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.
Integrated Ocean Drilling Program Site U1338 is located in the Equatorial Pacific and has produced a magnetic stratigraphy that spans much of the ~450 meter thick section. The site is shown to range in age from the ~ 15 Ma to Recent. Shipboard magnetic stratigraphy has been enhanced with discrete sample measurements done on 2x2 cm cubes measured in the magnetically shielded room in the paleomagnetics lab at the Lamont-Doherty Earth Observatory. These measurements on over 1000 samples confirmed and improved upon shipboard measurements on half cores. The section at U1338 from 90-300 meters composite depth covers the Pliocene to Middle Miocene (~4-12 Ma). Shipboard measurements of the magnetic stratigraphy provided good results for only a small portion of this interval, ~200-250 meters composite depth which was identified as the earlier part of Chron 4 and late Chron 5 (8.5-10.8 Ma). The rest of this 210-meter section provided no useful magnetostratigraphic results shipboard. Discrete sample measurements have defined a magnetic stratigraphy for the 3-8.5 Ma interval, but however confirmed the shipboard results for the 10.8-12 Ma interval where the low magnetic intensities of sediment make it impossible to make useful measurements. This work has identified at least one "cryptochron" C4n.2n-1 and tentatively two others within subchron C5n.2n. This work was part of collaborative effort working on eight IODP sites from Expedition 320 and 321 to produce magnetic stratigraphies for the sites, relative paleointensity records and to look at paleoenvironmental changes using magnetic properties data. Measurements of magnetic properties of samples from IODP Site U1338 show that the magnetization is carried by very fine grained magnetite, most likely of biogenic origin. The data generated from this study and published in peer-review publications will be deposited within the MagIC database maintained as part of EarthRef.org (http://earthref.org/MAGIC/).
