FIGURE 2.2 Illustration of the Cretaceous interior seaways, including the Western, Hudson, and Labrador seaways. The Cretaceous Period lasted from about 145 million to 65 million years ago. Coal-bearing basins in the western United States that are the subject of this report formed from organic-rich sediments (plant material) deposited in and along the wetlands of the Western Interior Seaway. The organic-rich sediments were deposited through Cretaceous and Paleocene (ca. 65 million to 56 million years ago) times during the rise and fall of intercontinental sea levels. SOURCE: W.A. Cobban and K.C. McKinney, USGS. Available at esp.cr.usgs.gov/research/fossils/ammonites.html.

FIGURE 2.2 Illustration of the Cretaceous interior seaways, including the Western, Hudson, and Labrador seaways. The Cretaceous Period lasted from about 145 million to 65 million years ago. Coal-bearing basins in the western United States that are the subject of this report formed from organic-rich sediments (plant material) deposited in and along the wetlands of the Western Interior Seaway. The organic-rich sediments were deposited through Cretaceous and Paleocene (ca. 65 million to 56 million years ago) times during the rise and fall of intercontinental sea levels. SOURCE: W.A. Cobban and K.C. McKinney, USGS. Available at esp.cr.usgs.gov/research/fossils/ammonites.html.

Coalbeds can serve as aquifers or subsurface rock layers that are sufficiently permeable1 to conduct groundwater and can provide sufficient water for human use. Other less permeable materials (e.g., siltstones, shales, clays) above and below the coal seams—sometimes

1

A permeable geological material, or a material’s “permeability,” refers to its ability to transmit fluids and is generally associated with the degree of connectivity between pores in the material. A higher degree of pore connectivity would indicate higher permeability or ability of the material to transmit fluids.



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