Fissure Ridge Research Articles

Tectonic and climate changes influences on distribution and morphology of Quaternary travertine, Kurkur oasis, Egypt

The present study aims to investigate the relationship between tectonic activity, climate changes and Quaternary travertine deposition around Kurkur Oasis in the southern Western Desert of Egypt. Our findings, based on field observations and structural investigations, revealed that extensional tectonics played a significant role in the formation and the distribution of travertine deposits in the study area. Three main travertine morphotypes are documented: fissure ridge, spring mound, and terrace mound along with four lithotypes: crystalline crust, fine-grained lithoclast, paper-thin raft, and reed. The spatial distribution of these travertine occurrences indicates that travertines located closest to the springs exhibit crystalline crust and paper-thin raft lithotypes. While, the reed and the fine-grained lithoclastic types are situated farther from the water sources. Terraces mounds are related to pluvial episodes, which led to travertine deposition in the suitable tectonically created depressions. A two-stage hypothesis for travertine deposition are proposed herein, involving tectonic fissuring and the circulation of carbonated water. These results may enhance our understanding of travertine formation and have broader implications for geological research in similar tectonic environments.

Depositional and diagenetic processes in travertines: A comprehensive examination of Tocomar basin lithotypes, Northwest Argentina

The use of travertines in active fault studies is known as travitonics. Their geobody shape, veins, faults and fractures, are commonly used as neotectonic proxies. The surficial travertines in the pull apart Tocomar Basin (Puna Plateau, Argentina) occur in the center of the Calama – Olacapato – El Toro (COT) transcurrent fault zone and have never been substantially buried. The Tocomar area exhibits complex tectonic with N–S thrust faults and NW-SE transfer faults, crucial in shaping its travertine deposits and geothermal activity. The travertine bodies are characterized in terms of geometry as a fissure ridge type, coexisting with ash tuff, siliciclastic sandstone, and conglomerate deposits. The travertines mainly consist of crystalline crusts, with occasional occurrences of granular, arborescent, and porous textures. Mineralogical analyses by X-ray diffraction (XRD) reveal the predominance of magnesian calcite, along with trace minerals identified as dolomite, anhydrite, gypsum, halite, fluorite, bassanite, and barite. Petrographic analyses, including cathodoluminerscence (CL), indicate intense diagenesis in the travertine samples. Isotopic signatures of C and O in these samples exhibit normally a negative trend, ranging from −6.38 to +2.45 ‰ VPDB for δ13C and from −20.48 to −11.21 ‰ VPDB for δ18O. Laboratory analysis and field observations allow to classify three distinct lithotypes in the Tocomar travertine: (1) crystalline crust, further divided into three sub-lithotypes: (1.1) laminated crystalline crust (LCC), (1.2) filamentous-like crystalline crust (FlCC) and (1.3) fiber-like crystalline crust (FbCC); (2) granular travertine (GT) and (3) porous travertine (PT). These different lithotypes likely reflect variations in fluid velocity during deposition, although some of them may result from diagenetic processes. The three lithotypes give rise to four facies association (steep slope, marshy/pools, drainage, and fracture-associated facies), forming two distinct depositional systems (slope and channel), which comprises the Tocomar travertine system.

Slovenská terminológia travertínov, penovcov a príbuzných terestrických vápencov

The paper follows on a review articles on Slovak travertines and tufa published in English in 2021. Geomorphological terms such as ‘fissure ridge’, ‘coalesced mound’, ‘self-buiding channel’, ‘keeled waterfall’, ‘smooth slope’, ‘terrased slope’, ‘dams along stream’, ‘peached springline deposits’, ‘moss pillow’ were defined as new in Slovak terminology. Travertine forms are formed by defined facies: ‘crystalline crusts’ with different crystal types, ‘radiating dendrites’, ‘coated bubbles’, ‘rafts’, and ‘breccias’ of various origin. Biogenic facies such as ‘microphyte mats’, ‘microphyte crusts’, ‘microphyte shrubs’, and ‘macrophyte facies’ appear in various tufas and travertines. In lakes, fens and marshes, the ‘lime-mudstones’ and the terms ‘mottling (marmorisation)’ and ‘pseudomikcokarst’ were defined. ‘Travertinized tufa’ was established as a transitional form between travertine and tufa.

