Fine clastic clayey cemented sedimentary rocks are. Clastic sedimentary rocks. Diagnostic signs of sedimentary rocks

Rocks of clastic (mechanical) origin

Breeds clastic(mechanical) origin are products of mechanical destruction of any parent rocks and are composed mainly of fragments of weathering-resistant minerals and rocks. They are divided according to the size of the fragments into coarse-clastic, medium-clastic (sandy), fine-clastic (silty) and fine-clastic (clayey). Among them, only clayey rocks are products of chemical decomposition of parent rocks, while the remaining rocks are composed of fragments that have not undergone significant weathering. Regardless of particle size, clastic rocks can be loose or cemented.

Loose coarse clastic rocks include varieties with rounded and angular shapes, formed as a result of the accumulation of large fragments. Among them are fragments measuring 1000... 100 mm, called boulders (rounded) or blocks (angular); 100 ... 10 mm - pebbles (rounded) or crushed stone (angular), 10 ... 1 mm - gravel (rounded) or rubble (angular).

Boulders (boulder stone) consist of roughly rounded fragments processed and transported by water or a glacier. According to its genesis, boulder stone can be glacial, river, sea, or lake. Its smaller varieties measuring 120... 300 mm are called cobblestone. Large boulder stone supplied for construction requires preliminary processing into piece material - checker, rubble stone, etc.

Pebbles and gravel are formed similarly to the first, when fragments are transported over long distances by rivers, mountain streams, and also under the influence of sea surf, while acquiring varying degrees of roundness and sorting. The quality of gravel is determined by its genesis, mineral composition, content of clay and organic impurities, etc. The best type of gravel is considered to be glacial gravel, which is less rounded. Gravel is used in reinforced concrete structures, road construction and as a filter material.

Blocks, crushed stone and debris They are accumulations of angular fragments of rocks, heterogeneous in mineral composition. These deposits are especially characteristic of desert and polar regions with intense processes of physical weathering. They are quite widespread in the middle and northern zone of the European part of our country.

Sandy (medium clastic) rocks They are a loose mixture of grains with sizes from 1 to 0.1 mm. They are usually divided according to grain size into coarse-grained with a particle diameter from 1 to 0.5 mm; medium-grained - 0.5 ... 0.25 mm; fine-grained - from 0.25 to 0.1 mm. The sands consist predominantly of quartz, the most resistant mineral to chemical weathering. Pure quartz sands of light color are monomineral rocks. Mixed (polymict) sands consist of a mixture of minerals, in which, in addition to quartz, there are feldspars, micas, amphiboles, etc. Among them, the most widespread are arkosic sands of red or gray color, predominantly of an acidic feldspathic composition, with a small admixture of quartz and other minerals. Marine and aeolian sediments are distinguished by the greatest purity and uniformity of grains; sea and river sands have rounded grains, and glacial sands have angular, most favorable for construction purposes, grain shapes. Clay and silt fractions (0.05... 0.005 mm) are harmful impurities in sand. When assessing the quality of sand as a building material, its mineral and granulometric composition, grain shape, porosity, filtration coefficient, etc. are taken into account. The density of sand is 2.64 g/cm3, and the average density is 1800 kg/m3. They are the main raw materials for the production of ceramics, dinas, glass, concrete and mortar, brick; used for road surfaces and in abrasive production. Distributed everywhere.

Silty (fine clastic) rocks consist of particles ranging in size from 0.1 to 0.01 mm and differ from sand in the content of smaller particles. A representative of these rocks is loess, a light-colored porous (46...50%) rock containing quartz, feldspars, up to 30% calcite and up to 50% clay minerals. The density of loess is 2.5 ... 2.8 g/cm3, and the average density is 1200 ... 1800 kg/m3.

They are characterized by subsidence and easily soak in water. They are used in the cement industry as an additive to concrete, in the production of bricks, tiles, etc. They are widespread in the European part of our country, in the south of Ukraine, in Central Asia, and southern Siberia.

Clayey (fine clastic) rocks consist of more than half of tiny (less than 0.01 ... 0.001 mm) scale-like particles of clay minerals, of which at least 25% have dimensions less than 0.001 mm. Clays are formed during the weathering of feldspathic and some other silicate rocks and consist predominantly of clay minerals such as kaolinite, montmorillonite and hydromica with an admixture of quartz, mica, secondary calcite, opal, etc. Most clays are polymineral, but among them there are the most valuable monomineral ones: kaolinite and montmorillonite varieties. The main factor in the use of clays in construction and the production of building materials is their mineral composition.

