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

Lewis Range The Lewis Range is a mountain range located in the Rocky Mountains of northern Montana, United States and extreme southern Alberta, Canada. It was formed as a result of the Lewis Overthrust, a geologic thrust fault resulted in the overlying of y ...

within Glacier National Park, in the U.S. state of

Montana Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columbi ...

. The formation is primarily

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...

and

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, p ...

deposited in a shallow sea during the

Proterozoic The Proterozoic () is a geological eon spanning the time interval from 2500 to 538.8million years ago. It is the most recent part of the Precambrian "supereon". It is also the longest eon of the Earth's geologic time scale, and it is subdivided ...

. Not far from the eastern entrance to the

Going-to-the-Sun Road Going-to-the-Sun Road is a scenic mountain road in the Rocky Mountains of the western United States, in Glacier National Park in Montana. The Sun Road, as it is sometimes abbreviated in National Park Service documents, is the only road that trave ...

St. Mary, Montana St. Mary (Blackfeet: , "Holy Woman") is an unincorporated community on the western border of the Blackfeet Indian Reservation adjacent to Glacier National Park in Glacier County, Montana, United States. The village is the eastern terminus of the ...

, the formation can be easily seen on the slopes of Singleshot Mountain. The Appekunny Formation contains bedding structures which may include the remains of the oldest metazoan (animal) on Earth known by the species name '' Horodyskia moniliformis''.

The Appekunny Formation is named after Apikuni Mountain and averages thick. The rock strata have been dated at between 1.2–1.4 billion years old.

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Further reading