ESR DATING OF POSTOJNA CA VE STALACTITE (WITH 5 FIGtJRES) DATIRANJE STALAKTITA IZ POSTOJNSKE JAME Z ESR METODO (S 5 SLIKAt,il) MOTOJI I:KEYA* TOSHIKATStJ MIKI** RADO GOSPODARič*** * Technical College, Yamaguchi University, Ube, Japan. ** Physikalisches Institut der Universitat Stuttgart, BRD. *** Inštitut za raziskovanje krasa ZRC SAZU, Po.stojna, YU. SPREJETO NA SEJI RAZREDA ZA NARAVOSLOVNE VEDE SLOVENSKE AKADEMIJE ZNANOSTI IN UMETNOSTI DNE 25. NOVEMBRA 1982 CONTENT - VSEBINA Abstract - Izvleček . . . INTRODUCTION . . . . EXPERIMENTAL PROCEDURES RESULTS AND DISCUSSION Thermoluminiscence . . . . Electron Spin Resonance . . The Age and Growth Velocity. GEOCHRONOLOGICAL DISCUSSION ACKNOWLEDGEMENT ..... . REFERENCES DATIRANJE STALAKTITA IZ POSTO,JNSKE ,JAME Z ESR METODO (Povzetek) . . . . . . . . . . . . . . . . . . . . . . . . . 120 { 4) 121 { 5) 121 { 5) 123 { 7) 124 { 8) 124 ( 8) 127 (11) 128 (12) 129 (13) 130 (14) 130 (14) Abstract UDC 551.442.4.001.5(497.12-14) Ikeya Motoji, Toshikatsu Miki, Rado Gospodarič: ESR Dating of Postojna Cave Stalactite. Acta carsologica, 11 (1982), 117-130, Ljubljana, 1983, Lit. 9. The growth rate (3-4 mm/100 years) and the age (about 190.000 years) of the initial stalactite layers by the ESR method is estimated. Some physico-chemical dating prob1ems of the achieved results from Postojna Cave compared with those from Akyoshi Cave in Japan are discussed. The geochronological commentary ranged the stalactite growth beginning at the end of Mindel - Riss Interglacial, the upper seven sinter layers belonging to the Riss Glacial, Riss-Wilum Interglacial and Wilrm Glacial. The high flood, expressed by the loam among some sinter layers had inter- rupted the stalactite growth in the Riss Glacial. Izvleček UDK 551.442.4.001.5(497.12-14) Ikeya Motoji, Toshikatsu Miki, Rado Gospodarič: Datiranje stalaktita iz Po- stojnske jame z ESR metodo. Acta carsologica, 11 (1982), 117-130, Ljubljana, 1983, lit. 9. Z ESR metodo je ugotovljena stopnja rasti (3-4 mm/100 let) in starost (okrog 190.000 let) sige v notranji plasti stalaktita. Fizikalno-kemični problemi datiranja pri dobljenih rezultatih iz Postojnske jame so primerjani s podobnimi problemi v ja- ponski jami Akvoshi. Geokronološka razlaga uvršča začetno rast stalaktita v konec mindel-riškega interglaciala, sedem nadaljnjih plasti stalaktita pa v riški glacial, riss-wilrmski interglacial in wilrmski glacial. Med dvema plastema sige ohranjena poplavna ilovica odraža visoko poplavo v riškem glacialu. INTRODUCTION Electron spin resonance (ESR) is a method of analysis in physics and chemistry utilizing the microwave absorption under the magnetic field. It can detect the unpaired electron with a magnetic moment. Natura! radiation of a, ~ and y rays, from the radionuclides (such as uranium and thorium) and their decay products, produces radiation damage in rocks, minerals and archa- eological materials (J. M. A it k en, 1974; S. F e min g, 1976). Radiation da- mage have been utilized to measure the radiation dose. Thermoluminiscence is a well known technique, which can be used like ESR to measure the concentration of defects. The thermoluminiscent dosimetry (TLD) of CaS04 (Trn) is generally used to monitor the radiation exposure of personel at nuclear reactor facilities. It is also used as a method of dating pottery and ceramics in archaeology. We introduced ESR dating similar to TL dating of cave deposits. We used the presence of radicals with unpaired electrons in stalactites, stalagmites and cave pearls (M. I k e y a, 1975) as well as in bones and tooth animal (M. I k e - y a, 1978) excavated by anthropologists. One ean estimate the total exposed dose of material due to natural radiation from its content of radicals by stan- darized the observed enhancement of radicals content using artifical irradiation (M. I k e y a, 1975). The total dose of natural radiation, sometimes called the archaeological dose (AD) can be used to estimate the age of the material if the annual radiation dose is known. Thus, a method of dating using radiation da-· mage produced by natural radiation has been established. Details of ESR dat- ing have been published elsewhere (M. I k e y a, 1975, 1978). This report covers ESR dating of a Postojna Cave stalactites and its natural radiation dose measured with the TLD of CaS04 (TM). Throughout this paper we denote the radiation dose with the unit of Rad, i.e. the unit of absorbed radiation energy, 100 erg. per gram of