Stable Carbon and Oxygen Isotopic Features of Banded Travertines from the Xiagei Fissure Ridge System (Shangri-La, China)

Banded travertines are important parts of fissure ridge systems, but studies on geochemical characterization of banded travertines are limited. This study investigated the lithofacies and stable carbon and oxygen isotopic features of banded travertines from Xiagei (southwestern China) to examine their formation mechanisms. Petrographic analyses of the banded travertines revealed two lithotypes: thick-laminated palisade crystalline crust and thin-laminated composite crystalline crust. δ13C and δ18O of the Xiagei banded travertines range from 2.82‰ to 4.50‰ V-PDB, and from −25.86‰ to −20.90‰ V-PDB. Parent CO2 evaluation shows that the Xiagei banded travertines mainly received CO2 from the decarbonation of marine carbonates, but the contributions of magmatic CO2 and the dissolution of marine carbonates are also unneglectable. Significantly, the magmatic-derived CO2 might indicate that the delamination of the lithosphere along with the asthenosphere upwelling could be taking place in the eastern Tibetan plateau. Paleotemperature calculation shows that the Xiagei travertines were precipitated from moderate- to high-temperature hot springs (44.3 to 86.8 °C). Interestingly, the thick-laminated palisade crystalline crust and thin-laminated composite crystalline crust display calculated paleotemperature between 66.6 and 86.8 °C and between 56.6 and 77.7 °C, respectively, reflecting the great role of water temperature in controlling the lithofacies of banded travertines. A comparison between the banded travertines at Xiagei and other areas also shows temperature is a non-negligible factor controlling banded travertine precipitation. However, this does not mean that water temperature is the decisive controlling factor and more studies on banded travertines are still indispensable to disclose the potential factors controlling the factors/processes affecting banded travertine lithofacies. This study provides a good example for understanding the relationship between lithofacies and stable isotopic geochemical characteristics of travertine deposits.

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.

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.

High geogenic arsenic concentrations in travertines and their spring waters: Assessment of the leachability and estimation of ecological and health risks

Travertines and their springs are rarely investigated as a source of toxicity. Remarkably high contents of As (up to 10 g/kg) have been found in travertine deposits and associated spring waters, nearby Ghorveh city (western Iran). Two types of travertines were distinguished: (i) Fissure ridge travertines, in areas with a carbonate-dominated basement, are characterized by a relatively low content and leaching of As. Their spring waters contain > 150 µg/L of As; (ii) Mound travertines, rich in non-carbonate impurities, occur in areas with volcanic substrates and contain high As concentrations (on average ~1,500 mg/kg) with high leachability. Their spring waters have lower As concentrations than equivalent fissure ridge waters. Principal Component Analyses of the elemental and mineralogical composition show the unstable association of As over a wide range of pH values to non-carbonate related elements, in particular iron, related to clay minerals. The high potential release of As may result in adverse ecotoxicological effects in surrounding agricultural soils and crops. An ecological risk assessment confirms the enrichment and very high potential ecological risk of As around mound carbonates. The human health risk assessment based on calculation via exposure factors suggests adverse non-carcinogenic and high carcinogenic risk with regard to As, both for adults and children.

Hydrochemical and geological model of the Bañitos-Gollete geothermal system in Valle del Cura, main Andes Cordillera of San Juan, Argentina

The main characteristics of geothermal systems at flat-slab segments are not well understood. This work reports a geological and fluid geochemistry survey at the southern thermal areas of the isolated Valle del Cura, located at the Frontal Andes Cordillera over the Pampean flat-slab. Deep circulation along deep-rooted N-S trend faults and fractures likely heats meteoric water through a locally anomalous geothermal gradient related to scattering Quaternary volcanism. Hot springs discharge up to 60 °C Na-Cl bearing water with high TDS (>5000 mg/L) from meteoric origin, according to the isotopic composition. At the top of an 11 m height travertine fissure ridge, intense gas flux is mainly composed of CO2. Enthalpy model, δD, and B suggest a similar evolution trend for the Bañitos and Gollete thermal waters, clearly separated by the trend evidenced for thermal waters of the northern thermal sites of the Valle del Cura (e.g., Despoblados). Reservoir probably develops below 2–3 km depth hosted by the ignimbrites of the Choiyoi Group. Cation and multicomponent geothermometers estimate a temperature of ~140 °C and quartz + albite + calcite + chlorite ± beidellite-Na ± montmorillonite-K was inferred as the mineral assemblage. Very low tritium contents and δ18O isotopic shift might be because of the water-rock interaction process at low permeability conditions. These findings are consistent with a long residence, fault-controlled deep fluid circulation path. During their rise, the thermal waters likely interacted with cold waters at the base of the Oligocene volcanic deposits, where secondary processes such as calcite and silica precipitation may occur. Further investigations are required to assess the geothermal potential of the study areas, but we hope that this study may represent an incentive for other detailed investigations to evaluate the geothermal systems over flat-slab geothermal plays.

