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New age data of buried peat deposits from the site "Fili Park" (Moscow, Russia) by the uraniumthorium dating and palynological analysis and its stratygraphic significance

Kuznetsov V. Yu., Arslanov K. A., Alekseev M. N., Pisareva V. V., Chernov S. B., Maksimov F. E., Baranova N. G.

Geochronometria

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2002

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Vol. 21

41-48

EN

The chronostratygraphically important Quaternary buried peats from the site "Fili Park" (located on the territory of Moscow) on the Russian Plain were studied by the methods of uranium-thorium dating (UTD) and palynological analysis. The deposits under study were the subject of intense debate: some number of the palynologists assigned ones to the Mikulino (Eem) Interglacial, while the another investigators - to the Odintzovo Interglacial (Middle Pleistocene). Detailed palynological study gave the possibility to mark out the 3 palynozones (M2, M3 and M4) in section vertical profile and refer the deposits to the Mikulino (Eem) Interglacial. The uranium-thorium dating (by "leachate alone" method) was carried out in the middle layers, which would be expected to be a closed system in respect to uranium and thorium isotopes. The direct uranium-thorium dating of inner layers showed the first UTD ages from 78.9 to 105.0 ka for deposits from the site "Fili Park". The corrected uranium-thorium age of buried peat turned out to be younger than the currently adopted boundaries of the last Interglacial (116-128 ka) and comprised 89š11 ka. There was probably an additional post-deposition uranium uptake in the internal section layers that in general have led to an underestimated age value. Nevertheless, we refered these questionable in chronostratigraphic respect deposits to the Mikulino Interlacial. The geochronological data obtained were compared with the uranium-thorium dating results (113š11 ka) for the closed geochemical samples from the Mikulino (Eem) Interglacial peats of the stratotypical section "Mikulino" (Russian Plain). This comparison confirmed the reliability of our conclusions.

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230Th/U and 14C dating of mollusc shells from the coasts of the Caspian, Barents, White and Black Seas

Arslanov K. A., Tertychny N. I., Kuznetsov V. Yu., Chernov S. B., Lokshin N. V., Gerasimova S. A, Maksimov F. E., Dodonov A. E

Geochronometria

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2002

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Vol. 21

49-56

EN

We dated Holocene and Late Pleistocene mollusc shells collected from coastal sediments of the Caspian, Barents, White and Black Seas by means of both a modified 230Th/U method and the radiocarbon method. Essence of the modification is the removal of the surface (about 1/3 of the weight) of the mollusc shells by nitric acid as it may contain adsorbed detrital 232Th and 230Th. The 230Th/U dates of the inner part of the shells do not require detrital correction with the 232Th activity and well agree with the corresponding reservoir-corrected and calibrated 14C ages of mollusc shells with ages between 1300 and 13,500 BP. We tested the modified 230Th/U method on thick-walled and well-preserved mollusc shells from the transgression sediments of the Barentz, White and Black Seas derived during the Mikulino Interglacial (MIS 5e) and the Early Valday Glaciation (MIS 5c). The 230Th/U ages of the inner part of the shells from the Boreal (Eem) transgression sediments of the Barentz and White Seas ranged from 86 to 114 ka and those from the Karangat (Eem) transgression in the Black Sea (Maly Kut and Eltigen sections) from 95 to 115 ka. The new 230Th/U dates of the shells from the section Eltigen ranged from 100 to 125 ka.

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230Th-excess and 14C dating of pelagic sediments from the hydrothermal zone of the North Atlantic

Kuznetsov V. Yu., Arslanov K. A., Shilov V. V., Cherkashev G. A., Chernov S. B.

Geochronometria

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2002

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Vol. 21

33-40

EN

A comprehensive geochronological study of a pelagic sediment core altered by hydrothermal processes from the Mid Atlantic Ridge (14.5°N) was carried out using both the 230Thexcess and the radiocarbon methods. Complementary foraminiferal tests and oxygen-isotope determinations were done. The main task was to check whether 230Thexcess dating of such diagenetically changed sediments yields reliable absolute ages. For this purpose the vertical distribution of the 238U, 234U, 232Th and 230Th activities along the core was measured. The results proved that it was not disturbed during the aging of the sediment. The long-term hydrothermal influence had been constant during at least the last 300 ka and did not change the natural 230Thexcess distribution along the core. Hence, 230Thexcess dating yields reliable ages and allows to calculate sedimentation rate. Between the uppermost and lowermost sublayers of the core we obtained 1.35š0.15 cm/ka which agrees with 1.47š0.03 cm/ka derived from conventional 14C ages. These numerical dates, the results of the foraminiferal tests and the d18O values place the studied sediments to the marine isotope stage 5 (MIS 5). These dates are well correlated with the corresponding sedimentary records from pelagic sediments of the North Atlantic Ocean.