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Although notoriously difficult to delineate from the wider family of carbonate rocks and sediments, non-marine carbonates represent an important subset, forming in a large variety of depositional settings such as lakes, rivers, hydrothermal vents, caves, soils and sites affected by alkaline pollution (Pentecost, 2005; Alonso Zarza & Tanner 2010; Capezzuoli et al., 2014; Della Porta, 2015) (Figure 1). Due to the erosive and dissolution effect of meteoric waters in terrestrial environments, such carbonates are generally characterised by low preservation potential and their geological record is likely discontinuous and highly altered. Nevertheless, non-marine carbonates represent a significant component of terrestrial sedimentary basins, providing useful proxies of palaeoenvironmental conditions and can offer a means of passive remediation of sites harmed by human industry, including sequestration and storage of carbon dioxide. Understanding the physico-chemical and microbially mediated processes involved in their precipitation helps to constrain biogeochemical cycles, investigate the geological past and plan for the future approaches to global changes.

The 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.

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.

ispartof: BASIN RESEARCH vol:33 issue:5 pages:2605-2635 status: published

En el registro geológico, los depósitos de tobas palustres extensos no son comunes. Este trabajo discute los factores para la formación y conservación de extensos depósitos palustres, tomando como ejemplo los depósitos del Pleistoceno medio-superior que se formaron en el tramo distal del sistema de tobas fluviales del río Ebrón (Cordillera Ibérica, en Teruel y Valencia). Los depósitos estudiados (área de Los Santos) constan de sedimentos detríticos en la base, asociados a incisiones fluviales profundas sobre el sustrato, seguidos por una sucesión de carbonatos con amplia variedad de facies tobáceas, con un mínimo de 19 m de espesor. Las facies más abundantes son los rudstones fitoclásticos, arenas y limos de carbonato con gasterópodos y ostrácodos, y los boundstones de tallos de plantas creciendo hacia arriba. Menos comunes son los boundstones de musgos y de tallos colgantes, y las calizas bioclásticas. Hasta cinco secuencias verticales de facies se han caracterizado. El modelo de facies corresponde al tramo al final de un sistema tobáceo fluvial escalonado con cascadas-barreras, en el que se formarían extensas áreas palustres, áreas encharcadas someras, algunas con estancamiento, y pequeñas cascadas. Las variaciones litológicas del sustrato pre-Cuaternario, desde rocas carbonáticas aguas arriba a rocas aluviales aguas abajo, permitió la formación de esa superficie amplia y de poca pendiente al final del sistema fluvial escalonado, en conjunto con facies de poca energía, lo cual apoya la ausencia de estromatolitos. Además, la escasez de procesos erosivos intensos permitiría que una densa cubierta de plantas hidrófilas prosperara en diversos ambientes, así como la acumulación y conservación de materia orgánica. El escaso espesor de la secuencia estudiada se relaciona con la disminución del contenido en calcio y bicarbonato disueltos en el agua (por la situación distal respecto a las fuentes alimentadas por el acuífero carbonatado) y la disminución de la intensidad de desgasificación de CO2 en ambientes de poca pendiente.

The tufa deposits in the Kurkur–Dungul area, southern Egypt, date from marine isotope stage (MIS) 11 to MIS 1. Springs across the region were active during glacial periods (with sea-level below –50 m), reflecting changed atmospheric circulation over the Indian Ocean, as well as peak interglacial periods. During times of low sea-level, reduced Indonesian throughflow promoted formation of an Indian Ocean Warm Pool, and anomalous rainfall on its western margin. We suggest that Egypt lies at the intersection of westerly (‘maghrebian’) and easterly (‘mashriqian’) rainfall provinces, which show different timing with relation to orbital forcing and different source water regions. Tufa-growth periods are therefore not mechanistically linked to ‘humid periods’ or ‘sapropel events’ identified elsewhere. Stable isotope and T(Δ47) data are also inconsistent with these spring systems being part of a larger system spanning northern Africa, and lack a clear interaction between northern hemisphere heating and mid-latitude rainfall. We also follow previous researchers in concluding that formation of springline deposit formation was probably delayed compared with rainfall, owing to aquifer flow distances. This delay is unlikely to be sufficient to explain why rainfall is out of phase with movements of the monsoon belts, but may complicate interpretation of these records.\ud \ud Supplementary material: A lithofacies description and supplementary figures and tables are available at https://doi.org/10.6084/m9.figshare.c.5246661

