Tertiary Calcareous Nannofossils from Southwestern Washington
Armentrout, John M.; Worsley, Thomas R.
published: Jul 27, 1980
Tertiary sediments of southwestern Washington yield fifty-six taxa of calcareous Nannoplankton from the Cowlitz, Lincoln Creek, and Astoria Formations of Late Eocene to Middle Miocene age (Pacific Coast Provincial Ages). Of the four-hundred sixty samples examined, sixtythree contain nannofloras of which nine have sufficient diversity and diagnostic species for tentative age determinations. Those samples which are datable are correlated within the same section with the benthonic foraminiferal biochronology applied to western Washington (RAU 1958, 1964, 1966). Trends in taxonomic diversity and stratigraphic distribution of ecologically indicative forms reflect deposition in shelf or nearshore environments with a Late Eocene, subtropical to warmtemperature water mass, modifying the cool-temperate conditions during Oligocene time, and warming in the Early Miocene.