Lesson plan
Cyclothems
, to describe a Pennsylvanian-age rock succession in western Illinois 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 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. 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. A more general interpretation of sequences invokes Milankovitch cycles.
Article summary
, to describe a Pennsylvanian-age rock succession in western Illinois 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 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. 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. A more general interpretation of sequences invokes Milankovitch cycles.
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Discussion questions
- Summarise the article in your own words. Which single claim would you verify first, and why?
- Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
- If two sources disagreed about one of these facts, what would you need in order to trust one over the other?
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