Polymineral clays are raw materials for the production of brick and tile products, rough ceramics, alumina, refractories, etc.

Kaolinite clays are composed mainly of kaolinite and are relatively free from impurities of iron oxides. They are white, fine-grained, greasy to the touch, low-plasticity rocks, which are products of the decomposition (hydrolysis) of aluminosilicates by dissociated water containing free hydrogen ions and dissolved CO2.

Kaolinite clays are continental sediments and form under acidic conditions. They are used in the production of porcelain and earthenware products, cement, and fireclay. Deposits of kaolinite clays are located in Ukraine, the Urals, Siberia, etc.

Montmorillonite clays appear during the decomposition of volcanic ash in an alkaline environment. Among them are soda clays that strongly swell in water, with a predominance of the Na cation over the Ca, Mg and K cations, and non-swelling calcium clays, with a predominance of Ca over the Na and Mg cations. The first include bentonites and floridins, rocks of white, grayish-white, pinkish and other colors, the characteristic feature of which is strong swelling when moistened with an increase in volume by about 16 times or more and high adsorption capacity. Most of these clays have a pronounced plasticity when mixed with water, retaining their given shape when dried, and after firing they form stone-like masses. With an increase in mechanical impurities in clays, their plasticity quickly decreases. Montmorillonite clays are used as excellent adsorbents, as they have high absorption capacity. Their deposits are found in Georgia, Crimea, the Dnieper region, Transcarpathia, and Central Asia.

Cemented clastic rocks were formed by the cementation of loose rocks by a variety of chemicals. The most durable is siliceous cement (secondary quartz, opal, chalcedony), less durable is ferruginous (limonite), carbonate (calcite) and clay cement has low cementing ability. Below is a description of the main representatives of this group.

Breccia are compact rocks consisting of angular fragments of gruss or crushed stone, cemented with some kind of cement. The petrographic composition of these fragments is homogeneous. The angular shape of the fragments ensures good adhesion to natural cements, so breccias with some types of cements have quite high strength and are used as finishing stones. Breccias have a limited distribution.

Conglomerates- accumulations of pebbles, gravel, small boulders, etc., cemented with natural cement, differing from breccias in the diversity of petrographic composition, a wide range of strength from 5 to 160 MPa and a change in average density in the range of 1500 ... 2900 kg/m3. Compared to breccias, conglomerates are less durable, since the rounded clastic material is rather weakly bonded to the cement. The practical significance of these rocks is small, but their characteristic structure (binding loose material) is the prototype of the most common ISC structure. Their weakly cemented varieties are used to obtain ballast, and beautiful ones are used as finishing decorative stones. Thick deposits of conglomerates are known in the Crimea and Central Asia.

Sandstones are formed by cementation of sand grains when various mineral solutions seep through them. Depending on the type of cement, siliceous, calcareous, ferruginous, gypsum, clayey, bituminous and other types of sandstones are distinguished. Their strength is determined by the type of natural cement, the nature of its adhesion to sand grains, and the density of the rock. It varies widely from 1 to 150 MPa and above, and the average density is from 1900 to 2800 kg/m3. The most durable (100... 150 MPa and more) are siliceous sandstones with an average density of up to 2800 kg/m3. Clay sandstones are characterized by low strength and are easily destroyed when saturated with water or cyclic freezing and thawing; calcareous sandstones are not water-resistant. In bituminous sandstones, the bitumen that permeates the rock strata accounts for up to 20% of their mass. The color of sandstones depends on the cement: siliceous and calcareous have white and light tones, ferruginous - yellow and reddish, etc. They are widespread in Karelia, Ukraine, the Volga region, etc. and are used to produce wall stone, rubble, crushed stone, as well as decorative finishing material. Their varieties, containing at least 97% silica, are used for the production of acid-resistant materials and raw materials, for the production of refractories, abrasives, etc.

These classes include the well-known loose rocks - sand, crushed stone, pebbles, gravel; cemented rocks, among which the most famous is sandstone, as well as clayey rocks - clay, loam, sandy loam.

The named rocks differ greatly from each other in composition and properties, but in nature the transition from clastic rocks to clayey rocks is very gradual, with a large number of mixed varieties, which makes it necessary to consider these classes within one section.

