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 Horton number is expresses the relative intensity of erosion process in a drainage basin [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.
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 rule (Keyword) returned 45 results for the whole karstbase:
Showing 1 to 15 of 45
The ecological classification of cave and fissure water in the underground water habitats., 1967, Husmann Siegfried
Bodies of waters in caves and in crevices of rocks are distinguished from the other subsoil water ecosystems ("eustygon", "stygorhithron", "stygopotamon") under the names "troglostygon" and "petrostygon". The colonisation of subsoil water biotopes involves a fundamental principle which controls the development of the main biotopes for the stygobiont undergroundwater organisms. According to this ecological rule, which is described in detail and formulated, the several interstitial biotopes (for example "eustygopsammal," "rhithrostygopsammal," "potamostygopsephal") are to be considered as the real biotopes of the stygobiont subsoil water organisms; waters in caves, on the contrary, are secondary biotopes of these animals. Caves which contain marine water are described as ecostystem "Thalassotroglon" in their relation to "limnotroglon" (= "stygotroglon"). In this why the contact between "limnospeology" and "thalassospeology" is established, and the limnic and marine microcavernal biotopes; "thalassopsammal" and "thalassopsephal"; are also taken in consideration. "Limnospeology" and "thalassospeology" as limnological and thalassological investigations of subsoil water are characterized as biological fields of work, which serve for the investigation of an ecological unit.

The ecological classification of cave and fissure water in the underground water habitats., 1967, Husmann Siegfried
Bodies of waters in caves and in crevices of rocks are distinguished from the other subsoil water ecosystems ("eustygon", "stygorhithron", "stygopotamon") under the names "troglostygon" and "petrostygon". The colonisation of subsoil water biotopes involves a fundamental principle which controls the development of the main biotopes for the stygobiont undergroundwater organisms. According to this ecological rule, which is described in detail and formulated, the several interstitial biotopes (for example "eustygopsammal," "rhithrostygopsammal," "potamostygopsephal") are to be considered as the real biotopes of the stygobiont subsoil water organisms; waters in caves, on the contrary, are secondary biotopes of these animals. Caves which contain marine water are described as ecostystem "Thalassotroglon" in their relation to "limnotroglon" (= "stygotroglon"). In this why the contact between "limnospeology" and "thalassospeology" is established, and the limnic and marine microcavernal biotopes; "thalassopsammal" and "thalassopsephal"; are also taken in consideration. "Limnospeology" and "thalassospeology" as limnological and thalassological investigations of subsoil water are characterized as biological fields of work, which serve for the investigation of an ecological unit.

Caves of Vakuta, Trobriand Islands, Papua, 1969, Ollier C. D. , Holdsworth D. K

In a previous paper (1968a) we described caves of Kiriwina, the largest of the Trobriand Islands, a group of coral islands situated 100 miles off the north-east coast of Papua. This paper records caves of Vakuta, a smaller island south of Kiriwina. Vakuta is shaped like a boomerang (Figure 1) and is separated from the southern tip of Kiriwina by Kasilamaka Passage, about half a mile wide. The area of Vakuta Island is approximately 11 square miles. The island contains three villages, the most important being Vakuta Village which has a Methodist (now United Church) Mission. A track links Vakuta Village to Kasilamaka Passage which can be crossed by native canoe; the track continues on Kiriwina to Losuia, 40 miles north. Vakuta Island has a population of about 500. The Vakutans are of the same mixed Melanesian-Polynesian stock as the people of Kiriwina. Woodcarving is not practised to the same extent as in Kiriwina and the quality is generally low. However, some canoes have particularly well decorated prows. The influence of the Mission is very evident in the dress of the Vakutans and in the village, old cast-off clothing, often quite dirty, is the rule. In the fields the women wear grass and fibre skirts though the men were not seen to wear a pubic leaf as usual in Kiriwina, but shorts. Papuan Airlines operate a weekly flight between Port Moresby and Losuia, the Administration Centre, using Skyvan aircraft. Weekend tourist charter flights in DC-3 aircraft arrive frequently, but irregularly, from Port Moresby and occasionally from Lae and Rabual. The authors visited Vakuta Island in December, 1968. Guides were recruited locally and we were fortunate to be assisted by Mr. Gilbert Heers, the only European resident of the island, who speaks fluent Kiriwini which made communication with our guides relatively easy. With his help, we were able to obtain accounts of the legends and traditions associated with the caves on the island. We have also had valuable discussions about Vakuta and the customs and legends of the Trobriand Islands with Mr. Lepani Watson, M.H.A., who was born on Vakuta, and Mr. John Kasaipwalova, a Trobriand Islander now studying at the University of Queensland. We are most grateful for the assistance of these people. Although the most accurate map of the Trobriands is an Admiralty chart, the authors used an old U.S. Army map which was based on a pre-war Government survey. The caves were roughly surveyed using 100 ft tape, prismatic compass and abney level. The village rest-house became the social centre of the village during our stay. We had no difficulty in finding food. A surprising variety of foods such as yams, sweet potato, eggs, pineapples, soursop, tomatoes and fresh coconut appeared and payment was accepted eagerly in stick tobacco and newspaper. Payment in cash was rarely appreciated, though it will become more useful now that a trade store has been established by the Village Co-operative. To avoid repetitive explanations of features in the accounts of individual caves, various general topics will be discussed first.


