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Pliocene to Holocene chronostratigraphy and palaeoenvironmental records from cave
sediments: Račiška pečina section (SW Slovenia)
Nadja Zupan Hajna, Andrej Mihevc, Pavel Bosák, Petr Pruner, Helena Hercman, Ivan
Horáček, Jan Wagner, Stanislav Čermák, Jacek Pawlak, Paula Sierpień, Šimon Kdýr,
Lucie Juřičková, Astrid Švara
PII: S1040-6182(21)00101-4
DOI: https://doi.org/10.1016/j.quaint.2021.02.035
Reference: JQI 8785
To appear in: Quaternary International
Received Date: 21 September 2020
Revised Date: 17 February 2021
Accepted Date: 19 February 2021
Please cite this article as: Hajna, N.Z., Mihevc, A., Bosák, P., Pruner, P., Hercman, H., Horáček, I.,
Wagner, J., Čermák, S., Pawlak, J., Sierpień, P., Kdýr, Š., Juřičková, L., Švara, A., Pliocene to Holocene
chronostratigraphy and palaeoenvironmental records from cave sediments: Račiška pečina section (SW
Slovenia), Quaternary International (2021), doi: https://doi.org/10.1016/j.quaint.2021.02.035.
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© 2021 Published by Elsevier Ltd.
Pliocene to Holocene chronostratigraphy and palaeoenvironmental records from cave 1
sediments: Račiška pečina section (SW Slovenia) 2
3
Nadja Zupan Hajna
a,
*, Andrej Mihevc
a
, Pavel Bosák
a,b
, Petr Pruner
a,b
, Helena Hercman
c
, Ivan 4
Horáček
d
, Jan Wagner
e
, Stanislav Čermák
b
, Jacek Pawlak
c
, Paula Sierpień
c
, Šimon Kdýr
b
, 5
Lucie Juřičková
d
, Astrid Švara
a
6
7
a
Karst Research Institute ZRC SAZU, Titov trg 2, 6230 Postojna, Slovenia 8
b
Institute of Geology of the Czech Academy of Sciences, Rozvojová 269, 165 00 Praha 6, 9
Czech Republic 10
c
Institute of Geological Sciences, Polish Academy of Sciences, ul. Twarda 55/58, 00-818 11
Warszawa, Poland 12
d
Department of Zoology, Faculty of Sciences, Charles University, Viničná 4, 128 45 Praha 2, 13
Czech Republic 14
e
Department of Palaeontology, National Museum, Václavské náměstí 68, 110 00 Praha 1, the 15
Czech Republic 16
* Corresponding author 17
E-mail address: nadja.zupan-hajna@zrc-sazu.si 18
19
Abstract 20
The sedimentological record in the Račiška pečina cave sediment sequence is one of the best-21
preserved cave records of palaeoenvironmental changes for the last 3.4 Ma. However, as it is 22
typical for cave terrestrial records, it contains many hiatuses in sedimentation. The section 23
study helped to change the state of knowledge and understanding of the long-lasting 24
deposition characteristics in the caves and provided enormous data on environmental changes 25
over time. In the sequence are by magnetostratigraphy well recorded Pliocene/Pleistocene 26
transition at 2.59 Ma, the Matuyama/Brunhes boundary at 0.773 Ma, and the presence of 27
Olduvai subchron between 1.78–1.925 Ma. Records of small mammals from the lower part of 28
the section (a molar of Apodemus cf. atavus and dental fragments of Borsodia sp., and 29
Pliomys sp.) suggest MN17 age, Clethrionomys cf. glareolus from the upper part suggests the 30
Late Early or Middle Pleistocene age. Also worth mentioning are records of snail shells 31
Aegopinella sp. and a troglobiont snail Zospeum sp. In the upper part of the section Ursus ex 32
gr. spelaeus was confirmed in the yellow clay layer older than ~72 ka, and soot material at the 33
top of the section was radiocarbon dated on ~11 ka, ~9 ka, and ~3 ka. A detailed chronology 34
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of the Račiška pečina section based on magnetostratigraphy and isotopic oxygen stratigraphy 35
was created and correlated with palaeontological, U-series, and radiocarbon results. The 36
climatic changes during the growth of the section were at about 2.6–2.5 Ma ago mostly 37
controlled by global Atlantic Ocean factors, while about 0.78 Ma ago by regional 38
Mediterranean Sea factors. 39
Keywords: Cave sediments; Dating, Climate changes, Pliocene/Pleistocene transition, 40
Matuyama/Brunhes boundary, Pleistocene fauna 41
42
1. Introduction 43
The work aims to summarize the results of the cave Račiška pečina (Fig. 1) sedimentary 44
section multiproxy research and to highlight its values for the Quaternary chronostratigraphy 45
and palaeoenvironmental records. Previously published results (Horáček et al., 2007; Zupan 46
Hajna et al., 2008, 2010, 2020; Pruner et al., 2009, 2010; Moldovan et al., 2011; Hercman et 47
al., 2019; Sierpień et al., 2021) are supplemented here with some recent results and 48
interpretations, as well as new data from unpublished research reports containing primary 49
analytical data (e.g. Pruner et al., 2008; Zupan Hajna et al., 2016). 50
Regarding the characteristics of karst areas where landscapes are exposed to chemical 51
denudation, cave sediments from different environments and hydrological zones are often the 52
only sediments representing the terrestrial phase of landscape evolution (e.g. Zupan Hajna et 53
al., 2020). Cave speleothems have been successfully used to obtain information on age and 54
palaeoclimate (e.g. Fairchild et al., 2006; Fairchild and Baker, 2012; Woodhead et al., 2010), 55
while allogenic sediments integrate sinking river catchment areas (e.g. Sasowsky and 56
Mylroie, 2004; White, 2007). When combined in caves, they have the enormous 57
chronological potential for understanding past events and the age of processes (e.g. Zupan 58
Hajna et al., 2008, 2020). 59
As a rule, the available cave sediments represent the youngest stage of sedimentary and 60
landscape evolution (e.g. Kukla and Ložek, 1958; Ford and Williams, 2007; Zupan Hajna et 61
al., 2020), just under favourable conditions, products of two or three of the last ones are 62
preserved (e.g. Horáček and Bosák, 1989; Bosák, 2002; Zupan Hajna et al., 2008, 2010, 63
2020). 64
Records in cave sediments covering the period of the last ~5 Ma years are not very 65
frequent, but in Slovenia, for example, we have a few cases (e.g. Bosák et al., 1998, 2000, 66
2002, 2004; Zupan Hajna et al., 2008, 2010, 2020; Häuselmann et al., 2015). The best-studied 67
sedimentary section with long-lasting depositional records is in the cave Račiška pečina (Fig. 68
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1) in the south-western part of Slovenia. The Račiška pečina sediment section (Fig. 2) 69
represents over 3 Ma of speleothem accumulation occasionally interrupted by infiltrated 70
sedimentary deposits with palaeontological remains (Horáček et al., 2007; Zupan Hajna et al., 71
2008, 2010, 2020; Pruner et al., 2010; Moldovan et al., 2011; Miko et al., 2012). In fifteen 72
years of research of this section, we have used a multiproxy approach: palaeomagnetism and 73
magnetostratigraphy, mineralogy, geochemistry, sedimentology, petrology, stable isotopes, 74
palaeontology, and dating. The main focus of our work was on the palaeomagnetic research of 75
the sediments, while numerical dating methods were used to improve the correlation of the 76
obtained palaeomagnetic results with GPTS (Cande and Kent, 1995; Grandstein et al., 2012; 77
Cohen and Gibbard, 2019), and palaeontological finds further contributed to the chronological 78
classification of the sediments. 79
Here we present an overview of geochronological and environmental studies of the 80
sedimentary sequence, covering the period from 3.4 Ma to the present, and of the 81
characteristics of sedimentation in cave environments with long-lasting depositional hiatuses. 82
83
2. Cave settings 84
The Račiška pečina (Reg. No. 935; 45°30´12,10˝N; 14°09´00,83˝E; 609 m a. s. l.) is 85
located in the south-western corner of Slovenia (Fig.1), which geographically belongs to the 86
NW edge of the Dinaric karst. Regarding climate conditions, the cave is located in the 87
transitional Mediterranean climate zone with an average annual temperature of about 10.4°C 88
and average annual precipitation of about 1,356 mm (http://meteo.arso.gov.si/). 89
From a geological point of view, the study area is located in the northwestern part of the 90
Dinarides, in the collision zone between the Adria microplate and Eurasia. The tectonic 91
evolution was largely controlled by the rotations of Adria (e.g. Handy et al., 2010), 92
consequently, the formation of the present relief was under influence of its CCW rotations 93
during the last 6 Ma. The northeastern microplate corner is bounded by the E–W-striking 94
South-Alpine and NW–SE-striking Dinaric thrust belts and cut by dextral strike-slip faults 95
(Vrabec and Fodor, 2006). The cave is formed in thick-bedded limestones and dolomite with 96
limestone breccias of the Lower Cretaceous, the beds dipping towards the north-east at an 97
angle of up to 30° (Šikič et al., 1972). From the cave towards the blind valleys (Fig. 1) there is 98
a succession of Lower Cretaceous limestones, dolomites, and their breccias through Upper 99
Cretaceous limestones and dolomites to Paleocene and Eocene limestones, all deposited under 100
different environments of the Adriatic Carbonate Platform. The marine carbonate 101
sedimentation ended with an onlap of Eocene flysch deposition. The wider region has the 102
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character of an anticlinorium (Placer, 1981), cut by numerous faults, reflect the multiphase 103
kinematic evolution since Cretaceous (Jurkovšek et al., 1996). Based on the regional geology 104
and the morphology of the cave passage, it can be assumed that the carbonate layers were 105
already folded when the cave and its associated passages (channels) were active. 106
107
Fig. 1. Here. 108
109
The cave genesis has been associated with the evolution of local contact karst 110
characteristics (Mihevc, 2001, 2007). The cave is part of a relict cave system formed by 111
allogenic streams flowing from the Eocene Flysch with ponors at about 630 m a.s.l. (Fig. 1). 112
The cave functioned as part of a channels network, which included the now unroofed cave 113
