ACTA CARSOLOGICA 33/2 13 219-238 LJUBLJANA 2004 COBISS: 1.01 PALAEOMAGNETIC AND U-SERIES DATING OF CAVE SEDIMENTS IN BARADLA CAVE, HUNGARY DATACIJE JAMSKIH SEDIMENTOV S PALEOMAGNETNO IN URAN TORIJEVO METODO V JAMI BARADLA NA v MADŽARSKEM PAVEL BOSÄK1 & HELENA HERCMAN2 & JAROSLAV KADLEC1 & JÄNOS MOGA3 & PETR PRUNER1 1 Institute of Geology, Academy of Sciences of the Czech Republic, Rozvojova 135, 165 02 Praha 6, Czech Republic, inst@gli.cas.cz 2 Institute of Geological Sciences, Polish Academy of Sciences, ul. Twarda 51/55, 00-818 Warszawa, Poland, hhercman@twarda.pan.pl 3 Eötvös Lorand University, TTK Geography Department, Päzmäny P. setäny 1/c, 1117 Budapest, Hungary, jmoga@freemail.hu Abstract UDC: 550.38:552.54(439) Pavel Bosak & Helena Hercman & Jaroslav Kadlec & Janos Moga & Petr Pruner: Palaeomagnetic and U-series dating of cave sediments in Baradla Cave, Hungary Fine-grained siliciclastic sediments from the main gallery and upper cave level show nearly uniform composition and sedimentary textures. Palaeomagnetic analysis indicates normal magnetic polarisation of all samples, i.e. the age younger than Brunhes/Matuyama boundary at 780 ka. Flowstone/stalagmite covering siliciclastics in the upper cave level contains reverse polarised samples dated by U-series method to about 114-115 ka, which can be identified as the Blake Event. The uniform composition of sediments can indicate the infill of the cave during a single event caused by the blockage of drainage routes due to geological (collapse) or palaeoclimatic (ice) changes, which took part before ca 130 to 150 ka as indicating by the oldest U-series data from the whole Domica-Baradla Cave System. Key words: cave sediments, palaeomagnetic dating, U/Th dating, Baradla Cave, Hungary. Izvleček UDK: 550.38:552.54(439) Pavel Bosak & Helena Hercman & Jaroslav Kadlec & Janos Moga & Petr Pruner: Datacije jamskih sedimentov s paleomagnetno in uran torijevo metodo v jami Baradla na Madžarskem Drobnozrnati siliklastični sedimenti glavne galerije in gornjega nivoja jame Baradla, izkazujejo veliko homogenost v zgradbi in sedimentnih teksturah. Paleomagnetne analize kažejo normalno polarizacijo vseh vzorcev, kar pomeni starost, ki je mlajša od meje Brunhes/Matuyama pri 780 ka. Siga oz. stalagmiti, ki pokrivajo siliklaste v gornjem jamskem nivoju, vsebujejo tudi reverzno polarizirane vzorce, katerih datacije z uran torijevo metodo kažejo na starost 114-115 ka, kar nakazuje na dogodek Blake. Homogenost sedimentov lahko razložimo z enkratnim dogodkom, kjer je zapolnitev s sedimentom povzročil zastoj pretoka. Temu so lahko botrovali geološki (npr. podor) ali paleoklimatski vzroki pred približno 130-150 ka, kolikor je tudi najvišja starost sedientov v sistemu Domica-Baradla izmerjena z metodo uran-torij. Ključne bedsede: jamski sedimenti, paleomagnetno datiranje, datiranje z metodo U/Th, jama Baradla, Madžarska. INTRODUCTION The Baradla Cave is located in NE Hungary in the Aggtelek Karst. The cave represents a part of extensive cave system Domica-Baradla crossing the Slovak/Hungarian border from ponors in the Slovak Karst (Silica Plateau) to resurgences in the Aggtelek Karst. The area represents the part of the World Heritage Site of UNESCO. The total length of the system is about 25 km, of which 5.4 km is on the Slovak territory. The area is built mostly of Mesozoic (dominantly Triassic) carbonate rocks belonging to the Silica Nappe of the Silicicum tectonic unit (cf. e.g., Mello et al., 1997; Plašienka, 1999). Carbonates are unconformably overlain by siliciclastics of the Poltär Formation (late Miocene - Pontian), which are interpreted as deposits of alluvial plain fed from erosion of uplifting mountain ranges in the Slovak territory (Mello et al., 1997). They encircle limestone outcrops from the west and southwest. The Cainozoic geomorphological evolution was described in detail by Moga (1999). Cave evolution was summarised e.g., by Jakucs (1956), Säsdi (1990), Bella (2000) or Zämbo et al. (2002). The field work started in August 2001 by checking the whole accessible