Travertine Deposits Research Articles

Effect of in-stream physicochemical processes on the seasonal variations in δ13C and δ18O values in laminated travertine deposits in a mountain stream channel

Travertines are potential archives of continental paleoclimate. Records of stable carbon and oxygen isotopic composition (δ13C and δ18O) in laminated travertine deposits from endogene spring waters show regular cyclic patterns which may be due to seasonal change in climate determinants such as temperature and rainfall. In this study, δ13C and δ18O measurements of three travertine specimens that grew naturally over the eight years, 2004–2011, at upstream, middle and downstream sites in a canal at Baishuitai, SW China, are presented. They exhibit clear seasonal variations that generally correlate with biannual laminations. Specifically, δ13C and δ18O values show significant positive correlation with each other for the three travertine specimens, with the correlation coefficients increasing downstream along the canal. To reveal the factors governing the seasonal and spatial variations in δ13C and δ18O values, newly formed travertines precipitated on Plexiglas substrates are also examined. Both δ13C and δ18O of the substrate travertines are low in the summer/rainy season and high in the winter/dry season, showing a great consistency with the patterns in the natural travertines. Spatially, isotope values increase downstream in both seasons, with higher increase rates in winter that are related to removal of larger fractions of dissolved inorganic carbon (DIC) from the solution and stronger kinetic isotopic fractionation in winter. Due to in-stream physicochemical processes, including CaCO3 precipitation and the associated degassing of CO2, seasonal changes in δ13C and δ18O in the travertines are amplified by two times between the upstream and downstream sites: this is opposite to trends for epigene (meteogene) tufas whose seasonal changes in stable isotope compositions are reduced downstream. We suggest in-stream physicochemical processes are a potential reason for underestimation of annual temperature ranges that are inferred from epigene tufa δ18O data.

Stephanorhinus hundsheimensis (Mammalia, Rhinocerotidae) from the late early Pleistocene deposits of the Denizli Basin (Anatolia, Turkey)

Pleistocene rhinoceroses are poorly documented in Turkey where they have been reported only from the late early Pleistocene (1.3–1.1Ma) travertine deposits of the Denizli Basin. In this work, new rhinoceros remains collected from this basin are assigned to a relatively large-sized Stephanorhinus hundsheimensis on the basis of their morphology and morphometry. The first Turkish record of this species is approximately coeval with the first appearance of S. hundsheimensis in Europe, chronologically referred to the late early Pleistocene, ca. 1.2Ma. During that time, S. etruscus still survived in Iberian Peninsula, central Italy and Dacian Basin. The presence of two successive evolutionary morphs for S. hundsheimensis during the Pleistocene is not confirmed.

Various morphological types of thermogenic travertines in Northern Euboea and Eastern Central Greece

In the northern part of Euboea Island and the neighbouring part of the mainland in eastern central Greece, many hot springs exist and some of them create travertine deposits. The objectives of the study were to identify and describe the various morphological types of the thermogenic travertine deposits. The samples were studied at the lab with optical microscopy, X-Ray Diffraction, Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS), in order to verify their main mineralogical composition and their mineral chemistry. The studied travertine deposits consist mainly of aragonite and calcite, but in some cases, as main mineral phase, an amorphous hydrous ferric oxyhydroxide (ferrihydrite), was also identified. The morphological types that were identified were of great variety (mounds, travertine caves etc) and some of them were quite rare (cascades, remora etc). Morphological data and field observations suggest possible inorganic and organic controls on carbonate precipitation. Similar morphological types have been recorded at large travertine systems like Mammoth hot springs, Yellowstone National Park in USA and at Rapolano Terme, Italy.

Evolution of Pleistocene travertine depositional system from terraced slope to fissure-ridge in a mixed travertine-alluvial succession (Jebel El Mida, Gafsa, southern Tunisia)

