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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 trellis is a geometrical arrangement of an interwoven pattern [16].?

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 scenario (Keyword) returned 76 results for the whole karstbase:
Showing 46 to 60 of 76
EVOLUTION OF CAVES IN POROUS LIMESTONE BY MIXING CORROSION: A MODEL APPROACH, 2009,
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Dreybrodt W. , Romanov D. , Kaufmann G.

When water from the surface, e.g. from a lake, flows through porous carbonate rocks down along some region with high hydraulic conductivity and encounters the water table of a phreatic aquifer both waters mix by diffusion along their boundary. In a carbonate aquifer, where both surface and phreatic waters are saturated with respect to calcite, mixing corrosion causes renewed dissolution capacity ?ceq of the carbonate rock in the diffusion-mixing zone extending from the boundary separating the phreatic water from the surface water encountering it. A numerical model is presented from which the initial change of porosity in such a diffusion-mixing zone is obtained. The initial change of porosity can be calculated from the local distribution of the mixing ratio and the second derivative of ?ceq with respect to m. m(x,y) is the spatial distribution of the mixing ratio m= Vsurf /( Vsuf + Vprh ) , and the V’s assign the corresponding volumes of surface and phreatic water. The second derivative has been calculated for three geochemical scenarios with differing CO2 -concentrations of surface and phreatic water by use of PHREEQC-2. The spatial distribution m(x,y) is obtained by using MODFLOW and MT3DMS in a modeling domain with constant hydraulic conductivity for various ?ow velocities of the phreatic aquifer. From the results the time scale of cave evolution is estimated. Passages of dimensions of about one meter in width and several 10 cm in height, extending in length along the border line where surface and phreatic water meet, can be created in time scales of 10 000 years. These caves are horizontal with blind ending passages and resemble closely the isolated caves observed in Central West Florida.


SIMULATING THE DEVELOPMENT OF SOLUTION CONDUITS IN HYPOGENE SETTINGS, 2009,
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Rehrl C. , Birk S. , Klimchouk A. B.

Karst aquifers develop where an enlargement of fractures due to dissolution creates highly permeable conduits. These conduits are embedded in the much less permeable fissured system of the surrounding rock. The hydrogeological characterisation of these heterogeneous, dualistic flow systems requires a deep understanding of the processes involved in karstification. During the last two decades many numerical models have been developed to simulate conduit evolution in karst terrains and to understand and analyze the mechanisms of speleogenesis. In this study, conduit development within a soluble unit of a multi-layer aquifer system is examined by process-based numerical modeling. The dual flow system is adequately represented by a coupled continuum-pipe flow model; the flow model is coupled to a module calculating dissolution rates and the corresponding widening of conduits depending on flow conditions. The simplified model scenarios are largely based on field observations compiled from the gypsum karst terrain of the Western Ukraine. It is demonstrated that the hydraulic conductivity of the rock formation is a crucial factor that controls the frequency distribution of conduit diameters in hypogene speleogenesis. If the permeability of the rock formation is sufficiently high, conduit development is found to be competitive and leads to bimodal aperture distributions. Otherwise flow in low-permeability formations is suppressed and as a consequence, there is a smooth transition from scarcely developed proto-conduits to well-developed conduits rather than a clear and distinct separation. This work further examines the influence of the variability of the initial apertures on dissolutional growth of fissures and the evolving cave patterns. The initial apertures were not spatially correlated and log normally distributed. The influence of the aperture variability was investigated in several scenarios. It is found that in an ensemble average sense the degree of heterogeneity determines the temporal development of the cave patterns, i.e. higher aperture variability generally decelerates the karstification process. The aperture variability, however, appears to be of minor relevance regarding the general structure and geometric properties of the evolving cave patterns.


