1,721,198 research outputs found
Ricostruzioni paleoclimatiche del Peri-Adriatico attraverso speleotemi: primi risultati
Full text linkNell’ambito di una tesi di dottorato presso l’Università di Bologna e l’Université de Savoie (Francia), ed in
collaborazione con l’Università di Melbourne (Australia), si sta portando avanti un ambizioso progetto di ricerca
con l’intento di individuare dei record paleoclimatici in speleotemi campionati in grotte d’Italia e del Carso
dinarico. In questa prima fase di campionamento, grazie al coinvolgimento degli speleologi locali, sono state
raccolte stalagmiti e colate già rotte in precedenza in grotte della Puglia, dell’Emilia Romagna, del Triestino,
della Slovenia, e della Bosnia Erzegovina. I campioni sono stati tagliati longitudinalmente lungo l’asse di
accrescimento e poi lucidati. Dei campioni più promettenti (con laminazione ben visibile, calcite primaria pulita,
senza evidenti segni di ricristalizzazione) sono stati datati bottom e top per il loro inquadramento cronologico. Il
successivo campionamento a microdrilling ha permesso di ricavare le polveri utili per le analisi degli isotopi
stabili dell’ossigeno e del carbonio, effettuate tramite spettrometria di massa. Tali studi permetteranno di
ricostruire il clima del passato delle aree di campionamento, fornendo un valido contributo allo studio
paleoclimatico del Mediterraneo centrale
Caratteristiche minero-petrografiche di alcuni particolari speleotemi delle grotte di Matanzas, Cuba
Full text linkDurante la spedizione organizzata da La Salle 3D – International Team, Photo, Video and Documentation nel
Dicembre 2012 sono state studiate diverse grotte nei pressi di Matanzas, sulla costa settentrionale dell’Isola di
Cuba a circa 90 km ad E dell’Avana. In particolare nella Cueva de Santa Catalina è presente una ricchissima
associazione di speleotemi tra cui le comuni stalagmiti, stalattiti, colonne, vaschette, colate e perle di grotta, di
recente formazione nelle attuali condizioni vadose, ma anche forme più rare come cave clouds, coni, calcite
flottante, folia e “funghi” formatisi in tempi passati quando la grotta era parzialmente allagata. Sono le ultime ad
aver reso famosa la grotta in tutto il mondo. In questo lavoro vengono illustrate le caratteristiche mineropetrografiche
di questi rari speleotemi, che insieme alla morfologia degli stessi, portano ad ipotizzare l’ambiente
molto particolare in cui si sono formate
Unsaturated flow in a structurally complex karst aquifer
Full text linkThe objective of this doctoral project was to unravel the functioning of the unsaturated zone of a karst aquifer that developed in a complex structural setting. The studied system, Bossea cave (Southern Piedmont, Italy) is located in the Ligurian Alps. A multidisciplinary approach was adopted to investigate the unsaturated flow dynamics of the system. Geological surveys, structural analysis and thin-section microscopy permitted to recognize the main circulation pathways. Bossea karst system developed taking advantage of a peculiar structural setting in which transpression between two left-lateral strike slip faults led to a disharmonic deformation of the Permian basement and the Mesozoic carbonates. Flow circulation developed along the bedding planes of the folded carbonate sequence, but when the water reached the disharmonic surface mechanical erosion of the basement non-carbonate rocks started. The hydrological monitoring of the underground river and several secondary tributaries permitted to recognize a complex and heterogeneous architecture in the unsaturated zone. Drip sites hydrological behavior is controlled by the fracture organization and permeability in the unsaturated zone. The drip sites show a piston flow behavior, but each inflow has peculiar flow characteristics that are related to the drainage of small perched reservoirs in the fractured rocks of the unsaturated zone. The recession analysis, cubic law inversion and fractal analysis confirmed that the fracture network architecture controls the discharge of the vadose inflows. Hydrochemical investigations permitted to recognize the influence of the different lithologies on the inflows discharge. This cave represented a unique opportunity to study in detail the dynamics of an unsaturated zone that is strongly influenced by inputs from different lithologies, in addition to the carbonates. The availability of a huge amount of data collected for more than 15 years permitted to study this system in a wide range of conditions, from drought to extreme flooding events
Structural and stratigraphic control on hypogene dissolution in carbonate rocks: case studies of cave analogues and implications for karst reservoirs
