How was Wyoming coal formed?
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 coal. The thick coal beds in the upper part of the formation
have burned 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.