part of the Baradla Cave and site pre-selection (P. Bosäk, J. Kadlec). During November 2001, samplig on profiles was carried out (J. Moga from the Geography Department of the ELFI, Budapest, Hungary, P Bosäk, P. Pruner, J. Kadlec, M. Chadima, L. Maggini from the Institute of Geology AS CR, Praha, Czech Republic, and S. Leel-Ossy from the Geology Department of the ELFI, Budapest, Hungary). In all 5 profiles of unconsolidated sediments were selected for sampling. Four profiles resulted from site pre-selection and one profile was sampled at the request of S. Leel-Ossy. Profiles were situated regularly in the plan of the cave and in different altitudes as follows (Fig. 1): Arany-utca (sample symbol BCA); Meseorszäg (BCB); Nädor utcäja (BCC); Räkosi-äg (BCD), and Münnich-täro (BCE). One profile was located in the main branch of the cave (Nädor utca) and two in the upper cave level (Münnich-täro, Meseorszäg). Profiles in Räkosi-äg and Arany-utca were situated in narrower side branches (invasion vadose passages from the south and east, i.e. from the landscape on siliciclastics of the Poltär Formation). In total 96 samples were taken (88 samples of unconsolidated sediments and 8 samples of speleothems; Tab. 1). The aim of the research was to detect palaeomagnetic and magnetostratigraphic properties of the cave fill and to compare them with similar data from Domica Cave (Slovakia; Pruner et al., 2000) Site Abbreviation Number of samples Type of demagnetisation Arany-utca BCA 21 1 AC TD Meseorszäg BCB 13 1 AC TD Nädor utcäja BCC 14 3 AC TD Räkosi-äg BCD 4 2 AC TD Münnich-täro BCE 36 1 AC TD Table 1 List of samples Explanations: AC - demagnetisation in alternating field, TD - thermal demagnetisation. and with numerical dating results from Baradla Cave (Lauritzen & Leel-Össy, 1994, and L. Zambo and D.C. Ford; L. Zambo, pers. com., 2003; cf. Fig. 1). Results of magnetostratigraphic research in Domica Cave (Pruner et al., 2000) indicate normal magnetic polarisation of all 4 profiles (Sucha Passage and Za Klenotnicou Passage). Profiles were composed mostly of silts to clays of brown to brownish red colour, sometimes slightly sandy, with sandy gravel in one profile. Intercalations of flowstones were relatively abundant. Short inverse polarised excursion older than Blake (Jamaica, Levantine) was detected in one of profiles (Sucha Passage), which was situated under flowstone cover of profile dated to 131 +10/-9,9 ka. Numerical dating of speloethems (U-series method) in Baradla Cave indicates similar low ages of 119 ka (Petofi's Tomb from the Chamber of Columns; Lauritzen & Leel-Össy 1994), and 100 to 150 ka (L. Zambo and D.C. Ford, unpubl.). SITE DESCRIPTION Arany-utca/Golden Passage (BCA) The site is situated in an invasion vadose passage entering from the east to the main cave corridor between Apollo Thermes and Szent Gellert Hill (Fig. 1). Natural profile (about 2 m in height) was situated on the left bank about 20 m from the junction with the main branch, behind a flowstone pillar (Fig. 2): 1 - flowstone, alternation of lighter and darker brown laminae up to 1 cm thick; 2 - clayey silt to silty clay, massive in the upper part, horizontally laminated in the lower part. It seems that those deposits overlay a 60-80 cm thick pebble layer at the passage junction. In the surroundings of the sampling site, close to the ceiling, a number of remains of flowstone crust could be traced almost at the same height as the crust at the top of the studied section. This indicates later erosion of sediments by invasion waters. Meseorszag/ Fairy Tale Chamber (BCB) Natural profile was situated in the eastern part of the Chamber belonging to the upper cave level. The whole section is covered by flowstone. Profile (about 1.2 m in height) was composed of (Fig. 2): 1 - flowstone, grey and white lamination, silty intercalations up to 0.3 mm thick; 2 - clayey silt, brown, horizontal and locally cross lamination; 3 - silty clay, reddish brown, massive, locally porous, in the upper part slightly laminated and cemented by carbonate; 4 - clayey