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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 adaptation is an inherited structural, functional, or behavioral characteristic that improves an organism's chances for survival in a particular habitat [23]. see also mutation.?

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


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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 margin (Keyword) returned 230 results for the whole karstbase:
Showing 16 to 30 of 230
Yates and other Guadalupian (Kazanian) oil fields, U. S. Permian Basin, 1990,
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Craig Dh,
More than 150 oil and gas fields in west Texas and southeast New Mexico produce from dolomites of Late Permian (Guadalupian [Kazanian]) age. A majority of these fields are situated on platforms or shelves and produce from gentle anticlines or stratigraphic traps sealed beneath a thick sequence of Late Permian evaporites. Many of the productive anticlinal structures are elongate parallel to the strike of depositional facies, are asymmetrical normal to facies strike, and have flank dips of no more than 6{degrees}. They appear to be related primarily to differential compaction over and around bars of skeletal grainstone and packstone. Where the trapping is stratigraphic, it is due to the presence of tight mudstones and wackestones and to secondary cementation by anhydrite and gypsum. The larger of the fields produce from San Andres-Grayburg shelf and shelf margin dolomites. Cumulative production from these fields amounts to more than 12 billion bbl (1.9 x 109 m3) of oil, which is approximately two-thirds of the oil produced from Palaeozoic rocks in the Permian Basin. Eighteen of the fields have produced in the range from 100 million to 1.7 billion bbl (16-271 x 106 m3). Among these large fields is Yates which, since its discovery in October 1926, has produced almost 1.2 billion bbl (192 x 106 m3) out of an estimated original oil-in-place of 4 billion bbl (638 x 106 m3). Flow potentials of 5000 to 20 000 bbl (800 to 3200 m3) per day were not unusual for early Yates wells. The exceptional storage and flow characteristics of the Yates reservoir can be explained in terms of the combined effects of several geologic factors: (1) a vast system of well interconnected pores, including a network of fractures and small caves; (2) oil storage lithologies dominated by porous and permeable bioclastic dolograinstones and dolopackstones; (3) a thick, upper seal of anhydrite and compact dolomite; (4) virtual freedom from the anhydrite cements that occlude much porosity in other fields which are stratigraphic analogues of Yates; (5) unusual structural prominence, which favourably affected diagenetic development of the reservoir and made the field a focus for large volumes of migrating primary and secondary oil; (6) early reservoir pressures considerably above the minimum required to cause wells to flow to the surface, probably related to pressures in a tributary regional aquifer

Approche gomorphologique des karsts du gypse de la Vanoise (la zone alpine et glaciaire du vallon du Fruit-Gbroulaz,Alpes), 1991,
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Chardon, M.
GYPSUM KARSTIC LANDFORMS IN VANOISE: the alpine and glacial valley of Vallon du Fruit-Gbroulaz (Alps, France) - In the inner part of the northern french Alps, the higher regions of the Vanoise offer outcrops of Triassic gypsum of which the surface and thickness vary. In the vallon du Fruit, the Gbroulaz glacier partially covers a long strip of gypsum, which reaches its highest point at the Roc de la Soufrire (2940 m). Rivers and springs in the vallon du Fruit are fed both by sub-aerial glacial outflows and by karstic underground flows, which are pro-glacial and sub-glacial. A very low chemical dissolution exists under the glacier and along the fast pro-glacial underground and sub-aerial flows, whereas the rate of karstic denudation is high in the margin of the glacier where it reaches 1500 mm/ky at around 2500m (1 ky = 1000 years). The formation and evolution of the dolines is rapid and occurs through underground sucking and dissolution once the area is deglaciated, thanks to underground active flows fed by the glacier and snow melting. Gypsum domes are uplifted under the effects of neotectonic movements and postglacial decompression brings about considerable superficial fissuring because of the elasticity of the rock. Over 10,000 years, the morphogenesis of these domes in the humid and cold climatic conditions of these high alpine mountains has transformed them into perforated ladle and domes. Small outcrops are changed into monoliths or gypsum inselberg. A model of the geomorphologic post-glacial evolution of these domes, over some 20,000 years, is proposed.