Holocene deposits from Neptunes Cave, Nordland, Norway , 2009,
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Faulkner Trevor, Hunt Chris

Neptune’s Cave in the Velfjord–Tosenfjord area of Nordland, Norway is described, together with its various organic deposits. Samples of attached barnacles, loose marine molluscs, animal bones and organic sediments were dated, with radiocarbon ages of 9840±90 and 9570±80 yr BP being derived for the barnacles and molluscs, based on the superseded but locally-used marine reservoir age of 440 years. A growth temperature of c. 7.5°C in undiluted seawater is deduced from the δ13C and δ18O values of both types of marine shell, which is consistent with their early Holocene age. From the dates, and an assessment of local Holocene uplift and Weichselian deglaciation, a scenario is constructed that could explain the situation and condition of the various deposits. The analysis uses assumed local isobases and sea-level curve to give results that are consistent with previous data, that equate the demise of the barnacles to the collapse of a tidewater glacier in Tosenfjord, and that constrain the minimum extent of local Holocene uplift. An elk fell into the cave in the mid-Holocene at 5100±70 yr BP, after which a much later single ‘bog-burst’ event at 1780±70 yr BP could explain the transport of the various loose deposits farther into the cave.

 


Fluids in geological processes The present state and future outlook, 2010,
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Mumm Andreas Schmidt, Brugger Joel, Zhao Chongbin, Schacht Ulrike

The research of fluids in the earth's crust is greatly benefiting from methodological (analytical) and experimental advances and the rapid development of increasingly powerful numerical modelling systems. New experimental data continuously refine the accuracy of numerical models aiming to quantitatively reconstruct geological processes. Geological modelling programs have moved on from linear or 2-dimensional approaches to integrating 3 or 4D geology with geothermal aspects, fluids flow and reactive transport processes into complex, quantitative scenarios. These combinations of refinement of the data base and advances in computational capacities are the stepping stones for the development of the predictive quality of mineralising models and hydrocarbon migration and accumulation, access to geothermal energy and the sequestration of CO2.

This special issue presents a selection of contributions on “Fluids in Geological Processes” following the VIth GEOFLUIDS meeting in Adelaide in 2009, emphasizing on recent developments in the different research trends in this field.


Influence of initial aperture variability on conduit development in hypogene settings, 2010,
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Rehrl C. , Birk S. , Klimchouk A. B.

The development of gypsum maze caves in hypogene settings is examined by process-based numerical modelling using a coupled continuum-pipe flow model. The model scenarios are largely based on field observations compiled from the gypsum karst terrain of the Western Ukraine. This area hosts the world\'s largest maze caves in gypsum and provides a well documented example of hypogene speleogenesis under artesian conditions. Building on previous studies that revealed the basic speleogenetic mechanisms in this type of setting, this work aims to examine the influence of the variability of the initial apertures on dissolutional growth of fissures and the evolving cave systems. To this end, the initial apertures were spatially uncorrelated and lognormally distributed and the influence of the coefficient of variation of the aperture data (?/?) was investigated in several scenarios on the basis of a set of four realisations. It is found that a small degree of heterogeneity leads to cave patterns similar to those obtained with uniform initial apertures. However, with increasing heterogeneity the karstification process decelerates and a significant amount of variability between the different realisations follows. In an ensemble average sense, the aperture variability is determining the temporal development of the cave patterns and generally decelerates the karstification process, but appears to be of minor relevance regarding the general structure and geometric properties of the evolving cave patterns.


Modeling three-dimensional karst aquifer evolution using different matrix-flow contributions, 2010,
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Kaufmann G. , Romanov D. , Hiller T.

We have developed the program package KARSTAQUIFER, which simulates flow and transport in a three-dimensional transient karst aquifer consisting of fractures and matrix elements. The fractures can be enlarged by chemical dissolution of calcite, increasing the secondary permeability of the karst aquifer. Boundary conditions for our model setup are guided by published benchmark models for karst aquifer evolution in two dimensions (length and width), with a 100 m high hydraulic head difference across the model domain responsible for relatively fast evolution of the aquifer. We are interested in the effect of the third dimension on the evolution of the karst aquifer, especially the effect of matrix flow, with a matrix defined either as porous medium or as fine fracture system, or both. We first discuss our model results using a pseudo-3D setup to be able to directly compare results to the 2D benchmark scenarios published. We then discuss real-3D models with a prominent fault located in the central part of the aquifer, connecting input and output regions. Finally, we replace the prominent fault with a statistical fracture diameter distribution. Our results compare well with existing 2D scenarios, and the additional third dimension offers new insights into the evolution of karst aquifers. Especially the role of matrix flow under fixed-head boundary conditions in their early phases can be studied in more detail.


Karstification in unconfined limestone aquifers by mixing of phreatic water with surface water from a local input: A model, 2010,
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Gabrovš, Ek F. , Dreybrodt W.