silt, brown, horizontal lamination. Around the walls of the Chamber, flowstone crust can be noticed indicating younger exhumation of the cave fill. Nador utcaja/Nador Street (BCC) Natural profile (about 1.5 in heigth), partly modified by works for opening the cave to tourists, was situated on the left bank of the riverbed, just at the concrete trail (near the Music Hall). The profile is a remnant of terrace, partly covered by flowstone and stalagmite (Fig. 2): 1 - loamy dump; 2 - sand and clayey silt, brown sandy laminae up to 0.7 cm thick and dark brown silty laminae up to 0.2 cm thick, horizontal, locally small trough bedding; 3 - flowstone, brown and rusty brown thin layers, locally grey and rusty brown lamination, calcite crystals up to 1 cm; 4 - sand and clayey silt, brown sandy laminae up to 0.7 cm thick and dark brown silty laminae up to 0.2 cm thick, horizontal bedding; 5 - flowstone, brown and rusty brown thin layers, locally grey and rusty brown lamination, calcite crystals up to 1 cm; 6 - sand and clayey silt, brown sandy laminae up to 0.7 cm thick and dark brown silty laminae up to 0.2 cm thick, horizontal, locally cross bedding; 7 - flowstone, brown and rusty brown thin layers, locally grey and rusty brown lamination, calcite crystals up to 1.5 cm; 8 - clayey silt, laminae of fine-grained brown sand up to 0.5 cm thick, horizontal, locally cross bedding; 9 - clay, dark brown, laminae of light brown to white grey (average thickness 0.05 cm) and dark brown (thickness 0.3-0.4 cm); at the base a white grey laminated flowstone crust up to 1 cm thick was deposited. Räkosi-äg/ Räkosi Passage (BCD) A small artificial excavation (about 1.3 m in height) was situated at the end of a short corridor on the left side of the main cave passage (Fig. 2): 1 - clayey silt to silty clay, brown, subhorizontal and locally cross lamination; 2 - flowstone, dark brown and light grey lamination, clayey intercalations and infillings of small cavities; 3 - clayey silt to silty clay, brown, subhorizontal and locally cross lamination; 4 - flowstone, honey brown, dark brown lamination, light colour in the lower part; 5 - sand, brown, medium grained, layers of clayey sandy gravel (Poltar Formation?) 5-10 cm thick, size of pebbles up to 1 cm. Münnich-täro/ Münnich Tunnel (BCE) Profile (about 1.2 m in height) was situated in the left wall of the artificial trench in the upper cave level (Figs. 2, 3): 1 - clay, reddish brown, yellow grey silty laminae 0.05-3 mm thick locally disintegrated, reddish brown laminae 0.5-1 cm thick, occasionally small charcoal; 2 - flowstone, Fig. 1: Map of Baradla Cave with position of studied sites and U-series dating results. Fig. 2: Sedimentary profiles BCA to BCE with with position of paleomagnetic samples and results of paleomagnetic analysis (black = normal/N; white = reverse/R). For description of lithology see the text. Fig. 3: Photo of profile in Münnich-taro (BCE) with speleothem crust and stalagmite (photo by J. Moga). Fig. 4: Sketch of profile BCB (Meseorszag) with the position of paleomagnetic samples and results of paleo-magnetic analysis (black = normal N; white = reverse R) Description of profile: 1 - flowstone, grey and white lamination, silty intercalations up to 0.3 mm thick; 2 - clayey silt, brown, horizontal and locally cross lamination; 3 - silty clay, reddish brown, massive, locally porous, in the upper part slightly laminated and cemented by carbonate; 4 - clayey silt, brown, horizontal lamination. Fig. 5: Location of the BCB profile (Meseorszag) (map after Szunyogh G., Baradla New Atlas, with the permission of the Hungarian Cave Research of Institute). Fig. 6: Cave sediments and sinter in the Meseorszag (BCB). white and light laminated carbonate; 3 - clayey silt, brown, massive, locally horizontal lamination, occasionally carbonate concretions up to 7 cm thick. LABORATORY PROCEDURES Palaeomagnetic analyses The laboratory procedures applied in the research of samples from the Baradla Cave are classical procedures of palaeomagnetic research of sediments and rocks. Laboratory