order of unconformities influences the stratigraphy of the karst through the amount of time available for subaerial processes to operate. The end of karstification can also be viewed from various perspectives. The final end occurs at the moment when the host
rock together with its karst phenomena is completely eroded/denuded. In such cases, nothing remains to be dated. Karst forms of individual evolution stages (cycles) can also be destroyed by erosion, denudation and abrasion without the necessity of the destruction of the whole sequence of karst rocks. Temporary and/or final interruption of the karstification process can be caused by the fossilisation of karst due to loss of its hydrological function. Such fossilisation can be caused by metamorphism, mineralisation,
marine transgressions, burial by continental deposits or volcanic products, tectonic movements, climatic change etc. Known karst records for the 1st and 2nd orders of stratigraphic discontinuity cover only from 5 to 60 % of geological time. The shorter the time available for karstification, the greater is the likelihood that karst phenomena will be preserved in the stratigraphic record. While products of short-lived karstification on shallow carbonate platforms can be preserved by deposition during the immediately succeeding sea-level rise, products of more pronounced karstification can be destroyed by a number of different geomorphic
processes. The longer the duration of subaerial exposure, the more complex are those geomorphic agents.
Owing to the fact that unmetamorphosed or only slightly metamorphosed karst rocks containing karst and caves have occurred since Archean, we can apply a wide range of geochronologic methods. Most established dating methods can be utilised for direct and/or indirect dating of karst and paleokarst. The karst/paleokarst fills are very varied in composition, including a wide range of clastic and chemogenic sediments, products of surface and subsurface volcanism (lava, volcaniclastic materials, tephra), and deepseated
processes (hydrothermal activity, etc). Stages of evolution can also be based on dating correlated sediments that do not fill karst voids directly. The application of individual dating methods depends on their time ranges: the older the subject of study, the more limited is the choice of method. Karst and cave fills are relatively special kinds of geologic materials. The karst environment favours both the preservation of paleontological remains and their destruction. On one hand, karst is well known for its richness of paleontological sites, on the other hand most cave fills are complete sterile, which is true especially for the inner-cave facies. Another
problematic feature of karst records is the reactivation of processes, which can degrade a record by mixing karst fills of different ages.

Distribution, morphology, and origins of Martian pit crater chains, 2004, Wyrick D. , Ferrill D. A. , Morris A. P. , Colton S. L. , Sims D. W. ,
Pit craters are circular to elliptical depressions found in alignments (chains), which in many cases coalesce into linear troughs. They are common on the surface of Mars and similar to features observed on Earth and other terrestrial bodies. Pit craters lack an elevated rim, ejecta deposits, or lava flows that are associated with impact craters or calderas. It is generally agreed that the pits are formed by collapse into a subsurface cavity or explosive eruption. Hypotheses regarding the formation of pit crater chains require development of a substantial subsurface void to accommodate collapse of the overlying material. Suggested mechanisms of formation include: collapsed lava tubes, dike swarms, collapsed magma chamber, substrate dissolution ( analogous to terrestrial karst), fissuring beneath loose material, and dilational faulting. The research described here is intended to constrain current interpretations of pit crater chain formation by analyzing their distribution and morphology. The western hemisphere of Mars was systematically mapped using Mars Orbiter Camera (MOC) images to generate ArcView(TM) Geographic Information System (GIS) coverages. All visible pit crater chains were mapped, including their orientations and associations with other structures. We found that pit chains commonly occur in areas that show regional extension or local fissuring. There is a strong correlation between pit chains and fault-bounded grabens. Frequently, there are transitions along strike from ( 1) visible faulting to ( 2) faults and pits to ( 3) pits alone. We performed a detailed quantitative analysis of pit crater morphology using MOC