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.
Improving stratigraphic resolution, our ability to correlate sedimentary sequences, is one of the great challenges for paleoceanography and hence for the study of past climate. The unprecedented stratigraphic resolution of Greenland and Antarctic ice cores has led to major advances in climate science, however, ice cores are restricted in time-span and geographic distribution. In Quaternary marine sediments, oxygen isotopes (d18O) provide the traditional stratigraphy although d18O is not usually a synchronous global signal due to variations in water temperature and chemistry. Magnetic polarity stratigraphy is the now an indispensible element of geologic timescales for the last 160 million years, mainly because polarity reversals are globally recorded and synchronous on millennial timescales, although polarity reversals are only useful for high-resolution correlation in their immediate stratigraphic vicinity. Another facet of the paleomagnetic record can, however, be utilized for correlation within polarity chrons. The intensity of the Earth’s dipole field, which has decreased by ~5%/century in the last few hundred years, is a parameter that varies on short timescales, and is manifest globally. Relative paleointensity (RPI) can be recorded at time of deposition by sediments in which (titano)magnetite, in a restricted submicron to few-micron grain-size range, is the sole magnetic mineral. RPI has been used quite extensively in sediments deposited during the last ~ 1 million years, and it is now well accepted that RPI is a parameter that can augment d18O for stratigraphic correlation in marine sediments. In this project, we have carried out, for the first time, a correlation involving RPI of older sediments, deposited 17-25 million years ago, at a time belonging to the Oligocene-Miocene interval of the geologic timescale. This is an important time in Earth history because it is a time when concentration of atmospheric carbon dioxide was even greater than it is today. It is therefore a time that provides analogues for future climate conditions. In this project, we established the polarity stratigraphy (using polarity reversals) for three sites from the equatorial Pacific: Integrated Ocean Drilling Program (IODP) Sites U1334 and U1335, and Ocean Drilling Project (ODP) Site 1218. We then generated RPI records from Site U1334 and from Site 1218. We then demonstrated that these two sites can be correlated to one another using RPI. A more rigorous test is whether the equatorial Pacific sites can be correlated into the Atlantic Ocean. In the South Atlantic, Ocean Drilling Project (ODP) Site 1090 covers the same time interval as Sites U1334 and 1218, and has a magnetic polarity stratigraphy that was published by us in 2003. We used the magnetic polarity stratigraphies to correlate three sites: Sites U1334, 1218 and 1090. We then successfully demonstrated that RPI records can be utilized for higher-resolution correlation among the sites. Why is this important? It shows that RPI can be used for correlation of sediment sequences from one ocean to another (e.g. globally). The timescale of changes in geomagnetic field intensity are such that RPI correlations have potential resolution at centennial, or at least millennial, timescales. RPI, therefore, provides a tool for high-resolution correlation of marine sediments, and hence for correlation of the climate records that they contain. This will be important in studies of climate change at times in Earth history, in the distant past, when atmospheric carbon dioxide concentration was greater than it is today.
