This study will conduct paleomagnetic analyses of equatorial Pacific sediment cores spanning the Eocene through the Pleistocene collected during IODP expeditions 320 and 321. Using high resolution U-channel measurements, this project will produce a high resolution magnetostratigraphic record that could serve as a very important chronostratigraphic tool. The project will address five objectives: 1) refine the shipboard magnetostratigraphies, 2) generate continuous geomagnetic intensity and directional paleosecular variation records, 3) generate environmental magnetic records, 4) improve the Cenezoic geologic timescale, and 5) improve our understanding of the Pacific apparent polar wander.
Broader impacts: The project would support undergraduate and/or graduate students at the universities of all four PIs. The project also effectively capitalizes on a large investment previously made in an IODP expedition and further enhances the collaborations and exchange of information between several international members of the expedition and the IODP community. By developing such an important chronological tool that helps refine the geologic timescale and improves the geomagnetic intensity record, the project significantly impacts the earth sciences.
We investigated the palaeomagnetic record from the Oligocene through Miocene part of Integrated Ocean Drilling Program (IODP) Site U1333 (10°30.996′N, 138°25.159′W), which is located in 4853-m deep water over seafloor with an estimated crustal age of 46 Ma. The magnetostratigraphic investigations are crucial to provide a sound age model for the study of the palaeoclimatic and palaeoceanographic history of the Cenozoic of the Equatorial Pacific and to improve the database of Pacific magnetostratigraphy. Rock magnetic measurements were carried out at high (1-cm) resolution on 81 U-channel samples from the composite section with the goal of extracting a detailed record of the magnetostratigraphy. Stepwise demagnetization of the natural remanent magnetization yielded a well-defined magnetostratigraphy over a time interval of approximately 10 m.y. between the base of Chron C6n (19.722 Ma) and the middle of Chron C11r (>29.9 Ma) and identification of the Oligocene-Miocene transition at the base of Subchron C6Cn.2n. The palaeomagnetic data are characterized by shallow inclinations, and by 180° alternations in declinations downhole, reflecting magnetic polarity zones. The relatively high temporal resolution allowed for the identification of three possible excursions previously not identified on the geomagnetic polarity time scale, which were recorded in Subchrons C8n.1r and C11n.2n and in Chron C11r.
