37. BIOSTRATIGRAPHIC AND MAGNETOSTRATIGRAPHY SUMMARY1

The magnetostratigraphic and biostratigraphic results of Ocean Drilling Program Sites 881-884 and 887 are summarized and combined to form age vs. depth models for these sites. The recovery of continuous magnetostratigraphic records of the upper lower Miocene through Pleistocene section at Sites 884 and 887 allows the first direct calibration of diatom and radiolarian datum levels with magnetostratigraphy between magnetic Subchrons C5En and C3Bn (18.317-6.744 Ma) in the North Pacific. Based on these records and temporally shorter magnetostratigraphic records at Sites 881-883, at least 25 diatom and 22 radiolarian datum levels appear to be isochronous in the late early Miocene through Pleistocene of the North Pacific. The use of calcareous nannofossils for biostratigraphy of the post-early middle Miocene appears to be limited to the late Pliocene and Quaternary in sections sampled by Leg 145. Biostratigraphy indicates that a composite section of Sites 883 and 884 represents a relatively complete record of the lower Eocene through the lower Miocene, although carbonate preservation is best and the section is less complicated by reworking at Site 883. Primary biostratigraphic control is provided by calcareous nannofossils. A large part of the upper middle Eocene and upper Eocene is missing at hiatuses at both Sites 883 and 884. A condensed upper Paleocene section is present at Site 883, unconformably overlying uppermost Cretaceous sediments. Late Maestrichtian calcareous nannofossils are documented in Site 883 immediately above the basalt.