Ulica and the connected cave Ulica pečina (Zupan Hajna et al., 2008), that transferred water 114
flow towards the springs. The gradient in the karst was low and the cave was at one time filled 115
with fluvial sediments and shaped by paragenesis. The cave was deep below the karst surface 116
during this time. Traces of phreatic (large cupolas and scallops), paragenetic and epiphreatic 117
speleogenesis are still preserved in the cave. Allogenic material present in some places 118
consists of weathered flysch remains (Zupan Hajna et al., 2008; e.g. quartz, muscovite/illite, 119
chlorite, kaolinite, and feldspars). The transition to the vadose zone resulted in the 120
exhumation and internal redistribution of the allogeneic cave fill and the beginning of the 121
growth of massive speleothems (large domes and stalagmites) on allogeneic deposits. Signs of 122
corrosion and erosion are visible on some of the oldest speleothems, possibly due to exposure 123
to floodwaters, but no allogenic sediments were found between the flowstone layers. 124
However, infiltrated clay- and silt-sized material is present between flowstone and other 125
speleothem layers, containing very similar minerals to the allogenic sediments, but enriched 126
in calcite, derived from weathered limestone and speleothem debris. 127
Before the studied speleothem dome (Fig. 2) began to grow under vadose zone conditions, 128
the cave was already disconnected from its hydrological function due to regional tectonic 129
uplift (Mihevc, 2007), and allogenic sediments were mostly eroded, but the cave remained 130
closed to direct ventilation. The cave was later opened by chemical denudation of the 131
overlying host-rocks and retreat of slopes towards the surface; with an average karst 132
denudation rate of 20–60 m/Ma (Mihevc, 2001) in the region, this occurred in the last 0.5 Ma. 133
After the opening of the present entrance, cave bears began to enter the cave. 134
The recent ponors conveying water from the flysch through the subsurface to the springs 135
are located at an elevation of about 500 m a.s.l.; the underground water connections to the 136
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springs at the Adriatic Sea were confirmed by tracer test (Krivic et al., 1989). The phreatic 137
conduits are located now about 150 m below Račiška pečina. Two of the sinking streams are 138
currently located only 2.5 km north and northeast of the cave (Fig.1). The largest flows into 139
the blind valley Račiška dana and sinks in the cave Račiške ponikve at about 480 m a.s.l. and 140
continues towards the springs. 141
142
Fig. 2. Here. 143
144
The entrance to the 304-meter-long cave passages is open to the north/northeast (Fig. 2). 145
The cave consists of a simple horizontal, N–S-directed passage that is a relic of an old cave 146
system partially opened to the surface. The passage is mostly over 10 m wide and 5–10 m 147
high. On the southern side, the passage ends with the breakdown material. Skeletal remains 148
(teeth, bones) and footprints were found on the cave floor, and scratch marks of the extinct 149
Ursus spelaeus sp. were found on the cave walls and speleothems (Mihevc, 2003). In the first 150
half of the 20th century, the cave was used as a military magazine. The sediments in the floor 151
of the cave were disturbed and mostly relocated. The cave floor was levelled and some large 152
trenches were made in old massive speleothem domes. Our studied section is located in one of 153
the trenches about 200 m from the cave entrance (Figs. 2 and 3A). Prior to military use of the 154
cave, biologists visited the cave and discovered cave beetles (Verhoeff, 1933). Although the 155
cave was remodeled and used as a military object for decades, it is still quite rich in 156
subterranean fauna (e.g. Polak et al., 2012). 157
158
159
3. Material and methods 160
The research covered a sedimentary section about 13 m long and 3 m high (Figs. 2 and 3), 161
consisting of flowstone layers intercalated by clay layers, in which paleontological material 162
was also present. The section was hewed out in speleothem sometime after 1933. The 163
speleothem layers were deposited from at least two sources of percolating water, from the S 164
and N of the section (Figs. 2 and 3), while the incorporated stalagmites and the uppermost 165
column were deposited by dripping water from the cave ceiling. 166
167
Fig. 3. Here. 168
169
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The section (Figs. 2 and 3) consists vertically of three main segments, and the thickness of 170
the composite sample was 6.34 m (Zupan Hajna et al., 2008, 2020). The lowest section 171
segment, located in the N part (coloured light brown in Fig. 3), is up to 180 cm high and 172
represents the growth stages of a large stalagmite dome. It consists of brown and reddish-173
brown, massive, porous speleothem layers with interlayers of red clay sediments (mostly 1–2 174
cm thick). Its accessible lowermost part ends with a distinct unconformity. The lowest layers 175
of the section could not be accessed due to the presence of concrete installations in the cave 176
floor. The middle segment (coloured white in Fig. 3) of the section is up to 368 cm high in the 177
central and S parts of the section, while it is up to 180 cm high in the N part. This segment 178
consists of laminated porous flowstone, densely interbedded with red clays (1 mm to 10 cm 179
thick). At the base of this segment are huge blocks of breakdown material and faunal remains 180
in the deposited silty clay. The most upper segment (up to 96 cm high; coloured light green in 181
Fig. 3) is represented by light-coloured, massive, laminated speleothem layers with two 182
intercalations of greyish-brown/yellow clays with cave bear bones. 183
Horizontally, at the bottom of the N part of the section huge speleothem dome is present. 184
This lowest dome stops growing at the end of the Pliocene/Pleistocene transition (Zupan 185
Hajna et al., 2008; Sierpień et al., 2021). Above this dome, the section is divided into two 186
parts by the stalagmite growing on the red clay layer, which represents the palaeomagnetic 187
sample A (Fig. 3B). Above this layer, the two parts of the section had a different evolution. 188
The S part represents the flowstone layers and rimstone pools above the breakdown material, 189
and the N part represents the layers with large bones in yellow clay at the top of the section. 190
The difference between these two parts is due to the different water sources that provided the 191
water for the growth of the flowstone layer. The S part had a more constant and larger water 192
inflow than the N part, which can be concluded from the presence of three layers of rimstone 193
pools which are filled with red clay, and from the higher number of flowstone layers. 194
The whole section is covered by younger speleothems: two stalagmite domes and a 195
column in the S part and a large stalagmite dome in the N part. On the section surface, above 196
the top of the dome is a 1.5 m high opening to the cave ceiling, parts of the broken pottery 197
were found by our team. The pottery still lies on micro and mezzo calcite gours which are 198
now dry. It appears that the gours are dry for a long time because the pottery is loose and not 199
attached by calcite in them. The pottery seems to date from the Bronze Age or later, but 200
younger than Roman. 201
202
3.1. Magnetic properties 203
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Flowstone layers were collected in narrow oriented cut slices or small blocks (Fig. 3B). 204
Samples were oriented and macroscopically described in the field. The unconsolidated clastic 205
sediments (clay, silt) were sampled in non-magnetic plastic cubes in a high-resolution profile 206
with cm-spaced sampling intervals. Cores were drilled using a HILTI DDEC-1 drill, equipped 207
with a 1-inch, diamond core drill bit, and later cut into 2.1 cm long specimens on the top left 208
and right speleothem dome and in the central column base. The orientation of the specimens 209
was performed using a standard compass-inclinometer to obtain the azimuth and dip of the 210
samples. 211
Palaeomagnetic and rock magnetic properties were determined at the Department of 212
Palaeomagnetism, Institute of Geology, Czech Academy of Sciences (Inst Geol, Czech Acad 213
Sci) in Průhonice. The natural remanent magnetization (NRM) was measured on JR-6A 214
spinner magnetometers and/or the 2G Superconducting Rock Magnetometer with 215
incorporated alternating field (AF) unit and the volume magnetic susceptibility (MS) was 216
measured using an AGICO KLF-4 magnetic susceptibility meter. Measurements of the 217
anisotropy of the low-field magnetic susceptibility (AMS) were performed throughout the 218
section as a complementary technique to magnetostratigraphy. The AMS was measured with 219
an Agico KLY-4S Kappabridge with an AF intensity of 300 A/m and an operating frequency 220
of 875 Hz. The AMS of any rock is dependent on the intrinsic MS, volume fraction, and 221
degree of preferred orientation of the individual rock-constituent minerals (Jelínek, 1973). 222
Samples were demagnetized by the AF and/or by thermal demagnetization (TD) using the 223
MAVACS (Magnetic Vacuum Control system; Příhoda et al., 1989) equipment. The LDA-3 224
and/or 2G apparatus were employed for the AF demagnetization (for a detailed description 225
see Zupan Hajna et al., 2008). 226
The characteristic remanent magnetization (ChRM) of each sample was determined by 227
subjecting its demagnetization results to the principal component analysis technique of 228
Kirschvink (1980) and the computer program Remasoft 3 (Chadima and Hrouda, 2006). 229
Sequences with the best magnetostratigraphic results were subdivided into segments 230
corresponding to N and R polarities of the palaeomagnetic field, solely based on the analysis 231
