Origin, classification of rocks. organic rocks

Rocks formed as a result of the life of organisms are called organic sedimentary rocks. They are formed from the remains of plants and animals deposited at the bottom of reservoirs. These include limestone, coal, oil, oil shale, peat, shell rock, chalk...

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ORGANIC ROCKS (from the Greek organon - organ and -genes - giving birth, born, biogenic rocks * a. organogenic rocks, biogenic rocks; and. organogene Gesteine; f. roches organogenes, roches biogenes; I. rocas organogenicas) - sedimentary rocks consisting of the remains of animals and plants and their metabolic products. Organisms have the ability to concentrate certain substances that do not reach saturation in natural waters, forming skeletons or tissues that are preserved in a fossil state.

According to the material composition, carbonate, siliceous, and some phosphate rocks, as well as coals (see), oil shale, oil, and solid bitumen, can be distinguished among organogenic rocks. Organogenic carbonate rocks () consist of shells of foraminifers, corals, bryozoans, brachiopods, mollusks, algae and other organisms.

Their peculiar representatives are reef limestones that make up atolls, barrier reefs and others, as well as writing chalk. Siliceous organogenic rocks include: diatomite, spongolite, radiolarite, etc. Diatomites consist of opal skeletons of diatoms, as well as spicules of flint sponges and radiolarians. Spongolites are rocks containing usually more than 50% spicules of flint sponges. Their cement is siliceous, of opal rounded bodies, or clayey, slightly calcareous, often including secondary chalcedony. Radiolarites are siliceous rocks, more than 50% consisting of radiolarian skeletons, which form radiolarian silt in modern oceans. In addition to radiolarians, they include sponge spicules, rare diatom shells, coccolithophores, and opal and clay particles. Many jaspers have a base of radiolarians.

Phosphate organogenic rocks do not have widespread. These include shell rocks from phosphate shells of Silurian brachiopods - obolid, accumulations of bones of fossil vertebrates (bone breccias), known in deposits different ages, as well as guano. Organogenic carbonaceous rocks - fossil coals and oil shale - are common, but their mass in the earth's crust is small compared to carbonate rocks. Oil and solid bitumen are peculiar rocks, the main material for the formation of which was phytoplankton.

According to the conditions of formation (mainly in relation to carbonate rocks), bioherms can be distinguished - the accumulation of the remains of organisms in their lifetime, thanato- and taphrocenoses - the joint burial of dead organisms that lived here or were carried by waves and currents; rocks that have arisen from planktonic organisms are called planktonic (for example, diatomite, chalk, foraminiferal limestone).

If organic remains are crushed as a result of the action of waves and surf, organogenic-clastic rocks are formed, consisting of fragments (detritus) of shells and skeletons held together by some mineral substance (for example,).

Rocks are a substance that makes up. Rocks consist of, homogeneous or heterogeneous, which are firmly or loosely connected.

Often they consist of cemented fragments of various rocks, sometimes with the presence of. Rocks were formed as a result of intraterrestrial or surface geological processes.

The structure of the rock is determined by its structure and texture. The structure is understood as the features of the connection of mineral grains, their sizes and shapes. Some rocks consist of large crystalline grains; others - from the smallest crystals visible only through a microscope; the third - from vitreous substance; fourth - combined, when separate large crystals are found against the background of the smallest crystals or vitreous substance. Texture is understood as mutual arrangement and distribution of the minerals that make up the rock. There are the following types of texture:

massive texture: no order in the placement of minerals is observed;
layered: the rock consists of layers of different composition;
shale: all minerals are flat and elongated in one direction;
porous: the entire rock is permeated with pores;
bubbly: there are voids in the rock from extruded ones.

By origin, rocks are divided into:

Igneous. These rocks are formed from the molten as it cools and solidifies. The structure of these rocks depends on the rate of cooling of the magma. At a depth in earth's crust it cools more slowly than on the surface. In this case, dense rocks with large crystals of minerals are formed. They are called deep igneous rocks. This variety includes, for example, granite, which has a granular structure. Granite (Italian granito - granular) is the most common rock on Earth. It is composed of quartz, potassium feldspar, acid plagioclase and mica. The granite layer contains a variety of non-ferrous, precious and rare metals. There is no granite layer in the oceanic crust. Granite is widely used in the economy, it is used as a decorative and building material.

Magma that has broken through to the surface along cracks and faults solidifies faster. Therefore, the rocks formed by the erupted magma consist of small crystals, they are sometimes difficult to distinguish with the naked eye. They are usually dense, heavy, hard. An example of such a rock is basalt (Latin basaltes - stone). It is the most common volcanic rock on Earth or dark gray in color. It is a very strong acid-resistant and iron-bearing rock. These properties are used for the manufacture of acid-resistant equipment, high current insulators. Basalt in a polished form becomes a beautiful facing stone. They paved Red Square in Moscow.

Pouring through cracks, magma creates vast basalt spaces (). Layering one on top of the other, these covers form stepped hills - traps. The thickness of these covers reaches hundreds of meters, and the areas occupied by them are hundreds of thousands of square kilometers. In addition to covers, basalt forms the lower layer of the earth's crust, which includes a large amount of iron.

In the event that the magma contains a lot of gases, it foams during the outpouring, the gases escape, and an igneous rock is formed, which has a spongy, porous structure. Pumice is one of these rocks. It is lightweight and does not sink in water. However, pumice is quite hard and is used as a grinding material.

