Abundance studies of extinct planktonic Foraminifera are proving a fruitful method of paleogeographic and paleoecologic analysis. Population counts of species and genera in fossil faunal assemblages give approximate percentage figures for paleo-faunal studies. Comparison of population data between two or more stratigraphic sections can be used as an indication of paleo-faunal differentiation and can outline paleogeographic distribution of species. Abundance analysis based on faunal sequences appears to reveal patterns that are repeated within sections from the same faunal province.

Application of this method of analysis to planktonic foraminiferal faunas from Maestrichtian and Paleocene assemblage zones in selected sections of the Atlantic, Gulf, and Mediterranean regions indicates distinct paleogeographic and paleoecologic differentiation. Broad generic distributions are evident, whereas there are more distinct geographic limitations on species in the Maestrichtian and Paleocene. There also is some indication of possible geographic subspecies variation. The most marked differentiation occurs along lines of longitude with more favorable comparisons and less marked differences along lines of latitude. A greater number of genera and species are found in low latitudes than in high latitudes in rocks of the Maestrichtian and Paleocene.

Faunas from sediments deposited in shallow-water environments are characterized by a limited number of species. The species that do occur usually are the most abundant elements in the planktonic faunas found in sediments deposited in deeper-water environments.

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