GENERAL CENOZOIC EVOLUTION OF THE MALDIVES CARBONATE SYSTEM (EQUATORIAL INDIAN-OCEAN), 1992,
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Aubert O, Droxler Aw,
Analyses and interpretation of an industrial multi-channel seismic grid, a 2.3 km-deep industrial well (NMA-1) and two ODP (Sites 715 and 716), have generated new insights into the evolution of the Maldives carbonate system, Equatorial Indian Ocean. The present physiography of the Maldives Archipelago, a double chain of atolls delineating an internal basin, corresponds only to the latest phase of a long and dynamic evolution, far more complex than the simple vertical build-up of reef caps on top of thermally subsiding volcanic edifices. Through the Cenozoic evolution of the Maldives carbonate system, distinct phases of vertical growth (aggradation), exposure, regional or local drowning, and recovery of the shallow banks by lateral growth (progradation) have been recognized. The volcanic basement underlying the Maldives Archipelago is interpreted to be part of a volcanic ridge generated by the northern drift of the Indian plate on top of the hotspot of the island of Reunion. The volcanic basement recovered at well NMA-1 and ODP Site 715 has been radiometrically dated as 57.2 1.8 Ma (late Paleocene) by 40Ar-39Ar. Seismic and magnetic data indicate that this volcanic basement has been affected by a series of NNE-SSW trending subvertical faults, possibly associated with an early Eocene strike-slip motion along an old transform zone. The structural topography of the volcanic basement apprears to have dictated the initial geometry of the Eocene and early Oligocene Maldives carbonate system. Biostratigraphic analyses of samples, recovered by drilling in Site 715 and exploration well NMA-1, show that the Maldives shallow carbonate system was initiated during the early Eocene on top of what were originally subaerial volcanic edifices. The Eocene shallow carbonate sequence, directly overlying the volcanic basement at NMA-1, is dolomitized and remains neritic in nature, suggesting low subsidence rates until the early Oligocene. During this first phase of the Maldives carbonate system evolution, shallow carbonate facies aggraded on top of basement highs and thick deep-water periplatform sediments were deposited in some central seaways, precursors of the current wider internal basins. In the middle Oligocene, a plate reorganization of the equatorial Indian Ocean resulted in the segmentation of the hotspot trace and the spreading of the Maldives away from the transform zone. This plate reorganization resulted in increasing subsidence rates at NMA-1, interpreted to be associated with thermal cooling of the volcanic basement underlying the Maldives carbonate system. This middle Oligocene event also coincides with a regional irregular topographic surface, considered to represent a karst surface produced by a major low-stand. Deep-water carbonate facies, as seen in cuttings from NMA-1, overlie the shallow-water facies beneath the karst surface which can, therefore, be interpreted as a drowning unconformity. In the late Oligocene, following this regional deepening event, one single central basin developed, wider than its Eocene counterparts, and the current intraplatform basin was established. Since the early to middle Miocene, the shallow carbonate facies underwent a stage of local recovery by progradation of neritic environments towards the central basin. The simultaneous onset in the early middle Miocene of the monsoonal wind regime may explain the development of bidirectional slope progradations in the Maldives. During the late Miocene and the early Pliocene, several carbonate banks were locally drowned, whereas others (i.e. Male atoll) display well-developed lateral growth through margin progradations during the same interval. Differential carbonate productivity among the atolls could explain these diverse bank responses. High-frequency glacialeustatic sea-level fluctuations in the late Pliocene and Pleistocene resulted in periodic intervals of bank exposure and flooding, and developed the present-day physiography of atolls, with numerous faros along their rims and within their lagoons