Sedimentary. These rocks, unlike igneous ones, are formed only on the surface of the earth's crust as a result of subsidence under the action of gravity and accumulation on the bottom and on land. According to the method of formation, sedimentary rocks are usually divided into groups:

a) debris. They consist of fragments of various rocks. Their origin is associated with the processes of movement of debris flowing waters, or and their accumulation (see). In this case, the fragments are crushed, crushed, rolled. Depending on the size of clastic rocks are coarse, medium and fine clastic. The rocks of this group include crushed stone, pebbles, gravel, sand, clay. Many of them are used as building material;

b) chemical. Rocks belonging to this group are formed from aqueous solutions of mineral substances. These are potash and common salt that settle to the bottom of reservoirs. Silica falls out of hot spring water. Many of the rocks of this group are used in the economy. For example, potash salts are raw materials for the production of potash fertilizers;

c) organic, or organogenic (Greek organon - organ and genes - giving birth). This group includes sedimentary rocks, consisting mainly of the remains of plants and animals that have accumulated over millions of years at the bottom of lakes, seas, and oceans.

This includes:

combustible;
phosphorites: phosphate shell rock, accumulation of bones;
limestones: limestone, chalk, shell rock. Organic rocks form numerous valuable minerals that are widely used in the economy. This group of sedimentary rocks is characterized by a layered texture. Between the layers, remains and prints of plants and animals can be found.

Sedimentary rocks cover earth's surface almost entirely. They make up 70% of the thickness of the earth's crust, forming its upper layer, the thickness of which can reach up to 25 km.

Metamorphic. These are rocks that were originally formed as sedimentary or igneous and have undergone changes in (Greek metamorphomai - I am transformed, undergoing transformation). Due to the impact of temperature and chemical solutions in the lower part of the earth's crust or in the mantle, compaction, recrystallization, changes in the structure and texture of the rock occur without a significant change in its chemical composition Basalts (42.5%) Granites (21.6%). In this case, one rock is significantly transformed into another, more stable and solid, without its dissolution or melting. For example, limestone turns into a crystalline rock - marble, sandstone - into quartzite, granite - into gneiss, clay - into shale. Metamorphic rocks, as well as igneous and sedimentary rocks, are used in the economy. For example, ferruginous quartzite is used as a (Kursk magnetic anomaly), and shale - as a roofing material.

So, the thickness of the earth's crust consists of rocks of igneous, sedimentary and metamorphic origin. They are the source of all minerals.

Major sedimentary rocks of organic and chemical origin

Classification of sedimentary clastic (terrigenous) rocks

Lecture topic: Structure and composition of the Earth. Earth in outer space. The shape and size of the earth. Internal structure Earth. Chemical and mineral composition of the Earth's interior. Physical fields of the Earth. The structure and composition of the earth's crust. Material composition of the earth's crust. Minerals. Rocks.

The earth is one of the countless celestial bodies scattered in the boundless space of the Universe. A general idea of the position of the Earth in world space and its relationship with other cosmic bodies is also necessary for the course of geology, since many processes occurring on the surface and in deep bowels the globe, are closely related to the influence external environment surrounding our planet. The knowledge of the Universe, the study of the state of various bodies and the processes occurring on them shed light on the problems of the origin of the Earth and the early stages of its development. Universe - ϶ᴛᴏ the whole world, boundless in time and space and infinitely diverse in the forms that matter takes in its development. The universe is made up of countless bodies, very different in structure and size. The following main forms of cosmic bodies are distinguished: stars, planets, interstellar matter. Stars are large active cosmic bodies. The radius of large stars can reach a billion kilometers, and the temperature even on the surface can reach many tens of thousands of degrees. Planets are relatively small cosmic bodies, usually cold and usually satellites of stars. The space between space bodies is filled with interstellar matter (gases, dust). Space bodies are grouped into systems within which they are interconnected by gravitational forces. The simplest system– The Earth with its satellite the Moon forms a system of a higher order – the Solar System. An even more complex structure is characterized by clusters of cosmic bodies of a higher order - galaxies. An example of such a system is the Milky Way galaxy, which includes the solar system. In shape, our galaxy resembles a biconvex lens, and in plan it is a bright cluster of stars in the core with spiraling star streams.

The structure of the solar system. Our solar system includes, in addition to the central luminary - the Sun, nine planets, their satellites, asteroids and comets. The Sun is a star, a hot plasma ball, a typical ʼʼyellow dwarfʼʼ, which is at the middle stage of stellar evolution. The Sun is located within one of the spiral arms of our Galaxy and revolves around the center of the Galaxies with a period of about 200 million years. The temperature inside the Sun reaches several million years. The source of the Sun's energy is the thermonuclear conversion of hydrogen into helium. Spectral study of the Sun made it possible to identify in its composition 70 elements known on Earth. The sun consists of 70% hydrogen, 27% helium, and about 3% of the rest of the elements. The Sun contains 99.886% of the total mass of the solar system. The sun has a huge influence on the Earth, on earthly life, its geological development. Our planet - the Earth is 149,600,000 km away from the Sun. The planets around the Sun are arranged in the following order: four inner - Mercury, Venus, Earth and Mars (terrestrial planets) and five outer - Jupiter, Saturn, Uranus, Neptune, Pluto. Between Mars and Jupiter is an asteroid belt - several thousand small solid bodies. For geologists, four inner planets are of interest, which are characterized by small size, high density, and low mass. These planets are closest in size, composition and internal structure to our Earth. By modern ideas the bodies of the solar system were formed from the initially cold cosmic solid and gaseous matter by compaction and thickening until the formation of the Sun from the central part. From the particles of the surrounding gas-dust matter, as a result of accretion, planets were formed that revolve in orbits around the Sun.

