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Travertine mounds are common spring-constructed landforms with highly variable geometries, but factors controlling their development have not yet been fully understood. To investigate processes linked with their lateral and vertical growth, this study investigated travertine mounds at Heinitang (China) and compared them with typical mounds around the world. Calcium concentration variation modelling and height evaluation of travertine mounds were also performed. The lateral extent of travertine mounds was found to be mainly controlled by Ca2+ and urn:x-wiley:00370746:media:sed12961:sed12961-math-0001 concentrations and water discharge: relatively small metre-scale mounds, like those from Heinitang, are largely the products of Ca2+-deficiency (

The Pre-Mesozoic units exposed in the inner Northern Apennines mostly consist of middle-late Carboniferous-Permian successions unconformably deposited on a continental crust consolidated at the end of the Variscan (i.e. Hercynian) orogenic cycle (Silurian-Carboniferous). In the inner Northern Apennines, exposures of this continental crust, Cambrian?-early Carboniferous in age, have been described in the Northern Tuscany, Elba Island (Tuscan Archipelago) and, partly, in scattered and isolated outcrops of southern Tuscany. In this contribution, we reappraise the most significative succession (i.e. Risanguigno Formation) exposed in southern Tuscany and considered by most authors as part of the Variscan Basement. New stratigraphic and structural studies, coupled with palynological analyses, allow us to refine the age of the Risanguigno Fm and its geological setting and evolution. Based on the microfloristic content, the structural setting and the fieldwork study, we attribute this formation to late Tournaisian-Visean (middle Mississipian) time interval and conclude it is not showing evidence of a pre-Alpine deformation. These results, together with the already existing data, allow us to presume that no exposures of rocks involved in the Variscan orogenesis occur in southern Tuscany.

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

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 (> 150 m) 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 12 m thick, developed within a > 200 m 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. © 2017 Elsevier B.V.