of the natural remanent magnetization (NRM) directions determined for the individual 232
samples collected from the section. The identification of the detected polarity zones is directly 233
related to the Earth's magnetic field and can be fitted against the sequence of polarity intervals 234
given by the Geomagnetic Polarity Timescales (GPTS; Cande and Kent, 1995; Gradstein et 235
al., 2012; Cohen and Gibbard, 2019). 236
237
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3.2. Palaeontology 238
Samples for palaeontological analysis taken at 4 main clay horizons were published by 239
Horáček et al. (2007) and 4 samples for fossil invertebrate fauna were analysed by Moldovan 240
et al. (2011). Another 10 samples of clay material were taken in 2019 for a more accurate 241
correlation with numerical and correlative dating results (Fig. 4); new specimens of bones of 242
large mammals were found in the yellow clay layer of palaeomagnetic sample C (Fig. 3B). 243
244
Fig. 4. Here. 245
246
After washing and sieving, small vertebrate fossils were extracted and identified. Fossil 247
samples were studied on CAMECA 100 microprobe (Inst Geol, Czech Acad Sci, Prague) and 248
JEOL 6386 scanning electron microscope (Faculty of Science, Charles University, Prague). 249
The bear bones and the tooth were measured by digital caliper, photos were made by digital 250
camera SONY α7RIII (National Museum, Prague). Measurements were taken according to 251
Fosse and Crégut-Bonnoure (2014: fig. 4) for the juvenile femur, Grandal d’Anglade (1993) 252
for calcaneus, and Alscher (2015) for the terminal phalanx. 253
254
3.3. Radiocarbon analyses 255
Organic matter separated from black laminae in speleothems was analyzed by the 256
radiocarbon AMS method at the Poznań Radiocarbon Laboratory, Poland (Goslar et al., 257
2004). Speleothems fragments with black layers were subjected to a typical chemical 258
procedure “acid-alkali-acid” (AAA) which is commonly used for most types of organic 259
samples (see description in Brock et al., 2010). 260
Carbon dioxide produced by sample combustion in closed (sealed under vacuum) quartz 261
tubes, together with CuO and Ag wool, at 900°C was dried in a vacuum line and reduced with 262
hydrogen with Fe powder as a catalyst. The obtained mixture of carbon and iron was then 263
pressed into a special aluminium holder (Czernik and Goslar, 2001). Standard samples, 264
samples not containing
14
C (coal), and international modern
14
C standard (Oxalic Acid II) 265
were prepared in the same manner. The
14
C content in a sample of carbon was measured on a 266
“Compact Carbon AMS” spectrometer (National Electrostatics Corporation, USA). The 267
conventional
14
C age was calculated using a correction for isotopic fractionation (Stuiver and 268
Polach, 1977) based on the
13
C/
12
C ratio measured by the AMS spectrometer simultaneously 269
with the
14
C/
12
C ratio. The reported errors are 1 standard deviation and are the best estimate of 270
the total uncertainty of measurement. Conventional radiocarbon ages were calibrated by 271
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OxCal 4.4.2 software (Bronk Ramsey, 1995, 2001, 2009, 2020) and the InCal20 calibration 272
curve (Reimer et al., 2020). 273
274
3.4. U-series 275
The samples for U-series dating using mass spectrometry were between 0.1 g and 0.5 g. 276
Chemical separation of uranium and thorium from the carbonate matrix by the 277
chromatographic method with TRU-Resin (Hellstrom, 2003) was performed at the U-series 278
Laboratory of the Institute of Geological Sciences of the Polish Academy of Sciences in 279
Warsaw. Mixtures of
233
U-
236
U-
229
Th, calibrated by uraninite analysis in secular equilibrium, 280
were used as a chemical procedure and isotopic fractionation control. The isotopic 281
composition of U and Th was measured at the Inst Geol, Czech Acad Sci in Prague, using a 282
double-focusing sector-field ICP mass analyser Element 2 (Thermo Finnigan MAT). The 283
measurement results were corrected for counting background and chemical blank. The 284
internal standard sample and blank sample were prepared simultaneously for any series of 285
studied samples and were used for necessary corrections and quality control. 286
We have also sampled speleothem layers from the section that should be older than 1 Ma 287
and given them to our colleagues at the University of Bergen, Norway (sampled in 2008) and 288
at the University of Melbourne, Australia (sampled in 2015) for U-Pb dating, but have not yet 289
been successful. 290
291
3.5. Stable isotopes 292
Samples for δ
13
C and δ
18
O analyses were drilled by Dremel drill with a bit diameter of 0.7 293
mm. All samples were taken at approximately 5 mm from the profile base, producing 375 294
samples (Sierpień et al., 2021). Analysis of carbon (C) and oxygen (O) isotope composition 295
(δ
13
C, δ
18
O) in carbonates were performed using Thermo Scientific equipment, KIEL IV 296
Carbonate Device coupled to Delta Plus IRMS using a dual inlet system. Sample preparation 297
was carried out automatically. About 100 μg of calcite reacted with anhydrous 298
orthophosphoric acid at 70°C for 5 minutes. The isotope composition of released CO
2
is then 299
measured using a mass spectrometer. The results were normalized to three international 300
standards NBS 19, NBS 18, and IAEA CO 8, and were reported relative to the V-PDB 301
international standard. Analytical precision (1σ) is better than 0.03 ‰ and 0.08 ‰ for δ
13
C 302
and δ
18
O, respectively. The reproducibility was checked by measurement of two internal 303
standards after every 12 samples (for δ
13
C: ± 0.03 ‰, for δ
18
O: ± 0.08 ‰). The analyses were 304
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performed in the Stable Isotope Laboratory (Institute of Geological Sciences, Polish Academy 305
of Sciences) in Warsaw. 306
307 4. Results and interpretations 308
As already mentioned, in this paper we summarize all published, unpublished and new 309
results on palaeomagnetism, palaeontology, mineralogy, age, and palaeoenvironmental 310
records of cave sediments from the Račiška pečina section. 311
312
4.1. Palaeomagnetism and magnetostratigraphy 313
Standard analytical procedures for the detection of palaeomagnetic properties were used 314
(see Zupan Hajna et al., 2008): TD for solid samples; and AF demagnetization for samples 315
both for solid (speleothem) and unconsolidated samples (clays). The data were at the high-316
resolution character with the distance between samples only a few centimetres. The mean 317
palaeomagnetic values and standard deviations (J
n
and k
n
moduls values) were published in 318
Zupan Hajna et al. (2008). Samples were characterized by very low up to very high J
n
and k
n
319
magnetic values. According to both values, the section may be divided into five segments and 320
categories. Sediments were characterized by a large scatter of NRM intensities (0.2–2,720 321
mA/m) and the MS values (-9–2,140 × 10-6 SI units). Multi-component analysis of the 322
remanence of 211 samples displayed a three-component RM. The A-component is undoubted 323
of viscous (weathering) origin and can be demagnetized in a temperature range of 20 to (60) 324
120°C. The B-component also had a secondary origin but had shown harder magnetic 325
properties which were demagnetized in a temperature range of about 120 to 360°C. The C-326
component was the most stable, with demagnetization in a temperature range of about 400 to 327
560°C. The Fisher distribution displays two defined sets of the samples with N and R 328
polarities. The mean palaeomagnetic directions of C-components with normal polarity were D 329
= 352°, I = 67°, and for reverse polarity are D = 180°, I = -64°. From the published and 330
reviewed data new detailed magnetostratigraphic profile was constructed (Fig. 5) where the 331
magnetostratigraphic profile was correlated with the GPTS (Cande and Kent, 1995; Gradstein 332
et al., 2012) and calibrated by palaeontological data (Horáček et al., 2007). 333
334
Fig. 5. Here. 335
336
The lower part, according to fauna determined in the middle part above, was dated from 337
~3.4 Ma at the bottom up to 2.595 Ma at its top, i.e. Pliocene/Pleistocene boundary. In the 338
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middle part, the boundary of N- and R-polarized magnetozone within the basal layer with 339
fauna (F) can be identified with the bottom of the C2n Olduvai subchron (1.925 Ma). The 340
sequence represents the whole Olduvai subchron and terminates at 1.78 Ma. At the beginning 341
of the upper part sample, RP 66 holds an excellent record of the Matuyama/Brunhes (M/B) 342
magnetic reversal; the reversal zone in the thickness of 6 mm was detected by high-resolution 343
palaeomagnetic analysis (Hercman et al., 2019). The work on the Matuyama/Brunhes 344
boundary climatic condition is still in progress. The most upper part of the section has normal 345
polarity. 346
On the top of the section, three cores (RK1, RK3, and RK5) were drilled into speleothem 347
domes and columns (see in Fig. 3). The mean palaeomagnetic directions of the samples from 348
boreholes were calculated (Table 1), while their dating is still in progress. 349
350
Table 1. Here 351
352
All palaeomagnetic samples from cores RK1 and RK3 express normal polarity (N). All 353
samples from core RK5 are reversal (R). Palaeomagnetic samples RK5, RK5A, R5KB 354
declination correspond to inverse polarity, but with very low inclination; RK5C declination 355
corresponding to normal polarity, but has the highest value of negative – R inclination. 356
Anomalously high values of NRM and MS are in the sample RK5A (R polarity), although it 357
has a relatively low inclination. 358
Given the fact that the cores have not yet been dated, the reversal can correspond to any of 359
the excursions during Brunhes, but in terms of correlation with the dated U-series sample in 360