General characteristics of the Earth. The shape and size of the earth. Under the figure, or the shape of the Earth, we understand the shape of its solid body, formed by the surface of the continents and the bottom of the seas and oceans. Geodetic measurements have shown that the simplified shape of the Earth approaches an ellipsoid of revolution (spheroid). The actual shape of the Earth is more complex, as there are many irregularities on its surface. The closest to the modern figure of the Earth is the figure, in relation to the surface of which the force of gravity is everywhere directed perpendicularly. It is called geoid, which literally means ʼʼearthlikeʼʼ. The surface of the geoid in the seas and oceans corresponds to the surface of the water, and on the continents - to the water level in imaginary channels that cross all the continents and communicate with the World Ocean. The surface of the geoid approaches the surface of the spheroid, deviating from it by about 100 m, on the continents it slightly rises relative to the surface of the spheroid, and in the oceans it decreases. Measurements of the dimensions of the Earth showed the following: equatorial radius - 6378.2 km; polar radius - 6356.8 km; the average radius of the Earth is 6371 km; polar compression - 1/298; surface area - 510 million square kilometers; the volume of the Earth-1, 083 billion. km cube; mass of the Earth-6*10 21 t; average density-5, 52 g/cm 3

Physical properties of the Earth. The earth has certain physical properties. As a result of their study, the general features of the structure of the Earth were revealed and it was possible to establish the presence of minerals in its bowels. The physical properties of the Earth include gravity, density, pressure, magnetic, thermal, elastic, electrical and other properties. Gravity, density, pressure. The force of gravity and centrifugal force are constantly acting on the Earth. The resultant of these forces determines the force of gravity. The force of gravity varies both horizontally, increasing from the equator to the poles, and vertically, decreasing with height. Due to the uneven distribution of matter in the earth's crust, the actual value of gravity deviates from normal. These deviations were called gravity anomalies. Οʜᴎ are positive (in the presence of denser rocks) or negative (in the presence of less dense rocks). Gravity anomalies are studied using gravimeters. The branch of applied geophysics that studies gravity anomalies in order to identify minerals or favorable geological structures in the depths is commonly called gravity exploration. According to gravimetric data, the average density of the Earth is 5.52 g / cm 3. The density of the rocks that make up the earth's crust is from 2.0 to 3.0 g / cm 3. The average density of the earth's crust is 2.8 g / cm 3. The difference between the average density of the Earth and the Earth's crust indicates a denser state of matter in the inner parts of the Earth, reaching about 12.0 g/cm 3 in the core. Simultaneously with the increase in density towards the center of the Earth, the pressure also increases. In the center of the Earth, the pressure reaches 3.5 million atm. Earth magnetism. The earth is a giant magnet with a force field around it. The Earth's magnetic poles are currently located near the geographic poles, but do not coincide with them. Distinguish between magnetic declination and magnetic inclination. Magnetic declination is called the angle of deviation of the magnetic needle of the compass from the geographic meridian. The declination must be western and eastern. Magnetic inclination is determined by the angle of the magnetic needle to the horizon. The greatest inclination is observed in the region of the magnetic poles. The influence of rocks containing ferromagnetic minerals (magnetite and some others) is superimposed on the general background of the magnetic field, due to which magnetic anomalies occur on the surface of the Earth. Magnetic prospecting is engaged in the identification of such anomalies in order to search for iron ores. Studies have shown that rocks containing ferromagnetic minerals have residual magnetization that preserves the direction of the magnetic field of time and the place of their formation. Paleomagnetic data are used to restore the features of the magnetic field of ancient epochs, as well as to solve problems of geochronology, stratigraphy, and paleogeography. Οʜᴎ had a great influence on the development of the theory of lithospheric plate tectonics.

Heat of the Earth. The thermal regime of the Earth is caused by two sources: heat received from the Sun; heat released from the Earth's interior. The Sun is the main source of heat on the Earth's surface. Heating by the Sun extends to an insignificant depth not exceeding 30 m. At a certain depth from the surface there is a belt of constant temperature equal to the average annual temperature of the area. In the vicinity of Moscow, at a depth of 20 m from the surface, a constant temperature equal to +4.2 0 is observed. Below the belt of constant temperature, an increase in temperature with depth associated with the heat flow coming from the inner parts of the Earth is established. The increase in temperature in degrees Celsius per unit of depth is called the geothermal gradient, and the depth interval in meters at which the temperature rises by 10 is called the geothermal step. The value of the geothermal step varies widely: in the Caucasus 12 m, in the Emba region 33 m, in the Karaganda basin 62 m, in Kamchatka 2-3 m. It is believed that the geothermal stage persists to a depth of 20 km. Below, the rise in temperature slows down. According to the calculations of scientists at a depth of 100 km, the temperature apparently reaches 1300 0 C. At a depth of 400 km - 1700 0 C, 2900 km - 3500 0 C. The sources of the Earth's internal heat are considered to be the radioactive decay of elements, during which a huge amount of heat is released, the energy of gravitational differentiation of matter, as well as the residual heat that has been preserved since the formation of the planet.

