French
DeutschCyclothems
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[edit]
- ^ Wanless, H.R.; Weller, J.M. (1932). "Correlation and extent of Pennsylvanian cyclothems". Geological Society of America Bulletin. 43 (4): 1003–1016. Bibcode:1932GSAB...43.1003W. doi:10.1130/gsab-43-1003.
- ^ 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
- ^ 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
- ^ Stanley, Steven M. Earth System History. New York: W.H. Freeman and Company, 1999. ISBN 0-7167-2882-6 (p. 426)
- ^ Milankovic cycles
- ^ Haq BU, Hardenbol J, Vail PR (1987) Chronology of fluctuating sea levels since the Triassic. Science, vol. 235 (issue 4793), pp. 1156-1167
External links[edit]
- Jacobson, R. J. (2000) Depositional History of the Pennsylvanian Rocks in Illinois. Geonote 2. Illinois State Geological Survey, Champaign, Illinois.