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