The structure of the earth. The earth is characterized by a shell structure. The shells of the Earth, or the geosphere, differ in composition, physical properties, state of matter and are divided into external, accessible for direct study, and internal, studied mainly by indirect methods (geological, geophysical, geochemical). The outer spheres of the Earth - the atmosphere, hydrosphere and biosphere make up salient feature structures of our planet and play important role in the formation and development of the earth's crust. Atmosphere- the gaseous shell of the Earth, plays one of the main roles in the development of life on Earth and determines the intensity of geological processes on the surface of the planet. The air shell of our planet, total weight which is estimated at 5.3 * 10 15 m is a mixture of various gases: nitrogen (78.09%), oxygen (20.95%), argon (0.93%). At the same time, there is carbon dioxide (0.03%), hydrogen, helium, neon and other gases, as well as water vapor (up to 4%), particles of volcanic, aeolian and cosmic dust. Air oxygen provides the processes of oxidation of various substances, as well as the respiration of organisms. There is ozone in the atmosphere at an altitude of 20-30 km. The presence of ozone protects the Earth from the damaging effects of ultraviolet and other radiation from the Sun. Carbon dioxide and water vapor act as a temperature regulator, as it condenses the heat received by the Earth. Carbon dioxide enters the air as a result of the decomposition of organisms and their respiration, as well as during volcanic processes, but is consumed to feed plants. air masses atmospheres are in in constant motion under the influence of uneven heating of the Earth's surface in different latitudes, uneven heating of continents and oceans. Air flows carry moisture, solid particles - dust, significantly affect the temperature of various regions of the Earth. The atmosphere is divided into five basic layers: troposphere, stratosphere, mesosphere, ionosphere and exosphere. For geology, the most interesting is the troposphere, which is in direct contact with the earth's surface and exerts a significant influence on it. Troposphere characterized by high density, the constant presence of water vapor, carbon dioxide and dust, a gradual decrease in temperature with height and the existence of vertical and horizontal air circulation.

Hydrosphere- a discontinuous shell of the Earth, including the waters of the oceans, seas, lakes and rivers, groundwater and water collected in the form of eternal snow and ice. The main part of the hydrosphere is the World Ocean, which unites all the oceans, marginal and associated inland seas. The amount of oceanic land waters is 4 million km 3, continental ice about 22 million km 3, groundwater 196 million km 3. The hydrosphere occupies 70.8% of the earth's surface (361 million km 2). The average depth is 3750 m, maximum depth confined to the Mariana Trench (11022m). Oceanic and sea waters characterized by a certain chemical composition and salinity. The normal salinity of the waters of the World Ocean is 3.5% (35 g of salts per 1 liter of water). The waters of the ocean contain almost every known chemical element. It is estimated that total salts dissolved in the water of the oceans, is 5 * 10 16 m. Carbonates, silica are widely extracted from water by marine organisms for the construction of skeletal parts. For this reason, the salt composition of ocean waters differs sharply from the composition of river waters. AT ocean waters chlorides (88.7%) - NaCl, MgCl 2 and sulfates (10.8%) prevail, and in river waters carbonates (60.1%) - CaCO 3 and sulfates (9.9%). In addition to salts, some gases are also dissolved in water - mainly nitrogen, oxygen, carbon dioxide. The waters of the hydrosphere, together with the substances dissolved in it, are actively involved in chemical reactions occurring in the hydrosphere, as well as in interaction with the atmosphere, the earth's crust and the biosphere. The hydrosphere, like the atmosphere, is the active force and medium of exogenous geological processes. The world ocean is playing huge role in the life of both the entire planet and humanity. In the ocean and in its bowels there are huge reserves of mineral resources, which are increasingly attracted for the needs of mankind (oil, chemical raw materials, etc.). The waters of the oceans are polluted by oil and oil products, radioactive and household waste. This circumstance is acquiring menacing proportions and requires an urgent solution.

Biosphere. The biosphere is the area of distribution of life on Earth. The modern biosphere includes the entire hydrosphere, the upper part of the atmosphere (troposphere). Below the soil layer, living organisms are found in deep cracks, underground waters, sometimes in oil-bearing layers at a depth of thousands of meters. The composition of living organisms includes at least 60 elements, and the main ones are C, O, H, S, P, K, Fe and some others. The living mass of the biosphere in terms of dry matter is about 10 15 tons. The bulk of the living matter is concentrated in green plants that can accumulate solar energy through photosynthesis. From a chemical point of view, photosynthesis is a redox reaction CO 2 + H 2 O-> CH 2 O + O 2, as a result of which, due to the absorption of carbon dioxide and water, organic matter and release free oxygen. The biosphere plays an important role in the energy of the Earth. Over millions of years, the biosphere has accumulated colossal reserves of energy in the depths - in the thickness of coal, oil, accumulations of combustible gas. Organisms are important rock-forming earth's crust.

Internal structure of the Earth. The study of the deep structure of the Earth is one of the main tasks of modern geology. Only the uppermost (down to depths of 12-15 km) horizons of the earth's crust, which come to the surface or are opened by mines and boreholes, are accessible to direct observation.

Ideas about the structure of the deeper zones of the Earth are based mainly on these complexes of geophysical methods. Of them special meaning has a seismic (Greek ʼʼ seismaʼʼ - shaking) method based on recording the propagation velocity in the Earth's body of waves caused by earthquakes or artificial explosions. In earthquake sources, longitudinal seismic waves arise, which are considered as a reaction of the medium to changes in volume, and transverse waves, which are a reaction of the medium to changes in shape and, therefore, propagate only in solids. Today, the available data confirm the spherically - symmetrical structure of the Earth's interior. Back in 1897 ᴦ. Professor of the University of Göttingen E. Wiechert expressed the idea of the shell structure of the Earth, which consists of an iron core, a stone mantle and the earth's crust. In 1910 ᴦ. Yugoslav geophysicist A. Mohorovichic, studying the propagation of seismic waves during an earthquake near the city of Zagreb, established the interface between the crust and the mantle at a depth of 50 km. Subsequently, this surface was revealed at various depths, but they were always clearly traced. She was given the name ʼʼsurface of Mohorovichićʼʼ, or Moho (M). In 1914, the German geophysicist B. Guttenberg established the boundary between the core and the mantle at a depth of 2900 km. It is called the Wiechert-Guttenberg surface. Danish scientist I. Leman in 1936ᴦ. substantiated the existence of the inner core of the Earth with a radius of 1250 km. The whole complex of modern geological and geophysical data confirms the idea of a shell structure of the Earth. To correctly understand the main features of this structure, geophysicists build special models. Well-known geophysicist V.N. Zharkov characterizes the model of the Earth: it is "like a section of our planet, which shows how its most important parameters change with depth, such as density, pressure, acceleration of gravity, seismic wave velocities, temperature, electrical conductivity, and others" (Zharkov, 1983, p. 153). The most common is the Bullen-Guttenberg model.

