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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 storm is 1. a disturbance of average meteorological conditions and usually connected with precipitation [16]. 2. a period of precipitation over a specific drainage basin [16].?

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

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What is Karstbase?



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KarstBase a bibliography database in karst and cave science.

Featured articles from Cave & Karst Science Journals
Chemistry and Karst, White, William B.
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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 succession (Keyword) returned 95 results for the whole karstbase:
Showing 1 to 15 of 95
Zonation and succession in brackish environments of the Eastern Adriatic, 1974,
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Lovri'_ Andrija,

Summaries of papers read at The Engineering Group Regional Meeting-Cardiff 1977: Engineering Geology of Soluble Rocks, 1978,
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Engineering Geology of the South Wales Coalfield and its margins--with particular reference to the Carboniferous Limestone. By J. G. C. Anderson. The stratigraphical succession of the Cardiff district ranges from Silurian to Lower Jurassic, while structurally the rocks have been affected by Caledonian, Hercynian and Alpine movements. Caledonian folding is relatively weak but powerful Hercynian (Asturian) folding and faulting took place about the end of the Westphalian; the elongate South Wales Coalfield Basin being formed at this time. Mesozoic strata, up to the Liassic, are also folded and faulted by movements which may have been as late as the Miocene. Silurian rocks which occur in the Usk and Rumney Inliers consist of sandstones, siltstones and shales (often calcareous) as well as some limestones. The argillaceous rocks often weather deeply and degenerate to clay with rock lithorelicts, consequently they pose problems in foundations and cuttings, e.g. on the east side of Cardiff. The Old Red Sandstone, both Lower and Upper divisions are present, is made up of marls, sandstones and conglomerates. Some of the sandstones are aquifers and provide water in commercial quantities. The marls, especially where steeply inclined are liable to slipping, as happened for example, in the Brynglas (M4) Tunnel at Newport. The Carboniferous Limestone surrounds the coalfield and consists mainly of limestone and dolomite (see also below). The Millstone Grit does not contain the gritty sandstones of the Pennines and is made up mainly of strong siliceous sandstones and shales. The Coal Measures show the usual lithology; a ... This 250-word extract was created in the absence of an abstract

Development of a Subterranean Meander Cutoff: The Abercrombie Caves, New South Wales, 1979,
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Frank R. , Jennings J. N.

The Abercrombie Caves are exemplary of a subterranean meander cutoff. The bedrock morphology, especially flat solution ceilings, permits reconstruction of an evolution from slow phreatic initiation to epiphreatic establishment of a substantial throughway, followed by progressive succession to vadose flow and phased channel incision. At two separate stages, there was twofold streamsink entry and underground junction of flow. Five 14C dates from alluvial sediments show that capture of the surface stream was certainly complete before c.15,000 BP and that by c.5,000 BP the stream had almost cut down to its present level.

Abstract: Darwin and Diprotodon: The Wellington Cave Fossils and the Law of Succession IN: Proceedings of the Linnean Society of New South Wales 104, 1980 for 1979:265-272, 1981,
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Dugan, Kathleen G.

The fossils from Wellington Caves, some of them 'giant', are well known to Australian speleologists, finds of importance for the study of Australian fauna from early discovered caves. What I think we did not appreciate was that the Wellington 'bones' have a place in the world history of science of significance also, the theme of this paper. Many of you will have watched the BBC-TV series on 'The Voyage of the Beagle'; much was made of the importance to Darwin in developing his theory of evolution of the fossils he found in southern South America. There fossils of giant relatives of sloths, llamas and armadillos helped to make clear to him the notion of the geological succession of life, a basic part of his theory along with the idea of natural selection to which the finches and the tortoises of the Galapagos Islands proved crucial. However it seems that Darwin was previously aware of the similar significance of the Wellington Caves bones for the law of succession from Charles Lyell's Principles of Geology which quotes William Clift's identifications of dasyures, wombats and kangaroos amongst them. The fact that these recently extinct animals were closely related to the distinctive modern marsupial fauna of Australia counted much against earlier conceptions such as Cuvier's catastrophic theory or Buckland's ideas of successive divine creations within a short time span. Watchers of the TV series will remember the devious role played by the palaeontologist, Sir Richard Owen, in organising public opposition to Darwin at the famous Oxford meeting of the British Association for the Advancement of Science. This article relates the series of rearguard actions of Owen to maintain that there was a fossil elephant component in the ancient Australian fauna, damaging to Darwinism. But the growing evidence from Australia, not all of it from caves, of course, finally extinguished this red herring, started by that doctrinaire N.S.W. colonial, the Reverend John Dunmore Lang.