Full text linkThe aim of this research is to improve the understanding of the factors that control the formation of karst porosity in hypogene settings and its associated patterns of void-conduit networks. Subsurface voids created by hypogene dissolution may span from few microns to decametric tubes providing interconnected conduit systems and forming highly anisotropic permeability domains in many reservoirs. Characterizing the spatial-morphological organization of hypogene karst is a challenging task that has dramatic implications for the applied industry, given that only partial data can be acquired from the subsurface by indirect techniques. Therefore, two outcropping cave analogues are examined: the Cavallone-Bove Cave in the Majella Massif (Italy), and the karst systems of the Salitre Formation (Brazil). In the latter, a peculiar example of hypogene speleogenesis associated with silicification has been studied, providing an analogue of many karstified reservoirs hosted in cherts or cherty-carbonates within mixed sedimentary sequences. The first part of the thesis is focused on the relationships between fracture patterns and flow pathways in deformed units in: 1) a fold-and-thrust setting (Majella Massif); 2) a cratonic block (Brazil). These settings represent potential playgrounds for the migration and accumulation of geofluids, where hypogene conduits may affect flow pathways, fluid storage, and reservoir properties. The results indicate that localized deformation producing cross-formational fracture zones associated with anticline hinges or fault damage zones is critical for hypogene fluid migration and karstification. The second part of the thesis deals with the multidisciplinary study of hydrothermal silicification and hypogene dissolution in Calixto Cave (Brazil). Petrophysical analyses and a geochemical characterization of silica deposits are used to unravel the spatial-morphological organization of the conduit system and its speleogenesis. The novel results obtained from this cave shed new light on the relationship between hydrothermal silicification, hypogene dissolution and the development of multistorey cave systems in layered carbonate-siliciclastic sequences
Speleogenesis of Sulfuric Acid caves in southern Italy
Full text linkThe main objectives of this research are: a) to investigate the main processes involved in sulfuric acid speleogenesis (SAS) of Italian caves, b) to estimate the dissolution-corrosion rate in several active SAS systems of southern Italy, and c) to contextualize landscape evolution using subhorizontal cave levels in the central-southern Apennine Chain.
SAS caves formed in hypogene conditions (i.e., rising fluids), and are influenced by H2S-rich waters, which gain their acidity in deep-seated settings. The geological situation of Italy allows it to host ~25% of the worldwide known SAS caves, located along the the Apennine Chain, Apulia, Sicily and Sardinia.
Geomorphological and mineralogical investigations can be used to identify inactive SAS environments, and recognize the conditions in which they originated. The most common geomorphological features refer to unconfined settings, which likely influenced the speleogenesis in the last stages of void formation, and are therefore, well-preserved.
Peculiar suites of secondary byproducts including gypsum, sulfur, alunite, natroalunite, and jarosite strongely contribute to clarify cave speleogenesis. Sulfur stable isotopes may contribute to elucidate the source of H2S, which in Italy seems to be mainly related to bacterial sulfate reduction of Triassic evaporites interacting with hydrocarbons and/or organic matter. Moreover, gypsum and alunite dating may help to pin down the chronology cave speleogenesis.
Active SAS caves show waters undersaturated with respect to gypsum and calcite and atmosphere composed of degassing hypogene H2S, CO2 and CH4. These special conditions promote the growth of microbial biofilms, composed of extremophile communities of bacteria and archaea able to arrange themselves into special structures. Active SAS caves can be used as laboratories to study the dissolution-corrosion rate, and calculate weight variation over time.
Finally, subhorizontal SAS levels and alunite ages can help in understanding the uplift and erosion rates of the mountain hosting the cave system
Speleogenesi e minerali secondari in ambiente quarzitico e quarzo-arenitico
Full text linkThe main objective of this research is to improve the comprehension of the processes controlling the formation of caves and karst-like morphologies in quartz-rich lithologies (more than 90% quartz), like quartz-sandstones and metamorphic quartzites. In the scientific community the processes actually most retained to be responsible of these formations are explained in the “Arenisation Theory”. This implies a slow but pervasive dissolution of the quartz grain/mineral boundaries increasing the general porosity until the rock becomes incohesive and can be easily eroded by running waters. The loose sands produced by the weathering processes are then evacuated to the surface through processes of piping due to the infiltration of waters from the fracture network or the bedding planes.
