Late Cenozoic planktonic foraminiferal biostratigraphy and paleoceanography of the Panama Basin

Foraminiferal assemblages from Late Miocene to Late Pleistocene sediments from Deep Sea Drilling Project (DSDP) Sites 157, 158, and 84 in the Panama Basin have been analyzed, using factor analysis and other quantitative techniques. As a working hypothesis, species in continuous evolutionary lineages and those similar in morphology to modern species are assumed to have environmental tolerances similar to the living representative. The Late Miocene of the Panama Basin is marked by major calcium carbonate dissolution. On the Carnegie and Cocos Ridges, samples from this interval have from 5 to 20 times as many benthic foraminifera and foraminiferal fragments as whole specimens of planktonic species. Dissolution is apparent, but less intense, in the Pliocene and Pleistocene. The faunas throughout consist generally of tropical and subtropical taxa admixed with a few temperate-water species. The Late Miocene is also marked by a gradual increase in the abundance of the Neogloboquadrina plexus relative to the abundance of tropical species. This may be associated with the emergence of the Isthmus of Panama and the separation of the tropical Pacific and Atlantic Oceans. The faunal elements of waters of highest latitude occur in the Early Pliocene on the Carnegie and Cocos Ridges and in the Pleistocene throughout the entire region. This introduction of a new assemblage reflects climatic cooling. There is also faunal evidence of climatic deterioration beginning in the Middle Pliocene. Important faunal elements are illustrated with scanning electron micrographs.