Recent biostratigraphic and sedimentological studies in the inner Northern Apennines (Italy) permit to refine the upper Palaeozoic successions of southern Tuscany, allowing new hypothesis to frame these formations in the palaeogeographic scenario inherited by the Variscan orogenesis. The Tuscan pre-Triassic successions, now exposed in the Monticiano-Roccastrada Unit, are generally barren or scarce in term of biomineralized fossiliferous content. They were mostly affected by HP-LT to LP-HT metamorphism that, together with their limited exposures, made difficult the stratigraphic correlations. This presentation is focused on three units (i.e. Falsacqua, Torrente Mersino and Carpineta formations) which age attribution and correlation were strongly debated. The Falsacqua Formation is mainly characterized by black to dark-grey phyllite, metasiltstone and metasandstone with dark metacarbonate intercalation. Due to the lack of biomineralized fossil content, by lithostratigraphic correlation with other Tuscan successions, this formation was referred to late Carboniferous-early Permian or Devonian. The Torrente Mersino Formation mainly consists of black to dark-grey quartz-phyllite, quartz metaconglomerate, light-grey quartzite, green phyllite and quartzite and light-grey phyllite. This formation is barren of fossil content and has been alternately assigned to Ordovician-Silurian, Silurian-Devonian, late Carboniferous-Permian and Triassic by lithostratigraphic correlation with other Tuscan and Sardinian successions. The Carpineta Formation is characterized by graphite-rich mudstones with carbonate-siltitic nodules. This unit was referred to the upper Visean-Serpukhovian based on its palaeontological content within the carbonate nodules. The first finding of a well-preserved microflora of middle Permian age in the Falsacqua and Torrente Mersino formations and of middle-late Permian age in the Carpineta Formation adds more constrains to the age attribution. This new age assignment permits to correlate the investigated Falsacqua and Torrente Mersino formations with the coeval ones belonging to southern Tuscany (i.e. Farma and Poggio al Carpino formations) and Elba Island (Rio Marina Formation) characterized by a similar microfloral content and to support a younger deposition of the Carpineta Formation than the Farma Formation one. Moreover, the occurrence of Gondwana-related sporomorphs in all the considered formations proposes a new palaeogeographic scenario for the northern Gondwana margin. Specifically, the present integrated study suggests that the northern margin of Gondwana fragmented through a series of transtensional phases. In this framework, the investigated upper Palaeozoic formations recorded marine siliciclastic sedimentation within either coeval pull-apart basins or laterally related facies of the same basin.

The tectonic setting of Neogene is under debate, being interpreted as a contractional, pulsing or extensional framework. On the key-areas to unravel this issue is the Gavorrano monzogranite, located nearby the Tyrrhenian seacoast, in the inner zone of the Northern Apennines (southern Tuscany), where a Neogene monzogranite body (estimated in about 3 km long, 1.5 km wide, and 0.7 km thick) emplaced during early Pliocene. This magmatic intrusion is partially exposed in a ridge bounded by regional faults delimiting broad structural depressions. A widespread circulation of geothermal fluids accompanied the cooling of the magmatic body and gave rise to an extensive Fe-ore deposit (mainly pyrite) exploited during the past century. Data from a new fieldwork dataset, integrated with information from the mining activity, have been integrated to refine the geological setting of the whole crustal sector where the Gavorrano monzogranite was emplaced and exhumed. Our review, implemented by new palynological, petrological and structural data pointed out that: i) the age of the Palaeozoic phyllite (hosting rocks) is middle-late Permian, thus resulting younger than previously described (i.e. pre-Carboniferous); ii) the P-T conditions at which the metamorphic aureole developed are estimated at about 660 °C and at a maximum depth of c. 5 km; iii) the tectonic evolution which determined the emplacement and exhumation of the monzogranite is constrained in a transfer zone, in the frame of the extensional tectonics affecting the area continuously since Miocene.

In the Iano area (Southern Tuscany) a small tectonic window of Tuscan metamorphic units is observed. This belongs to the northernmost part of the so-called Mid-Tuscan ridge and, during Pliocene, formed a submarine high, now defining the easternmost shoulder of the Volterra Pliocene basin. The area gives the opportunity to investigate the complete cycle of negative inversion from crustal thickening to crustal thinning, which characterizes Southern Tuscany. Our new data focus on the western margin of the Iano ridge, and in particular on a system of high angle normal faults that represents the youngest structures of the investigated area. These structures, deformed low angle regional detachments locally juxtaposing the uppermost units of contractional nappe stack (the ophiolite-bearing Ligurian units), with the Tuscan metamorphic units, with an almost complete excision of at least 3.5 Km thick Mesozoic to Tertiary Tuscan nappe succession. The high angle normal faults show variable Plio-Quaternary vertical displacements from few meters to about 500 meters, and acted as pathways for the upwelling of hydrothermal fluids, as revealed by Pleistocene travertine deposits, hydrothermal alteration and occurrence of different generations of fluid inclusions in hydrothermal veins associated with these fault systems. Fluid inclusions were studied in quartz veins hosted in the Verrucano metasediments forming the top of the Tuscan metamorphic unit, as well as in some carbonate lithotypes (Cretaceous to Tertiary in age) of the overlying Tuscan Nappe. Two different kinds of fluid inclusions were documented. The Type 1 are multiphase (liquid + vapor + 1 daughter mineral) liquid-rich fluid inclusions whereas the Type 2 are two-phase (liquid + vapor) liquid-rich fluid inclusions. Type 1 fluid inclusions are primary in origin and were found only in quartz veins present in Verrucano metarudites, whereas Type 2 fluid inclusions occur in quartz veins present in both Verrucano phyllites and quartzites and in the carbonate units of the Tuscan Nappe. These are secondary and can be furthermore distinguished in two sub-populations (Type 2a and Type 2b) on the basis of petrographic observation and microthermometric data. Fluid inclusion investigation evidenced an evolution of the hydrothermal fluids from relatively high-T (~265°C) and hypersaline (35 wt.% NaClequiv.) fluids trapped at about 100 MPa, to lower temperature (~195°C) and salinity (~9.5 wt.% NaClequiv.) fluids, having circulated in the high-angle fault system. Based on the new data and a revision of the local tectonic setting a fluid-rock interaction history has been reconstructed with new hints and constraints for the Plio-Quaternary extensional history of the Volterra basin.

