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Enviroscan Ukrainian Institute of Speleology and Karstology


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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 hydrodynamic dispersion is 1. the spreading (at the macroscopic level) of the solute front during transport resulting from both mechanical dispersion and molecular diffusion [22]. 2. the dynamic dispersion of fluid particles in flow through a porous medium due to velocity changes in the pore channels [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.
See all featured articles
Featured articles from other Geoscience Journals
Karst environment, Culver D.C.
Mushroom Speleothems: Stromatolites That Formed in the Absence of Phototrophs, Bontognali, Tomaso R.R.; D’Angeli Ilenia M.; Tisato, Nicola; Vasconcelos, Crisogono; Bernasconi, Stefano M.; Gonzales, Esteban R. G.; De Waele, Jo
Calculating flux to predict future cave radon concentrations, Rowberry, Matt; Marti, Xavi; Frontera, Carlos; Van De Wiel, Marco; Briestensky, Milos
Microbial mediation of complex subterranean mineral structures, Tirato, Nicola; Torriano, Stefano F.F;, Monteux, Sylvain; Sauro, Francesco; De Waele, Jo; Lavagna, Maria Luisa; D’Angeli, Ilenia Maria; Chailloux, Daniel; Renda, Michel; Eglinton, Timothy I.; Bontognali, Tomaso Renzo Rezio
Evidence of a plate-wide tectonic pressure pulse provided by extensometric monitoring in the Balkan Mountains (Bulgaria), Briestensky, Milos; Rowberry, Matt; Stemberk, Josef; Stefanov, Petar; Vozar, Jozef; Sebela, Stanka; Petro, Lubomir; Bella, Pavel; Gaal, Ludovit; Ormukov, Cholponbek;
See all featured articles from other geoscience journals

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Your search for flux (Keyword) returned 160 results for the whole karstbase:
Showing 136 to 150 of 160
From soil to cave: Transport of trace metals by natural organic matter in karst dripwaters, 2012,
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Hartland A. , Fairchild I. J. , Lead J. R. , Borsato A. , Baker A. , Frisia S. , Baalousha M.

This paper aims to establish evidence for the widespread existence of metal binding and transport by natural organic matter (NOM) in karst dripwaters, the imprint of which in speleothems may have important climatic significance. We studied the concentration of trace metals and organic carbon (OC) in sequentially filtered dripwaters and soil leachates from three contrasting sites: Poole's Cavern (Derbyshire, UK), Lower Balls Green Mine (Gloucestershire, UK) and Grotta di Ernesto (Trentino, Italy). The size-distribution of metals in the three soils was highly similar, but distinct from that found in fractionated dripwaters: surface-reactive metals were concentrated in the coarse fraction (>100 nm) of soils, but in the fine colloidal (b100 nm) and nominally dissolved (b1 nm) fractions of dripwaters. The concentration of Cu, Ni and Co in dripwater samples across all sites were well correlated (R2=0.84 and 0.70, Cu vs. Ni, Cu vs. Co, respectively), indicating a common association. Furthermore, metal ratios (Cu:Ni, Cu:Co) were consistent with NICA-Donnan n1 humic binding affinity ratios for these metals, consistent with a competitive hierarchy of binding affinity (Cu>Ni>Co) for sites in colloidal or dissolved NOM. Large shifts in Cu:Ni in dripwaters coincided with high fluxes of particulate OC (following peak infiltration) and showed increased similarity to ratios in soils, diagnostic of qualitative changes in NOMsupply (i.e. fresh inputs of more aromatic/hydrophobic soil organic matter (SOM) with Cu outcompeting Ni for suitable binding sites). Results indicate that at high-flows (i.e. where fracture-fed flow dominates) particulates and colloids migrate at similar rates, whereas, in slow seepage-flow dripwaters, particulates (>1 μm) and small colloids (1–100 nm) decouple, resulting in two distinct modes of NOM–metal transport: high-flux and low-flux. At the hyperalkaline drip site PE1 (in Poole's Cavern), high-fluxes of metals (Cu, Ni, Zn, Ti, Mn, Fe) and particulate NOM occurred in rapid, short-lived pulses following peak infiltration events, whereas low-fluxes of metals (Co and V>Cu, Ni and Ti) and fluorescent NOM (b ca. 100 nm) were offset from infiltration events, probably because small organic colloids (1–100 nm) and solutes (b1 nm) were slower to migate through the porous matrix than particulates. These results demonstrate the widespread occurrence of both colloidal and particulate NOM–metal transport in cave dripwaters and the importance of karst hydrology in affecting the breakthrough times of different species. Constraints imposed by soil processes (colloid/particle release), direct contributions of metals and NOM from rainfall, and flow-routing (colloid/particle migration) are expected to determine the strength of correlations between NOM-transported metals in speleothems and climatic signals. Changes in trace metal ratios (e.g. Cu:Ni) in speleothems may encode information on NOMcomposition, potentially aiding in targeting of compound-specific investigations and for the assessment of changes in the quality of soil organic matter.


