Phosphoria Formation

The Phosphoria Formation of the western United States is a geological formation of Early Permian age. It represents some 15 million years of sedimentation, reaches a thickness of 420 metres (1,380 ft) and covers an area of 350,000 square kilometres (140,000 sq mi).

Phosphoria Formation

Stratigraphic range:
An outcrop of the Phosphoria Formation near the Big Hole River in western Montana.
TypeGeological formation
UnderliesDinwoody Formation
OverliesCasper Formation, Park City Formation, Tensleep Sandstone
Area350,000 sq. km (140,000 sq. mi)
ThicknessUp to 420 metres (1,380 ft)
Lithology
PrimaryLimestone, dolomite, shale
OtherChert, phosphorite, sandstone
Location
RegionIdaho, Montana, Utah, Wyoming
Country USA
Type section
Named forPhosphoria Gulch, Idaho
Named byRichards and Mansfield, 1912

The Phosphoria includes phosphorite beds that are an important source of phosphorus. Many of its shales are rich in organic matter and are petroleum source rocks, and some of its dolomites include petroleum reservoirs.

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