The Quaternary stratigraphic record of Jebel El Mida, composed of continental deposits, is a useful example of concomitant travertines and alluvial deposition in an extensional setting. Travertine deposition occurred in a faulted Pleistocene alluvial fan giving rise to seven (recognised) facies interfingering with five other alluvial ones. The travertine depositional events indicate a tectonically driven evolution from terraced slope (facies group FC1–FC6) to a travertine fissure ridge-type depositing phase (facies group of FC1–FC7). Interfingering between travertine and alluvial facies indicates the co-existence of adjacent and time-equivalent depositional environments. The travertine deposition resulted from deep origin hydrothermal fluids channelled along damaged rocks volumes associated to a regional fault system, named as the Gafsa Fault (GF). The travertine–terrigenous succession in Jebel El Mida highlights the major role played by the GF in controlling: (i) the hydrothermal fluid flow, still active as also indicated by the numerous thermal springs aligned along the fault zone; (ii) paleoflow directions, discharge locations, volume, rate and fluctuations of the water supply. The paleoclimatic correlation with adjacent localities reveals that, at that time, humid episodes could have contributed to the recharge of the hydrothermal system and to the deposition of alluvial sediments.

Age determination for segments of the North Anatolian Fault (NAF) northern branch by 234 U/ 230 Th dating of Soğucak (Yalova) range-front travertines, south Marmara, Turkey

Abstract The Sogucak travertine occurrences developed along north segment of the North Anatolian Fault (NAF) in Yalova province, Marmara Region, Turkey. The range-front type travertines outcropping over an approximately 1 km2 area with 20–40 m thickness are middle-thick bedded and back-tilted southward or horizontally. Lithology of the travertines includes physolite, stalactites-stalagmites, cave pearls, sharp pebble carbonate nodules, spherical-roller-intricate shapes and laminated banded travertines. Geochemical analysis was performed on six samples of the travertines. The samples showed high calcite composition (averagely 98%) and Mg carbonite content varying from 0.87 to 1.33%. The travertines were deposited by means of normal faults as indicated by structural and morphological relationship with active tectonics. 234U/230Th dating of the travertines provided an age range from 61.318 (±3.091) to 231.944 (±141.902) ka. Findings show that the travertine deposition and deployment of faults in the region occurred approximately at 231 ka, corresponding to Middle Pleistocene. Therefore, the age of both travertines and NAF was determined as Middle Pleistocene.

Research of Alteration Minerals and Its Impact on the Environment around the Tehoru Hot Springs, Central of Moluccas

Research was conducted to identify the rocks that were taken in and around the Tehoru hot springs, Central Maluku regency. The rock samples were analyzed using petrography. The results of sample analysis identifies a sinter travertine deposition dominated by the presence of the mineral calcium carbonate (CaCO3) or calcite in the area around the Tehoru hot springs. Petrographic analysis shows that calcite incision initially preparing amorphous precipitated sinter travertine has been transformed into a microcrystalline calcite size is less than 0.01 mm. The sinter travertine also contains several other minerals were observed through an incision petrographic, ie anhydrite, iron oxides and quartz fragments. The deposition of sinter travelin form of mineral calcium carbonate or calcite, which is dominant around the Tehoru hot springs leave a good impact on the health of which is to improve the performance and efficiency of the body for its users, as a supplier of stimuli nerve from one cell to another and can kill certain germs or bacteria that attack the skin. In addition, sediment sinter travelin soluble in water will soon be absorbed by the roots of plants, because these substances are necessary for plant growth to be around the hot springs.

Comparative study of the Pleistocene Cakmak quarry (Denizli Basin, Turkey) and modern Mammoth Hot Springs deposits (Yellowstone National Park, USA)

This study compares and contrasts the travertine depositional facies of two of the largest sites of travertine formation, located in very different geological contexts, i.e. the modern Mammoth Hot Spring (MHS) system in the active volcanic complex of Yellowstone National Park (USA) and the Pleistocene Cakmak quarry, a well-exposed example of the Ballik travertines in the extensional Denizli Basin (Turkey). New, 2D to 3D facies maps of both travertine systems, combined with microscopy, assist in proposing an integrated spring depositional model, based on the existing MHS facies model, understanding general controls on meter to kilometer scale travertine deposit architecture and its preservation, and provide quantitative estimates of facies spatial coverage and slope using GIS. The comparison resulted in the distinction of eight facies, grouped in five downstream facies zones from Vent to Distal Slope. Notwithstanding the different geological context of both travertine systems, observations show that several of the facies are strikingly comparable (draping Apron and Channel Facies, top-slope Pond Facies, crystalline Proximal Slope Facies and Distal Slope Facies), whereas other facies do not have a precise, exposed equivalent (Vent Facies, pavement Apron and Channel Facies, extended Pond facies and phyto Proximal Slope Facies). Combining observations of active springs at MHS with the Cakmak vertical travertine quarry exposures demonstrates that lateral and vertical facies transitions are a sensitive record of changes in the spring dynamics (flow intensity and paths) that become well-preserved in the geological record, and can be recognized as prograding, aggrading, retrograding trends or erosive surfaces, traceable over tens to hundreds of meters. Quantification of facies specific coverage at MHS shows that Proximal and Distal Slope Facies deposits cover as much as ∼90% of the total mapped surface area. In addition, only ∼7% of the surface is found to be marked by a waterfilm related to an active flowing spring. Slope statistics reveal that strong slope breaks can often be related to transgressive Apron and Channel Facies belts and that variable, but steep slopes (up to 40°) are dominated by Proximal Slope Facies, in agreement with the Cakmak exposures. Integrating travertine facies and architecture of deposits formed in distinct geological contexts can improve the prediction of general spring facies distributions and controls in other, modern and ancient, subsurface travertine systems.

