2.1. Geology of the Cave
The Za Hajovnou cave (49° 40´ N, 16° 55´E) is a former sinkhole located in the Javoricko Karst in the Moravia region of the Czech Republic (Lundberg et al., 2014; Musil, 2014) (Fig. 1). The Javoricko Karst was formed from the dissolution of light-gray-colored massive Devonian limestone that overlies Precambrian phyllite (Lundberg et al., 2014; Musil, 2014). The Spranek and Javoricka Rivers flow through the karst. While Za Hajovnou cave is situated on the northwestern bank of the Javoricka River on the southern slope of Pani Hora hill (Lundberg et al., 2014; Žák et al., 2018), both the Spranek and Javoricka watersheds may have contributed to sediment development in this cave (Fig. 1c).
Za Hajovnou cave is an approximately 500-m-long system (Musil, 2005; Bábek et al., 2015). Previously, ~200 m of the cave was explored, and the cave currently consists of two main parallel corridors with slightly different sedimentological records (Musil, 2014; Musil et al., 2014) (Fig. 1d). One corridor (local name is “Excavated Corridor”, which used to be a sinkhole entrance) and the other corridor (local name is “Birthday Corridor”) have separate entrances, and they are connected by the Connecting Passage Corridor (Fig. 1d). Sediments from the Excavated Corridor continue to the Birthday Corridor and partially fill the Connecting Passage Corridor (Musil et al., 2014) (Fig. 1d).
The upper sediments in the cave (Fig. 2a and d) were dated by U/Th dating of flowstones from 118 ± 1 to 267 ± 3 ka, and the sediment spans the time of the Cromerian Interglacial Complex in northwestern Europe, which begins with the interglacial period of the marine isotope stage (MIS 19; 773 ka; Cohen and Gibbard, 2019) and the Matuyama-Brunhes reversal (Kadlec et al., 2005, 2014; Musil, 2005, 2014; Musil et al., 2014; Lundberg et al., 2014; Bábek et al., 2015; Žák et al., 2018).
The Matuyama-Brunhes boundary was identified (by Kadlec et al., 2005, 2014) in the upper part of the backwater fine sediments deposited from suspension (total thickness up to 4.3 m) in the flooded cave. These sediments underlie mostly nonfluvial deposits that enter the cave through a steep passage and fill the Connecting Passage Corridor (Kadlec et al., 2014; Lundberg et al., 2014; Musil et al., 2014).
The sedimentary sections studied by Kadlec et al. (2005, 2014) in the Excavated Corridor of Za Hajovnou cave were composed of two parts. The first part, which is 0.8 m thick (Section No. 1, in Fig. 1d) and located approximately 28 m from the cave entrance, was interpreted by Kadlec et al. (2014) to contain the Matuyama-Brunhes transition from reversed to normal polarity. This section corresponds to Bed Nos. 4 and 5 (Fig. 2d) in Profile 1 (Fig. 1d) of Kadlec et al. (2005). The second part, which is ~3.3 m thick (Section No. 2 (Profile 2 of Kadlec et al. (2005)), in Fig. 1d), underlies Section No. 1 and corresponds to the lower part in Profile 1 of Kadlec et al. (2005) (Fig. 2d). Kadlec et al. (2014) indicated that this section only contained sediment with reversed polarity. The interpretation of the paleomagnetic data was difficult because the magnetization of the sediments was too weak for the sensitivity of the Agico JR-5A spinner magnetometer. This difficulty was the motivation for the present research. Here, we collected 44 new oriented discrete sedimentary samples from the Excavated Corridor near upper backwater sedimentary Section No. 1 (Fig. 1d and 2).