Enrico Capezzuoli

Tectonic control on travertine and calcareous tufa deposition in a low-temperature geothermal system (Sarteano, Central Italy)

This paper presents an integrated study directed toward an understanding of the tectonic control on the hydrothermal circulation and resulting deposition of Middle–Late Pleistocene travertine in a low-temperature geothermal field of southern Tuscany, located in the Sarteano area (Central Italy). The study area is characterized by thermal springs (c. 25 °C) and related continental carbonate deposits, structurally controlled by SW–NE-trending oblique to strike-slip faults dissecting previous normal faults. Sedimentological–stratigraphical data and 230Th/234U radiometric age determination for the travertine indicate that continental carbonates were deposited in a tectonically controlled, perched-spring system from 268 ± 22 ka (at least) to the present. The hydrothermal system is (and was) characterized by meteoric waters with a minor contribution from fluids of deeper origin. Meteoric waters infiltrated to depth through tectonically damaged zones of Mesozoic and Cenozoic carbonate rocks and overheated as a result of localized, anomalous geothermal gradient. Then, fluids enriched in bicarbonate–sulphate moved up along highly fractured rock masses at the intersection between strike-slip faults and normal faults. This paper highlights the use of continental carbonates in the reconstruction of palaeohydrothermal systems, in terms of the location of the main conduits for hydrothermal fluid flow, age of faulting and physical properties of hydrothermal fluids.

Evolution of a fault-controlled fissure-ridge type travertine deposit in the western Anatolia extensional province: the Çukurbağ fissure-ridge (Pamukkale, Turkey)

In recent decades various interpretations have been proposed to explain the evolution of fissure-ridge-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 Çukurbağ) located in the Pamukkale geothermal area (western Turkey). The Çukurbağ 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 fissure-ridge evolution. The Çukurbağ 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.

Calcareous tufa as indicators of climatic variability: a case study from southern Tuscany (Italy)

Abstract A carbonate terraced succession mainly consisting of fluvial/palustrine calcareous tufa and of lacustrine limestone was deposited during recent Quaternary in a limited segment of the Valdelsa fluvial pattern (southern Tuscany, Italy). The radiometric data obtained from three carbonate terraces indicate that the depositional/erosional history of the Valdelsa succession during Late Pleistocene–Holocene, has been constrained by the same cyclic events observed in coeval detrital lacustrine successions of Central Italy. At least three of the Valdelsa carbonate Synthems and the interposed erosional phases can be correlated with the major climatic changes recognized in the European–Mediterranean area, from the Last Glacial Interstadial through the Younger Dryas to the Atlantic ‘Optimum Climatic’, the Sub-Boreal and finally at 2.5 ka the last Sub-Atlantic oscillation. This climatic correlation and the radiometric data imply that the deposition of calcareous tufa in Valdelsa was mainly dependent on rainfall availability and, consequently, was active during the milder oscillations within the cold periods.

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

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

The Tuscan Nappe structures in the Monte Amiata geothermal area (central Italy): a review

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.

Earthquake impact on fissure-ridge type travertine deposition

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.

Stratigraphic and paleopedological aspects from the Middle Pleistocene continental deposits of the southern Valdelsa Basin

A multidisciplinary approach on mainly continental carbonate deposits outcropping in the southern part of the Valdelsa Basin has allowed the recognition of two units, the Strove Synthem (STR) and the Campiglia dei Foci Synthem (CDF), both previously attributed altogether to a single indistinct sequence. The presence of a mammalian fauna suggests that the STR Synthem belongs to the Early-Middle Pleistocene, whereas the CDF Synthem is assigned to Middle Pleistocene because of its stratigraphic position. Lateral correlation with continental deposits cropping out in the adjacent Lower Valdarno Basin suggests an age not younger of the Stage 11 of the isotope scale. A paleopedological study of the soils on the synthems has distinguished two pedogenetic typologies: a Cutanic Alisol (Manganiferric) on Gleyic Vertisol for STR Synthem and a Haplic Cambisol on Rhodic Luvisol on Rhodic Nitisol for CDF Synthem. The different pedogenetic development corroborated the hypothesis of two distinct synthems. The attitude of the STR Synthem (tilted deposits) in comparison with the CDF Synthem (sub-horizontal bedding) shows that the former was affected by a tectonic phase which ended before the deposition of the latter synthem. The chronostratigraphic attribution of the two synthems allow us to tentatively relate this tectonic phase with the regional Middle Pleistocene tectonic uplift, which caused the present Northern Apennine mountain chain.

Key travertine tectofacies for neotectonics and palaeoseismicity reconstruction: effects of hydrothermal overpressured fluid injection

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.