PALUSTRINE CARBONATES AND THE FLORIDA EVERGLADES - TOWARDS AN EXPOSURE INDEX FOR THE FRESH-WATER ENVIRONMENT, 1992,
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Platt N. H. , Wright V. P. ,
Palustrine carbonates are shallow fresh-water deposits showing evidence of subaqueous deposition and subaerial exposure. These facies are common in the geological record. The intensity of modification is highly variable depending on the climate and the length of emergence. Palustrine limestones have previously been interpreted as marginal lacustrine deposits from fluctuating, low-salinity carbonate lakes, but several problems remain with existing facies models: 1) palustrine carbonates possess a lacustrine biota but commonly display fabrics similar to those of calcretes and peritidal carbonates; 2) the co-occurrence of calcrete horizons and karst-like cavities is somewhat unusual and appears to indicate contemporaneous carbonate precipitation and dissolution in the vadose zone; 3) the dominance of gray colors indicates water-saturation, apparently inconsistent with the evidence for strong desiccation overprint; 4) profundal lake deposits are generally absent from palustrine sequences, and sublittoral facies commonly make up only a small proportion of total thicknesses; 5) no good modem analogue has been identified for the palustrine environment. Analogy with the Florida Everglades suggests a re-interpretation of palustrine limestones, not as pedogenically modified lake margin facies but as the deposits of extensive, very shallow carbonate marshes. The distribution of environments in the Everglades is determined by the local hydrology, reflecting the control of seasonal water-level fluctuations and topography. Climate and topography were the main controls on deposition of ancient palustrine carbonates. As in peritidal sequences, aggradational cycles are capped by a range of lithologies (evaporites, desiccation and microkarst breccias, calcretes, lignite or coal horizons etc.), permitting interpretation of the climate. Careful analysis of lateral facies variations may permit reconstruction of subtle topography. Consideration of the Florida Everglades as a modem analogue for the palustrine environment has suggested the development of an exposure index for fresh-water carbonates

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.

INFLUENCE OF THE FRACTURATION IN THE PRECAMBRIAN BASEMENT AND OF DISSOLUTION PHENOMENA IN THE LITHOMARGIN ON THE GEOMORPHOLOGICAL EVOLUTION IN WEST NIGER, 1993,
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Willems L. , Lenoir F. , Levecq J. M. , Vicat J. P. ,
The observation of several forms in the Precambrian formations, in Tertiary and Quaternary deposits brings us to propose a model of topographic evolution mainly generated by a pseudo-karst. This latter is developed in sedimentary deposits and in the lithomargin, in relation with fracturation of the basement

ROADWAY DESIGN IN KARST, 1993,
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Fischer Ja, Fischer Jj, Greene Rw,
To minimize costs in conventional roadway design, as much low or valley areas as possible are utilized. In many areas of the eastern United States, these valleys are filled with carbonate rocks. Excavation is used to minimize grades-this removes protective overburden or rock cover over cavities; fill also is used to minimize grades-this can increase loads on marginally stable soil arches or rock cavity roofs. Surface water runoff is directed toward low areas-the low areas are likely zones of weakness or solutioning, thereby increasing the potential for sinkhole development and providing an opportunity for groundwater contamination, and remediation usually consists of blindly filling rock cavities, thus either channeling the still-contaminated surface flows someplace else or perhaps eliminating useful ground water recharge conduits. The authors suggest that the key to proper design, construction, and remediation for roadways planned in karst is to understand the geologic and hydrogeologic setting of the route(s) or locale, perform true geotechnical engineering design, and remediate with an understanding of the overall engineering geologic, hydrogeologic, and environmental picture

