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Enviroscan Ukrainian Institute of Speleology and Karstology


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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 subsidence is lowering of the surface of the ground because of removal of support. caused in karst areas by subterranean solution or collapse of caves [10].?

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


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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.
See all featured articles
Featured articles from other Geoscience Journals
Karst environment, Culver D.C.
Mushroom Speleothems: Stromatolites That Formed in the Absence of Phototrophs, Bontognali, Tomaso R.R.; D’Angeli Ilenia M.; Tisato, Nicola; Vasconcelos, Crisogono; Bernasconi, Stefano M.; Gonzales, Esteban R. G.; De Waele, Jo
Calculating flux to predict future cave radon concentrations, Rowberry, Matt; Marti, Xavi; Frontera, Carlos; Van De Wiel, Marco; Briestensky, Milos
Microbial mediation of complex subterranean mineral structures, Tirato, Nicola; Torriano, Stefano F.F;, Monteux, Sylvain; Sauro, Francesco; De Waele, Jo; Lavagna, Maria Luisa; D’Angeli, Ilenia Maria; Chailloux, Daniel; Renda, Michel; Eglinton, Timothy I.; Bontognali, Tomaso Renzo Rezio
Evidence of a plate-wide tectonic pressure pulse provided by extensometric monitoring in the Balkan Mountains (Bulgaria), Briestensky, Milos; Rowberry, Matt; Stemberk, Josef; Stefanov, Petar; Vozar, Jozef; Sebela, Stanka; Petro, Lubomir; Bella, Pavel; Gaal, Ludovit; Ormukov, Cholponbek;
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Your search for overlap (Keyword) returned 32 results for the whole karstbase:
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Hydrogologie karstique des Alpes-Maritimes, 1984,
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Baissas, P.
Karst hydrogeology in the Alpes-Maritimes - In the Marguareis, the systems penetrate very quickly by transverse faults, to reach the impermeable basement and then follow the dip. All the waters, even those on the French side, belong to the P basin. In the Roya arc, underflows are to be found going round the base of the Argentera-Mercantour. In the Nice arc, the karstification depends principally on tectonic factors and according to the places, the water follows either the overlaps or transverse faults. In the Grasse plateaus, the galleries follow at the outset the slopes and the dips of the synclinal hinges; the tectonic factors determine the location of the resurgences ; at depth, the karst is always phreatic, with relations between tectonic compartments during floods. In the cover of the Tanneron-Esterel basement and Barrot Dome, lithological factors determine flow.

Hydrogologie karstique du polj d'lrmene, Bodrum (Turquie), 1985,
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Canik, B.
KARSTIC HYDROGEOLOGY OF THE IRMENE POLJE - BODRUM (TURKEY) - The Irmene polje (25 km2) is located in the Bodrum peninsula, Turkey. The formation exposed, are coloured argilaceous schists, blackish shales and sandstones of a paleozoic age. They are overlapped by unconformable carbonate formations of Early Triassic to Late Jurassic. The karstification is mostly developed on the non-dolomitic parts of the fissured limestones. The groundwater flow is generally northwards, towards coastal or submarine springs. Thus, it is calculated that a discharge of about 40 l/s can be obtained from possible wells to supply water for the Irmene village. We propose to increase the infiltration rate within the karstic aquifer by building barriers, which would favour runoff towards natural wells or sinks not active for the moment.

Etude d'un chevauchement dans les gouffres du Calernam et des Baoudillouns (Cipires, Alpes-Maritimes), 1991,
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Gilli, E.
Study of a trust plane in the Baoudillouns and Calernam Caves (Alpes Maritimes, France) - The shafts of Calernam and Baoudillouns are to be found in the Prealps of Grasse (Alpes-Maritimes). They are formed in inclined and over-lap folds, issued from the southward sliding of the sedimentary cover during the alpine orogeny. The cave studied here is the only example to date of a cave that totally crosses a tectonic slice and permits the observation of the thrust plane. Through this study, it can be observed that the bottom of the limestone series has been entirely planed and that abnormal contact (mechanical unconformity) resembles in most cases a normal one. No obvious neotectonic sign has been observed for the moment.

