Uran-Thorium Datierung

Transkript

1 Uran-Thorium Datierung Axel Berger Institut für Ur- und Frühgeschichte Universität zu Köln Seminar: Datierungsmethoden Wintersemester 2013/14 PD Dr. Daniel Richter

2 Gliederung 1 Grundlagen und Methode 2 Probleme und Fehlerursachen 3 Anwendungen 4 Résumé

3 Die 238 U / 206 Pb Zerfallsreihe Ge05

4 Die Zerfallsreihe in der Nuklidkarte NU98

5 Entwicklung der Aktivitätsverhältnisse Ge05

6 Entwicklung der Aktivitätsverhältnisse Ge08

7 Dating Using Long-Lived and Short-Lived Radioactive Isotopes Entwicklungslinien im U/U Th/U Diagramm U/ 238 U activity ratio ka 50 ka 100 ka 200 ka 300 ka 400 ka 600 ka Th/ 234 U activity ratio Wa05

8 Uran und Thorium im Periodensystem PS02

9 Korrektur der Verunreinigung mithilfe der Rosholt-Geraden Die Steigung der Rosholt-Geraden entspricht dem Verhältnis des radiogenen Anteils von 230 Th zum Mutternuklid 234 U [Ge05, 96]. Ge05

10 Ein Niedermoor als teiloffenes verunreinigtes System Ge08

11 Ein Niedermoor als teiloffenes verunreinigtes System Ge08

12 Die Meßwerte der Torfproben Ge08

13 Korrektur Ge08

14 Das korrigierte Ergebnis Ge08

15 one of the most rium-230 in a geological or biogenic material, to operate on milligrams of such material ( 5, through Höhlenkunst decay of uranium mit incorporated Kalzitschichten 6) (see the figure). nders Datierung of tens of von rehistory. Found within it at its time of formation. When it was Cave art is typically found in carbonate fundamental for t human culture t, despite great ogies, it remains mine the age of a ave or rock sheloften limited to onology by comwhere available, us links to other artietric uably techin the ble to other n ( 2)., Pike study from pplied uraating first applied almost 50 years ago, this technique required samples of 100 g or more in the case of cave formations such as those now dated by Pike et al. In 1987, Edwards et al. showed that U-Th dating could be conducted by mass spectrometric analysis ( 4). Through this and subsequent advances, the efficiency of measurement has increased by more than four orders of magnitude, enabling hypersensitive techniques like that used by Pike et al. ~1 mm terrains, where the majority of caves have developed worldwide. The stalagmites, stalactites, and similar formations that grow in such caves, collectively known as speleothems, all contain trace amounts of uranium and are thus amenable to U-Th dating. Very thin sheets or drapes of this material can sometimes be found grown over the top of Paleolithic cave art, and in some cases may also underlie or even sandwich it ( 7, 8). s the tho- ~100 g ~5 g <0.01 g Pi12, He12 U-Th sampling of calcite overgrowths. Since U-Th dating was first introduced in the 1960s, sample size requirements have

16 Plausibiltätskontrolle an dicken Schichten Supplementary Figures Fig. S1. Uranium series dates on paired samples. Aliquots of samples were removed, representing the Pi12

