Karst and Cave RSS news feed Like us on Facebook! follow us on Twitter!
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. ...

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. ...

Speleology in Kazakhstan

Shakalov on 11 Jul, 2012
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 conformal mapping is the transposition and solution of plane flow problems in a complex plane [16].?

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

What is Karstbase?

Search KARSTBASE:

keyword
author

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.
Engineering challenges in Karst, Stevanović, Zoran; Milanović, Petar
See all featured articles
Featured articles from other Geoscience Journals
Geochemical and mineralogical fingerprints to distinguish the exploited ferruginous mineralisations of Grotta della Monaca (Calabria, Italy), Dimuccio, L.A.; Rodrigues, N.; Larocca, F.; Pratas, J.; Amado, A.M.; Batista de Carvalho, L.A.
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
See all featured articles from other geoscience journals

Search in KarstBase

Your search for transgression (Keyword) returned 57 results for the whole karstbase:
Showing 1 to 15 of 57
Fauna of the brackish underground waters of Central Asia., 1965, Birstein Jakov Avadievich, Ljovuschkin S. I.
In the cave Kaptar-Khana (south-western Turkmenistan) was discovered a lake filled with water with a salinity of 11,68/oo. This lake is inhabited by a fauna of marine origin; Foraminifera (three species), Molluscs (Pseudocaspia ljovuschkini sp.n.), Harpacticoida (genera Ectinosoma, Schizopera and Nitocra), Isopoda (Microcharon halophilus sp.n.) and possibly Nematoda (Oncholaimidae). The majority of the discovered species are related to species of circum-Mediterranean origin. Geological data do not permit to consider this fauna as a relict of any of the Tertiary seas. The same applies to all other cases when animals of marine origin were discovered in subterranean waters of Central Asia (as for instance Microcharon kirghisicus Jank. on the shores of the lake Issyk-Kul). We can either admit a far greater anciennity of this fauna or an ability of its components to disperse very widely beyond the boundaries of marine transgressions.

Evolution of the Wellington Caves Landscape, 1973, Francis, G.

Wellington Caves, New South Wales (figure 1), have attracted scientific attention for more than a century, largely through discoveries in the cave sediments of bones from extinct animals. These bone discoveries provided impetus for a number of early speculations about the geomorphology of the caves area and its relationship to the caves. Notable among these was the conjecture of Mitchell (1839) that the valley floor sediments of the Bell River and the cave fills had been deposited during a marine transgression about one million years ago. The first systematic geomorphological work was carried out by Colditz (1943), who argued for two distinct relict erosion levels in the Bell Valley; the older level was assigned to the Lower Pliocene and the younger to the Upper Pliocene. Colditz considered that these levels provided evidence for two phases of uplift in late Tertiary times. More recently Frank (1971) made detailed studies of the cave sediments, and devoted some attention to landscape evolution. He believed that the Bell River had been captured by Catombal Creek, during the late Pliocene or early Pleistocene.