Caves of Kitava and Tuma, Trobriand Islands, 1971, Ollier C. D. , Holdsworth D. K. , Heers G.

The Trobriand group of coral islands is situated a hundred miles off the north-east coast of Papua and north of the D 'Entr'ecasteaux Islands. In previous papers we have described caves on Kiriwina (the main island), Vakuta and Kitava (see References). We now describe caves of Kaileuna and Tuma (see Figures l and 2). In August 1970, we spent one week of intensive search for caves on these two islands, making our headquarters in the copra store in the village of Kadawaga. Kaileuna island is six miles long and almost four miles wide, and supports a population of 1,079 (1969 Census). It is separated from the large island of Kiriwina by a channel two miles wide between Mamamada Point and Boll Point, though the main village of Kadawaga on the west coast of Kaileuna is 18 miles from Losuia and 14 miles from Kaibola. The island is generally swampy in the centre with a rim of uplifted coral around the edge. We were assured that the correct name of the island is Laileula, but since Kaileuna is used on all previous maps it is retained here. However, we prefer Kadawaga to the Kudawaga or Kaduwaga that appear on some maps. The inhabitants are of mixed Melanesian-Polynesian Stock, who are almost totally self-supporting, being in the main farmers and fishermen. The yam (taitu) constitutes the staple crop and the harvest is still gathered in with ceremonies unchanged for centuries. There is great competition among families for the quantity and quality of the crop, which is displayed firstly in garden arbours (kalimonio), later in the village outside the houses; traditionally styled yam huts (bwaima) are then constructed to display the harvest until the next season. The transfer of yams from the garden to the village is occasion for a long procession of gatherers to parade through the village blowing conch shells and chanting traditional airs (sawili) to attract the attention of villagers to the harvesting party, After storage of the harvest, a period of dancing and feasting (milamala) continues for a month or more, Traditional clothing is the rule, Women and girls wear fibre skirts (doba), most of the men, especially the older ones, wear a pubic leaf (vivia) made from the sepal of the betel nut palm flower (Areca catechu Linn.). Tuma, the northernmost of the main islands in the Trobriand group, is six miles long and less than a mile wide. It is a low ridge of coral with swamps in the centre and along much of the western side. The island has been uninhabited since 1963 when the last few residents abandoned it and moved to Kiriwina, but it is still visited from time to time by other islanders who collect copra and fish. Tuma is believed by all Trobriand Islanders to be inhabited now by the spirits of the dead. It is also generally believed that Tuma is the original home of the TrobIiand ancestors; these ancestors are also said to have emerged at Labai Cave on Kiriwina Island, and from many other places of emergence or 'bwala". Lack of consistency in the legends does not appear to concern the Trobrianders very much. The cave maps in this paper are sketches based mainly on estimated dimensions, with a few actual measurements and compass bearings. Bwabwatu was surveyed more accurately, using a 100 ft steel reinforced tape and prismatic compass throughout.


