The Tertiary in Wyoming, US

Paleontology and geology

Tertiary sediments are widespread in Wyoming, covering the floors of the Bighorn, Powder River, Wind River, and Green River Basins with thousands of feet of sediment eroded off the rising Rockies. The Early Tertiary climate favored the growth of luxurious forests that grew on the basin floors. The coals formed from these forests are mined in the state today, and fossil plants are common in many Tertiary formations. The Green River Formation, organic-rich rock referred to as oil shale, was deposited as sediment on the floor of an Early Tertiary (Eocene) lake that formed in the Green River Basin. These rocks contain abundant, beautifully preserved fish fossils, including the Wyoming State Fossil, Knightia eocaena, a herring-like fish. Less well known to most people are the fossils of flamingos, crocodiles, boas, and bats that have been found in the Green River shales. Large volcanic eruptions periodically deposited thick layers of ash across the state during the Middle Tertiary (Oligocene and Miocene), as the Rockies continued to rise.