Diagenesis of continental carbonate country rocks underlying surficial travertine spring deposits

Abstract Diagenesis of Miocene-Pliocene continental rocks in extensional Teruel Basin related to deposition of a travertine at surface has been studied. Most of the diagenetic processes described here are in relation to the travertine deposition, so they are not widespread along the basin. Due to their high induration degree these rocks may be misinterpreted with travertine/tufa facies, so there is a need of clear criteria for their recognition as they can supply important hydrological and paleoenvironmental information. The diagenetic processes, that deeply modified the substrate, include dissolution, recrystallization and cementation and lead to a high induration of the Miocene-Pliocene rocks. These processes were driven by groundwater flow leading to travertine deposition at surface and appeared to be closely related to the fluvial incision of Alfambra River and to extensional fracturation during Middle Pleistocene times, probably under humid conditions. The cementation sequences and the organization of fractures and vadose micrite point to alternating vadose-phreatic conditions and syndiagenetic movements of the faults. Isotopic signal show lighter δ 18 O than that of the unaltered Miocene-Pliocene rocks and similar δ 13 C, suggesting lighter oxygen signal in waters during interglacial Pleistocene periods, and a common origin for carbon from marine Mesozoic rocks from the substrate of the basin. All of that suggest the strong control of tectonics, and climate at different timescales in diagenesis of the rocks serving as substrate for surficial travertine deposition.

Population response of the invasive crayfish Orconectes virilis (Hagen, 1870) (Decapoda: Astacoidea: Cambaridae) to restoration: what are the consequences of changes in predatory regulation and physical habitat in Fossil Creek, Arizona, USA?

We examined the response of a population of an invading non-indigenous crayfish, Orconectes virilis (Hagen, 1870), to a stream restoration project in travertine-forming Fossil Creek, Arizona, USA. Restoration included the re-establishment of the natural flow regime after the decommissioning of a dam and removal of non-native predatory fishes. The goal was to determine if changes in the dominant predatory fishes or changes in physical habitat variables, including substrate modification and base flow influence changes in crayfish abundance. We predicted that increased and unregulated flows and velocities would not generally decrease crayfish abundance, and that the removal of non-native fishes would increase the number of crayfish while local substrate modification by travertine deposition, a form of limestone which fills in interstitial spaces, would decrease the number of crayfish. Consistent with our predictions, there were not generalized decreases in crayfish abundance throughout the river following restoration. More detailed observations of different reaches, however, indicates that fish species and density exert some regulation over crayfish numbers. Crayfish abundance decreased following restoration where exotic fishes remain but slightly increased in numbers where they were removed. Areas in the river with increased travertine deposition had the largest declines following restoration. These observations suggest that crayfish abundance in this system is limited by substrate modification by travertine and to a lesser extent by regulation of fish predation.