Earthquakes-related soft-sediment deformations (seismites) are relevant structures to help reconstructing the palaeoseismicity in a region. Nevertheless, although seismites have been described for a large variety of palaeo-environments and stratigraphic settings, they are rare and, in some cases, ambiguous structures. In this paper, we document, for the first time, impressive seismites affecting a latest Quaternary travertine deposit located in southern Tuscany (Serre di Rapolano, Italy). These structures are extremely relevant, as seismites have been never described for this kind of terrestrial deposits. The seismites developed within a 2.5 m thick stratigraphic succession made of alternating terrigenous and carbonate sediments, embedded within the travertine deposits. Earthquake produced liquefaction and fluidization of some terrigenous levels and the injection of fluidized silty sediments (dykes and sills) into carbonate and terrigenous levels; slumped levels and associated decollement surfaces produced highly non-cylindrical folds, overall induced by the loss of brittle shear strength along the basin slopes. The occurrence of these soft-sediment deformations implies an important seismic event that took place in a time spam encompassed between 84 ± 8 and 48.92 ± 5.08 ka, in an area characterized by low seismicity and scarce knowledge of its seismotectonic setting. Their spectacular exposition and preservation in saw-cuts of an abandoned quarry (Cava Oliviera quarry) highlights their relevance and importance.

A revision of late Palaeozoic tectonics recorded in Tuscany, Calabria and Corsica is here presented. We propose that, in Tuscany, upper Carboniferous-Permian shallow-marine to continental sedimentary basins, characterized by unconformities and abrupt changes in sedimentary facies, coal-measures, red fanglomerate deposits and felsic magmatism, may be related with a transtensional setting where upper-crustal splay faults are linked with a mid-crustal shear zone. The remnants of the latter can be found in the deep-well logs of Pontremoli and Larderello-Travale in northern and southern Tuscany respectively. In Calabria (Sila, Serre and Aspromonte), a continuous pre-Mesozoic crustal section is exposed, where the lower-crustal portion mainly includes granulites and migmatitic paragneisses, together with subordinate marbles and metabasites. The mid-crustal section, up to 13 km-thick, includes granitoids, tonalitic to granitic in composition, emplaced between 306 and 295 Ma. They were progressively deformed during retrograde extensional shearing, with a final magmatic activity, between 295 ± 1 and 277 ± 1 Ma, when shallower dykes were emplaced in a transtensional regime. The section is completed by an upper crustal portion, mainly formed by a Palaeozoic sedimentary succession deformed as a low-grade fold and thrust belt, and locally overlaying medium-grade paragneiss units. As a whole, these features are reminiscent of the nappe zone domains of the Sardinia Variscan Orogen. In Corsica, besides the well-known effusive and intrusive Permian magmatism of the “Autochthonous” domain, the Alpine Santa Lucia Nappe exposes a kilometer-scale portion of the Permian lower to mid-crust, exhibiting many similarities to the Ivrea Zone. The distinct Mafic and Granitic complexes characterizing this crustal domain are juxtaposed through an oblique-slip shear zone named Santa Lucia Shear Zone. Structural and petrological data witness the interaction between magmatism, metamorphism and retrograde shearing during Permian, in a temperature range of c. 800–400 °C. We frame the outlined paleotectonic domains within a regional-scale, strain–partitioned, tectonic setting controlled by a first-order transcurrent/transtensional fault network that includes a westernmost fault (Santa Lucia Fault) and an easternmost one (East Tuscan Fault), with intervening crustal domains affected by extensional to transtensional deformation. As a whole, our revision allows new suggestions for a better understanding of the tectonic framework and evolution of the Central Mediterranean during the late Palaeozoic.

An updated revision of the upper Carboniferous-Permian tectonics recorded in Corsica, Calabria and Tuscany is here proposed. We combine our and literature data to document how the sedimentary, tectono-metamorphic and magmatic upper Carboniferous-Permian record fits with a regional-scale tectonic scenario characterized by trascurrent fault systems associated with stretched crustal domains in which extensional regional structures, magmatism and transtensional basins developed. In Corsica, altogether with well-known effusive and intrusive Permian magmatism, the alpine S.Lucia nappe exposes a kilometer-scale portion of the Permian lower to mid-crust, with many similarities to the Ivrea-Verbano zone. The two distinct Mafic and Leucogranitic complexes, which characterize this crustal domain are juxtposed by an oblique-slip shear zone named as S.Lucia Shear Zone. Structural and petrological data document interaction between magmatism, metamorphism and shearing during Permian in the c. 800-400 °C temperature range. In Calabria (Sila, Serre and Aspromonte), a continuous pre-Mesozoic crustal section is exposed. The lower crust portion of such section is mainly made up of granulites and migmatitic paragneisses with subordinate marbles and metabasites. The mid-crustal section includes an up to 13 km thick sequence of granitoids of tonalitic to granitic composition, emplaced between 306 and 295 Ma and progressively deformed during retrograde extensional shearing to end with a final magmatic activity between 295 and 277 Ma, consisting in the injection of shallower dykes in a transtensional regime. The section is completed by an upper crustal portion mainly formed by a Paleozoic succession deformed as a low-grade fold and thrust belt, locally overlaying medium-grade paragneiss units, and therefore as a whole reminiscent of the external/nappe zone domains of Sardinia Hercynian orogen. In Tuscany we document, how late Carboniferous/Permian shallow marine to continental sedimentary basins characterized by unconformity and abrupt change in sedimentary facies (coal-measures, red fanglomerate deposits) and acid magmatism well fit a transtensional setting with a mid-crustal shear zone linked with a system of E-W trending (in present orientation) upper crust splay faults. We will frame the whole dataset in a regional framework of first-order transcurrent shear zones network which includes a westernmost S.Lucia Shear Zone and an easternmost East Tuscan Shear Zone, with intervening crustal domains in which extensional to transtensional shearing occured.

