Travertine Deposits Research Articles

Insights into geochemical characteristics of the geothermal fluids of northwestern algeria: An updated conceptual model

The vigorous tectonic activity that affected the Northwestern part of Algeria has generated a Mio-Plio-Quaternary volcanic activity and led to the emergence of several thermal resurgences. These latter consist of thermal springs, travertine deposits and some hydrothermal alteration zones. The chemistry of twenty-one hot spring water samples highlight the heterogeneity of the water mineralization process in NW Algeria. Four major types of water are described. Na+-Cl− and Na+-SO42− with a high salinity up to 3794 mg/L accompanied by higher concentrations of F−, B, Li+, Br− and Cs. These are probably derived from halite and gypsum rich evaporites from the surrounding environment. The other two types are Ca2+-HCO3− and Na+-HCO3−. Chloride rich waters are associated with local carbonate formations. The stable isotopes (δ18O and δ2 H) reveal a fossil system since a large depletion of both isotopes from present-time meteoric waters cannot only be plausibly explained in terms of "inland" and "altitude" effects, we may suppose their recharge under climatic conditions much colder than the present ones taking place probably during the glacial period. The gas mixing models of N2He*1000-Ar*100 with O2CO2He*1000 demonstrate an unarguable meteoric origin for the thermal waters, displaying air-saturated water (ASW) signatures.The collected thermal waters are ‘immature’ while the deep geothermal reservoir temperatures were estimated to be about at 133 °C. The updated geochemical conceptual model indicates two main processes in the flow path of the fossil meteoric water. 1) In the Bouhdjar geothermal zone, the infiltrated meteoric waters are conductively heated at depth because of the high heat flow (∼120 mW/m2), during their ascent, along hydrothermal conduits and towards the ground surface, they have possibly been influenced by heat advection from the underlying magma chambers and/or a percolation with intrusive bodies beneath spring vents. 2) The meteoric waters are recharged from high altitude areas of the Atlasic lands and are deeply circulated and heated at greater depths, hot waters probably mix with cooler Mg-rich waters and/or leach Mg2+ from the surrounding rocks when rising to the surface. Since the locations of the hot springs are close to populated areas, a direct use of this resource is feasible to supply some energy demands that include electricity generation using binary cycles or direct uses of heat.

Factors governing travertine deposition in fluvial systems: The Bagni San Filippo (central Italy) case study

Although fossil fluvial travertines have been described, factors controlling their formation are poorly understood because of the paucity of their modern counterparts. To disclose processes affecting their deposition, a modern fluvial travertine system at Bagni San Filippo (Siena, central Italy) was studied here and compared with other cases. The studied travertines occur in a valley with an ephemeral stream, but continuous water influx from hot springs on the hillside makes part of the stream become perennial. Four sub-environments were recognized: slopes, waterfalls, pools, and channels. The first two are mainly composed of laminated crystalline crust-boundstone. In contrast, pools are mainly covered by lime mud and some post-flood travertine-encrusted breccia, while channels commonly display abundant travertine-encrusted breccia. Many erosional features and products were also found and are largely the result of episodic erosion triggered by heavy rainfalls and accompanied floods. The predominant erosional processes might include abrasion and plucking. Based on environment distribution, stream bed morphology, and erosional distinctions, the fluvial system was distinguished into slope-pool-waterfall and channel-pool-waterfall subsystems. Such system differentiation is attributed to the original stream bed difference: wide beds promoted the development of slopes, while narrow beds encouraged travertine erosion and subsequent gravel accumulation during flood events, favoring the formation of channels. The comparison shows that fluvial travertine deposition largely occurs within existing rivers. The relative contribution of spring water to original river water controls the deposit composition (the higher contribution ratios, the more abundant carbonate/travertine facies). Furthermore, erosion might be common and unavoidable because the reported fluvial travertines were all formed in non-arid regions. These findings suggest that fluvial travertine deposition is influenced by topography, hot spring contribution, original river bed geometry, and fluvial erosion, and might aid in the interpretation of ancient fluvial travertine systems. Additionally, downstream fluvial travertine systems might show similar characteristics to fluvial tufas, but their formation is clearly hot spring influenced, indicating the importance of analyzing facies distribution and δ13C-δ18O signatures in fluvial carbonate studies.

