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Il complesso carsico Grotta del Fiume - Grotta Grande del Vento e l'evoluzione geomorfologica della gola di Frasassi (Appennino umbro-marchigiano).

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... The karst tunnels are arranged on at least four main levels, the evolution of which is linked to standstill and deepening phases of the surface hydrographic network. The lower and most recent levels, between 200 and 300 m. a.s.l., probably originated in the middle Pleistocene and late Pleistocene periods, as indicated by the correlations with the terraced alluvial deposits [3] and by the dating of speleothems, with ages reaching 200,000 years old [4]. ...
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One of the most fascinating aspects of the work of geologist lies in knowing how to read the physical landscape as an expression of the geological and geomorphological phenomena that shaped the Earth’s relief over time. The necessity to disseminate these vast areas of knowledges and skills starts from here, with the aim to enhance the concept of geodiversity and to raise awareness for its protection and promotion. This work aims to share some examples of projects realized following the subscription of agreement between different public authorities in the Apennine territory of Marche Region in Italy, such as the Geology Section of the University of Camerino (MC), “Consorzio Frasassi” (which manages the underground karst complex of Frasassi caves) and municipality of Genga (AN), where Frasassi caves are located. Thanks to this partnership, our research group realized didactic geological notebooks for school groups visiting the caves and interactive museum laboratories in 3D, showing the geological evolution of the area. This sharing of knowledge will contribute to educate communities about the importance of the geological heritage. At the same time, this project can serve as motivation to establishing the same type of collaborations in those territories where similar projects can be replicated.
... The southwestern side of Sala del Fuoco is bound by boulder breccia deposits, which testify to a history of collapses of the vaults probably caused by strong earthquakes (Fig. 5A). These boulder breccias are a common feature in all large rooms of the Grotta del Fiume-Grotta Grande del Vento cave complex (Bocchini & Coltorti, 1990), including Sala delle Ossa, which is adjacent to Sala del Fuoco. However, in a small area on the northern end of Sala del Fuoco's boulder breccia (Site 4 in Fig. 5A; see panoramic view in Fig. 11), we noticed an unusual deposit of handsize, 1 to 3 cm-thick slabs made up of speleothemic calcite, covering an area of about 1.5 x 1.5 m. ...
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In the late fall of 1986, a team of cavers from the Gruppo Speleologico Marchigiano of Ancona reported to the regional Archeological Superintendence their discovery in a room of the Grotta del Fiume Cave (Marche region of central Italy) of archeological finds such as the charcoal remains of a bonfire, a number of ibex bones, and four chert artifacts. However, since the discovery and archival of all this material, no further research or focused studies were carried out about this important archeological site. Therefore, we engaged in a thorough re-examination of this site by mapping this part of the Grotta del Fiume Cave with modern surveying approaches, including terrestrial laser scanner and ground penetrating radar. Moreover, we have radiocarbon dated a few ibex bones and also charcoal samples from the main fireplace and other smaller charcoal deposits we found scattered around the room's floor. The chert artifacts were examined in detail and their typology classified accordingly. U-Th dating of calcite from speleothems helped us reconstruct this hypogeal environment at the time it was frequented by man. We also studied a puzzling deposit of speleothem crust slabs piled up in a corner of the cave, which may represent a funeral earthen mound. All in all, the absence of artifacts other than the four chert blades, the few ibex bones, the one main fireplace and three other minor charcoal deposits in the room, and the probable earthen mound located tens of meters underground from a now debris-sealed entrance, lead us to hypothesize that this cave room does not represent a residential dwelling but rather a worship place sporadically utilized by few representatives of a local Epigravettian hunter community.
... The hypogenic karst model of Galdenzi (1990) and Bocchini and Coltorti (1990), which was inspired by the geomorphologic study of Cattuto (1976), and corroborated by the speleothem U-Th geochronology of Taddeucci et al. (1992Taddeucci et al. ( , 1994, explains the multistory architecture of the Frasassi cave complex as a result of Pleistocene tectonic uplifting coupled with river erosion and incision of this region. Therefore, it seems puzzling that the slack-water samples from the Sala della Sabbia (SDS) and the Caverna del Carbone (CDC), which are both located on the third cave floor at the same elevation of ~235 m asl (i.e., ~30 m above present thalweg), yielded significantly different luminescence ages. ...