Carbon cycle in the epikarst systems and its ecological effects in South China, 2012,
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Jiang Z. , Lian Y. , Qin X.

The carbon cycle in a global sense is the biogeochemical process by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the earth. For epikarst systems, it is the exchange of carbon among the atmosphere, water, and carbonate rocks. Southern China is located in the subtropical zone; its warm and humid weather creates favorable conditions for the dynamic physical, chemical, and ecological processes of the carbon cycle. This paper presents the mechanisms and characteristics of the carbon cycle in the epikarst systems in south China. The CO2 concentration in soils has clear seasonal variations, and its peak correlates well with the warm and rainy months. Stable carbon isotope analysis shows that a majority of the carbon in this cycle is from soils. The flow rate and flow velocity in an epikarst system and the composition of carbonate rocks control the carbon fluxes. It was estimated that the karst areas in south China contribute to about half of the total carbon sink by the carbonate system in China. By enhancing the movement of elements and dissolution of more chemical components, the active carbon cycle in the epikarst system helps to expand plant species. It also creates favorable environments for the calciphilic plants and biomass accumulation in the region. The findings from this study should help in better understanding of the carbon cycle in karst systems in south China, an essential component for the best management practices in combating rock desertification and in the ongoing study of the total carbon sink by the karst flow systems in China


A new eyeless species of cave-dwelling trechine beetle from northeastern Guizhou Province, China (Insecta: Coleoptera: Carabidae: Trechinae), 2012,
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Tian Mingyi, Clarke Arthur

Qianaphaenops emersoni n. sp. is described from Gan Dong, a limestone cave in Yanhe Xian, northeastern Guizhou Province, China. Likely to be a narrow range endemic species, Q. emersoni is only known from two almost adjacent type locality sites in Gan Dong cave. Q. emersoni is the fifth species to be described in this genus of eyeless troglobitic trechine beetles, known only from caves in northeastern Guizhou; a distributional map of the genus Qianaphaenops Uéno is provided. Q. emersoni belongs to the Qianaphaenops tenuis species group which contains two described species: Q. tenuis and Q. rotundicollis (Uéno, 2000). Q. emersoni is very similar to Q. rotundicollis Uéno, but easily distinguished from the latter by its broader head and elytra, narrower pronotum and its more elongate and slender aedeagus. Some explanation of the exploration of Gan Dong is provided, along with habitat details of the trechine beetle Type Locality sites located approximately 950 metres into the cave. The subsequent discovery of an efflux cave, presumed to be the Gan Dong Resurgence, is also discussed.


