Relative Paleointensity Record of Integrated Ocean Drilling Program Site U1396 in the Caribbean Sea: Geomagnetic and Chronostratigraphic Observations in the Pliocene

Continuous sedimentary records of paleomagnetic directional variability and relative paleointensity (RPI) provide valuable information on the evolution of the geodynamo while also facilitating stratigraphic correlation and age control. While the Quaternary RPI record has received much attention, Pliocene records are relatively rare. Here, a u-channel paleomagnetic study from Integrated Ocean Drilling Program (IODP) Site U1396 in the Caribbean Sea refines the shipboard-derived polarity stratigraphy and generates an RPI and directional record extending back 4.5 Ma. Rock magnetic data reveal changes in magnetic coercivity around 2.1 Ma that influences the quality of the paleomagnetic record; while the older record is well-resolved and passes RPI quality criteria, much of the younger section does not. To facilitate the development of the RPI record, spike noise associated with discrete intervals of volcanogenic sediments are filtered from the data set. The resulting record passes RPI reliability criteria between 0-0.6 Ma and 2.1-4.5 Ma and represents the highest resolution RPI record extending into the early Pliocene. We use this record to refine the existing benthic delta O-18 chronology and open the door to high-resolution RPI chronostratigraphies during the Pliocene. Although we find no evidence for a previously observed increase in magnetic field intensity after similar to 4 million years ago, we do observe an asymmetrical form to RPI in the normal polarity intervals of the Gauss chron. We also find a polarity bias in inclination that cannot be simply explained by a drill string overprint, suggesting polarity-driven field asymmetries that are particularly pronounced during the Pliocene.

Automated summary

This study utilizes u-channel paleomagnetic study from IODP Site U1396 in the Caribbean Sea to investigate RPI and directional record extending back 4.5 Ma. The results show magnetic coercivity changes around 2.1 Ma affecting the quality of paleomagnetic record, and filtering spike noise associated with discrete intervals of volcanogenic sediments helps to develop a high-resolution RPI record. The study opens the door for high-resolution RPI chronostratigraphies during the early Pliocene, revealing asymmetrical RPI form and polarity-driven field asymmetries particularly pronounced during this time period.