Petrophysics and sediment variability in a mixed alluvial to lacustrine carbonate system (Miocene, Madrid Basin, Central Spain)

AbstractThis study evaluates variations in petrophysical properties within a mixed alluvial to lacustrine carbonate system (Miocene, Madrid Basin, Central Spain). The transition from alluvial environments to lake margins settings displays a shift from alluvial, siliciclastic red sandstones and mudstones to palustrine–lacustrine mudstones to packstones. Fluctuations in lake‐water level enabled land plants to occupy the lake margins during periods of low lake levels. The palustrine carbonates include features like pseudo‐microkarst, nodular and mottled limestones; the lacustrine deposits include enlarged root cavities, desiccation cracks and channel bodies. Scarce fresh water biota comprises charophytes, gastropods and ostracods. The sediments possess high natural, irregular varying, gamma‐ray values at the alluvial–lacustrine transition, and low, but constant values at full lacustrine sites. Acoustic properties agree with lithological variations within individual facies. Porosity is the most important parameter influencing P‐wave and S‐wave velocities. The scatter in the velocity–porosity relationship links to the porosity type; macro‐porosity or microporosity. The wide range of pore types and pore sizes results in a weak porosity to permeability relationship for the carbonate‐dominated rocks with low permeability for microporous and high permeability for macro‐porous carbonates. The sandstones (probably only inhibiting interparticle porosity), and to a lesser extent the sandy wackestones to packstones, show quite a strong relationship between porosity and permeability. Elastic properties of mixed alluvial–lacustrine deposits (this study) and marine deposits (literature data) overlap as variations in pore structures and porosity values are similar. Only 16% of the marine and lacustrine carbonate sediments display Equivalent Pore Aspect Ratio values above 0.2. In travertine deposits, 83% of the samples exceed Equivalent Pore Aspect Ratio values above 0.2, which highlights that travertine deposits are dominated by larger Equivalent Pore Aspect Ratios compared to lacustrine and marine carbonate deposits. Travertines display other rock frameworks with different pore types, pore distribution and amount of porosity.

Sedimentary evolution of the Dawan travertines and their geological environmental significance, Huanglong, China

AbstractThe Huanglong travertine landscape, which is located on the eastern edge of the Qinghai‐Tibet Plateau, is a World Natural Heritage Site with important tourism, aesthetic and scientific research value. However, no convincing travertine sedimentary age data have been reported for this area, and these late Cenozoic terrestrial carbonates have not been effectively included in studies of the Qinghai‐Tibet Plateau geological environment. In this study, U‐series dating of the travertines was carried out using a multi‐collector inductively coupled plasma mass spectrometer to determine a time series for travertine deposition in the Dawan Valley (only a mountain away from Huanglong). The analyses of the processes operating during travertine deposition as the trench system evolved are performed based on a comprehensive study of the geological setting, structure and glacial landforms. The results suggest that travertine deposition in the Dawan Valley started at ca 13 ka and had begun to wane by the early Holocene (ca 7 ka). At the same time, the Huanglong Valley travertines began to be deposited on a large scale in response to a hydrological transition event. This event might reflect tectonic activity in particular, or possibly earthquakes or glacial retreat caused by climate warming. The findings reported here provide age data for late Cenozoic geological and environmental events such as climate variations and continental activity on the eastern margin of the Qinghai‐Tibet Plateau. It also presents new insights for research on glaciation, tectonic activity and seismicity; however, depositional breaks and forcing factors need to be explored further.

