Zoe GentesAndrew Infante

Amy LombariDennis Titterton

Jen Sullivan

Eastern Coals

Where are major coal deposits located in the Eastern USA?

What were the conditions that prompted these coals to form?

What is the specific facies sequence in these coal deposits?

What can the sequence tell us about paleoenvironment?

Objectives

Metamorphic, combustible rock formed from ancient peat deposits

Peat: partially decayed vascular organic matter

Stagnant water + anaerobic conditions = environment in which aggradation or organic matter exceeds degradation

Add pressure, heat, and time… Coal!

What is Coal?

Not necessarily tropicalIreland, Rhode Island

Dense vegetation must accumulate and be covered in mud or sediment, away from oxygen and bacteria, to begin coal formation“A major extinction of peat-forming plants

occurred at the end of the Middle Pennsylvanian in the lowland tropics of North America, due to changing climatic conditions, probably protracted moisture deficits or exaggeration of seasonal dryness” (DiMichele, 1996).

Conditions

The explosion of luxuriant plant growth and coal bed formation that occurred 286 - 360 million years ago is the "Carboniferous Period.“Most coals from the Pennsylvanian Period (320 to 286

million years ago) (Cengage, 2003).Low and flat land, rivers flowing westward.Densely vegetated floodplains and coastal swamps,

where peat accumulated. Rivers periodically overflowed producing lacustrine

swamps, burying and compressing the peat under thick layers of sand and mud.

These layers formed specific sequences…

Carboniferous Period

SequenceCyclothem

Coal commonly occurs in this sequence of sedimentary strata.

Formed from repetition of a pattern of sediment layers.Typical Illinois

Cyclothem

*Different for each area of coal depositsIn general, driven by eustatic sea level

changes, or thrust loading, or a combination.An idealized Pennsylvanian cyclothem:

sandstone, shale, limestone, underclay, coal, shale, limestone, shale.

In any one locality, cyclothems commonly repeat tens of times with each cycle of deposition accumulated on a previous one (Nevins, 1976).

The Cycle

Where in the Eastern USA?•Relatively high-grade coals

•Kansas Coals(Interior Province)

•Illinois Basin(Interior Province)

•Appalachian Basin

(Eastern Province)

Empiric Sea in the mid-continent North America.

This sea transgressed and regressed repetitively over millions of years.

Marine carbonate cyclothems accumulated on a relatively stable platform affected only moderately by collision tectonics of North American margins.

These cycles are eustatic, caused by the change in sea levels (Klein, 1989).

Kansas Coal

Peat deposited as sea level rose.

More than 100 cyclothems in the Pennsylvanian and Lower Permian rock succession of Kansas (Moore, 1964).

(Moore, 1964)

Origin of depositional environment: evolution of resurgent foreland basins in Paleozoic time.The Appalachian Basin was an equatorial

foreland basin bounded by the Allegheny Range, Central Pangea Mountains to the southeast, and open westward to the sea

Depositional environment: 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).

Appalachian Basin

(Garcés, 1996)

Evolution of connected fluvial systems controlled by subsidence in an active foreland basin, rather than to short-term climatic change or eustacy.

Base level changes in the fluvial system as influenced by eustacy are considered only a very minor control of the Appalachian cyclothem pattern.

There are about a hundred successive cyclothems in West Virginia (Appalachian basin) (Nevins, 1976).

Projected time scale of deposition of one 'cycle' = about tens of thousands of years (Garcés, 1996).

Linked to Appalachian Basin through the same erogeny and the building of the foreland basins.

Also close to Kansas deposits, and thus affected by changes in sea level and containing some marine sediments (limestones).

Cyclothems are intermediate between the two end-member processes of flexural tectonics and glacial eustasy characterizing Appalacian-type cyclothems and Kansas-type cyclothems (Klein, 1989).

Illinois Basin

Drop in sea level = steeper river gradient = less pooling

Rise in sea level = shallower river gradient = more pooling.

50 successive cycles in Illinois (Nevins, 1976).

(Miall. 1997)

Main condition for peat: oxygen-poor moisture in which the rate of organic accumulation exceeds the rate of degradation.

Coal found in East USA in the Appalachian, Illinois, and Kansas Basins.

Coal deposits formed in Carboniferous Period (Pennsylvanian Period 320 to 286 MYA).

Predominant sequence of strata is many-layered cyclothems, caused by recurrent thrust loading and eustatic changes in sea level.

Farther west towards mid-continent = more marine deposits and more eustatically controlled strata.

Conclusions

Cengage, Gale, 2003, Pennsylvanian Period, World of Earth Science.,Ed. K. Lee Lerner and Brenda Wilmoth Lerner, 2006

DiMichele, William A., Tom L. Phillips, 1996, Climate change, plant extinctions and vegetational recovery during the Middle-Late Pennsylvanian Transition: the Case of tropical peat-forming environments in North America, Geological Society, London, Special Publications, v. 102; p. 201-221

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.

Miall, Andrew D.,1997. The Geology of Stratigraphic Sequences, Springer-Verlag Berlin Heidelberg, New York, p.162.

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, Dallax, 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 .

References