Onzole Formation

The Onzole Formation is an Early Pliocene (Montehermosan to Chapadmalalan in the SALMA classification) geologic formation in the Borbón Basin of northwestern Ecuador. The formation consists of a shallow marine sandstone member containing many fish fossils, among which megalodon, and a deep water member comprising tuffaceous shales and mudstones containing gastropods, bivalves and scaphopods.
Subdivision.
The formation consists of the Esmeraldas Member, which is a unit comprising highly foraminiferal tuffaceous calcareous shale. They were deposited by shallow water gravity flows, which brought the Esmeraldas fauna into the deep water () from shallow water, on the order of .
The Esmeraldas Member is covered by the Súa Member comprising burrowed, bioturbated, silty sandstones deposited in a coastal environment.
Fossil content.
The formation has provided bivalve, gastropod, and scaphopod fossils and the following vertebrates: