Investigation of the isotopic ratio I-129/I in petrified wood

Author(s)

Tania Jabbar, Peter Steier, Gabriele Wallner, Otto Cichocki, Johannes H. Sterba

Abstract

In fossil specimens, measurements of the natural isotopic ratio ¹²⁹I/I may provide a method to estimate the age of sample. The motivation for measuring the isotopic composition (¹²⁹I/I)

of petrified wood samples collected from Austria was to check this

feasibility. Alkaline fusion together with anion exchange was used to

extract iodine from the sample. Typical sample size for this study was

10–90 g. An atomic ratio as low as 10⁻¹⁴ was determined using

accelerator mass spectrometry (AMS). Uranium concentrations measured by

instrumental neutron activation analysis (INAA) and α-spectrometry were

found to be less than 3 mg kg⁻¹, therefore the contribution from fissiogenic ¹²⁹I was small and an estimation of ages was based on the decrease of the initial ratio (due to decay of the cosmogenic ¹²⁹I in a closed system) after subtraction of the fissiogenic ¹²⁹I. The value of the prenuclear ratio is crucial for the use of the ¹²⁹I system for dating purposes in the terrestrial environment. From the preanthropogenic (initial) ratio of 1.5 × 10⁻¹² of the hydrosphere and the results of the present study for the samples from Altenburg (1.05 × 10⁻¹²) and Fuerwald (6.16 × 10⁻¹³),

respective ages of 8 ± 2.2 and 20.2 ± 2.2 million years were derived.

Since samples were collected from a stratum deposited in the Upper

Oligocene/Ergerien period (∼25–30 million years ago), it can be

concluded that these isotopic ratios do not show ages but an elapsed

time since fossil wood was isolated from mineral rich water.

Paleontological investigation shows that samples from Altenburg had

mixed characteristics of old and modern Tertiary plants, thus an origin

from a younger stratum re-sedimented with Oligocene cannot be excluded.

However, the sample from Drasenhofen reflects that the ¹²⁹I/I system might not always be suitable for the dating of petrified wood sample due to fixation of anthropogenic ¹²⁹I into surface fractures.

Organisation(s)

Department of Inorganic Chemistry, Isotope Physics, Department of Palaeontology, Vienna Institute for Archaeological Science, Department of Prehistoric and Historical Archaeology

External organisation(s)

Technische Universität Wien

Journal

Journal of Environmental Radioactivity

Volume

120

Pages

33-38

No. of pages

6

ISSN

0265-931X

DOI

https://doi.org/10.1016/j.jenvrad.2012.12.010

Publication date

06-2013

Peer reviewed

Yes

Austrian Fields of Science 2012

1030 Physics, Astronomy, 1070 Other Natural Sciences, 105118 Palaeontology, 107001 Archaeometry

Keywords

Sustainable Development Goals

SDG 14 - Life Below Water

Portal url

https://ucrisportal.univie.ac.at/en/publications/230e1cc7-8e97-4ee6-adb9-0869583773d9