The history of the formation of the early Vendian alluvial system in the southwest of the Siberian platform

Olga V. Postnikova Gubkin Russian State University of oil and gas (National Research University) Moscow
Elena S. Iz’yurova Gubkin Russian State University of oil and gas (National Research University) Moscow
Olga A. Zueva Gubkin Russian State University of oil and gas (National Research University) Moscow
Ivan V. Gorlov Gazprom nedra Moscow
Alexander S. Smirnov Gazprom nedra Moscow

The aim of this work was to reconstruct the conditions of formation and forecast the distribution and properties of reservoir rocks of productive deposits of the Vendian Aleshinskaya Formation in the southwest of the Siberian platform. Lithological studies of rocks, as well as earlier U-Pb dating of detrital zircons from the base of the Aleshinskaya Formation, confirmed the Early Vendian age of the deposits and showed that a significant role in the formation of the studied terrigenous strata was played by sources of different ages, located both within the platform and on the surrounding territories. According to the results of cyclostratigraphic analysis, 10 sedimentation cyclites were identified in the section of the Aleshinskaya Formation, each of which has a transgressive structure. The distribution patterns of sedimentation cyclites reflect the development of the Vendian sedimentary basin. Reservoir rocks are confined to the lower parts of sedimentary cyclites of the Aleshinskaya Formation and are mainly associated with the facies of the channel valley. The facies factor, secondary processes of authigenic mineral formation and fracturing determined the spatial distribution of reservoir rocks in the Early Vendian deposits of the Lower Angara region.

Materials and methods
The work is based on core material from deep drilling wells in the Lower Angara region, materials of geophysical studies of wells, as well as stock geological and geophysical data. The results of studying rocks in thin sections, on an electron microscope and an X-ray diffractometer were used. Experimental studies were carried out using a polarizing microscope Axio Imager A2m Carl Zeiss and a stereomicroscope Carl Zeiss Micro Imaging GmbH; studies of the mineral composition of lithotypes, as well as the elemental composition of rocks, were performed using an energydispersive spectrometer on a scanning electron microscope (SEM) JEOL JSM-6610LV with an attachment for microanalysis OXFORD INSTRUMENTS IE350-IW500-HKL; The study of the mineral composition of the rocks was carried out using a RIGAKU (XRD) SmartLab X-ray diffractometer.

Siberian Platform, Lower Angara, Vendian, Taseeva group, Aleshinskaya Formation, alluvial deposits, paleogeographic conditions
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