Post-depositional remanent magnetization lock-in for marine sediments deduced from ¹⁰Be and paleomagnetic records through the Matuyama-Brunhes boundary

Geomagnetic field intensity records from marine sediments have contributed to improved understanding of variations in the Earth's magnetic field, and have helped to establish age models for marine sediments. However, lock-in of the geomagnetic signal below the sediment-water interface in marine sediments through acquisition of a post-depositional remanent magnetization (PDRM) adds uncertainty to synchronization of marine sedimentary records. Although quantitative models enable assessment of delays in remanence acquisition associated with PDRM processes, the nature of the filter function and the PDRM lock-in zone thickness remain topics of debate. We performed both forward numerical simulations and inverse parameter estimation to assess the best-fit filter function and PDRM lock-in zone thickness in marine sediments based on a comparison of ¹⁰Be flux and relative paleointensity records. Our simulations reveal that the rate of PDRM lock-in increases in the middle of the lock-in zone and that a Gaussian function with a 17cm lock-in zone thickness provides a good approximation to the PDRM lock-in within the studied core. With this function, PDRM lock-in is delayed, but with relatively little distortion of the geomagnetic signal. Our results also imply that a PDRM is not simply locked due to progressive marine sediment consolidation and dewatering, and that the arbitrary functions (linear, cubic, and exponential) that are often used to model PDRM lock-in starting from the base of the surface mixed layer cannot explain fully the observed paleomagnetic signal.