Department of Geology

Pennsylvanian Cyclothems and Marine Units (Appalachian Basin)

Dr. J Bret

This figure is taken from a paper (Bennington, 2002) which examines the interaction of sediment supply and eustacy (sea level change) in creating facies patterns in the Magoffin Member, an Appalachian Basin cyclothem.

Cyclothems are packages of strata characteristic of the Pennsylvanian and Permian Periods. An individual cyclothem typically contains a sequence of rock layers that indicate a progressive change in depositional environments from coal swamp, to marine, to non-marine, and back to coal swamp. Cyclothems appear to be generated by changing sea level, although the mechanism of sea level change continues to be controversial. Relative sea level change is controlled by the interaction of tectonic subsidence, sedimentation, and eustacy (changes in global sea level). Cyclothems developed in the Appalachian Basin in the eastern United States have traditionally been seen as controlled primarily by the interaction of tectonic subsidence and sedimentary deposition. This is because the Appalachian Basin formed due to subsidence of a foreland basin adjacent to the Alleghenian Orogen, which was then filled with sediments shed from the erosion of the rising mountains. However, my studies of the Magoffin Member, a cyclothem developed during a particularly large sea level rise, suggest that eustacy was, nevertheless, an important factor in the deposition of Appalachian Basin cyclothems.

Publications related to this topic include:

Bennington, J Bret, 2002. Eustacy in cyclothems is masked by loss of marine biofacies with increasing proximity to a detrital source: An example from the Central Appalachian Basin, U.S.A. In Carboniferous and Permian of the World, L.V. Hills, C.M. Henderson, and E.W. Bamber, eds., Canadian Society of Petroleum Geologists, Memoir 19, p.12-21. (Full-text PDF 852 K)

Bennington, J Bret, 1996. Stratigraphic and biofacies patterns in the Middle Pennsylvanian Magoffin Marine Unit in the Appalachian Basin, U.S.A. International Journal of Coal Geology 31:169-194. (Full-text PDF 1.1 mb)

Bennington, J Bret, and R. K. Bambach, 1994. Marine Transgressions in the Pennsylvanian Breathitt Formation of Eastern Kentucky. Southeastern Section Geological Society of America,
Blacksburg, VA, April 7-9, 1994, Virginia Tech Department of Geological Sciences Guidebook Number 10, p. 249-264.

Bennington, J Bret, 1992. Preliminary analysis of a marine interval near the Howland lookout tower on the Kentucky A-A Highway. in Rice,C.L., R.L. Martino, and E. Slucher, eds.
Regional Aspects of Pottsville and Allegheny Stratigraphy and Depositional Environments, Ohio and Kentucky, U.S.G.S. Open File Report 92-558, pp. 34-40.

Last modified 6-22-04 by Bret Bennington. All rights reserved by the author. This document may not be distributed or posted in any format or reposted on any other server without permission.
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