material. EXPERIMENTAL PROCEDURES The ESR spectrum of the stalactite was measured with a 100 kHz field modulation and 4 gauss amplitude at room temperature before and after y-ray irradiation. The thermoluminiscence glow curve of the stalactite was also mea- sured at the rate of the temperature increase of about 1,5 °C/min after the powder carbonate had been washed with acetic acid to remove defects created by the milling and grinding procedure. Details of the ESR and TL dating have been described in earlier works (1,1. I k e y a, 1978; T. Mi ki, M. I k e y a, 1978). y-ray irradiation was made using 6°Co al the source at Katherin Hospital in Stuttgart, Nagoya University and Reactor Institute of Kyoto University. 121 Acta carsologica XI, 1982 (1983) Fig. l. Photo od: Postojna Cave stalactite and its cross ,section. The pattern of the dark loam sediment between white sinte r layers indicate the growth condi- ti,ons. The longitudinal growth has recently almost stopped Sl. l. Prerezan stalaktit iz Postojnske jame. Vzorec temnejšega ilovnatega sedi- menta med sigovimi plastmi nakazuj e razmere m ed rastjo. Vzdolžna rast se je danes skoraj ustavila 122 M. lkleya ... , ESR Daui.ng of Postojna Cave Stalactite The total natura! radiation dose received by the stalactite was obtained by assuming a linear relation between the concentration of defects and the radia- tion dose. No further studies like the radioactive elements determination have been performed for the Postojna Cave stalactites. RESULTS AND DISCUSSION Fig. 1 is a photo of the Postojna Cave stalactite obtained during the author's visit in 1977. The cross section shows the brown sediment which indi- cate that the stalactite took some impurities during its growth in the past. We suggest (M. I k e y a, 1978) that the main brown sediment were formed about the same tirne as the high water levels. The shape of the brown sedi- ment clearly indicates that the growth direction was shifted presumably be- {!ause of tilting ob the cave floor or because of the relative shift of the ceiling from where the water is supplied. The longitudinal growth seemed to have essentially stopped for the large stalactite (I) while the small ones were still 4-------------------------, Postojna Stalactite -3 ::, o >, ...., V) 2 C ~ ..... C _J ~ 100 200 300 400 T ( 0 G) Fig. 2. Thermolumniscence (TL) curve of Postojna Cave stalactite. The TL peaks at 510 and 620 K was obserwed. The backg1round termal glow due to the heating is also shown Sl. 2. Termoluminiscenčna krivulja (TL) stalaktita j,z Postojnske jame. Opazne so TL konice pri 510 K in 620 K. Razvidno je tudi ozadno termalno žarenje zaradi segrevanja 123 8 Acta carsologioo XI, 1982 (1983) growing. The growth might come from the splashing of dropping water since the radial growth in one specific direction is dominant. Thermoluminiscence Fig. 2 shows the TL glow curve of the Postojna stalactite. The TL peaks at 510 and 620 K have been observed for Petralona stalagmites. The peak height at 510 K is enchanced by an artificial y-irradiation. The peak at 320 K was formed by y-irradiation but is unstable. One can determine the AD with TL as has been done for Akiyoshi stalactite (T. Mi ki, M. I k e y a, 1978). However, precautions must be taken to reduce the tribothermoluminiscence due to the grinding. Samples must be mixed well to obtain the AD with the TL method, since the locally high concentrations of impurities cause a flucta- tion in the data. We had not studied the Postojna stalactite further with TL because of the complicated procedure for sample preparation but tried to date it with ESR. Electron spin resonance Fig. 3 shows ESR spectra of the Postojna stalactite before and after y-ir- radiation. The spectra of Mn ++ and of the radical were detected as indicated by the lines and arrows. The relative intensity of the spectrum is taken to be arbitrary. The intensity of the radical signal is enchanced by the artificial y-irradiation at room temperature. The samples were annealed, at 100 °C for POSTOJNA STALACTJTE; Magnetic Field C G l Fig. 3. ESR derivative absorption spectra of Postojna Cave stalactite before and after the artificial y-irradiation from 60Co. The radical signal at the central position is enhanced by the irradiation. The other signals are associated with Mn++ and ca++ sites in the carbonate Sl. 3.' ESR absorbcijski spektri stalaktita iz Postojnske jame pred in Po umetnem y obsevanju s 60Co. Osnovni signal na osrednjem mestu je povečan zaradi obsevanja. Ostali signali se nanašajo na gnezda Mn++ in ca++ v karbonatu 124 M. Ikieya ... , ESR Datling of Postoj.n:a Cave Stalactite -20 -10 .C .... o 15-r-------------, / / / / / / -AD/ 0-+---....