A multi–methodological approach to reconstruct the configuration of a travertine fissure ridge system: The case of the Cukor quarry (Süttő, Gerecse Hills, Hungary)

Travertines are continental carbonates that precipitate from spring waters, mainly due to CO2 degassing. They are widely quarried as building stone, which has led to numerous (often abandoned) travertine quarry outcrops. These and other outcrops, however, merely represent the surface expressions of the complex architecture of travertine bodies and their deep–rooted feeding systems. Integration of field observations and geochemical analyses with crucial subsurface geophysical data is required in order to fully understand travertine systems and their relationship to the local geological framework. Such a multi-methodological approach is illustrated here for the case of the abandoned Cukor quarry. Radio-magnetotelluric (RMT) and Electrical Resistivity Tomography (ERT) surveys provide unique insights into local tectonics, geobody architecture and the topography preceding travertine deposition. Altogether, the lens–shaped, isolated domal geobody with spring-proximal lithofacies and subvertical bedding, in addition to the contrasting geochemistry and age with surrounding travertine, enabled the unequivocal reconstruction of the dismantled Cukor fissure ridge. This study illustrates the high potential of this multi–methodological approach on poorly exposed, strongly weathered, quarried and tectonically deformed travertine bodies, and provides information on the complex feeding system beneath travertine deposits. Their reconstruction can be interpreted in light of the neo–tectonic expression of regional uplift, helps to complete the regional tectonic history and provides insights into older landscapes that lack preservation or would no longer be immediately recognized at the surface.

Substrate geology controlling different morphology, sedimentology, diagenesis and geochemistry of adjacent travertine bodies: A case study from the Sanandaj-Sirjan zone (western Iran)

A travertine fissure ridge and travertine mound are situated ~800 m from each other at the western margin of the active tectono-volcanic Sanandaj-Sirjan zone (western Iran). Despite their close proximity, the two geobodies show a difference in morphology, lithofacies, lithotypes, diagenesis and geochemistry. Petrographic analysis of the fissure ridge carbonates revealed homogeneous sparitic fabrics with dendritic structures reflecting precipitation under fast-flowing conditions from calcite supersaturated spring water. The mound carbonates are much more heterogeneous and display dominantly micritic fabrics with (mainly volcanic) clasts reflecting a lower energy flow regime and lower calcite saturation. In contrast to the limited diagenetic overprint of the fissure ridge carbonates, the more porous mound carbonates are affected by dissolution, cementation, and formation of Mn/Fe-oxide/hydroxides, attesting of a strong control on porosity by early diagenetic processes. The widespread bright luminescent calcite phases especially in sparitic fabrics within both geobodies display high Mn concentrations in calcite indicating suboxic precipitation conditions.The overlapping 87Sr/86Sr signatures and δ13C signatures point to a mixture of CO2 that dominantly originated from dissolution of the marine carbonate Qom Formation (Oligo-Miocene). The different δ18O signatures, indicate different upwelling systems caused by different substrate settings. The fissure ridge formed on a hard and brittle limestone substrate with precipitation from dominantly subsurface-sourced fluids. The mound travertine formed on top of fairly unconsolidated and fractured volcanic strata. The depleted δ18O signatures and impure micrite-dominated fabrics of the mound travertine reflect precipitation from thermal water that mixed with surrounding groundwater. This difference is also reflected in a different calculated precipitation temperature that varies between 4 and 21 °C for the mound versus 25–50 °C for the fissure ridge.Our findings show that subsurface geology exerts a major control on precipitation processes resulting in differences in travertine morphology, sedimentology, diagenesis, and geochemistry, despite that the travertine bodies occur adjacent to each other.

