Introduction 8
Chapter LGeological and geographical outline of the study area 9
1.1 Brief physical and geographical outline of the study area 9
1.2 Geological structure of the Southern Ural 12
Chapter 2. Origin and composition of lake sapropels 15
2.1 Characteristics and classification of sapropel 17
Chapter 3.Characteristic of bottom sediments of Lake Turgoyak 21
3.1 Position of the core columns and samples collection 21
3.2 Lithological description of samples 23
Chapter 4. Methods 25
4.1. Magnetic susceptibility and normalremanent magnetization (NRM) 25
4.2. Coercive spectrometry 26
4.3. The differential-thermomagnetic analysis 27
4.4. Determination of the elemental composition of bottom sediments 28
4.5. Determination of the mineral composition of bottom sediments 30
4.6. Radiocarbon dating 30
4.7. Microscopy of magnetic separate of samples 32
Chapter 5. The results 35
5.1 Elemental composition of sediments 35
5.2 Mineralogical composition of sediments 45
5.3 The correlation of core columns 49
5.4 The results of geochemical investigation 57
Conclusion 64
REFERENCES
This paper is based on materials collected during the expedition in the summer of 2017 to Lake Turgoyak by the staff of institute of geology and petroleum technologies. The author of the final qualifying work is a laboratory researcher at the «Laboratory of Paleoclimatology, Paleoecology, Paleomagnetism» of institute of geology and petroleum technologies the Department of Geophysics and Geoinformation Technologies since September 2016.
The aim of the work is: Finding the levels of humidification and aridization of the climate based on the obtained results of magnetic-mineralogical and geochemical studies. The interpretation of those levels as analog sources of organic matter for formation hydrocarbons.
Objectives of the study: collecting information about the object of study, its geological and geophysical knowledge, measurements of samples of bottom sediments by magnetic and geochemical methods, processing and interpretation of the data obtained.
The all studies allowed to determine the peculiarities of the material composition and the formation conditions of lake Turgoyak sediments by conducting magnetic-mineralogical and geochemical studies, calculating loss on ignition, calculating chemical index of weathering, for to identify climate changes. On the basis of the researches revealed:
•The concentration of most chemical elements of Lake Turgoyak occurs in a depth of 3.9 m;
• Changes in chemical elements and mineralogy are compared with a time geological scale, as a result of which stages of aridization and humidification are revealed. It allowed to divide the section into two parts: the first is from 0 to 3.9 m - level of aridization, and the second is from 3.9 to 5.4 m - level of humidification;
• The change in sedimentation conditions occurred about 12,000 years ago;
The bottom formations of lake Turgoyak are mineral and organic deposits containing from 12 to 40% organic matter are sapropelites called to by Cordaye’s classification (1960).
The content of C, O, H in the Turgoyak lake sediments was determined to interpret the levels of aridization and humidification as analog sources of organic matter for the formation of hydrocarbons. The Sediments are at the stage of diagenesis and are close to the type IV kerogen zone. Kerogen is only being formed and its composition depends on the saturation of the sedimentary environment with oxygen, the rate of sedimentation and the rate of conservation of sedimentary material, redox conditions, climatic changes — changes in wetting and drying of catchment areas — a supplier of plant and detrital material. It is necessary to take more samples vertically and laterally to further understand the likely evolution of organic matter in the sediments of Lake Turgoyak.