This study aims to hydrochemically characterise three CO2-bearing springs representing distinct hydrofacies in NW Gorveh (western Iran) and interpret them in the light of their geological setting. The results of laboratory measurements of elemental concentrations, stable oxygen, carbon and hydrogen isotopes, dissolved and particulate organic and inorganic carbon (DIC, DOC, POC, PIC) and alkalinity are combined with in situ measurements of pH and temperature. Parameters such as alkalinity, DIC, Ca2+ and pCO2 concentration display strong, positively correlated values, with systematic decrease from the spring vent in down-flow direction for the three spring systems. The inverse correlation of pH and δ13CDIC is caused by CO2 degassing. The δ18O and δD values show no significant variation, related to minor or no evaporation due to normal ambient temperatures. The low concentration of POC, PIC and DOC compared to that of DIC and the lack of correlation between them reflect predominant inorganic carbon in these fluids. Spring I is oversaturated in calcite with additional dissolution of CO2, and despite high concentrations of Na+ and Cl−, undersaturated in halite, indicating a fluid of geothermal origin and/or reflecting steady state dissolution. This is related to water-rock interaction processes with carbonate and evaporitic rocks, that affected the isotopic signature of δ18O, which is shifted to the right of the global meteoric water line. Spring I also represents a partially equilibrated and mature (deep) chloride type water. Spring II and III are less saline and represent a different fluid circulation and/or shorter residence time. The two latter springs are characterized by peripheral (shallow) dilute chloride-bicarbonate type waters. Decreasing key parameters especially in Spring III during the winter suggest that superficial mixing with rain and meteoric water results in high temporal variations. Cation and stable carbon isotope geothermometry applied to the studied springs reveals an average reservoir temperature of ~210, 110 and 90 °C for Spring I and II and III, respectively. The geochemical and isotopic data allowed to depict a conceptual model where the hydrothermal reservoir for Spring I is residing in carbonate and evaporitic rocks (most likely the Qom Formation) situated at a depth of 3–4 km whereas those of Spring II and III are likely sourced from a shallower depth (1–2 km) in correspondence with carbonate and porous and permeable volcanic rocks. Integration of hydrofacies with conceptual hydrological and geological models forms the base towards a proper understanding of water circulation patterns, increasingly important for sustainable water management and geothermal applications.

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.

Travertine deposits have long been considered as powerful tools for investigating neotectonics and reconstructing palaeoseismic events. We document, for the first time, the effects of overpressured hydrothermal fluids injected within travertine deposits. We also describe tectofacies interpreted as a consequence of coseismic events. Calcite veins, banded or massive, associated with hydrofracture and fluid-escape features, promoted hydrothermal eruptions and lithoclast formation in latest Quaternary travertine exposed in two quarries near Rapolano Terme (Northern Apennines, Italy). The isotopic composition of the calcite veins confirms the hydrothermal origin of the parent fluids and their rapid ascent, as indicated by the estimated palaeo-temperatures (43 – 50°C). Integration of U–Th ages obtained for the calcite veins with palaeoseismic evidence from a local archaeological site built at the top of one of the analysed travertine deposits suggests that hydrofracture and fluid-escape structures were associated with five main seismic events that occurred from the latest Pleistocene to the fourth century AD. In sum, the travertine tectofacies have a key role in better constraining the seismotectonic setting of a region and thus offer a powerful tool for the evaluation of seismic hazard for areas characterized by low seismicity and travertine deposition.

Travertines from Tivoli area (Central Italy) possess abundant shrub-like fabrics that are laterally continuous over hundreds of square meters. They occur dominantly in horizontal layers with aggradational and progradational stacking patterns. Their fabrics and morphologies are remarkably similar to the shrubs lithotypes reported in literature for the Pre-Salt reservoirs, offshore Brazil and Angola, with huge oil accumulations. Petrographic and micro-computer tomography analyses allowed the identification of six shrub morpho-types (i.e., narrow dendriform, wide dendriform, fili dendriform, arborescent, arbustiform and pustular). Dendriform shrubs are the most common lithotype in Tivoli area, and three different subtypes could be distinguished according to the arrangement of their branches. The shrubs consist largely of peloidal micritic aggregates engulfed in spar calcite, ranging in average from 1 to 3 cm in height. The shrubs are interpreted to have developed in very shallow extensive waterlogged slightly inclined flat areas, changing laterally into a slope system with crusts as the main lithotype. Changes in the hydrodynamic conditions with episodes of stagnancy influenced the shrub morpho-types making them very variegated. Shrub morphologies likely reflect specific (micro-) environments that are controlled by water flow rates, evaporation and microbial activity. The latter processes influenced shrub fabric and morphology. Under high flow conditions, CO 2 degassing is the main process leading to carbonate precipitation. Consequently, denser and tightly packed morphologies will precipitate, composing mainly the crust lithotype. In this scenario microbes are less dominant. Dendriform shrubs, with narrow, wide and fili morphologies are interpreted to occur in moderate to low energy water flows. Narrow dendriform shrubs reflect faster flowing conditions, with decreasing impact of flow on the morphological aspects from wide dendriform shrubs to fili dendriform shrubs. Slow to very slow flowing waters are more characteristic for the arborescent, arbustiform and pustular shrubs that possibly are highly influenced by evaporation. A decrease of water flow likely allows higher microbial activity, and consequently, shrub morphologies become more fragile and enriched in peloidal micritic aggregate fabrics.

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 70 m. 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 > 10 m 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.

