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.