--> Abstract: Cretaceous Nannofossil Zonations: A New Look at Fossil Datums for Biostratigraphic Applications, by J. A. Bergen and R. A. Salomon; #90987 (1993).

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BERGEN, JAMES A., and RALPH A. SALOMON, Amoco Production Company, Houston, TX

ABSTRACT: Cretaceous Nannofossil Zonations: A New Look at Fossil Datums for Biostratigraphic Applications

Recent investigation of the nannofossils recovered from numerous Cretaceous outcrop sections demonstrates that the biostratigraphic resolution of this microfossil group can be increased significantly. The sections included in the current study are located in the same basins and include some of the same sections upon which the pioneering biostratigraphic zonations of the Cretaceous are based. Refinement of these original biostratigraphic schemes is not only based on the recognition of new species, but also on the biostratigraphic utility of previously described taxa. For the Lower Cretaceous, a sequence of biostratigraphic events can be recognized both in the Vocontian Basin (southeastern France) and at DSDP Site 534 (western North Atlantic). This sequence has been tied to the Tethyan mmonite biostratigraphy in the Vocontian basin (including several of the stage stratotype sections), thus providing an excellent reference for the nannofossil biostratigraphy. For the Upper Cretaceous, outcrop sections in Tunisia provide the foundation for the current investigation. Additional sections in southern England and the United States (Gulf Coast and Western Interior) demonstrate that many of these events can be recognized over a broad geographic area.

Although the current results are preliminary, dramatic improvements in biostratigraphic resolution are demonstrated for the Valanginian, Hauterivian, Cenomanian, and Campanian-early Maastrichtian. Except for the early Valanginian, these were also times when species extinctions predominated over originations. The Family Zygodiscaceae is given as an example of the potential biostratigraphic resolution that future detailed taxonomic study may yield.

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