Developmental chronology and evolution of calcium storage and urate containing cells in Niphargus schellenbergi Karaman., 1975, Graf Franois, Michaut Philippe.
The intra-marsupial development of Niphargus schellenbergi is divided into three phases: within the chorion, embryonic intermoult and juvenile intermoult. The disappearance of the chorion divides the first phase from the second. A double exuviation exists between the last two. The chronology of the embryonic development and of the beginning of post-embryonic development is established. On hatching the juvenile N. schellenbergi has one pair of hepatopancreatic caeca. During the first post-embryonic intermoults the ventral hepatopancreatic caeca, posterior caeca and anterior caecum are formed. The relation between posterior caeca and the aorta is described. The study of calcium storage before moulting showed that calcareous concretions located in posterior caeca and midgut have the typical form, volume, quantity and distribution of the species. This calcium accumulation process occurs in the midgut following the first posternbryonic exuviation. It is only when the sixth exuviation is attained that storage in the posterior caeca is similar to the one in adults. The urate containing cells located at the lower face of the pericardial septum begin to accumulate urate spherules 15 days before hatching. They vary in form, volume, localization and composition, and so may be considered as storage sites for urate, pigments and various ions (P, K, Ca, S, Cl, Na, Mg) which are returned to circulation.

A preliminary note on the spatial distribution of Meta menardi, Triphosa dubitata, Triphosa sabaudiata, Nelima aurantiaca and Culex pipiens within a cave ecosystem (Grotte de la Scierie: Haute-Savoie)., 1976, Bourne John D.
Following 8 months of observations in a richly populated cave, (Grotte de la Scierie, HauteSavoie, France), it has been possible to outline the movements and distribution of Meta menardi (Araneae), Nelima aurantiaca (Opiliones), Triphosa dubitata and Triphosa sabaudiata (Lepidoptera) and Culex pipiens (Diptera) within the cave ecosystem. Although no general rule can be postulated it appears that the morphology of the cave walls and the climatic conditions regulate the distribution of these 5 species within the cave ecosystem. The interactions between the 5 species have been investigated.

Karst in China: Landscapes, Types, Rules, 1985, Lu Y.

Etude statistique des cavits karstiques de la rgion monpelliraine, 1989, Brun, J. F.
Statistic study of karst caves of the Montpellier area - A statistical study of a speleological file concerning the karstic area of Montpellier was undertaken, aiming to detect some factors statistically linked with cave distribution or speleometry. Shafts are generally disconnected from horizontal systems, but they use sometimes pre-existing galleries. They are significantly deeper when grouped, or when presenting parallel shafts, or when being old shaped shafts with a large entrance. Splited zones contain more potholes, yet they are not statistically deeper. Horizontal caves exhibit a discontinuous distribution by altitude levels, which are regularly observed in every sector, when the effect of diastrophism is taken into account. Total filling seems to be the rule as soon as galleries have stopped their activity: use or re-use by present streams is required to avoid this process. Old levels of caves, above Upper Miocene surfaces, exhibit different orientation patterns of galleries than younger ones. Some limestone facies seems to allow a stronger vertical (or horizontal) cave development. A schematic history of cave development in this area is proposed.

