Eastern Coals
Andrew Infante
Zoe Gentes
Amy Lombari
Jennifer Sullivan
Dennis Titterton
4 November 2009
Abstract
There are three relatively high-grade coal deposits in the Eastern United States.
These deposits range through the spectrum of sea level driven in the west and thrust
loading driven in the east. The facies of theses deposits called cyclothems show what the
paleoenvironments were at the time of deposition.
Introduction
Coal is metamorphic, combustible rock that is composed of ancient peat deposits. Peat is
dense, partially decayed vascular organic matter that when metamorphosed turns into coal. This
process does not take place under any random conditions however. In particular, it takes an
environment in which aggradation or organic matter exceeds the rate of degradation. This takes
place in areas containing stagnant water in which anaerobic conditions halt bacterial decay. This
organic matter must be compressed under sediment, where time, heat, and pressure change the
peat’s composition, turning it into a more organic compound: coal.
The conditions do not necessarily have to be tropical, comparable subtropical areas such
as Rhode Island and Ireland both contain perfect conditions for coal formation. These areas just
need for dense vegetation to accumulate and be covered by mud or sediment, away from oxygen
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or bacteria for coal formation to begin. The explosion of luxuriant plant growth and coal bed
formation that occurred 286 - 360 million years ago is the “Carboniferous Period.” Most coals
within this period are from the Pennsylvanian Period (320 to 286 million years ago) (Cengage,
2003). This is the result of a time in which there were many low, flat lying areas with intricate
river systems flowing westward to an empiric sea. These densely vegetated flood plains were
havens for peat formation.
Rivers periodically overflowed producing lacustrine swamps, burying and compressing
the peat under thick layers of sand and mud. These layers formed specific sequences or facies
called cyclothems. A cyclothem is a cyclical, repetitious pattern of sediment layers that coal
commonly occurs in. These cyclothems commonly rotate between nonmarine and marine
sediments that are separated by coal formations. This cycle changes for each coal deposit, but
generally is driven by eustatic sea level changes or thrust loading, and sometimes a combination
of the two. “In any one locality, cyclothems commonly repeat tens of times with each cycle of
deposition accumulated on a previous one (Nevins, 1976).” These strata cycles give us an idea
of what conditions were present to cause the coal formation. The different cyclothem patterns
can be used to assume the environment of each of the three relatively high-grade coal formations
in the Eastern United States.
Kansas Coals
The most western coal deposits east of the Mississippi River are found in Kansas. They
are part of the Interior Basin coal formation and are the results of the empiric sea that was
present in Mid-Western North America at the time. This sea had transgressed and regressed
many times during its presence, leaving the perfect stage for coal formation. When sea level
raised it overlapped and deposited marine sediments over plant matter, cutting off any type of
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bacterial decomposition with a lack of oxygen. These deposits are then continually deposited
over which begins the cycle with peat formation due to consistent heat and pressure.
“[There are over] one hundred cyclothems in the Pennsylvanian and Lower Permian rock
succession of Kansas (Moore, 1964).” These Marine carbonate cyclothems accumulated on a
relatively stable platform affected only moderately by collision tectonics of North American
margins. These cyclothems show a general sequence of non-marine sediments (sandstone, sandy
shale, freshwater limestone), an underclay layer (indicative of the leaching that occurs in swamps
and other wetland areas), then a layer of coal, overlaid by marine sediments (limestone and
shale). This cycle repeats itself and shows the correlation between sea level and coal formation.
In times of low sea level organic material
grows in abundance and lays the framework
for peat formation. The coal layer shows the
beginning of the transgressing sea, which was
at one point the organic matter being turned
into peat under marine sediments. The marine
sediments show how peat formation is never
stable but occurs in spurts in between a rising
and falling sea. Once the sea level is too high
no more organic matter can grow, then as the
sea regresses again the cycle begins again.
Appalachian Basin
To the east, and on the opposite end of the spectrum, lie the Appalachian basin coals.
