Half lie radiometric dating
Even a snake, Boavus idelmani, found its way into a lake and was preserved in the mudstone. The Green River Formation contains the largest oil shale deposit in the world.
The first documented records of (invertebrate) fossils from what is now called the Green River Formation are in the journals of early missionaries and explorers such as S. It has been estimated that the oil shale reserves could be 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).
Tectonic highlands supplied the Eocene sedimentary basins with sediment from all directions: the Uinta Mountains in the center; the Wind River Mountains to the north; the Front Range, Park Range and Sawatch Range of the Colorado Rockies to the east; the Uncompahgre Plateau and the San Juan Mountains to the south and finally, the Wasatch Mountains of Utah and the ranges of eastern Idaho to the west.
The lithology of the lake sediments is varied and includes sandstones, mudstones, siltstones, oil shales, coal beds, saline evaporite beds, and a variety of lacustrine limestones and dolostones.
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.
Volcanic ash layers within the various sediments from the then active Absaroka Volcanic field to the north in the vicinity of Yellowstone and the San Juan volcanic field to the southeast provide dateable horizons within the sediments.
The trona (hydrated sodium bicarbonate carbonate) beds of Sweetwater County, Wyoming are noted for a variety of rare evaporite minerals.
The catfish are found mostly in the deepest parts of the lake.
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.
Insects were preserved whole, even delicate wing membranes and spider spinnerets.
Vertebrates were preserved too, including the scutes of Borealosuchus, the crocodile that was an early clue to the mild Eocene climate of Western North America. The fossils of the herring-like Knightia, sometimes in dense layers, as if a school had wandered into anoxic water levels and were overcome, are familiar to fossil-lovers and are among the most commonly available fossils on the commercial market.
Besides fishes they include at least eleven species of reptiles, and some birds and one armadillo-like mammal, Brachianodon westorum, with some scattered vertebrae of others, like the dog-sized Meniscotherium and Notharctus, one of the first primates. Ferdinand Vandeveer Hayden (geologist-in-charge of the United States Geological and Geographical Survey of the Territories, the forerunner of the United States Geological Survey) first used the name "Green River Shales" for the fossil sites in 1869.