Abiotic and biotic processes controlling travertine deposition: Insights from eight hot springs in Japan

AbstractContributions of abiotic and biotic processes on travertine deposition are still not well‐understood due to technical difficulties, despite that the travertines draw attention as analogues for ancient microbial carbonates and oil reservoirs. To evaluate their contributions, this study examined eight hot springs in Japan. Water chemistry analyses showed common downstream trends: a decrease in CO2 concentration and increases in CO32− concentration and pH. Mineralogical analysis showed that the constituent minerals of travertines at six hot springs were both calcite and aragonite, while one was just calcite and another only aragonite. Microscopic observations of travertine surfaces indicated the dominance of cyanobacteria secreting extracellular polymeric substances without a detectable amount of carboxyl groups. Small particles were sometimes entangled/covered by these cyanobacteria. Microelectrode measurements showed the occurrence of abiotic CaCO3 precipitation and photosynthetic induction/inhibition of CaCO3 precipitation, the extent of which was different at each site. By integrating these results, the contributions of abiotic and biotic processes were evaluated. Cyanobacteria inhabiting travertine surfaces were generally not calcified regardless of an ambient high CaCO3 saturation state; instead, they contributed to creating pore spaces and trap/bind suspended particles. Downstream CO2 degassing increased the CaCO3 saturation state by shifting carbonate chemical equilibrium and caused abiotic CaCO3 precipitation. Suspended particles trapped by cyanobacteria increased the surface area for crystal growth to further accelerate precipitation. The contribution of photosynthesis‐induced CaCO3 precipitation was low because of several factors, including variable cyanobacteria populations and photosynthetic inhibition of CaCO3 precipitation. The average contributions of photosynthesis‐induced CaCO3 precipitation, Ca2+ adsorption and abiotic precipitation in the eight hot springs were 16%, 3% and 81%, respectively, indicating predominance of the abiotic process for travertine deposition. Mineralogical composition of travertines significantly correlated with concentrations of SO42− and Mg2+, much more than with Mg/Ca ratio and water temperature, suggesting their importance for controlling CaCO3 polymorphs in travertines.

Determining the role of chemical and biological factors in controlling precipitation of tufa and travertine deposits in Shurab area, Northern Iran

Determining the role of chemical and biological factors in controlling precipitation of tufa and travertine deposits in Shurab area, Northern Iran

The role of tectonic activity, topographic gradient and river flood events in the Testina travertine (Acque Albule Basin, Tivoli, Central Italy)

AbstractThe Acque Albule Basin in Tivoli (Rome, Central Italy) represents one of the largest exposures of travertine deposits in the world. A detailed study of the Upper Pleistocene Testina travertine, constituting the poorly lithified top part of the Lapis Tiburtinus travertines, is presented. Fieldwork performed in an area of 10 km2 and petrographic analysis allow the recognition of six geobodies with different geometries, degree of diagenetic alteration and architectural elements, composed of seven lithotypes. The Testina travertine appears in general as a poorly lithified travertine, even if it shows a high degree of cementation. It is mainly characterised by blocky, drusy or bladed microsparite and sparite calcite cements, related to thermal and meteoric phreatic to vadose water circulation, affecting in particular those travertine deposits located in the northern part of the study area. The Testina, neglected until now in the several studies performed in the Acque Albule Basin, shows a progradational trend from the north to the south and is characterised by environments, evidencing deposition on a gentle slope, in an alluvial plain and in a shallow lake, with gradual transitions between low‐energy environments and high‐energy environments. Furthermore, based on correlation between the different geobodies in the overall study area, the Testina travertine depositional system was influenced by tectonic activity in the northern part, by an increasing topographic gradient and water discharge flow in the central part and by flooding events related to the Aniene River in the southern part. This study aims to differentiate such influencing factors facilitating the analysis of other travertine depositional systems and also to aid in the interpretation of subsurface analogues, as in the case of South Atlantic Pre‐Salt reservoirs.

