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.