Donnees geomorphologiques sur la region de Fresh Creek, Ile Andros (Bahama), 1974, Bourrouilh F,
A geomorphological study of the east coast of Andros (Fresh Creek area) shows the existence of a paleotopography represented by low-altitude hills (few metres). This paleotopography is protected by the presence of a calcitic Quaternary crust which covers Pleistocene calcarenite.In the western part of the area, there are long woody axes, oriented NE-SW, parallel to the channels of the creek. They end at two kilometres from the coast, along which is a second kind of lower hills, orthogonal to the first.The first axes can be interpreted as megaripples as seen at the present time on modern deposits (on the Great Bahama Bank) and fossilized by the upper crust. The second direction is made by accretion ripples along the coast.The surface of the Bahamian calcarenite has been studied. The Bahamian karst presents two topographical forms: “blue holes” like those outside the island, which are 60-80 m in diameter and both sparse and deep; and “washtub” dolines; these are numerous and shallow, and, from low altitude, exhibit a honeycombed aspect on the surface. This karstic topography with dolines and blue holes is also seen through the water of the Creek the hard bottom of which is covered only here and there with a few centimetres of sediments. Hence, there is a submerged karstic topography, made of the same elements as the aerial karst, but submerged by the Holocene transgression. The present karstic relief, in relation with the different eustatic levels of the Quaternary, has begun 120,000 years ago, according to the isotopic ages, and might be composed by different steps, difficult to show now, in the topography.The blue holes in the interior of the island of young and little evolved karst, were formed more by solution than by collapse of the karstic caves, because of the absence of a real river to drain the Andros shelf at the time of low sea levels. Blue holes of the inside of the island, as they are called, with submarine openings, have the same salinity as the water of the creek (17.5 g/l). The dolines with very low salinity (0.7 g/l to 3.8 g/l) are filled with stromatolites and charophytes, slowly forming sediments made up essentially of high-magnesian calcite.It seems that the Andros Island karst can be compared with that of the Yucatan, where there are round and deep open pits, called cenote, of which the Bahamian equivalent would be the blue holes which were drowned by the Holocene transgression.ResumeSur l'ile Andros, zone emergee du Grand Banc de Bahama, l'auteur montre l'existence d'une paleotopographie comprenant deux categories de rides d'orientation differente et semblant fossilisee par une croute calcitique recente et l'existence d'un karst aux formes jeunes, bien qu'heritage d'un karst holocene en voie de submersion. Ces formes sont des “blue holes” ou trous bleus circulaires (60 a 80 m de diametre) et peu nombreux, et des dolines, dites en baquet. Dans ces dolines se deposent actuellement des croutes stromatolithiques calcitiques dont l'etude est faite par diffractometrie de rayons X et microscopie electronique a balayage

Messinian event in the black sea, 1979, Hsu Kenneth J. , Giovanoli Federico,
Three holes were drilled during the 1975 DSDP Leg 42B drilling the Black Sea. A section from Hole 380, at 2107 m water depth on the western edge of the abyssal plain, is 1074 m thick, and provides the most complete stratigraphic section. Dating of the sediments is based upon (1) fossil evidence from pollen, crustaceans, benthic foraminifera, and diatoms, (2) correlation with climatic changes and with unusual isochronous events that have been dated elsewhere, (3) paleomagnetic data, and (4) estimates of sedimentation rate.The history of Black Sea sedimentation recorded by the DSDP cores includes black shale sedimentation during the Late Miocene, followed by periodic chemical sedimentation from Late Miocene to Early Quaternary, and a change to dominantly terrigenous sedimentation from the Middle Quaternary. These hemipelagic and turbiditic sediments were deposited in lacustrine and brackish marine environments. The Messinian sediments, however, consist of stromatolitic dolomite, oolitic sands, and coarse gravels, deposited in supratidal and intertidal environments. The intercalation of the shallow-water sediments in a deep-water sequence suggests a drastic lowering of the water-level within the Black Sea basin during the Messinian so that the edge of the present abyssal plain was then the edge of a shallow lake.The Messinian draw-down phase of the Black Sea was in existence for about 100,000 years during the Lago-Mare stage of the salinity crisis. The evaporated waters formed an alkaline lake before it was drowned by a brackish marine transgression correlative to the Trubi transgression of the Mediterranean

Karst et littoral du Bec de Caux (Seine-Maritime), 1983, Rodet, J.
KARST AND COAST OF BEC DE CAUX, (SEINE-MARITIME, FRANCE) - The Pays de Caux seaside takes a preferential place in the importance of karstic features in the chalk of Normandy, because of the section of the sea cliffs. This exceptional frame allows three main observations. The first one is the investigation of springs, which places flooded paleo-karst in a prominent position. Those karstic phases, under the seal evel, have their counterpart above it. Study of development and the distribution of the passages in the Cap Fagnet underground pattern, shows these different karstic bases, and their relations, giving a true underground delta of active springs. The second aspect concerns the relations between dry caves and coastal-line carvings. It appears a typology, showing the influence of karstification in the morphology of caps. The third point is about quality of entrance infillings, as paleogeographic witness, and contributor in valuation of the shoreline evolution, in Etretat area, especially during the Flandrian transgression.