Classification

The section examines five classes of rocks: coarse-clastic, sandy, fine-clastic, clayey and mixed. For brevity, we will agree to call them all clastic and clayey. As can be seen, they are all classified according to size, clast shape, cementation and connectivity.

Sedimentary clastics, clayey and mixed rocks

Structure and particle size, mm	Breed name
	Texture
	Uncemented		Cemented		Messenger
	Angular wreckage	Rounded wreckage	Angular wreckage	Rounded wreckage
1. Coarse clastics: more than 1000	Neoka- data blocks	Lumps	Blocky breccia	Blocky conglomerate
200-1000	Neoka- data boulders (stones)	Boulders	Valunnaya breccia	Boulder conglomerate
10-200	Crushed stone	Pebble	Bre^ia	Conglo- merat
2-10	Dresva (small crushed stone)	Gravel	Small breccia	Gravelite
2. Middle clastic - sandy (0.05-2):	Sands (according to the predominant fraction): gravelly (rough)		Sandstones (by predominant fraction): gravelly (rough)
0,5-1	large		large
0,25-0,5	average		average
0,1-0,25	small		small
0,05-0,1	dusty (thin)		dusty (thin)
3. Fine clastic - dusty: 0.002...0.05	Silt		Siltstone		Loess
4. Micro-grained - clayey: less than 0.002 (0.005)	Clay		Argillite		Clay
5. Mixed	Silty-clayey sand with crushed stone and gravel, pebbles with sandy gravel filler, etc.		Sandy conglomerate, sandy gravel, etc.		Clay, loam, sandy loam

Compound

These rocks consist of products of mechanical and chemical destruction and transformation of other rocks on the surface of the earth. In the vast majority of cases, they are soil-forming material; most of the construction and other environmental management is carried out on them; they are most often called “soil”.

The composition of clastic and clayey rocks consists of three main components - fragments, cement and clayey material.

Clastic material

Clastic material- the main component of clastic rocks is stone material consisting of blocks, boulders, pebbles, gravel, crushed stone, grains of sand forming sand, quartz mineral dust. All this can be represented by various rocky or semi-rocky rocks, and the name of the original rock can only be mentioned - granite crushed stone, limestone pebbles, quartz sand. Cobblestone, rubble, pebbles, cobbles - natural or specially processed and selected stone tens of centimeters in size, used in construction for paving roads and laying foundations.

Based on their shape, there are two main types of fragments - angular and rounded; there are also several transitional types between them.

Stone fragments of various shapes

a - angular; b - rounded (rounded); c - semi-rounded

The widespread moraine is usually called gravelly loam, while the stone inclusions present in it are more likely to be closer to rounded pebbles than to angular crushed stone.

The fragments are angular in shape.They are formed during weathering and breaking off pieces from the bedrock.In nature, this process is most intensively developed on slopes; the resulting debris accumulates at the foot of the slopes, forming stone screes. With horizontal relief, angular fragments remain in place, and the weathering process quickly fades with depth. This is how weathering crusts are formed.

Angular fragments in the composition of weathering crust and stone scree

Scree rocks and weathering crusts, depending on the size of the fragments, are called blocks, crushed stone, gruss, or cartilage. They can serve as a building material in the places where they are distributed, although crushed stone, blocks, etc. are actually used in construction. much more often they are artificially crushed stones, mined in quarries using explosions. Based on them, it is possible to obtain more durable materials for construction than when using weathered and cracked natural stone, especially since the majority of the Russian population lives in flat areas where these screes and weathering crusts are practically absent.

Rounded (rounded) fragments acquire this shape as a result of treatment with water (sea surf, rivers, water-glacial flows), and less often - with wind. Boulders are formed from angular blocks, pebbles are formed from crushed stone, and gravel is formed from rubble (fine crushed stone). The smaller the fragments, the more often they are round. For example, sands with angular fragments occur in nature, but are extremely rare. The silty fraction—quartz fragments measuring 0.002–0.05 mm in size—is always round. Due to their small size, they begin to demonstrate colloidal properties - they easily stick together, and when agitated, they slowly settle in water.