A transient fault-valve mechanism operating in upper crustal level, Sierras Pampeanas, Argentina

Located in the Sierras Pampeanas (the broken-foreland of the Pampean flat slab segment in the southern Central Andes), the Cerro Tiporco volcanic field shows Neogene hydrothermal activity linked to migration of arc-magmatism into the foreland. Late Neogene deposits comprise epithermal vein systems emplaced in Precambrian—Early Palaeozoic igneous-metamorphic basement, Late Miocene sedimentary rocks and Early Pliocene volcaniclastic rocks. Mineralization consists of calcareous onyx, aragonite and calcite veins as well as travertine deposits. Onyx and aragonite occur as fill of low-displacement nearly vertical reverse-sinistral faults striking NW, and nearly horizontal dilatant fractures. The latter consist of load-removal induced fractures affecting the igneous-metamorphic rocks, as well as bedding planes in the Late Miocene sediments. The presence of veins recording multiple fracture episodes and crack-and-seal growth of veins suggests relatively low differential stress and supralithostatic fluid pressure, as well as cyclic changes in pore pressure and high mineral-deposition/fracture-opening ratio. These conditions support a mechanism of fault-valve behaviour during onyx and aragonite vein emplacement. The fault-valve mechanism involves fractures associated with impermeable barriers between environments with different fluid pressure. Faulting generated an appreciable directional permeability triggering fluid migration from the highest to the lowest pressure region, with subsequent deposition and sealing that started a new pressurization-faulting-sealing cycle. Late aragonite and calcite veins suggest a change in kinematics indicating the onset of tectonic-load conditions.

Tectonics, hydrothermalism, and paleoclimate recorded by Quaternary travertines and their spatio-temporal distribution in the Albegna basin, central Italy: Insights on Tyrrhenian margin neotectonics

The Neogene–Quaternary Albegna basin (southern Tuscany, central Italy), located to the south of the active geothermal field of Monte Amiata, hosts fossil and active thermogene travertine deposits, which are used in this study to reconstruct the spatio-temporal evolution of the feeding hydrothermal system. Travertine deposition is controlled by regional tectonics that operated through distributed N-S– and approximately E-W–striking transtensional fault arrays. The geochronological data set ( 230 Th/ 234 U, uranium-series disequilibrium) indicates a general rejuvenation (from >350 to 13 C and positive δ 18 O trends with younger deposition ages and lower depositional elevations provide evidence for a change in space and time of the hydrothermal fluid supply, suggesting a progressive dilution of the endogenic fluid sources by increasing meteoric water inputs. Comparison with paleoclimate records suggests increased travertine deposition during humid interglacial periods characterized by highstands of the water table. Travertine deposits of the Albegna basin record the interactions and feedbacks among tectonics, hydrothermalism, and paleoclimate within a region of positive geothermal anomaly during the Quaternary. Our study also sheds light on the neotectonic evolution of the Tyrrhenian margin of central Italy, where hydrothermalism has been distributed along margin-transverse structures during the Pleistocene and Holocene. It is hypothesized that originally upper-crustal, margin-transverse faults have evolved to through-going crustal features during the Quaternary, providing structurally controlled pathways for hydrothermal fluids. We suggest that this was the consequence of a change in the relative magnitude of the principal stress vectors along the Tyrrhenian margin that occurred under a regional stress field dominated by a continuous extensional regime.

Hydrothermal fluids circulation and travertine deposition in an active tectonic setting: Insights from the Kamara geothermal area (western Anatolia, Turkey)

Coexistence of thermal springs, travertine deposits and tectonic activity is a recurring feature for most geothermal areas. Although such a certainty, their relationships are debated mainly addressing on the role of the tectonic activity in triggering and controlling fluids flow and travertine deposition. In this paper, we present the results of an integrated study carried out in a geothermal area located in western Anatolia (Turkey), nearby the well-known Pamukkale area (Denizli Basin). Our study focused on the relationships among hydrothermal fluids circulation, travertine deposition and tectonic activity, with particular emphasis on the role of faults in controlling fluids upwelling, thermal springs location and deposition of travertine masses. New field mapping and structural/kinematics analyses allowed us to recognize two main faults systems (NW- and NE-trending), framed in the Neogene–Quaternary extensional tectonic evolution of western Anatolia. A geo-radar (GPR) prospection was also provided in a key-area, permitting us to reconstruct a buried fault zone and its relationships with the development of a fissure-ridge travertine deposit (Kamara fissure-ridge). The integration among structural and geophysical studies, fluids inclusion, geochemical, isotopic data and 230Th/238U radiometric age determination on travertine deposits, depict the characteristics of the geothermal fluids and their pathway, up to the surface. Hydrological and seismological data have been also taken in account to investigate the relation between local seismicity and fluid upwelling. As a main conclusion we found strict relationships among tectonic activity, earthquakes occurrence, and variation of the physical/chemical features of the hydrothermal fluids, presently exploited at depth, or flowing out in thermal springs. In the same way, we underline the tectonic role in controlling the travertine deposition, making travertine (mainly banded travertine) a useful proxy to reconstruct the seismological history of an area, as well as the characteristics of the parent geothermal fluids, adding an effective tool for geothermal exploration tasks.