The new global lithological map database GLiM: A representation of rock properties at the Earth surface, 2012,
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Hartmann Jens, Moosdorf Nils

Lithology describes the geochemical, mineralogical, and physical properties of rocks. It plays a key role in many processes at the Earth surface, especially the fluxes of matter to soils, ecosystems, rivers, and oceans. Understanding these processes at the global scale requires a high resolution description of lithology. A new high resolution global lithological map (GLiM) was assembled from existing regional geological maps translated into lithological information with the help of regional literature. The GLiM represents the rock types of the Earth surface with 1,235,400 polygons. The lithological classification consists of three levels. The first level contains 16 lithological classes comparable to previously applied definitions in global lithological maps. The additional two levels contain 12 and 14 subclasses, respectively, which describe more specific rock attributes. According to the GLiM, the Earth is covered by 64% sediments (a third of which are carbonates), 13% metamorphics, 7% plutonics, and 6% volcanics, and 10% are covered by water or ice. The high resolution of the GLiM allows observation of regional lithological distributions which often vary from the global average. The GLiM enables regional analysis of Earth surface processes at global scales. A gridded version of the GLiM is available at the PANGEA Database (http://dx.doi.org/10.1594/PANGAEA.788537).


Stratigraphy, petrography and chronology of speleothem deposition at Tana che Urla (Lucca, Italy): paleoclimatic implications, 2012,
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Regattieri E. , Isola I. , Zanchetta G. , Drysdale R. N. , Hellstrom J. , Baneschi I.

In this work we present the results of a stratigraphic and lithologic study of a flowstone from Tana che Urla Cave, Apuan Alps (central Italy) which grew intermittently between ca. 160 and 8 ka. The studied succession consists of an alternation of two different lithofacies (Lf-A, Lf-B): a brown, detrital-rich (Lf-A) and a white, inclusion-poor calcite (Lf-B). Using available growth rate data, the difference between the two lithofacies is thought to be the result of different amounts of meteoric precipitation, with Lf-A related to low growth rates at times of low precipitation during phases of climatic deterioration (stadial or glacial) and a higher flux of clastic material, and Lf-B related to high growth rates due to high infiltration under conditions of higher precipitation during wetter (interstadial/interglacial) periods, with lower clastic flux. Following this interpretation and the available chronology, the flowstone investigated shows a basal portion of Lf-A that was deposited during MIS6. The flowstone then passed from Lf-A to Lf B at the MIS6-5 transition, with Lf-B lasting for the full interglacial of MIS5e.
A long growth interruption (hiatus H1) can be correlated with the MIS5d stadial, with resumption of lithofacies Lf-B occurring during the climatic amelioration of interstadial MIS5c. The age profile of the upper part of the flowstone is poorly constrained, and is characterised by several growth interruptions, suggesting that the last glacial was more severe compared to MIS6


The Grosmont: the worlds largest unconventional oil reservoir hosted in polyphase-polygenetic karst, 2013,
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Machel Hans G. , Borrero Mary Luz, Dembicki Eugene, Huebscher Harald4

The Upper Devonian Grosmont platform in Alberta, Canada, is the world’s largest heavy oil reservoir hosted in carbonates, with 400-500 billion barrels of IOIP at an average depth of about 250 – 400 m. Advanced thermal recovery technologies, such as SAGD and electrical in-situ retorting, much higher world market prices for oil and certain political pressures have led to a flurry of activity in the Grosmont since 2006.
The sedimentary stratigraphy of the Grosmont reservoir consists of six stacked car-bonate units interbedded with marls and some evaporites. The latter two originally acted as aquitards during diagenesis but are breached or missing in parts of the area today. Dolomitization by density-driven reflux was the first pervasive diagenetic pro-cess. A dense fracture network was created in three or four phases. Most fractures probably originated from collapse following subsurface salt dissolution and/or from Laramide tectonics far to the west, whereby pulsed crustal loading in the fold-and-thrust belt created a dynamic forebulge in the Grosmont region via multiple pulses of basin-wide crustal flexing, each followed by relaxation. The fracture network probably was reactivated and/or expanded by glacial loading and post-glacial isostatic rebound in the Pleistocene and Holocene, respectively.
The region experienced three or four prolonged periods of epigene karstification, alt-hough there is tangible evidence for only two of them in the Grosmont platform. The first of these episodes was a ‘warm epigene karstification’ during the Jurassic - Creta-ceous, and the second was/is a ‘cold epigene karstification’ that started sometime in the Cenozoic and is continuing to this day. In addition, there is circumstantial evidence for hypogene ‘karstification’ (= dissolution) throughout much of the geologic history of the Grosmont since the Late Devonian. Karstification was accompanied and/or by fol-lowed by extensive hydrocarbon biodegradation.