... using limestone tablets and demonstrated that the highest values (68-119 mm ka -1 ) of dissolution-corrosion occurred where the flow of sulfidic waters was quite fast. These measurements, in agreement with the previous theories, confirmed that the Fiume-Vento system originated during the middle-upper Pleistocene (Bocchini and Coltorti, 1990;Taddeucci et al., 1992). ...
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Many active and inactive hypogene sulfuric acid cave systems are known along the Apennines, Italy. The Cavallone-Bove cave system is located in the external part of the central Apennine Chain, in the Majella Massif, and opens at 1470 m asl along the Taranta Gorge (South of Chieti). The presence in these caves of peculiar geomorphological features, such as feeders, rising channels, megacusps, cupolas, and replacement pockets, offers evidence of rising acidic fluids. The secondary mineral deposits, including meter-size white gypsum deposits, alunite, jarosite, black layers of iron‑manganese oxides and hydroxides, along with a rare association of authigenic rutile-ilmenite minerals indicate a sulfuric acid origin. Stable isotope analyses of sulfates further confirm a sulfuric acid speleogenetic (SAS) origin of these minerals and, in general, of the whole cave system, with H 2 S coming from the bacterial sulfate reduction of deep-seated Triassic evaporites interacting with hydrocarbons. Alunite dating demonstrates this water table SAS cave to have been active at least until 1.52 ± 0.28 Ma. All the evidence suggests that Cavallone-Bove is an ancient sulfuric acid karst system that was uplifted <1 km above pre-existing base level. The age of speleogenesis further suggests that tectonic uplift of this area was as high as 670 m My ⁻¹ over the last 1.5 Ma.
... using limestone tablets and demonstrated that the highest values (68-119 mm ka -1 ) of dissolution-corrosion occurred where the flow of sulfidic waters was quite fast. These measurements, in agreement with the previous theories, confirmed that the Fiume-Vento system originated during the middle-upper Pleistocene (Bocchini and Coltorti, 1990;Taddeucci et al., 1992). ...
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In Italy, especially along the Apennine Chain, numerous active and inactive sulfuric acid speleogenetic (SAS) caves have been documented in the last two decades. Here we present an overview of these peculiar hypogene systems, illustrating their main geomorphological and mineralogical features, and the microbial signatures observed in the active underground environment. SAS caves are widely distributed in the northern and central Apennines, whereas they are less abundant in the southern Apennines, in the Apulian foreland, in Sicily and in Sardinia. Their location is significantly influenced by lithological and structural rock properties, as they occur in carbonate areas where acidic fluids, deriving from the interactions with deep-seated sulfates and/or sulfides, rise through deeply rooted geological structures. Geomorphological observations demonstrated sub-horizontal maze passages to be one of the most favorite arrangements for SAS caves, whereas gypsum, sulfur and alunite supergroup minerals are the most typical sulfuric acid by-products. The δ ³⁴ S results demonstrated the deep-seated H 2 S sources to be mainly related to the interaction between Triassic evaporites and hydrocarbons.
... Le grotte di Frasassi si aprono nel versante adriatico dell'Ap pen nino Umbro Marchi giano, a circa 40 km dal mare, in una piccola dorsale anti cli nale tagliata da una profonda gola incisa dal torrente Sentino (Fig. 1concen tra zioni fino a 18 mg/l; queste acque devono il loro chimismo alla risa lita attra verso sotto stanti rocce evapo ri tiche ed alla misce la zione con quan tità variabili stagio nal mente di acque meteo riche (SIGHI NOLFI,TAZIOLI et al., 1990;GALDENZI et al., 1999a& COLTORTI, 1990;TADDEUCCI et al., 1992).I piani infe riori delle cavità, compresi tra quote di 200 e 300 m, si sono svilup pati in condi zioni idro geolo giche analoghe a quelle attuali; ciò è chia ra mente testi mo niato dalle morfo logie simili, sia in grande che in detta glio, nonché dalla iden tica confor ma zione del reti colo ipogeo; nei piani ubicati a quote più elevate (tra i 300 ed i 500 m) le carat te ri stiche morfo lo giche sono invece parzial mente diffe renti. Ogni piano presenta un anda mento essen zialmente rami forme, con grandi ambienti che termi nano improv vi sa mente su strette fessure e cuni coli in cui possono svilup parsi zone a spon ge work; non mancano tratti labi rin tici, gene ral mente impo stati su sistemi di frat ture. ...