Fissure Ridges: A Reappraisal of Faulting and Travertine Deposition (Travitonics)

The mechanical discontinuities in the upper crust (i.e., faults and related fractures) lead to the uprising of geothermal fluids to the Earth’s surface. If fluids are enriched in Ca2+ and HCO3-, masses of CaCO3 (i.e., travertine deposits) can form mainly due to the CO2 leakage from the thermal waters. Among other things, fissure-ridge-type deposits are peculiar travertine bodies made of bedded carbonate that gently to steeply dip away from the apical part where a central fissure is located, corresponding to the fracture trace intersecting the substratum; these morpho-tectonic features are the most useful deposits for tectonic and paleoseismological investigation, as their development is contemporaneous with the activity of faults leading to the enhancement of permeability that serves to guarantee the circulation of fluids and their emergence. Therefore, the fissure ridge architecture sheds light on the interplay among fault activity, travertine deposition, and ridge evolution, providing key geo-chronologic constraints due to the fact that travertine can be dated by different radiometric methods. In recent years, studies dealing with travertine fissure ridges have been considerably improved to provide a large amount of information. In this paper, we report the state of the art of knowledge on this topic refining the literature data as well as adding original data, mainly focusing on the fissure ridge morphology, internal architecture, depositional facies, growth mechanisms, tectonic setting in which the fissure ridges develop, and advantages of using the fissure ridges for neotectonic and seismotectonic studies.

3D reconstruction of the Lapis Tiburtinus (Tivoli, Central Italy): The control of climatic and sea‐level changes on travertine deposition

Abstract3D modelling is a fundamental tool to visualize and understand the history of sedimentary basin filling and to reconstruct the geobody architecture. Spatial distribution of discontinuity surfaces and geobody characteristics provide valuable information on the factors controlling the sedimentary evolution of basins. Several Neogene‐Quaternary basins of central‐western Italy are controlled by extensional and strike‐slip tectonics and characterized by travertine deposition, related to hydrothermal fluids rising up along discontinuities and fractured carbonate bedrocks. This study presents the 3D modelling results of the quarry area within the tectonically controlled Acque Albule Basin (Tivoli, Central Italy) that hosts the Pleistocene Lapis Tiburtinus travertine. The 3D reconstruction of the different surfaces bounding the travertine units shows a complex architecture composed of depressions, reliefs and channels as predominant morphological elements related to four different depositional environments (subaqueous, palustrine, slope and travertine channel). The reconstructed surface maps highlight the presence of laterally migrating, E–W‐oriented lens‐shaped geometries, with a drainage system persistent through time oriented towards the southern part of the study area in the direction of the Aniene River, bordering the Acque Albule Basin in the South. The Lapis Tiburtinus travertine developed in an area of 28 km2, accumulated in a system composed of sub‐basins (approximately 1–2 km2 wide) with subaqueous conditions interconnected by a hydrographic network, controlled through time by fluctuations of the Aniene River base level. Based on the results obtained, base‐level fluctuations of the Aniene River, related to glacio‐eustatic sea‐level oscillations of the last 115 kyrs associated with alternation of humid and arid climatic conditions, arise as the most important factor affecting the architecture of the travertine geobodies.

The fate of a travertine record: Impact of early diagenesis on the Y‐10 core (Mammoth Hot Springs, Yellowstone National Park, USA)

AbstractSpring systems are efficient and fast precipitating non‐marine carbonate factories, but they are also prone to (early) diagenesis. Evidence of diagenesis in travertines remains controversial as the resulting textures have been considered primary in other deposits and the impact on geochemical/palaeo‐environmental signals is often poorly addressed. This study revisits the Y‐10 core, taken in 1967 at one of the upper terraces of Mammoth Hot Springs in Yellowstone National Park (USA). The travertine depositional facies in the upper 50 m of the core show a general distal to proximal facies trend upwards. To unravel the nature, impact and timing of early diagenesis, fabrics and geochemical signatures are also compared to modern hot spring carbonates. Secondary ion mass spectrometry and detailed microscopy proved powerful in determining the stable isotope signature of different cement generations, thereby detangling the fluid history. Diagenesis starts during spring activity, but these warm waters not only precipitate CaCO3 at the top, they also seem to have circulated through the porous spring fabrics below. It resulted in coarsening and homogenization of the primary textures through neomorphism of aragonite and calcite cementation, often resulting in new intracrystalline microporosity within the calcite crystals. Subsequent circulation of meteoric fluids led to dissolution and cementation, particularly near the top of the core. Careful interpretation of U/Th dates suggests that travertine deposition started at the beginning of the Holocene/end Pleistocene. Calculated depositional (precipitation) rates vary between 2 and 20 mm/year, assuming a constant rate between samples at different depths. Aragonite deposits are completely transformed to calcite below depths of 5–10 m, corresponding to a time span of 4,000 years. Core and petrography observations, together with dating, suggest that travertine strata below marine sandstones in the lower part of the core may relate to fault displacement after the onset of travertine deposition.

