Лессовидные породы на вулканическом конусе Хурай-Хобок в Тункинской впадине

Abstract

The results of studying the chemical, granulometric and mineral composition of a 2.8-meter sequence of sediment layers exposed on the slope of the cinder cone of the Khurai-Khobok volcano are presented. The lower age limit of sedimentary deposits is determined by the K–Ar dating of 1.57±0.3 Ma for the volcanic cone basalts, which is consistent with the reverse magnetization of the Matuyama Epoch rocks. The lower layers are represented by clayey sands, the middle layers by layered clayey sands, and the upper layers by clayey loess-like rocks. Clay minerals of the layers are identified using X-ray diffraction analysis and scanning electron microscopy. From the results obtained, a conclusion was made about the accumulation of the lower layers in mixed subaqueous and subaerial conditions, the middle ones – in subaqueous conditions, and the upper ones – in conditions of eolian transport of material. The processing of the material was carried out in the joint laboratory of modern research methods in dynamic and engineering geology of ISU and IPC SB RAS. Studies of clay minerals were carried out using a scanning electron microscope (SEM) with an EDS spectrometer at the Limnological Institute of the Siberian Branch of the Russian Academy of Sciences. To determine the mineral composition, samples ground in an agate mortar with alcohol were studied by powder diffraction on a DRON-3.0 X-ray diffractometer. Recording conditions: radiation – СuКα, Ni – filter, V = 30 kV, I = 20 mA, scanning step – 0.05°.