Modern planktonic foraminiferal ecology serves to define limitations of Cenozoic zonation. Modern tropical species are abundant and diverse, temperate zone species are sparse and diverse, and cool temperate and polar areas have an extreme abundance of very few species. Keeled globorotaloids are restricted to water temperatures higher than about 17° C., non-keeled globorotaloids to waters warmer than about 9° C., and there are no globorotaloids in polar regions. Thus, a keeled planktonic line is one criterion for the recognition of boundaries of tropical and warm temperate areas in the Cretaceous and Cenozoic. Large heavy tests of planktonic species are indicative of bathyal environments.

Planktonic zonation for the Cenozoic is considered to have general worldwide uniformity and thus provides a means of recognizing the standard European stages in open marine deeper-water facies of tropical areas of the world. General planktonic parameters include: (1) the development of keeled globorotaloids in the Paleocene and their decline and disappearance in the Middle Eocene; (2) a second development of keeled globorotaloids in the Burdigalian and their continued dominance into the Recent; and (3) the recognition of important times of appearance of specific groups--the Globigerinoides triloba datum at the base of the Aquitanian, the Orbulina datum at the base of the Burdigalian, the Globorotalia menardii datum near the top of the Burdigalian, and the Sphaeroidinella dehiscens dat m at the base of the Pliocene.

End_of_Article - Last_Page 1768------------