HIGH-RESOLUTION SEISMIC EXPRESSION OF KARST EVOLUTION WITHIN THE UPPER FLORIDIAN AQUIFER SYSTEM - CROOKED LAKE, POLK COUNTY, FLORIDA, 1994,
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Evans Mw, Snyder Sw, Hine Ac,
We collected 43 km of high resolution seismic reflection profiles from a 14.5-hectare lake in the central Florida sinkhole district and data from three adjacent boreholes to determine the relationship between falling lake levels and the underlying karst stratigraphy. The lake is separated from karstified Paleogene to early Neogene carbonates by 65-80 m of siliciclastic sands and clays. The carbonate and clastic strata include three aquifer systems separated by clay-confining units: a surficial aquifer system (fine to medium quartz sand in the upper 20-30 m), the 25-35 m thick intermediate aquifer system (in Neogene siliciclastics), and the highly permeable upper Floridan aquifer system in Paleogene to early Neogene limestones. Hydraulic connection between these aquifer systems is indicated by superjacent karst structures throughout the section. Collapse zones of up to 1000 m in diameter and > 50 m depth extend downward from a prominent Middle Miocene unconformity into Oligocene and Upper Eocene limestones. Smaller sinkholes (30-100 m diameter, 10-25 m depth) are present in Middle to Late Neogene clays, sands, and carbonates and extend downward to or below the Middle Miocene unconformity. Filled and open shafts (30-40 m diameter; 10-25 m depth) ring the lake margin and overlie subsurface karst features. The large collapse zones are localized along a northeast-southwest line in the northern ponds and disrupt or deform Neogene to Quaternary strata and at least 50 m of the underlying Paleogene carbonate rocks. The timing and vertical distribution of karst structures are used to formulate a four-stage model that emphasizes stratigraphic and hydrogeologic co-evolution. (1) Fracture-selective shallow karst features formed on Paleogene/early Neogene carbonates. (2) Widespread karstification was limited by deposition of Middle Miocene clays, but vertical karst propagation continued and was focused because of the topographic effects of antecedent karst. (3) Groundwater heads, increase with the deposition of thick sequences of clastics over the semipermeable clays during Middle and Late Neogene time. The higher water table and groundwater heads allowed the accumulation of acidic, organic-rich soils and chemically aggressive waters that percolated down to Paleogene carbonates via localized karst features. (4) After sufficient subsurface dissolution, the Paleogene carbonates collapsed, causing disruption and deformation of overlying strata. The seismic profiles document an episodic, vertically progressive karst that allows localized vertical leakage through the clay-confining units. The spatial and temporal karst distribution is a result of deposition of sediments with different permeabilities during high sea levels and enhanced karst dissolution during low sea levels. Recent decreases in the potentiometric elevation of the Floridan Aquifer System simulates a sea-level lowstand, suggesting that karst dissolution will increase in frequency and magnitude

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

Etapes et facteurs de la splogense dans le sud-est de la France, 1995,
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Blanc, J. J.
The examination of karstic erosion surfaces and of some caves presents three stages of unequal duration in the speleogenesis processes : 1) Oldest paleokarsts linked to a tropical and oxydizing climate (Cretaceous, Eocene, Oligocene and Miocene) are affected by the tectonic effects in relation with the western European and liguro-provencal riftings, the mediterranean opening phases and the main karstic levelling. 2) The Messinian crisis, characterized by a significant lowering of the water-table level, is responsible for a major vertical network development and the first canyon sinking phase; hence the erosion of the high surfaces and the drying up of networks. The formation of new over-sized karst is the result of this evolution. 3) From Pliocene (5.3 My) to Quaternary and present time (passive mediterranean margins), the karstic evolution tends towards new drainages and volumes adjusted to the next climatic and eustatic control, with several oscillations and discontinuities. After a compression period, there is a slowing down of the tectogenesis. We can observe orientation flow changes and speleogenesis induced by cold and wet climatic phases. From Tardiglacial times, speleogenesis mechanisms have slowed down.