When water from the surface of a limestone plain seeps down through the fractured rock to the water table of an unconfined aquifer with low hydraulic gradient containing water saturated with respect to calcite, mixing of these waters causes renewed aggressivity. A model is presented, which describes the evolution of karstification by dissolutional widening of the fractures downgradient from the local input of surface water. The model couples flow in the fractures with dissolution rates. Dissolution rates are given by F = k (1 [1] c (x)/ceq)4, where c (x) is the calcium concentration at distance x from the entrance of the fracture, ceq is the equilibrium calcium concentration of the H2O–CaCO3–CO2 solution in the fracture, and k is a rate constant. The model describes two domains of waters saturated with respect to calcite at different partial pressure of CO2. At the borders of these domains the waters mix and create dissolutional widening of the fractures by mixing corrosion. A channel evolves along the border in the downgradient direction by about 100 m in 100 ky. Below this channel a zone of fractures with aperture widths up to 1 cm has originated. The change of the hydraulic conductivity in the mixing zone shifts the border of the domains, allowing the channel to grow in the downgradient direction. Below it the zone of widened fractures is invaded by saturated phreatic water and dissolution stops. This process continues at the downgradient part of the conduit. In summary, we find cave conduits evolving close to the water table, leaving significant cavernous structures below them. A variety of modelling scenarios with different choices of parameters show that this evolution is typical and changes only in details but not in its basic behaviour.


Karstification of aquifers interspersed with non-soluble rocks: From basic principles towards case studies, 2010,
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Romanov D. , Kaufmann G. , Hiller T.

We have developed a numerical model able to describe the karstification of aquifers in fractured rocks containing soluble (limestone or gypsum) and insoluble layers. When water is flowing along fractures crossing the soluble layers, it is able to dissolve the material there, to increase the aperture width of the conduit, and consequently to increase the local hydraulic conductivity. Depending on the thickness and the distribution of these layers, the dissolution can be active only for limited periods, or during the whole evolution time. Fractures located in insoluble layers do not change at all. We are interested in the integral effect of these local processes and study four simplified scenarios of karstification along a prominent wide conduit crossing a fractured limestone block. We keep the initial and the boundary conditions the same for all scenarios and vary only in the amount and the distribution of the soluble material. We demonstrate that aquifers in 100% limestone, without any insoluble layers, develop along areas with high hydraulic conductivities and high hydraulic gradients, creating channel like pathways. On the other hand aquifers containing soluble layers with limited thickness develop faster and exhibit diffuse patterns determined by the chemical properties of the rock. The second part of the paper is a step towards modeling of real karst systems. We present the evolution of an aquifer located in the vicinity of a large hydraulic structure. All initial and boundary conditions, except the amount and the distribution of the soluble rock, remain the same for all scenarios. As a material example for the bedrock, we chose Gipskeuper from an aquifer along the Birs river in Switzerland. This rock consists of soluble gypsum layers and insoluble clays and marls, with typical layer thickness in the range of millimeters to centimeters. The basic processes discussed in the first part of the paper remain valid. We demonstrate that large insoluble zones can impair the karstification process and even completely block it, while areas with thin soluble layers can provide a preferential pathway and decrease the evolution times considerably. Finally we show that the evolution of the leakage rates and the head distribution within the aquifer can sometimes reveal misleading information about the stage of karstification and the safeness of the dam. Our model can be used not only to study simplified geological settings and basic processes, but also to address some of the complications arising when modeling real aquifers.


Karstification beneath dam-sites: From conceptual models to realistic scenarios, 2011,
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Hiller Thomas, Kaufmann Georg, Romanov Douchko

Dam-sites and reservoirs located above soluble rock are often damaged by increased leakage through the sub-surface within the life-time of the structure. The high hydraulic gradients driving the water through the fracture and fissure system of the bedrock have a strong impact on the aquifer evolution. The increased permeability, if not prevented, leads to an imminent danger of high leakage rates (breakthrough) as well. As a result, the structural safety of the dam-site itself is at risk. Past experience has shown that this may have large environmental and economical consequences.

