GEOCHEMICAL FEATURES OF THE OLDUVEI EVENT IN THE SEDIMENTS OF LAKE EL’GYGYTGYN (ANADYR PLATEAU)
P.S. Minyuk
N.A. Shilo North-East Interdisciplinary Scientific Research Institute, Far Eastern Branch of the Russian Academy of Sciences, Magadan, Russia
Keywords: Olduvai event, geochemistry, Pleistocene, Lake El’gygytgyn, orbital cycles
Abstract
The distribution of geochemical characteristics in the sediments of Lake El’gygytgyn (Chukotka) formed during the Olduvai event has been studied. A clear geochemical and rock magnetic zones of the section has been established, reflecting global climatic changes. The geochemical zones coincide with the marine isotope stages 75-61. Sediments of the warm stages are characterized by increased contents of mobile elements (SiO2, CaO, Na2O, K2O, Sr), high values of magnetic susceptibility, low contents of Fe2O3, MgO, TiO2, Al2O3, Rb, Zr, Ni, low values of LOI, paramagnetic component, chemical indices of alteration. The reverse pattern is observed for sediment of the cold stages. The low values of magnetic susceptibility in sediments of the optimal stages of MIS 63, 65, 71 and 75 are due to the dilution of detritus material by biogenic. The upper boundary of the Olduvai event takes place in the warm stage of MIS 63, the lower one coincides with the boundary of the stages of MIS 74 and MIS 75. The catchment for the sediments of Lake El’gygytgyn were the products of weathering of acidic Cretaceous rocks of the Pykarvaam and Ergyvaam formations, located near the lake. According to the geochemical and rock magnetic data, the cyclicity of sedimentation during the Olduvai event was established with periods of about 54, 40-43, 23 thousand years. Orbital cycles of 40-43 and 23 thousand years indicate global causes of changes in geochemical characteristics.
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