The problem of the age of “greenstones” in the Western Alps: the perspective of Carlo Bruno

Luca Barale¹, Pietro Mosca¹, Fabiana Console² & Marco Pantaloni^3
1CNR Torino, Institute of Geosciences and Earth Resources.
²Istituto Superiore per la Protezione e la Ricerca Ambientale, Biblioteca.
³Istituto Superiore per la Protezione e la Ricerca Ambientale, Servizio Geologico d'Italia.
Corresponding author e-mail: pietro.mosca@cnr.it

Carlo Bruno (1831–1916) collaborated in the late 1860s and 1870s on the geological mapping of the Western Alps under the direction of Bartolomeo Gastaldi. During his surveys in the Ligurian and Maritime Alps, Bruno became convinced that the ophiolite-bearing Zona delle Pietre Verdi—considered Paleozoic by Gastaldi— should instead be attributed to the Triassic. This reinterpretation was based on Bruno’s discovery of Triassic fossils within dolomitic limestones at several localities in the region. In early 1880, he presented his findings and geological interpretation in two unpublished letters addressed to Felice Giordano, in which he also requested the appointment of a geological commission to verify his claims. No such commission was ever formed, likely due to subsequent field inspections by Martino Baretti and TorquatoTaramelli, who concluded that Bruno had misinterpreted the stratigraphic relationships between the fossiliferous carbonates and the adjacent ophiolite-bearing succession. Although Bruno had announced plans to publish a comprehensive paper on the geology of the Maritime and Ligurian Alps, the project was never completed. His letters to Giordano thus remain the only record of his alternative geological interpretation of the region.

Carlo Bruno, Western Alps, ophiolite, history of geology.