For a better understanding of the evolution of karst aquifer systems in the vicinity of dam-sites, a three-dimensional conceptual model is presented. We show the evolution of the karst aquifer for simple three-dimensional dam-site setups. Keeping the symmetry and simplicity of the models we can relate our results to the two- and one-dimensional scenarios presented in the past. Implementing a statistical fracture network and topographic information to this basic setup we show that these complex three-dimensional properties of the real aquifers, have a significant influence on the karstification, and cannot always be addressed by two -and one-dimensional models.

Research highlights
- Three-dimensional karst evolution modeling of dam-sites. - Relating the 3D models to former 2D and 1D models. - Implementation of statistical fracture network and topography.


Tracing the sources of cave sulfates: a unique case from Cerna Valley, Romania, 2011,
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Onac Bogdan P. , Wynn Jonathan G. , Sumrall Jonathan B.

In order to reliably distinguish between different genetic processes of cave sulfate formation and to quantify the role of thermo-mineral waters on mineral deposition and cave morphology, it is critical to understand sulfur (S) sources and S transformations during hydrological and speleogenetic processes. Previous work has shown that sulfuric acid speleogenesis (SAS) often produces sulfate deposits with 34S-depleted isotopic signatures compared to those of the original source of S in sulfate rocks. However, 34S-depleted isotopic composition of S-bearing minerals alone does not provide enough information to clearly distinguish SAS from other speleogenetic processes driven by carbonic acid, geothermal heat, or other processes. The isotopic composition (δ18O and δ34S) of sulfate minerals (mainly gypsum) from seven caves of the Cerna Valley (Romania) defines three distinct populations, and demonstrates that the δ34S values of SAS-precipitated cave sulfates depend not only on the source of the S, but also on the H2S:SO4 2− ratio during aqueous S species reactions and mineral precipitation. Population 1 includes sulfates that are characterized by relatively low δ34S values (−19.4 to −27.9‰) with δ18O values between 0.2 and 4.3‰ that are consistent with oxidation of dissolved sulfide produced during methane-limited thermochemical sulfate reduction (TSR) that presently characterizes the chemistry of springs in the upper Cerna Valley. Population 2 of cave sulfates has 34S enriched δ34S values (14.3 to 19.4‰) and more 18O-depleted δ18O values (from −1.8 to −10.0‰). These values argue for oxidation of dissolved sulfide produced during sulfate-limited TSR that presently characterizes the chemistry of springs further downstream in the Cerna Valley. The δ18O values of cave sulfates from Population 1 are consistent with oxidation under more oxic aqueous conditions than those of Population 2. δ34S values of cave sulfates within Population 3 (δ34S: 5.8 to 6.5‰) may be consistent with several scenarios (i.e., pyrite oxidation, oxidation of dissolved sulfide produced during methane-limited TSR coupled with O2-limited oxidation during SAS). However, comparatively 18O-enriched δ18OSO4 values (11.9 to 13.9‰) suggest the majority of this sulfate O was derived from atmospheric O2 in gas-phase oxidation prior to hydration. Thus, the combined use of oxygen- and sulfur-isotope systematics of sulfate minerals precipitated in a variety of cave settings along Cerna Valley may serve as an example of how more complex cave systems can be deconvoluted to allow for more complete recognition of the range of processes and parameters that may be involved in SAS.


Karst, Uranium, Gold and Water Lessons from South Africa for Reconciling Mining Activities and Sustainable Water Use in Semi-arid Karst Areas: A Case Study, 2011,
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Winde, Frank

Despite the fact that much of the water stored in dams and reservoirs is lost to the atmosphere due to prevailing semi-arid conditions, South Africa traditionally relies mainly on surface water. Owing to an ever increasing demand that approaches the limits of economically exploitable surface water, the focus increasingly shifts towards groundwater as a long neglected resource. In this context, dolomitic karst aquifers that store large volumes of water protected from evaporation in vast underground cavities are of particular importance. This even more so as some of these aquifers are located in highly industrialised and densely populated areas such as the Gauteng Province, where water demand by far exceeds local supply and necessitates the expensive import of water from catchments as far as Lesotho. However, owing to impacts related to the century-old, deep-level gold mining that initiated South Africa’s economic development, many of the karst aquifers are currently not usable. Using the Far West Rand goldfield as an example, the extent, type and magnitude of mining-related impacts on dolomitic karst aquifers are analysed. This includes impacts on the geohydrological conditions in the area as well as water availability and ground stability associated with the large-scale dewatering of dolomitic aquifers that overly mine workings. Of particular concern is the mining-related contamination of groundwater and surface water with uranium which accompanies gold in most of the mined ore bodies. Finally, possible scenarios for water-related impacts of future mine closure are outlined and associated research needs identified. 