-------.------,---- 0 5 10 15 20 o-Ray (kR) Fig. 4. The enchancement of radical signal intensity as a function of the radiation dose of y-rays from 60Co. The archaeological dose (AD) ha.s been obtained by extrapolating the linear growth Sl. 4. Povečanje intenzivnosti osnovnega signala kot funkcija obsevalne doze y-žarčenja 6°Co. Arheološko doz.o smo dobili z ekstrapoliranjem linearne rasti 10 minutes, to remove the unstable radical soon after y-irradiation. The typical enchancement of the signal intensity by the y-irradiation is shown in Fig. 3. The linear extrapolation of the signal intensity versus dose gives the AD. Fig. 4 shows the obtained AD as a function of the position from the sur- face. The AD at the surface of the stalactite is somewhat larger than the AD at the position close to the surface. Naturally AD increased in the old inside position until close to the central position. The maximum AD, obtained for this stalactite was (38±3) kRad. Neglecting the surface data point which sometimes gives a large AD for unknown reasons, one can roughly obtain the growth velocity of (2.2 ± 0.2) µm/Rad for the old inside of the stalactite. The AD obtained for the other stalactites ranges in the some order of magnitude. In this case, the porous stalactite sometimes gives small AD, pre- sumably because of recrystalization. 125 10 40 ~ 30 (1,) U) o o L.. <( 10 o o Acta carsologica XI, 1982 (1983) flood loam 1 younger -E- ~ older Stalact ite tayers ? tA .,, ... _,,.,,, ... --/ \ 1 I • r----, o 1-f-1/ C 10 20 30 Distance from Stalactite Surface (mm) Fig. 5. The archaeological dose (AD) in kRad of Postojna Cave stalactite as a function of a distance from the surface. The reason for the large AD at the surface is not known. The growth velocity per Rad has been obtained. The growth is rapid in recent years Sl. 5. Arheološka doza (AD) stalaktita iz Postojnske jame kot funkcija oddaljeno- sti od površja, izražena v kRad. Vzrok velikih vrednosti AD na površju ni znan. Dobili smo podatke o hitrosti rasti na Rad. Ta je velika v zadnjih. letih 126 M. I~eya ... , ESR Da1!ing of Postojna Cave Stalactite 11 The Age and Growth Velocity Unfortunately measurements of the radioactive elements in Postojna Cave deposits have not been done. We have rneasured the natural y-ray radiation outside and inside the Postojna Cave with the therrnolurniniscence dosirneter (TLD} of CaSO4 (TM) (National TLD-110S). The annual dose was 98±4 mR/yr outside the cave and 38±2 rnR/yr inside the cave. The amount inside the cave is highter than 20 mR in the Akiyoshi Cave, the largest cave in J apan. The terra rossa ar the soils flown as well as a high concentration of atmospheric radioactivities accumulated in the cave may cause this high results. Recent study of atmospheric radioactivity in the Akiyoshi cave indicates o high con- centration of 3 pCi/1. (T. Mi ki, M. I k e y a , 1979) The concentration may reach one working level (WL) measure used in uranium mines, 100 pCi/1) for along cave like Postojna Cave. The annual dose rate used to convert the AD into real age in years is not the y-ray dose rate obtained by the TLD measurement. It involves the radiation of a, f3 and y-rays from inside the stalactite. The contents of the radioactivi- ties in 238U, 232 Th series and 4°K are not known at present. We simply assume the annual radiation dose of 0.1-0.2 Rad/yr. Considering the relatively high y-rays dose rate determined with TLD, the dose rate around 0.2 R/yr might be appropriated. The ages and the growth velocities are thus calculated from the AD (Fig. 5). The age and the position close to the center is 1.9 X 105 yrs. The recent radial growth rate is thus (0.44±0.04) µm/yr. The average growth velocity in the past before about 5.0 X 104 yrs, is (0.06 ± 0.02) µmiyr. It is interesting to note that the radia! growth rate of Akiyoshi stalactite is recently 0.45 µm/yr as compared to the value 0.045 µm/yr estimated for older periods before 7.0 X 104 years. The radial growth rates coincide roughly. The estimated age of the stalactite in the present work exceeds the pre- viously expected. Our ESR dating of flowstones indicates a very young forma- tion and a fast growth rate. However, the pattern of brown sediment of the present stalactite suggests that longitudinal growth had been stopped in the past. We have cross checked the age of some stalagmites with U/Th rnethod and 14C dating and could show a reasonable agreement. Thus, it would not be doubtful that we have picked up a very old stalactite that had stopped in the lcmgitudinal growth. The ESR dating of the stalagmite in Grotta Castellana gave an AD of 6.8 k Rad and a radial growth velocity of 6 µm/rad: correspond- ing to 3.4 . 