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Abstract

The Cenomanian-Turonian boundary extinctions, as observed near Pueblo, Colorado, are represented by a series of events reflecting accelerated macrofaunal evolutionary and extinction rates. Four main events are recognized near Pueblo which are cumulatively responsible for 80% species-level and about 30% genera-level macrofaunal extinction. The two main extinction events near Pueblo occured about 250 and 200 Ka before the terminal extinctions at the stage boundary. In addition to the evolutionary and extinction related faunal turnover, fluctuations in the relative abundances of inoceramid bivalves, oysters and ammonites appear to be related to substrate and inferred habitat changes reflected by the climatically controlled lithologie cyclicity. The increased rates of evolution and extinction observed through the Cenomanian-Turonian boundary interval may have been driven by increased biotic stress resulting from eustatic highstand and increased climatic variability influencing temperature, salinity, and benthic oxygenation within the Western Interior seaway and globally.

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