Barbuda--an emerging reef and lagoon complex on the edge of the Lesser Antilles island are, 1985, Brasier M, Donahue J,
The Pliocene to Holocene limestones of Barbuda have formed on a wide, shallow, outlying bank of the Lesser Antilles island arc, some 50 km east of the older axis of the Limestone Caribbees and 100 km east of the newer axis of the active Volcanic Caribbees. Contrasts with neighbouring islands of similar size include the lack of exposed igneous basement or mid-Tertiary sediments, the dominance of younger flat-lying carbonates, and the greater frequency of earthquake shocks. The history of emergence of the island has been studied through aerial reconnaissance, mapping, logging, hand coring, facies and microfacies analysis. These show a pattern of progressively falling high sea level stands (from more than 50 m down to the present level) on which are superimposed at least three major phases of subaerial exposure, when sea levels were close to, or below, their present level. This sequence can be summarized as follows: 1, bank edge facies (early Pliocene Highlands Formation) deposited at not more than c. 50-100 m above the present sea level; 2, emergence with moderate upwarping in the north, associated with the Bat Hole subaerial phase forming widespread karst; 3, older Pleistocene transgression with fringing reefs and protected bays formed at l0 to l5 m high sea level stands (Beazer Formation); 4, Marl Pits subaerial phase with widespread karst and soil formation; 5, late Pleistocene transgression up to m high stand with fringing and barrier reefs, protected backreefs and bays (Codrington Formation Phase I); 6, gradual regression resulting in emergence of reefs, enclosure of lagoons, and progradation of beach ridges at heights falling from c. 5 m to below present sea level (Codrington Phase II); 7, Castle Bay subaerial phase produced karst, caliche and coastal dunes that built eastwards to below present sea level; and 8, Holocene transgression producing the present mosaic, with reefs, lagoons and prograding beach ridge complexes, with the present sea level reached before c. 4085 years BP. The evidence suggests that slight uplift took place in the north of the island after early Pliocene times. Subsequent shoreline fluctuations are consistent with glacio-eustatic changes in sea level, indicating that the island has not experienced significant uplift during the Quaternary

Mangroves, Mountains and Munching Molluscs: The Evolution of a Tropical Coastline, 1988, Kiernan, Kevin

The highly scenic Andaman coast of peninsular Thailand is locally dominated by steep limestone hills and karst towers that rise from broad alluvial plains, from mangrove swamps or from the sea. The karst terrain stretches north and west across the Malay peninsula to the Gulf of Siam. Some of the variations in the style of this karst have resulted from lithological and structural factors. However, steepening of the slopes by marine erosion at times of formerly high sea levels has probably been important to the development of the most spectacular part of this landscape. Notches and caves cut in limestone towers up to 10-15m above present sea level may represent the maximum transgression of the Last Interglacial. Morphological evidence hints that former shorelines may now lie hundreds of metres above present sea level due to diastrophic movements during the late Cainozoic. However, this evidence is equivocal and it has been argued that similar landforms in neighboring parts of Malaysia may be the result of terrestrial planation processes that operated independent of sea level during the Pleistocene glacial stages.