Quantification of carbon fluxes between solid Earth and its atmosphere is necessary to understand the global geological carbon cycle. Some of the main CO2 contributors are metamorphism and magmatic-mantle degassing. CO2 is discharged from active and quiescent volcanoes, fault zones, geothermal systems and CO2 rich groundwater. Here a new method for the estimation of the geogenic flux of CO2 from tectonically active regions, based on the volume, composition and age of travertine deposits, is proposed. The method is applied to the travertine deposits of western Central Italy where travertine deposition is driven by degassing of CO2 charged groundwater. Results show that the study areas are characterized, since Middle Pleistocene, by diffuse CO2 degassing processes with time averaged CO2 fluxes ranging between 1.24 ± 0.12 106 mol y−1 km−2 and 1.38 ± 0.42 106 mol y−1 km−2. These values are of the same order of magnitude of carbon dioxide fluxes measured by different methods in western central Italy and are higher than the global baseline CO2 flux from high heat flow regions. The review of the available 234U/230Th and 14C data shows that the CO2 degassing processes that affects western Central Italy nowadays were already active at least 350 Ka ago, proving that this region is a globally relevant case for the study of Earth degassing. Considering the widespread occurrence of travertine deposits in tectonically active areas worldwide, the proposed approach can be used as a reliable tool to estimate the CO2 flux in different geodynamic settings within system Earth.

3D modelling represents a powerful tool to characterize the geobody architecture of depositional systems. Several examples have been proposed in literature both for marine carbonates and siliciclastics rocks. For modelling, quantitative data related to orientation, shape and dimension are fundamental. Continental carbonates, however, are not considered yet, likely because they cover a large range of deposits such as speleothems, tufas, lacustrine carbonates and travertines. The interpretation of the depositional environments of the latter is still in fact debated by the scientific community. However, the interest in continental carbonates and especially travertines increased over the last decades due to the discovery of supergiant unconventional reservoirs in the Southern Atlantic (i.e. the so-called “Pre-salt play”). Aim of this paper is to present an innovative workflow to investigate and describe continental carbonates as geobodies based on a hierarchical approach applied to three large scale travertine settings, i.e. Terme di San Giovanni (Italy), Pamukkale (Turkey) and the Lapis Tiburtinus travertines (Italy). Travertine depo-systems are divided in three different depo-zones, namely proximal, intermediate and distal, that are characterized by different depo-elements, depo-shapes and depo-facies. Finally, a 3D morphological model is created based on numerical and vector approaches and interpolation of both. The model can be applied to seismic data of Brazilian and Angolan Pre-salt, highlighting the similarities between these systems and for the first time the scale independence of these depositional system, representing an important advantage in their interpretation. The 3D model and the approach proposed facilitates seismic interpretation, allowing to define and characterize geometries of inaccessible geological contexts.

Summary For the deep South-Atlantic Pre-Salt carbonate reservoirs information on reservoir heterogeneity between core and seismic scale is lacking. Worldwide non-marine carbonate reservoir analogues provide quantitative geometrical and petrophysical data. Large-scale outcrops with similar sedimentological, diagenetic, petrophysical and structural features give insight in reservoir controlling parameters from below core-scale up to seismic scale

The dataset presented in this article is used in the Quaternary Science Review research article "Evaluating the geogenic CO2 flux from geothermal areas by analysing Quaternary travertine masses. New data from western Central Italy and review of previous CO2 flux data" [1]. The present data article reports the physical properties and new compositional data of 86 travertine samples from Rapolano, Canino and Tivoli travertine deposits (Italy). The dataset include the following parameters: mass, volume, porosity, bulk density, CaCO3 content and insoluble fraction. The dataset is integrated with the photographic documentation of the sampling areas, the location and the stratigraphic position of each sample. ispartof: DATA IN BRIEF vol:25 ispartof: location:Netherlands status: published

The geothermal area of Acquasanta Terme has often been studied for its active and fossil travertine deposits to elucidate fluid origin, geodynamic and hydrological setting. Even though present-day thermal springs are usually used to obtain most information, the three travertine terraces bordering the Tronto river contain a plethora of information. A combination of elemental and isotope analyses (δ18O, δ13C and 87Sr/86Sr-ratio), fluid inclusion microthermometry and U Th dating is used to verify the hydrogeology and its timing. These analyses point out two fluid reservoirs with distinctly different fluids, one with low salinity of 0.7 wt% NaCl eq. and another with 28.5 wt% NaCl eq., which corresponds to the fluid composition of present-day spring fluids. Furthermore, it is demonstrated that geothermal sources were intermittently active in the past 221 ka mainly during uneven-numbered marine isotope stages, which are related to humid, interglacial periods and resulted in three different travertine terraces around 210.5, 126.5, and 36.5 ka. Accordingly, an uplift rate for this area could be estimated at around 1 mm/ka. The fluids were tapped at a depth of approximately 3 km in the tectonized, cataclastic fraction of the Triassic Anidriti di Burano Formation, the Calcare Cavernoso Formation and are originally meteoric based on geochemical evidence of a uniform 87Sr/86Sr-ratio of 0.707914 ± 0.00019 and a δ18Oaragonite value of −11.90 ± 0.34‰, which has been depressed by elevated precipitation temperatures between 22.2 and 50 °C. The characterization and dating of fossil travertine deposits gives valuable data providing insights in long-term fluid flow and orogenic uplift rates, adding valuable information to present-day spring fluid characterization.