Le palokarst littoral de Provence (Estaque, Calanques et zone de Bandol), 1993,
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Blanc, J. J.
The general features of coastal paleokarst in Provence are describes: suspended gallery sections and drain-pipes cut across by fracturations or fault reactivation. The types of deformations and breaking observed are tilting, stalactite fall, extension fault sealing, reactivation and speleothem shearing, coastal wall and karstic cleft collapse as well as network deformation. The influence of structural environment is represented by overlapping strata, coastal faults and crossed-fault systems. Emphasis has been laid on the tectonic inheritance as well as the geodynamic context. To conclude, the importance of provenal-ligurian rifting mechanisms and the transition to faulted and distorted margin is underlined.

Life cycle and population ecology of the cave cricket Dolichopoda geniculata (Costa) from Valmarino cave (Central Italy), 1994,
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Carchini Gianmaria, Rampini Mauro, Sbordoni Valerio
A D. geniculata population inhabiting a natural cave at low altitude near seashore was followed during two years. The population size, distribution in three age classes, spatial distribution, feeding habits were recorded. The life-cycle was found semivoltine, with overlaps between next choorts in each age class. A comparison to other Dolichopoda showed that the population of Valmarino cave is one of the best adapted to cave life, and this may be related with both historical and present geographical and ecological conditions of the cave.

Some remarks on the genus Microcharon Karaman in Greece, and description of M. agripensis n. sp. (Crustacea, Isopoda, Microparasellidae), 1994,
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De Laurentiis Paola, Galassi Diana M. P. , Pesce Giuseppe L.
Several samples of microparasellid isopods of the genus Microcharon Karaman were obtained in groundwater habitats of Greece. Four species are identified, and taxonomical and zoogeographical remarks on some rare or poorly known taxa are made. One species, herein described as Microcharon agripensis n. sp., is new to Science. M. latus prespensis Karaman, 1954, on account of the different morphology of the first and second male pleopods, and its partially overlapping distribution, in respect to M. latus Karaman, 1934, is definitively raised at specific rank. Supplementary descriptions and illustrations are reported for incompletely described species such as M. latus, M. prespensis stat. nov., M. major Karaman, 1954 and M. othrys Argano & Pesce, 1979. For some species, such as M. latus, M. othrys and M. antonellae Galassi, 1991, SEM preparations of the mouthparts, not well detailed with the optical microscopy, were carried out. According to data from the present study, a paleogeographical scenario of the Balkan Peninsula is briefly depicted in order to sketch the most significative events which led to the colonization and speciation of the Microcharon species in this area.

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

Hydrogeological investigations in northwestern Yucatan, Mexico, using resistivity surveys, 1996,
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Steinich B. , Marin L. E. ,
Eight Schlumberger soundings and four Wenner anisotropy measurements were conducted in the northwestern section of the Yucatan Peninsula for hydrogeological investigations of a karst aquifer. This system is influenced by a circular high permeability zone (Ring of Cenotes) probably related to the Chicxulub Impact Crater. Schlumberger soundings and Wenner anisotropy measurements show that the karst aquifer can be modeled as an electrically anisotropic medium. Anisotropy is related to preferential permeability directions channeling ground-water flow within the aquifer. Directions of maximum permeability were determined using Wenner anisotropy measurements. Electrical soundings were conducted at different sites near the Ring of Cenotes. Resistivity values decrease toward the Ring of Cenotes supporting the hypothesis that selected segments of the Ring have high permeability. Several soundings were conducted in order to study lateral permeability variations along the Ring. A high permeability section can be identified by low resistivity models and is related to a zone of high cenote density. A low permeability section of the Ring was found showing high resistivity models. This zone overlaps with an area of low cenote density. Electrical soundings were used to determine the depth of the fresh-water lens; the interface was detected along two profiles perpendicular and parallel to the Ring of Cenotes resulting in a depth that ranged from 18 m near the coast up to 110 m in the southeastern part of the study area. The predicted depths of the interface using electrical methods showed a good correlation with Ghyben-Herzberg and measured interface depths at some sites. Discrepancies between calculated and interpreted interface depths at two sites may be explained by horizontal-to-vertical permeability anisotropy