To deal with these problems we adopted a multidisciplinary approach through the exploration and the study of several cave systems in different tepuis. The first step was to build a theoretical model of the arenisation process, considering the most recent knowledge about the dissolution kinetics of quartz, the intergranular/grain boundaries diffusion processes, the primary diffusion porosity, in the simplified conditions of an open fracture crossed by a continuous flow of undersatured water. The results of the model were then compared with the world’s widest dataset (more than 150 analyses) of water geochemistry collected till now on the tepui, in superficial and cave settings.
All these studies allowed verifying the importance and the effectiveness of the arenisation process that is confirmed to be the main process responsible of the primary formation of these caves and of the karst-like superficial morphologies. The numerical modelling and the field observations allowed evaluating a possible age of the cave systems around 20-30 million of years
Morfometria della Grotta dell'Orso (Ponte di Veja, Monti Lessini) mediante laserscanner
Full text linkUn rilievo laserscanner della Grotta dell'Orso, vicino al Ponte di Veja (Monti Lessini) ha consentito di descrivere in dettaglio questo sistema carsico e trarre alcune conclusioni dal punto di vista morfometrico e speleogenetico
Mushroom speleothems: stromatolites that formed in the absence of phototrophs.
No full textUnusual speleothems resembling giant mushrooms occur in Santa Catalina Cave, Cuba. Although these mineral buildups are considered a natural heritage, their composition and formation mechanism remain poorly understood. Here we characterize their morphology and mineralogy and present a model for their genesis. We propose that the mushrooms, which are mainly comprised of calcite and aragonite, formed during four different phases within an evolving cave environment. The stipe of the mushroom is an assemblage of three well-known speleothems: a stalagmite surrounded by calcite rafts that were subsequently encrusted by cave clouds (mammilaries). More peculiar is the cap of the mushroom, which is morphologically similar to cerebroid stromatolites and thrombolites of microbial origin occurring in marine environments. Scanning electron microscopy investigations of this last unit revealed the presence of fossilized extracellular polymeric substances (EPS) – the constituents of biofilms microbial mats. These organic microstructures are partially mineralized with Ca-carbonate, suggesting that the mushroom cap formed through a microbially-influenced mineralization process. The existence of cerebroid Ca-carbonate buildups forming in dark caves (i.e., in the absence of phototrophs) has interesting implications for the study of fossil microbialites preserved in ancient rocks, which are today considered as one of the earliest evidence for life on Earth
Exploring Holocene Climate Signals Recorded in Stalagmites from Bosnia. A Multi Proxy Approach Coupling Petrography and Geochemistry
No full textThe Mediterranean area is a densely populated region characterised by an extremely complex atmospheric circulation, which is particularly sensitive to any modification of air mass dynamics. Thus, the understanding of past climate fluctuations in this area is of great importance to gain insight in the pattern of regional climate variability in response to global climate changes. The central Mediterranean area displayed contrasting climatic responses to atmospheric circulation re-organization following the last glacial period: drier/wetter conditions lasted until about 4.5 ka in the northern/southern regions, followed by an opposite trend.
To better understand Holocene climate dynamics in the Balkans, a region where only few palaeoclimate reconstructions are available, five stalagmites were collected from two Bosnian caves. Rainfall and cave monitoring was set up in order to understand present day cave hydrology and better interpret the climate and/or environmental signal transfer to the karst.
All stalagmites were dated using the U-Th method. Stable carbon and isotope ratios were analysed along the growth axis. Indeed, these values can provide information about temperature, precipitation regime and vegetation cover if calcite is deposited close to isotopic equilibrium conditions. Unfortunately, stable isotope profiles were noisy and not interpretable straightforwardly. Therefore, a multi proxy approach was adopted, coupling stable isotope and trace element profiles with detailed petrographic observations. This allowed for the interpretation of geochemical proxies and petrography variations in relation to hydrological changes. In particular, a trend towards relatively drier conditions appears since about 4 kyr, suggesting a local response to climate change similar to the one of the southern Mediterranean sites.
A marginal part of this project involved the examination of a dark lamina deposited around 1.2 ka in the 4 samples from Mračna Pećina cave. This layer, appearing fluorescent under the fluorescence optic microscope, was identified with SEM observation, which demonstrated its soot nature
Le Grotte di Miniera. Tra economia mineraria ed economia turistica.
No full textAtti del Convegno internazionale "Le Grotte di Miniera. Tra economia mineraria ed economia turistica" tenutosi nella Miniera di Monteponi ad Iglesias il 1-5 Dicembre 2004
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