page_title: Green River Formation
section_title: Oil shale
hierarchical_section_title: Green River Formation / Oil shale
caption_attribution_description: English: Oil Shale from the Mahogany Zone of the Green River Formation, Colorado.
context_page_description: The Green River Formation is an Eocene geologic formation that records the sedimentation in a group of intermountain lakes in three basins along the present-day Green River in Colorado, Wyoming, and Utah. The sediments are deposited in very fine layers, a dark layer during the growing season and a light-hue inorganic layer in the dry season. Each pair of layers is called a varve and represents one year. The sediments of the Green River Formation present a continuous record of six million years. The mean thickness of a varve here is 0.18 mm, with a minimum thickness of 0.014 mm and maximum of 9.8 mm.
  The sedimentary layers were formed in a large area named for the Green River, a tributary of the Colorado River. The three separate basins lie around the Uinta Mountains of northeastern Utah:
  an area in northwestern Colorado east of the Uintas
  a larger area in the southwest corner of Wyoming just north of the Uintas known as Lake Gosiute
  the largest area, in northeastern Utah and western Colorado south of the Uintas, known as Lake Uinta
context_section_description: The Green River Formation contains the largest oil shale deposit in the world. It has been estimated that the oil shale reserves  could equal up to 3 trillion barrels (480 billion cubic metres) of shale oil, up to half of which may be recoverable by shale oil extraction technologies (pyrolysis, hydrogenation, or thermal dissolution of kerogen in oil shale). However, the estimates of recoverable oil has been questioned, back in 2013, by geophysicist Raymond T. Pierrehumbert, who argued that the technology for recovering oil from the Green River oil shale deposit had not been developed and had not been profitably implemented at any significant scale.
  Green River oil shale is lacustrine type lamosite. The organic matter is from blue-green algae (cyanobacteria).
caption: Oil Shale from the Mahogany Zone of the Green River Formation, Colorado. Weathered surface on right; fresh surface on left.
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