Evaporite karst of northern lower Michigan, 1997,
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Black Tj,
Michigan has three main zones of evaporite karst: collapse breccia in Late Silurian deposits of the Mackinac Straits region; breccia, collapse sinks, and mega-block collapse in Middle Devonian deposits of Northern Lower Michigan, which overlaps the preceding area; and areas of soil swallows in sinks of Mississippian deposits between Turner and Alabaster in Arenac and Iosco counties, and near Grand Rapids in Kent County. The author has focused his study on evaporite karst of the Middle Devonian deposits. The Middle Devonian deposits are the Detroit River Group: a series consisting of limestone, dolomite, shale, salt, gypsum and anhydrite. The group occurs from subcrop, near the surface, to nearly 1400 feet deep from the northern tip of the Southern Peninsula to the south edge of the ''solution front'' Glacial drift is from zero to 350 feet thick. Oil and gas exploration has encountered some significant lost-circulation zones throughout the area. Drilling without fluid returns, casing seal failures, and lost holes are strong risks in some parts of the region. Lost fluid returns near the top of the group in nearby areas indicate some karst development shortly after deposition. Large and irregular lost-circulation zones, linear and patch trends of large sink holes, and 0.25 mile wide blocks of down-dropped land in the northern Lower Peninsula of Michigan were caused by surface- and ground-water movement along faults into the Detroit River Group. Glaciation has removed some evidence of the karst area at the surface. Sinkhole development, collapse valleys, and swallows developed since retreat of the glacier reveal an active solution front in the Detroit River Group

Remplissages karstiques tectoniss de la rgion de Marseille, 1999,
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Monteau, Raymond
The paleokarst fillings in the Riou and Frioul archipelagoes, the coastal ranges of MarseiIleveyre (Calanques) Notre Dame de la Garde (the Bay of Marseille) show several examples of various tectonic mechanisms due to compressive stresses. A chronology of the various phases is described: compartment process, overlapping, tilting. These deformations and the several after-episodes observed can be dated between the Lower Eocene and the Upper Pleistocene, but it is still difficult to give a more precise date. The tertiary fillings show the action of local decompression and tilting in some cases. In the detailed study of the karstic lithified deposits two kinds of tectonised sequences are shown in connection with the local tectonics.

Diagenetic History of Pipe Creek Jr. Reef, Silurian, North-Central Indiana, U.S.A, 2000,
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Simo J. A. , Lehmann Patrick J. ,
Calcite cements in the Silurian (Ludlovian) Pipe Creek Jr. Reef, north-central Indiana, are compositionally zoned with characteristic minor-element concentrations and stable-isotope signatures, and were precipitated in different diagenetic environments. Superposition and crosscutting relationships allow us to group cement zones and to relate them to the sequence stratigraphic evolution of the reef. Pipe Creek Jr. Reef grew in normal marine waters, with the reef top high (greater than 50 m) above the platform floor. Flank facies are volumetrically important and are preserved largely as limestone, in contrast to most dolomitized Silurian reefs in the midcontinent. Syndepositional marine cements fill primary porosity and synsedimentary fractures and are interlayered with marine internal sediment. Now low-magnesium calcite, their isotopic compositions are similar to those of depositional grains and cements estimated to have precipitated from Ludlovian sea waters. Depositional porosity was reduced by 75% by the precipitation of these syndepositional cements, which stabilized the steeply dipping flank slope. Postdepositional, clear calcite cements are interpreted as shallow-phreatic and burial cements on the basis of their relationship to periods of karstification and fracturing. Shallow-phreatic cements, with concentric cathodoluminescent (CL) zonation, precipitated in primary pores and are postdated by fractures and caves filled with Middle Devonian sandstone. CL zonal boundaries are sharp, and some, near a major stratigraphic unconformity, show evidence of dissolution. The volumetric abundance of the individual CL zones varies in the reef, indicating a complex superposition of waters of varying chemistry and rock-water interaction that are probably related to relative sea-level changes. This important aspect of the reef stratigraphy is recorded only by the diagenetic succession, because evidence of earlier sea-level changes is removed by a major later regional unconformity. Burial cements are the youngest diagenetic feature recognized, and they rest conformably or unconformably over older cements. They exhibit both concentric CL zonation and sectoral zoning, they are ferroan to nonferroan, and they contain thin sulfide zones along growth-band boundaries. Their isotopic compositions do not overlap with shallow-phreatic or marine cement values. Degraded oil postdates burial cements, and is composed of the same sterane class as the Devonian-age Antrim Shale, the probable source rock. This source contrasts with that of reef reservoirs in the Michigan Basin, where Silurian strata are commonly the hydrocarbon source