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Le ricerche condotte nei livelli inferiori delle Grotte di Frasassi (Italia centrale), interessati dalla circolazione di acque freatiche sulfuree, hanno evidenziato l'importanza dei processi redox tra l'idrogeno solforato contenuto nelle acque freatiche e l'Ossigeno presente in atmosfera e nelle acque meteoriche. Presso la superficie freatica ricche comunità di batteri chemioautotrofici utilizzano l'energia chimica rilasciata dall'ossidazione dell'H2S per produrre in situ materia organica, che rappresenta la base per la catena alimentare ipogea. Una ricca e diversificata fauna ipogea si è adattata a queste particolari condizioni ecologiche: la maggior parte delle specie sono endemiche e la loro diffusione è limitata ai soli rami sulfurei delle grotte. I processi di ossidazione batterica dell'H2S giocano un importante ruolo anche nella speleogenesi: gli ioni H + ed SO4 = , liberati dal metabolismo batterico, interagiscono con il calcare favorendo i processi di soluzione in ambiente freatico e causando la formazione di gesso in ambiente vadoso. La corrosione carsica appare così concentrata nelle zone prossime alla superficie freatica, in conseguenza dei processi redox in cui è implicata l'attività batterica. I livelli superiori delle grotte di Frasassi, fossili per l'abbassamento del locale livello di base, sono interessati da ampia diffusione di depositi gessosi dovuti ad una passata circolazione di acque sulfuree: ciò evidenzia l'importanza dei processi di ossidoriduzione dello zolfo durante la genesi dell'intero complesso carsico. Lo sviluppo delle gallerie carsiche avveniva principalmente nella zona freatica poco profonda, dove le acque sulfuree risalienti si miscelavano con acque d'infiltrazione, ossigenate, mentre croste e depositi gessosi si formavano al di sopra del livello freatico per effetto dei vapori sulfurei. PAROLE CHIAVE: chemiosintesi, batteri solfossidanti, comunità autotrofiche, speleogenesi, gesso, grotte di Frasassi. Abstract CHEMOSYNTHESIS AND SPELEOGENESIS IN A HYPOGEAN ECOSYSTEM: THE SULFIDIC SECTIONS OF THE FRASASSI CAVES (central Italy). The lower levels of Frasassi caves (central Italy) are intersected by the flow of sulfide-rich phreatic waters. Recent investigations pointed out the relationship between the redox interface in these caves (hydrogen sulfide in groundwater-oxygen in the atmosphere and in the seepage water) and their biological and geomorphologic characteristics. Chemoautotrophic microorganisms living at this interface thrive using the chemical energy resulting from the oxidation of H2S. They form microbial mats covering the surface of the water, the sediments, and the cave walls. These rich microbial communities use the chemical energy to produce organic matter in situ, and this represents the food base for rich and abundant communities of invertebrates that inhabit the sulphidic sections of the caves. Stable isotope investigations using carbon and nitrogen provided conclusive evidences that the cave ecosystems are indeed chemoautotrophically based. Most of the invertebrate species living in the deep sections of these caves are endemic, and seven new species have been identified so far. These cave communities live only in the proximity of the redox interface; the upper dry non-sulphidic cave passages are usually very poor in fauna. The sulfur-oxidizing bacteria play an important role in the ecology of the caves as well as in speleogenesis: they excrete sulfate ions that interact with the limestone bedrock determining its solubilization in the phreatic zone and its re place ment by gypsum in the vadose sectors of the caves. Consequently, most of the limestone corrosion takes place in the upper part of the phreatic zone and is a consequence of the oxido-reduction phenomena involving the bacterial activity. At the present time, the upper levels of Frasassi caves are not intersected by sulphidic water circulation as a result of the lowering of the water table. Gypsum deposits are widespread in these upper cave levels and they consist mainly of re place ment crusts on the cave walls and white, finely grained floor deposits in the large cave rooms. Both these types of gypsum deposits are the result of H2S-oxidation above the old sulphidic water level. The morphology of the caves and the presence of gypsum deposits in the upper passages show that sulfur-oxidation has played a very important role in the development of the Frasassi caves. Solutional passages formed mainly in the shallow phreatic zone, where rising H2S-rich groundwaters mix with oxygenated seepage waters, while gypsum re place ment crusts formed above the water table as a result of condensation phenomena.