the RP 1 slice (~120 ka) from the nearest layer (Fig. 3B), the reversal most likely corresponds 361
to one of 17 to 41 ka excursions (Singer, 2014; Laj and Kissel, 2015). 362
363
4. 2. Palaeontology 364
All thicker clay layers of the section were examined for faunal remains. Previously 365
published results (Horáček et al., 2007) contributed to match the obtained 366
magnetostratigraphic profile with the GPTS (Cande and Kent, 1995; Gradstein et al., 2012) 367
and to interpret the cave environment (Moldovan et al., 2011). New material was sampled in 368
2019 and the results are presented below. The locations of the collected palaeontological 369
samples are in Figure 3. 370
The bone fragments of Ursus spelaeus were found in yellow-grey clayey sediments 371
(Horáček et al., 2007) in the upper part of the section (C in Fig. 3). The middle part of the 372
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section consists of sub-horizontally laminated, mostly porous flowstones intercalated by 373
calcite rimstones and thick layers of red clay. They contained rare fauna remains (F in Fig. 4) 374
mostly composed of small fragments of tooth enamel (Horáček et al., 2007). Among the non-375
mammalian remains were ?Potamon (Crustacea) and teeth of a cyprinid fish, most likely 376
Barbus sp. Mammals were represented by Rodentia (incl. ?Borsodia), Apodemus (Sylvaemus) 377
sp.. In the F sample (Horáček et al., 2007) Clethrionomys and Borsodia were identified. 378
Moldovan et al. (2011) found the palaeontological remains just in their sample R4 (in Fig. 4) 379
which correlated with the position of the palaeomagnetic sample RP51–52 (Figs. 3B and 4). 380
There were Oribatida invertebrates (genera Oppiella, Miracarus, and Suctobelbella) 381
inhabiting forest litter, shrublands, ecotone zones and grasslands, and vertebrates indicating 382
both arboreal and steppe habitats, typical habitats for Clethrionomys and Borsodia. The latest 383
results are presented here. 384
385
4.2.1. Ursids 386
Bones of large mammals were collected in clays (Figs. 3 and 4) of palaeomagnetic 387
samples C below II (sample C II), and at top of the B (sample B). 388
The most relevant finds were yielded by sample C II (Fig. 6). Except for the figured 389
specimens, there were some additional small bone fragments of a juvenile bear. From the top 390
of the B layer (sample B), two small rib fragments were obtained. If they belong to a cave 391
bear, they represent a neonate individual, much younger than those from layer C, but we were 392
unable to determine them with certainty. 393
394
Fig. 6. Here. 395
396
4.2.1.1. Taxonomic determination 397
Only three specimens are, at least partially, useful for taxonomical interpretation. 398
Fragment of d4 (Fig. 6.4) bears a small mesial metastylid. This secondary cusp is sometimes 399
present in the milk teeth of Ursus ex gr. spelaeus (Pappa, 2014; Sabol, 2019) but seems to be 400
missing or only very rarely present (we have only limited knowledge about phenotypic 401
variability in brown bear milk teeth) in U. arctos (cf. Baryshnikov and Averianov, 1992). The 402
size and general morphology of calcaneus (Fig. 6.2) fit well with the situation in Ursus ex gr. 403
spelaeus (see e.g. Altuna, 1973; Torres Perez-Hidalgo, 1988). The terminal phalanx (Fig. 6.3) 404
has spelaeoid morphology (see e.g. Koby and Schaefer, 1960; Tores Perez-Hidalgo, 1988). It 405
is possible to summarize that the available morphological evidence supports the assignment of 406
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studied specimens to large cave bears (Ursus ex gr. spelaeus) and, on the other hand, the 407
present material does not bear any characters which would be diagnostic for brown bears. 408
This determination is supported also by the finding circumstances. 409
410
4.2.1.2. Age and number of individuals 411
Discussing the possible individual age of preserved juvenile specimens, it is necessary to 412
have in mind, that it is very approximatively determined due to large individual size 413
variability in ursids, missing detailed knowledge about the ontogenetic development in extant 414
U. arctos/U. maritimus, the fragmentary fossil record, etc. Teeth eruption sequences in cave 415
bears are either supposed to be the same as in extant brown bears (e.g. Debeljak, 1997) or 416
somewhat quicker (e.g. Veitschegger et al., 2019). Debeljak (1997), who follows the brown 417
bear model, stated that d4 is fully erupted ca. in the second month of life and is lost/replaced 418
in the seventh/eighth-month latest. So, if we supposed that the fragment of d4 was still in 419
place when the animal died, we could propose age 8 months or less (which is more probable) 420
for this individual. 421
There are only limited data concerning the correlation of femur size and individual age 422
(see e.g. Ehrenberg, 1964; Fosse and Crégut-Bonnoure, 2014). The studied femur is larger 423
than that one from Bärenhöhle in Hertlesgraben (Austria) for which Ehrenberg (1964) 424
supposed age of 7 months (but it can be somewhat younger – comp. Debeljak, 1997; Fosse 425
and Crégut-Bonnoure, 2014; Germonpré and Sablin, 2001). When available data of size 426
development in the femur (and humerus) are taken into consideration, the age around 10 to 12 427
months seems to be plausible. It is possible, that the cub died during the first hibernation 428
season. The fusion of both epiphyses of the femur is rather late in brown bears (Weinstock, 429
2009) and a similar sequence can be supposed also for cave bears. It is therefore not in 430
contradiction with our age estimation but also does not yield any additional information. 431
Calcaneus is large. Even with the missing posterior part (which, on the other hand, does not 432
change the maximal length fundamentally), it reaches the maximal length of a (smaller) adult 433
individual (see e.g. Kavcik and Rabeder, 2004). We do not know any data about calcaneus 434
size changes during ontogenetic development. According to Weinstock (2009), the fusing in 435
calcaneus of brown bears starts in the third year of life earliest. At the moment, we are not 436
able to propose any individual age for this bone. 437
The other ursid specimens from sample C II (isolated epiphysis or diaphysis and rib 438
fragments, etc. – all of them of small size, never fused) represent a young individual. They 439
probably belong to an individual one-year-old or somewhat younger. It is probable, that the 440
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d4 belongs to an individual slightly younger than that one represented by the femur. But the 441
possibility that both remains represent the same individual cannot be unequivocally excluded. 442
Although without real evidence, we supposed that the size of the calcaneus is too large to 443
belong to a bear cub about 1-year-old. But a detailed analysis of the ontogenetic development 444
of calcaneus would be necessary to confirm this assumption. It seems that at least 2, maybe 3 445
individuals are recorded in yellow clay layer C. 446
447
4.2.2. Small mammals 448
The record of small mammals is restricted to a set of very small and heavily corroded 449
bone fragments, in three sites (PONV, RD1, F2 in Fig. 4) including minute enamel fragments 450
of rodent incisors and five fragments of rooted arvicolid molars: four from the upper part of 451
the sections (PONV, RD1), one from F2. The best-preserved item comes from the site PONV: 452
it represents a lingual wall of a small-sized M3 showing the initial stage of root development 453
(Figs. 7.1a–1b). In metrical characters, the shape of particular occlusal triangles with deeply 454
postvergent synclines (in terms of Rabeder, 1981) and a derived form of posteroconid 455
complex the tooth conforms well the situation in extant Clethrionomys glareolus (see 456
Kryštufek et al., 2020 for nomenclatural details) or the Middle Pleistocene forms closely 457
related to it (such as Clethrionomys acrorhiza). The forms of the genus appearing in the 458
MN17 or Q1 assemblages lack the distal occlusal triangle and a deep postvergent synclinal 459
pattern obvious in the present specimen (comp. e.g. Rabeder o.c.). 460
Out of three enamel fragments obtained from RD1 and examined for the pattern of enamel 461
microarchitecture with aid of SEM, a fragment of the distal wall of m1 provided a relevant 462
picture (Figs. 7.2a–2d): (i) an inner layer composed of a dense radial enamel of narrow 463
columnar prisms reaching from one third to nearly a half of total enamel thickness, sharply 464
alternated with (ii) a layer of thin lamellar enamel of transversal orientation with dispersed 465
interprismatic matrix at distal enamel zone which towards the enamel surface takes the 466
appearance of (iii) a rather thick layer of compact glass-like aprismatic enamel. The 467
transitional zones between neighbouring enamel layers, which at the same time markedly 468
differ in their prismatic pattern, are more or less gradual. In all these characters as well as in 469
proportions of particular layers the fragments understudy correspond quite well to the 470
situation characteristic for Clethrionomys glareolus. A rather small enamel fragment from the 471
site F2 (Figs. 7.3a–3c), supposedly originating from a lingual wall of M3 posteroconid, seems 472
to exhibit certain differences from the above-surveyed pattern. A well-marked zone of 473
lamellar enamel (situated at the inner third of the enamel thickness) is formed by rather thin 474
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prisms with filamentary extensions and show a distinct prism decussation. The aprismatic 475
layer is restricted to the surface margin while the whole outer enamel zone composing almost 476
a half of enamel coat thickness is formed by dense radial prisms with frequent anastomoses. 477
