Planktic foraminifera, asteroids, and marine production: Death and recovery at the Cretaceous-Tertiary boundary

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The Cretaceous/Tertiary (K/T) impact radically changed the long-term state of the open-marine ecosystem. Comparison of range data from multiple sites indicates that more than 90% of planktic foraminiferal species went extinct at or shortly after the time of the K/T impact. Nearly complete replacement of planktic foraminiferal faunas began at the impact horizon. This turnover resulted in the disappearance of onshore-offshore provincialization of low- and mid-latitude planktic foraminiferal faunas. Drastic decreases in calcareous nannofossil production and organic export from surface to deep waters coincided with this destruction of faunal provincialization. Precessional chronometry of South Atlantic sites indicates that the initiation of faunal replacement and the decrease in nannofossil production occurred in an unresolvably short interval of time. Recovery of planktic foraminiferal assemblages was very dynamic. A rapid burst of first occurrences closely followed the impact. Despite the rapidity of this evolutionary radiation, long-term assemblage stabilization and recovery of organic export did not occur for at least a few hundred k.y. after the impact. Calcareous nannoplankton production remained below preimpact levels for two million years or more. There is some evidence that organic export to deep waters remained below preimpact levels for a similar interval of time. The coincidence of the K/T impact with planktic foraminiferal mass extinction, faunal turnover, and strong decreases in organic export and nannofossil production is very compatible with an impact model of mass extinction. In contrast, the proximate causes of the geologically long delay in postimpact recovery of organic export and nannofossil production remain unresolved. This presents a major challenge to our understanding of the ecologic and oceanographic consequences of large impacts and mass extinctions.

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Special Paper of the Geological Society of America