THE FIRST CALIBRATED LATE NEOGENE PLANKTIC FORAMINIFERAL BIOSTRATIGRAPHY ACROSS THE KUROSHIO CURRENT EXTENSION, NORTHWEST PACIFIC OCEAN

Currently, a robust planktic foraminiferal age model is available for low-latitude (tropical and sub-tropical) regions. However, mid-latitude regions characterized by western boundary currents and their ecotones, lack an orbitally or magnetostratigraphically-calibrated biostratigraphy that can be correlated with low-latitude sites. Here, we present an amended late Neogene (15-0 Ma) zonation scheme based on planktic foraminiferal evolutionary events directly 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 on Shatsky Rise. These sites lie to the north, directly underneath, and to the south, respectively, of the Kuroshio Current Extension, spanning approximately 5˚ latitude. All three sites contain fantastic magnetostratigraphic records, providing a unique opportunity to calibrate planktic foraminiferal datums in the northwest Pacific Ocean from subtropical to transitional water masses. Planktic foraminifer datums were constrained at approximately ± 95 kyr at Site 1207; ± 15 kyr at Site 1208; and ± 82 kyr at Site 1209. As reported for mid-latitude sites in the southwest Pacific Ocean, datums are fewer in number in the northwest Pacific and have rare occurrences of or lack several tropical Pleistocene and Pliocene species (e.g, Globorotalia flexuosa, Gr. miocenica, Gr. pertenuis, Globigerinella calida). The zonation schemes developed from southwest mid-latitude Deep Sea Drilling Project Legs 29 and 90 were applied to all sites, with all zonal markers recognized. In addition, two tropical zones were recognized at Sites 1208 and 1209; only one was recognized at Site 1207. A new late Pleistocene zone, based on the first occurrence of Hirsutella hirsuta, is defined and recognized at all sites. Diachroneity among datums at the three sites is on the order of 1-750 kyr. Diachroneity is largest between the Shatsky Rise sites and tropical datums, on the order of 12 kyr to 3 million years. This may be partially due to intense dissolution in Miocene sediments at Site 1208. These results indicate that detailed, high-resolution planktic foraminiferal biostratigraphic schemes are necessary for regions characterized by differing water masses created by western boundary currents.