Compared to the inner zone of radial enamel, the amount of interprismatic matrix is much 478
lesser, and the overall pattern is distinctly more compact. These characteristics, as well as the 479
supposedly larger size of the tooth, conform better to representatives of the genus Pliomys 480
than to Clethrionomys (or other arvicolid genera). The respective genus is a constant element 481
of the MN16–Q1 assemblages (Pliomys episcopalis, P. hungaricus, P. simplicior, P. 482
hollitzeri, etc.; see Rabeder (1981) for details), the extant member of that clade (Dinaromys 483
bogdanovi) is an endemic of the SW Balkans and was recorded even in several Late 484
Pleistocene sites of Slovenia (Horáček, unpublished). 485
486
Fig. 7. Here. 487
488
All items obtained from the upper part of the Račiška pečina section seem to belong to 489
Clethrionomys glareolus or a form closely related to that extant species. The respective 490
species ranks among the most common member of small ground mammal communities from 491
the late Early Pleistocene (Q2 sensu Horáček and Ložek, 1988) to Recent. It is an index 492
element of woodland habitats, quite characteristic for the interglacial assemblages throughout 493
Europe. The fragment from F2 can be tentatively attributed to the genus Pliomys, in which 494
major radiation appeared during the earliest Pleistocene (MN17–Q1). 495
496
4.2.3. Gastropods 497
Gastropods, their fragments, and imprints were found in 3 samples of red silty clays 498
correlating with paleomagnetic samples (Figs. 3B and 4): PONV (left of RP 20–22), RP 51–499
52, and F2 (including paleomagnetic samples RP 59–65; also the upper part of F from 500
Horáček et al., 2007, and R2 from Moldovan et al., 2011). In sample PONV (left of RP 20–501
22) were found fragments (ca 11 pcs) of Zospeum sp. (?Zospeum cf. exiguum) and 1 pc of 502
Aegopinella sp. In sample RP 51–52 were found 2 specimens of Zospeum sp. (?Zospeum 503
alpestre); and in sample F2, were found 3 imprints and 1 specimen (juv.) of Zospeum sp. For 504
nomenclatural details see Bole (1974) and Jochum et al. (2015). Characteristic findings of 505
gastropods are shown in Figure 8. 506
507
Fig. 8. Here. 508
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509
In the studied samples were present specimens and fragments of troglobiotic snails of the 510
genus Zospeum sp. (Figs. 8A, 8C, 8D). Regarding their location among the section and facts 511
that all clay layers were covered by younger speleothem layers, that dome was cut and 512
exposed to the cave after 1933, and their imprints in sediments, we believe that they are fossil 513
ones. But that should be studied more in detail in the future. The authors believe that these are 514
the first fossil subterranean snails founds in general and because of that, important to notice. 515
Therefore, their determination and comparison were not possible in such a short time. Genus 516
Zospeum represents subterranean animals living in caves, mostly of Dinaric karst, where some 517
species are endemics (e.g. Bole, 1974). Also from the RPC, the find of recent Zospeum sp. 518
was reported (Polak et al., 2012). These subterranean snails are most often found on moist 519
speleothems and cave walls, especially where rainwater rich with organic material seeps from 520
the surface. If the water flow is too high, they can be washed from the speleothems as detritus, 521
and their shells can accumulate in cave clastic deposits (clay, silt). Specimens and their 522
fragments present in the clays prove that they were washed down the speleothems by the 523
water of higher energy, which also brought the clay sediments into the cave and deposited 524
them between speleothem layers. 525
The other gastropod found in sample PONV was Aegopinella sp. (Fig. 8B), which is a 526
genus of small, air-breathing land snails that are not living in the cave. They can be brought 527
into the cave by percolating water from the surface above the cave. Its presence and 528
undamaged shell in the clay of the PONV sample confirm that clays were brought from the 529
surface (now about 40 m above the cave; Fig. 2A) by percolating (infiltrating) water. 530
531
4.3. Radiocarbon ages 532
Three samples of speleothem layers from the top of the section were selected for 533
radiocarbon dating. Dated were dark layers, that most probably the soot, from the 534
palaeomagnetic samples (slices) RP I (Figs. 3A and 9) at the top of the section below the 535
speleothem column, and RP II at the top of the section close to the N speleothem dome (Figs. 536
3B and 9). 537
538
Fig. 9. Here. 539
540
From the palaeomagnetic sample RP I, a dark-coloured top was removed (about 2 mm) 541
and below the layer of about 1 cm thickness was analysed (Fig. 9C). Results (Table 2) have 542
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given uncalibrated age 11,360±130 BP; and calibrated age (2σ range) 13,471–12,986 cal BP 543
(95.4%). From palaeomagnetic sample RP II, two samples were analysed. In the zone of 2–544
2.5 cm, thick dark layers (there were 3 main ones and a few thin ones) the sample marked RP 545
II/1 (Fig. 9B) was analysed. Results have given conventional age 9,050±110 BP; and 546
calibrated age (2σ range) 10,513–9,793 cal BP (95.4%). In the upper part, approx. 5 cm below 547
the top of the section is the zone with dark layers from there is analysed sample marked 548
RPII/2 (Fig. 9C). Results (Table 2) have given conventional age 3,280±40 BP; and calibrated 549
age (2σ range) 3,607–3,402 cal BP (95.4%). 550
551
Table 2. Here 552
553
4.4. U-series ages 554
The U-series ages, presented in Table 3, were calculated iteratively from the
230
Th/
234
U 555
and
234
U/
238
U activity ratios, and are given herein with the two standard deviations error limit 556
(confidence level of at least 95.4%). Age errors do not include uncertainties related to the 557
decay constants. Corrected ages were adjusted for detrital contamination indicated by the 558
presence of
232
Th using the typical silicate activity ratio
230
Th/
232
Th of 0.83 (±0.42) derived 559
from the
232
Th/
238
U activity ratio of 1.21 (±0.6),
230
Th/
238
U activity ratio of 1.0 (±0.1), and 560
234
U/
238
U activity ratio of 1.0 (±0.1; cf. Cruz et al., 2005). The initial value of the
234
U/
238
U 561
activity ratio (Table 3) was calculated based on the corrected activity ratio and sample age. 562
563
Table 3 Here. 564
565
Calculations used the decay constant of Jaffey et al. (1971;
238
U), Cheng et al. (2013;
234
U 566
and
230
Th), and Holden (1990;
232
Th). Ages do not include uncertainties associated with decay 567
constants, and AR is an activity ratio. Corrected ages using typical silicate activity ratio 568
230
Th
/232
Th = 0.83±0.42 derived from the
232
Th/
238
U activity ratio = 1.21±0.6,
230
Th/
238
U 569
activity ratio = 1.0±0.1, and
234
U/
238
U activity ratio = 1.0±0.1 (e.g. Cruz et al., 2005). 570
Calculated age based on
234
U/
238
U AR corrected for detrital contamination and corrected age. 571
Analysed samples from RP I and RP III have indicate open system behaviour of uranium 572
and/or thorium, measured
230
Th/
234
U activity ratios were out of possible values for the close 573
system. Results from those analyses we didn’t take into account. 574
575
4.5. Stable isotopes and correlation with magnetostratigraphy 576
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The δ
13
C and δ
18
O records from 375 analysed samples (Sierpień et al., 2021) show 577
significant changes during the deposition of the Račiška pečina section. There is no 578
correlation between δ
13
C and δ
18
O values (R
2
= 0.1235, Fig. 10). However, the visible weak 579
trend of isotope depletion (Fig. 10) can be caused by the effect of kinetic fractionation or by 580
changes in vegetation cover and solid development (Lachniet, 2009). Some of the offset 581
points may reflect airflow conditions in the open cave (Hendy, 1971), which may be related to 582
the dynamic change of the cave elevation. The δ
13
C values ranged from -3.36‰ to -11.19‰, 583
while δ
18
O values varied between -4.19‰ and -7.11‰ (Fig. 11, columns B and C). 584
585
Fig. 10. Here. 586
587
The O and C isotope compositions show very high variability of paleoenvironmental 588
conditions during the deposition of speleothem layers along the RPC section (Sierpień et al., 589
2021). 590
591
5. Discussion 592
The sedimentation in the cave reflected the evolution of the surrounding landscape, i.e. the 593
regional uplift and climatic changes from the Late Pliocene to the Holocene. When the cave 594
acted as a conduit between ponors at blind valleys and springs on the Adriatic Coast, 595
allogenic sediments were deposited. After the cave was detached from its hydrological 596
function due to the regional uplift (Mihevc, 2007), speleothems started to deposit in the 597
vadose zone. Clay sediments were deposited on existing speleothems only from infiltration 598
waters. From our results, we can conclude that under the drier conditions no speleothem 599
deposition occurred, which is reflected in short and long-lasting hiatuses in the studied 600
section. It is also obvious that during a period of stronger rainfall events (higher water energy) 601
the deposition of infiltrated clay material occurred over the existing speleothems. During the 602
same events, existing fauna remains were washed and deposited in the currently active clay 603
layer of the section. All clay layers were then covered with overlying flowstone layers, 604
making them inaccessible from the surface and at the same time protecting them from 605
younger erosion. With such an order of sedimentation, the fauna present in the respective 606
layers represents the approximate sedimentation time. 607
Some of the upper flowstone layers (Fig. 9) contain black laminae enriched in organic 608
carbon (soot), which can be attributed to repeated human visitors to the cave. These layers 609