Assessment of acid-base status and calcification risk after hemodialysis session

Arabia Terra is a region of Mars where signs of past-water occurrence are recorded in several landforms. Broad and local scale geomorphological, compositional and hydrological analyses point towards pervasive fluid circulation through time. In this work we focus on mound fields located in the interior of three casters larger than 40 km (Firsoff, Kotido and unnamed crater 20 km to the east) and showing strong morphological and textural resemblance to terrestrial mud volcanoes and spring-related features. We infer that these landforms likely testify the presence of a pressurized fluid reservoir at depth and past fluid upwelling. We have performed morphometric analyses to characterize the mound morphologies and consequently retrieve an accurate automated mapping of the mounds within the craters for spatial distribution and fractal clustering analysis. The outcome of the fractal clustering yields information about the possible extent of the percolating fracture network at depth below the craters. We have been able to constrain the depth of the pressurized fluid reservoir between ∼2.5 and 3.2 km of depth and hence, we propose that mounds and mounds alignments are most likely associated to the presence of fissure ridges and fluid outflow. Their process of formation is genetically linked to the formation of large intra-crater bulges previously interpreted as large scale spring deposits. The overburden removal caused by the impact crater formation is the inferred triggering mechanism for fluid pressurization and upwelling, that through time led to the formation of the intra-crater bulges and, after compaction and sealing, to the widespread mound fields in their surroundings.

Groundwater Control and Process Variability on the Equatorial Layered Deposits of Kotido Crater, Mars

AbstractUnderstanding the origin of the Hesperian‐aged sulfate‐bearing Equatorial Layered Deposits (ELDs) is crucial to infer Mars' climatic conditions during their formation and to assess their habitability potential. We investigated well‐exposed ELDs in Kotido crater (Arabia Terra) and produced a detailed geological map of the crater infill, distinguishing different units within the ELDs based upon their morphological and sedimentological characteristics.The ELDs consist of interbedded light‐toned, darker‐toned deposits and mounds, associated with possible fissure ridges. Although heavily eroded by younger eolian processes, we interpret these deposits and their associated morphologies as remnants of depositional features and propose that they are the result of fluid, gas, and sediment expulsion processes sourced from the groundwater. The textural characteristics, their depositional geometry, the associated morphologies, and the inferred composition of the light‐toned deposits suggest an evaporitic origin, whereas the darker‐toned deposits might reflect clastic sedimentary processes, related or not to fluid expulsion and/or residual deposition following dissolution of the evaporites. The relative ratio of fluids, salts, and clasts controlled the depositional process, analogous to what happens in terrestrial playas. The controls on fluid expulsion is interpreted to depend on groundwater emplacement and fluctuations, possibly related to climatic changes, and to the interactions with the fractures related to the crater formation, which allowed the actual upwelling from a pressurized aquifer.

Fluids mobilization in Arabia Terra, Mars: Depth of pressurized reservoir from mounds self-similar clustering

Arabia Terra is a region of Mars where signs of past-water occurrence are recorded in several landforms. Broad and local scale geomorphological, compositional and hydrological analyses point towards pervasive fluid circulation through time. In this work we focus on mound fields located in the interior of three casters larger than 40 km (Firsoff, Kotido and unnamed crater 20 km to the east) and showing strong morphological and textural resemblance to terrestrial mud volcanoes and spring-related features. We infer that these landforms likely testify the presence of a pressurized fluid reservoir at depth and past fluid upwelling. We have performed morphometric analyses to characterize the mound morphologies and consequently retrieve an accurate automated mapping of the mounds within the craters for spatial distribution and fractal clustering analysis. The outcome of the fractal clustering yields information about the possible extent of the percolating fracture network at depth below the craters. We have been able to constrain the depth of the pressurized fluid reservoir between ∼2.5 and 3.2 km of depth and hence, we propose that mounds and mounds alignments are most likely associated to the presence of fissure ridges and fluid outflow. Their process of formation is genetically linked to the formation of large intra-crater bulges previously interpreted as large scale spring deposits. The overburden removal caused by the impact crater formation is the inferred triggering mechanism for fluid pressurization and upwelling, that through time led to the formation of the intra-crater bulges and, after compaction and sealing, to the widespread mound fields in their surroundings.