STABLE ISOTOPIC COMPOSITION OF METEORIC CALCITES - EVIDENCE FOR EARLY MISSISSIPPIAN CLIMATE-CHANGE IN THE MISSION CANYON FORMATION, MONTANA, 1993, Smith T. M. , Dorobek S. L. ,
The Lower Mississippian Mission Canyon Formation of central to southwestern Montana was deposited under dominantly semiarid to arid climatic conditions during Osagean to early Meramecian times. Following deposition, a pronounced climatic shift to more humid conditions occurred during middle Meramecian times. This climatic change is indicated by extensive, post-depositional karst fabrics and in the stable isotopic composition of early, meteoric calcite cements and diagenetically altered sediments. Early meteoric calcite cement in Mission Canyon limestones is generally nonluminescent and fills intergranular and fenestral porosity. Petrographic data indicate that this cement formed during intermittent subaerial exposure of the Mission Canyon platform during Osagean times. This initial generation of meteoric calcite cement has deltaO-18 values from -8.1 to -2.6 parts per thousand PDB. These data, and the oxygen isotopic values from nonluminescent skeletal grains and micrite in host limestone indicate that Osagean meteoric water may have had deltaO-18 values as low as -6.0 parts per thousand SMOW. A second generation of petrographically similar, but isotopically distinct, calcite cement fills biomolds and porosity within solution-collapse breccias in the Mission Canyon Formation. This cement generation postdates earlier nonluminescent Osagean calcite cement and is volumetrically most abundant near the top of the Mission Canyon Formation. DeltaO-18 values from these cements and from nonluminescent lime mudstone clasts and matrix in solution collapse breccias range from -13.8 to -8.2 parts per thousand PDB. These data indicate that Meramecian meteoric water may have had deltaO-18 values as low as - 12.0 parts per thousand. However, a higher-temperature burial overprint on the deltaO-18 values of the calcite cement cannot be ruled out. The more positive deltaO-18 values of the Osagean calcite components probably indicate warm and arid conditions during short-term [10(4)(?) yr) subaerial exposure along intraformational sequence and parasequence boundaries. The more negative deltaO-18 values from Meramecian calcite components and the extensive karst associated with the post-Mission Canyon unconformity may have developed because of cooler and more humid climatic conditions and possible rain-out effects during middle Meramecian times. A dramatic shift towards cooler and more humid climatic conditions may be coincident with the onset of major continental glaciation in the Early Carboniferous. The post-Mission Canyon unconformity has been attributed to a major fall in sea level that may have glacio-eustatic origins. Growth of continental glaciers during a time of global cooling would have caused migration of polar fronts further toward the paleoequator. These polar fronts in turn, would have pushed moist, mid-latitude weather systems toward the paleoequator, resulting in cooler, more humid conditions in low-latitude settings during ''icehouse'' times

Ground-water silicifications in the calcareous facies of the Tertiary piedmont deposits of the Atlas Mountain (Hamada du Guir, Morocco), 1997, 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

Rapport entre karst et glaciers durant les glaciations dans les valles pralpines du sud des Alpes, 1998, Bini Alfredo, Tognini Paola, Zuccoli Luisa
At least 13 glaciations occurred during the last 2.6Ma in the Southern pre_alpine valleys. The glaciers scouring alpine and pre-alpine valleys had all the same feature, being valley temperated glaciers. Their tracks and feeding areas were always the same, just like the petrological contents of their deposits. Contrary to previous assumptions until a few years ago, the origin of these valleys and of the lakes occupying the floor of some of them (Orta, Maggiore, Como, Iseo, Garda Lakes) is due to fluvial erosion related to Messinian marine regression. The valley slopes modelling is Messinian in age, too, while most caves are older. As a general rule, glaciers worked on valley slopes just as a re_modelling agent, while their effects were greater on valley floors. The karstic evolution began as soon as the area was lifted above sea level (upper Oligocene - lower Miocene), in a palaeogeographical environment quite different from the present one, although the main valley floors were already working as a base level. During Messinian age, the excavation of deep canyons along pre-existing valleys caused a dramatic lowering of the base level, followed by a complete re-arrangement of the karstic networks, which got deeper and deeper. The Pliocene marine transgression caused a new re-arrangement, the karst network getting mostly drowned under sea level. During these periods, the climate was hot-wet tropical, characterised by a great amount of water circulating during the wet season. At the same time tectonic upliftings were at work, causing breaking up of the karst networks and a continuous rearrangement of the underground drainage system. In any case, karstic networks were already well developed long before the beginning of Plio-Quaternary glaciations. During glaciations, karst systems in pre-alpine valleys could have been submitted to different drainage conditions, being: a) isolated, without any glacial water flowing; b) flooded, connected to the glacier water-filled zone; c) active, scoured by a stream sinking at glacier sides or in a sub glacial position. The stream could flow to the flooded zone (b), or scour all the unflooded system long down to the resurgence zone, the latter being generally located in a sub glacier position. The glacier/karst system is a very dynamic one: it could get active, flooded or isolated depending on endo- and sub-glacial drainage variations. Furthermore, glaciers show different influences on karstic networks, thus working with a different effect during their advance, fluctuations, covering and recession phases. Many authors believe, or believed, the development of most surface and underground karst in the Alps is due to glaciations, with the last one held to be mostly responsible for this. Whatever the role of glaciers on karstic systems, in pre-alpine valleys caves, we do not have evidence either of development of new caves or of remarkable changes in their features during glaciations. It is of course possible some pits or galleries could have developed during Plio-Quaternary glaciations, but as a general rule glaciers do not seem to have affected karstic systems in the Southern pre-alpine valleys with any remarkable speleogenetic effects: the glaciers effects on them is generally restricted to the transport of great amounts of debris and sediments into caves. The spotting of boulders and pebbles trapped between roof stalactites shows that several phases of in- and out-filling of galleries occurred with no remarkable changing in pre-dating features, including cave decorations. The presence of suspended karst systems does not prove a glacial origin of the valleys, since most of them pre-date any Plio-Quaternary glaciation, as shown by calcite cave deposits older than 1,5Ma. The sediments driven into caves might have caused a partial or total occlusion of most galleries, with a remarkable re-arrangement of the underground drainage system. In caves submitted to periglacial conditions all glaciations long, we can find deposits coming from weathered surface sediments, sharp-edged gelifraction debris and, more rarely, alluvial deposits whose origin is not related to the circulation of the glacial meltwater. In caves lower than or close to the glaciers limit we generally find large amounts of glacier-related deposits, often partly or totally occluding cave galleries. These sediments may be directly related to glaciers, i.e. carried into caves by glacial meltwaters, resulting from surface glacial deposit erosion. They generally show 3 dominant facies: A) lacustrine deposits; B) alluvial deposits and C) debris flow deposits facies. The only way of testing the soundness of the forementioned hypothesis is to study the main characters and spreading of cave sediments, since they are the only real data on connection of glaciers to endokarst networks.

