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

100%

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

Geochronometria

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2002

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tom 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.

2

First 230Th/U date of middle Pleistocene peat bog in Siberia (key section Krivosheino, Western Siberia)

100%

Maksimov F. E. F. E. , Laukhin S. A. , Arslanov K. A. , Kuznetsov V. Y. , Shilova G. N.

Geochronometria

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2012

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tom Vol. 39, no. 4

241-251

EN

A ¹⁴C date older than 53900 yrs BP was obtained for the uppermost part of the buried peat bog in Krivosheino section (Middle Pleistocene of Western Siberia). These sediments also yielded ²³⁰Th/U dates of 195 _-9.1 ka using the leachate alone (L/L) and 204 ⁺¹⁷ _-13 ka using total sample dissolution (TSD) models. Peculiarities of 230Th/U dating are discussed. Palynological investigation of the buried peat bog together with underlying and overlaying sediments, and comparison with palynologi-cal data from Baikal and Elgygytgyn lakes revealed that the peat layer in Krivosheino section was formed at the end of Shirta Interglacial (Marine Isotopic-Oxygenous stages MIS-7), when climate conditions at all studied sites were more severe compared to the modern ones.

3

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

86%

Kuznetsov V. Y. , 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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tom 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.

4

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

72%

Arslanov K. A. , Tertychny N. I. , Kuznetsov V. Y. , 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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tom 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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Absolute chronology of fluvial events in the Upper Dnieper River system and its palaeogeographic implications

72%

Panin A. V. , Adamiec G. , Arslanov K. A. , Bronnikova M. A. , Filippov V. V. , Sheremetskaya E. D. , Zaretskaya N. E. , Zazovskaya E. P.

Geochronometria

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2014

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tom Vol. 41, no. 3

278--293

EN

A set of 121 radiocarbon and OSL dates has been compiled from the Upper Dnieper River and tributary valleys, Western European Russia. Each date was attributed according to geomorphic/sedimentological events and classes of fluvial activity. Summed probability density functions for each class were used to establish phases of increasing and reducing fluvial activity. The oldest detected reduction of fluvial activity was probably due to glacial damming at LGM. Within the Holocene three palaeohydrological epochs of millennial-scale were found: (1) high activity at 12,000–8,000 cal BP marked by large river palaeochannels; (2) low activity at 8,000–3,000 cal BP marked by formation of zonal-type soils on -floodplains; short episodes of high floods occurred between 6,500—4,400 cal BP; (3) contrasting hydrological oscillations since 3,000 cal BP with periods of high floods between 3,000–2,300 (2,000) and 900–100 cal BP separated by long interval of low floods 2,300 (2,000)-900 cal BP when floodplains were not inundated — zonal-type soils were developing and permanent settlements existed on floodplains. In the last millennium, four centennial-scale intervals were found: high flooding intervals are mid-11–mid-15th century and mid-17–mid-20th century. Intervals of flood activity similar to the present-day were: mid-15–mid-17th century and since mid-19th century till present. In the context of palaeohydrological changes, discussed are selected palaeogeographic issues such as: position of the glacial boundary at LGM, role of changing amounts of river runoff in the Black Sea level changes, floodplain occupation by Early Medieval population.