Cement

Some rocks in nature resemble in their composition such well-known artificial materials as hardened cement mortar or concrete, in that they consist of stone fragments held together with cement. It is possible that the idea of creating concrete was borrowed by people from nature. Natural cement is similar in composition to some chemical sedimentary rocks. It can be carbonate, siliceous, sulfate, ferruginous and clayey - then it is called clay aggregate. Carbonate cement is similar in composition to chemical limestone and is determined by its reaction with acid. Siliceous is the most durable and hardest of cements; sometimes it has a greasy sheen and does not react with acid. Sulfate is not durable, it can be scratched with a fingernail, and sometimes sugar-like crystals are visible on it. Ferrous cement is recognized by its rusty color. Clay cement is scratched with a fingernail and becomes soaked in water.

The formation of cement is possible in two ways:

in marine conditions with simultaneous accumulation of chemical sediment along with debris;
due to the precipitation of chemical material from groundwater within the clastic strata after its accumulation.

Rocks with different types of cement

a - basal cement; b - pore cement; in — contact

Clay minerals

In coarse-grained rocks, clay minerals can play the role of filler between stone particles and actually act as cement. When clay minerals are mixed with sandy and fine-clastic material, so-called clayey rocks are formed - loams, sandy loams and natural clays. Clay minerals acquire the role of the main component, giving the entire mixture the properties of clay rocks, the main of which are moisture capacity, water impermeability and cohesion - the ability to become plastic when moistened and hard when dried.

Structure, granulometric and mineral composition

These characteristics are closely related to each other. The structure of the material is determined depending on the particle size. Particles of a certain size are usually called fractions. The boundaries of the fractions are taken according to GOST 25100-2011 “Soils”, they, with very minor changes, repeat the boundaries accepted in the geological literature, only the names of the fractions differ; geological data are given in parentheses.

Structures and approximate composition of clastic, clayey and mixed rocks

Structure and fraction - particle size	Approximate composition
1. Coarse clastic (psephytes) - larger than 2 mm	Fragments of any rocks
2. Medium clastic - sandy (psammites) - 0.05-2 mm	Quartz predominates, feldspar may be present, other minerals are very few
3. Fine clastic - silty (silt) - 0.002-0.05 mm	Quartz - almost the entire faction
4. Micro-grained - clayey (pelites) - less than 0.002 mm (less than 0.005 mm)	Kaolinite, montmorillonite, glauconite and other clay minerals, quartz, limonite
5. Mixed - clastic-sandy, sandy-clayey, etc.	Various mixtures of particles of fractions 1–4

It is known that the finer the material is crushed, the faster it dissolves and enters into chemical reactions. Therefore, among large-sized fragments (blocks, boulders, crushed stone, pebbles), almost all rocks are found with the exception of the most soluble ones - gypsum, anhydrite, rock and other salts. Among the medium-sized fragments one finds mainly quartz, the most weathering-resistant mineral, less commonly feldspar, and even more rarely other minerals. Medium clastic rocks are sands.

Among the fine-clastic (silty) particles, there are almost no other minerals except quartz. Rocks: loess, siltstone, siltstone.

Micrograined rocks are composed of kaolinite, montmorillonite, hydromicas and other clay minerals. The type is pure clay.

Mixed rocks - most often a mixture of sand, silt and clay fractions - these are clays, loams and sandy loams. The terms “sandy-clayey” and “clayey rocks” are widely used, used as synonyms.

The percentage weight content of particles of various fractions is calledgranulometric composition (granular composition). To determine it, a soil sample is passed through a set of sieves with further weighing of each fraction. Next, according to a small set of rules, the breed is given a formally correct name. This applies to unconsolidated coarse, sandy and partly some clayey rocks, which will be discussed below.

Division of coarse and sandy soils

Varieties of coarse soils and sands	Particle size, mm
Coarse:
boulder (blocky)	>200	> 50
pebble (crushed stone)	> 10	> 50
gravel (wood)		> 50
Sands:
gravelly
large	>0,50	> 50
medium size	>0,25	> 50
small	> 0,10
dusty	>0,10	< 75

Correctly naming sandy and clayey soils is an important task in geology and soil science. The type of soil (in fact, the name) determines the various tabular values of the parameters included in the foundation calculations, which is important for designers. Therefore, the granular composition, along with other laboratory properties of soils, is one of the most important indicators of properties and is determined en masse during surveys.

As you can see, everything begins in mountainous conditions with weathering, landslides and shedding of angular stone fragments - sonatural blocks and crushed stone. During the process of weathering (chemical),clay minerals, which are easily carried away by water, and if granites and gneisses, which are very common in nature, are destroyed, then detrital quartz with sandy and silty particles is also formed.