The present knowledge on the structures affecting the Tuscan Nappe in the Monte Amiata area is here presented, highlighting that the tectonic evolution of the area is incorporated in the inner Northern Apennines framework. In fact, field and subsurface data indicate that the Tuscan Nappe is internally characterized by tectonic doublings, occurred during the collisional stage. Subsequently, as well as in the whole southern Tuscany, Miocene extension determined the lateral segmentation of the Tuscan Nappe; in the Mt. Amiata area, it resulted in three isolated geological bodies, partly cropping out. During Pliocene, the Tuscan Nappe was cross-cut by normal to oblique faults which contributed to channel the hydrothermal fluids that gave rise to the Pleistocene Hg-Sb ore deposits and Present geothermal resources. As it regards the deformation ages, since the late Oligocene-Aquitanian Macigno Fm is involved in the thrusts, the internal stacking of the Tuscan Nappe is related to the post-Aquitanian and pre-Langhian time period, on the basis of the Langhian sediments deposited in an extensional setting and presently recognised underneath the sediments of the nearby Pliocene Radicofani extensional Basin. It is therefore concluded that the switch from compression to extension occurred in a time span encompassed between early Burdigalian and early Langhian.

Southern Tuscany (Italy) hosts geothermal anomalies with associated widespread CO2 gas-rich manifestations and active travertine-deposing thermal springs. Geothermal anomalies have been active since the Late Miocene and have led to the formation of widespread Late Miocene-Pleistocene travertine deposits and meso- and epithermal mineralizations. This study investigates the travertine deposit exposed in the Castelnuovo dell'Abate area of southern Tuscany. Here, a fissure-ridge type travertine deposit and its feeding conduits, currently filled with banded calcite veins (i.e. banded travertine), represent a spectacular example of fossil hydrothermal circulation in the peripheral area of the exploited Monte Amiata geothermal field. The Castelnuovo dell'Abate travertine deposit and associated calcite veins were analysed to establish the characteristics of the parent hydrothermal fluids, and the age of this circulation. The focus of the study was on fluid inclusions, rarely considered in travertine studies, but able to provide direct information on the physico-chemical characteristics of the original fluid. Uranium-thorium geochronological data provided further constraints on the: (1) age of tectonic activity; (2) age of the hydrothermal circulation; and (3) evolution of the Monte Amiata geothermal anomaly. Results indicate that brittle deformation (NW- and SE-trending normal to oblique-slip faults) was active during at least the Middle Pleistocene and controlled a hydrothermal circulation mainly characterized by fluids of meteoric origin, and as old as 300-350 ka. This is the oldest circulation documented to date in the Monte Amiata area. The fluid chemical composition is comparable to that of fluids currently exploited in the shallow reservoir of the Monte Amiata geothermal field, therefore suggesting that fluid composition has not changed substantially over time. These fluids, however, have cooled by about 70 °C in the last 300-350 ka, corresponding to a cooling rate of the Monte Amiata geothermal area of about 20 °C 100 ka-1.

Traditionally, fresh water carbonate research has focused on the sedimentology and palaeontology of ancient lacustrine deposits. Lithofacies in such low-energy deposits are typically fine-grained, developed uniformly in a generally concentric distribution (‘bulls-eye’ pattern) and are predictable even when preserved imperfectly. In contrast, because of their local lithofacies and palaeontological complexities, fluvial carbonates were either delegated to a status of ‘minor geomorphological features’ or barely considered prior to the 1970s. This viewpoint was based on the depositional record of fluvial and spring-fed fresh water carbonates, which were considered to be restricted generally to localized karstic areas. Such deposits are often preserved as scattered patches of ambient temperature tufa. Occasionally, however, in active tectonic areas, localized travertine deposits are also developed from deeply circulating hydrothermal waters. With a few exceptions (for example, basins with high subsidence rates or in arid climate zones), these fresh water carbonates are prone to erosion from continuing river incision and thus may not be preserved in the geological record. A partial record of fluvial and spring-deposited carbonates is often preserved in Quaternary deposits, but the record in older deposits is typically fragmentary and often diagenetically modified. Yet once their unique facies architecture (and specialized nomenclature) is understood, these carbonates provide an important record of past sedimentological cycles of great value in palaeoenvironmental landscape modelling. The emphasis of modern research is to acquire information that explains how active systems function. In this respect, tufas reveal much of how carbonate precipitation is a shared product of physico-chemical and microbiological biomediation processes. Likewise, travertines not only show an intimate interrelation with active tectonism but also hold great potential as monitors of past volcanic carbon dioxide emissions. In addition, both tufas and travertines contain palynological records that can be used as proxy indicators of climate change. Perhaps no other field of sedimentology has witnessed more developments and applications over such a brief period of study.

In the extensional province of SW-Anatolia, the cross-cutting relationship between the NW- and NE-oriented Neogene and Quaternary basins is an ongoing debate in the understanding of the tectonic evolution of this area. In order to contribute to this issue, we carried out a structural and kinematic study along the seismogenic NW-trending Dinar Fault Zone (DFZ). This structure was initially controlled by the sedimentary and tectonic evolution of the NE-oriented Neogene Baklan, Acigöl and Burdur basins and, later, by the NW-oriented Quaternary Dinar Basin.On the basis of >. 1000 structural and kinematic data, in conjunction with basin stratigraphy, the DFZ can be divided into three almost parallel and continuous bands, that are: (a) the Hangingwall where Quaternary sediments are deformed by normal faults with mechanical striations; (b) the Inner Zone, corresponding to the present Dinar fault scarp, where NW-trending normal faults with mechanical striations are dominant, and (c) the Outer Zone, located in the footwall of the structure comprising the area between the fault scarp and undeformed bedrock, where faults exhibit variable orientation and kinematics, from strike-slip to normal dip-slip. These kinematics are mainly indicated by calcite shear veins and superimposed mechanical striations, respectively. This suggests that the DFZ changed kinematics over time, i.e., the DFZ initiated as dominant dextral strike-slip to oblique-slip fault system and continued with a dominant normal movement. Therefore, we hypothesize that the NW-trending DFZ was initially a transfer zone during the late Miocene-Pliocene, coeval to the sedimentary and structural evolution of the NE-trending Baklan, Acigöl and Burdur basins. During the Quaternary the DFZ, representing an already weakened crustal sector, played the role of a normal fault system providing the accommodation space for the Quaternary Dinar Basin. Hydrothermal circulation and volcanism at NE-/NW-trending faults intersection implies structurally-driven conduits channeling fluids from depth to surface. © 2013 Elsevier B.V.