The influence of hydrodynamics on the carbon isotope composition of inorganically precipitated calcite

It is often assumed that the carbon isotope composition (δ13C) of carbonate minerals records that of the dissolved inorganic carbon (DIC) species with insignificant disequilibrium effect. However, results from field observations and laboratory experiments have shown that the δ13C difference between calcite and solution can vary up to 3‰ even under a similar set of solution composition and temperature, raising uncertainties on the δ13C's paleoclimate and paleoecology implications. One likely cause is the variable calcite precipitation rates and pH values induced by different thicknesses of the stagnant liquid layer between solid and well mixed bulk solution (i.e., diffusion boundary layer, DBL). To test this hypothesis, we selected a well-studied natural travertine deposit (Baishuitai, SW China) which consists of meter-scale travertine terraces. Calcite crystals at both the pool bottom and the rim of the terraces are inorganically precipitated from solutions identical in chemical, isotopic composition and temperature, but different only in hydrodynamics. This difference results in thicker DBL for water at the pool-bottom than for water flowing across the rim. We found that the δ13C and Mg/Ca ratios are higher while Sr/Ca ratios are lower for the pool-bottom calcites than for the rim calcites. By applying a mass transfer model, we quantitatively link the differences in carbon isotope and elemental compositions of the abiogenic calcites to the different hydrodynamic conditions. The inverse variation in Mg/Ca and Sr/Ca ratios in calcites arises from the different precipitation rates between at the pool-bottom and at the rim, while the consistently lower δ13C for calcites at the rim is due to their higher pH at the solid-solution interface than for calcites precipitated at the pool-bottom. In contrast, calcite precipitation rate has little influence on carbon isotope fractionation between calcite and HCO−3. Our results demonstrate the role of DBL thickness in governing the δ13C of HCO−3 at mineral surface, which can assist to interpret the variable δ13C values of calcites in riverine or cave environments.

Record of Neotectonics and Deep Crustal Fluid Circulation Along the Santa Fe Fault Zone in Travertine Deposits of the Lucero Uplift, New Mexico, USA

AbstractTravertine deposits preserve an invaluable record of both ancient and modern fluid flow. The goal of this study is to reconstruct spatial and temporal patterns in travertine deposition associated with tectonic and climatic controls along the Lucero Uplift in New Mexico, USA. Uranium‐series ages of travertine deposits in the Lucero Uplift range from 0.94 ± 0.01 to 592 ± 110 ka, indicating that travertine formation has been episodically active since at least ∼600 ka. We find minimal evidence to attribute glacial and interglacial cycles to travertine formation in the Lucero Uplift. δ13C values in travertine deposits range from 2‰ to 9‰ (Vienna Pee Dee Belemnite), δ18O values range from 21‰ to 25‰ (Vienna Standard Mean Ocean Water). Positive correlation between travertine δ13C and δ18O values indicate travertine formation is closely associated with various degrees of CO2 degassing. 87Sr/86Sr values in travertine deposits range from 0.714 to 0.717 and (234U/238U)i values exhibit a remarkably wide range from 3.6 to 9.3, indicative of fluid‐rock interaction during deep crustal circulation in more radiogenic basement rocks. Reconstructed δ13C, δ18O, and (234U/238U)i values in the inferred deep fluid sources showed systematic variations with travertine formation ages, while 87Sr/86Sr values remain relatively constant. Based on dating of undeformed travertine deposits, which overlie tilted Santa Fe Group units, and high (234U/238U)i we infer that the Santa Fe fault has not produced a ground‐rupturing earthquake within the last 490 ± 52 to 592 ± 110 ka (2σ). Our study suggest that travertine formation is driven by fluid flow facilitated by tectonic and mantle structures.