have been dated to ~11 ka, ~9 ka, and ~3 ka. Although no archaeological excavations have 610
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been conducted, the location of the cave in close proximity to the natural pass between 611
Adriatic Basin and inland may indicate that occasional visitors stopped here during their 612
migrations from the very beginning of the Holocene (11.7 ka according to Cohen and 613
Gibbard, 2019) up to ~9 ka. The 3 ka old soot layer corresponds to the beginning of the 614
Bronze Age in Europe (e.g. Langgut et al., 2015). In recent years, many studies deal with 615
ancient human migrations (e.g. Palmisano et al., 2021) influenced by past climatic 616
fluctuations detected also in stalagmites (e.g. Finné et al., 2017). The upper part of our studied 617
section also contains evidence of such variability. 618
All fossil fauna finds from the Račiška pečina section are listed in Table 4. The previous 619
finds of small mammals in sample F (Fig. 4, Table 4) of the section (Horáček et al., 2007) 620
suggested dating to the mid-late MN17 mammalian biozone – the upper boundary of MN17 621
well-marked by FAD Microtus (Allophaiomys) pliocaenicus (see Horáček et al., 2007 for 622
details) and related radical rearrangements in the structure of mammalian communities is 623
correlated with the onset of the Olduvai event (Moldovan et al. (2011) found the fossil 624
invertebrates of oribatid mites belonging to the same ecological group of forest inhabitants in 625
their sample R4 (Fig. 4, Table 4); this fauna was also determined as MN17–Q2 fauna. 626
627
Table 4. Here. 628
629
In new samples from the yellow clay layers of the palaeomagnetic samples B, C, and D 630
(Fig. 3B, Table 4) we looked after large mammal bones as previous investigations proved 631
cave bear bones and teeth in sample C (Horáček et al., 2007). Unfortunately, only two bones 632
and a tooth fragment obtained during the last sampling could be used for taxonomic 633
evaluation (Fig. 6). However, we prefer to assign all ursid specimens to the same taxon 634
regarding their characteristic, to – Ursus ex gr. spelaeus. With U-series dating we also 635
confirmed that the studied bones of large cave bears are older than ~72 ka. 636
Small mammals were found in three of seven clay samples PONV, RD1 and F2 (see Figs. 637
4, 7, Table 4); new finds confirmed the previous dating of the section (Horáček et al., 2007; 638
Pruner et al., 2009; Zupan Hajna et al., 2020). The best-preserved finds determined as 639
Clethrionomys glareolus are from the site PONV. The same genus was also determined in the 640
sample RD1. Clethrionomys is available from MN17– to recent, from the late Early 641
Pleistocene (Q2 sensu Horáček and Ložek, 1988) it represents the most common member of 642
small ground mammal communities of Europe. The enamel fragment from F2 belongs to 643
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Pliomys, the genus which major radiation took place during the earliest Pleistocene (MN17–644
Q1). 645
The most impressive of the last fauna finds were specimens, fragments, and imprints 646
(partly petrified) of the troglobiotic snail Zospeum sp. in three samples PONV, RP 51–51, F2 647
of different ages (Fig. 4, Table 4). With the regard to DNA studies and molecular delimitation 648
modelling (Weigand et al., 2013), the Zospeum belongs to subterranean evolutionary lineages 649
which diversification is characterized by rare, long-range colonization events with in situ 650
radiation into several lineages occupying isolated cave systems. With the respect to 651
geographic distribution and evolutionary history of the group, these studies also assumed that 652
European Zospeum originated no earlier than the beginning of the Early Cenozoic 653
(approximately 65 Ma) with the start of Alpine orogeny. However, in our case, where the 654
studied cave is located in the NW part of the Dinarides, the flysch was deposited over older 655
carbonate rocks during Eocene. Here the maximum theoretical age can be set to the 656
Eocene/Oligocene transition (approximately 40 Ma; Drobne et al., 2009). 657
The findings of fossil subterranean snails presented here are the first palaeontological 658
discoveries in general and can thus contribute to the knowledge of the maximum age and 659
evolutionary history of this group. The only other true subterranean animal found so far in 660
cave sediments was Marifugia cavatica (Annelida: Serpulidae) from Črnotiče unroofed cave 661
(Mihevc, 2000; Bosák et al., 2004). 662
The palaeoclimatic reconstruction of the 3.4 Ma history in the studied section was 663
correlated with the obtained magnetostratigraphy (Fig. 11). The section starts with the 664
deposition of flowstone in a warm period with intense vegetation (MIS Km3). This was 665
followed by a sudden stop of speleothem crystallization for a period of ~60 ka (MIS Km2–666
K2). Such a long hiatus may reflect changing climatic conditions in the Mediterranean, 667
probably related to the onset of permanent glaciation in the Arctic region, which turned 668
towards the Gulf Stream intensification described by Prescott et al. (2017) and Suc (1984). 669
Just before the Pliocene/Pleistocene boundary, about 2.6 Ma ago, a rather long depositional 670
hiatus (the main disconformity) with duration of ~100 ka was detected. The hiatus, 671
comprising four Marine Isotope Stages (MIS 102–99; Fig. 11), can be associated with 672
Northern Hemisphere Glaciations (NHG) and changes in ocean circulation (Lisiecki and 673
Raymo, 2007). Above the hiatus, a deposition reflects cyclic climatic character with 674
alternation of glacial’s and interglacial’s characteristics of the Pleistocene. Overlying 675
speleothem layers indicate that glacial conditions returned during MIS 80, followed by a short 676
warming episode in MIS 79. The cyclic nature of the climate (glacial/interglacial) is well 677
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expressed after the renewal of sedimentation following the next hiatus (at ~1.52 Ma). The 678
Brunhes/Matuyama boundary occurred in MIS 19 at about 773 ka. The changes in the C and 679
O curves reflect the interglacial climate with the increase in temperature and decrease in 680
humidity. Then, the transition to glacial conditions is observed again during MIS 18, followed 681
by another break-in deposition (~100 ka; MIS 18–16). Sedimentation in the studied S part of 682
the section stopped at the end of MIS 5, about 80 ka ago. 683
684
Fig. 11. Here. 685
686
The Olduvai section is worth of interest. With its thickness of ~200 cm (after clay/silt 687
compaction) lasted for ~150 ka (1.78–1.925 Ma after Cohen and Gibbard, 2019). The OIS 688
model of the Olduvai section detected any longer hiatus (Fig. 11). It could be interpreted as 689
continued deposition without substantial interruptions even during clay/silt deposition. The 690
calculated average deposition rate of the Olduvai section was about 1.2 cm/ka, if taking into 691
account eventual erosion of the clay/silt intercalations and corrosion of the speleothem calcite, 692
we can speculate on a depositional rate up to 2 cm/ka. There are 6 thicker clay/silt layers and 693
~12 principal bedding planes in flowstones within the Olduvai section. If we accept, that (1) 694
clay/silt deposition may be associated (in Fig. 11) with a wetter surface climate that allowed 695
the erosion of the surface red soils and their transport and deposition over section by 696
infiltrating (percolating) water, and (2) the flowstone crystallization reflects a less wet surface 697
climate, with no or limited soil erosion and no deposition from water load inside the cave. We 698
can speculate that the clay/silt and flowstone layers reflect changes in palaeoenvironmental 699
conditions at the surface. The periodicity of principal bedding planes in the flowstones and 700
clay/silt interbeds could, with all uncertainties, indicate the periodicity of the principal 701
changes in periods with durations of ~15 ka and ~30 ka, respectively, i.e. very close to 11 and 702
40 ka long Milankovitch cycles (Milankovitch, 1941) or 13-17 ka and 21-23 ka cyclicity of 703
mean sea-level changes (Chapanov et al., 2015). The number of very thin clay/silt 704
intercalations allows us to speculate more on finer palaeoclimatic oscillations outside the cave 705
(needs further research), and their influence on depositional processes and history in the cave 706
interior facies, deep within the cave. 707
There are episodes of lower amplitude on the stable isotope curves (δ
13
C and δ
18
O) and 708
the same number of episodes with higher amplitude values. The first episode with lower 709
amplitude is from the beginning of the section sedimentation to the main disconformity. The 710
amplitude in this case is ~3‰ on the δ
13
C curve and ~0.5‰ on the δ
18
O curve. The next low 711
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amplitude episode (on the δ
13
C curve is ~3‰ and on the δ
18
O curve ~1.5‰) occurred from 712
1,950 ka to 1,650 ka. The last such event occurred from 900 ka to 300 ka, where the 713
amplitude on the C curve is ~2.5‰, and on the O curve is ~2‰. The first episode of higher 714
amplitude was from the main disconformity up to 1,950 ka, where the amplitude on the δ13C 715
curve is ~5.5‰ and on the δ
18
O curve is ~2.6‰. The second such episode occurred from 716
1,500 ka to 700 ka and the amplitude on the δ
13
C value is ~7.2‰ and on the δ
18
O ~2.25‰. 717
The last episode of higher amplitude occurred from 350 ka to the top of the sampled section 718
(amplitude at δ
13
C value is ~5‰ and at δ
18
O value is ~2.25‰); the gradual onset of this 719
change can be seen at ~500 ka. Such episodic amplitude oscillations on the stable isotope 720
curves may be related to dynamic changes in the surface morphology around the cave 721
(opening and/or closing of the cave, with/without connection to the outer atmosphere). 722
