Appekunny Formation is a thick series of rock strata located in the Lewis Range

Lewis Range

The Lewis Range is a mountain range located in the Rocky Mountains of northern Montana, U.S. and extreme southern Alberta, Canada. Formed by the Lewis Overthrust beginning 170 million years ago, an enormous slab of Precambrian rocks 3 miles thick, wide and long faulted and slid over newer...

 within Glacier National Park, Montana

Montana

Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...

, USA. The formation is primarily mudstone

Mudstone

Mudstone is a fine grained sedimentary rock whose original constituents were clays or muds. Grain size is up to 0.0625 mm with individual grains too small to be distinguished without a microscope. With increased pressure over time the platey clay minerals may become aligned, with the...

 and siltstone

Siltstone

Siltstone is a sedimentary rock which has a grain size in the silt range, finer than sandstone and coarser than claystones.- Description :As its name implies, it is primarily composed of silt sized particles, defined as grains 1/16 - 1/256 mm or 4 to 8 on the Krumbein phi scale...

 deposited in a shallow sea during the Proterozoic

Proterozoic

The Proterozoic is a geological eon representing a period before the first abundant complex life on Earth. The name Proterozoic comes from the Greek "earlier life"...

. 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

Apikuni Mountain

Apikuni Mountain is located in the Lewis Range, Glacier National Park in the U.S. state of Montana....

and averages 1970 feet (600.5 m) thick. The rock strata have been dated at between 1.2–1.4 billion years old.