The Castillo Formation is an Early Miocene (Burdigalian, Colhuehuapian to Santacrucian in the SALMA classification) geologic formation in the of Venezuela. The formation unconformably overlies the , , and . The Castillo Formation is overlain by Quaternary alluvium and in places by the . The formation, deposited in a calm near-shore lagoonal brackish environment, with possibly fluvial influence, has provided a rich assemblage of fossil crocodylians, turtles, giant sloths and various types of fish.