Cartographic data for the northeastern side of the Monte Amiata area suggest a very complicated geometric setting for the Tuscan Nappe cropping out in the Poggio Zoccolino and Campiglia d'Orcia areas. The occurrence of some outcrops consisting of "Calcare Cavernoso" and "Calcari a Rhaetavicula Contorta" Fms., exposed at the top of the Poggio Zoccolino hill, represents a problem highlighted by previous fieldwork. In fact, the altitude of these Late Triassic Tuscan Nappe formations, bounded by Ligurian l.s. Units, is greater then the Cretaceous-Oligocene "Scaglia Toscana" Fm. which represents the uppermost formation of the Tuscan Nappe, entirely exposed in the easternmost slope of Poggio Zoccolino hill. At the base of Poggio Zoccolino hill, close to Bagni di S. Filippo village, Late Triassic evaporites and the overlying Jurassic carbonate succession crop out; at the top of the hill the "Scaglia Toscana" Fm. is widely exposed and lies on the Jurassic carbonates. Fieldwork and structural analysis have not resolved the problematic geometrical relationships between the Triassic successions ("Calcare Cavernoso" and "Calcari a Rhaetavicula Contorta" Fms.) and the "Scaglia Toscana" Fm. Seismic reflection profiles crossing the study area, acquired by ENEL GreenPower for geothermal purposes, provide new structural information for better understanding of the tectonic evolution and structural setting of the Tuscan Nappe in the Mt. Amiata geothermal area. The seismic interpretation indicates that the Late Triassic formations exposed at the top of the Poggio Zoccolino hill are a Tuscan Nappe sequence probably overthrust during the syn-collisional tectonics of the Northern Apennines.

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