The Earth's crust is the hard upper shell of the Earth. Its thickness varies from 5-12 km under the waters of the oceans, to 30-40 km in flat areas and up to 50-750 km in mountainous areas. The Earth's mantle extends to a depth of 2900 km. It is subdivided into two parts: the upper to a depth of 670 km and the lower to a depth of 2900 km. A seismic method in the upper mantle has established a layer in which a decrease in the speed of seismic waves, especially transverse ones, and an increase in electrical conductivity are observed, which indicates a state of matter that differs from the higher and lower layers. The features of this layer, called the asthenosphere (Greek astyanos-weak) are explained by its melting in the range of 1-2 to 10%, which occurs as a result of a faster increase in temperature with depth than an increase in pressure. The asthenospheric layer is located closest to the surface under the oceans, from 10-20 km to 80-200 km, from 80 to 400 km under the continents. The earth's crust and part of the upper mantle above the asthenosphere is called the lithosphere. The lithosphere is cold, therefore it is rigid and can withstand heavy loads. The lower mantle is characterized by a further increase in the density of matter and a smooth increase in the velocity of seismic waves. The core occupies central part Earth. It consists of an outer core, a transitional shell and an inner core. The outer core consists of a substance in a molten-liquid state. The inner core occupies the core of our planet. Within the inner core, the longitudinal and shear waves increases, which indicates the solid state of the substance. The inner core consists of an iron-nickel alloy.

Composition and structure of the earth's crust. The most reliable information is available on the chemical composition of the uppermost part of the earth's crust, accessible for direct analysis (down to a depth of 16-20 km). The first figures on the chemical composition of the earth's crust were published in 1889 ᴦ. American scientist F. Clark. Subsequently, A.E. Fersman suggested calling the percentage of an element in the earth's crust the clarke of this element. According to A.B. Ronov and A.A. Yaroshevsky (1976 ᴦ.), eight elements (in weight%) are the most common in the composition of the earth's crust, making up more than 98% in total: oxygen - 46.50; silicon-25.70; aluminum-7.65; iron-6.24; calcium-5.79; magnesium-3.23; sodium-1.81; potassium-1.34. According to the features of the geological structure, geophysical characteristics and composition, the earth's crust is divided into three basic types: continental, oceanic and intermediate. The continental layer consists of a sedimentary layer 20-25 km thick, granite (granite-metamorphic) layer up to 30 km thick and basalt layer up to 40 km thick. The oceanic crust consists of the first sedimentary layer up to 1 km thick, the second basalt layer 1.5-2.0 km thick and the third gabbro-serpentinite layer 5-6 km thick. The substance of the earth's crust consists of minerals and rocks. Rocks are composed of minerals or products of their destruction. Rocks containing useful components and individual minerals, the extraction of which is economically feasible, are called minerals.

Main literature: 1

Test questions:

1 The origin of the solar system.

2 The shape and size of the Earth.

3 Physical fields of the Earth.

4 The internal structure of the Earth.

5 The structure and composition of the earth's crust.

3 Lecture topic: Rocks as a container for oil and gas. Rock - ϶ᴛᴏ natural, most often, solid, consisting of one (limestone, anhydrite) or several minerals (polymictic sandstone, granite). In other words, it is a natural natural association of minerals. All rocks by origin (genesis) are divided into three large classes: igneous, metamorphic and sedimentary.

Igneous rocks were formed as a result of the introduction of magma (silicate melt) into the earth's crust and the solidification of the latter in it (intrusive igneous rocks) or the outpouring of lava (silicate melt) to the bottom of the seas, oceans or the earth's surface (effusive igneous rocks). Both lava and magma are originally ϶ᴛᴏ silicate melts of the inner spheres of the Earth. Magma, having penetrated into the earth's crust, solidifies in it unchanged, and lava, pouring out onto the surface of the Earth or to the bottom of the seas and oceans, loses the gases dissolved in it, water vapor and some other components. Because of this, intrusive igneous rocks differ sharply in composition, structure, and texture from effusive ones. Granite (an intrusive rock) and basalt (an effusive rock) are examples of the most common igneous rocks.

Metamorphic rocks were formed as a result of a radical transformation (metamorphism) of all other pre-existing rocks under the influence of high temperatures, pressures and often with the introduction into them or the removal of individual chemical elements from them. Typical representatives of metamorphic rocks are marble (formed from limestone), various shales and gneisses (formed from clayey sedimentary rocks).

Sedimentary rocks were formed due to the destruction of other rocks that previously formed the earth's surface and the deposition of these mineral substances mainly in an aqueous, less often air environment as a result of the manifestation of exogenous (surface) geological processes. Sedimentary rocks according to the method (conditions) of their formation are divided into three groups: sedimentary clastic (terrigenous), organogenic and chemogenic.