La karstification de l'le haute carbonate de Makatea (Polynsie franaise) et les cycles eustatiques et climatiques quaternaires, 1991, Dessay J. , Pouchan Y. , Girou A. , Humbert L. , Malezieux J.
THE KARST 0F MAKATEA ISLAND (FRENCH POLYNESIA) AND THE CLIMATIC AND GLACIO-EUSTATISM SETTING - Located in the Central Pacific, in the northwestern part of the Tuamotu Archipelago, Makatea island (148 15 W - 15 50 S) is an uplifted, karstic, carbonate construction of Early Miocene age, which reaches 113m in height. From 1906 to 1966, phosphate deposits were exploited on Makatea Island. These phosphate deposits (apatite) overlaid the Miocene series and filled the karstic cavities in the higher regions of the island. Several traces of ancient shorelines can be observed on Makatea: 1/ three different reef formations, which reach about +27m, +7m, +1m above the present mean sea level and respectively dated 400,000 100,000 yr BP, 140,000 30,000 yr BP, between 4,470 150 yr BP and 3,720 13O yr BP; 2/ four distinct marine notch lines on the Early Miocene cliff at about +1m, +7m, +27m and +56m (or +47m on the west coast caused by tilt) above the present mean sea level; 3/ two exposed marine platforms respectively at +29m and +7m above the present mean sea level. The ages of the former makatean shores are inferred by using: (1) the Pacific glacio-eustatic sea-level curve for the last 140,000 yr BP, (2) the Pacific oxygen isotope curve for the last 900,000 yr BP, and (3) a constant uplift rate during the Pleistocene. In this way, according to their age and elevation, the sea-level indicators at about +1m, +7m and +27m (+29m) above the present mean sea level can be respectively related to the Holocene transgression (Flandrian) dated between 6,000 and 1,500 yr BP, to the last Pleistocene interglacial period (Sangamon) dated between about 130,000 and 110,000 yr BP, and to a Middle Pleistocene interglacial period (Yarmouth) dated between about 315,000 and 485,000 yr BP. If we assume that a sea level similar to the present occurred during the Yarmouth inter-glacial period, the uplift rate is valued at 0.085 mm/yr to 0.056 mm/yr. Thus the sea-level associated with the marine notch at about +56m (+47m) may be about 650,000 yr to 1 M.y. old and can be associated with another Pleistocene interglacial period (Aftonian). Consequently, as indicated by the former shores, the sea level fluctuations can be related to the major glacio-eustatic quaternary events. This climatic and eustatic setting is used to explain the karst observed on the Makatea island. Carbonate dissolution and essentially vertical karst genesis were the result of the superposition of several cycles. Each cycle was initially composed of a solution of the carbonates during an interglacial period, followed by a drainage of the saturated solutions during the marine regression associated with the consecutive glacial period. Nevertheless, this scheme is not enough to explain the specific morphology of the makatean karstic cavities and we suggest using insular phosphatisation to explain this karst genesis. It is generally accepted that phosphate rock deposits on coral reef islands are the result of chemical reaction between seabird guano and reef limestone. Furthermore, petrographic and stable isotope studies suggest several generations of phosphorite formation and reworking episodes in the history of these deposits. The primary deposition of phosphates must have begun during a glacial period. This deposition was followed by some redistribution of phosphorites during the interglacial period and by additional precipitation of apatite from meteoric waters. This assumed process of phosphogenesis is consistent with both the field observations and the geodynamic evolution of Makatea. Thus, the particular morphology of the makatean karst can be the result of the dissolution of the carbonates caused by phosphoric acid etching. This acid is derived from the evolution of the phosphorites during the pleistocene interglacial periods.

Rapports entre la karstification _primditerranenne et la crise de salinit messinienne, lexemple du karst lombard (Italie), 1994, Bini, A.
The Mediterraean dessiccation theory suggests that during the Messinian the Mediterranean sea lad almost completely dried up did a thick succession of evaporites was laid down Due to dessiccation the erosional base level through the whole Mediterranean area was lowered, with the consequent development of long and deep fluviatile canyons (e.g. Nile, Rhne, Var, etc). This lowering strongly affected karst evolution This paper concerns the karst in Lombardy, around the southalpine lakes. The old evolutionary models, predating dessiccation theory, assume that the lacustine valleys were scoured by the quaternary glaciers. ln this case the karst should have been characterized by some features, like for example the altitudinal cave distribution as a consequence of the valley lowering after each glaciation. Seismic experiments through the lakes and their tributaries have shown that these valleys are deep fluviatile canyons. The study of caves has demonstrated that the caves themselves predate the entrenchment of the valleys and the glaciations. During the latter the caves were filled up and emptied several times, without any modifications of their inner morphology, including stalactites. Moreover the U/Th age determinations indicate that a great number of concretions are older than 350 ky, and that a few are older than 1.5 Ma. As a conse-quence, a general model of karst evolution can be proposed. The former karstic drainage system developed after the Oligo-Miocene emersion. Paleogeography obviously diffe-red from the present day landscape but the main valley had already been scoured. During the Messinian the dramatic lowering of base level determined major changes in karstic evolution and a reorganisation of the karst drainage system that was consequently lowered considerably. The Pliocene transgression determined a new karst evolution, after which a great number of caves were located well below the sea level base. This evolution occurred during hot and wet climate period, with seasonal high flows and relevant discharges of the karstic rivers The great caves of the Lombardian karst developed within the climatic stage.