Dolomitization and Dolomite Neomorphism: Trenton and Black River Limestones (Middle Ordovician) Northern Indiana, U.S.A, 2000,
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Yoo Chan Min, Gregg Jay M. , Shelton Kevin L. ,
The Trenton and Black River Limestones are dolomitized extensively along the axis of the Kankakee Arch in Indiana, with the proportion of dolomite decreasing to the south and southeast of the arch. Planar and nonplanar dolomite replacement textures and rhombic (type 1) and saddle (type 2) void-filling dolomite cements are present. Three stages of dolomitization, involving different fluids, are inferred on the basis of petrographic and geochemical characteristics of the dolomites. Nonferroan planar dolomite has relatively high {delta}18O values (-1.8 to -6.1{per thousand} PDB) and has 87Sr/86Sr ratios (0.70833 to 0.70856) that overlap those of Middle Ordovician seawater. Petrography, geochemistry, and the geometry of the dolomitized body suggest that the planar dolomite was formed in Middle and Late Ordovician seawater during the deposition of the overlying Maquoketa Shale. Ferroan planar and nonplanar dolomite occurs in the upper few meters of the Trenton Limestone, confined to areas underlain by planar dolomite. This dolomite contains patches of nonferroan dolomite with cathodoluminescence (CL) characteristics similar to underlying planar dolomite. Ferroan dolomite has relatively low {delta}18O values (-5.1 to -7.3{per thousand} PDB) and has slightly radiogenic 87Sr/86Sr ratios (0.70915 to 0.70969) similar to those obtained for the overlying Maquoketa Shale. These data indicate that ferroan dolomite formed by neomorphism of nonferroan planar dolomite as fluids were expelled from the overlying Maquoketa Shale during burial. The absence of ferroan dolomite at the Trenton-Maquoketa contact, in areas where the earlier-formed nonferroan planar dolomite also is absent, indicates that the fluid expelled from the overlying shale did not contain enough Mg2 to dolomitize limestone. Type 1 dolomite cement has isotopic compositions similar to those of the ferroan dolomite, suggesting that it also formed from shale-derived burial fluids. CL growth zoning patterns in these cements suggest that diagenetic fluids moved stratigraphically downward and toward the southeast along the axis of the Kankakee Arch. Type 2 saddle dolomite cements precipitated late; their low {delta}18O values (-6.0 to -7.0{per thousand} PDB) are similar to those of the type 1 dolomite cement. However, fluid-inclusion data indicate that the saddle dolomite was precipitated from more saline, basinal fluids and at higher temperatures (94{degrees} to 143{degrees}C) than the type 1 cements (80{degrees} to 104{degrees}C). A trend of decreasing fluid-inclusion homogenization temperatures and salinities from the Michigan Basin to the axis of Kankakee Arch suggests that these fluids emerged from the Michigan Basin after precipitation of type 1 cement

