Fig. 2. Map of the Za Hajovnou cave (modified after Kadlec et
al., 2014; Lundberg et al., 2014; Musil, 2014). Locations marked by
“Section No. 1” and “Section No. 2” are discussed in the text
(Kadlec et al., 2005, 2014). The map shows the relation between
Connecting Passage Corridor, Birthday Corridor, and Excavated Corridor
(m a.s.l.: meter above sea level).
Upper sediments of the cave were dated by U/Th dating of flowstones from
118 ± 1 to 267 ± 3 ka and the sediment sequence below was inferred to
contain the Matuyama-Brunhes boundary in Section No. 1 (Fig. 3) (Musil,
2005; Kadlec et al., 2005, 2014; Lundberg et al., 2014; Bábek et al.,
2015). The sedimentation in the cave corridors was active from the Early
Pleistocene until the beginning of the Middle Pleistocene. The sediment
then consists of Pleistocene glacial time in north-western Europe called
the Cromerian Interglacials complex (Muller, 1992), MIS19 (marine
isotope stage) which is interglacial period ~780 ka (Pol
et al ., 2019), and Matuyama-Brunhes reversal (Kadlec et al.,
2005, 2014; Lundberg et al., 2014; Musil, 2014; Musil et al., 2014; Žák
et al., 2018).
The Matuyama-Brunhes boundary (781 ka) was suggested in the upper part
of the backwater fine sediments, deposited from suspension in the
flooded cave. These sediments underlay mostly non-fluvial deposits which
entered the cave through a steep passage and filled the Connecting
Passage Corridor (Kadlec et al., 2014; Lundberg et al., 2014; Musil et
al., 2014). The total thickness of the sediments, deposited from
suspension, reaches up to 4.3 m.
Sedimentary sections retrieved in the Za Hajovnou cave by Kadlec et al.
(2005, 2014) were composed of two parts. The first part (Section No. 1,
in Fig. 2) was situated in the Excavated Corridor about 28 m from the
cave entrance (Kadlec et al., 2005) (Fig. 2). It was intepreted to
contain the magnetic transition from a reversed to normal polarity and
inferred from the age dates of the overlying non- fluvial sediments,
that our data indicate that the reversal is the actual Matuyama-Brunhes
reversal. Sediment thickness in the Section No. 1 is 0.8 m. The second
sedimentary section (Section No. 2) partially overlapped the Section No.
1 and was located in the Excavated Corridor (Kadlec et al., 2014) (Fig.
2). Kadlec et al. (2014) indicated that this section had sediment with
just reversed polarity except for the upper part of the sediment where
the magnetization was difficult to interpret because the sediments had
weak magnetization for which the sensitivity of the Agico JR-5A spinner
magnetometer was insufficient. Section No. 2 underlies the Section No. 1
and contains older backwater sediment with reversed magnetic polarity
(age > 781 ka) (Kadlec et al., 2014).
The difficulties in the interpretation of the primary study by Kadlec et
al. (2014) was the motivation for the presented research. Here we
collected 44 oriented discrete sedimentary samples from the Excavated
Corridor near the upper backwater sedimentary Section No. 1 (Fig. 2, 3).