Depositional history of the late Pleistocene limestones of the Kenya coast, 1984,
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Braithwaite Cjr,
The coastal limestones of Kenya extend approximately 180 km N-S from Malindi to the Tanzanian border. They are at least 20 m thick and may be subdivided into sedimentary units representing major periods of marine deposition punctuated by sub-aerial erosion. Their foundations are formed by thick fluvial and aeolian quartz sands but there is local evidence of marine deposition following these. In the main limestone unit, deposited about 240,000 years ago, initial high energy shallow-shelf deposition was replaced by quiet water sediments with scattered corals. Sea level stood about 8 m higher than at present. Quartzose sands were confined to western areas. A return to shallow water heralded a new phase of emergence and erosion, producing karst surfaces and sub-aerial sediments. These are overlain by herring-bone cross-bedded quartz-rich calcarenites which were the products of a tidally dominated shelf and, at Watamu and Wasini, pass upwards into aeolian dune deposits. However, these were also emersed and subject to karst erosion before deposition of a further widespread marine limestone. Within this, coral knolls are well developed. Much of the sediment accumulated in shallow water, but the ecological succession indicates that knolls were at times in deeper waters. These deposits formed about 125,000 years ago when sea level ultimately stood 15-20 m above its present position. More recently in the area sea level has again fallen. However, the descent was not continuous and pauses were marked by marine terrace formation and subsequent karst erosion with sub-aerial deposition. Brief reversals caused both terraces and sediments to be overlain by thin marine deposits. Sea level paused at its present position about 30,000 years ago when the present reef platform was probably defined. It continued to fall to a maximum of about-120 m before rising to its existing level 7000 years ago and beginning the current cycle of sediment accumulation

General characteristics of the landforms in the Alps and Julian Prealps and in Trieste Karst., 1989,
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Vaia Franco
The morphology of the Julian Alps and Prealps and of the Triestian Karst are here shortly described; the structures, which defined its origin and development, are also considered. We can notice some cliffs which follow one another from the State boundary to the Adriatic sea; they are made up by lithologic successions, which repeat themselves according to the latitude. Anyway we recognize a general outcropping of rock masses which are decreasing little by little southward as regards the altitude, the age and than the erodibility. There are some differences between the western (Carnian) and the eastern (Julian) bend of the regional mounts according not only to the latitude but to the longitude, because of the lithology. In fact, the Julian mountains often look like the Dolomities in the northern zone. The southern ones, particularly near the high alluvial plain, are rounded and gently dipping. The drainage networks are quite different too. In the upper zone it is a trellis net, in the lower one is locally a trellis net and than it becomes a dendritic system. The glacial erosion follows the same principle too, coming southward along the main and the subordined valley cuts. At last, the Karst morphology shows itself strongly conditioned by the structural scheme as well as by the lateral lithologic changes. It comes out an anisotropic whole of surface forms and of subsurface ones, clearly referred to those reasons. The whole area here described shows moreover a high evolutive dynamics, connected with the recent tectonic phases.

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Pysek P. ,
In the second part of the study on vegetation of village settlements at the territory of the Bohemian Karst, ecological and successional characteristics of communities are given. Ellenberg indicator values for temperature, moisture, nitrogen and soil reaction were used to investigate habitat conditions. Successional relations of communities are presented. Quantitative data on the composition of vegetation cover were obtained which made it possible to compare the study area with other regions