RELATIONSHIP BETWEEN FRACTURES AND KARSTIFICATION - THE OIL-BEARING PALEOKARST OF ROSPO MARE (ITALY), 1994, Soudet H. J. , Sorriaux P. , Rolando J. P. ,
The Rospo Mare oil field is located in the Adriatic Sea, 20 km off the Italian coast. The reservoir lies at a depth of 1300 m and consists of a paleokarst oi Oligocene to Miocene age which developed within Cretaceous limestones, now covered by 1200 m of Mio-Pliocene sequences. The oil column is about 140 m 8 high. The karstic nature of the reservoir was identified through vertical, cored drill holes which allowed us to analyse the various solution features and the sedimentary infilling (speleothems, terra rossa, marine clays), as well as their vertical distribution. Erosion morphology at the top of the karst is highly irregular, including in particular paleovalleys as well as many pit-shaped sink holes. Detailed geophysical knowledge of that morphology helped to optimize the development of the field through horizontal drilling. Observations concerning the upper part of the reservoir were compared to a palaeokarst of the same age, outcropping widely onshore, in quarries located nearby. The Rospo Mare paleokarst is an integral part of the ante Miocene paleokarst assemblages of the periphery of the Mediterranean which were formed in tropical conditions. Only the fractures enhanced by meteoric water during the formation of the karat are important for reservoir connectivity. During the formation of the karst there were several phases of dissolution and infilling which modified the geometry of the open fissures and only these fractures play an important role in the reservoir drainage. Vertically we can distinguish three very different zones from top to bottom: at the top the epikarst (0-35 m) in a zone of extension. All the fractures have been enlarged by dissolution but the amount of infilling by clay is substantial. The clays are derived either from alteration of the karat fabric or by deposition during the Miocene transgression; the percolation zone (15-45 m) is characterized by its network of large fractures vertically enlarged by dissolution which corresponds to the relict absorption zones in the paleokarst. These fractures, which usually have a pluridecametric spacing, connect the epi-karst with the former sub-horizontal river system. This zone has been intersected by the horizontal wells during the field development. In this zone there are local, horizontal barriers oi impermeable clay which can block vertical transmissibility. In these low permeability zones the vertical fractures have not been enlarged due to dissolution hence the horizontal barrier; the zone of underground rivers (35-70 m) is characterized by numerous horizontal galleries which housed the subterranean ground water circulation. When these fissures are plurimetric in extent this can lead to gallery collapse with the associated fill by rock fall breccia. This can partly block the river system but always leaves a higher zone of free circulation with high permeabilities of several hundreds of Darcys. These galleries form along the natural fracture system relative to the paleohydraulic gradient which in some cases has been preserved. The zone below permanent ground water level with no circulation of fluids is characterized by dissolution limited to non-connected vugs. Very locally these fissures can be enlarged by tectonic fractures which are non-connected and unimportant for reservoir drainage. Laterally, only the uppermost zone can be resolved by seismic imaging linked with horizontal well data (the wells are located at the top of the percolation zone). The Rospo Mare reservoir shows three distinct horizontal zones: a relict paleokarst plateau with a high index of open connected fractures, (area around the A and B platforms); a zone bordering the plateau (to the north-east of the plateau zone) very karstified but intensely infilled by cap rock shales (Miocene - Oligocene age); a zone of intensely disturbed and irregular karst paleotopography which has been totally infilled by shales. The performance of the production wells is dependent on their position with respect to the three zones noted above and their distance from local irregularities in the karst paleotopography (dolines, paleovalleys)

