Radiocarbon AMS dating of isotopic diagrams of Late Pleistocene ice wedges

Vasil’chuk, Y.K.; Kim, J.C.; Vasil’chuk, A.C.

Авторы: Vasil’chuk Yu K., Kim J.C., Vasil’chuk A.C.
Журнал: Doklady Earth Sciences
Том: 383
Номер: 3
Год издания: 2002
Издательство: Maik Nauka/Interperiodica Publishing
Местоположение издательства: Russian Federation
Первая страница: 282
Последняя страница: 287
Аннотация: The prime object of this work was to elaborate a new strategy for the radiocarbon dating of Late Pleistocene syngenetic ice wedges and the precise temporal correlation of diagrams of the distribution of stable isotopes using the method of amplified mass-spectrometry (AMS). Three principal problems should be addressed in carrying out geochronological reconstructions with the application of the AMS method: (1) the sampling technique and the necessity of collecting sufficiently large and appropriate (i.e., nonredeposited or synchronous to sedimentation) samples; (2) the comparison and use of dates previously obtained for large samples with new AMS dates obtained for very small samples; (3) unambiguous interpretation of AMS dates in connection with an overestimation of the age of sediments because of a considerable redeposition of the old material, which is often impossible to identify visually or by any other means except dating. At early stages of our work, oxygen isotope diagrams for ice wedges were indirectly dated, on the basis of dates obtained for synchronous (relative to ice) host rocks. Though being one of the most precise paleogeographic methods, the radiocarbon dating of permafrost has run into difficulties related to a prolonged preservation of the organic material in permafrost and its multiple redeposition from older to younger sequences. This phenomenon is much more widespread than was previously assumed. Older dates of redeposited organic material are typical not only for Late Pleistocene fluvial deposits but for Holocene peat bogs as well. This led to the appearance of overestimated values for Late Pleistocene sequences, underestimated values of sedimentation rates, and consequent significant discrepancies in the correlation of isotope diagrams. Therefore, we attempted to find methods for the direct dating of organic material extracted from syngenetic ice wedges. At the first stage of this work, we collected very large samples (more than 60 kg) of ice wedges (age 14-21 ka) from the Seyakha section, Yamal Peninsula. Then, the samples were enriched by settling the organic material and removing a part of water. The treated samples were delivered in containers (mass 1 kg) to the AMS Laboratory of Groningen University for I4C dating. At the second stage of our work, related to ice wedges of the Bizon section in the Kolyma region (26-33 ka), we decreased the mass of the initial ice sample to 30 kg and obtained satisfactory dates. The technique of measurement and preliminary processing of samples is rapidly upgraded, and it is possible to obtain dates for samples with a carbon content of less than 1 mg. Therefore, we assumed that even smaller amounts of the organic material in small samples may be dated. We used small water samples (40 g) with an organic impurity not less than 0.5-1 mg. The samples were taken from ice in the Yakutia region in 1983-1991. Here, the detailed oxygen isotope diagrams were available for four sections. Three sections are located in lower reaches of the Kolyma River (Zelenyi Mys, Duvannyi Yar, and Plakhinskii Yar), while the fourth section is situated in the Aldan River region (Mamontova Gora). The correlation of all the sections was made at first by the radiocarbon dating of various organic materials selected from host sediments. The direct dating of the organic material collected from ice showed that the correlation had been made correctly but the new data obtained radically changed the inference on the age of ice wedges from the Mamontova Gora section
Добавил в систему: Васильчук Юрий Кириллович

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1.	Полный текст		Vasilchuk_2002_DAN_IW_14C_Rus.pdf	2,2 МБ	19 мая 2012 [vasilchuk]
2.	Vasilchuk_2002_DAN_IW_14C_Engl.pdf		Vasilchuk_2002_DAN_IW_14C_Engl.pdf	4,4 МБ	9 марта 2015 [vasilchuk]

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Radiocarbon AMS dating of isotopic diagrams of Late Pleistocene ice wedgesстатья

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