Growth of a Pleistocene giant carbonate vein and nearby thermogene travertine deposits at Semproniano, southern Tuscany, Italy: Estimate of CO2 leakage

A giant carbonate vein (≥50m thick; fissure ridge travertines) and nearby travertine plateaus in the Semproniano area (Mt. Amiata geothermal field, southern Tuscany, Italy) are investigated through a multidisciplinary approach, including field and laboratory geochemical analyses (U/Th geochronology, C, Nd, O and Sr isotope systematics, REE abundances, and fluid inclusion microthermometry). The main aim of this work is to understand: (1) modes and rates for the growth of the giant vein and nearby travertine deposits within a Quaternary volcano-tectonic domain; (2) implications in terms of the CO2 leakage; and (3) possible relationships with Quaternary paleoclimate and hydrological oscillations. Results show that the giant vein was the inner portion of a large fissure ridge travertine and grew asymmetrically and ataxially through repeated shallow fluid injections between >650 and 85ka, with growth rates in the 10−2–10−3mm/a order. The giant vein developed mainly during warm humid (interglacial) periods, partially overlapping with the growth of nearby travertine plateaus. Estimated values of CO2 leakage connected with the vein precipitation are between about 5×106 and 3×107mola−1km−2, approximately representing one millionth of the present global CO2 leakage from volcanic areas. Temperature estimates obtained from O-isotopes and fluid inclusion microthermometry indicate epithermal conditions (90–50°C) for the circulating fluid during the giant vein growth, with only slight evidence of cooling with time. Geochemical and isotope data document that the travertine deposits formed mainly during Pleistocene warm humid periods, within a tectonically-controlled convective fluid circuit fed by meteoric infiltration and maintained by the regional geothermal anomaly hosted by the carbonate reservoir of the Mt. Amiata field.

Origin and K-Ar age of the phreatomagmatic breccia at the Trepča Pb-Zn-Ag skarn deposit, Kosovo: Implications for ore-forming processes

The Trepca Pb-Zn-Ag skarn deposit in Kosovo is spatially and temporarily related to the phreatomagmatic breccia of Oligocene age (~23 Ma). The deposit shows features typical for skarn deposits worldwide, including a stage of isochemical metamorphism, a prograde stage of an anhydrous, low oxygen and low sulfur fugacity character and a retrograde stage characterized by an increase in the water activity as well as by an increase in oxygen and sulfur fugacities. The mineralization is hosted by the recrystallized Upper Triassic limestone. The prograde mineralization consists mainly of Ca-Fe-Mn±Mg pyroxenes. The host recrystallized limestone at the contact with the prograde (skarn) mineralization have the increased content of Fe, Mn, Mo, As, Au, Cs, Ga, REE and Y suggesting their transport by infiltrating magmatic fluids. The decreased d13C and d18O values reflect a contribution of magmatic CO2. The retrograde mineral assemblage comprises ilvaite, magnetite, arsenopyrite, pyrrhotite, marcasite, pyrite, Ca-Fe-Mn±Mg carbonates and quartz. Hydrothermal ore minerals, mostly galena, sphalerite and pyrite, were deposited contemporaneously with the retrograde stage of the skarn development. Syn-ore and post-ore carbonates reflect a diminishing influence of magmatic CO2. Syn-ore carbonates are enriched in Fe, Mg, Mn, many chalcophile elements, including Ag, As, Bi, Cd, Cu, Pb, Sb and Zn, as well as in Au, Y and REE. The post-ore stage accompanied the precipitation of significant amount of Ca-rich carbonates including the travertine deposits at the deposit surface. The phreatomagmatic breccia was developed along a NW dipping contact between the ore bearing recrystallized limestone and the overlying schist. It has an inverted cone shape with the vertical extension up to 800 m and diameter up to 150-m. The upper part of the diatreme (an underground segment of the phreatomagmatic breccia) is characterized by the presence of a hydrothermally altered rootless quartz-latite dike surrounded by an unsorted polymict breccia mantle. Despite the alteration processes, the dike has a preserved porphyritic texture. Partly preserved sanidine, accompanied with the mixture of muscovite and quartz, reflects a near-neutral to weakly acidic environment. The clasts of country rocks and skarn mineralization underwent intense milling and mixing due to repeated magmatic penetrations. Sericitization of the breccia matrix, locally accompanied with minor kaolinitization, point to an increased water activity under near-neutral to weakly acidic conditions. Large fragments originally composed of anhydrous skarn minerals (pyroxenes) are usually completely altered to a mixture of fibroradial magnetite, quartz and various amount of carbonates suggesting an increase in oxygen fugacity. Their pyrite rims reflect that the increase in oxygen fugacity was followed by an increase in sulfur fugacity. The clast predominantly composed of Fe-sulfides and minor Bi-sulfides point that the increase in sulfur fugacity was locally sufficient to complete sulfidation of hedenbergite to pyrrhotite and/or pyrite. Although the phreatomagmatic breccia at the Trepca Pb-Zn-Ag skarn deposit does not carry significant amounts of the ore mineralization, its formation was crucial for the ore deposition. Phreatomagmatic explosions and formation of the breccia turned the system from the lithostatic to hydrostatic regime and triggered the retrograde stage increasing the water activity and oxygen fugacity in the system. In addition, cooling and decompression of the system contributed to more effective degassing of magmatic sulfur increased the sulfur fugacity.

