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Castel Guelfo di Bologna, Italy

De Waele J.,Italian Institute of Speleology | Lauritzen S.-E.,University of Bergen | Parise M.,National Research Council Italy
Earth Surface Processes and Landforms | Year: 2011

A large number of uniform cone-shaped dissolution pipes has been observed and studied in Quaternary coastal calcareous arenites in Apulia and Sardinia (Italy) and Tunisia. These cylindrical tubes have a mean diameter of 52·8cm and are up to 970cm deep (mean depth for sediment-free pipes is 1·38m). They generally have smooth walls along their length, are perfectly vertical and taper out towards their bottoms. Their development is not influenced by bedding nor fractures. Sometimes their walls are coated by a calcrete crust. Their morphology has been studied in detail and their relationships with the surrounding rocks and with the environment have been analysed. The perfectly vertical development is a clear evidence of their genesis controlled by gravity. The depth of the dissolution pipes can be described by an exponential distribution law (the Milanovic distribution), strongly suggesting they developed by a diffusion mechanism from the surface vertically downward. We believe dissolution pipes preferentially form in a covered karst setting. Local patches of soil and vegetation cause infiltration water to be enriched in carbon dioxide enhancing dissolution of carbonate cement and local small-scale subsidence. This process causes the formation of a depression cone that guides infiltrating waters towards these spots giving rise to the downward growth of gravity-controlled dissolution pipes. A change of climate from wetter phases to drier and hotter ones causes the formation of a calcrete lining, fossilizing the pipes. When the pipes become exposed to surface agents by erosion of the sediment cover or are laterally breached the loose quartz sand filling them may be transported elsewhere. © 2010 John Wiley & Sons, Ltd. Source

Ruggieri R.,Centro Ibleo Of Ricerche Speleo Idrogeologiche | Ruggieri R.,University of Nova Gorica | De Waele J.,Italian Institute of Speleology
Acta Carsologica | Year: 2014

The peninsula of San Vito Lo Capo, 50 km West of Palermo (Sicily), is characterised by the presence of a wide set of evidences of past sea level changes, such as marine terraces, notches, marine and coastal caves with phreatic overgrowths on speleothems, and continental and marine deposits. The exceptional good preservation of these landforms and deposits has been used by different authors for the reconstruction of sea level changes and neotectonic movements. Among the many caves discussed by previous authors, most are of marine origin and can preserve signs of old sea level highstands such as notches and marine or continental sediments. However, two caves in particular, Fantasma Cave and Falesia Rocca Rumena I cave, show evidences to be flank margin caves. Both caves are records of rising and falling sea level, and their position and the correlation with marine terraces suggest them to be around 0.8 and 1.1-1.2 Ma old respectively. This study shows that not all sea level high stands are preserved in the stratigraphical and geomorphological record. Source

A detailed petrographic, structural and morphometric investigation of different types of caves carved in the quartz-sandstones of the "tepui" table mountains in Venezuela has allowed identification of the main speleogenetic factors guiding cave pattern development and the formation of particular features commonly found in these caves, such as funnel-shaped pillars, pendants and floor bumps. Samples of fresh and weathered quartz-sandstone of the Mataui Formation (Roraima Supergroup) were characterised through WDS dispersive X-ray chemical analyses, picnometer measurements, EDAX analyses, SEM and thin-section microscopy. In all the caves two compositionally different strata were identified: almost pure quartz-sandstones, with content of silica over 95% and high primary porosity (around 4%), and phyllosilicate-rich quartz-sandstone, with contents of aluminium over 10% and low primary porosity (lower than 0.5%). Phyllosilicates are mainly pyrophyllite and kaolinite. SEM images on weathered samples showed clear evidence of dissolution on quartz grains to different degrees of development, depending on the alteration state of the samples. Grain boundary dissolution increases the rock porosity and gradually releases the quartz grains, suggesting that arenisation is a widespread and effective weathering process in these caves. The primary porosity and the degree of fracturing of the quartz-sandstone beds are the main factors controlling the intensity and distribution of the arenisation process. Weathering along iron hydroxide or silt layers, which represent inception horizons, or a strata-bounded fracture network, predisposes the formation of horizontal caves in specific stratigraphic positions. The loose sands produced by arenisation are removed by piping processes, gradually creating anastomosing open-fracture systems and forming braided mazes, geometric networks or main conduit patterns, depending on the local lithological and structural guidance on the weathering process. This study demonstrates that all the typical morphologies documented in these quartz-sandstone caves can be explained as a result of arenisation, which is guided by layers with particular petrographic characteristics (primary porosity, content of phyllosilicates and iron hydroxides), and different degrees of fracturing (strata-bounded fractures or continuous dilational joints). © 2014 Elsevier B.V. Source

