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Paleocene |
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Time: |
66.4 to 57.8 mya |
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Duration: |
78 my |
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The
majority of the Paleocene coals formed from long linear wetlands adjacent to the
retreating Cretaceous inland (epeiric) sea that had at times extended from the Arctic
Ocean to the Gulf of Mexico. The final regression of this long-lasting sea (some 40
million years) resulted in broad flatlands covering hundreds of thousands of square miles,
much of which was a wetland for some period of time. Those peats that were subsequently
deeply buried were transformed into subituminous coal, while those not buried as
deep became the huge lignite deposits of Montana, North Dakota and Texas. Coals associated
with a retreating sea tend to be higher in ash and sulfur. |
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The rising
of the Rocky Mountains created a second type of wetland environment in the Paleocene.
These were the intermontane valley swamps that had no connection what-so-ever with the
retreating sea. These swamps, particularly in Wyoming and southern Montana, produced some
of the world's thickest, largest, cleanest, low sulfur coal deposits. subituminous coal
beds of 50 to 100 feet are common here with some over 200 feet
thick. A contributing factor to
the thick peat production was the fact that the central North American climate was
subtropical during the Paleocene.
During the this major coal forming period, the world-wide climate was warm and humid.
In Wyoming, the average temperature was 80o F, similar to
present day Panama. The
swamps were enormous, covering tens of thousands of square miles in the U. S. The shear
size of each protected the central portions from sediment influx by rivers flooding around
the edges. Unfortunately, many of the Pennsylvanian Period swamps of eastern U.S. were
subsequently covered by marine sediment deposited by transgressing inland (epriric) seas.
Salts and sulfates seeped into the peat buried below, lowering the quality. |
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