Origin and paleoenvironment of Pleistocene–Holocene Travertine deposit from the Mbéré sedimentary sub-basin along the Central Cameroon shear zone: Insights from petrology and palynology and evidence for neotectonics

The Mbéré sub-basin belongs to the Mbéré-Djerem intra-continental basin of Central North Cameroon. In this sub-basin, a travertine outcrop has been discovered and investigated palynologically and petrologically in this study. The sporopollinic content of the studied travertine is mainly composed of fungal spores (Rhyzophagites sp., Monoporisporites sp …) associated with rare fresh water algae spores such as Chomotriletes minor and angiosperm pollens (compositae, graminae, …). This sporopollinic association is indicative of hot and semi-arid to arid paleoclimate and reveals a Pleistocene–Holocene depositional age. The whole rock major element geochemistry shows relative enrichment of CaO (49.48%) and CO2 (38.49%). The origin of CO2 is probably from magmatic and/or metamorphic fluids. Compared to other travertines, SiO2 and Al2O3 contents are significant with average concentrations of 5.68% and 2.58% respectively. The mineralogical composition revealed by a microscopic study of bulk rocks is dominated by calcite (90–92%) associated to quartz (2–4%) and feldspar (2–3%), meanwhile the heavy mineral concentrate is formed by various mineral types such as zircon (most abundant), garnet, tourmaline, epidote, biotite, peridot and aegirine augite suggesting that the underground water has crossed both volcanic, plutonic and metamorphic rocks. With the mineral composition made of both chemical and detrital derived elements, the Mbéré travertine corresponds to chemico-lithoclastic/detrital limestone. In the Mbéré trough, numerous thermo-mineral springs are located along major fractures and faults. This result suggests that the Mbéré travertine deposit is related to the rising of deep water with the help of a fracturing system, similar to those of Irdi (Morocco), Italy and Turkey where there is much volcanism.

Calcium isotopic fractionation during travertine deposition under different hydrodynamic conditions: Examples from Baishuitai (Yunnan, SW China)