INVESTIGATIONS INTO THE POTENTIAL FOR HYPOGENE SPELEOGENESIS IN THE CUMBERLAND PLATEAU OF SOUTHEAST KENTUCKY, U.S.A., 2013,
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Florea Lee J.

 

This manuscript offers preliminary geochemical evidence that investigates the potential for hypogene speleogenesis in the Cumberland Plateau of southeastern Kentucky, U.S.A. The region was traditionally considered a classic example of epigenic karst, but new insights have uncovered tantalizing observations that suggest alternatives to simple carbonic acid speleogenesis. Such first-order observations have included natural petroleum seeps at the surface and in caves, occasional cave morphologies consistent with action of hypogene fluids, and prolific gypsum within cave passages. To this point, geochemical data from caves and springs verify carbonic acid as the primary dissolutional agent; however, these same analyses cannot rule out sulfuric acid as a secondary source of dissolution. In this paper, Principal Component Analysis of ionic data reveals two components that coordinate with parameters associated with “karst water” and shallow brine. In contrast, molar ratios of Ca+ and Mg+ as compared to HCO3 - and SO4 2- closely follow the reaction pathway stipulated by the carbonate equilibria reactions. Despite these data, the role, if any, of hypogene speleogenesis in the karst of the Cumberland Plateau remains inconclusive. It is very likely that carbonic acid dominates speleogenesis; however, contributions from sulfuric acid may influence our understanding of “inception” and carbon flux within these aquifers.


KARST PROCESSES AND CARBON FLUX IN THE FRASASSI CAVES, ITALY, 2013,
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Menichetti Marco

 

Hypogean speleogenesis is the main cave formation process in the Frasassi area. The carbon flux represents an important proxy for the evalution of the different speleogenetic processes. The main sources of CO2 in the underground karst system are related to endogenic fluid emissions due to crustal regional degassing. Another important CO2 source is hydrogen sulfide oxidation. A small amount of CO2 is also contributed by visitors to the parts of the cave open to the public.


DEEP TIME ORIGINS OF SINKHOLE COLLAPSE FAILURES IN SEWAGE LAGOONS IN SOUTHEAST MINNESOTA, 2013,
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Alexander Jr. E. C. , Runkel A. C. , Tipping R. G.

Three of the approximately twenty-three municipal wastewater treatment lagoons constructed in the 1970s and 1980s in southeastern Minnesota’s karst region have failed through sinkhole collapse. Those collapses occurred between 1974 and 1992. All three failures occurred at almost exactly the same stratigraphic position. That stratigraphic interval, just above the unconformable contact between the Shakopee and Oneota Formations of the Ordovician Prairie du Chien Group is now recognized as one of the most ubiquitous, regional-scale, karst hydraulic high-transmissivity zones in the Paleozoic hydrostratigraphy of southeastern Minnesota. These karst aquifers have been developing multi-porosity conduit flow systems since the initial deposition of the carbonates about 480 million years ago. The existence of syndepositional interstratal karst unconformities between the Oneota and Shakopee Formations and between the Shakopee and St. Peter Formations, were recognized in the 1800s. About 270 million years ago galena, sphalerite and iron sulfides were deposited in pre-existing solution enlarged joints, bedding planes and caves. The region has been above sea level since the Cretaceous and huge volumes of fresh water have flowed through these rocks. The regional flow systems have changed from east-to-west in the Cenozoic, to north-to-south in or before the Pleistocene. The incision of the Mississippi River and its tributaries has and is profoundly rearranging the ground water flow systems as it varies the regional base levels during glacial cycles. The Pleistocene glacial cycles have removed many of the surficial karst features and buried even more of them under glacial sediments. High erosion rates from row crop agriculture between the us1850s and 1930s filled many of the conduit systems with soil. Over eighty years of soil conservation efforts have significantly reduced the flux of mobilized soil into the conduits. Those conduits are currently flushing much of those stored soils out of their spring outlets. Finally, the increased frequency and intensity of major storm events is reactivating conduit segments that have been clogged and inactive for millions of years.The karst solution voids into which the lagoons collapsed have formed over 480 million years. The recognition and mapping of this major karst zone will allow much more accurate karst hazard maps to be constructed and used in sustainable resource management decisions.