Gazquez F.,University of Almeria | Calaforra J.-M.,University of Almeria | Forti P.,Italian Institute of Speleology | Rull F.,University of Valladolid | And 3 more authors.
International Journal of Speleology | Year: 2012

Some of the most outstanding hypogenic gypsum speleothems worldwide have been recently discovered in the Naica mines. The Cueva de las Espadas (Swords Cave), which lies at 120 m depth, hosts a rare type of speleothem called "espada" ("sword"). This study contributes to the understanding of the mineralogical composition of these singular speleothems, by means of their examination using micro-Raman spectroscopy, FT-IR spectroscopy and EDX microprobe. Our data revealed a complex mineralogy comprising a high-purity selenite core covered by several layers of calcite, aragonite and gypsum. Solid inclusions of polymetallic oxides (Mn-Pb-Zn) and graphite were also detected. The position of the water table during the genesis of the "espada" speleothems (over the past 60 kyr) was deduced from their mineralogy. Water level fluctuations at around -120 m depth led to environmental changes within the Cueva de las Espadas. The selenite core and gypsum layers were precipitated under biphasic (water-rock) conditions when the cave was submerged under hydrothermal water. The aragonite precipitation required triphasic (air-water-rock) conditions and occurred when the water table intercepted the cave, allowing the CO2 exchange necessary for carbonate precipitation. Solid inclusions were trapped in an aerobic environment when the gypsum-aragonite boundary condition occurred. A thin calcite layer was precipitated under vadose conditions after the water table definitively moved out of the cave. Source

Du Preez G.C.,North West University South Africa | Forti P.,Italian Institute of Speleology | Jacobs G.,North West University South Africa | Jordaan A.,North West University South Africa | Tiedt L.R.,North West University South Africa
International Journal of Speleology | Year: 2015

Ngamiland in northwestern Botswana hosts the Gcwihaba Caves which present unique subterranean environments and host speleothems never before recorded. Cave atmospheric conditions can be extreme with temperatures as high as 28°C and relative humidity nearing 99.9%. Within Dimapo and Diviner’s Caves peculiar root speleothems that we named ‘Hairy Stalagmites’ were found. These stalagmites are closely associated with the roots of Namaqua fig (Ficus cordata) trees that enter the cave environment in search of water. Pieces of broken stalagmites were sampled from Dimapo Cave for further investigations. Stereo and electron microscopy revealed that the Hairy Stalagmites consist of multiple intertwined tubes created when thin films of CaCO3are deposited around fine lateral roots. The importance of the roots is substantiated with evidence of calcified epidermal cells, apical meristems and epidermal imprints. The development of these stalagmites starts when roots accumulate on the cave floor in the vicinity of a water drip and a root nest is created to capture the water. From this point the roots grow upwards (positive hydrotropism) allowing the development of the calcite structure, and as CO2diffusion and evaporation occurs, CaCO3is deposited. The environmental conditions necessary for the growth of Hairy Stalagmites, as well their developmental mechanism, are discussed and illustrated. © 2015, Societa Speleologica Italiana. All rights reserved. Source

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