... The lower parts of the cave system are developed near the present local base level, at 200 m elevation, and include two main levels at 225 and 250 m, with some minor levels. These cave levels formed in the middle and upper Pleistocene, as confirmed by correlation with the gravel terraces in the river valleys (Bocchini and Coltorti 1990) and by uranium series dating of speleothems, with ages of up to 200,000 years (Taddeucci et al. 1992). ...
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The Frasassi caves present a unique opportunity to study sulfuric acid speleogenesis in a large karst system that contains active sulfidic processes as well as relict features produced by past speleogenetic episodes. The caves consist of a network of ramifying, mainly subhorizontal passages that reach more than 30 km in total length, and are organized in superimposed and interconnected levels. Sulfidic groundwaters are accessible in the lowermost levels. The water chemistry in the shallow phreatic zone is influenced by mixing phenomena between the sulfidic groundwaters and descending oxygenated water and, to some extent, gas exchange with the cave atmosphere. The sulfidic waters are corrosive with respect to limestone, with average limestone dissolution rates around 100 mm 10⁻³ year⁻¹ for submerged tablets. The release of gases to the air also causes wall corrosion (linear corrosion rate up to 85 mm 10⁻³ year⁻¹), which produces gypsum replacement crusts above the water table. Morphological and isotopic analyses show that large relict gypsum deposits in the upper dry levels were created by the same mechanism. Sulfide-oxidizing chemosynthetic bacteria living in the cave produce organic matter and support a rich and diverse ecosystem in the sulfidic branches, and these microorganisms contribute to sulfur cycling and cave formation processes. The evolution of the older cave levels during the Pleistocene was a complex result of changing regional geomorphological and hydrogeological regimes as well as local factors that affect water movement and gas exchange in the shallow phreatic zone within the cave.
... Nella grotta sono molto comuni docce inverse e cupole, origi natesi per effetto della risa lita, dell'accumulo o della condensazione dei gas (CO 2 e H 2 S) provenienti dalla falda (CIGNA & FORTI, 1986); molto diffuse anche croste gessose, deri vate proprio dall'interazione tra i vapori sulfurei e le pareti calcaree al di sopra del livello frea tico (BERTO LANI et al., 1977), e grandi depositi massivi deposti per accumolo gravitativo in ambiente vadoso (GALDENZI, 1990;GALDENZI & SARBU, 2000). Lo sviluppo di simili forme e depositi è favo rito dall'esi stenza di contatti diretti tra la falda e l'atmosfera della grotta, situazione che faci litaBOCCHINI & COLTORTI, 1990). Ciascun piano rappresenta un momento di stabilità del livello frea tico, protrat tosi suffi cientemente a lungo da consentire il pieno sviluppo delle morfo logie in grande ed in dettaglio legate ai processi di ossidazione dello zolfo. ...
