Cretaceous paleogeography: implications of endemic ammonite faunas

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Young, Keith, 1918-2004

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University of Texas at Austin. Bureau of Economic Geology


Endemic ammonite faunas evolved from cosmopolitan faunas in a series of successive episodes over about 35 million years of the Cretaceous of the Gulf Coast of the United States. During basin-basin-margin tectonic adjustments the Cretaceous barrier reef was inundated or circumvented so that a cosmopolitan fauna entered the back-reef area. Gradual isolation of the fauna behind the barrier produced endemism. With the next basin adjustment the endemic fauna became extinct, and a new cosmopolitan fauna migrated into the back-reef area, likewise evolving into an endemic fauna in its turn. Six cosmopolitan-endemic cycles have been identified. Geological evidence suggests two or three additional cycles.


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Young, K. P., 1972, Cretaceous Paleogeography: Implications of Endemic Ammonite Faunas: The Universijty of Texas at Austin, Bureau of Economic Geology, Geological Circular 72-2, 13 p.