Petrographical and mineralogical study of detrital strata near and within the Ballık travertine deposit (SW Turkey): architecture of a mixed clastic–carbonate succession

The Ballik area (SW Turkey) was studied as a mixed clastic–continental carbonate reservoir analogue, in which kilometre wide and up to 70-m-thick tufa and travertine lithologies are found in an envelope of detrital sediments, which locally strongly interfinger with these porous carbonates. Former studies focussed on the carbonate lithologies, since they are considered as pre-salt analogues. This study aims to describe the adjacent non-carbonate lithologies, unravel their depositional setting, and address their influence on the overall sedimentary architecture. This study relies on an extensive field campaign, during which 142 samples of all different detrital lithologies were collected. Optical, fluorescence, cathodoluminescence, and Scanning Electron Microscopy (SEM) yielded important insights in the petrography of these lithologies, based on which 5 main lithologies were differentiated: i.e., (1) laminated marls, (2) polygenetic conglomerates, (3) massive marls, (4) tabular sandstones, and (5) coquina accumulations. These were interpreted to represent three different sedimentary facies corresponding to lacustrine, fluvial, and shoreline facies. The (clay) mineralogy of lacustrine sediments was extensively studied by bulk and clay-specific XRD. In this respect, special emphasis was laid on the depositional setting of the lacustrine facies, in which both authigenic palygorskite and poorly ordered dolomite were identified. Petrophysical properties of 16 plugs were determined by He porosimetry and N2-permeability, indicating that the detrital sediments are characterised by poor reservoir properties. The latter causes them to act, after assumed burial compaction, as potential barriers within a continental carbonate reservoir system.

Geochemical Survey of low- temperature geothermal resource of the Reşadiye Spa (Tokat, Northern Turkey)

The low-temperature geothermal area of Reşadiye is located within the Kelkit Valley in the middle of the Black Sea region of Turkey. The area is covered with widespread travertine deposits which are acquired immediately on deposition from hot spring waters. Thermal waters have temperatures between 42 °C and 49 °C and the discharge rate is 3 L/sec. Total dissolved solids range from 3686 to 4204 mg/L. These thermal waters are of Na-HCO3-Cl type. A geothermal reservoir having probable temperature of about 100° is the source of thermal water for the springs. Before emerging along the margins of exposed carbonate formations through the faults and fractures, the waters interacts sometimes with Na-rich Neogene sediments and/or with B-rich rising geothermal fluids as confirmed by high concentrations of Cl, and, to a greater degree, by the presence of B. The conductive process along with the mixing of thermal waters with shallow groundwaters is the main cooling mechanism. Deuterium and oxygen-18 signatures of thermal groundwater indicate its meteoric origin. Equilibrium states of the Reşadiye thermal waters studied by means of the Na–K–Mg triangular diagram, K–Mg–Ca geoindicator diagram, and finally the activity diagrams in the systems composed of Na2O–CaO–MgO-K2O–Al2O3–SiO2–CO2–H2O phases indicate that the springs and low-temperature geothermal well waters in the area can be classified as shallow or mixed waters which are likely to be equilibrated with muscovit at temperature similar to those calculated from the chemical geothermometers. It was also observed that mineral equilibrium in Reşadiye waters is largely controlled by CO2 concentration. Based on acquired data, a conceptual model of the geothermal system of Reşadiye is proposed.

Geochemical proxies and formation mechanism of Hatay (Başlamış) travertine and relation with Dead Sea Fault Zone (S-Turkey)