104 yrs and the 1.2 µm/yr. The longitudinal growth rate was esti- mated as 35±5 µm/yr. This value corresponds to growth rates of 3-4 mm in one hundred years and agrees with the rates reported by 14C dating far stalag- mites in the postglacial period. The assumption of 0.2 Rad/yr rnay not be appropriate because there rnay be a high concentration of radioactive elements in the stalaktite. We are not certain on this point. A high AD at the surface is sometimes observed. It would not be due to radioactivity from 222Rn and its daughters. The atmospheric ra- dioactivity from the decay of 222Rn and its daughter emanating from cracks and fissures in the cave will certainly produce y and cx.-rays. But the inner parts have once represented the surface of the stalactite. Therefore, unless 127 12 Acta carsologic,a XI, 1982 (1983) some drastic change in the cave environment has occured recently, the surface damage must not be observed so high. It is also hard to consider that the damage was caused by nuclear bomb tests. Our investigation indicates the presence of 137Cs in the bottom soil of doline but not in the cave so far as Japanese cave Akiyoshi is concerned. The effect of some biological species is suspected. Thus, the large AD at the surface is a question open to further research in nuclear archaeo-speleology. GEOCHRONOLOGICAL DISCUSSION One of the most interesting tasks of the speleology is the study of relative and absolute sinter age. The caves of Classical Karst around Postojna are richly concretioned therefore the studies and testing of the research methods, originating here and abroad, are the most brought forward. Till now in the Postojna Cave System the relative dating methods have been successfully used and some data about the radiometric sinter age have been obtained by 14C and U/Th methods. The additional dating experiment about the absolute sinter age from Po- stojna Cave has been made by M. Ikeya with ESR method, as it is evident from this oontribution. We try to give some explanations to this article concerning the analysed sample and the geochronological interpretation of the obtained results. In the last years we studied the sinter and its age in Pisani rov (The Co- loured Gallery) of the Postojna Cave. We studied the recent sinter growth by chemical methods and we distinguished the generations of stalactites and sta- lagmites of various shapes by geological methods. In Pisani rov we know at least three sinter generations which growth was several times interrupted because of changeable Pleistocene climate and because of flooded channel. Tak- ing in account the brown loams on the sinter and on the rocky channel walls it is possible to conclude that the muddy flood water several times reached the channel and at least once reached so high (up to 540 m above the sea level, it means 30 m higher as lies actual entrance to the cave) that the channel was flooded up to the ceiling. In this period the sinter could not be deposited, the percolating water simply melted together with flood water. On the older sta- lactites the brown loam coming from ponor flysch hinterland was deposited. Such layer of brown loam (layer E) is preserved in analysed stalactite. A lot of different coloured layers on the stalactite, distinguished among them (Fig. 1) prove, that the sinter growth on the ceiling was several times interrupted, the last tirne in the period when the analysed stalactite was broken from the ceiling and has fallen to the gallery's floor. There it was namely found and chosen for the analysis. The ESR method of dating fixes the origin of stalactite nucleus to 190.000 years b.p. thus we can conclude that the sinter growth phase occurred at the end of Riss-Mindel Interglacial, while the highest flood period was in Riss Glacial. The next sinter layer on the stalactite above the loam could be from the Upper Riss Glacial and Riss-Wilrm Interglacial. The upper layers can be ranged in Wilrm Interstadials, because the Holocene age could not be taken into acoount, becaues the chosen stalactite group had been already broken from 128 M. Ikleya ..