17 Altersverteilung der 50 gemessenen Proben Pi12

18 Beispiele datierter Felskunst Pi12

19 Die beiden ältesten Proben aus der El-Castillo-Höhle Pi12

20 Die beiden ältesten Proben aus der El-Castillo-Höhle Pi12

21 Die beiden ältesten Proben aus der El-Castillo-Höhle Pi12

22 Auswahl derergebnisse Sample BIG-UTh- Site O-53 Altamira O-80 El Castillo O-58 El Castillo O-21 Tito Bustillo O-69 El Castillo O-50 Altamira O-82 El Castillo O-83 El Castillo O-87 El Castillo O-48 Tito Bustillo Description Overlays red spotted outline horse of Techo de los Polícromos chamber Overlays black outline drawing of indeterminate animal of corridor of Techo de las Manos Overlays red stippled negative hand stencil of Techo de las Manos Red pigment associated with anthropomorphic figure of Galería de los Antropomorfos Large red disk of Galería de los Discos Large red claviform-like symbol of Techo de los Polícromos Sample overlays red negative hand stencil, and underlies yellow outline bison of Panel de las Manos Overlays large red stippled disk of Panel de las Manos Underlies large red disk of Galería de los Discos (same panel as O-69) Underlies red anthropomorph figure of Galería de los Antropomorfos (see also O-21) 230 Th/ 238 U Minimum ages 234 U/ 238 U 230 Th/ 232 Th Uncorrected age (ky) Corrected age (ky) T T T T T T T T T T T T T T T T T T T T T 0.55 * T T T T T T T T T T T T T T T T T T T T 0.57 Maximum ages T T T T T T T T T T T 0.39 Pi12

23 Die Xianrenhöhle in Südchina Sh13

24 10 mm Der gebänderte Stalagmit Sh13

25 Die Verteilung der Meßwerte Sh13

26 Das Ergebnis Sh13

27 70 Quaternary Dating Methods Grundlagen Probleme Anwendungen Résumé Résumé Table 3.1 Reliability/unreliability of uranium-series dates for terrestrial materials arising from deviations from closed-system behaviour and contamination by 230 Th and 234 U from detrital material (after Smart, 1991a) Reliability Material Closed system? Contaminated? Reliable Unaltered coral Closed Clean Clean speleothem Clean Volcanic rocks Dirty speleothem Contaminated Possibly reliable Ferruginous concretions Possibly closed Contaminated Tufa Contaminated Mollusc shells Contaminated Phosphates Contaminated Generally unreliable Diagenetically altered corals Open Clean Bone? Evaporites Contaminated Caliche Contaminated Stromatolites Contaminated Peat and wood? Unter idealen Bedingungen ist die Genauigkeit des Verfahrens deutlich besser als ±1 %. Es wird deshalb häufig zur Kalibration anderer Methoden verwendet, uranium into carbonate shells after their death (McLaren and Rowe, 1996), while some vor allem calcitic deposits 14 C jenseits der Dendrogrenze. (such as travertines 5 ) may have been partly recrystallised after deposition. In the case of the latter, however, such open-system activity may be detectable by careful petrographic analysis of the calcite prior to dating (Schwarcz, 1989). Wa05

28 Handout und Literatur Vielen Dank Das Handout und Literatur liegen auf:

29 Literatur Ei93 A. Eisenhauer, G. J. Wasserburg, J. H. Chen, G. Bonani, L. B. Collins, Z. R. Zhu & K. H. Wyrwoll, Holocene sea-level determination relative to the Australian continent, U/Th (TIMS) and 14 C (AMS) dating of coral cores from the Abrolhos Islands. Earth and Planetary Science Letters 114 (1993), Ge05 Mebus A. Geyh, Handbuch der physikalischen und chemischen Altersbestimmung. (Darmstadt 2005). Ge08 Mebus A. Geyh, 230 Th/U-dating of interglacial and interstadial fen peat and lignite: Potential and limits. Eiszeitalter & Gegenwart 57 (2008), He12 John Hellstrom, Absolute Dating of Cave Art. science 336 (2012), NU98 G. Pfennig, H. Klewe-Nebenius & W. Seelmann-Eggebert, Karlsruher Nuklidkarte. (Karlsruhe ). Pi12 Alistair W. G. Pike, U-Series Dating of Paleolithic Art in 11 Caves in Spain. science 336 (2012), PS02 Ekkehard Fluck & Klaus G. Heumann, Periodensystem der Elemente. (Weinheim ). Sh13 Chuan-Chou Shen, Ke Lin, Wuhui Duan, Xiuyang Jiang, Judson W. Partin, R. Lawrence Edwards, Hai Cheng & Ming Tan, Testing the annual nature of speleothem banding. Scientific Reports 3 (2013), DOI: /srep02633.

30 Literatur (cont.) Wa05 Mike Walker, Quaternary Dating Methods. (Chichester 2005). Wa98 Wagner, Age determination of young rocks and artifacts, Physical and chemical clocks in Quaternary geology and archaeology. (Berlin 1998).