Cyclothems

Cyclothems
Originally proposed by Harold Wanless of the University of Illinois, to describe a Pennsylvanian-age rock succession in western Illinois[1] .

In geology, cyclothems are alternating stratigraphic sequences of marine and non-marine sediments, sometimes interbedded with coal seams. Historically, the term was defined by the European coal geologists[2] that worked in coal basins formed during the Carboniferous and earliest Permian periods. The cyclothems consist in repeated sequences, each typically several meters thick, of sandstone resting upon an erosional surface, passing upwards to pelites (finer-grained than sandstone) and topped by coal.

The term is somewhat outdated. Depositional sequences have been thoroughly studied by oil geologists using geophysical profiles of continental and marine basins. A general theory of basin-scale deposition has been formalized under the name of Sequence Stratigraphy.[3]

Some cyclothems might have formed as a result of marine transgressions and regressions related to decay and growth of ice sheets,[4] respectively, as the Carboniferous was a time of widespread glaciation in the Southern hemisphere. A more general interpretation of sequences invokes Milankovitch cycles.[5][6]

References

  1. ^ Wanless, H.R.; Weller, J.M. (1932). "Correlation and extent of Pennsylvanian cyclothems". Geological Society of America Bulletin 43: 1003–1016. 
  2. ^ Hampson G, Stollhofen H, Flint S (1999) A sequence stratigraphic model for the Lower Coal Measures (Upper Carboniferous) of the Ruhr district, north-west Germany. Sedimentology vol. 46 (issue 6), pp. 1199-1231
  3. ^ Haq BU, Schutter SR (2008) A chronology of Paleozoic sea-level changes. Science, vol. 322 (issue 5898), pp. 64-68. DOI: 10.1126/science.116164
  4. ^ Stanley, Steven M. Earth System History. New York: W.H. Freeman and Company, 1999. ISBN 0-7167-2882-6 (p. 426)
  5. ^ Milankovic cycles
  6. ^ Haq BU, Hardenbol J, Vail PR (1987) Chronology of fluctuating sea levels since the Triassic. Science, vol. 235 (issue 4793), pp. 1156-1167

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