Английская Википедия:Cyclothems

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Шаблон:Short description

Файл:Cyclothems.jpg
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. The cyclothems consist of repeated sequences, each typically several meters thick, of sandstone resting upon an erosion surface, passing upwards to pelites (finer-grained than sandstone) and topped by coal.

Historically, the term was defined by the European coal geologists[2] who worked in coal basins formed during the Carboniferous and earliest Permian periods. 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 may have formed as a result of marine regressions and transgressions related to growth and decay of ice sheets, respectively, as the Carboniferous was a time of widespread glaciation in the southern hemisphere.[4] A more general interpretation of sequences invokes Milankovitch cycles.[5][6]

References

Шаблон:Reflist

External links

Jacobson, R. J. (2000) Depositional History of the Pennsylvanian Rocks in Illinois. Geonote 2. Illinois State Geological Survey, Champaign, Illinois.

  1. Шаблон:Cite journal
  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. Шаблон:Doi
  4. Stanley, Steven M. Earth System History. New York: W.H. Freeman and Company, 1999. Шаблон:ISBN (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