Sedimentary clastic (terrigenous) rocks are composed of fragments of pre-existing minerals and rocks (Table 1). Organogenic rocks consist of the remains (skeletons) of living organisms and their metabolic products ( biological pathway formations) Chemogenic sedimentary rocks were formed as a result of precipitation of chemical elements or minerals from aqueous solutions (Table 2). Typical representatives of sedimentary clastic rocks are sandstones and siltstones, sedimentary organogenic - various types organogenic limestones, chalk, coals, oil shale, oil, sedimentary chemogenic - rock salt, gypsum, anhydrite. For a petroleum geologist, sedimentary rocks are dominant, since they not only contain 99.9% of the world's oil and gas reserves, but, according to the organic theory of the origin of oil and gas, are the generators of these hydrocarbons. Sedimentary rocks make up the upper sedimentary layer of the earth's crust, which is not distributed throughout the Earth's area, but only within the so-called plates that are part of the platforms - large stable sections of the earth's crust, intermountain depressions and foothill troughs. The thickness of sedimentary rocks varies widely from a few meters to 22-24 km in the center of the Caspian depression, located in Western Kazakhstan. The sedimentary layer in petroleum geology is usually called the sedimentary cover. Under the sedimentary cover is the lower structural floor, called the foundation. The foundation is composed of igneous and metamorphic rocks. The basement rocks contain only 0.1% of the world's oil and gas reserves. Oil and gas in the earth's crust fills the smallest and smallest pores, cracks, caverns of rock, just as water saturates a sponge. Therefore, in order for a rock to contain oil, gas and water, it must be qualitatively different from rocks that do not contain fluids, ᴛ.ᴇ. it must have pores, cracks or cavities, must be porous. Today, most of all industrial accumulations of oil and gas contain sedimentary detrital (terrigenous) rocks, then carbonate rocks of organogenic genesis and, finally, chemogenic carbonates (oolitic and fractured limestones and marls). In the earth's crust, porous rocks containing oil and gas must be interbedded with qualitatively different rocks that do not contain fluids, but function as insulators for oil and gas saturated bodies. Tables 1 and 2 show lithofacies of rocks containing oil and gas and serving as seals.

Table 1

Breed group	Debris dimensions, mm	Loose rocks	cemented rocks
Rounded Debris	Unrounded wreckage	Rounded debris	Unrounded wreckage

Coarse clastic (psephites)	Large > 200	boulders	lumps	boulder conglomerates	blocky breccias
Medium 200-10	pebble (pebble)	rubble	pebble conglomerate	breccia
Small 10-2	Gravel is oil and gas saturated	gruss can be oil and gas saturated	gravelstones are oil and gas saturated (gravel conglomerates)
Sandy (psammites)	2-1	Coarse-grained sands are very often oil and gas saturated	Coarse-grained sandstones are very often oil and gas saturated
1-0,5	Coarse-grained sands are very often oil and gas saturated	Coarse-grained sandstones are very often oil and gas saturated
0,5-0,25	Medium-grained sands are very often oil and gas saturated	Medium-grained sandstones are very often oil and gas saturated
0,25-0,1	Fine-grained sands are very often oil and gas saturated	Fine-grained sandstones are very often oil and gas saturated
Silty rocks (aleurites)	0,1-0,01	silt (loess, sandy loam, loam) is often oil and gas saturated	siltstone is often oil and gas saturated
Clay rocks (Pelites)	< 0,01	clay (physical) is never oil and gas saturated (fluid seal)	argillite is not oil and gas saturated (fluid seal)

Table 2.

Breed group	Organogenic rocks	Chemogenic rocks

Carbonate	coral limestone - (СaCO 3) (very often oil and gas saturated) shell limestone - (СaCO 3) (very often oil and gas saturated) detritus limestone - (СaCO 3) (very often oil and gas saturated) Chalk (as a rule, it does not happen very often oil and gas saturated) Marl ( rarely fractured oil and gas saturated)	limestone dense limestone oolitic (very often oil and gas saturated) calcareous tuff sintered limestone dolomite - (СaMgCO 3) 2 (very often oil and gas saturated) marl siderite (rarely fractured is oil and gas saturated)
Siliceous	diatomite flask	siliceous tuff flint
Ferrous	-	limonite
Halogen	-	rock salt (highest quality sealant)
sulfate	-	Gypsum CaSO 4 *H 2 O, anhydrite CaSO 4 (usually seals)
Aluminum	-	Bauxite
Phosphate	-	Phosphorite

Analysis of tables 1 and 2 shows that most terrigenous rocks in nature are oil and gas saturated. Therefore, it is no coincidence that for the first time oil and gas were discovered in these rocks and for a long historical period they were extracted from these rocks. But only recent decades In the twentieth century, huge reserves of oil and gas were discovered in many regions in carbonate strata. This is, first of all, in coral, detritus and oolitic limestones and dolomites. So, the following lithofacies of clastic sedimentary rocks are very often oil-and-gas-bearing rocks: sands and sandstones, siltstones and silts, gravelstones and gravels. From the group of carbonate rocks, the following lithofacies serve as oil and gas bearing rocks: coral limestone, shell limestone, detritus and oolitic limestones and dolomites.

The following lithofacies of sedimentary rocks do not contain oil and gas, but perform the function of insulators: rock salt - the highest quality fluid seal, clay, mudstone (non-fractured), marl (not fractured), gypsum and anhydrite are dense, limestone is dense pelitomorphic, chalk and other strong and not fractured rocks. Individual porous sedimentary rocks can only contain industrial hydrocarbon accumulations when they are interbedded with insulating rocks that do not contain oil and gas.

Main literature: 4, 5

Mineralogical and chemical composition

The main minerals that make up carbonate rocks are: calcite, which crystallizes in a trigonal syngony, aragonite, a rhombic variety of CaCO3, and dolomite, which is a double carbon dioxide salt of calcium and magnesium (CaCO 3 * MgCO 3). Recent sediments also contain powdered and colloidal varieties of calcite (druite or nadsonite, bugleite, etc.).

The determination of the mineral and chemical composition of carbonate rocks is carried out in thin sections, as well as using thermal and chemical analyzes and according to the Shcherbina method.