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Riassunto Nella regione marchigiana si ha una forte concentrazione di cavità carsiche in alcuni massicci montuosi, in conseguenza della circolazione, attuale o passata, di acque sulfuree all'interno delle rocce calcaree. Lo sviluppo di queste grotte è dovuto ad azioni c or r os iv e a ttiv at e pr in c ip alme nte dai pr oc e s s i d i ossido-riduzione che interessano lo zolfo. Queste grotte possono essere definite ipogeniche, in quanto originate da azioni provenienti dall'interno della montagna. Le particolari condizioni ambientali fanno sì che queste grotte abbiano un elevato interesse naturalistico e scientifico. Grotte epigeniche, originate per l'azione diretta delle acque meteoriche assorbite nel sottosuolo, sono presenti in tutti i rilievi montuosi, ma le piccole dimensioni e le morfologie differenziano sostanzialmente queste cavità dai pochi grandi sistemi ipogenici. Alla sommità delle strutture carsificate si aprono soltanto brevi grotte di andamento verticale, generalmente fossili, che non presentano relazioni con la presente morfologia superficiale; un trasferimento rapido delle acque meteoriche verso il basso è comunque assicurato da una rete di fessurazione e da canali carsici di piccole dimensioni che possono intercettare preesistenti gallerie carsiche originate in differenti condizioni. Alcune risorgenti parzialmente attive, costituite da gallerie tubolari poco ramificate, si aprono a bassa quota sui fianchi delle principali anticlinali entro piccoli acquiferi minori sospesi, lateralmente compresi entro formazioni impermeabili. Negli acquiferi principali, al nucleo delle principali strutture anticlinali, prevale invece uno scorrimento freatico diffuso attraverso sistemi di fratturazione, con emergenze che presentano scarse variazioni stagionali. La possibilità di rapidi flussi nella zona di trasferimento, documentata con prove indirette ma anche grazie alla diretta esplorazione di canali carsici di piccole dimensioni, origina comunque una potenziale vulnerabilità agli inquinanti. Abstract In the central part of Umbria Marche Apennines the distribution and development of caves appears to be quite irregular. Limestone outcrops are generally covered by a thin layer of soil; here the surface karst landforms are rare and a diffuse autogenic recharge prevails. The lithological characteristics and the geomorphological evolution influenced the different development rates of caves in the area. Recent research, however, showed that the origin of the few large caves can be related to H2S-enrichment of ground water. H2S-rich water rises from evaporites underlying carbonate rocks; near the water table H2S is oxidized to H2SO4, increasing the water aggressiveness and causing dissolution of the carbonates. The many small caves scattered throughout the mountain chain are epigenic in origin: their small size and their features contrast with the large hypogenic caves originated through H2S oxidation. The most common epigenic caves consist of relict shaft caves and occasionally active emergences. The relict shaft caves open at the mountains surface, usually along fault lines; they reach a low depth due to marly formations interbedded in the limestone sequence and have no relationship with the present geomorphology and hydrography. The water flow inside these caves is only occasional, but a rapid drainage of the meteoric waters in to the subsurface karst is ensured by a network of fractures and very narrow meanders and pits. The emergence caves consist of simple or very low branched small tubes, up to 600 m long, that originated exclusively in the phreatic zone and became relict as a consequence of the lowering of the water table. These caves are located in the flanks of the main anticlines and their origin can be related to the possibility of phreatic flow inside small karst perched aquifers, developed between low permeable levels surrounding the anticlines. These phreatic caves show no direct connection with relict shaft caves present in recharge areas, but they receive a fast meteoric water recharge through the network of fractures and small karst passages The main regional aquifers are hosted in the core of the main anticlines, where significant cave development is possible only if H2S-rich waters rising occurs. Otherwise the phreatic drainage is slow through fractures and pore systems in the saturated zone, with a very regular discharge and non-karstic characteristics; the possibility of a fast recharge through the small size network of fractures and karst fissures developed in the transfer zone determine a potential vulnerability to pollutants. Introduzione Le reali funzioni di una grotta nella circolazione delle acque sotterranee sono state comprese solo recentemente; per lungo tempo infatti lo sviluppo delle cavità sotterranee è stato attribuito alle più svariate cause, con ipotesi talvolta stravaganti. Ancora nel XIX secolo l'azione erosiva delle onde era frequentemente invocata anche in zone di alta montagna.