Speleogenesis under deep-seated and confined settings, 2000,
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Klimchouk A. B.
The terms deep-seated, hypogenic and artesian speleogenesis refer to closely related and overlapping (although not entirely equivalent) concepts. Concerning groundwater hydrodynamics, the vast majority of deep-seated and hypogenic karst develops under confined settings, or settings that are unconfined but paragenetic or subsequent to confinement. Certain diagnostic features of confined groundwater circulation and deep-seated environments distinguish these conditions from those formed in unconfined settings. The last few decades have seen a growing recognition of the variety and importance of hypogenic dissolution processes and of speleogenesis under confined settings which commonly precedes unconfined development. Views of artesian speleogenesis are controversial. It was commonly ignored as a site for cave origin because the classic concept of artesian flow implies long lateral travel distances for groundwater within a soluble unit, resulting in a low capacity to generate caves within the confined area. However, the recognition of aspects derived from non-classical views of artesian flow, namely the role of cross-formation hydraulic communication within artesian basins, the concept of transverse speleogenesis, and the inversion of hydrogeologic function of beds in a sequence, allows a revision of the theory of artesian speleogenesis and views on the origin of many cave types. Under artesian speleogenesis, discharge through a cave is always hydraulically controlled, being constrained either by the hydraulic capacity of the passages or by that of the major confining bed or other overlying formations. In contrast to normal phreatic conditions, the discharge and enlargement rate do not increase dramatically after the kinetic breakthrough in the early evolution of conduits. Dissolution rates depend mainly on the mass balance rather than on solution kinetics during the artesian stage. Artesian speleogenesis is immensely important to speleo-inception, but it also accounts for the development of some of the largest known caves in the world and of many smaller caves. Typical conditions of recharge, the flow pattern through the soluble rocks, and groundwater aggressiveness favor uniform, rather than competing, development of conduits, resulting in maze caves where the proper structural prerequisites exist. The most common flow pattern favoring artesian speleogenesis is upward cross-formation flow in areas of topographic/potentiometric lows. The hydrodynamic influence of prominent valleys or depressions may extend more than a thousand meters below the surface. Artesian speleogenesis and flow through soluble beds are commonly transverse, with conduit development occurring across the beds rather than laterally. Cross-formational flow favors a variety of dissolution mechanisms that commonly involve mixing. Hydrogeochemical mechanisms of speleogenesis are particularly diverse and potent where carbonate and sulfate beds alternate and within or adjacent to hydrocarbon-bearing basins.