GEOLOGY AND KARST GEOMORPHOLOGY OF SAN-SALVADOR ISLAND, BAHAMAS, 1995,
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Mylroie J. E. , Carew J. L. ,
The exposed carbonates of the Bahamas consist of late Quaternary limestones that were deposited during glacio-eustatic highstands of sea level. Each highstand event produced transgressive-phase, stillstand-phase, and regressive-phase units. Because of slow platform subsidence, Pleistocene carbonates deposited on highstands prior to the last interglacial (oxygen isotope substage 5e, circa 125,000 years ago) are represented solely by eolianites. The Owl's Hole Formation comprises these eolianites, which are generally fossiliferous pelsparites. The deposits of the last interglacial form the Grotto Beach Formation, and contain a complete sequence of subtidal intertidal and eolian carbonates. These deposits are predominantly oolitic. Holocene deposits are represented by the Rice Bay Formation, which consists of intertidal and eolian pelsparites deposited during the transgressive-phase and stillstand-phase of the current sea-level highstand. The three formations are separated from one another by well-developed terra-rossa paleosols or other erosion surfaces that formed predominantly during intervening sea-level lowstands. The karst landforms of San Salvador consist of karren, depressions, caves, and blue holes. Karren are small-scale dissolutional etchings on exposed and soil-covered bedrock that grade downward into the epikarst, the system of tubes and holes that drain the bedrock surface. Depressions are constructional features, such as swales between eolian ridges, but they have been dissolutionally maintained. Pit caves are vertical voids in the vadose zone that link the epikarst to the water table. Flank margin caves are horizontal voids that formed in the distal margin of a past fresh-water lens; whereas banana holes are horizontal voids that developed at the top of a past fresh-water lens, landward of the lens margin. Lake drains are conduits that connect some flooded depressions to the sea. Blue holes are flooded vertical shafts, of polygenetic origin, that may lead into caves systems at depth. The paleokarst of San Salvador is represented by flank margin caves and banana holes formed in a past fresh-water lens elevated by the last interglacial sea-level highstand, and by epikarst buried under paleosols formed during sea-level lowstands. Both carbonate deposition and its subsequent karstification is controlled by glacio-eustatic sea-level position. On San Salvador, the geographic isolation of the island, its small size, and the rapidity of past sea level changes have placed major constraints on the production of the paleokarst

BLUE HOLES - DEFINITION AND GENESIS, 1995,
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Mylroie J. E. , Carew J. L. , Moore A. I. ,
Blue holes are karst features that were initially described from Bahamian islands and banks, which have been documented for over 100 years. They are water-fined vertical openings in the carbonate rock that exhibit complex morphologies, ecologies, and water chemistries. Their deep blue color, for which they are named, is the result of their great depth, and they may lead to cave systems below sea level Blue holes are polygenetic in origin, having formed: by drowning of dissolutional sinkholes and shafts developed in the vadose zone; by phreatic dissolution along an ascending halocline; by progradational collapse upward from deep dissolution voids produced in the phreatic zone; or by fracture of the bank: margin. Blue holes are the cumulative result of carbonate deposition and dissolution cycles which have been controlled by Quaternary glacioeustatic fluctuations of sea-level. Blue holes have been widely studied during the past 30 years, and they have provided information regarding karst processes, global climate change, marine ecology, and carbonate geochemistry. The literature contains a wealth of references regarding blue holes that are at times misleading, and often confusing. To standardize use of the term blue hob, and to familiarize the scientific community with their nature, we herein define them as follows: ''Blue holes are subsurface voids that are developed in carbonate banks and islands; are open to the earth's surface; contain tidally-influenced waters of fresh, marine, or mixed chemistry; extend below sea level for a majority of their depth; and may provide access to submerged cave passages.'' Blue holes are found in two settings: ocean holes open directly into the present marine environment and usually contain marine water with tidal now; inland blue holes are isolated by present topography from surface marine conditions, and open directly onto the land surface or into an isolated pond or lake, and contain tidally-influenced water of a variety of chemistries from fresh to marine

