• Radiocarbon Dating of Millimole-Sized Gaseous Samples

      Srdoč, Dušan; Obelić, Bogomil; Horvatinčić, Nada (American Journal of Science, 1983-01-01)
      As an alternative to the accelerator technique, a simple, compact, small counter system has been developed and tested for routine 14C dating. Our small counter is an all-metal design made of the OFHC copper with quartz supports for the anode (25 micrometers stainless steel). Careful selection of materials for the counter construction was made based on the measurements of the alpha contamination. Methane as the counter filling gave better resolution and gas gain stability, whereas CO2 gave lower background counting rate and it was easier to prepare and to handle. The long term run using CH4 showed that the gas gain remained stable within 1-2% for months after the initial drop which followed the counter filling. A 7-day counting period was sufficient to achieve a 3% relative standard deviation which was considered acceptable for routine dating of younger samples.
    • Radiocarbon Dating of Tufa in Paleoclimatic Studies

      Srdoč, Dušan; Horvatinčić, Nada; Obelić, Bogomil; Sliepčević, Adela (American Journal of Science, 1983-01-01)
      Calcareous deposits known as tufa or travertine contain biogenic carbon and are a potential source of geochronologic information. Many dated samples from Karstic regions in Yugoslavia proved that 14C analyses of tufa can provide reliable data reflecting climatic conditions in the past. Systematic dating of tufa samples revealed two distinct groups of deposits: recent tufa deposits, with a sharp age limit of ∼6000 +/- 500 years BP, and old tufa deposits with 14C age ranges from 25,000 +/- 2300 years BP to the lowest limit of our 14C dating system (∼37,000 years). A histogram based on the initial activity AO = 0.85 shows the age distribution of randomly sampled tufas vs sample frequency. A time gap between ∼6000 BP and ∼23,000 BP is evident, reflecting cooler climatic conditions. The start of peat deposition is coincident with that of tufa growth in the Holocene. Paleoclimatic implications of tufa growth periods obtained by 14C dating are as follows: climatic conditions that favor tufa formation at least in karstic regions, are very stringent. Therefore, climatic conditions, such as mean annual temperature and humidity, as well as hydrologic and vegetational conditions, must have been very similar in periods of tufa growth. While recent tufa deposits are coincident with the warm Holocene period, old tufa can be associated with warm interstadials in the Würm.