In the field, determined by reaction with dilute HCl. Dolomites boil only in powder.

Theoretical chemical composition calcite and limestone ~ CaO - 56%, CO 2 - 44%, in dolomites - 22-30% CaO and 14-21% MgO.

Naturally, if clastic material is present in the rocks, then the content of SiO 2 will sharply increase (sometimes up to 26%).

Main rock types

Limestones - the color of limestones is diverse and is determined, first of all, by the nature of impurities. Pure limestones are colored white, yellowish, gray, dark gray, and sometimes black.

An important feature of limestones is their fracture, the nature of which is determined by the structure of the rock. Very fine-grained calcareous rocks with a weak cohesion of grains (for example, chalk) have an earthy fracture. Coarse-grained - have a sparkling fracture, m / s of the rock - a sugar-like fracture, etc.

For limestones, the following main types of structures can be distinguished:

Crystalline granular structure, among which several varieties are distinguished depending on the diameter of the grains: coarse-grained (grain size in diameter 0.5 mm), medium-grained (from 0.5 to 0.1 mm), fine-grained (from 0.10 to 0.05 mm), fine-grained (from 0.05 to 0.01 mm) and micro-grained (less than 0.01 mm) structures.

Organogenic structure, in which three most significant varieties are distinguished:

a). actually organogenic, when the rock consists of calcareous organic residues (without signs of their transfer), interspersed in t/z carbonate material;

b). organogenic-detrital, when crushed and often rounded organic remains are present in the rock, located among the t / s of carbonate material;

in). detritus, when the rock is composed only of crushed organic remains without a noticeable amount of heavy carbonate particles.

The clastic structure is observed in limestones formed by the accumulation of fragments arising from the destruction of older carbonate rocks. Here, as well as in some organic limestones, in addition to fragments, a calcareous cementing mass is clearly visible.

The oolitic structure is characterized by the presence of concentrically folded oolites, usually clastic grains are often present.

Sometimes oolites acquire a radially radiant structure.

Inlay and crustification structures are also observed. In the first case, the presence of crusts of a concentric structure is characteristic, filling the former large voids. In the second case, growths of elongated carbonate crystals are observed, located radially relative to the fragments or organic remains that make up the rock.

In the process of transition from sediment to rock and petrification, many limestones undergo significant changes. These changes are manifested, in particular, in recrystallization, petrification, dolomitization, ferruginization and partial dissolution with the formation of stillolites.

Varieties of limestone

Organic limestones

This is one of the most widely used varieties. They are composed of shells of benthic crinoids, algae, corals and other benthic organisms. Much less often, limestones form due to the accumulation of shells of planktonic forms.

Typical representatives of organogenic limestones are reef (biohermic), limestones, consisting largely of the remains of reef-forming organisms and living in a community of other forms.

Writing chalk.

It is one of the very peculiar representatives of calcareous rocks, which stand out sharply in their appearance. It is characterized by white color, uniform structure, low hardness and fine grain. Complicated - mainly calcium carbonate (no dolomite) with a slight admixture of clay and sand particles.

Organic residues make up most of the chalk. Among them, the remains of coccolithophorids, unicellular calcareous algae, composing 10-75% of chalk and chalk-like marls in the form of small (0.002-0.005 mm) plates, discs and tubes, are especially common. Foraminifera are found in chalk, usually in an amount of 5-6% (sometimes up to 40%). There are also shells of mollusks (mainly inocerams, less often oysters and pectinids) and a few belemnites, and in places also ammonite shells. Remains of bryozoans, sea lilies, urchins, corals and tube worms, although they are observed, they do not serve as rock-forming elements of the chalk.

Limestones of chemical origin.

This type of limestone is conditionally separated from other types, because. in most limestones there is always some amount of calcite precipitated from the water by a purely chemical means. You can easily and quickly buy a suitcase in Moscow on the website caseplus.ru. Also here you will find many different bags and backpacks, various leather goods and just the necessary accessories.

Typical limestones of chemical origin are microgranular, devoid of organic residues and occur in the form of layers, and sometimes accumulations of concretions. Often they contain a system of small calcite veins, which form, with a decrease in the volume, initially colloidal sediments. Often there are geodes with large and well-formed calcite crystals.

Clastic limestones.

This type of limestone contains a significant admixture of quartz grains and is usually associated with sandy rocks. Clastic limestones are characterized by oblique bedding.

Clastic limestones are composed of carbonate grains of various sizes, the diameter of which is measured in tenths of a millimeter, less often several millimeters. There are also conglomerate-like limestones, consisting of large fragments. Clastic carbonate grains are usually well rounded and similar in size.

Secondary limestones.

This group includes limestones occurring in the upper part of salt domes, and limestones arising in the process of transformation of dolomites during their weathering (razdolomitization or dedolomiticization).

Broken rocks are medium- or coarse-grained limestones, dense, but sometimes porous or cavernous. They lie in the form of solid masses. In some cases, they contain lenticular inclusions of fine-grained and fine-grained dolomites, sometimes loose and soiling fingers. More rarely, they form inclusions and branching veins in the thickness of dolomites.

Dolomites

They are carbonate rocks, consisting mainly of the mineral - dolomite. Pure dolomite corresponds to the formula CaMg(CO 3) 2 and contains 30.4% CaO, 21.8% MgO and 47.8% CO 2 or 54.3% CaCO 3 and 45.7% MgCO 3 . The weight ratio of CaO:Mg is 1.39.