Scheme of formation of clastic rocks

Due to gravity, slope processes, temporary water flows and rivers, angular clastic material reaches the sea coast. Here the material formed due to the destruction of the shore by waves is added to it. In the surf zone, the stone material is further crushed, the fragments are rounded, and boulders, pebbles, gravel, sand and quartz dust - alewrite material. Some of the material dissolves. Waves and sea currents carry sediments to greater depths, where perhaps cementady and transformation into cemented analogues occur - conglomerates, gravelites, sandstones, siltstones.

Similar processes on a smaller scale can occur due to the geological work of mountain rivers, glaciers and water-glacial flows. If there is no rounding phase, then during cementation of angular material,sedimentary breccias.

Tectonic brecciasare formed in zones of tectonic disturbances. Clastic material is produced by the movement of tectonic blocks along fault planes, and cementation is produced by the release of chemical sediment from groundwater that easily circulates through the fractured zone.

SEDIMENTARY, SANDY, CLAY AND MIXED (SAND-CLAY) ROCKS

Clastic rocks and their classifications

These classes include well-known loose rocks - sand, crushed stone, pebbles, gravel; cemented rocks, among which the most famous is sandstone, as well as clayey rocks - clay, loam, sandy loam.

Classification. The section examines five classes of rocks - coarse-grained, sandy, fine-grained, clayey and mixed. For brevity, we will agree to call them all together clastic and clayey. As can be seen, they are all classified according to size, clast shape, cementation and connectivity (Table 3.5).

Sedimentary clastics, clayey and mixed rocks

Table 3.5

Structure and particle size, mm	Breed name
	Texture
	Uncemented		Cemented
	Angular	Rounded	Angular	Rounded
1. Coarse clastics: more than 1000			Blocky	Block conglomerate
	Neo-rocked boulders (stones)		Valunnaya	Boulder conglomerate
		Pebble		Conglomerate
				Gravelite
2. Medium clastic - sandy (0.05-2):	Sands (according to the predominant fraction): gravelly (rough)		Sandstones (according to the predominant fraction): gravelly (rough)



	dusty (thin)		dusty (thin)
3. Fine clastic - dusty: 0.002...0.05			Siltstone
4. Micro-grained - clayey: less than 0.002 (0.005)			Argillite
5. Mixed	Silty-clayey sand with crushed stone and gravel, pebbles with sandy gravel filler, etc.		Sandy conglomerate, sandy gravel, etc.		loam,

Compound. These rocks consist of products of mechanical and chemical destruction and transformation of other rocks on the surface of the earth. In the vast majority of cases, they are soil-forming material; most of the construction and other environmental management is carried out on them; they are most often called “soil”.

The composition of clastic and clayey rocks consists of three main components - fragments, cement and clayey material.

1. Clastic material - The main component of clastic rocks is stone material consisting of blocks, boulders, pebbles, gravel, crushed stone, grains of sand that form sand, and quartz mineral dust. All this can be represented by various rocky or semi-rocky rocks, and the name of the original rock can only be mentioned - granite crushed stone, limestone pebbles, quartz sand. Cobblestone, rubble, pebbles, paving stones are natural or specially processed and selected stones tens of centimeters in size, used in construction for paving roads and laying foundations.

Based on their shape, there are two main types of fragments - angular and rounded; there are also several transitional types between them (Fig. 3.12).

Rice. 3.12. Stone fragments of various shapes: A- angular; b- rounded (rounded); V- semi-rounded

The widespread moraine is usually called gravelly loam, while the stone inclusions present in it are more likely to be closer to rounded pebbles than to angular rubble.

1.1. The fragments are angular in shape. They are formed by weathering and breaking off pieces from bedrock.

In nature, this process is most intensively developed on slopes; the resulting debris accumulates at the foot of the slopes, forming stone screes. With horizontal relief, angular fragments remain in place, and the weathering process quickly fades with depth. This is how weathering crusts are formed (Fig. 3.13).

Rice. 3.13.

