During the late Cretaceous to early Tertiary period in Wyoming, thousands of feet of rock debris were eroding from the mountains. All this rock was deposited in basins (or valleys) between the mountains. The climate was humid and mild (which is a marked contrast with the present climate). The basin floors were covered with dense, rich forests and were often filled with water. Then, the region was uplifted again and debris was deposited in the lower basins.
The Rocky Mountains were forming and continuing to rise which blocked the flow of moist air from the Pacific. The climate was drying and the forests were being replaced by grasslands. Then, the area was uplifted again. Volcanic activity and earthquakes were common during this period. The steepening gradients spurred a period of erosion, and sediments were again deposited in the basins.
Coal can trace its ancestry back to the time of the dinosaurs. It developed from the remains of trees, ferns, and other plants that existed and died. Geologic processes involving pressure and temperature compressed and altered the plant remains, increasing the amount of carbon present. Millions of years later, the materials that once was living is transformed into coal. Coal that was formed from swamps covered by sea (salt) water contain high amount of sulfur. Low sulfur coal, like that found in Wyoming, was formed from freshwater swamps. Coal is not technically a mineral, but is a black, burnable rock. Along with petroleum and natural gas, coal is a "fossil fuel".
The Powder River Basin, which covers 12,000 square miles in northeastern Wyoming, is a result of millions of years of upfolds and downfolds.The basin is underlain by coal-bearing Fort Union and Wasatch formations. This is one of the world's largest deposits of extensively in the areas where the coal has "outcropped" on the surface. The heat generated from the coal burning has baked and fused the overlying clay and rocks. These red "clinker knobs" dominate the landscape of northeastern Wyoming.
The basin contains 5.3 billion tons of coal, all or which is under less than 1,000 feet of overburden. Of this 2.44 billion tons are in beds where the coal is more than 10 feet thick, and 1.8 billon tons of coal can be recovered economically using surface mining techniques.
For more of the story, click on the Wyoming Coal logo below.
Last Update 01/28/01
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