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Standard planktonic foraminiferal zones developed for tropical faunas can be estimated in mid- to high-latitude faunal assemblages of the northeast Pacific on the basis of recognition of major paleoclimatic-paleoceanographic events, quantitative distribution of Neogloboquadrina pachyderma morphotypes, and coiling ratio of this species in addition to the presence of key taxa. The late Neogene foraminiferal assemblages of DSDP site 173, off northern California, have been quantitatively analyzed and zoned by correlation with the central North Pacific DSDP site 310; multiple correlations of other microfossil groups support this correlation. Site 173 can thus serve as a reference section for zonation of sediments exposed at Centerville Beach, northern California, and in general for mid- to high-latitude faunas of the northeast Pacific. Correlation of planktonic foraminiferal assemblages of the Centerville Beach section with assemblages of site 173 indicate that the Eel River and Rio Dell Formations represent lower Pliocene to lower Pleistocene deposits. The base of the Eel River Formation lies within the upper part of foraminiferal zone N19, the Pliocene-Pleistocene boundary lies within the upper part of the middle member of the Rio Dell Formation, and extrapolation suggests that the top of the Rio Dell Formation is no younger than 0.7 m.y. This correlation is supported by analysis of other planktonic microfossil groups and by recent magnetostratigraphic work by Dodd and others and Kodama.

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