According to Tarhule-Lips and Ford (2004), values on the δ
13
C curve approaching 0‰ may 723
indicate that the cave is cut off which increases the range of amplitude oscillations on the 724
stable isotope curves. 725
The OIS model, which dates the last principal changes on the stable isotope curves to 726
between ~500 ka and ~350 ka, corresponds well with the expected rate of chemical 727
denudation of the carbonate host-rocks and the opening of the cave to the surface at about 500 728
ka. The period from ~500 to ~350 ka may easily correspond to a gradual opening of the cave 729
due to changes in surface morphology and tectonic uplift of the area. The third high 730
oscillation amplitude on the stable isotope curves was reached at ~350 ka, when the present 731
cave entrance was fully opened to the surface. Since that time, large mammals, such as cave 732
bears, have been able to enter the cave. 733
With the latest research, we have found that the origin of the section is even more 734
complicated than we thought in the first studies (e.g. Horáček et al., 2007; Zupan Hajna et al., 735
2008). With the new results from fauna, radiocarbon, and U-series dating, we were able to 736
show that the N and S parts of the section have a different history of flowstone deposition and 737
that the section actually consists of at least three overgrown speleothem domes (Fig. 12). 738
739
Fig. 12. Here. 740
741
On the N side of the section (Fig. 12), the oldest speleothem dome (grey in Fig. 12) grew 742
during Late Pliocene and its deposition terminated at the Pliocene/Quaternary transition. After 743
that, two stalagmites were deposited from dripping water. For the middle speleothem dome 744
(pink in Fig. 12) we do not know where it was fed from, but it grew during the Early 745
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Pleistocene and part of the Olduvai subchron. From time to time infiltrated silty clays were 746
deposited between the speleothem layers, containing remains of fauna and broken soda 747
straws. The deposition of this middle dome was significantly interrupted by a red clay layer 748
(sample A) that was traced across the entire section. The palaeontological sample (RD1) from 749
this layer already contains Late Pleistocene fauna (see Table 4). Stalagmite was deposited 750
above this clay layer, which overlaid all the older calcite layers, and the section was divided 751
horizontally into two parts. From there, the N and S sides of the section have different 752
evolution and flowstone layers deposited by different water sources. The S speleothem dome 753
(blue in Fig. 12) grew over the red clay layer A and contains the well-recorded 754
Matuyama/Brunhes boundary. The only layer recorded in both upper parts is yellow clay, 755
containing remains of Ursus spelaeus. At the top of the middle part of the section, the central 756
upper dome (green in Fig. 12) has grown. 757
The results obtained by all methods helped to reconstruct the history of the deposition of 758
the speleothem layers and to classify them well in time. The fossil fauna and their 759
biostratigraphic determinations by Horáček et al. (2007), Moldovan et al. (2011), and the 760
present study were crucial in correlating the palaeomagnetic results with the GPTS (Cande 761
and Kent, 1995; Gradstein et al., 2012; Cohen and Gibbard, 2019). But regarding the Račiška 762
pečina section complicated structure, there are still parts of it that have not been studied or 763
dated. 764
765
6. Conclusion 766
The studied sedimentary sequence of the Račiška pečina was mainly characterized by the 767
deposition of speleothem layers with long hiatuses deposited in the vadose zone after the cave 768
was detached from its hydrological function. Occasional deposition of speleothem layers was 769
interrupted by sedimentation of clayey to silty material infiltrated from the surface above the 770
cave. A rare fauna was present in these clastic sediments, in which we also found specimens 771
of the subterranean gastropod Zospeum sp. 772
Multiproxy studies were used to identify the alternation of N- and R-polarized 773
magnetozones and short-term excursions of the magnetic field, the palaeomagnetic log was 774
calibrated by palaeontological data and U-series dating to obtain the time of deposition of the 775
section, and stable isotopes were recorded to detect changing climate conditions during the 776
last 3.2 Ma. The Pliocene/Quaternary boundary, as well as some boundaries of Pleistocene 777
chronostratigraphic units, were detected, of which the Matuyama/Brunhes boundary was the 778
most distinct. 779
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The Račiška pečina section deposited from ca 3.4 Ma to ca 80 ka (MIS Km3 to MIS 5). 780
The section was divided in terms of stable isotope studies into two segments separated by 781
principal disconformity (hiatus). The palaeoenvironmental changes associated with these 782
disconformities were well expressed by the changing values of stable isotopes. The lower 783
segment correlates better with the regional Medi curve (Wang et al., 2010), while the upper 784
segment – with the global LR04 curve (Lisiecki and Raymo, 2005). This indicates changes in 785
the main factors controlling environmental conditions in the area. From about 2.6–2.5 Ma 786
climatic conditions were mainly controlled by global Atlantic Ocean factors. The 787
Brunhes/Matuyama boundary occurred at MIS 19, at about 773 ka. Changes in the C and O 788
isotopic records reflect the interglacial climate with the increase in temperature and decrease 789
in humidity at this time and also the opening of the cave to the surface sometime between 500 790
ka and 350 ka ago. 791
Large cave bears (Ursus ex gr. spelaeus) are typical representatives of European Late 792
Pleistocene faunas which disappeared around 26,100–24,300 cal. years BP (Pacher and Stuart, 793
2008; Baca et al., 2016). The bones described here were deposited in the yellow clay (layer C) 794
before ~72 ka ago. The presence of small mammals confirmed previous findings of Early and 795
Late Pleistocene fauna (Horáček et al., 2007). According to the findings of fossil subterranean 796
snails (samples F2, RP51–52, RP20–22) in clay layers dated by other methods, we can predict 797
that they inhabited the cave at least since 2 Ma ago. 798
The Račiška pečina section, like similar sediment types from other karst caves, does not 799
allow continuous isotope records as in stalagmites but contains information about an 800
extremely long depositional period. The Račiška pečina section is a really important source of 801
climate information for the last 3 Ma including the Pliocene/Quaternary and 802
Matuyama/Brunhes transitions. We can conclude that the records from the Račiška pečina 803
section have added to the knowledge of regional tectonic and climatic conditions, as well as 804
palaeoclimatic transitions during the enclosed time in general. 805
The research of this section has also shown that speleothem domes contain a lot of 806
different data that cannot be recorded in a single borehole or a single stalagmite. 807
808
Acknowledgments 809
The authors would like to thank Dr. Guzel Dunkalova for encouraging them to write this 810
paper and the reviewers for useful comments and suggestions. We also thank Jana Rajlichová, 811
who drew and corrected the drawing countless times, Richard Walters (Commendium LTD) 812
for the Terrestrial Laser Scanning of the cave and section, and colleagues from the authors’ 813
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Institutes and also around the world for their help with fieldwork, analyses in the laboratories, 814
and constructive debates during the years of studies. Results are mostly thanks to the 815
collaboration of the Karst Research Institute of Research Centre of the Slovenian Academy of 816
Sciences and Arts in Postojna, the Institute of Geology, Czech Academy of Science in Prague 817
(MOBILITY project SAZU-19-01) with contributions of the Institute of Geological Sciences, 818
Polish Academy of Sciences in Warszawa, Department of Zoology, Faculty of Sciences, 819
Charles University in Prague, and Department of Palaeontology, National Museum in Prague. 820
Analyses developed in our projects were funded by the Slovenian Research Agency 821
[research core funding No. P6-0119]; and the Institutional Financing of Institute of Geology, 822
Czech Academy of Science [No. RVO6798531]. 823
824
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1107
Tables captions
1108
Table 1 Mean palaeomagnetic directions of samples, Račiška pečina – boreholes.
1109
Legend: N – normal polarity, R – reverse polarity; D, I – declination and inclination of the remanent
1110
magnetization after dip correction; α95 – semi-vertical angle of the cone of confidence calculated
1111
according to Fischer (1953) at the 95% probability level; k – precision parameter; n – number of
1112
analysed samples.
1113
1114
Table 2. Radiocarbon dating results.
1115
1116
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Table 3 U-series dating results (ICP-MS data).
1117
1118
Table 4 Fossil fauna finds in Račiška pečina section.
1119
1120
1121
Figures captions
1122
Fig. 1. Location of the cave Račiška pečina. DEM of the contact karst area (RS Lidar data, Geodetski
1123
oddelek ARSO) with studied cave position and schematic cross-section of the area. The carbonate
1124
rocks are covered with numerous dolines, and fluvial relief is developed on the flysch rocks. Legend:
1125
1– carbonates (limestones and dolomites from the Early Cretaceous to the Palaeocene and Eocene)
1126
dissected by faults, 2– Eocene flysch rocks, 3– schematic outline of the relief from the time when
1127
Račiška pečina was an active water passage with supposed sinking stream, 4– sinking streams in blind
1128
valleys, 5– cave entrances and caves.