procedures have been designed to combine the way that enabled the derivation of the respective magnetic remanence components in different temperature intervals, during progressive thermal demagnetisation (TD), and the demagnetisation by alternating field (AF), the determination of moduli and directions of remanene defined by the presence of magnetic minerals, carriers of respective remanence components, and their phase changes. Standard sampling procedure for determination of magnetostratigraphic and rock-magnetic properties was applied using plastic cube boxes (20x20x20 mm; Japan production), which were pushed into the unconsolidated sediments in an interval of about 10 cm. In one profile, blocks of sediments were cut from the section and later in the laboratory, cubes were pushed into them. Solid samples taken from speleothems intercalated within profiles and from flowstones covering some of them were later cut in the lab into cubes 20x20x20 mm. All samples were oriented in the respect to magnetic north. Samples were measured on the spinner magnetometers JR-4 and JR-5 (Jel^nek, 1966). Laboratory specimens in their natural state were subjected to progressive TD using the MAVACS (Magnetic Vacuum Control System) apparatus securing generation of a high magnetic vacuum in medium of thermally demagnetised specimens (Pr^hoda et al., 1989). All of the peci-mens were also demagnetised by the alternating Fig. 7: Nador utcaja, Sketch of profile BCC with the position of paleomagnetic samples and results of paleomagnetic analysis (black = normal N ; white = reverse R). Description of profile: 1 - loamy dump; 2 - sand and clayey silt, brown sandy laminae up to 0.7 cm thick and dark brown silty laminae up to 0.2 cm thick, horizontal, locally small trough bedding; 3 - flowstone, brown and rusty brown thin layers, locally grey and rusty brown lamination, calcite crystals up to 1 cm; 4 - sand and clayey silt, brown sandy laminae up to 0.7 cm thick and dark brown silty laminae up to 0.2 cm thick, horizontal bedding; 5 - flowstone, brown and rusty brown thin layers, locally grey and rusty brown lamination, calcite crystals up to 1 cm; 6 - sand and clayey silt, brown sandy laminae up to 0.7 cm thick and dark brown silty laminae up to 0.2 cm thick, horizontal, locally cross bedding; 7 - flowstone, brown and rusty brown thin layers, locally grey and rusty brown lamination, calcite crystals up to 1.5 cm; 8 - clayey silt, laminae of fine-grained brown sand up to 0.5 cm thick, horizontal, locally cross bedding; 9 - clay, dark brown, laminae of light brown to white grey (average thickness 0.05 cm) and dark brown (thickness 0.3-0.4 cm), at the base a white grey laminated flowstone crust up to 1 cm thick was deposited. field procedures, up to a field of 1,000 Oe (Schonstedt GSD-1). Remanent magnetisation of specimens in their natural state (NRM) was identified by the symbol Jn, the corresponding remanent magnetic moment by the symbol M. Graphs of normalised values of M/Mo = F(t) were constructed for each analysed specimen. Directions of Jn and those of the remanent magnetisation of TD or AF demagnetised specimens in the course of progressive demagnetisation procedures were expressed in stereographic projection. The orthogonal projection of the remanent magnetisation vectors were plotted into the Zijderveld diagrams. Phase or mineralogical changes of magnetically active (mostly Fe-oxides) minerals frequently occur during the laboratory thermal tests, especially at low temperature intervals. These changes can be derived from the graphs of normalised values of kt/kn = f(t), where kn designates the volume magnetic susceptibility of specimens in natural state and kt the susceptibility of specimens demagnetised at temperature t °C. The kt and kn values will be measured on a kappa-bridge KLY-2 (Jel^nek, 1973). Separation of the respective remanent magnetisation components was carried out by multi-component Kirschvink analysis (Kirschvink, 1980). The statistics of Fisher (1953) were employed for calculation of mean directions of the pertinent remanence components derived by the multi-component analysis. Palaeomagnetic analyses were carried out in the Laboratory of Paleomagnetics in Praha-Pruhonice (Institute of Geology AS CR). U-series dating Dating of carbonates employed the 230Th/234U method. 