Mineral composition of terrigenous components in loess and clay deposits of Western Mongolia

Introduction. The paper considers the results of a study associated with the mineral composition of terrigenous components in loess and clay deposits of Western Mongolia. The study was performed by the method of quantitative immersion analysis using samples obtained in the framework of geological studies during the seismic microzoning of certain cities.

Aim. Determination and analysis of variations in the mineral composition of terrigenous components of loess quaternary alluvial, eolian, diluvial-eolian and diluvial-proluvial complexes, as well as Neogene-lower Quaternary lake-alluvial and Cretaceous-Paleogene lake “brick” clays.

Materials and methods. The database is represented by quantitative data on the content of light and heavy minerals (0.01—0.25 mm fraction) in various geological and genetic deposit complexes, sampled from outcrops with the thickness of 6–8 m and test wells with the depth of 20–30 m (72 samples in total). During the compositional characterisation of light and heavy fractions, mineral associations were established, as well as maturity (Кz) and stability coefficients (KU) were calculated. Four territorial zones, including northern (territory of Sükhbaatar and Mörön), central (Zuunmod), western (Uliastai) and southern (Dalanzadgad), were isolated. A Q-type cluster analysis program was applied to process mineralogical data.

Results. Variations in mineral associations of the studied objects were established related both to their belonging to the selected geological and genetic complexes and the possibility of eolian process effects. The factors of influence include climatic conditions during the formation of complexes, the composition of rocks in geological formations abundant in these territories and contemporary climatic zoning.

Conclusion. Representative data were obtained for the central and southern zones, where the mineral composition of terrigenous components was determined using samples from test wells having clearly observed variations in the mineral composition of deposits during the change of a geological and genetic complex. Since the immersion method is still essential for studies of sedimentary rocks, the information on a new object, represented by the territory of West Mongolia, obtained for the first time, appears to be of a particular interest both from scientific and practical points of view.

1. Baturin V.P. Petrographic analysis of the geological past on terrigenous components. Moscow— Leningrad. 1947. 339 p. (In Russian).

2. Belousova O.N., Mikhina V.V. General course of petrography. Moscow: Nedra. 1972. 344 p. (In Russian).

3. Bolotova N.Ya. On the stratigraphy of the Cenozoic deposits of Northeastern Mongolia // Materials on the geology of the Mongolian People’s Republic. Moscow: Nedra. 1966. P. 79—85 (In Russian).

4. Bulakh A.G. Mineralogy with the basics of crystallography. Moscow: Nedra. 1989. 351 p. (In Russian).

5. Vasiliev V.I., Sheshenya N.L., Chekhovskiy A.L. Formation of engineering-geological conditions of the Central Mongolia. Moscow: Nauka. 1987. 142 p. (In Russian).

6. Danilov B.S. Cluster analysis in EXCEL // Structure of the lithosphere and geodynamics. Irkutsk, 2001. P. 18—19 (In Russian).

7. Engineering geology of the USSR. T. 3. The Eastern Siberia / Ed. by Golodkovskaya G.A. Moscow: Publishing House of Moscow State University. 1977. 659 p. (In Russian).

8. Ryashchenko T.G., Akulova V.V., Ukhova N.N., et al. Loess soils of the Mongolian-Siberian region. Irkutsk: Institute of the Earth’s Crust, SB RAS. 2014. 241 p. (In Russian).

9. Logvinenko N.V. Petrography of the sedimentary rocks (with the basics of research methods). Moscow: Higher school. 1974. 400 p. (In Russian).

10. Milash A.V. Accessory minerals of the Eifelian, Givetian and the Lower Frasnian deposits of the southeast of the Voronezh anteclise // Bulletin of the Voronezh University. Series Geology. 2017. P. 31—42 (In Russian).

11. Oknova N.S. Lithological-paleogeographic and geodynamic reconstructions in the search for non-anticlinal hydrocarbon traps (on the example of the TimanPechora province). St. Petersburg: Publishing House of St. Petersburg State University. 1998. 108 p. (In Russian).

12. Dzhurik V.I., Serebrennikov S.P., Ryashchenko T.G., et al. Zoning of the seismic hazard of the territory of the city of Erdenet. Irkutsk: Institute of the Earth’s Crust, SB RAS. 2011. 122 p. (In Russian).

13. Ryashchenko T.G. Material composition and properties of rocks // The Boguchanskiy reservoir. Groundwater and engineering geology. Novosibirsk: Nauka. 1979. P. 61—83 (In Russian).

14. Ryashchenko T.G. Grouping of geological objects by cluster analysis (on the example of mineralogical data of the Quaternary rocks of the Middle Angara region) // Methodological aspects of forecasting natural phenomena in Siberia. Novosibirsk: Nauka. 1980. P. 92—102 (In Russian).

15. Ryashchenko T.G. Lithogenesis and engineering-geological assessment of the Quaternary deposits (the Eastern Siberia). Novosibirsk: Nauka. 1984. 164 p. (In Russian).

16. Dzhurik V.I., Potapov V.A., Kochetkov V.M., et al. Seismic microzoning of the aimag centers of the Mongolia. Ulaanbaatar: Publishing Center for Astronomy and Geophysics. 1998. 248 p. (In Russian).

17. Tatarskiy V.B. Crystal optics and immersion method for studying minerals. Moscow: Nedra, 1965. 306 p. (In Russian).

18. Shlykov V.G., Kharitonov V.D. On the method of quantitative X-ray analysis of the mineral composition of soils / Geoecology. 2001. No. 2. P. 129—140 (In Russian).

19. Shlykov V.G., Trapeznikov P.V. Lost classification feature of loess soils // Geoecology. 2002. No. 2. P. 156—162 (In Russian).

20. Yubelt R. Determinant of minerals (translated from German). Moscow: Publishing house “Mir”. 1978. 325 p. (In Russian).

21. Complex geophysical and seismological investigations in the Mongolia / Eds. V.I. Dzhurik, T. Dugarmaa. Ulaanbaatar—Irkutsk. 2004. 315 p.

22. Hubbard C.R., Snuder R.I. RIR. Measurement and Use in Quantitative XRD // Powder Diffraction.1988. V. 3. P. 74—77.

23. Ryashchenko T.G., Akulova V.V., Ukhova N.N. Processes of loess lithogenesis during Pleistocene — Holocene // Quaternary International. 2011. No. 240. P. 150—155.

24. Zimbardo M., et al. The open metastable structure of a collapsible sand: fabric and bonding // Bulletin Engineering Geology and the Environment. 2016. V. 75. No. 1. P. 125—139.