Pliocene Record of Relative Paleointensity from IODP Site U1396 in the Caribbean Sea: Chronostratigraphic and Paleogeomagnetic Opportunities.
Abstract
Long sedimentary records of relative geomagnetic paleointensity (RPI) offer unique insights into geodynamo behavior and can be developed into chronostratigraphic templates capable of (sub-)orbital scale age control. The Quaternary record of RPI has received much attention, but records extending back into the Pliocene are relatively rare. Here we report 4.5 Myrs of paleomagnetic and rock magnetic data obtained from Integrated Ocean Drilling Program (IODP) Site U1396 in the Caribbean Sea. Discrete, high amplitude, spikes in magnetic concentration that punctuate the entire record are associated with tephra deposition, while a baseline shift in magnetic coercivity at ~ 2.1 Ma is likely linked to the longer-term evolution of the Lesser Antilles Volcanic Arc. These variations affect paleomagnetic data quality and, as the older interval preserves a cleaner paleomagnetic record, we focus on the 2.1 - 4.5 Myr interval here. The normalized intensity record is refined using a multi-step screening process that uses sedimentological, rock magnetic, and paleomagnetic properties to remove intervals that are unlikely to accurately preserve past geomagnetic field behavior. The filtered record, which preserves 84 % of the data and passes quality criteria for RPI estimates, is then compared to existing late Pliocene and early Pleistocene RPI records to determine whether a RPI-proxy is preserved. Coherence with EPAPIS and North Atlantic RPI records establishes a common geomagnetic driver that then facilitates revision of the existing stable isotope chronology in the early Matuyama. The 2.1 - 4.5 Myr RPI record has few analogs, but, a comparison to the preliminary Pliocene-age RPI record from IODP Site U1489 in the western equatorial Pacific suggests characteristic RPI variability is preserved since the early Pliocene. Neither of these records support evidence from the eastern equatorial Pacific for a baseline increase in intensity during the early Pliocene, nor do they reproduce an asymmetrical saw-tooth intensity pattern. Shallower than GAD inclination observed during reversed polarities cannot easily be explained by rock magnetic variability or a pervasive overprint. The development of these long Pliocene-age records opens the door to extending the success stories of Pleistocene RPI deeper into pre-Quaternary times.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMGP003..06H
- Keywords:
-
- 1520 Magnetostratigraphy;
- GEOMAGNETISM AND PALEOMAGNETISM;
- 1527 Paleomagnetism applied to geologic processes;
- GEOMAGNETISM AND PALEOMAGNETISM;
- 1540 Rock and mineral magnetism;
- GEOMAGNETISM AND PALEOMAGNETISM