
Posidoniids, a key for Early-Middle Jurassic
The Posidoniid-bearing rhythmic deposits, Toarcian to Aalenian (Early/Middle Jurassic) in age, of the Umbria-Marche basins (Fiuminata Colle Corno and Valdorbia type section) consist of hundred couplets, each composed by two semicouplets, a calcium carbonate-poor bed and a calcium carbonate-rich bed, respectively (CacO3 between 10% to 85%), where event tempestite beds randomly occurs. The aim of this work is to show ichnocoenoses and taphocoenoses as well as the faunistic vari