1.2. Rounded (rounded) wreckage they acquire this form as a result of treatment with water (sea surf, rivers, glacier flows), less often - with wind. Boulders are formed from angular blocks, pebbles are formed from crushed stone, and gravel is formed from gruss (fine crushed stone). The smaller the fragments, the more often they are round. For example, sands with angular fragments occur in nature, but are extremely rare. Silt fraction - quartz fragments 0.002-0.05 mm in size are always round. Due to their small size, they begin to demonstrate colloidal properties - they easily stick together, and when agitated, they slowly settle in water.
2. Cement. Some rocks in nature resemble in their composition such well-known artificial materials as hardened cement mortar or concrete, in that they consist of stone fragments held together with cement. It is possible that the idea of creating concrete was borrowed from nature by people. Natural cement is similar in composition to some chemical sedimentary rocks. It can be carbonate, siliceous, sulfate, ferruginous and clayey - then it is called clay aggregate. Carbonate cement is similar in composition to chemical limestone and is determined by its reaction with acid. Siliceous cement is the most durable and hard cement; sometimes it has a greasy sheen and does not react with acid. Sulfate is not durable, it is scratched with a fingernail, and sometimes sugar-like crystals are visible on it. Ferrous cement is recognized by its rusty color. Clay cement is scratched with a fingernail and becomes soaked in water.

The formation of cement is possible in two ways:

1) in marine conditions with simultaneous accumulation of chemical sediment along with debris;
2) due to the precipitation of chemical material from groundwater within the clastic strata after its accumulation.

Rocks with the most common types of cementation are shown in Fig. 3.14.

Rice. 3.14. Rocks with different types of cement: A- basal cement; b - pore cement; V- contact

3. Clay minerals. In coarse rocks, clay minerals can act as a filler between rock particles and actually act as cement. When clay minerals are mixed with sandy and fine-clastic material, so-called clayey rocks are formed - loams, sandy loams and natural clays. Clay minerals acquire the role of the main component, giving the entire mixture the properties of clay rocks, the main of which are moisture capacity, water resistance and cohesion - the ability to become plastic when moistened and hard when dried.

Structure, granulometric and mineral composition. These characteristics are closely related. The structure of the material is determined depending on the particle size. Particles of a certain size are usually called fractions. The boundaries of the fractions are taken according to GOST 25100-2011 “Soils”, they, with very minor changes, repeat the boundaries accepted in the geological literature, only the names of the fractions differ; geological data are given in brackets (Table 3.6).

Table 3.6

Structures and approximate composition of clastic, clayey and mixed rocks

Structure and fraction - particle size	Approximate composition
1. Coarse clastic (psephytes) - larger than 2 mm	Fragments of any rocks
2. Medium clastic - sandy (psammites) - 0.05-2 mm	Quartz predominates, feldspar may be present, other minerals are very few
3. Fine clastic - silty (silt) - 0.002-0.05 mm	Quartz - almost the entire faction
4. Micro-grained - clayey (pelites) - less than 0.002 mm (less than 0.005 mm)	Kaolinite, montmorillonite, glauconite and other clay minerals, quartz, limonite
5. Mixed - clastic-sandy, sandy-clayey, etc.	Various mixtures of particles of fractions 1-4

It is known that the finer the material is crushed, the faster it dissolves and enters into chemical reactions. Therefore, among large-sized fragments (blocks, boulders, crushed stone, pebbles) almost all rocks are found with the exception of the most soluble ones - gypsum, anhydrite, rock and other salts. Among the medium-sized fragments, one finds mainly quartz, the most weather-resistant mineral, less commonly feldspar, and even more rarely other minerals. Medium clastic rocks are sands.

Among the fine-clastic (silty) particles, there are almost no other minerals except quartz. Rocks: loess, siltstone, siltstone.

Micrograined rocks are composed of kaolinite, montmorillonite, hydromicas and other clay minerals. The rocks are pure clay.

Mixed rocks - most often a mixture of sand, silt and clay fractions - these are clays, loams and sandy loams. The terms “sandy-clayey” and “clayey rocks” are widely used, used as synonyms.

The percentage by weight of particles of different fractions is called granulometric composition (by personnel). To determine it, a soil sample is passed through a set of sieves with further weighing of each fraction. Next, according to a small set of rules, the breed is given a formally correct name (Table 3.7). This applies to unconsolidated coarse, sandy and partly some clayey rocks, which will be discussed below.

Table 3.7

Division of coarse and sandy soils

Correctly naming sandy and clayey soils is an important task in geology and soil science. Various tabular values of the parameters included in foundation calculations depend on the type of soil (in fact, on the name), which is important for designers. Therefore, the granular composition, along with other laboratory properties of soils, is one of the most important indicators of properties and is determined en masse during surveys.

Origin of clastic rocks shown schematically in Fig. 3.15.