Revealing the potential of Ca isotopes in the research of travertine formation processes is the principal goal of this study. To achieve this, the hydrochemistry, travertine precipitation rates, and variations in Ca isotopic compositions (δ44/40Ca) of present-day endogenic (thermogenic) travertine in two different hydrodynamic systems (canal and pool) are studied at Baishuitai (Yunnan, SW China). In the canal, where the travertine precipitation is faster, δ44/40Ca values of both solution and travertine show a downstream increase, with Ca isotopic fractionation (Δ44/40CaCaCO3-aq) equal to ~−1.6‰. Compared to the canal, Ca isotopic fractionation between travertine and aqueous Ca2+ is smaller (Δ44/40CaCaCO3-aq≈−1.2‰) in the pools where travertine precipitation rates are lower. The spatial variations in δ44/40Ca values of solution and travertine are related to the amount of Ca removed from the solution when δ44/40Ca values of spring water remain stable. In addition, the results confirm the control of precipitation rates on Ca isotopic fractionation between calcite and parent aqueous Ca2+ using natural samples. The observed negative correlation between Δ44/40CaCaCO3-aq and travertine precipitation rates can be explained by the steady-state kinetic surface reaction model proposed by DePaolo (2011), with equilibrium and kinetic fractionation factors of αeq=1.0000±0.0001 and αf=0.9983±0.0002, respectively. An important consequence of this study is that Ca isotopes in travertine systems are good tools to have access to variations of δ44/40Caaq, which are directly linked to the amount of precipitated Ca. This could then be useful for reconstructing past hydrodynamic conditions when applied to travertine core data.

“Per tremoto o per sostegno manco”: The Geology of Dante Alighieri’s Inferno

The purpose of the present paper is to analyse the geological elements and references found in Dante Alighieri's Inferno, which have never been treated in complete and comprehensive manner. Dante used wisely and in a unique manner the elements of nature, especially of landscape, to build the material foundation on which the fiction of the underworld journey is based. Specific kinds of rocks, steep cliffs, landslide bodies, lakes of hydrothermal water, waterfalls, become basic material in the hands of the Florentine poet, on which to base metaphors and similes. In Dante's Inferno there are references to hydrogeology, earthquakes, mountain structures, deposition of travertine, landscape modelling, meteorological phenomena, structure of the Earth and of the entire cosmos. The grandeur and mastery of Dante lies in being able to communicate, in short lines, the strong separation between scientific facts of natural phenomena and their use for aesthetic, poetic, political, and even ethical purposes. In dealing with complex issues such as the geophysical equilibrium and the reason for the current distribution of land and ocean, Dante does not simply accept the theories of Aristotle (as stated by several exegetes) but shows a critical and deep analysis in the field of geology sensu lato, considering and preferring the phenomenal datum to the abstract theories. The work of Dante and his contemporaries did not impersonate the dark period for science, as found in many interpretations of the Middle Ages, but the cultural context where those questions were posed which served as foundation and propellant for the subsequent scientific revolution.

An overview on the characteristics of geothermal carbonate reservoirs in southern Tuscany

This paper focuses on brittle deformation and fluid-rock interaction, for enhancing permeability in carbonate geothermal reservoir. The relationships between fractures and fluid flow at different structural levels within a geothermal circuit are described through examples from exhumed geothermal systems cropping out in southern Tuscany, with emphasis on the carbonate reservoirs, located within the late Triassic evaporite level and/or at the base of the Tuscan Nappe. The description is based on the fact that geothermal fluids are mainly made up of meteoric water channelled to depth through structural conduits, affecting regionally hot rocks. In this pathway, the meteoric water is transformed in geothermal fluid, becoming chemically aggressive, thus favouring leaching of hosting rocks, and enhancing and maintaining permeability. The fluid-rock interaction is promoted by existing fractures and/or by unhomogeneities in the rock-textures, as it is the case of the Miocene cataclasite located within the late Triassic evaporite. Travertine deposits can occur if fluids reach the surface after having circulated in carbonate reservoirs. Since permeability is controlled by fluid-rock geochemistry and by the possibility to have fluids continuously renewed, we conclude that the fluid-rock interaction and high temperature of hosting rocks make the geothermal issue a specific case of study and therefore the conclusion on oil reservoirs formation cannot be completely transferred to geothermal exploitation issue.

