Early or Late Structures in Thermogene Travertines? Open-Air Lessons Across Rome to Focus on and Answer this Question

Themogene travertines are U-series-dateable, continental, CaCO3 precipitates often used for neotectonic, paleoclimate, paleohydrological-hydrothermal, and further geological reconstructions both in space and in time. Recognizing early (primary or depositional) and late (secondary, postdepositional, or diagenetic) structures of travertines is essential for their correct use in geology. This problem can be tackled in an easy and efficient way through open-air lessons opposite to travertine-made buildings in cities such as Rome, Italy, where huge quantities of the closely quarried Tivoli travertine have been used for millennia for construction and decoration. Five brief open-air lessons through Rome are proposed to provide indications on how to distinguish early and late structures in travertines. Chimney-like veins, matrix-supported breccias, and undulated veins are recognized as late structures on the basis of their cross-cutting/superimposition relationships with primary porous beds. Limitations of this method are explained. These lessons may be helpful to those willing to use thermogene travertines as recorders of geological processes. In the future, the presented instances, together with further building stones exposed in cities, may be included in open geographic databases for easy, efficient, and accessible field experiences and geological fieldwork in urban environments, as to increase sensibility in the geology, environment, and resources offered by our planet.