10-15 g of clean, compact calcite with no visible traces of detrital admixtures have been separated from lower and upper layer of selected Fig. 8: Location of the profile BCC (Nador utcaja) map sheet No. 3 of the Baradla-Barlang 1: 1000, 1989). Fig. 9: Sketch of profile BCD (Räkosi-äg) with the position of paleomagnetic samples and results of paleomagnetic analysis (black = normal N ; white = reverse R). Description of profile: 1 - clayey silt to silty clay, brown, subhorizontal and locally cross lamination; 2 - flowstone, dark brown and light grey lamination, clayey intercalations and infillings of small cavities; 3 - clayey silt to silty clay, brown, subhorizontal and local cross lamination; 4 - flowstone, honey brown, dark brown lamination, light colour in the lower part; 5 - sand, brown, medium grained, layers of clayey sandy gravel (the Poltär Formation) 5-10 cm thick, size of pebbles up to 1 cm. part of stalagmite BCE 4. Standard chemical procedure for Uranium and Thorium separation from carbonate samples has been used (Ivanovich & Harmon, 1992). 228Th-232U mixture has been used as a controller of chemical procedure efficiency. Uranium and Thorium have been separated by ion exchange using DOWEX 1x8 resin. After final purification, U and Th have been electro-deposited on steel disks. Energetic spectra of alpha particles have been collected using OCTETE PC spectrometer made by EG&G ORTEC. Spectra analyses and age calculations were done using "URANOTHOR 2.6" software, which is standard software developed in U-Series Laboratory in Warsaw (Gorka & Hercman, 2002). The quoted errors are 1o. U-series analyses were carried out in U-Series Laboratory of the Institute of Geological Sciences PAS in Warszawa, Poland. RESULTS Palaeomagnetism and magnetostratigraphy Principal petromag-netic and palaeomagnetic parameters are documented in Table 2 for all five profiles. Values of the moduli of natural remanent magnetisation Jn and those of magnetic susceptibility k of the studied rocks in n their natural state show small scatter. The natural remanent magnetisation Jn from samples of the profile BCA range from 0.12 to 0.48 [mA/m]. The mean values of magnetic susceptibility kn from samples of the profile BCA are kn = 526 ± 285 x 10-6[SI]. The natural remanent magnetisation Jn from samples of the profile BCB range from 0.25 to 0.66 [ mA/ m] . The mean values of magnetic susceptibility kn from samples of the profile BCB are kn = 607 ± 388 x 10-6[SI°]. The natural remanent magneti- Fig. 10: Position of the BCD profile (Rakosi-ag) (map after Szunyogh G., Baradla New Atlas, with the permission of the Hungarian Cave Research Institute). sation Jn and the mean values of magnetic susceptibility kn from samples of the profile BCC indicate bigger sncatter Jn is from 0.04 to 0.32 [mA/m] and kn = 244 x 10-6 [SI] and range from 6 to 625 x 10-6 [ SI. The natural remanent magnetisation Jn from samples of the profile BCD range from 0.02 to 0.31 [mA/m]. The mean values of magnetic susceptibility kn from samples of the profile BCD are kn = 328 x 10-6 [ SI ] and range from -4 to 506 x 10-6 [ SI ]. The natural remanent magnetisation Jn from sediments of the profile BCE ranges from 0.02 to 0.83 [mA/m], from samples of stalagmite from 0.0008 to 0.0017 [mA/m]. The mean values of magnetic susceptibility kn from soft samples of the profile BCE are kn = 897 x 10-6 [SI], from samples of stalagmite range from -9 to -11 x 10-6 [SI]. This group of samples from stalagmite is characterised by very low magnetic values of J and k . Directions of remanent macnetisatinn inferred hv the above civen nroeerliires were tested using H KEDI *u«t «HU I i =9 S ^lfiiuiiiijiijjjtm — i: T—J J—J f ~— MT" Fit«*dmrt*r C Q5-1 K4 4ni «««I K4«f bor«^ ppi^ KEbU K C U-* KCU. KE [H* ■CEDK KE DrA «Mark KEMl KE4K KL