Hydrothermal travertines develop various depositional geometries, from tabular to high-relief mounds or aprons with steep slopes, under the control of local topography, location and geometry of the vents, fault activity, hydrology, water physico-chemical properties, rates of thermal water flow and carbonate precipitation rates. This study focuses on two Pleistocene, tens of metres thick, travertine slope aprons accumulated on fluvial terraces in the Tronto River Valley (Acquasanta Terme, Central Italy) to investigate their facies character, geochemical signature, porosity and evolution of the depositional geometry through time. The two travertine aprons consist of four aggradational-progradational units, vertically and laterally stacked with onlap and downlap stratal terminations, separated by erosional unconformities produced by events of non-deposition and erosion, due to temporary interruptions of vent activity, shifts of the vent location and/or deviation of the flow directions. The travertine units include various depositional environments: 1) smooth slope, 2) terraced slope with metre-scale sub-horizontal pools separated by rounded rims and vertical walls, and 3) sub-horizontal, tens of metres wide ponds. Smooth slope clinoforms are made of centimetre to decimetre thick layers of crystalline dendrite cementstone, laminated boundstone and radial coated grain grainstone, precipitated by fast-flowing water on inclined substrates. Rims and walls of terraced slopes are built by crystalline dendrites and laminated boundstone. Sub-horizontal layers of terrace pools and ponds consist of facies precipitated by slow-flowing to standing water (clotted peloidal micrite dendrite, coated bubble boundstone, raft rudstone) associated with radial coated grains and laminated boundstone. Carbonate coated reeds occur in distal ponds adjacent to toe of slopes or overlie packstone/rudstone with travertine intraclasts and substrate extraclasts, marking events of subaerial exposure and erosion. Travertine facies porosity and permeability range from 4 to 21% and 0.03 to 669 mD, respectively, showing no direct correlation. Stable isotope values (δ 13 C: 5.7–9.3‰; δ 18 O −9.6‰ to −12.2‰) are similar to other travertines precipitated by thermal water in Central Italy. This study identifies the centimetre-scale travertine facies variability linking it to the environment of deposition and to the depositional geometry of travertine units affected by the substrate topography and lateral shifts of the active springs. Despite the different scale and facies composition, the geometry of aggradational-progradational units of travertine aprons might resemble marine flat-topped high-relief carbonate platforms. Travertine units in the subsurface, if present with sizes that can be seismically resolved, might be wrongly interpreted as carbonate platforms with steep slopes without a detailed facies analysis.

Billi et al. (2017) proposed a new interpretation for the origin and internal structure of thermogene travertine deposits. On the basis of evidence from two quarries located in southern Tuscany (Italy), they interpreted some travertine beds as calcite veins and argued that undulating travertine beds formed by syn-diagenetic (i.e. non-tectonic) folding that was caused by laterally-confined volume expansion caused by incremental veining. They assumed that such a process causes changes to the rock properties, including porosity reduction, rock strengthening, and age rejuvenation. The interpretations by Billi et al. (2017) challenge and question the current understanding and interpretation of thermogene travertine deposits. This understanding, based on numerous studies since the 1980s, is that these deposits form from thermal water flowing downslope, and precipitating calcium carbonate. Here, we explain how the comparison with active depositional systems is essential for the understanding the origin of structures in older, inactive travertine deposits, such as those studied by Billi et al. (2017). We further argue that the three-dimensional setting of travertine deposits should be taken into account in order to discuss the possible development of secondary structures. Indeed travertine deposition on slopes typically leads to the formation of terraced morphologies with pools bordered by rounded rims and separated from each other by steep walls. The resulting three-dimensional structures can be misinterpreted as asymmetric folds in two-dimensional views (i.e., in saw-cut walls of quarry). In this paper we debate the interpretations offered by Billi et al. (2017) and their criteria to recognise syn-diagenetic, non-tectonic folds in travertine deposits, and explain why many of their ideas are questionable.

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.

Borgia et al. (2014) illustrated an active volcanic spreading model for the Amiata volcanic area (southern Tuscany, Italy). Although, at first glance, the model may appear appealing, this is not fully supported by the available data and the paper does not take into account their discussion. Accordingly, the supposed negative consequences of the Borgia et al. (2014) model on both contamination of shallow water and geothermal exploitation can likely be regarded as speculative.

The terrestrial limestones forming at the emergence of thermal springs show a variety of unusual depositional facies. The specific lithological and petrological features of these deposits have few counterparts in the marine, and continental, karst-related carbonates, but they are typical of the epigean limestone that has been quarried since antiquity in the surroundings of Tivoli (Rome) under the name of travertine, where it is still forming in hydro-geothermal fields linked to extensional tectonics. The physicochemical, hydrodynamic and geological conditions specific to the Tivoli thermal spring system imply hypersaturated alkaline–sulphate, warm to hot waters, upwelling from springs fed through open fractures/faults in extensional and/or volcanic regimes. These features, together with the hydrodynamic behaviour of the water flows running from the vents, control the petrogenetic features of the travertine, a well-bedded, mostly finely laminated, porous but quite compact limestone. The results of a detailed comparative petrological analysis carried out on the lithofacies of travertine limestones, and of those observed during formation within numerous active thermal spring fields, provide the elements required for an exhaustive textural classification of the travertine lithofacies, which has not yet been described systematically. According to the genetic processes and fabrics, the thermal deposits that originate from such hypersaturated alkaline–sulphate, warm to hot waters, can be subdivided into: abiotic crystalline crusts, microbially mediated crusts (microbialites) and granular deposits mostly represented by small accumulations of lime-mudstone. Some of the granular deposits and the microbialites are only partially comparable with analogous sediments forming on tidal flats/sabkhas or other continental sites; however, the facies association of crystalline crusts and laminar curled microbialites has no counterpart in the marine realm. The widespread presence of thermophile bacteria and sulphobacteria, and the general absence of autochthonous eukaryote organisms, unable to live in poisonous sulphate waters, are also undeniable evidence of their thermal origin.