The sequence stratigraphy, sedimentology, and economic importance of evaporite-carbonate transitions: a review, 2001,
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Sarg J. F. ,
World-class hydrocarbon accumulations occur in many ancient evaporite-related basins. Seals and traps of such accumulations are, in many cases, controlled by the stratigraphic distribution of carbonate-evaporite facies transitions. Evaporites may occur in each of the systems tracts within depositional sequences. Thick evaporite successions are best developed during sea level lowstands due to evaporative drawdown. Type 1 lowstand evaporite systems are characterized by thick wedges that fill basin centers, and onlap basin margins. Very thick successions (i.e. saline giants) represent 2nd-order supersequence set (20-50 m.y.) lowstand systems that cap basin fills, and provide the ultimate top seals for the hydrocarbons contained within such basins.Where slope carbonate buildups occur, lowstand evaporites that onlap and overlap these buildups show a lateral facies mosaic directly related to the paleo-relief of the buildups. This facies mosaic, as exemplified in the Silurian of the Michigan basin, ranges from nodular mosaic anhydrite of supratidal sabkha origin deposited over the crests of the buildups, to downslope subaqueous facies of bedded massive/mosaic anhydrite and allochthonous dolomite-anhydrite breccias. Facies transitions near the updip onlap edges of evaporite wedges can provide lateral seals to hydrocarbons. Porous dolomites at the updip edges of lowstand evaporites will trap hydrocarbons where they onlap nonporous platform slope deposits. The Desert Creek Member of the Paradox Formation illustrates this transition. On the margins of the giant Aneth oil field in southeastern Utah, separate downdip oil pools have accumulated where dolomudstones and dolowackestones with microcrystalline porosity onlap the underlying highstand platform slope.Where lowstand carbonate units exist in arid basins, the updip facies change from carbonates to evaporite-rich facies can also provide traps for hydrocarbons. The change from porous dolomites composed of high-energy, shallow water grainstones and packstones to nonporous evaporitic lagoonal dolomite and sabkha anhydrite occurs in the Upper Permian San Andres/Grayburg sequences of the Permian basin. This facies change provides the trap for secondary oil pools on the basinward flanks of fields that are productive from highstand facies identical to the lowstand dolograinstones. Type 2 lowstand systems, like the Smackover Limestone of the Gulf of Mexico, show a similar relationship. Commonly, these evaporite systems are a facies mosaic of salina and sabkha evaporites admixed with wadi siliciclastics. They overlie and seal highstand carbonate platforms containing reservoir facies of shoalwater nonskeletal and skeletal grainstones. Further basinward these evaporites change facies into similar porous platform facies, and contain separate hydrocarbon traps.Transgressions in arid settings over underfilled platforms (e.g. Zechstein (Permian) of Europe; Ferry Lake Anhydrite (Cretaceous), Gulf of Mexico) can result in deposition of alternating cyclic carbonates and evaporites in broad, shallow subaqueous hypersaline environments. Evaporites include bedded and palmate gypsum layers. Mudstones and wackestones are deposited in mesosaline, shallow subtidal to low intertidal environments during periodic flooding of the platform interior.Highstand systems tracts are characterized by thick successions of m-scale, brining upward parasequences in platform interior settings. The Seven Rivers Formation (Guadalupian) of the Permian basin typifies this transition. An intertonguing of carbonate and sulfates is interpreted to occur in a broad, shallow subaqueous hypersaline shelf lagoon behind the main restricting shelf-edge carbonate complex. Underlying paleodepositional highs appear to control the position of the initial facies transition. Periodic flooding of the shelf interior results in widespread carbonate deposition comprised of mesosaline, skeletal-poor peloid dolowackestones/mudstones. Progressive restriction due to active carbonate deposition and/or an environment of net evaporation causes brining upward and deposition of lagoonal gypsum. Condensed sections of organic-rich black lime mudstones occur in basinal areas seaward of the transgressive and highstand carbonate platforms and have sourced significant quantities of hydrocarbons

Comparisons Among Ground-Water Flow Models and Analysis of Discrepancies in Simulated Transmissivities of the Upper Floridan Aquifer in Ground-Water Flow Model Overlap Areas, 2001,
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Sepulveda N.

Discrepancies in simulated transmissivities of the Upper Floridan aquifer were identified in the overlap areas of seven ground-water flow models in southwest and west-central Florida. Discrepancies in transmissivity are generally the result of uncertainty and spatial variability in other aquifer properties. All ground-water flow models were used to simulate the potentiometric surface of the Upper Floridan aquifer for approximated steady-state conditions from August 1993 through July 1994 using the time-independent hydraulic properties assigned to the models. Specifiedhead and general-head boundary data used to generate boundary conditions appropriate to these models were obtained from the estimated annual average heads for the steady-state period. Water-use data and the approximated surficial aquifer system water table were updated to reflect conditions during the approximated steady-state period. Simulated heads at control points, vertical leakage rates to the Upper Floridan aquifer, and spring flows were used to analyze the discrepancies in transmissivities in model overlap areas. Factors causing transmissivity discrepancies in model overlap areas include differences among directly applied recharge rates, differences among model simulated vertical leakance values assigned to the overlaying confining unit resulting in varying leakage rates to the Upper Floridan aquifer, differences in heads and conductances used in general-head boundary cells, and differences in transmissivities assigned in the vicinity of springs. Additional factors include the grid resolution and algorithm used to approximate the heads of the surficial aquifer system when these are used as a source/sink layer. 


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