Dolomites usually contain less clastic impurities than limestones. Also characteristic is the presence of minerals precipitated by a purely chemical means during the formation of a sediment or arising during its diagenesis (calcite, gypsum, anhydrite, celestite, rhodochrosite, magnesite, iron oxides, less often silica in the form of opal and chalcedony, organic matter, etc.). In some cases, the presence of pseudomorphs along the crystals of various salts is observed.

In appearance, many dolomites are very similar to limestones, with which they are brought together by color and the inability to distinguish calcite from dolomite in a finely crystalline state with the naked eye.

Among the dolomites there are completely homogeneous varieties from micro-grained (porcelain-like), sometimes soiling the hands and having a conchoidal fracture, to fine- and coarse-grained varieties, composed of dolomite rhomboids of approximately the same size (usually 0.25-0.05 mm). The leached varieties of these rocks are somewhat reminiscent of sandstones in appearance.

Dolomites are sometimes characterized by vugginess, in particular due to leaching of shells, porosity (especially in natural outcrops) and fracturing. Some dolomites have the ability to spontaneous cracking. Well-preserved organic remains in dolomites are rare. Dolomites are mostly colored in light shades of yellowish, pinkish, reddish, greenish and other tones. Some dolomites are somewhat reminiscent of mother-of-pearl in their color and brilliance.

Dolomites are characterized by a crystalline granular (mosaic) structure, which is also common for limestones, and various kinds of relict structures caused by the replacement of calcareous organic residues, oolites or carbonate fragments during dolomitization. There is sometimes an oolitic, as well as an incrustation structure formed as a result of various cavities, usually in reef massifs.

For rocks transitional from limestones to dolomites, a porphyritic structure is typical, when separate large rhombohedrons of dolomite are present against the background of a finely crystalline calcite mass.

Varieties of dolomites

By origin, dolomites are divided into primary sedimentary, syngenetic, diagenetic and epigenetic. The first three types are often grouped under the name of primary dolomites, while epigenetic dolomites are also called secondary.

Primary sedimentary dolomites.

These dolomites arose in sea bays and lagoons with high salinity water due to the direct precipitation of dolomite from the water. These rocks lie in the form of well-seasoned layers, within which thin bedding is sometimes clearly expressed. Primary vugginess and porosity, as well as organic residues, are absent. Interlayering of such dolomites with gypsum is often observed. The contacts of the layers are even, slightly wavy, or gradual. Sometimes there are inclusions of gypsum or anhydrite.

The structure of primary sedimentary dolomites is uniformly microgranular. The predominant grain size is ~0.01 mm. Calcite occurs only as a minor admixture. Sometimes there is petrification, sometimes intense.

Syngenetic and diagenetic dolomites.

Among them is the predominant part of the dolomites. It is not always possible to distinguish between them. They arise due to the transformation of lime sludge.

These dolomites occur in the form of layers and lenticular deposits. They are strong rocks with uneven, rough fractures, usually with unclear layering. The structure of syngenetic dolomites is often uniformly microgranular. For diagenetic, unevenly granular is more typical (their grain diameters vary from 0.1 to 0.01 mm). Characteristic of diagenetic dolomites is also an irregularly rhombohedral or oval shape of dolomite grains, often having a concentric zonal structure. In the central part of the grains there are dark dust-like accumulations.

In some cases, gypsuming of the rock occurs. At the same time, the most permeable for solutions areas of carbonate rock (in particular, organic remains), as well as accumulations of pelitomorphic dolomite, were most easily replaced by gypsum.

Secondary (epigenetic) dolomites.

This type of dolomite is formed in the process of replacement with the help of solutions of already solid limestones, fully formed as rocks. Epigenetic dolomites usually occur in the form of lenses among unchanged limestones or contain areas of residual limestone.

Epigenetic dolomites are characterized by massiveness or indistinct layering, uneven-grained and heterogeneous structure. They are coarse and inhomogeneously porous. Near areas completely dolomitized, there are areas almost unaffected by this process. The boundary between such areas is sinuous, uneven, and sometimes passes in the middle of the shells.

Mergeli

Marl refers to rocks that are transitional between carbonate and clay, containing 25-95% CaCO 3 . Their most carbonate varieties (75-95% CaCO 3), in the case of significant compaction of the rock, are called clayey limestones.

Marls are divided into three main groups:

1. Actually marls, with a CaCO 3 content of 50-70%,

2. Lime marls, in which the content of CaCO 3 varies within 75-95%,

3. Clay marls with CaCO 3 content from 25 to 50%.

Typical marls are rock of a homogeneous structure, very soft, consisting of a mixture of clay and carbonate particles and often having a certain plasticity when wet. Usually marls are painted in light colors, but there are also brightly colored varieties - red, brown, purple(especially in red-colored strata). Thin layering is not typical for marls, but many of them occur in the form of thin layers. Some marls form regular rhythmic interlayers with thin clayey and sandy layers.

As an impurity, marls contain organic residues, detrital grains of quartz and other minerals, sulfates, iron oxides, glauconite, etc.

Siderite rocks

The chemical formula of siderite is FeCO 3 , with iron containing 48.2%. The name of the mineral itself comes from the Greek "sideros" - iron.

Siderite rocks are an accumulation of granular or earthy aggregates, dense, sometimes representing spherical concretions (spherosiderite).

Their color is brownish-yellow, brown. Siderite easily decomposes in HCl, while the drop turns yellow due to the formation of FeCl 3 .

Origin.

1. Hydrothermal - occurs in polymetallic deposits as a vein mineral. 2. When replacing limestone, it forms metasomatic deposits. 3. Siderites can also be of sedimentary origin; as a rule, they have an oolitic structure. 4. There is siderite of metamorphic origin, formed during the metamorphism of sedimentary iron deposits. In the oxidation zone, it easily decomposes and passes into iron oxide hydrates, forming iron hats.