1. Introduction
Matuyama-Brunhes magnetic reversal occured approximately 781 kyr ago
(Lourens et al., 2004). Studies in recent years (Channel et al., 2010;
Giaccio et al., 2013; Jin and Liu, 2011; Kitaba et al., 2013; Liu et
al., 2016; Okada et al., 2017; Pares et al., 2016; Sagnotti et al.,
2010, 2014; Suganuma et al., 2010; Valet et al., 2014; Bella et al.,
2019) have shown that this event is well recorded by respective
sediments that had sufficient sedimentation rate and could be analyzed,
in detail, by paleomagnetism.
Sediments acquire remanent magnetization during their deposition. The
alignment of ferromagnetic 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 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 time,
barriers may be overcome, the magnetic domains change their arrangement
and rocks can acquire secondary magnetizations. The new secondary
magnetization has an orientation in the direction of the Earth’s field.
Then rocks can acquire a viscous magnetization (VRM) long time after
their formation due to an exposure to geomagnetic field. VRM contrinutes
to a noise in paleomagnetic data (Lanza and Meloni, 2005; Butler, 1997).
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 influence
on the position of the lock-in-depth in the sediments (Sagnotti et al.,
2005; Bleil and von Dobeneck, 1999). 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 sediment layer of thickness that equal to the lock-in-depth.
For example, if the sediment has accumulation speed 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, has a potential record of Matuyama-Brunhes transition. Here we
obtained a new paleomagnetic dataset from three vertical sediment
profiles found in this cave.