narrow angle images, Thermal Emission Imaging System (THEMIS) visual images, and Mars Orbiter Laser Altimeter (MOLA) data. This allowed us to determine a pattern of pit chain evolution and calculate pit depth, slope, and volume. Volumes of approximately 150 pits from five areas were calculated to determine volume size distribution and regional trends. The information collected in the study was then compared with non-Martian examples of pit chains and physical analog models. We evaluated the various mechanisms for pit chain development based on the data collected and conclude that dilational normal faulting and sub-vertical fissuring provide the simplest and most comprehensive mechanisms to explain the regional associations, detailed geometry, and progression of pit chain development

The geochemistry of fluids from an active shallow submarine hydrothermal system: Milos island, Hellenic Volcanic Arc, 2005, Valsamijones E. , Baltatzis E. , Bailey E. H. , Boyce A. J. , Alexander J. L. , Magganas A. , Anderson L. , Waldron S. , Ragnarsdottir K. V. ,
Geothermal activity in the Aegean island of Milos (Greece), associated with island-arc volcanism, is abundant both on-and off-shore. Hydrothermal fluids venting from several sites, mainly shallow submarine (up to 10 m), but also just above seawater level in one locality, were sampled over four summer field seasons. Some of the discharging fluids are associated with the formation of hydrothermal edifices. Overall, the main characteristics of the hydrothermal fluids are low pH and variable chlorinity. The lowest recorded pH was 1.7, and chlorinity ranged from 0.1 to 2.5 times that of seawater. The highest fluid temperatures recorded on site were 115 degrees C. Two main types of fluids were identified: low-chlorinity fluids containing low concentrations of alkalis (potassium, lithium, sodium) and calcium, and high concentrations of silica and sulphate; and high-chlorinity fluids containing high concentrations of alkalis and calcium, and lower concentrations of silica and sulphate. The type locality of the high-chlorinity fluids is shallow submarine in Palaeochori, near the cast end of the south coast of the island, whereas the type locality of the low-chlorinity fluids is a cave to the west of Palaeochori. The two fluid types are therefore often referred to as 'submarine' and 'cave' fluids respectively. Both fluid types had low magnesium and high metal concentrations but were otherwise consistently different from each other. The low-chlorinity fluids had the highest cobalt, nickel, aluminium, iron and chromium (up to 1.6 mu M, 3.6 mu M, 1586 mu M, 936 mu M and 3.0 mu M, respectively) and the high-chlorinity fluids had the highest zinc, cadmium, manganese and lead (up to 4.1 mu M, 1.0 mu M, 230 mu M and 32 mu M, respectively). Geochemical modelling suggests that metals in the former are likely to have been transported as sulphate species or free ions and in the latter as chloride species or free ions. Isotopic values for both water types range between delta D -12 to 33 parts per thousand and delta(18)O 1.2 to 4.6 parts per thousand. The range of fluid compositions and isotopic contents indicates a complex history of evolution for the system. Both types of fluids appear to be derived from seawater and thus are likely to represent end members of a single fluid phase that underwent phase separation at depth. Crown Copyright (c) 2005 Published by Elsevier B.V. All rights reserved

Evolution of the Adriatic carbonate platform: Palaeogeography, main events and depositional dynamics, 2005, Vlahovic I. , Tisljar J. , Velic I. , Maticec D. ,
The Adriatic Carbonate Platform (AdCP) is one of the largest Mesozoic carbonate platforms of the Perimediterranean region. Its deposits comprise a major part of the entire carbonate succession of the Croatian Karst (External or Outer) Dinarides, which is very thick (in places more than 8000 m), and ranges in age from the Middle Permian (or even Upper Carboniferous) to the Eocene. However, only deposits ranging from the top of the Lower Jurassic (Toarcian) to the top of the Cretaceous can be attributed to the AdCP (defined as an isolated palaeogeographical entity). Although the entire carbonate succession of the Karst Dinarides was deposited within carbonate platform environments, there were different types of carbonate platforms located in different palaeogeographical settings. Carboniferous to Middle Triassic mixed siliciclastic-carbonate deposits were accumulated along the Gondwanian margin, on a spacious epeiric carbonate platform. After tectonic activity, culminating by regional Middle Triassic