Mapping Chicxulub crater structure with gravity and seismic reflection data, 1998, Hildebrand A. R. , Pilkington M. , Ortizaleman C. , Chavez R. E. , Urrutiafucugauchi J. , Connors M. , Granielcastro E. , Camarazi A. , Halpenny J. F. , Niehaus D. ,
Aside from its significance in establishing the impact-mass extinction paradigm, the Chicxulub crater will probably come to exemplify the structure of large complex craters. Much of Chicxulub's structure may be mapped' by tying its gravity expression to seismic-reflection profiles revealing an [~]180 km diameter for the now-buried crater. The distribution of karst topography aids in outlining the peripheral crater structure as also revealed by the horizontal gradient of the gravity anomaly. The fracturing inferred to control groundwater flow is apparently related to subsidence of the crater fill. Modelling the crater's gravity expression based on a schematic structural model reveals that the crater fill is also responsible for the majority of the negative anomaly. The crater's melt sheet and central structural uplift are the other significant contributors to its gravity expression. The Chicxulub impact released [~]1.2 x 1031 ergs based on the observed collapsed disruption cavity of [~]86 km diameter reconstructed to an apparent disruption cavity (Dad) of [~]94 km diameter (equivalent to the excavation cavity) and an apparent transient cavity (Dat) of [~]80 km diameter. This impact energy, together with the observed [~]2 x 1011 g global Ir fluence in the Cretaceous-Tertiary (K-T) fireball layer indicates that the impactor was a comet estimated as massing [~]1.8 x 1018 g of [~]16.5 km diameter assuming a 0.6 gcm-3 density. Dust-induced darkness and cold, wind, giant waves, thermal pulses from the impact fireball and re-entering ejecta, acid rain, ozone-layer depletion, cooling from stratospheric aerosols, H2O greenhouse, CO2 greenhouse, poisons and mutagens, and oscillatory climate have been proposed as deleterious environmental effects of the Chicxulub impact with durations ranging from a few minutes to a million years. This succession of effects defines a temperature curve that is characteristic of large impacts. Although some patterns may be recognized in the K-T extinctions, and the survivorship rules changed across the boundary, relating specific environmental effects to species' extinctions is not yet possible. Geochemical records across the boundary support the occurrence a prompt thermal pulse, acid rain and a [~]5000 year-long greenhouse. The period of extinctions seems to extend into the earliest Tertiary