Ascending speleogenesis of Sokola Hill: a step towards a speleogenetic model of the Polish Jura, 2011,
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Gradziń, Ski M. , Hercman H. , Kiciń, Ska D. , Pura D. , Urban J.

The paper deals with the origin of caves in Sokola Hill (Polish Jura). the caves abound in solution cavities in the walls and ceilings, many of them arranged hierarchically, some others arranged in rising sets. blind chimneys and ceiling half-tubes are also present. these features collectively indicate that the caves originated under phreatic conditions by an ascending flow of water, probably of elevated temperature. Phreatic calcite spar, crystallized from water of elevated temperature, lines the cave walls. during the formation of the caves the Jurassic limestone aquifer was confined by impermeable cover. three possible scenarios for the origin of the caves are suggested. the first scenario points to formation of the caves during the Palaeogene prior to the removal of the confining cretaceous marls. the second connects the origin of the caves with regional palaeoflow driven by tectonic loading by carpathian nappes to the south, while the third refers to local topographically driven palaeoflow. both the second and third scenarios assume that the Polish Jura had a cover of Miocene impermeable clastics. All the scenarios account for the origin of the caves in Sokola Hill and explain the common occurrence of ascending caves throughout the Polish Jura.

In the subsequent stages of evolution the caves were partly filled with various deposits. conglomerates composed of Jurassic limestone clasts, quartz sands and sandstones are preserved as erosional remnants, locally covered by or interfingered with calcite flowstones. the clastic deposits were laid down by surface streams that invaded the caves earlier than 1.2 Ma. the caves were not invaded by water from Pleistocene glaciers, which is proved by the assemblage of heavy minerals in the cave clastics.


Dades sobre paleocarst i espeleocronologia de les illes Balears , 2011,
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Gines J. , Gines A. , Fornos J. J.

The litho-stratigraphic record of the Balearic Islands, basically composed by carbonate rocks, include noticeable paleokarstic phenomena particularly owing to the complex tectonic structuration experienced by the Western Mediterranean basin all along its geological history. The most outstanding paleokarst features and associated breccia deposits are observed in the Jurassic limestones and, especially, in the postorogenic Upper Miocene carbonate rocks, where abundant funnel-shaped collapse structures (Messinian in age) have tightly conditioned the geomorphological evolution of the eastern coast of Mallorca. Regarding the karstification occurred in Pliocene and Quaternary times, the islands arise as exceptional scenarios in order to obtain valuable speleochronological data from quite different sources. The base level variations –controlled in turn by oscillations of the sea level–, as well as the evolutionary trends of endemic vertebrates that lived in the Balearic Islands, provide a solid chronological frame to undertake the geomorphologic study of Balearic caves and its sediments. Particularly, the glacio-eustatic oscillations experienced by the Mediterranean Sea remain accurately recorded by means of horizontal paleolevels of phreatic speleothems, mostly corresponding to Upper Pleistocene and Holocene sea-stands. The isotopic investigations (U-Th, 14C) carried out on these carbonate precipitates, as well as on speleothems in general, have supplied abundant absolute dating which strongly contribute to the chronological assessment of the endokarst evolution undergone in our islands. All the evidences gathered till now seem to place in the Pliocene, and in some cases even before, the main speleogenetic phases occurred in the archipelago. During the Middle and Upper Pleistocene, the caves in the Balearic Islands had only experienced minor morpho-sedimentary modifications embracing –in a significant number of cave sites– the deposition of abundant speleothems together with the emplacement of paleontological deposits that include endemic vertebrate fauna.