The role of travertine fissure-ridges in reconstructing tectonics and related earthquakes is a challenging issue of recent debate directed at delineating historical/prehistorical seismic records. Indeed, direct measurements on a travertine fissure-ridge immediately after a seismic event have never been previously performed. We describe the co- and post-seismic effects of a M = 3.6 earthquake on fluid flow and travertine deposition in a geothermal area of Tuscany (Italy). Direct observation allows us to demonstrate that thermal spring (re)activation is directly influenced by transient seismic waves, therefore providing a basis for reconstructing seismic events in the past.

Defining the most recent Quaternary tectonics represents a challenging task for neotectonic, palaeoseis- mological and seismotectonic studies. This paper focuses on an integrated approach to reconstructing the latest Quaternary deformation affecting the northern part of the Siena Basin (inner Northern Apen- nines, i.e., southern Tuscany, Italy) near the town of Siena, and to discuss the seismological implications. Field work and structural and stratigraphic analyses, coupled with the interpretation of reflection seis- mic lines, have been combined to define the geometry, kinematics and age of mesoscopic to map-scale faults which have affected the mainly Quaternary continental and Pliocene marine deposits. The result- ing dataset describes a tectonic setting characterized by coeval SW- and NW-trending transtensional and normal faults, respectively, dissecting alluvial sediments younger than 23.9 ± 0.23 ka. Seismic interpre- tation sheds light on the geometrical setting of the faults at deeper levels, down to 1–2 km, and provides support for the presence of a wide brittle shear zone defined by conjugated fault segments, locally giving rise to an asymmetrical negative flower-like structure. Faults and their damage zones have controlled (and still control) the discharge of gas vents (mainly CO2 and H2S) and hydrothermal circulation (which deposits travertine) since at least 23.216 ± 0.124 ka. The resulting complete data set provides support for our description of the Neogene–Quaternary tectonics which were active until the late Quaternary, providing additional information about the seismotectonic framework of an area characterized by low seismicity and generally low-magnitude earthquakes (M < 4), but having experienced significant seismic events over the last few centuries.

In recent decades various interpretations have been proposed to explain the evolution of fissureridge- type travertine deposits. In this paper, we discuss the relationships between fissure-ridges and brittle structures affecting their substratum, through a detailed analysis of an inactive fissure-ridge (near Çukurbag) located in the Pamukkale geothermal area (western Turkey). The Çukurbag fissure-ridge can be taken as a model as it offers an opportunity to examine its internal structure on the walls of a Roman quarry; in addition, this ridge has been studied by several researchers who have discussed the processes promoting the fissureridge evolution. The Çukurbag fissure-ridge is composed of irregularly alternating travertine laminated facies (bedded travertine) crosscut into rather large lithons by subvertical crystalline veins (banded travertine). The relationships between bedded and banded travertine indicate that the banded veins are diachronous and migrated through time, suggesting a progressive fault zone enlargement in the footwall. Such a fault zone was characterized by polycyclic activity, with normal to transtensional kinematics, and was active during the latest Quaternary. We demonstrate that formation of banded veins is coeval with bedded travertine deposition and strictly depends on fault activity, therefore highlighting the fundamental role of travertine fissure-ridges in reconstructing palaeotectonic activity in a region. © 2014 The Geological Society of London.

Calcareous tufa, as well as other types of continental carbonates, are largely sensitive to climate variations. As a consequence, the relationship between climate variations and tufa deposition is relatively well known and calcareous tufa deposits are often used as a reliable climatic proxy in many geological settings. Conversely, the response of tufa to tectonics and uplifting processes is relatively poorly known, due to their genetic independence from geothermally heated groundwater springs and associated tectonic-controlled upwelling conduits in tectonically active settings. The aim of this paper is to describe a peculiar stratigraphic succession where calcareous tufa deposits are closely associated and interbedded with coarse-grained clastic deposits. The study area is located in southern Tuscany (Massa Marittima), where extensional tectonic processes, responsible for the emplacement of magmatic bodies at shallow crustal levels, have been active from Pliocene to Quaternary age, and caused a diffuse uplift as well as local volcanic eruptions and hydrothermal fluid circulation. The succession described in the paper recorded phases of calcareous tufa-dominated deposition (i.e. overall, medium/low hydrodynamic energetic settings) repeatedly interbedded with coarse-grained clastic fluvial sediments which testify an abrupt change in both the energy of the depositional environment and the sediment supply. Nevertheless, during the phases dominated by clastic sedimentation, tufa deposition was not inhibited as it would be expected for climate-influenced settings, suggesting that the observed stratigraphic settings were a consequence of a local uplift of the catchment area. These findings indicate that calcareous tufa deposits could be a sensitive proxy to tectonics when they are associated with coarse-grained clastic deposits, in a geological setting where the origin of the clastic sediments cannot be explained by autocyclic or climate-induced factors.