Possible crystalline gastroliths of large marine Vertebrata from Oligocene pelitic sediments of the Northern Apennines, Italy

Randomly dispersed erratic clasts are found within the pelagic marly-shaly sequences of the Oligocene Scisti Varicolori Formation (Cervarola-Falterona unit of the Tuscan domain). These clasts are centimeters to decimeters in size and subrounded to well rounded; their shape suggests an origin in a fluvial and partly littoral environment. The clasts are composed of low- to medium-grade metamorphic rocks, andesitic volcanic rocks, and Late Jurassic-Early Cretaceous pelagic limestones. The source area of the crystalline material is interpreted to be the central-western sector of the Alpine chain or the Corsica-Sardinia area. In addition, the peculiar surfaces of these clasts, as well as their isolated occurrence in the pelagic shales of the Scisti Varicolori, suggest an uncommon depositional mechanism, such as redeposited gastroliths of large marine Vertebrata.