MID-LATITUDE PLANKTIC FORAMINIFERAL BIOSTRATIGRAPHY FOR THE NORTHWEST PACIFIC OCEAN, SHATSKY RISE, OCEAN DRILLING PROGRAM HOLES 1207A, 1208A, AND 1209A

Currently an astronomically-tuned planktic foraminiferal age model is available for low-latitude (tropical and sub-tropical) regions. However, mid-latitude regions, including western boundary currents and their ecotones, still lack a tuned, robust biostratigraphy that can be correlated with low-latitude sites. Here we present an amended Late Neogene (15-0 Ma) zonation scheme with planktic foraminifer evolutionary events calibrated to the geomagnetic polarity timescale. In 2001, Ocean Drilling Program Leg 198 recovered nearly complete and expanded late Neogene sediments from Sites 1207, 1208, and 1209. These sites lie to the north, directly underneath, and to the south, respectively, of the modern-day Kuroshio Current Extension, spanning approximately 5˚ of latitude. All three sites contain fantastic magnetostratigraphic records, providing a unique opportunity to calibrate planktic foraminiferal datums for the northwest Pacific from subtropical to transitional water masses. Planktic foraminifer datums were constrained to an average of ±0.84 kyr at all sites. As reported for other mid-latitude sites, datums are fewer in the northwest Pacific and lack several tropical Pleistocene and Pliocene species (e.g, Globorotalia flexuosa, Globigerinoides fistulosus, Globorotalia pseudomiocenica, Globorotalia lenguaensis, Globigerinella calida). Generally, Shatsky Rise and low-latitude primary datums differ by 1.1-0.2 myr, with diachroneity also apparent among the three holes. The southwest Pacific zonation schemes developed from Deep Sea Drilling Project Legs 29 and 90 across the Tasman Front were utilized at the Shatsky Rise sites. All of the warm and cool subtropical zones were identified at Hole 1209A, which we have renamed the subtropical northwest Pacific zonation scheme. At Holes 1207A and 1208A, all zones in the southwest Pacific temperate scheme were identified. We have named a new zone in the upper middle Pleistocene based on the first common occurrence of Globorotalia hirsuta, called the Gr. hirsuta Taxon Range Zone, which is identified at all three holes. These new biostratigraphic zonation schemes highlight the need for detailed, high-resolution planktic foraminiferal biostratigraphic schemes for regions characterized by differing water masses created by western boundary currents.