A Geomagnetic Paleointensity Record of 0.6 to 3.2 Ma From Sediments in the Western Equatorial Pacific and Remanent Magnetization Lock‐In Depth

Abstract

AbstractInformation of past geomagnetic intensity variations is important for better understanding of the geodynamo, and efforts to recover continuous paleointensity records continue, in particular for ages older than 2 Ma. In this study, a new relative paleointensity (RPI) record of 0.6 to 3.2 Ma was obtained from a sediment core in the western equatorial Pacific, which has good age control by the oxygen isotope stratigraphy from 2.0 to 3.2 Ma. The RPI record could well be correlated to existing RPI templates despite the low sedimentation rate of ~5 m/Ma and will be useful for future construction of a stacked paleointensity curve beyond 2 Ma. Magnetic minerals of the core consist mainly of biogenic and terrigenous oxidized magnetite. Some rock magnetic contamination to long‐term RPI changes is recognized; RPI inversely correlates with the ratio of anhysteretic remanent magnetization to saturation remanent magnetization, which may be caused by differences in remanence acquisition efficiency between the biogenic and terrigenous magnetic components. The lock‐in depth of the studied core is estimated to be approximately 0 from a line of evidence including no apparent offset between RPI and cosmogenic beryllium nuclide flux changes across some polarity boundaries. Lock‐in depths vary locally from core to core or even within a single core and have no obvious relation with sedimentation rates and carbonate contents. Lock‐in depths may be controlled by factors that are currently difficult to be evaluated, such as variations in sediment flocculation sizes and biogeochemical remanent magnetization dependent to chemical conditions of sediments.