• , ESR Dat!ing of Postoj111a Cave Stalactite 13 the ceiling in this tirne. Several other cases in Pisani rov namely show that Pleistocene collapsed sinters are already thickly covered by Holocene white sinter (R. Gospodarič, 1976). The recent physico-chemical methods of absolute sinter dations, among them the ESR method, complete the stratigraphic rangement of autochtonous and allochthonous cave sediments. Thus they give a contribution to knowledge o± Quaternary geology in karst caves and on karst in general. ACKNOWLEDGEMENT The authors wish to thank to Institute for Karst Research SAZU at Po- stojna for the help by sampling of stalactite and settling the TLD capsules. Presented laboratory work has been made first at II. Physikalisches Institut in Stuttgart as a research fellow of Alexander von Humbolt Foundation and then at Reactor Institute of Kyoto University as a Joint Use of University Reactor. 129 14 Acta carsologica XI, 1982 (1983) REFERENCES A it k en, J. M.: Physics and Archaeology, 2nd edition, Clarendon Press, Oxford (1974). F 1 e min g, S.: Dating in Archaeology, J. M. Dent & Sons, London (1976). G o s p o dar i č, R.: Acta carsologica, 7, Slovenska akademija znanosti in umetnosti, Ljubljana (1976), 5-135. G o s p o da r i č, R.: Acta carsologica, 9, Slovenska akademija znanosti in umetnosti, Ljubljana (1981), 87-100. I k e y a, M.: Nature, 255 (1975), 48-50. I k e y a, M.: Archaeomoetry, 20 (1978), 147-158. I k e y a, M.: Naturwissenschaften, 65 (1978), 489. Mi ki, T., M. Ikeya: Japan J. Appl. Phys., 17 (1978), 1703-1904. :;_y1 i ki, T., M. Ikeya: Article submitted to Health Phys. (1979). DATIRANJE STALAKTITA IZ POSTOJNSKE JAME Z ERS METODO Povzetek Preučevanje relativne in radiometrične starosti sige sodi med najbolj zanimive naloge speleologije. Ker so jame klasičnega krasa okrog Postojne bogato zasigane, je razumljivo, da je prav tod možno uveljaviti in preizkusiti ustrezne raziskovalne metode, ki se porajajo doma in v svetu. V Postojnskem jamskem sistemu so bile doslej koristno uveljavljene relativne metode datiranja (R. Go s p oda r i č, 1976), nekaj podatkov o radiometrični starosti sige pa smo dobili tudi z 14 C in U/Th metodama (R. G o spod ari č, 1981). Nadaljnji poskus datiranja sige iz Postojnske jame sta izpeljala Motoji Ikeya in Toshikatsu Miki z ESR metodo, kar je razvidno in pojasnjeno v pričujočem pri- spevku. Za boljše razumevanje teh analitičnih podatkov pa je treba dodati še nekaj geokronološluh pojasnil. V preteklih 111ekaj letih smo preučevali sige in njeno starost v Pisanem rovu Postojnske jame. S kemičnimi metodami smo ugotavljali recentno rast sige, z geo- loškimi metodami pa razlikovali generacije oblikovno pestrih stalaktitov in stalag- mitov. V Pisanem rovu poznamo vsaj tli generacije sige, katerih rast je bila več­ krat prekinjena zaradi spremenljive pleistocenske klime in zaradi poplavljenega rova. Po rjavi ilovici na sigi in skalnih stenah rova je možno sklepati, da je kalna po- plavna voda večkrat zašla v rov, vsaj enkrat tako visoko (do 540 m nadmorske vi- šine, to je 10 m više kot je današ1I1ji turistični vhod v jamo), da ga je zalila do stropa Tedaj se siga ni mogla odlagati, ker se je prenikla voda preprosto zlila s poplavno vodo. Ta je na starejše stalaktite odložila rjavo alohtono ilovico, kakršna je ohranjena v analiziranem stalaktitu (plast E). Več raznobarvnih, med seboj ločenih plasti sta- laktita (sl. 1) pa nadalje govorijo, da je bila rast sige na stropu še večkrat prekinjena, nazadnje tedaj, ko se je analizirani stalaktit odlomil od stropa in padel na tla. Tam smo ga nar.ireč našli in izbrali za analizo. Ker je ESR metoda datiranja pokazala, da je jedro stalaktita staro 190.000 let b. p., je možno sklepati na sigotvorno fazo ob koncu riško-mindelskega interglaciala, na omenjeno najvišjo poplavno dobo pa v riškem glacialu. Naslednja plast sige na stalaktitu (nad ilovico) je lahko iz mlajšega riškega glaciala in interglaciala riss- wilrm, nadalje krovne plasti pa je možno uvrstiti v wilrmske interstadiale, saj holo- censka starost ne pride več v poštev, ker se je v našem primeru izbrana stalaktitna skupina tedaj že odlomila od stropa. Novejše fizikallllo-kemične metode radiometričnega datiranja sige, med njimi tudi ESR metoda, dopolnjujejo stratigrafsko uvrščanje avtohtonih in alohtonih jam- skih sedimentov. S tem prispevajo k poznavanju kvartarne geologije kraških jam in krasa nasploh. 131