Controls on paleokarst heterogeneity. Integrated study of the Upper Permian syngenetic karst in Rattlesnake Canyon, Guadalupe Mountains, USA, 2011,
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Labraa De Miguel, Gemma

The present study contributes to a better understanding of early dissolution mechanisms for syngenetic karst development and provides constraints on the timing of formation of the Rattlesnake Canyon paleokarst system in the Guadalupe Mountains, New Mexico, U.S.A. Paleozoic paleokarsts commonly undergo burial and collapse, which reduces significantly the preservation of early fracture networks and geometries of dissolution. Rattlesnake Canyon constitutes a magnificent scenario for the study of global controls on Upper Permian karsting since early fracture networks and dissolution geometries are extremely well preserved and lack major tectonic deformation. This thesis sheds light on the scientific knowledge of paleokarsts and can be of interest to the oil industry since paleokarsts are common targets of exploration. As the evolution of the reservoir properties is often diagenetically controlled, the diagenetic study was particularly useful in determining the degree of sealing following hydrocarbon charge. 1) Aims This thesis seeks to improve our understanding of the relationship between early syndepositional fracture networks that are typically found in platform margins and syngenetic karst development. The thesis includes multidisciplinary carbonate studies aimed at understanding the multiscale paleokarst heterogeneity by means of (i) the development of a conceptual model for the karst evolution, (ii) the construction of a 3D paleokarst model, (iii) the determination of the diagenetic history of the paleokarst system and (iv) the paleokarst reservoir characterization. 2) Thesis Structure The thesis consists of 9 chapters and 2 appendices. Chapter 1 sets out the rationale for this thesis. Chapter 2 provides an introduction to the most basic aspects of karst science and to the hydrogeological model of Carbonate Island as well as an overview of the state-of-the-art paleokarst studies. The geological setting and the study area is detailed in Chapter 3. The results of the thesis are contained in Chapters 4 to 7. Because of the multidisciplinary nature of this thesis, each of these chapters is dedicated to one discipline. Chapter 4 focuses on the analysis of field data to obtain a conceptual model for the evolution of the paleokarst system. Chapter 5 discusses the methodology to implement the 3D paleokarst model and provides data to assess the dimensions of the system in subsurface. Chapter 6 focuses on the diagenetic stages that affected and controlled the karst development. Finally, Chapter 6 offers a paleokarst reservoir characterization. A comprehensive approach and discussion of the results obtained in each of these chapters are included in Chapter 8. General and specific conclusions are presented in Chapter 9. Appendix One contains a representative image compendium of the petrographic features observed in the paleokarst filling sequence of Fault N. Appendix Two sets out the raw data from the geochemical analysis. The paleokarst analysis using different disciplines provides a complete characterization of paleokarst heterogeneity and enables us to elucidate the controls of the system.


Oxygen isotopes in calcite grown under cave-analogue conditions, 2011,
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Day C. C. , Henderson G. M.

Speleothem oxygen isotopes and growth rates are valuable proxies for reconstructing climate history. There is debate, however, about the conditions that allow speleothems to grow in oxygen isotope equilibrium, and about the correct equilibrium fractionation factors. We report results from a series of carbonate growth experiments in karst-analogue conditions in the laboratory. The setup closely mimics natural processes (e.g. precipitation driven by CO2-degassing, low ionic strength solution, thin solution film) but with a tight control on growth conditions (temperature, pCO2, drip rate, calcite saturation index and the composition of the initial solution). Calcite is dissolved in water in a 20,000 ppmV pCO2 environment. This solution is dripped onto glass plates (coated with seed-carbonate) in a lower pCO2 environment (and rapid depletion of the dissolved inorganic carbon reservoir (rapid DIC-depletion). The impact of evaporation can be large so caves with high relative humidity are also preferable for palaeoclimate reconstruction. Even allowing for the maximum offsets that may have been induced by evaporation and rapid DIC-depletion, d18O measured in some of our experiments remain higher than those predicted by Kim and O’Neil (1997). Our new results are well explained by equilibrium at a significantly higher acalcite–water, with a kinetic-isotope effect that favours 16O incorporation as growth rate increases. This scenario agrees with recent studies by Coplen (2007) and Dietzel et al. (2009). Overall, our results suggest that three separate processes cause d18O to deviate from true isotope equilibrium in the cave environment. Two of these drive d18O to higher values (evaporation and rapid DIC-depletion) while one drives d18O to lower values (preferential incorporation of 16O in the solid carbonate at faster growth rates). While evaporation and DIC-depletion can be avoided in some settings, the third may be inescapable in the cave environment and means that any temperature to d18O relationship is an approximation. The controlled conditions of the present experiments also display limitations in the use of the Hendy test to identifying equilibrium growth.


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