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

Abstract

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.