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Problem 2 (REVISION)
Problem 2 Presentation
Problem 3 - coals
Problem 3 Paper
Problem 4 - Rifting
Problem 4 - Synthesis Paper
Problem 5 - Climate Change
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Problem 3 Paper
Main questions posed for REVISION:
Why is sea level rising and falling over and over again? The issue would be more interesting if you had a tighter handle on how much time is represented by a cyclothem; then you could rule out some kinds of processes as being occurring on a different timescale.
What are the thicknesses of the sediment piles in each of these basins?
What are the thicknesses of a single cyclothem in each basin?
How much time is represented by the full wedge of sediment in the basin?
How much by a single cyclothem?
How many cyclothems are present in each basin? be accurate in citing
Would one expect that the number of cyclothems in each basin would be approximately the same (if this is a linked system as you imply)?
What is the record of sea level rise and fall for the Late Carboniferous?
Do the timescales on which cyclothems appear to have occurred match those expected for the tectonically driven events?
If the cyclicity is rapid, what could be the driving force behind the rapid changes that produced the cyclothems? If it's eustatic sea level as you suggest, why is sea level changing in this way? (glacieral activity?)
Why was plant life so abundant? Was it more abundant than in other times in Earth history? (CO2 levels?)
Fluvial responses to climate and sea-level change.pdf
Sea level change.pdf
Was glaciation responsible for the formation of northern hemisphere cyclothems?
Phanerozoic Sea level Changes
On the periodicity and magnitude of Late Carboniferous glacio-eustatie sea-level changes
Pre Quaternay Sea Level Changes
Sequence Stratigraphy of Upper Mississippian Strata in the Central Appalachians: A Record of Glacioeustasy and Tectonoeustasy in a Foreland Basin Setting
Daniel J. Miller1 and Kenneth A. Eriksson2
Deciphering the mid-Carboniferous eustatic event in the central Appalachian foreland basin, southern West Virginia, USA
GEO- Eastern Coals Paper.docx
*having a hard time getting pictures from powerpoint onto here...only added one of the cyclothems.
4 November 2009
Coal, formed from ancient peat deposits, requires specific conditions and paleoenvironments in order to begin forming. There are three relatively high-grade coal deposits in the Eastern United States: Kansas Coals, the Appalachian Basin, and the Illinois Basin.
These coals began forming in the Carboniferous Period. The facies of each of these deposits, termed cyclothems, show what the paleoenvironments were at the time of deposition. In the West, the pattern of peat formation is more sea level driven with more marine sediments such as limestone, whereas in the East the main cause is thrust loading with more lacustrine and siliciclastic sediments.
Coal is metamorphic, combustible rock that is composed of ancient peat deposits.
Peat can be defined dense, partially decayed, vascular organic matter that when metamorphosed turns into coal.
This process only occurs when certain, specific conditions are met.
In particular, it requires an environment in which aggradation or organic matter exceeds the rate of degradation, resulting in net accumulation of peat.
This takes place in areas containing stagnant water in which anaerobic conditions (conditions with limited oxygen) halt bacterial decay.
This organic matter must be compressed under sediment, after which time, heat, and pressure change the peat’s composition, turning it into the harder organic compound known as coal.
Although the coal deposits we studied were formed during a time when the North American continent was lying along the equator, the conditions needed to form peat are not exclusive to a tropical climate. Today, there is peat forming in other areas such as Rhode Island and Ireland, and both contain perfect conditions for coal formation.
The key to forming peat is not tropical climate, but moisture. Wet areas only need a net accumulation of dense vegetation to be covered by mud or sediment, away from oxygen or bacteria for coal formation to begin.
The coal that is found in the deposits in the Eastern United States formed during the Carboniferous Period. During this time, there was an explosion of luxuriant plant growth and coal bed formation that occurred 286 - 360 million years ago.
Most coals found withing this period are from the Pennsylvanian Period (320 to 286 million years ago) (Cengage, 2003).
During this time, there were many low, flat-lying areas in the Eastern United States, with intricate river systems flowing westward across flood plains and deltas to an empiric sea.
These densely vegetated flood plains were havens for peat formation. In addition to the coastal swamps and bogs near the empiric sea that housed peat formation, the rivers periodically overflowed, producing lacustrine swamps, burying and compressing the peat under thick layers of sand and mud.
These layers formed specific sequences of 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 is different for each coal deposit, but generally is driven by eustatic sea level changes or thrust loading of sediments, and sometimes by 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 paleoenvironment of each of the three relatively high-grade coal formations in the Eastern United States.
The most Western coal deposits in the Eastern United States 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 during the Carboniferous Period. 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 bacterial decomposition with a lack of oxygen.
These deposits are then continually deposited over which begins the cycle with peat formation.
“[There are over] one hundred cyclothems in the Pennsylvanian and Lower Permian rock succession of Kansas” (Moore, 1964).
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.
To the East, and on the opposite end of the cyclothem spectrum, lie the Appalachian Basin coals.
These are some of the most abundant coals in North America and, unlike the Kansas coals, are the result of subsidence.
Tectonic instability in the area, orogeny in particular, is the main force driving this process.
In Paleozoic time, 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 to the West of these mountains 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 and additional subsidence due to the added weight of transported sediments.
"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"
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.
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 Basin by the same orogeny processes and foreland basin development; it is also near Kansas deposits and thus affected by changes in sea level, containing some marine sediments (limestones in particular).
“Cyclothems are intermediate between the two end-member processes of flexural 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 to accommodate the angle, 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).
We determined many aspects about coal deposition and paleoenvironments in the Eastern United States. 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 and towards the middle of the continent the formation is, the more marine deposits it will contain and the more affected by eustatic changes the cyclothems will be; In the East, the deposits are negligibly affected by sea level and more a product of thrust loading. Following this theory, the Appalachian Basin cyclothems were based on subsidence and thrust loading patterns, the Kansas coals were based on seal level changes, and Illinois was a hybrid of the two.
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.
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