U-series dating and origin of Yaprakhisar (Güzelyurt-Aksaray) travertines in Central Anatolian Volcanic Province, Turkey

This study reveals the age, setting, and geochemistry of fissure ridge travertines outcropping in Yaprakhisar (Guzelyurt-Aksaray) that is located in the Central Anatolian Volcanic Province (CAVP) and investigates their relationship with main tectonic structures. Dating studies with the U-series analysis method identified that travertine formations were deposited from 3 to 147 ka BP. The travertines in the study area were divided into two groups based on the age and extension direction. The first group consists of fissure ridge travertines with 70° NE and deposited in the range of 126–147 ka BP. The second group has 10° NW strike and are fissure ridge travertines dated to 3–47 ka BP. The association between the travertine groups and the significant fault zones in the region was investigated, and three different formation models are presented. The relationship between the fissure ridge travertines and faults deforming the CAVP was determined using paleo-discontinuities. The Yaprakhisar travertines were determined to have Ce and Eu anomalies, along with low Ba and relatively low Sr values. When the trace element and REE content of the Yaprakhisar travertines are considered together, the travertines are concluded to have been deposited under oxic conditions from limestone-evaporite-dolomite-sourced hypogene water with low acidity and relatively low temperature.

Stable isotope geochemistry and petrography of the Qorveh–Takab travertines in northwest Iran

Abstract The Qorveh-Takab travertines, which are connected to thermal springs, are situated in the northwest of the Sanandaj- Sirjan metamorphic zone in Iran. In this study, the travertines were investigated applying petrography, mineralogy and isotope geochemistry. Oxygen and carbon isotope geochemistry, petrography, scanning electron microscopy (SEM) and X-ray powder diffraction (XRD) analysis were used to determine the source of the CO2 and the lithofacies and to classify the travertines. Isotope studies, morphological and mineralogical observations and distribution of travertines revealed that the travertines of the Qorveh-Takab could be of thermal water origin and, therefore, belong to the thermogene travertine category. These travertines are usually massive with mound-type morphology and are essentially found in regions with recent volcanic or high tectonic activity. The measured δ13C values of the travertines indicate that the δ13C of the CO2 released from the water during travertine deposition, while the source of the CO2 in the water springs seems to have been of crustal magmatic affinity. These travertines are divided into two lithofacies: (1) crystalline crust travertine and (2) pebbly (phytoclastic travertine with pebble- size extraclasts) travertine. δ18O and δ13C values of travertines are -0.6 to -11.9 (‰VPDB) and +6.08 to +9.84 (‰VPDB), respectively. A probable reason for the heavy carbon isotope content observed in these deposits is the presence of algae microorganisms, which was verified by SEM images. Fissure ridges, fluvial crusts with oncoids, and mound morphological features are observed in the study area. Based on the petrographic and SEM criteria, Qorveh-Takab travertines are classified into four groups: (1) compacted, (2) laminated, (3) iron-rich spring deposit and (4) aragonite-bearing travertines. Stable isotope compositions of Turkish travertines are largely similar to the travertines in the study area.

U/Th Dating of the Akhüyük Fissure Ridge Travertines in Ereğli, Konya (Central Anatolia, Turkey): Their Relationship to Active Tectonics

Fissure ridge travertines that form the Akhuyuk travertine mass are located in Central Anatolia and are exposed in an area of 1.5 km $$^{2}$$ with N30 $$^{\circ }$$ W direction. These fissure ridge travertines have ages determined between 3345 ± 105 yr and 47850 ± 980 yr by U-series dating methods. Development of the travertines can be correlated with faults that have been active since the late Pleistocene. The dilation rate in the Eregli (Konya) basin was determined using age data and the widths of the banded travertines at the opening center of the fissure ridge travertines. The dilation rate for the formation of Akhuyuk travertines yields 0.025–0.05 mm yr $$^{-1}$$ on average. When considering positions and extension directions of fissure ridge travertines, they are consistent with the Tuz Golu Fault Zone which is one of the most important structures in the region. The maximum earthquake intensity potential in this region is estimated to be $$M_\mathrm{s}$$ 6.3, when the dilation rate of the fissure ridge travertines is taken to be 0.05 mm yr $$^{-1}$$ and with a 10,000-year earthquake recurrence interval.

