1. Introduction
The Matuyama-Brunhes magnetic reversal occurred approximately 773 kyr ago (Cohen and Gibbard, 2019), as several recent studies have shown (Channell et al., 2010 (773 ± 0.4 ka); Suganuma et al., 2015 (770.2 ± 7.3 ka); Singer et al., 2019 (773 ± 2 ka); Valet et al., 2019 (772.4 ± 6.6 ka); Haneda et al., 2020 (772.9 ± 5.4 ka)). This event was well recorded by sediments that had sufficient sedimentation rates and could be analyzed in detail by paleomagnetism (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).
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. The acquisition of primary magnetization due to this sedimentation process is called depositional or detrital remanent magnetization (DRM) (Gubbins and Herrero, 2007). Remanent magnetization protected by potential energy barriers can last over geologic time scales. However, due to thermal and/or chemical processes, such as reheating, oxidation, and iron hydroxide formation, over time, secondary magnetizations can occur by crossing potential energy barriers or by the generation of chemical remanences. The new secondary magnetization has an orientation in the direction of Earth’s magnetic field at the time of alteration rather than the time of original deposition. Rocks can acquire viscous remanent magnetization (VRM) a long time after their formation due to exposure to the geomagnetic field. VRM contributes to noise in the paleomagnetic data (Butler, 1992; Lanza and Meloni, 2006).
Lock-in-depth affects the nature of the paleomagnetic recording process in sediments. Lock-in-depth is defined as the depth at which the remanent magnetization stabilizes. The position of the lock-in-depth in the sediments is influenced by lithology, the grain-size distribution of the sediment matrix, sedimentation rate, and bioturbation (Bleil and von Dobeneck, 1999; Sagnotti et al., 2005). When assuming a steady sedimentation rate, the lock-in-depth result is a delay in magnetization that corresponds to the time required to accumulate a sediment layer equal to the lock-in-depth. For example, if the sediment has an accumulation speed of 1 mm/kyr and the lock-in depth is 10 mm, the magnetization age is 10 kyr younger than the actual sediment (Sagnotti et al., 2005).
Paleomagnetic analysis of magnetic reversals in cave sediments has been carried out in different locations around the world, including western Europe (Pares et al., 2018), South Africa (Nami et al., 2016), South America (Jaqueto et al., 2016), North America (Stock et al., 2005), southern Europe (Pruner et al., 2010), and eastern Asia (Morinaga et al., 1992). 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 the present study is to analyze the reversal using more detailed paleomagnetic methods and to identify the magnetic carrier of the cave sediment. Here, we obtained a new paleomagnetic dataset from three vertical sediment profiles in this cave. The contribution of the central European paleomagnetic record in cave sediment will be valuable for investigating the characteristic behavior of the Earth’s magnetic field during the Matuyama-Brunhes magnetic reversal. Because the sedimentation rate in the cave is not well understood, details of the timing of the transition are not yet known, making our estimation in this study even more crucial.