volcanism recorded throughout Adria (the African promontory), a huge isolated carbonate Southern Tethyan Megaplatform (abbreviated as STM) was formed, with the area of the future AdCP located in its inner part. Tectonic disintegration of the Megaplatform during the middle to late Early Jurassic resulted in the establishment of several carbonate platforms (including the Adriatic, Apenninic and Apulian) separated by newly drowned deeper marine areas (including the Adriatic Basin as a connection between the Ionian and Belluno basins, Lagonero, Basin, and the area of the Slovenian and Bosnian troughs). The AdCP was characterised by predominantly shallow-marine deposition, although short or long periods of emergence were numerous, as a consequence of the interaction of synsedimentary tectonics and eustatic changes. Also, several events of temporary platform drowning were recorded, especially in the Late Cretaceous, when synsedimentary tectonics became stronger, leading up to the final disintegration of the AdCP. The thickness of deposits formed during the 125 My of the AdCP's existence is variable (between 3500 and 5000 m). The end of AdCP deposition was marked by regional emergence between the Cretaceous and the Palaeogene. Deposition during the Palaeogene was mainly controlled by intense synsedimentary tectonic deformation of the former platform area-some carbonates (mostly Eocene in age) were deposited on irregular ramp type carbonate platforms surrounding newly formed flysch basins, and the final uplift of the Dinarides reached its maximum in the Oligocene/Miocene. The Adriatic Carbonate Platform represents a part (although a relatively large and well-preserved one) of the broader shallow-water carbonate platform that extended from NE Italy to Turkey (although its continuity is somewhat debatable in the area near Albanian/Greece boundary). This large carbonate body, which was deformed mostly in the Cenozoic (including a significant reduction of its width), needs a specific name, and the Central Mediterranean Carbonate Platform is proposed (abbreviated to CMCP), although the local names (such as AdCP for its NW part) should be kept to enable easier communication, and to facilitate description of local differences in platform evolution,

Sedimentary manganese metallogenesis in response to the evolution of the Earth system, 2006, Roy Supriya,
The concentration of manganese in solution and its precipitation in inorganic systems are primarily redox-controlled, guided by several Earth processes most of which were tectonically induced. The Early Archean atmosphere-hydrosphere system was extremely O2-deficient. Thus, the very high mantle heat flux producing superplumes, severe outgassing and high-temperature hydrothermal activity introduced substantial Mn2 in anoxic oceans but prevented its precipitation. During the Late Archean, centered at ca. 2.75[no-break space]Ga, the introduction of Photosystem II and decrease of the oxygen sinks led to a limited buildup of surface O2-content locally, initiating modest deposition of manganese in shallow basin-margin oxygenated niches (e.g., deposits in India and Brazil). Rapid burial of organic matter, decline of reduced gases from a progressively oxygenated mantle and a net increase in photosynthetic oxygen marked the Archean-Proterozoic transition. Concurrently, a massive drawdown of atmospheric CO2 owing to increased weathering rates on the tectonically expanded freeboard of the assembled supercontinents caused Paleoproterozoic glaciations (2.45-2.22[no-break space]Ga). The spectacular sedimentary manganese deposits (at ca. 2.4[no-break space]Ga) of Transvaal Supergroup, South Africa, were formed by oxidation of hydrothermally derived Mn2 transferred from a stratified ocean to the continental shelf by transgression. Episodes of increased burial rate of organic matter during ca. 2.4 and 2.06[no-break space]Ga are correlatable to ocean stratification and further rise of oxygen in the atmosphere. Black shale-hosted Mn carbonate deposits in the Birimian sequence (ca. 2.3-2.0[no-break space]Ga), West Africa, its equivalents in South America and those in the Francevillian sequence (ca. 2.2-2.1[no-break space]Ga), Gabon are correlatable to this period. Tectonically forced doming-up, attenuation and substantial increase in freeboard areas prompted increased silicate weathering and atmospheric CO2 drawdown causing glaciation on the Neoproterozoic Rodinia supercontinent. Tectonic rifting and mantle outgassing led to deglaciation. Dissolved Mn2 and Fe2 concentrated earlier in highly saline stagnant seawater below the ice cover were exported