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Approximately sixty transgressive-regressive depositional sequences are present in Carboniferous and Permian shallow-marine successions on the world's stable cratonic shelves. These sequences were synchronous depositional events that resulted from eustatic sea-level changes. Based on currently available age correlations of rapidly evolved late Paleozoic tropical, subtropical, and temperate shelf faunas, the sequences on different cratonic shelves were time equivalent. These transgressive-regressive sequences averaged about 2 million years and ranged from 1.2 to 4.0 million years in duration.

Local depositional conditions are important in controlling sedimentary patterns on different cratonic shelves. These conditions are affected by changes in sea level, strandline position, and drainage base level and are reflected in the sedimentary record. Because midsize sea-level fluctuations are usually widely identifiable in the stratigraphic record, they are useful aids in correlation. They are particularly helpful between regions that have contrasting depositional conditions, such as between a carbonate shelf starved of clastic sediments and a clastic-dominated shelf on which carbonates are rare.

The appearance of new species and genera generally occurs above unconformities that signal new marine transgressive events and new depositional sequences. The durations of the hiatuses between these transgressive-regressive sequences are difficult to estimate. The hiatuses may represent cumulatively as much time, if not more, than the rock record. The numerous worldwide synchronous unconformities marking hiatuses of considerable duration within late Paleozoic shelf strata suggest that the fossil record may be very incomplete and preserves mostly biota that were extant during times of high sea level. Such an incomplete fossil record could easily be misinterpreted as a punctuated evolution having a highly irregular mutation rate.

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