SIGNIFICANCE OF GRANULOMETRIC COMPOSITION AND PHYSICOCHEMICAL PROPERTIES FOR INTERPRETING THE LAKE GRAND SEDIMENTATION
P.S. Minyuk
N.A. Shilo North-East Interdisciplinary Scientific Research Institute, Far Eastern Branch of the Russian Academy of Sciences, ul. Portovaya 16, Magadan, 685000, Russia
Keywords: Slope deposits, weathering, petromagnetism, geochemical composition of sediments, Lake Grand
Abstract
The paper is concerned with a study of the slope deposits being weathering products of rhyolites and their tuffs in the vicinity of Lake Grand (northern Okhotsk area). The samples were divided into grain size fractions of 2500, 250, 140, 100, 63, 40, 20, and 1 µm. Analysis for major and trace elements and mineralogical and petrophysical studies were performed for each fraction. It is shown that a decrease in the fraction size is accompanied by the enrichment of the sediments with Al2O3, Fe2O3, TiO2, MgO, Y, Rb, Ni, and paramagnetic minerals and by an increase in LOI. The fine fractions are characterized by low contents of SiO2 and Na2O and high values of CIA, PIA, and Rb/Sr. The maximum magnetic susceptibility, saturation magnetization, and contents of CaO, Sr, and Zr are established in the fractions of 40 μm. The values of magnetic susceptibility, Js , and Jrs decrease in passing from the fractions of 40 μm to the fractions of 1 μm, whereas the values of Bc and Bcr increase. A specific feature of these fractions is high paramagnetic susceptibility and the presence of lepidocrocite. The qualitative composition of ferrimagnetic minerals is the same for the slope deposits and lacustrine sediments. In passing from coarse fractions to fine ones, the contents of quartz and K-feldspar decrease, and the contents of muscovite, biotite, chlorite, and kaolinite increase. The distribution of petromagnetic and geochemical characteristics in the Lake Grand sediments of varying grain size is similar to that in the slope deposits. The complex characteristics of the lacustrine sediments that formed in cold and warm periods are consistent with the distribution of these parameters in various fractions of deluvium and colluvium. Moreover, the fine-grained material acquired specific geochemical, mineralogical, and petrophysical properties when being on the slopes. Comparison of the SiO2/TiO2 and Fe2O3/TiO2 ratios of the slope deposits and lacustrine sediments makes it possible to identify the intervals of biogenic and chemogenic sedimentation in water basins.
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