Determination of stream-incision rate in the Appalachian plateaus by using cave-sediment magnetostratigraphy, 1995,
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Sasowsky Ira D. , White William B. , Schmidt Victor A. ,
Paleomagnetic dating of clastic fluvial sediments contained in caves within the walls of a steeply incised gorge allowed calculation of a maximum incision rate for the East Fork Obey River. The maximum incision rate for this major stream on the western margin of the Cumberland Plateau, north-central Tennessee, was found to be 0.06 m/ka. This rate was determined on the basis of the paleohydraulic relation between the caves and the surface stream, the presence of a normal-to-reverse polarity transition in clastic fluvial sediments deposited within the caves, and the vertical distribution of polarity found in sediments throughout the gorge. The dating results indicate that this highly developed fluviokarst, containing several of the longest known caves in the United States, developed wholly within the Pleistocene and Holocene

CYCLOSTRATIGRAPHY OF MIDDLE DEVONIAN CARBONATES OF THE EASTERN GREAT-BASIN, 1995,
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Elrick M,
Middle Devonian carbonates (250-430 m thick) of the eastern Great Basin were deposited along a low energy, westward-thickening, distally steepened ramp. Four third-order sequences can be correlated across the ramp-to-basin transition and are composed of meter-scale, upward-shallowing carbonate cycles (or parasequences). Peritidal cycles (shallow subtidal facies capped by tidal-flat laminites) constitute 90% of all measured cycles and are present across the entire ramp. The peritidal cycles are regressive- and transgressive-prone (upward-deepening followed by upward-shallowing facies trends). Approximately 80% of the peritidal cycle caps show evidence of prolonged subaerial exposure including sediment-filled dissolution cavities, horizontal to vertical desiccation cracks, rubble and karst breccias, and pedogenic alteration; locally these features are present down to 2 m below the cycle caps. Subtidal cycles (capped by shallow subtidal facies) are present along the middle-outer ramp and ramp margin and indicate incomplete shallowing. submerged subtidal cycles (64% of all subtidal cycles) are composed of deeper subtidal facies overlain by shallow subtidal facies. Exposed subtidal cycles are composed of deeper subtidal facies overlain by shallow subtidal facies that are capped by features indicative of prolonged subaerial exposure (dissolution cavities and brecciation). Average peritidal and subtidal cycle durations are between approximately 50 and 130 k.y. (fourth- to fifth-order). The combined evidence of abundant exposure-capped peritidal and subtidal cycles, transgressive-prone cycles, and subtidal cycles correlative with updip peritidal cycles indicates that the cycles formed in response to fourth- to fifth-order, glacio-eustatic sea-level oscillations. Sea-level oscillations of relatively low magnitude (< 10 m) are suggested by the abundance of peritidal cycles, the lack of widely varying, water-depth-dependent facies within individual cycles, and the presence of noncyclic stratigraphic intervals within intrashelf-basin, slope, and basin facies. Noncyclic intervals represent missed subtidal beats when the seafloor lay too deep to record the effects of the short-term sea-level oscillations. Exposure surfaces at the tops of peritidal and subtidal cycles represent one, or more likely several, missed sea-level oscillations when the platform lay above fluctuating sea level, but the amplitude of fourth- to fifth-order sea-level oscillation(s) were not high enough to flood the ramp. The large number of missed beats (exposure-capped cycles), specifically in Sequences 2 and 4, results in Fischer plots that show poorly developed rising and falling limbs (subdued wave-like patterns); consequently the Fischer plots: are of limited use as a correlation tool for these particular depositional sequences. The abundance of missed beats also explains why Milankovitch-type cycle ratios (similar to 5:1 or similar to 4:1) are not observed and why such ratios would not be expected along many peritidal-cycle-dominated carbonate platforms

TECTONIC AND PALEOCLIMATIC SIGNIFICANCE OF A PROMINENT UPPER PENNSYLVANIAN (VIRGILIAN STEPHANIAN) WEATHERING PROFILE, IOWA AND NEBRASKA, USA, 1995,
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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

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