This study is the first investigation of the Başlamış (Hatay) travertines formed in the northern part of the left-lateral strike-slip Dead Sea Fault Zone. In this study, Başlamış travertines are examined in terms of structural, mineralogical and formation mechanism by conducting geochemical, hydrogeochemical and facies analysis. The Başlamış travertine occurrences are characterized by successions of terraces and pools developed in slope depositional system, mound depositional system and depression depositional system. The travertines have been classified into five lithotypes, namely: laminated, coated bubble, reed, intraclasts and micritic travertine. According to the thin section, XRD, SEM and EDX analysis, the Başlamış travertines are divided into two groups, the first group contains aragonite and secondary minerals such as silica and clay minerals, while the second group consists only of calcite minerals, therefore, the travertines are morphologically classified as aragonite-bearing travertines and massive calcite bearing travertines. The negative correlation between Ca and Sr abundances in travertine samples indicates that some Ca was replaced by Sr in the calcite lattice. Relatively rich trace element content in the Başlamış travertines is attributed to leaching of the underlying gabbro and limestone. Higher concentrations of some of the elements were probably the result of diagenetic processes and syngenetic mineralization. The Başlamış travertines are defined as meteogene travertine deposits and are fed with meteoric-origin waters along Dead Sea Fault Zone in terms of hydrogeochemical results. The conceptual model of the Başlamış travertine shows that the travertines are formed by precipitation of dissolving the limestone. The heat source of the geothermal fluid forming the travertines is of tectonic origin.

Geothermal Fluid Variation Recorded by Banded Ca-Carbonate Veins in a Fault-Related, Fissure Ridge-Type Travertine Depositional System (Iano, southern Tuscany, Italy)

Banded Ca-carbonate veins in travertine deposits are efficient recorders of the compositional fluctuations of geothermal fluids flowing (or flowed) from deep reservoirs up to the surface, within fault zones. In this view, these veins represent key tools for decoding those factors that influenced the geochemical variations. We have analyzed veins developed in fractures channeling geothermal fluids forming travertine deposits. The studied veins cut a fossil travertine fissure ridge, near the Larderello geothermal area (Iano area, southern Tuscany) where geothermal fluid circulation is favored by NE-trending strike-to-oblique-slip faults and their intersections with NW-trending normal ones. U-Th dating indicates that fluid circulation occurred from (at least) 172 ka to 21 ka. In this time span, the geothermal fluid changed in composition, and the banded Ca-carbonate veins recorded these variations in terms of mineralogical and stable isotope composition and temperature ( T ) of deposition. We also documented for the first time the occurrence of Mn-rich black tree-shaped structures within the veins. Mineralogy coupled with stable and clumped isotope measurements allows the reconstruction of some features (i.e., crystal texture, temperature, and CO2 origin) and the inference of the processes (i.e., pH, T, and pCO2 variations) that have controlled the fluid evolution through time. Multiple-stage and one-stage deposition processes have played an important role in modifying the stable isotope composition of banded Ca-carbonate veins; temperature coupled with pCO2 also influenced their mineralogical composition. Interpreted in the context of the tectonic setting, the data show that the NW-trending faults have mainly controlled travertine deposition. Their intersection with NE-trending faults, interpreted as transfer faults, highlights the important role of transfer zones in channeling the geothermal fluids.

Travertine deposition and diagenesis in Ca-deficiency perched hot spring systems: A case from Shihuadong, Tengchong, China

Travertines are generally considered as carbonate deposits related to Ca-rich hot springs. Ca-deficiency hot springs, however, can also produce travertines under suitable conditions and little is known about the travertine deposition and diagenesis in these systems. Therefore, we studied a fossil perched Ca-deficiency spring system at Shihuadong, China to discuss its genesis and diagenesis. This system is a platform-like build-up with travertines developing mainly in the steep frontal area. The travertines were deposited from high-temperature fluids (dominantly 45 °C to 55 °C) with strong interaction mostly with underground Gaoligong Group metamorphic rocks. Their parent CO2 was originated from magmatic CO2 and a little soil CO2. The travertine-depositing paleofluid was predominantly Ca-deficiency hot spring water, but stream water possibly from cold springs on surrounding hills might make a small contribution. The low calcium levels and flat substrate on the top area of the studied system handicapped the travertine deposition, only developing a small perched travertine channel entirely composed of crystalline crust. On the contrary, progressive CO2 degassing in the top area and increasing CO2 degassing and water flow rates in the frontal area induced the formation of abundant travertines. However, water scattering/dispersion in the frontal area might not heavily increase the water flow rate and only induced boundstone deposition. After the travertine deposition, underground thermal water, meteoric water, and microbial activity progressively altered the primary fabrics, forming mosaic and need fiber calcite cements, dissolution pores, microborings, and dissolution-induced and microbe-induced micritization. The studied perched spring system shows limited scales, notable progradation but slight aggradation, and the dearth of distal autochthonous travertines, unlike those formed by Ca-rich hot springs, which might extend widely and produce striking distal travertine deposits away from the frontal slope/waterfall. These findings suggest the significant roles of water chemistry and local topography in travertine deposition and the influence of slowly underground thermal water seeping on the diagenesis of travertines in hilly areas and might be used to recognize fossil Ca-deficiency and Ca-rich hot spring systems.