Carbon fluxes in Karst aquifers: Sources, sinks, and the effect of storm flow, 2013,
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White William B.

An effective carbon loading can be calculated from measured alkalinity and pH of karst waters. The carbon loading is independent of the degree of saturation of the water and does not depend on the water being in equilibrium with the carbonate wall rock. A substantial data base of spring water analyses accumulated by students over the past 40 years has been used to probe the CO2 generation, transport, and storage in a variety of drainage basins that feed karst springs. Carbon loading in the water exiting karst drainage basins depends on the rate of CO2 generation in the soils of the catchment areas and on the partitioning between CO2 dissolved in infiltration water and CO2 lost by diffusion upward to the atmosphere. For any given drainage basin there are also influences due to vegetative cover, soil type, and the fraction of the water provided by sinking stream recharge. Losses of CO2 back to the atmosphere occur by speleothem deposition in air-filled caves, by degassing of CO2 in spring runs, and by tufa deposition in spring runs. There are seasonal cycles of CO2 generation that relate growing season and contrasts in winter/summer rates of CO2 generation. Overall, it appears that karst aquifers are a net, but leaky, sink for atmospheric CO2


Do carbonate karst terrains affect the global carbon cycle?, 2013,
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Martin Jonathan B. , Brown Amy, Ezell John

Carbonate minerals comprise the largest reservoir of carbon in the earth’s lithosphere, but they are generally assumed to have no net impact on the global carbon cycle if rapid dissolution and precipitation reactions represent equal sources and sinks of atmospheric carbon. Observations of both terrestrial and marine carbonate systems indicate that carbonate minerals may simultaneously dissolve and precipitate within different portions of individual hydrologic systems. In all cases reported here, the dissolution and precipitation reactions are related to primary production, which fixes atmospheric CO2 as organic carbon, and the subsequent remineralization in watersheds of the organic carbon to dissolved CO2. Deposition of carbonate minerals in the ocean represents a flux of CO2 to the atmosphere. The dissolution of oceanic carbonate minerals can act either as a sink for atmospheric CO2 if dissolved by carbonic acid, or as a source of CO2 if dissolved through sulfide oxidation at the freshwater-saltwater boundary. Since dissolution and precipitation of carbonate minerals depend on ecological processes, changes in these processes due to shifts in rainfall patterns, earth surface temperatures, and sea level should also alter the potential magnitudes of sources and sinks for atmospheric CO2 from carbonate terrains, providing feedbacks to the global carbon cycle that differ from modern feedbacks.


Organic matter flux in the epikarst of the Dorvan karst, France, 2013,
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Simon, Kevin S.

Availability of organic matter plays an important role in karst ecosystems. Somewhat surprisingly, study of the composition and distribution of organic matter in karst aquifers is rare. The most comprehensive study or organic matter flux to date is a two year continuous monitoring of detritus and animal flux in epikarst drip waters and an epikarst-fed cave stream in the Dorvan karst, France. Analysis of those data reveals high temporal variation in detritus and animal flux in both habitats, but little evidence of seasonality in flux. water flux explained 30-69% of the variation in animal flux in both habitats and detritus flux in the epikarst seepage water. Detritus flux in the cave stream was better explained by peak monthly discharge. Lack of coherence between organic matter flux in epikarst seepage and the epikarst stream suggests organic matter transport is governed by differing factors in the two habitats. Overall, much of the particulate organic matter flux in the epikarst occurs as living animals suggesting a dominant role of ecological processes in organic matter transport.


