1. Introduction
Matuyama-Brunhes magnetic reversal occurred approximately 781 kyr ago
(Gradstein et al. 2004). Published studies (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)
showed that this event is well recorded by respective sediments that had
sufficient sedimentation rate and could be analyzed, in detail, by
paleomagnetism. Also, studies in the recent years have shown a younger
age for the reversal around 773 kyr (Channell et al., 2010 (773 ± 0.4
kyr); Suganuma et al., 2015 (770.2 ± 7.3 kyr); Simon et al., 2019 (773.9
kyr); Singer et al., 2019 (773 ± 2 kyr); Valet et al., 2019 (772.4 ± 6.6
kyr); Haneda et al., 2020 (772.9 ± 5.4 kyr)).
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 and acquisition of primary magnetization due
to this sedimentation process is called depositional or detrital
remanent magnetization (DRM) (Gubbins and Herrero, 2017). Remanent
magnetization protected by potential energy barriers can last over
geologic time scales. Nevertheless, due to thermal and/or chemical
processes such as reheating, oxidation and formation of iron hydroxides
during the time, secondary magnetizations can be acquired by crossing
potential energy barriers or generation of chemical remanences. The new
secondary magnetization has an orientation in the direction of the
Earth’s field. Then rocks can acquire a viscous remanent magnetization
(VRM) a long time after their formation due to exposure to the
geomagnetic field. VRM contributes to noise in paleomagnetic data
(Butler, 1992; Lanza and Meloni, 2006).
Lock-in-depth affects the nature of the paleomagnetic recording process
in sediments. It is defined as the depth at which the remanent
magnetization is stabilized. Lithology, grain-size distribution of the
sediment matrix, sedimentation rate and bioturbation, all have an
influence on the position of the lock-in-depth in the sediments (Bleil
and von Dobeneck, 1999; Sagnotti et al., 2005). When assuming the steady
sedimentation rate, the result of lock-in-depth stabilization is younger
magnetization than the sediment itself by an amount of time required to
accumulate a sediment layer of thickness that equal to the
lock-in-depth. For example, if the sediment has an accumulation speed of
1 mm per 1000 years, and lock-in-depth is 10 mm, the magnetization age
is 10 000 years younger than the sediment itself (Sagnotti et al.,
2005).
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 our study is to
analyze the reversal in detail paleomagnetic method and to identify the
magnetic carrier of the cave sediment. Here, we obtained a new
paleomagnetic dataset from three vertical sediment profiles found in
this cave. A central European paleomagnetic record of the B/M boundary
will be valuable for investigation of the characteristic behavior of the
Earth’s magnetic field during Matuyama-Brunhes magnetic reversal. The
sedimentation rate of the cave sediment is not known yet in terms of
understanding the transition. It makes our estimation even more crucial
in this study.