ASSOCIATION OF TEPEES AND PALEOKARST IN THE LADINIAN CALCARE-ROSSO (SOUTHERN ALPS, ITALY), 1994, Mutti M. ,
The Ladinian Calcare Rosso of the Southern Alps provides a rare opportunity to examine the temporal relationships between tepees and palaeokarst. This unit comprises peritidal strata pervasively deformed into tepees, repeatedly capped by palaeokarst surfaces mantled by terra rossa. Palaeokarsts, characterized by a regional distribution across the Southern Alps, occur at the base and at the top of the unit. Local palaeokarsts, confined to this part of the platform, occur within the Calcare Rosso and strongly affected depositional facies. Tepee deformation ranges from simple antiformal structures (peritidal tepecs) to composite breccias floating in synsedimentary cements and internal sediments (senile tepees). Peritidal tepees commonly occur at the top of one peritidal cycle, in association with subaerial exposure at the cycle top, while senile tepees affect several peritidal cycles, and are always capped by a palaeokarst surface. Cements and internal sediments form up to 80% of the total rock volume of senile tepees. The paragenesis of senile tepees is extremely complex and records several, superimposed episodes of dissolution, cement precipitation (fibrous cements, laminated crusts, mega-rays) and deposition of internal sediments (marine sediment and terra rossa). Petrographical observations and stable isotope geochemistry indicate that cements associated with senile tepees precipitated in a coastal karstic environment under frequently changing conditions, ranging from marine to meteoric, and were altered soon after precipitation in the presence of either meteoric or mixed marine/meteoric waters. Stable isotope data for the cements and the host rock show the influence of meteoric water (average deltaO-18 = - 5.8 parts per thousand), while strontium isotopes (average Sr-87/Sr-86 = 0.707891) indicate that cements were precipitated and altered in the presence of marine Triassic waters. Field relationships, sedimentological associations and paragenetic sequences document that formation of senile tepees was coeval with karsting. Senile tepees formed in a karst-dominated environment in the presence of extensive meteoric water circulation, in contrast to previous interpretations that tepees formed in arid environments, under the influence of vadose diagenesis. Tepees initiated in a peritidal setting when subaerial exposure led to the formation of sheet cracks and up-buckling of strata. This porosity acted as a later conduit for either meteoric or mixed marine/meteoric fluids, when a karst system developed in association with prolonged subaerial exposure. Relative sea level variations, inducing changes in the water table, played a key role in exposing the peritidal cycles to marine, mixed marine/meteoric and meteoric diagenetic environments leading to the formation of senile tepees. The formation and preservation in the stratigraphic record of vertically stacked senile tepees implies that they formed during an overall period of transgression, punctuated by different orders of sea level variations, which allowed formation and later freezing of the cave infills

DIAGENESIS OF AN UPPER TRIASSIC REEF COMPLEX, WILDE-KIRCHE, NORTHERN CALCAREOUS ALPS, AUSTRIA, 1994, Satterley A. K. , Marshall J. D. , Fairchild I. J. ,
The Wilde Kirche reef complex (Early-Late Rhaetian) grew as an isolated carbonate structure within the shallow Kossen Basin. At the Triassic/Jurassic boundary a single brief(c. 10-50 ka) period of subaerial exposure occurred. The preserved karst profile (70 m thick) displays a vadose zone, enhanced dissolution at a possible palaeo-watertable (5-15m below the exposure surface), and a freshwater phreatic zone. Karst porosity was predominantly biomouldic. primary cavities and biomoulds were enlarged and interconnected in the freshwater phreatic zone; cavity networks developed preferentially in patch reef facies. Resubmegence of the reef complex allowed minor modification of the palaeokarst surface by sea floor dissolution and Fe-Mn crust deposition on a sediment-starved passive margin. Fibrous calcite (FC), radiaxial fibrous calcite (RFC) and fascicular optic calcite (FOC) cements preserved as low Mg calcite (LMC) are abundant in primary and karst dissolution cavities. FC cement is restricted to primary porosity, particularly as a synsedimentary cement at the windward reef margin. FC, RFC and FOC contain microdolomite inclusions and show patchy non-/bright cathodoluminescence. delta(18)O values ofnon-luminescent portions (interpreted as near original) are -1.16 to -1.82 parts per thousand (close to the inferred delta(18)O of calcite precipitated from Late Triassic sea water). delta(13)C values are constant ( to .2 parts per thousand). These observations suggest FC, RFC and FOC were originally marine high Mg calcite (HMC) precipitates, and that the bulk of porosity occlusion occurred not in the karst environment but in the marine environment during and after marine transgression. The HMC to LMC transition may have occurred in contact with meteoric water only in the case of FC cement. The most altered (brightly luminescent) portions of RFC/FOC cements yield delta(18)O = -2.44 to -5.8 parts per thousand, suggesting HMC to LMC alteration at up to 34 degrees C, in the shallow burial environment at depths of 180-250 m. Abundant equant cements with delta(18)O = -4.1 to -7.1 parts per thousand show crisp, uniform or zoned dull luminescence. They are interpreted as unaltered cements precipitated at 33-36 degrees C at 200-290 m burial depth, from marine-derived fluids under a slightly enhanced geothermal gradient. Fluids carrying the equant cements may have induced the HMC to LMC transition in the fibrous cements