1129
1130
1131
Fig. 2. The 3D cave image (cross-section and ground plan) of the Račiška pečina cave and the studied
1132
section. The location of the section and the schematic thickness of the cave roof are indicated, as well
1133
as the position of the surface. The scale belongs to figures A and B.
1134
1135
Fig. 3. The studied sedimentary section Račiška pečina with the positions and numbers of
1136
palaeomagnetic samples. 1 – rimstone pools, 2 – red clay layers, 3 – yellow clay layers, 4 –
1137
stalagmites, 5 – breakdown blocks of limestone, 6 – youngest speleothems, 7 – slices of speleothem
1138
layers for palaeomagnetic analyses, 8 – cubes, 9 – positions of cores (RK), 10 – lower segment, 11 –
1139
middle segment, 12 – upper segment, 13 – schematic position of stable isotopes samples.
1140
1141
1142
Fig. 4. Locations of the palaeontological samples. Sample F (Horáček et al., 2007), samples R1–4
1143
(Moldovan et al., 2011) and yellow boxes with their names represent novel results.
1144
1145
1146
Fig. 5. The new magnetostratigraphic profile was correlated with GPTS (Cande and Kent, 1995;
1147
Gradstein et al., 2012; Cohen and Gibbard, 2019) and calibrated with palaeontological data (Horáček
1148
et al., 2007). Polarity log: black – normal polarity, white – reverse polarity, grey – transitional polarity.
1149
1150
1151
Fig. 6. The material of Ursus ex gr. spelaeus from Račiška pečina Cave (sample C II). Legend: 1 –
1152
diaphysis of the right femur (max. L 219.4 mm, distal W of preserved part 48.0 mm) of a young
1153
individual with an isolated distal epiphysis (W of preserved part 68.6 mm) probably belonging to the
1154
same specimen; a: cranial view, b: caudal view, c: isolated distal epiphysis. 2 – right calcaneus with
1155
the missing posterior end of tuber calcanei (max. L of preserved part 97.8 mm, max. W ca. 69.9 mm)
1156
and isolated end of tuber calcanei (max. L 38.6 mm, max. W 36.0 mm) most probably belonging to the
1157
same specimen; a: dorsal view, b: medial view, c: isolated posterior end of tuber calcanei. 3 – terminal
1158
phalanx (max. L 40.4 mm, proximal W 15.7 mm, proximal H 25.8 mm, dorsalmost part missing). 4 –
1159
rib fragment of a young individual. 5 – a mesial fragment of milk premolar (d4 dex.); see a small
1160
accessory cusp marked by the arrow (mesial metastylid sensu Rabeder, 1999); a: occlusal view, b:
1161
lingual view. L – length, W – width, H – height. Scale bar 50 mm for bones, 10 mm for the tooth
1162
(photo L. Váchová).
1163
1164
1165
Fig. 7. The record of small mammals from Račiška pečina section samples PONV, RD1, and F2.
1166
Legend: 1a–1b – the M3 fragment of Clethrionomys cf. glareolus from the site PONV, 1a – occlusal
1167
view, 1b – lingual view; 2a–2c – the distal enamel wall of m1 from the site RD1 (supposedly
1168
Clethrionomys cf. glareolus), 2a – the original specimen, 2b – broken surface after HCl etching, 2c–2d
1169
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– detailed views of enamel microarchitecture; 3a–3b – the fragment of enamel (supposedly a lingual
1170
wall of M3 Pliomys sp.) from the site F2, 3a – broken surface after HCl etching, 3b – lateral view of
1171
the fragment (note a distinct layer of lamellar prisms), 3c – detailed view of enamel microarchitecture.
1172
1173
1174
Fig. 8. Some of the gastropod materials from Račiška pečina section samples PONV (A. fragments of
1175
Zospeum sp., B.
Aegopinella sp.
), RP 51–52 (C. specimens of Zospeum sp.), and F2 (D1–2. imprints
1176
of Zospeum sp.). Scales on the photos = 1 mm.
1177
1178
1179
Fig. 9. Location of the radiocarbon-dated samples with the calibration of their results and the U-series
1180
samples in RP II slice.
1181
1182
1183
Fig 10. Correlation of δ
13
C and δ
18
O values from the entire Račiška pečina section (p < 0.05) modified
1184
from Sierpień et al. (2021).
1185
1186
1187
Fig. 11. Interpretation of oxygen and carbon record in the age scale. Legend: A – the scale of Marine
1188
Isotope Stages (MIS; warm – red; clod – blue; Lisiecki and Raymo, 2005); B – the record of oxygen
1189
stable isotope (smoothed data –blue; raw data – grey); C – the isotopes record of carbon stable
1190
isotopes (smoothed data – black; raw data – grey); D – the temperature curve; E – the humidity curve;
1191
F – the vegetation curve (low – the negligible presence of plants around the cave; the high –
1192
significant presence of plants around the cave); G – magnetostratigraphy log according to Pruner et al.
1193
(2009); black – normal polarity, white – reverse polarity, grey – transitional polarity, wavy line – the
1194
main disconformity; grey boxes – hiatuses; dark grey box – the main disconformity.
1195
1196
1197
Fig. 12. Račiška pečina section with speleothem domes growth relations, dating results, and detected
1198
chron and subchron boundaries. Legend: 1 – N oldest dome, 2 – N middle dome, 3 – S dome, 4 –
1199
central top dome, 5 – N youngest dome, 6 – central stalagmites, 7 –chron and subchron boundaries, 8
1200
– radiocarbon results, 9 – U-series results, 10 – palaeontological samples with results, 11 – schematic
1201
location of stable isotopes log.
1202
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Table 1.
Borehole
Polarity
Mean palaeomagnetic
directions
α
95
[
o
]
k
n
D [
o
]
I [
o
]
RK 1
N
310.13
73.24
6.69
36.48
12
RK 3
N
345.24
68.65
5.54
159.94
4
RK 5
R+R?
173.56
-8.88
12.23
32.75
4
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Table 2
Sample
number
14
C
[BP] 68.2% conf. interval 95.4% conf. interval
Cal. Age range
[cal BP] Prob.
[%] Cal. Age range
[cal BP] Prob.
[%]
RP II/2a 3290±40 3560-3529
3514-3459 28.2
40.1 3626-3603
3590-3442
3430-3401
2.3
89.2
4.0
RP II/1a 9050±110 10380-10120
10064-10036
10029-10010
9991-9960
56.0
4.4
2.6
5.3
10508-9888
9845-9785 93.5
2.0
RP I 11360±130
13345-13116 68.3 13571-13560
13504-13066
13018-13010
0.3
94.9
0.2
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Table 3
Sample Lab
no U cont.
[ppm]
234
U/
238
U AR
230
Th/
234
U AR
230
Th/
232
Th AR
Age
[ka] Corrected
age
[ka]
Initial
234
U/
238
U AR
RP II-A 1491 0.0707±0.0003 1.1530±0.0039 0.2274±0.0038 6.96±0.12 28.12±0.53 25.0±0.6 1.164±0.028
RP II-B 1492 0.0775±0.0004 1.1651±0.0048 0.5254±0.0081 6.125±0.092 79.9±1.8 72±2 1.202±0.034
RP 1 1537 0.1236±0.0061 1.117±0.067 0.698±0.045 14±3 +14
126
-13 120±20
RP 66 1538 0.1239±0.0049 1.239±0.059 1.068±0.051 1.184±0.052 >450 +inf
440
-130
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Table 4
Layer PM
sample Horáček et al., 2007 Moldovan et al., 2011 New samples MN
zonation Age
Correlation to
GPTS
No Fossils No Fossils
(invertebrates) No Fossils
1. RP D RUD 0
2. RP C CII Ursus spelaeus
sp, CII Ursus ex gr.
spelaeus >72 ka
3. RP B B Ursus ex gr.
spelaeus
4. S of RP
20-22 PONV Clethrionomys
glareolus,
Zospeum sp,
Aegopinella sp.
From
MN17-Q2
to recent
Brunhes chron
5. RP 20-22
RP 20-
22 0
6. RP 51-54
R4 Oppiella
(Rhinoppia),
Miracarus sp.n.,
Suctobelbella
sp.?
RP 51-
52 Zospeum sp. MN17-Q2
Late
Pleistocene
(termination
of the
Olduvai-
subchron)
7. A RD1 Clethrionomys
glareolus From
MN17-Q2
to recent
Olduvai-
subchron
8. RP 23-25
R3 0 RP 23-
24 0 MN17
9. RP 26 F Crustacea (cf.
Potamon);
Cyprinid fish
(Barbus sp.);
Mammalia
(Apodemus,
cf. Borsodia,
Mimomys
(Cseria) sp.;
Apodemus
(Sylvaemus) sp.
– cf. atavus)
F2 Pliomys,
Zospeum sp. MN17-Q1
Early
Pleistocene
10. RP 59-65
R1 0 F1 0 MN17 ±2 Ma
R2 0
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Declaration of interests
☒
The authors declare that they have no known competing financial interests or personal relationships
that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered
as potential competing interests:
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