Appekunny Formation is a thick series of rock strata located in the Lewis Range within Glacier National Park, Montana, USA. The formation is primarily mudstone and siltstone deposited in a shallow sea during the Proterozoic. The Appekunny Formation contains bedding structures which may include the remains of the oldest metazoan (animal) on Earth.
The Appekunny Formation is named after Apikuni Mountain and averages 1,970 feet (600 m) thick. The rock strata have been dated at between 1.2–1.4 billion years old.