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Jones B. ,
Caves, fossil mouldic cavities, sinkholes and solution-widened joints are common in the Cayman and Pedro Castle members of the Bluff Formation (Oligocene Miocene) on Grand Cayman and Cayman Brac because they have been subjected to repeated periods of karst development over the last 30 million years. Many voids contain a diverse array of sediments and/or precipitates derived from marine or terrestrial environs, mineral aerosols, and groundwater. Exogenic sediment was transported to the cavities by oceanic storm waves, transgressive seas, runoff following tropical rain storms and/or in groundwater. At least three periods of deposition were responsible for the occlusion of voids in the Cayman and Pedro Castle members. Voids in the Cayman Member were initially filled or partly filled during the Late Oligocene and Early Miocene. This was terminated with the deposition of the Pedro Castle Member in the Middle Miocene. Subsequent exposure led to further karst development and void-filling sedimentation in both the Cayman and Pedro Castle members. Speleothems are notably absent. The void-filling deposits formed during these two periods, which were predominantly marine in origin, were pervasively dolomitized along with the host rock 2 5 million years ago. The third period of void-filling deposition. after dolomitization of the Bluff Formation, produced limestone, various types of breccia, terra rossa, speleothemic calcite and terrestrial oncoids. Most of these deposits formed since the Sangamon highstand 125 000 years ago. Voids in the present day karst are commonly filled or partly filled with unconsolidated sediments. Study of the Bluff Formation of Grand Cayman and Cayman Brac shows that karst terrains on isolated oceanic islands are characterized by complex successions of void-filling deposits that include speleothems and a variety of sediment types. The heterogenetic nature of these void-filling deposits is related to changes in sea level and climatic conditions through time

Rapports entre la karstification _primditerranenne et la crise de salinit messinienne, lexemple du karst lombard (Italie), 1994,
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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.

Guab As, une grotte dans de la dolomie mgascristalline hydrothermale (Namibie occidentale), 1995,
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Marais E. , Martini J. , Irish J.
The authors describe a cave in the semi-desert area of the Hakos Mountains, 100km to the southwest of Windhoek, Namibia. The cave is significant due to the very unusual country rock, with which it is associated. It formed by dissolution of the dolomite core of a large quartz vein, which is 800 m long and 200 m wide, developed in mica-schist. The cave consists of a complex succession of large chambers, more or less overlapping each others, with walls generally consisting of quartz. In most instances the dolomite has been completely dissolved or occurs under the floor, concealed by dust and scree. Although the cave developed within a very small volume of carbonate, the total length reaches 695 m and the depth 85 m. The bottom is occu-pied by a pool which is only temporarily filled with water and probably marks the position of a perched water-table. The cave formed in a perched phreatic environment during an undetermined period

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Joeckel R. M. ,
A Virgilian (Stephanian) weathering profile up to 4 m deep, containing a paleosol (basal Rakes Creek paleosol) in the basal mudstone of the Rakes Creek Member and karstified marine sediments in the Ost, Kenosha, and Avoca members below, is restricted to southeastern Nebraska (specifically the Weeping Water Valley) and the Missouri River Valley bluffs of adjacent easternmost Iowa. This weathering profile, informally referred to as the Weeping Water weathering profile, disappears farther eastward into the shallow Forest City Basin in southwestern Iowa. Weeping Water weathering profile features are prominent in comparison to other Midcontinent Pennsylvanian subaerial exposure surfaces, indicating prolonged subaerial exposure, relatively high elevation, and a marked drop in water table along the Nemaha Uplift in southeastern Nebraska. Eastward, on the margin of the Forest City Basin, the basal Rakes Creek paleosol and underlying karst are thinner and relatively poorly developed; paleosol characteristics indicate formation on lower landscape positions. Comparative pedology, the contrasting of paleosol variability, morphology, and micromorphology between different paleosols in the same regional succession, provides a basis for interpreting the larger significance of the basal Rakes Creek paleosol. The stratigraphically older upper Lawrence and Snyderville paleosols in the same area are significantly different in patterns of lateral variability and overall soil characteristics. Weaker eustatic control and stronger tectonic activity may explain the greater west-east variability (and eventual eastward disappearance) of the basal Rakes Creek paleosol. Differences in soil characteristics between the Vertisol-like upper Lawrence and Snyderville paleosols and the non-Vertisol-like basal Rakes Creek paleosol appear to be due to climate change, particularly a shift from more seasonal to more uniform rainfall. This climate change hypothesis is compatible with overall Virgilian stratigraphic trends in the northern Midcontinent outcrop area

Contribution to geomorphological and hydrogeological study of karst in Mediterranean environment: the Aït Abdi plateau (central limestone High Atlas, Maroc),PhD thesis, 1995,
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Perritaz, L.

