1. Introduction
The Matuyama-Brunhes magnetic reversal occurred approximately 773 kyr
ago (Cohen and Gibbard, 2019), as several recent studies have shown
(Channell et al., 2010 (773 ± 0.4 ka); Suganuma et al., 2015 (770.2 ±
7.3 ka); Singer et al., 2019 (773 ± 2 ka); Valet et al., 2019 (772.4 ±
6.6 ka); Haneda et al., 2020 (772.9 ± 5.4 ka)). This event was well
recorded by sediments that had sufficient sedimentation rates and could
be analyzed in detail by paleomagnetism (Channel et al., 2010; Sagnotti
et al., 2010, 2014; Suganuma et al., 2010; Jin and Liu, 2011; Giaccio et
al., 2013; Kitaba et al., 2013; Pares et al., 2013; Valet et al., 2014;
Liu et al., 2016; Okada et al., 2017; Bella et al., 2019).
Sediments acquire remanent magnetization during their deposition. The
alignment of magnetic moments of the grains occurs in the direction of
the Earth’s magnetic field. The acquisition of primary magnetization due
to this sedimentation process is called depositional or detrital
remanent magnetization (DRM) (Gubbins and Herrero, 2007). Remanent
magnetization protected by potential energy barriers can last over
geologic time scales. However, due to thermal and/or chemical processes,
such as reheating, oxidation, and iron hydroxide formation, over time,
secondary magnetizations can occur by crossing potential energy barriers
or by the generation of chemical remanences. The new secondary
magnetization has an orientation in the direction of Earth’s magnetic
field at the time of alteration rather than the time of original
deposition. Rocks can acquire viscous remanent magnetization (VRM) a
long time after their formation due to exposure to the geomagnetic
field. VRM contributes to noise in the paleomagnetic data (Butler, 1992;
Lanza and Meloni, 2006).
Lock-in-depth affects the nature of the paleomagnetic recording process
in sediments. Lock-in-depth is defined as the depth at which the
remanent magnetization stabilizes. The position of the lock-in-depth in
the sediments is influenced by lithology, the grain-size distribution of
the sediment matrix, sedimentation rate, and bioturbation (Bleil and von
Dobeneck, 1999; Sagnotti et al., 2005). When assuming a steady
sedimentation rate, the lock-in-depth result is a delay in magnetization
that corresponds to the time required to accumulate a sediment layer
equal to the lock-in-depth. For example, if the sediment has an
accumulation speed of 1 mm/kyr and the lock-in depth is 10 mm, the
magnetization age is 10 kyr younger than the actual sediment (Sagnotti
et al., 2005).
Paleomagnetic analysis of magnetic reversals in cave sediments has been
carried out in different locations around the world, including western
Europe (Pares et al., 2018), South Africa (Nami et al., 2016), South
America (Jaqueto et al., 2016), North America (Stock et al., 2005),
southern Europe (Pruner et al., 2010), and eastern Asia (Morinaga et
al., 1992). Kadlec et al. (2005, 2014) reported that the central
European cave (local name “Za Hajovnou”) in the Moravia region of the
Czech Republic records the Matuyama-Brunhes transition. The aim of the
present study is to analyze the reversal using more detailed
paleomagnetic methods and to identify the magnetic carrier of the cave
sediment. Here, we obtained a new paleomagnetic dataset from three
vertical sediment profiles in this cave. The contribution of the central
European paleomagnetic record in cave sediment will be valuable for
investigating the characteristic behavior of the Earth’s magnetic field
during the Matuyama-Brunhes magnetic reversal. Because the sedimentation
rate in the cave is not well understood, details of the timing of the
transition are not yet known, making our estimation in this study even
more crucial.