to shallow shelves by transgression during deglaciation. During the Sturtian glacial-interglacial event (ca. 750-700[no-break space]Ma), interstratified Mn oxide and BIF deposits of Damara sequence, Namibia, was formed. The Varangian ([identical to] Marinoan; ca. 600[no-break space]Ma) cryogenic event produced Mn oxide and BIF deposits at Urucum, Jacadigo Group, Brazil. The Datangpo interglacial sequence, South China (Liantuo-Nantuo [identical to] Varangian event) contains black shale-hosted Mn carbonate deposits. The Early Paleozoic witnessed several glacioeustatic sea level changes producing small Mn carbonate deposits of Tiantaishan (Early Cambrian) and Taojiang (Mid-Ordovician) in black shale sequences, China, and the major Mn oxide-carbonate deposits of Karadzhal-type, Central Kazakhstan (Late Devonian). The Mesozoic period of intense plate movements and volcanism produced greenhouse climate and stratified oceans. During the Early Jurassic OAE, organic-rich sediments host many Mn carbonate deposits in Europe (e.g., Urkut, Hungary) in black shale sequences. The Late Jurassic giant Mn Carbonate deposit at Molango, Mexico, was also genetically related to sea level change. Mn carbonates were always derived from Mn oxyhydroxides during early diagenesis. Large Mn oxide deposits of Cretaceous age at Groote Eylandt, Australia and Imini-Tasdremt, Morocco, were also formed during transgression-regression in greenhouse climate. The Early Oligocene giant Mn oxide-carbonate deposit of Chiatura (Georgia) and Nikopol (Ukraine) were developed in a similar situation. Thereafter, manganese sedimentation was entirely shifted to the deep seafloor and since ca. 15[no-break space]Ma B.P. was climatically controlled (glaciation-deglaciation) assisted by oxygenated polar bottom currents (AABW, NADW). The changes in climate and the sea level were mainly tectonically forced

Formes et formations superficielles de la partie ouest du Causse de Sauveterre (Grands Causses, Aveyron et Lozre), 2007, Bruxelles Laurent , Simoncoinon Rgine, Guendon Jeanlouis, Ambert Paul
MORPHOLOGY AND SUPERFICIAL FORMATIONS OF THE WESTERN PART OF THE CAUSSE DE SAUVETERRE (GRANDS CAUSSES, AVEYRON AND LOZ?RE, FRANCE). In 2002, the Natural Regional Park of Grands Causses has coordinated a hydrogeological study of the western part of the Causse de Sauveterre, the northernmost of the Grands Causses. A multidisciplinary approach (geology, geomorphology, geochemistry and hydrology) was used to delineate the catchment area of the main springs and to estimate the vulnerability of karstic aquifers. The Grands Causses are situated in the southern part of the French Massif Central. The landscape is characterised by huge limestone plateaus cut by deep canyons. The morphologic study of the western part of the Causse de Sauveterre (Causse de Massegros and Causse de S?v?rac), combined with analysis of superficial formations, allows us to identify the main steps of landscape evolution. The discovery of bauxite and of many outcrops of Upper Cretaceous sandstone confirm that the Coniacian ingression invaded some paleo-landscapes developed within a long period of continental evolution which was initiated at the end of the Jurassic. During the Tertiary, many residual formations form covers of the limestone plateaus. We can distinguish alterites developed from different formations of the stratigraphic series (clay with cherts from Bajocian, dolomitic sand from Bathonian and Callovian, sandy clays from Cretaceous deposits) from some allochtonous deposits which can be found in some parts of the Causse de Massegros. These formations are found in association with morphological features (shelves, polj?s, fluvio-karstic valleys, sinkholes) and are more or less responsible of their development. Furthermore, some volcanic rocks cut through or even reused some of them. With the deepening of canyons and the base level drop, horizontal morphologies are preserved only where superficial formations are abundant and thick enough to maintain crypto-corrosion. Elsewhere, karst unplugging removes most of the superficial formations, and the karstic evolution tends to show a vertical development of morphologies and caves. Some springs, which benefit from a favourable lithologic, structural and hydrologic context, are more competitive and expand their catchment area at the expense of the other springs. Many superficial features express this dynamism on the plateau and allow us to determine the most sensible areas for water pollution and the most fragile ones for human activities.

Results 1 to 15 of 25
You probably didn't submit anything to search for