No abstract

ABSTRACT. This work focuses on the preparation and dating of sporomorph (pollen and spores) concentrates of high purity. Three sediment cores recovered from Lake Baikal within the EU-Project CONTINENT were subjected to palynological analyses and accelerator mass spectrometry (AMS) radiocarbon dating. Laboratory processing of concentrates was aimed at the removal of non-sporomorph organic matter by means of chemical treatment, micro-sieving, and heavy liquid separation. The obtained concentrates were checked under the microscope and sample purity was estimated on the basis of particle counts. The results of AMS 14 C dating show differences in the sedimentation rate among 3 sites of Lake Baikal. METHODSLake Baikal is situated in southeast Siberia in the eastern part of the Russian Federation near the Mongolian border. It is the largest (20% of the total volume of surface freshwater), deepest (>1600 m), and probably oldest (about 25 million yr) lake on Earth.Radiocarbon dating of Lake Baikal sediments is a difficult challenge, as previous studies have proved (Coleman 1996). The main problem is the scarcity of material suitable for dating because the sediments are very poor in organic matter and carbonates. Our work focused on the preparation and dating of high-purity sporomorph concentrates.Three sediment cores recovered from Lake Baikal were subjected to palynological analyses and AMS 14 C dating. The cores come from 3 different locations: Posolskoe Bank, Vydrino Shoulder, and Continent Ridge (see Figure 1). The cores subjected to dating were collected with the use of a Kasten corer, which gives the best assurance of complete recovery of the sediment.The preliminary knowledge about sporomorph concentrations and sporomorph assemblages in Holocene and Late Glacial core sections, necessary for selecting appropriate subsampling levels, was gained during palynological analyses of these cores. Sample sizes ranged between 20 and 160 cm 3 (see Table 1), depending on available material, pollen concentrations, and a rough calculation of pollen mass and carbon content using data available from previous studies (Erdtman 1969;Brown et al. 1989). The volume of samples taken for preparation was adjusted to obtain a minimum carbon content of about 2-4 mg per sample. Extraction of SporomorphsLaboratory processing of pollen and spore concentrates was aimed at achieving a high purity of the samples. The removal of inorganic and non-sporomorph organic matter was carried out using chemical treatment, micro-sieving, and heavy liquid separation.

No abstract

No abstract

No abstract

No abstract

Abstract:The TL dating of sinter crust of Morasko meteorites proves that the extraterrestrial matter fell about 5000 yr BP. Similar data were obtained for the Kaali impact. The OSL analyses show incomplete bleaching of old rock material especially in the Estonian craters. Almost all data obtained for the immediate impact area indicate ages younger than the Quaternary morphogenesis. The method used seems promising for determining the age of impacts and the origin of small depressions of unknown genesis.

No abstract