Mineralogy of travertine deposit in Ciseeng geothermal field, Parung, West Java, Indonesia

Travertine deposits are carbonate rocks consists mainly of calcium carbonate minerals, supersaturated from bicarbonate-rich water. Both recent and fossil travertine deposits are found in Ciseeng geothermal field, West Java. The travertine deposits are distributed around three distinctive areas Tirta Sayaga, Mount Panjang and Mount Peyek. This study aims to determine minerals found in travertine deposits in Ciseeng geothermal field. Mineralogical analysis can determine the evolution of hydrology system and local climate change. Principal methods of analysis consists of petrographic and diffraction methods. Analysis results indicate similar mineral composition of calcite and microcrystalline carbonate (micrite) between recent and fossil travertine deposit with more diverse texture in fossil travertine due to the evolution of water composition affecting deposition and diagenesis process. The absence of aragonite indicates a low-temperature geothermal system.

A new discovery of Neanderthal settlements in Turkey: Sürmecik open-air campsite in Western Anatolia

Western Anatolia is the poorest region in terms of Turkey's Palaeolithic finds. In the past years, only a few Palaeolithic artefacts were known from the surface in the provinces of İzmir, Manisa, Kütahya and Afyonkarahisar in western Anatolia. After the fossil Homo erectus skull fragment was found in the travertine deposits in Kocabaş (Denizli) in 2002, the importance of the region more increased. After this important discovery, Dr. Kadriye Özçelik started a Palaeolithic survey in Denizli and found a large number of chipped stone tools from the Lower and Middle Palaeolithic periods. Nevertheless, the last important Palaeolithic discovery in the region was made in Sürmecik (Banaz-Uşak) in 2015. This is an open-air campsite belonging to the Middle Palaeolithic period. Here is also a mining area where a mining operation is conducted. The chipped stone artefacts of the Sürmecik Palaeolithic open-air campsite come from a clay layer between hematite and limonite deposits under a travertine layer of about 4.5–5 meters in thickness. Faunal remains represent mostly by equids species. All stages of Mousterian culture are clearly visible in this open-air campsite. Sürmecik is the richest middle Palaeolithic open-air campsite in Turkey. The 83,002 lithic pieces were collected in the excavations carried out in 2016 and 2017. It is thought that the lithic assemblage will exceed 100,000 with the ongoing studies. The group of bifacial leaf points in this collection is seen in Turkey for the first time. Four master thesis studies started on the lithic material of Sürmecik. It is planned to take some samples for dating analysis along with ongoing studies.

Evaluation of uncertainties in travertine rock mass for the Antalya (Turkey) Metro tunnel excavation

The uncertainty in the measurement of rock mass is largely due to the inherently heterogeneous nature of the rock mass itself. A variety of environmental conditions influence the engineering behaviour of the rock mass. Antalya settlement area is located on the travertine deposits. Travertines were affected by domestic and industrial liquid waste, which was injected directly into the travertine plateau through septic holes in Antalya prior to 2000. This situation resulted in poor engineering properties in travertine rocks, such as high deformation and low strength. It can cause issues in travertine foundation excavations. Determining all engineering parameters, ordering their weights and clarifying their uncertainty effects are especially difficult tasks in tunnel excavations. This paper addresses the most important aspects of the Antalya 3rd Stage Rail System tunnel project and examines the rock mass properties of karstic travertines.