The Ait Abdi karstic plateau is located in the heart of the calcareous High Atlas (32°N/6°W). With an area of 160 km2, it is situated between 2,200 and 3,000 meters above sea level, i.e. 800 meters above the nearest valleys and canyons. It consists of a large series of massive Bajocian limestones which form a large brachysyncline, the axial plane of which dips gently to the NE. These limestones overlie a thick series of Toarcian-Aalenian detritic sediments forming the regional aquiclude and the top of the half captive Middle Liasic aquifer. The plateau is limited both in the N and S by strong changes in dip to the vertical of the sedimentary layers (ejective thrusted anticlines), and in the W and E by deep canyons created by major rivers. Therefore the plateau is a totally isolated calcareous compartment, from both a morphologic and a hydrogeologic point of view.
The climate of this region is Mediterranean with an altitude modification: maximum rainfall occurs in winter and in spring, snow cover is not durable but sometimes important, storms are common for dry season in summer. The precipitations comprise only 500 to 700 mm/year (subhumide zone) and the effective evapotranspiration is approximately 400 mm/year, including the losses due to sublimation. The snow coefficient is 60 %. This means that the recharge of the aquifer, occurring almost entirely during snow melting, is limited, but the large bare surfaces of the plateau with typical well developed karst forms (dolines, poljes, dry valleys, holes) improve the infiltration rate (40%). The specific discharge is only 8.1 L/s/km2.
The morphologic peculiarity of this nival karst consist of a succession of small parallel and asymmetric dry valleys forming some "waves". For that reason, the French geomorphologist Couvreur termed these climate controlled features "karst en vagues". The role of wind and snow in the genesis of these forms is predominant. The most of time structure controlled plateau's poljes are quasi inactive today. All kinds of high mountain karren landforms are present on the plateau and prove the great role of snow role in the microforms genesis.
An ancient speleological network with vertical shafts occluded lower down suggest of ancient more humid climatic conditions. U-Th dating indicates ages between 3,200 and 220,000 years, or outside the range of the method (more than 400,000 years). The lateral flow is conducted by an interstrata network, inactive and dry in the upper part, or active and phreatic at the base, near the regional aquiclude, attesting three karstification phases.
The water discharges as typically karstic hillfoot springs, most of the time oversaturated and forming tufas. Large doleritic vertical dykes cut the plateau and form major drainpipes. The physical-chemical and chemical signature of these spring waters is quite different of the signature of other springs of this area, which discharge whether from small local Toarcian-Aalenian aquifers or from the huge semi confined karstic Middle Liasic aquifer. The plateau springs hydrodynamic response is characteristic for an elevated karstic aquifer with rapid flow. The aquifer geometry does not allow important reserves, but the mean discharge from all perennial springs (about 1 m3/s) is a precious resource for the population of this far area of the Atlas Mountains.

Le karst en vagues des At Abdi (Haut-Atlas central, Maroc), 1996,
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Perritaz, L.
The At Abdi plateau (2200-3000 m, 160 km2) is located in the calcareous High Atlas (32? N). It consists of massive Bajocian limestones, which form a large brachysyncline and overlie the clastic Toarcian-Aalenian forming the regional aquiclude and the top of the half captive Middle Liassic aquifer. The rainfall comprises only 500 to 700 mm/yr and the effective evapotranspiration is about 400 mm/yr with a snow coefficient of 60 % and an infiltration rate of 40 %. This means that the recharge of the aquifer mainly occurs during snow melting. The morphology of this nival karst consists in a succession of little parallel and asymmetric dry valleys forming some "waves" ("karst en vagues"). The role of wind and snow in the genesis of these forms is predominant. An old cave system with vertical shafts occluded lower down is proof of ancient more humid climatic conditions. U-Th dating methods on speleothems indicate ages between 3,200 and 220,000 yrs, or more than 400,000 yrs. The horizontal transfer is made by an interstrata network, ancient and dry in the upper part, or recent and phreatic at the base, near the regional aquiclude, attesting three karstification phases.

The Hawaiian cave planthoppers (Homoptera: Fulgoroidea: Cixiidae); A model for rapid subterranean speciation?, 1997,
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Hoch Hannelore
After the successful colonization of a single ancestral species in the Hawaiian Islands, planthoppers of the cixiid genus Oliarus underwent intensive adaptive radiation resulting in 80 described endemic species. Oliarus habitats range from montaneous rain forests to dry coastal biotopes and subterranean environments. At least 7 independant evolutionary lines represented by different species have adapted to lava tubes on Molokai (1), Maui (3), and Hawaii Island (3). Behavioral and morphological studies on one of these evolutionary lines on Hawaii Island, the blind, flight- and pigmentless Oliarus polyphentus have provided evidence for reproductive isolation between allopatric populations which may in fact be separate species. Significant differences in song parameters were observed even between populations from neighbouring lava tubes, although the planthoppers are capable of underground migration through the voids and cracks of the mesocavernous rock system which is extant in young basalt: after a little more than 20 years, lava tubes within the Mauna Ulu 1974 flow had been colonized by O. 'polyphenius" individuals, most probably originating from a near-by forestkipuka. Amazingly, this species complex is found on the youngest of the Hawaiian Islands, with probably less than 0.5 m.y., which suggests rapid speciation processes. Field observations have led to the development of a hypothesis to match underground speciation with the dynamics of vegetational succession on the surface of active volcanoes. Planthopper range partitioning and geographic separation of populations by young lava flows, founder events and small population size may be important factors involved in rapid divergence.