CONDENSATION CORROSION: MEASUREMENTS AND GEOMORPHIC EVIDENCE IN THE FRASASSI CAVES, 2014,
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Galdenzi S. , Jones D. , Macalady J.

The condensation of acidic waters on subaerial carbonate surfaces (condensation corrosion) can be an important speleogenetic agent under certain conditions (Cigna and Forti, 1986; Sarbu and Lascu, 1997). Specific morphologies associated with condensation corrosion include notches, niches, cupolas, megascallops and domes (Audra, 2009), and have been recognized in many caves from different regions of the world and from different geologic settings. Condensation corrosion can be particularly important in thermal caves, where temperature differences facilitate air convection and water condensation, as well as in sulphidic caves, where degassing and subsequent oxidation of hydrogen sulphide (H2S) gas provides a ready source of acidity to the subaerial cave environment.
In pioneering studies on the formation of sulphidic caves, condensation corrosion via H2S degassing and oxidation to sulphuric acid was considered the primary mechanism for speleogenesis (Principi, 1931; Egemeier, 1981). However, recent research has cast doubt on the importance of subaerial H2S oxidation for sulphidic cave formation (Engel et al., 2004). In the Frasassi cave system, Italy, morphological evidence for both subaerial and subaqueous limestone dissolution has been extensively documented (Galdenzi, 1990; Galdenzi and Maruoka, 2003). In particular, corrosion above the water table has resulted in the formation of massive gypsum deposits as well as specific passage morphologies. Measured rates by Galdenzi et al. (1997) corroborated morphological evidence that condensation corrosion is important at least under certain conditions. Therefore, in order to better define the role of subaerial processes in the Frasassi cave system, we quantified sulphide flux to the cave atmosphere in the modern cave environment, and documented morphological evidence for subaerial corrosion in the past


HELIUM ISOTOPES AS INDICATOR OF CURRENT HYPOGENIC KARST DEVELOPMENT IN TAURIDS KARST REGION, TURKEY, 2014,
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Ozyurt N. N. , Bayari C. S.

Hypogenic karst development by means of the aggressiveness of hydrothermal fluids driven and fed by mantle heat and mass flux is a known phenomenon. However, in cases when hydrothermal fluid cools down upon thermal conduction in the near-surface environment and is diluted by near-surface cool groundwater, evidences of this phenomenon may be erased completely. Recent data on the isotopes of helium dissolved in cool karst groundwater samples collected from three different karst aquifers in Turkey suggest an apparent mass flux from mantle, as well as from the crust. In the cases considered, helium content from the mantle increases with the increasing age of groundwater. All cases are located nearby the suture zones which may be easing the upward heat and mass flux. Despite sampling difficulties and high analysis costs, helium isotopes dissolved in cool karst groundwater seem to be useful tool to detect the current hypogenesis at the depths of karst aquifers


Karstification of Dolomitic Hills at south of Coimbra (western-central Portugal) - Depositional facies and stratigraphic controls of the (palaeo)karst affecting the Coimbra Group (Lower Jurassic), 2014,
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Dimuccio, Luca Antonio

An evolutionary model is proposed to explain the spatio-temporal distribution of karstification affecting the Lower Jurassic shallow-marine carbonate succession (Coimbra Group) of the Lusitanian Basin, cropping out in the Coimbra-Penela region (western-central Portugal), in a specific morphostructural setting (Dolomitic Hills). Indeed, in the Coimbra Group, despite the local lateral and vertical distributions of dolomitic character and the presence of few thick sandy-argillaceous/shale and marly interbeds, some (meso)karstification was identified, including several microkarstification features. All types of karst forms are commonly filled by autochthonous and/or allochthonous post-Jurassic siliciclastics, implying a palaeokarstic nature.