Land use in the karstic lands in the Mediterranean region, 1999, Atalay Ibrahim
Karstic lands have special importance in terms of soil formation and land-use. Soil appears only on the flat and slightly undulating karstic lands, while soils are found along the cracks and bedding surfaces between the layers on the hilly karst areas although these lands are rocky in appearance. Karstic lands in the hilly area are not conducive to cultivation. But rocky areas create a favourable habitat for the growth of forests except in an arid climate. Because the tree roots easily follow and develop along the cracks in the limestone. As a general rule soil erosion does not occur on sub-horizontal karst surfaces due to the fact that atmospheric waters easily infiltrate along the cracks. Natural generation of vegetation like the maquis-type occurs via the root suckers, but coniferous trees such as cedar, fir, pine through seed dispersal. The clearance of natural vegetation on the karstic lands leads to the formation of bare lands. That is why the slopes of the limestone hillsides have been converted into bare and/or rocky terrains in places where natural vegetation has been completely destroyed.

The Makapansgat Australopithecine site from a speleological perspective, 1999, Latham Alf G. , Herries Andrew, Quinney Patrick, Sinclair Anthony, Kuykendall Kevin,
Remains of Australopithecus africanus from the Limeworks Cave, Makapansgat, South Africa, are believed to belong mainly to a metre-thick, bone-rich, speleothem layer. The flowstone is one stratum among a sequence of speleothems, muds, silts, sands and fine and coarse breccias, the study of which has evoked some disagreement. The limeworkers' excavations revealed some stratigraphic relationships but they have obscured others. Partly because of this, controversy surrounds the supposition about whether there are separated depositional basins within the overall site and, if so, whether strata can be securely correlated. This is important because a reconstruction of an overall stratigraphic sequence was used as a basis for a magnetostratigraphic reversal record and by which the site has been tentatively dated. There is qualification and disagreement about the origin of the various flowstones and the actual depositional environment of the muds and silts. Evidence is presented which rules out some previous interpretations. From the point of view of the Australopithecine fossils themselves, it can be said that the calcite matrix in which they were provenanced was a low-energy environment and that the dense bone accumulation of this layer almost certainly did not arise by the action of floods, as previously supposed. The most likely main cause of the dense accumulation was hyena denning activity. It is clear that further work is needed to see how a reliable overall sequence can be established and that closer sampling is required for magnetostratigraphy

Radon concentration changes in the air of two caves in Poland, 1999, Przylibski T. A. ,
The paper presents spatial and seasonal radon concentration changes in the air of two caves in Poland on the basis of measurements during 1995-1997. A process of seasonal radon concentration changes in the caves' air was identified, based on research on radon occurrence in caves carried out for over 20 years. A major role in this process was ascribed to ventilation caused by atmospheric temperature changes. High radon concentrations are observed in the warm half-year (May-August), when the average air temperature exceeds the average temperature of the cave interior. Low concentrations occur, however, in the cold half-year (December-January), and a relatively sharp increase or decrease in radon concentration is related to changes in atmospheric temperatures relative to the average temperature in the cave interior. The amplitude of these radon concentration changes may reach several kBq m(-3). In the Radochowska Cave the lowest monthly radon concentration (0.06 kBq m(-3)) was recorded in December 1996, while the highest (1.37 kBq m(-3)) was observed in August 1996. In the Niedzwiedzia Cave the lowest value (0.10 kBq m(-3)) was observed in January 1997 and the highest (4.18 kBq m(-3)) was noted in March 1997. The spatial variation of radon concentrations is mainly due to the morphology of the chambers and corridors of a cave, and by the distance between the measurement point and the entrance holes. As a rule, locations further from the entrance have poorer ventilation and higher radon concentrations. (C) 1999 Elsevier Science Ltd. All rights reserved

Results 1 to 15 of 45
You probably didn't submit anything to search for