Ground-water silicifications in the calcareous facies of the Tertiary piedmont deposits of the Atlas Mountain (Hamada du Guir, Morocco), 1997,
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Thiry M. , Benbrahim M. ,
The Tertiary piedmont deposits (Hamada Formations), on the southern edge of the Haut-Atlas mountains, form extensive tablelands in the Boudenib area. They consist of two main sedimentary sequences, the Hamada de Boudenib and the Hamada du Guir, of Eocene and Miocene age. Both sequences show elastic facies at their base (conglomerates, calcareous sandstones, silty clays) and end with thick lacustrine limestones and pedogenic calcretes are characterised by rather confined facies, palygorskite-rich, with some gypsum in the second sequence. The recent evolution of the region is marked by the dissection of the tableland that is lined with high cliffs. The water flaw is mainly through wide karst features as there is no major river on the tableland. Silicifications which affect the different facies, form pods of various shape and size, and show an erratic spatial distribution. In the calcareous sandstones, there are irregularly shaped tubules of about 5 cm in diameter, more planar bodies from 5 to 50 cm thick, which frequently display voids lined with translucent silica concretions. The conglomerates display relatively few silicifications, the more characteristic ones consist of a silica cortex on some Limestone pebble and silica plates fitting closely the base of the pebbles. The lacustrine limestones and the calcretes from the upper part of the formation show frequently well developed silicifications. These show very variable shapes; horizontally stretching layers, interconnected or isolated amoeba-like bodies, thin slabs, karst micro-breccia, with frequent concretionnary structures, and quartz crystallisations. Limestone nodules remain often included in these silicifications. The more argillaceous facies display either small tubules or thin plates formed of translucent concretionnary silica. As a rule, the importance of the voids and related structures (concretions, drusy crystals) has to be noticed in all these silicifications, sometimes they are also linked with fractures or karst pipes. Petrography of the silica minerals, their relation with the primary structures. their distribution and their succession, give invaluable information on the silicification processes. Microcrystalline and fibrous quartz are the most common silica minerals, including minor amounts of opal and euhedral quartz. But micrographic arrangements show clearly that primary opal deposits have been more extensive and have recrystallized into chalcedony, microcrystalline quartz, or even ''flame-like'' quartz. Silica deposits in voids make up an important part of the silica pods. The tubules and thin plates of translucent silica of the argillaceous facies are formed of laminar chalcedony deposited around voids. Silica deposits in voids are also particularly obvious in the sandstones. The pores between the quartz grains are then cemented by fibrous quartz and little opal. Some samples show very large cemented voids that cannot be related to the primary porosity of the sandstone. These large voids correspond to the dissolution of the primary calcareous cement, which even led to the collapse of the sandstone fabric. In the limestones, there are silicified micro-karst breccia with a very high primary porosity cemented by quartz crystals, and even in the large microcrystalline quartz zones there are numerous void fillings, the primary porosity often exceeding 50%. There is obviously the alternation of silica deposits and calcite dissolution. Beside the void filling, silicifications comprise also matrix epigenesis, that is replacement of the carbonate by silica with preservation of most of the limestone structures, without development of voids. Nevertheless, the epigenesis of the limestone matrix is restricted to the vicinity of the voids. The silicifications relate to diagenetic processes. The main part of the silica is formed of void deposits and matrix replacement (epigenesis) on the edge of the voids. These void deposits give evidence of the feeding solutions. The regularity of the deposits all around the voids point out to a hydrologic regime characterised by a ground-water our now. Silica originates most probably from alteration of the magnesian clay minerals along the ground-water path. Regarding the low solubility of silica in surficial waters, high flows are needed in order to renew continuously the silica precipitated from solution. This points to a relatively humid climate at time of silicification, and to relief and incised landscapes to bring about these high flows

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