The main aim of this work is to infer the interplay between depositional facies, diagenesis, syn- and postdepositional discontinuities and the spatio-temporal distribution of palaeokarst. Here, the palaeokarst concept is not limited to the definition of a landform and/or possibly to an associated deposit (both resulting from one or more processes/mechanisms), but is considered as part of the local and regional geological record.

Detailed field information from 21 stratigraphic sections (among several dozens of other observations) and from structural-geology and geomorphological surveys, was mapped and recorded on graphic logs showing the lithological succession, including sedimentological, palaeontological and structural data. Facies determination was based on field observations of textures and sedimentary structures and laboratory petrographic analysis of thin-sections. The karst and palaeokarst forms (both superficial and underground) were classified and judged on the basis of present-day geographic location, morphology, associated discontinuities, stratigraphic position and degree of burial by post-Jurassic siliciclastics that allowed to distinguish a exposed karst (denuded or completely exhumed) than a palaeokarst (covered or partially buried).

A formal lithostratigrafic framework was proposed for the local ca. 110-m-thick combined successions of Coimbra Group, ranging in age from the early Sinemurian to the early Pliensbachian and recorded in two distinct subunits: the Coimbra formation, essentially dolomitic; and the overlying S. Miguel formation, essentially dolomitic-limestone and marly-limestone.

The 15 identified facies were subsequently grouped into 4 genetically related facies associations indicative of sedimentation within supra/intertidal, shallow partially restricted subtidal-lagoonal, shoal and more open-marine (sub)environments - in the context of depositional systems of a tidal flat and a very shallow, inner part of a low-gradient, carbonate ramp. In some cases, thick bedded breccia bodies (tempestites/sismites) are associated to synsedimentary deformation structures (slumps, sliding to the W to NW), showing the important activity of N–S and NNE–SSW faults, during the Sinemurian. All these deposits are arranged into metre-scale, mostly shallowing-upward cycles, in some cases truncated by subaerial exposure events. However, no evidence of mature pedogenetic alteration, or the development of distinct soil horizons, was observed. These facts reflect very short-term subaerial exposure intervals (intermittent/ephemeral), in a semiarid palaeoclimatic setting but with an increase in the humidity conditions during the eogenetic stage of the Coimbra Group, which may have promoted the development of micropalaeokarstic dissolution (eogenetic karst).

Two types of dolomitization are recognized: one (a) syndepositional (or early diagenetic), massive-stratiform, of “penesaline type”, possibly resulting from refluxing brines (shallow-subtidal), with a primary dolomite related to the evaporation of seawater, under semiarid conditions (supra/intertidal) and the concurrent action of microbial activity; another (b) later, localized, common during diagenesis (sometimes with dedolomitization), particularly where fluids followed discontinuities such as joints, faults, bedding planes and, in some cases, pre-existing palaeokarstic features.

The very specific stratigraphic position of the (palaeo)karst features is understood as a consequence of high facies/microfacies heterogeneities and contrasts in porosity (both depositional and its early diagenetic modifications), providing efficient hydraulic circulation through the development of meso- and macropermeability contributed by syn- and postdepositional discontinuities such as bedding planes, joints and faults. These hydraulic connections significantly influenced and controlled the earliest karst-forming processes (inception), as well as the degree of subsequent karstification during the mesogenetic/telogenetic stages of the Coimbra Group. Multiple and complex karstification (polyphase and polygenic) were recognized, including 8 main phases, to local scale, integrated in 4 periods, to regional scale: Jurassic, Lower Cretaceous, pre-Pliocene and Pliocene-Quaternary. Each phase of karstification comprise a specific type of (palaeo)karst (eogenetic, subjacent, denuded, mantled-buried and exhumed).

Finally, geological, geomorphological and hydrogeological characteristics allowed to describe the local aquifer. The elaborated map of intrinsic vulnerability shows a karst/fissured and partially buried aquifer (palaeokarst) with high to very high susceptibility to the contamination.


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