Доклады Академии наукДоклады Академии наук0869-5652The Russian Academy of Sciences1288210.31857/S0869-56524853356-360Research Article238U/235U isotopic ratio as redox conditions marker in ediacarian paleobasin: section in Chaya river, Baikal-Patom highland, south of middle SiberiaChugaevA. V.vassachav@mail.ruChernyshevI. V.<p>academician of the RAS</p>vassachav@mail.ruPokrovskyB. G.vassachav@mail.ruMandzhievaG. V.vassachav@mail.ruGareevB. I.vassachav@mail.ruSadasyukA. S.vassachav@mail.ruBatalinG. A.vassachav@mail.ruInstitute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry of the Russian Academy of SciencesGeological Institute RAS, Research Organization of the Russian Academy of SciencesKazan Federal University2105201948533563602305201923052019Copyright © 2019, Russian academy of sciences2019<p>This article is devoted to a study of variations in the U isotopic composition (<sup>238</sup>U/<sup>235</sup>U) in the section of clas- tic-carbonate Ediacaran sediments exposed along the Chaya River in the southern part of Central Siberia (Russia). Measurements of <sup>238</sup>U/<sup>235</sup>U in the rocks were performed using a high-precision (0.07%o, 2SD) MC-ICP- MS with a <sup>233</sup>U-<sup>236</sup>U double isotope spike. The total variation range of S<sup>238</sup>U in the studied carbonate rocks was -0.91 to -0.01%. Extremely low values of S<sup>238</sup>U (-0.91%, -0.9%, and -0.84%), which were found in a number of samples from the lower part of the section, are interpreted as the result of postsedimentation processes affecting the rocks. In the overlying sediments, the range of S<sup>238</sup>U variations is smaller from -0.49 to -0.01%. Here, regular weighting of the U isotopic composition observed upwards through the section indicates an increase in the reduction conditions at this time (about 550 Ma) in the paleobasin. This conclusion is consistent with the elevated concentrations of U, Mo, and V in the Late Ediacaran sedimentary rocks of the region studied.</p>238U/235U isotopic ratioMC-ICP-MS methodEdiacarian Periodcarbonate rocksREDOX condition238U/235U-изотопное отношениеMC-ICP–MS-методэдиакарский периодкарбонатные породыокислительно-восстановительные условия[Andersen M. B., Stirling C. H., Weyer S. // Rev. Mineral. & Geochem. 2017. V. 82. P. 799-850.][Stirling C. H., Anderson M.B., Potter E.K, Halliday A. N. // Earth and Planet. Sci. Lett. 2007. V. 264. P. 208-225.][Brennecka G. A., Herrmann A. D., Algeo T. J., Anbar A. D. // Proc. Natl. Acad. Sci. USA. 2011. V. 108. P. 17 631-17 634.][Kendall B., Brennecka G. A., Weyer S., Anbar A. D. // Chem. Geol. 2013. V. 362. P. 105-114.][Rolison J.M., Stirling C.H., Middag R., Rijken- berg M.J. // Geochim. et Cosmochim. Acta. 2017. V. 203. P. 69-88.][Чугаев А. В., Чернышев И. В., Будяк А. Е., Манджи- ева Г. В., Садасюк А. С., Гареев Б. И. // ДАН. 2019. Т. 484. № 4.][Lyons T. W., Reinhard C. T., Planavsky N. J. // Nature. 2014. V. 506. № 7488. P. 307-315.][Немеров В. К., Станевич А. М., Развозжаева Э. А. Будяк А. Е., Корнилова Т. А. // Геология и геофизика. 2010. Т. 51. № 5. С. 729-747.][Чугаев А. В., Будяк А. Е., Чернышев И. В., Дубинина Е. О., Гареев Б. И., Шатагин К. Н., Тарасова Ю. И., Горячев Н. А., Скузоватов С. Ю. // Петрология. 2018. Т. 26. № 3. С. 213-244.][Покровский Б. Г., Буякайте М. И. // Литология и полез. ископаемые. 2015. № 2. С. 159-186.][Чернышев И. В., Голубев В. Н., Чугаев А. В., Баранова А. Н. // Геохимия. 2014. № 12. С. 1059-1078.][Richter S., Eykens R, Kuhn H., Aregbe Y., Verbruggen A., Weyer S. // Int. J. Mass Spectrometry. 2010. V. 295. P. 94-97.][Манджиева Г. В., Садасюк А. С., Чернышев И. В., Шатагин К. Н., Чугаев А. В., Гареев Б. И. // Масс- спектрометрия. 2018. Т. 15. № 1. С. 12-21.][Romaniello S. J., Herrmann A.D., Anbar A. D. // Chem. Geol. 2013. V. 362. P. 305-316.][Halverson G. P., Wade B. P., Hurtgen M. T., Baro- vich K. M. // Precambr. Res. 2010. V. 182. P. 337-350.]