--> Abstract: Nannoplankton Succession Across the KIT Boundary: El Kef Revisited, by J. J. Pospichal; #90987 (1993).

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POSPICHAL, JAMES J., Department of Geology, Florida State University, Tallahassee, FL

ABSTRACT: Nannoplankton Succession Across the KIT Boundary: El Kef Revisited

The Cretaceous/Tertiary boundary preserved in the limestone, marls, and clays that crop out near El Kef, Tunisia is the most expanded K/T sequence known. The marine section has been studied in detail by both foraminiferal and nannofossil paleontologists, who have attempted to reconcile their results with popular models for the causes of mass extinction such as bolide impact or excessive volcanism. Controversy presently exists among foraminiferal paleontologists who have worked this section as to whether extinctions were gradual or stepwise across the boundary or whether they were synchronous at the boundary.

Detailed quantitative study of well-preserved nannofossil assemblages on closely spaced samples through the boundary interval reveal that: (1) There appears to be no stepwise extinction of nannoplankton in the upper four meters of Maastrichtian marls as reported for foraminifers (analyzed from splits of the same samples); (2) Cretaceous nannofossil species abruptly drop in abundance at the base of the boundary clay at the level of the iridium anomaly; (3) Few Cretaceous species survive to give rise to a base Tertiary stock; (4) Cretaceous species are present in variable amounts in all Danian samples, and at this time, it cannot be statistically proven whether they are reworked, as classically viewed, or whether their gradual reduction is the result of an extended period of extinction. (5) The abundance record of the earliest Danian species of Biscutum reveals a pattern of highly variable productivity reflecting unstable oceanographic conditions such as surface temperature and nutrient supply.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.