4.2. Sediment Deposition and Sedimentation Rate
According to Lundberg et al. (2014) the cave was filled with water
during the sedimentation which was continuously active without any
climatic change or hiatus. This provides the continuous magnetic record
of the reversal in the cave sediment and allows the sediment to acquire
and keep the primary magnetization without the possibility of secondary
mineralization. Also, there are no obvious marks in the studied sediment
section that one would expect if breaks in deposition (e.g. lithological
boundaries, desiccation cracks).
Our estimate of the Za Hajovnou cave’s sedimentation rate (0.2 cm/kyr –
1.0 cm/kyr) seems to be significantly lower than the sediments from
other studies (Sagnotti et al., 2010; Jin and Liu, 2011; Giaccio et al.,
2013; Liu et al., 2016; Okada et al., 2017). This is likely due to
contrasting sediment types. While the duration of the M/B transition was
reported to last between 4-13 kyr (Yamazaki and Oda, 2001; Suganuma et
al., 2010; Valet et al., 2014; Okada et al., 2017), the averaged
sedimentation rate of 0.6 cm/kyr in this study suggests transition
duration of 9.66 kyr (7.1-12.8 cm sediment transition depth section) and
thus strengthen our confidence to the reliability of our sedimentation
rate and paleomagnetic record estimates. Additionally, low sedimentation
rates (<1 cm/kyr) were reported in previous Matuyama-Brunhes
magnetic reversal studies (Clark, 1970; Love and Mazaud, 1997; Nowaczyk
et al., 2001).
Analyzes of cave sediments by paleomagnetism carried out in different
locations around the earth such as in Western Europe (Parés 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), Eastern Asia (Morinaga et al., 1992) showed that cave
sediments recorded magnetic reversals. Morinaga et al. (1992) suggested
a low sedimentation rate for the Western Japan cave sediments 1.6 cm/kyr
which shows a similar rate with our Central European cave sediment
estimation. King and Channell (1991) suggested that large ”lock-in”
depths are associated with interparticle rigidity and strength,
characteristic of clayey low accumulation rate sediments (<1
cm/kyr) which results in delays of magnetic acquisition. This shows that
magnetic polarity reversal could have a large (25 kyr) apparent age
offset between sediments with high and very low accumulation rates (King
and Channell, 1991).