Petrographic and facies analysis of Pleistocene travertines in southern Tuscany, central Italy

A travertine unit (Upper Pleistocene-Holocene) in Southern Tuscany (Saturnia, Albegna Valley, central Italy) was investigated in an active quarry in terms of carbonate fabrics, geometry of the sedimentary bodies, and spatial evolution. Travertines were precipitated by H2S-rich hydrothermal water in an extensional tectonic setting. The quarry faces exhibit a travertine terraced slope system (30-35 m thick) in which terrace walls (several cm to 2 m high), pools (1-10 m wide), pool rims (few cm to 1 m high) and waterfalls (2-3 m high) were identified.
Thirteen carbonate fabrics at the cm-scale were distinguished: 1) crystalline crusts; 2) micritic precipitates including bubbles, irregular mm-size voids; 3) mm-thick microsparitic laminae; 4) cm-tick layers with carbonate mud and travertine lithoclasts representing erosional surfaces; 5) shrubs consisting of clotted peloidal micrite in bush-like structures that locally form dm-thick bioherms; 6) aggregates of mm shrubs and mm-thick lamination; 6) elongated rafts; 8) transitional forms from shrubs to feather crystals; 9) fragments of shrubs and pisoids in a micritic matrix with irregular cavities; 10) sub-mm stromatolite-like laminae; 11) veined micrite with locally bubbles and lamination; 12) microbreccia with a dense matrix, typically organized in cm pockets; 13) mm elongated reed stems floating in micrite. Ostracodes, probably larval cases, reeds and gastropods occur within the travertines.
The travertine fabrics can be subdivided between those occurring in areas of fast flowing water and those precipitating in horizontal, a few cm-deep pools. Pool rims and cascades consist of sub-vertical crystalline crusts dominated by feather crystals. In pools, different fabrics occur including: shrubs, elongated rafts, undulated sub-mm stromatolites-like structures, pisoids, micrite layers, and coated bubbles.
The Saturnia travertines exhibit 5-20% primary porosity (1-15 mm in diameter) that is mainly produced by coated bubbles, biomolds of encrusted reeds, interparticle space in between shrubs (where meteoric sparite did not completely occlude it), and irregular elongated pores in between stromatolitic laminae.
The study of Saturnia travertines provides fundamental information about the depositional facies, fabric types, their diagenesis, and spatial distribution. This can improve the understanding of comparable carbonate reservoirs in the subsurface.