四川黄龙钙华沉积剖面的矿物学特征及其指示意义

近年对四川黄龙沟地表水体的研究发现，现代黄龙钙华共生有大量硅藻、蓝藻等优势藻类种属和多类细菌种属。对微生物是否参与钙华沉积及其在沉积中的作用得到了国内外学者的关注。本文通过对黄龙钙华沉积剖面进行矿物学特征及指示意义的研究，以调查微生物是否参与了黄龙钙华的沉积和为揭示黄龙钙华的形成机理提供科学证据。XRD晶体结构精修解析表明，黄龙钙华为三方晶系方解石结构的单一物相，沿晶胞C轴存在拉伸，晶胞体积扩大的特征，与生物矿化作用形成的方解石晶胞特征一致。化学成分和热分析表明，历史钙华存在微生物参与钙华沉积的可能。但因地质作用的影响，本文未能发现保留完整微生物化石，从而为微生物参与黄龙钙华沉积提供直接证据。 In recent years, the studies of surface water in Huanglong ravine, Sichuan Province find that mod-ern Huanglong travertine is symbiosis with abundant species of diatoms, cyanobacteria and mi-crobes. The role of biotic influence in mineralization of calcium carbon has gained attention of the scholars at home and abroad with the aim of ascertaining whether microbiological activity plays a relevant role in depositing fossil travertine. The presented study focuses on studying mineralogical characteristics and environmental significances in Huanglong travertine deposition profile. The objectives are exploring whether the microbes are involved in the deposition of Huanglong travertine and providing scientific evidence for revealing the possible Huanglong travertine for-mation mechanism. The crystalline refinement results of X-Ray Diffraction (XRD) identified the travertine in Huanglong was a typical single crystalline calcite with anisotropic lattice distortions of along axes of C, suggesting some level of metabolic mediation during mineralization. The chemical composition and IR spectra of the history of travertine indicated that the possibility of microbes participated in travertine deposition. However, because of the influence of geological pro- cesses, the presented study didn’t find intact microbial fossils which provided directly evidence.

Depositional architecture of a mixed travertine-terrigenous system in a fault-controlled continental extensional basin (Messinian, Southern Tuscany, Central Italy)

The extensional Neogene Albegna Basin (Southern Tuscany, Italy) includes several thermogene travertine units dating from the Miocene to Holocene time. During the late Miocene (Messinian), a continental fault-controlled basin (of nearly 500-km2 width) was filled by precipitated travertine and detrital terrigenous strata, characterized by a wedge-shaped geometry that thinned northward, with a maximum thickness of nearly 70m. This mixed travertine–terrigenous succession was investigated in terms of lithofacies types, depositional environment and architecture and the variety of precipitated travertine fabrics.Deposited as beds with thickness ranging from centimetres to a few decimetres, carbonates include nine travertine facies types: F1) clotted peloidal micrite and microsparite boundstone, F2) raft rudstone/floatstone, F3) sub-rounded radial coated grain grainstone, F4) coated gas bubble boundstone, F5) crystalline dendrite cementstone, F6) laminated boundstone, F7) coated reed boundstone and rudstone, F8) peloidal skeletal grainstone and F9) calci-mudstone and microsparstone. Beds of terrigenous deposits with thickness varying from a decimetre to >10m include five lithofacies: F10) breccia, F11) conglomerate, F12) massive sandstone, F13) laminated sandstone and F14) claystone.The succession recorded the following three phases of evolution of the depositional setting: 1) At the base, a northward-thinning thermogene travertine terraced slope (Phase I, travertine slope lithofacies association, F1–F6) developed close to the extensional fault system, placed southward with respect to the travertine deposition. 2) In Phase II, the accumulation of travertines was interrupted by the deposition of colluvial fan deposits with a thickness of several metres (colluvial fan lithofacies association, F10 and F12), which consisted of massive breccias, adjacent to the alluvial plain lithofacies association (F11–F14) including massive claystone and sandstone and channelized conglomerates. Travertine lenses, of 2–3-m thickness, appeared intermittently alternating with the colluvial fan breccias. 3) In the third phase, the filled fault-controlled basin evolved into an alluvial plain with ponds rich in coated reed travertines, which record the influence of freshwater (travertine flat lithofacies association, F7–F9).This study shows the stratigraphic architecture and sedimentary evolution of a continental succession, wherein the hydrothermal activity and consequent travertine precipitation were driven by the extensional tectonic regime, with faults acting as fluid paths for the thermal water. Fault activity created the accommodation space for travertine and colluvial fan accumulation. Erosion of the uplifted footwall blocks provided the source of sediments for the colluvial fan breccias, which alternated with the thermogene travertine precipitation. Climatic oscillations might have led to the recharge of the aquifer that fed the hydrothermal vents.The studied continental succession in an extensional basin provides valuable information about the interplay between thermogene travertine and alluvial/colluvial deposition, which in turn might improve the understanding of similar fault-controlled continental depositional systems in outcrops and the subsurface.