RELATIVE PALEOINTENSITY (RPI) OBSERVATIONS FROM IODP EXPEDITIONS 340 AND 363; TOWARDS A NEW PLIOCENE TUNING TARGET (Invited Presentation)

Studying past variations in the direction and strength of the earth’s magnetic field provides insights into the working of the geodynamo and offers stratigraphic opportunities over a range of temporal scales. Much of our detailed understanding of magnetic reversals, excursions, and relative changes in geomagnetic intensity come from the long, continuous, and undisturbed marine sediment cores recovered from scientific ocean drilling. Over the past few decades these high-quality, high-resolution observations have allowed us to move beyond polarity stratigraphy and develop variations in relative paleointensity (RPI) of the earth’s magnetic field into a chronostratigraphic tool that has the potential to provide within chron age control, independent of, and complementary to, carbonate based stable-isotope stratigraphy. While RPI records have been developed from ODP/IODP sites for the Pleistocene, the Pliocene RPI record remains poorly documented and understood. Here we focus on the ongoing development of Pliocene RPI records from Site U1396 from the Lesser Antilles (IODP EXP 340) and U1489 from the West Pacific Warm Pool (IODP EXP 363). Splices at both sites were sampled using u-channels and the natural remanent magnetization (NRM) was measured at centimeter scale following stepwise alternating field demagnetization. Low maximum angular deviation values imply the paleomagnetic records are well resolved at both sites and NRM directions document all 18 polarity reversals over the past 4.5 Myrs. Measurements of magnetic susceptibility and anhysteretic remanent magnetization characterize the environmental variability in both regions and provide a normalizer for the NRM to generate estimates of RPI that compare well to existing Pleistocene observations. The Plio-Pleistocene age model for Site U1489 is derived through correlation of preliminary δ¹⁸O data from planktonic and benthic foraminifera to the LR04 benthic δ¹⁸O stack. Using this chronology we document Plio-Pleistocene RPI variability, provide the first continuous and independently dated RPI record back into the early Pliocene, and generate an important Pliocene-age chronostratigraphic tuning target that will prove useful for all future scientific ocean drilling endeavors.