Theoretical investigation of the pDRM process: a flexible lock-in
function approach
Abstract
The primary data sources for reconstructing the geomagnetic field of the
past millennia are archaeomagnetic and sedimentary paleomagnetic data.
Sediment records, in particular, are crucial in extending the temporal
and spatial coverage of global geomagnetic field models, especially when
archaeomagnetic data is sparse. However, the post-depositional detrital
remanent magnetization (pDRM) process is still poorly understood and can
cause smoothing of the magnetic signal and offsets with respect to the
sediment age. To make effective use of sedimentary data, it is essential
to understand the lock-in process and its impact on the magnetic signal.
In this study, we investigate the lock-in process theoretically and
derive a parameterized lock-in function that can approximate possible
lock-in behaviors. Additionally, we demonstrate that a lock-in function
that is independent of absolute parameters can only be applied to the
magnetic direction components (declination and inclination), but not to
the relative intensity. Integrating this lock-in function into the
ArchKalmag14k modeling procedure
\cite{schanner2022archkalmag14k} allows including data
from sediment records. The parameters of the lock-in function are
estimated by the maximum likelihood method using archaeomagnetic data as
a reference. The effectiveness of the proposed method is evaluated
through synthetic tests. Additionally, we apply our technique to
sediment records from two lakes in Sweden (Kälksjön and Gyltigesjön) as
first case studies. Our results demonstrate that the proposed method is
capable of effectively correcting the distortion caused by the lock-in
process, making data from sedimentary records a more reliable and
informative source for geomagnetic field reconstructions.