Calcite veining and feeding conduits in a hydrothermal system: Insights from a natural section across the Pleistocene Gölemezli travertine depositional system (western Anatolia, Turkey)

Linking the architecture of structural conduits with the hydrothermal fluids migrating from the reservoir up to the surface is a key-factor in geothermal research. A contribution to this achievement derives from the study of spring-related travertine deposits, but although travertine depositional systems occur widely, their feeding conduits are only rarely exposed. The integrated study carried out in the geothermal Gölemezli area, nearby the well-known Pamukkale area (Denizli Basin, western Anatolia, Turkey), focused on onyx-like calcite veins (banded travertine) and bedded travertine well exposed in a natural cross-section allowing the reconstruction of the shallower part of a geothermal system. The onyx-like veins represent the thickest vein network (>150m) so far known. New field mapping and structural/kinematic analyses allowed to document a partially dismantled travertine complex (bedded travertine) formed by proximal fissure ridges and distal terraced/pools depositional systems. The banded calcite veins, WNW-trending and up to 12m thick, developed within a >200m thick damaged rock volume produced by parallel fault zones. Th/U dating indicates a long lasting (middle-late Pleistocene) fluids circulation in a palaeo-geothermal system that, due to its location and chemical characteristics, can be considered the analogue of the nearby, still active, Pamukkale system. The isotopic characteristics of the calcite veins together with data from fluid inclusions analyses, allow the reconstruction of some properties (i.e. temperature, salinity and isotopic composition) and processes (i.e. temperature variation and intensity of degassing) that characterized the parent fluids and the relation between degassing intensity and specific microfabric of calcite crystals (elongated/microsparite-micrite bands), controlled by changes/fluctuations of the physico-chemical fluid characteristics.

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.

Equatorial layered deposits in Arabia Terra, Mars: Facies and process variability

We investigated the equatorial layered deposits (ELDs) of Arabia Terra, Mars, in Firsoff crater and on the adjacent plateau. We produced a detailed geological map that included a survey of the relative stratigraphic relations and crater count dating. We reconstructed the geometry of the layered deposits and inferred some compositional constraints. ELDs drape and onlap the plateau materials of late Noachian age, while they are unconformably covered by early and middle Amazonian units. ELDs show the presence of polyhydrated sulfates. The bulge morphology of the Firsoff crater ELDs appears to be largely depositional. The ELDs on the plateau display a sheet-drape geometry. ELDs show different characteristics between the crater and the plateau occurrences. In the crater they consist of mounds made of breccia sometimes displaying an apical pit laterally grading into a light-toned layered unit disrupted in a meter-scale polygonal pattern. These units are commonly associated with fissure ridges suggestive of subsurface sources. We interpret the ELDs inside the craters as spring deposits, originated by fluid upwelling through the pathways likely provided by the fractures related to the crater formations, and debouching at the surface through the fissure ridges and the mounds, leading to evaporite precipitation. On the plateau, ELDs consist of rare mounds, flat-lying deposits, and cross-bedded dune fields. We interpret these mounds as possible smaller spring deposits, the flat-lying deposits as playa deposits, and the cross-bedded dune fields as aeolian deposits. Groundwater fluctuations appear to be the major factor controlling ELD deposition.

Relationship between Akhüyük fissure ridge travertines and active tectonics: their neotecteonic significance (Ereğli-Konya, Central Anatolia)

The Akhuyuk travertine mass crops out approximately 10 km to the north of Eregli (Konya, Central Anatolia). Its morphology and relationship with the main controlling fault zones are investigated. The morhpological properties of six different fissure ridge travertines which make up the travertine mass are classified into four groups based on their geometrical properties and orientation. The fissure ridge travertines having a banded travertine thickness of 120 and 170 cm are considered as the oldest travertines in the study area. Sill-like structures and dilation are observed, indicative of the ongoing deformation after travertine precipitation. The height-to-width ratio of the fissure ridge travertines vary between 0.08 and 0.5. The morhological structures and parameters observed in the fissure ridge travertines are interpreted to stem from the low deformation rate in the study area. The relationship of the formation of the Akhuyuk Fissure Ridge travertine with the Tuz Golu (TGFZ) and Nigde fault zones (NFZ) is investigated. The TGFZ is determined to be the most significant structure that controls the Akhuyuk fissure ridge travertines based on the extension direction determined, the location of the travertines, and the fact that the faults on the central and southeastern end of the TGFZ display the active normal fault zone with a right-lateral strike-slip component.