4. Discussion
Even though some samples could not be demagnetized up to 100 mT, our
data show that minerals with low coercivity are responsible for cave
sediment magnetization. This finding is supported by rock magnetism
results that indicate the behavior of maghemite for most of the samples.
Our data indicate that the Matuyama-Brunhes transition boundary
constitutes 5.7 cm between 7.1 and 12.8 cm depth in the sampled
sedimentary section of Za Hajovnou cave. The magnetic reversal is
characterized and represented by frequent fluctuations in the
inclination angle (Fig. 6e) and VGP latitude (Fig. 7a). We think that
fluctuations in the declination data indicate instability in the Earth’s
magnetic field and remanent magnetization. On the other hand,
similarities seen in previous studies (Fig. 6e-o) demonstrate the
reliability of the data.
The migration of the magnetic North pole from eastern Africa to western
North America is a key point for the behavior of the magnetic field
during the transition. Although the data in this study and Okada et al.
(2017) belong to geographically different locations and sediment types,
the similarity during polar migration (Fig. 8) shows that the reversal
was a dipole transition, and the non-dipole field component was less
significant (Oda et al., 2000; Mochizuki et al., 2011; Simon et al.,
2019).
Note that most of the sediment section contains samples from the
polarity transition. The data show that the magnetic field was already
unstable in reversed polarity for our oldest sample. This observation
agrees with Haneda et al. (2020), who showed that the magnetic pole was
unstable a long time before the reversal boundary (Fig. 7b), and the
magnetic field started to fluctuate almost 20 kyr before the actual
transition in their relative paleointensity (RPI) data. We think that
our data illustrate the same instability, which is why no paleomagnetic
samples have VGP latitudes that deviate less than 25° from the reversed
position. We provide a more detailed explanation of the reversed VGP
behavior in our data, showing reversed polarity fluctuation well before
the actual magnetic reversal.