These are some of the most abundant coals in North America and unlike the Kansas coals, are
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the result of subsidence. Tectonic instability in the area, orogeny in particular, is the main force
driving this process. In the Paleozoic, the Appalachian basin was a resurgent foreland basin
bounded by the Allegheny Range, the Central Pangaea Mountains to the southeast, and open
westward to the sea. This basin is described as being, “A large wetland complex drained by a
fluvial system containing a mosaic of channels, freshwater siliciclastic and carbonate lakes, and
peat swamps on a siliciclastic floodplain (Garcés, 1996).”
Sediments that eroded down the western mountain face were brought into the wetland
basin. Organic matter in this area was buried under these sediments and was metamorphosed
when the land collapsed on itself from shifts in the water content. "The occurrence of lacustrine
carbonates in the Allegheny Group (upper Middle Pennsylvanian) continental cyclothems of the
northern Appalachian Basin has been attributed to climatic alternation of wet (coal deposition)
and dry (carbonate deposition) periods (Garcés, 1996).” These wet periods were periods in
which flourishing plants were spreading at a rate greater than decomposition. Eustatic changes
are thought to have had negligible effects on peat formation in the area. The deposits in this area
are some of the oldest and richest, and areas such as West Virginia and Pennsylvania are
considered to be the coal capitols of the world. In West Virginia there are one hundred
successive cyclothems, each cycle having an age of tens of thousands of years.
Illinois Basin
In between these two basins laid the Illinois basin. This basin is also part of the Interior
Basin, and is a product of both environments. It is linked to the Appalachian by the same
orogeny processes and foreland basin development; it is also near Kansas deposits and thus
affected by changes in sea level and containing some marine sediments (limestones in
particular). “Cyclothems are intermediate between the two end-member processes of flexural
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tectonics and glacial eustasy characterizing Appalachian-type cyclothems and Kansas-type
cyclothems (Klein, 1989).” Though it is too far from the empiric sea to be submerged by water,
sea level played its part through the rivers that drained through the basin and into the sea. In
times of lower sea level the river gradient steepened which meant that the water flowed faster
and less pooling occurred upstream. But in times of higher sea level, more water was present
and the river became “backed up.” The river gradient became shallower and water slowed down,
making pooling more likely upstream. In Illinois deposits, there are roughly 50 successive
cycles, making it the smallest of the three (Nevins, 1976).
Conclusion
In conclusion, the main condition for peat formation is oxygen-poor moisture in which
the rate of organic accumulation exceeds the rate of degradation. In the Eastern United States,
the three dominant relatively high-grade coal formations are in the Kansas, Illinois, and
Appalachian basins. These coal deposits formed during the organic boom in the Carboniferous
Period (286 - 360 million years ago), and more distinctly the Pennsylvanian Period (320 – 286
million years ago) (Cengage, 2003). The predominant sequence of strata is many-layered
cyclothems, caused by recurrent thrust loading and eustatic changes in sea level. These
cyclothems prove that the farther west, towards the middle of the continent, the formation is, the
more marine deposits it will contain, and in the east the deposits are negligibly affected by sea
level and more a product of thrust loading.
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References Cited
Cengage, Gale, 2003, Pennsylvanian Period, World of Earth Science.,Ed. K. Lee Lerner and
Brenda Wilmoth Lerner, 2006
Garcés, Blas L. Valero; Gierlowski-Kordesch, Elizabeth; Bragonier, William A.; 1996.
Pennsylvanian continental cyclothem development: no evidence of direct climatic control
in the Upper Freeport Formation (Allegheny Group) of Pennsylvania (northern
Appalachian Basin), Sedimentary Geology. Elsevier Science B.V., pp. 305.
Klein, George; Willard, Debra A.; 1989. Origin of the Pennsylvanian coal-bearing cyclothems of
North America, University of Illinois at Urbana-Champaign, Illinois 61801-2999.
Moore, Raymond C., 1964, Paleoecological Aspects of Kansas Pennsylvanian and Permian
Cyclothems, Symposium on cyclic sedimentation: Kansas Geological Survey, Bulletin
169, pp. 287-380.
Nevins, Stuart E., 1976. The Origin of Coal, Institute for Creation Research, Dallas, TX. Weller,
J. Marvin, 1930, Cyclical Sedimentation of the Pennsylvanian Period and its
Significance, The Journal of Geology, Vol. 38, No. 2, pp. 97-135.