Geochemical Features of the Olduvai Event in the Sediments of Lake El’gygytgyn (Anadyr Plateau, Chukchi Peninsula)

—The paper is concerned with study of the distribution of geochemical characteristics in the sediments of Lake El’gygytgyn (Chukchi Peninsula) formed during the Olduvai event. A clear geochemical and rock-magnetic zoning of the section has been established, which reflects global climatic changes. The geochemical zones coincide with marine isotope stages MIS 75–MIS 61. The sediments of warm stages are characterized by elevated contents of mobile components (SiO2, CaO, Na2O, K2O, and Sr), high values of magnetic susceptibility, low contents of Fe2O3, MgO, TiO2, Al2O3, Rb, Zr, and Ni, and low values of LOI, paramagnetic component, and chemical indices of alteration. The reverse pattern is observed for the sediments of cold stages. The low values of magnetic susceptibility in the sediments of optimal stages MIS 63, MIS 65, MIS 71, and MIS 75 are due to the dilution of detrital material with a biogenic one. The upper boundary of the Olduvai event passes in warm stage MIS 63, and the lower boundary coincides with the boundary between MIS 74 and MIS 75. The products of weathering of the Cretaceous felsic rocks of the Pykarvaam and Ergyvaam formations located near Lake El’gygytgyn were the provenances for its sediments. According to the geochemical and rock-magnetic data, the sedimentation during the Olduvai event was a cyclic process with periods of ca. 54, 40–43, and 23 kyr. The orbital cycles of 40–43 and 23 kyr indicate global causes of geochemical changes.