Paleoalpine karstification - The longest paleokarst period in the Western Carpathians (Slovakia), 1995, Cincura J, Kohler E,
The considerable areal extent and great thicknesses of Middle/Upper Triassic carbonate complexes influenced favourably the formation of karst during subaerial periods. The lower boundary of the Paleoalpine karst period is age-determined by the gradual emergence of the basement - during the Upper Cretaceous in the Central Western Carpathians and even earlier in the Inner Carpathians. The upper boundary can be dated by marine transgression The start of the transgression is not synchronous and it varies in a broad range from Upper Cretaceous to Upper Eocene and maybe even up to Oligocene/Miocene. The typical products of the period include typical karst bauxites filling karst cavities, ferri crusts, red clays, collapse and crackle breccias with speleothems, freshwater limestones or polymict conglomerates

GEOLOGY AND ORE GENESIS OF THE MANGANESE ORE-DEPOSITS OF THE POSTMASBURG MANGANESE-FIELD, SOUTH-AFRICA, 1995, Vonplehweleisen E. , Klemm D. D. ,
The Postmasburg Mn/Fe-ores occur exclusively in dolomitic Precambrian sinkhole structures with siliceous breccias and shales as hostrocks. The main manganese minerals are braunite and bixbyite, apart from secondary alteration products of the psilomelane-manganomelane family. Various generations of ore minerals could be identified. The ore mineralization is subdivided into three different genetic types. They are classified either as pure karst deposits or as combined formations of karst origin and shallow marine sedimentation due to the transgression of the Banded Iron Formation (BIF) sea. Post-sedimentary metamorphism is identified as very low grade. The development of the different ore types is illustrated schematically

L'halloysite karstique; comparaison des gisements types de Wallonie (Belgique) et du Perigord (France), 1997, Perruchot A. , Dupuis C. , Brouard E. , Nicaise D. , Ertus R. ,
Two cryptokarstic (covered karsts) halloysitic deposits were compared: the Entre Sambre et Meuse in Belgium and the Perigord in France. Both belong to a continental margin subject to marine transgression and regression cycles which enhance the karstic activity. This geodynamic context appears to be very favourable to the formation of halloysite. The similarity of the geodynamic context of both sites leads to a genetic convergence linked to specific properties of the cryptokarstic system, especially, the ability to collect the percolating waters and to juxtapose the conditions of precipitation, accumulation and maturation of the halloysite silico-aluminous gel precursors. However, each site also displays pronounced specificities relevant to: the nature of the host rock of the halloysite (a partly silicified limestone in the first, a smectite-kaolinite argilite in the second); the aluminium source (allochthonous in the first, relatively autochthonous in the second); and the halloysite content of the deposits (of approximately 100% in the first, and 40% maximum in the second)

Results 1 to 15 of 57
You probably didn't submit anything to search for