As you can see, everything begins in mountainous conditions with weathering, landslides and shedding of angular stone fragments - this is how natural blocks And crushed stone During the process of weathering (chemical), clay minerals, which are easily carried away by water, and if granites and gneisses, which are very common in nature, are destroyed, then detrital quartz with sandy and silty particles is also formed.

Rice. 3.15.

Due to gravity, slope processes, temporary water flows and rivers, angular clastic material reaches the sea coast. Here the material formed due to the destruction of the shore by waves is added to it. In the surf zone, the stone material is further crushed, the fragments are rounded, and boulders, pebbles, gravel, sand And quartz dust- material silts. Some of the material dissolves. Waves and sea currents carry sediments to greater depths, where perhaps cementation and transformation into cemented analogues occur - conglomerates, gravelstones, sandstones, siltstones.

Tectonic breccias are formed in zones of tectonic disturbances. Clastic material is produced by the movement of tectonic blocks along fault planes, and cementation is produced by the release of chemical sediment from groundwater that easily circulates through the fractured zone.

Artificial pebbles, artificial beach. If it is necessary to increase the area of the natural pebble beach, crushed stone is transported to the coast and dumped into the surf zone. The rate of rounding of the debris depends on the strength of the original rock and usually takes several months, after which the beach is again ready for use. An artificial beach must be regularly replenished with crushed stone and protected from erosion, since in nature there are constant processes of grinding pebbles and carrying them away with sea currents. Increasing the area of sandy beaches is carried out in a similar way, but protecting them from erosion is even more difficult.

Texture of clastic, sandy and mixed rocks. The rocks of this group have a wide variety of textures and composition due to the diversity of the rocks themselves (Table 3.8).

In terms of density, rocks can be dense, porous, micro- and macroporous, fractured and weathered. Among the rocks of this group, only well-cemented breccias, conglomerates, gravelites, sandstones and siltstones have dense textures. All uncemented rocks are porous due to the spaces between fragments and particles - boulders, pebbles, crushed stone, gravel, sand, silt, etc. Microporous - all clayey rocks due to micropores invisible to the naked eye.

The porosity of unconsolidated clastic and clay rocks can be 20-35% and exceed 50% in loess. Widely used terms (dense clay, dense sand, etc.) are relative and indicate the minimum porosity of these rocks, amounting to 10-25% of the volume. For sandy and clayey rocks, porosity is measured during surveys and is an indicator by which the compression of these rocks at the base of structures is calculated.

According to the relative arrangement of particles, clastic rocks, like most sedimentary rocks, are layered and non-layered. Highly compacted layered varieties are sometimes called schistose because of their external resemblance to a group of metamorphic schists. In contrast, sedimentary shale rocks become wet.

Based on the connections between particles (this characteristic can also be attributed to the structure), clastic rocks are defined as unconsolidated (loose, loose), cemented and cohesive (loose). The term “connected” is used in relation to sandy Table 3.8

Textures and some features of the composition of sedimentary clastic, clayey and mixed (clastic-clayey) rocks

Type of texture	Characteristic
1. Texture determined by density
1.1. Dense	Pores are not visible, water is not absorbed into a dry sample - cemented clastic rocks
1.2. Microporous	Inherent in clayey rocks. The exact porosity is determined in the laboratory. Some samples are light
1.3. Porous, finely porous, cavernous	Pores are visible to the naked eye. This is typical for weakly cemented and uncemented rocks.
1.4. Macroporous	The term is used only for loess that has not only microporosity, but also visible pores with a diameter of about 1 mm, called macropores, visible to the naked eye.
1.5. Fissured	There are cracks in the rock
1.6. You are the wind	Cracks and voids in the rock are widened as a result of weathering processes. The breed is weakened
2. Textures determined by the relative position of particles in the rock
2.1. Layered: a) macrolayered	Visible only in outcrop due to changes in color, composition, and composition of the rock
b) finely layered	Sometimes visible in samples
c) schistose	Thin, fine layering of clayey rocks of a refractory and hard consistency. Samples are broken into slab blocks according to bedding
2.2. Non-layered	Rocks do not have layering - loess, moraine
3. Textures determined by the bonds between particles
3.1. Cemented	Rock particles are held together by cement
3.2. Uncemented (loose, loose)	The rock particles are not held together
3.3. Connected (loose)	Inherent in clayey rocks. The rock is connected due to colloidal bonds between particles. The rock is plastic when soaked, becomes hard when dried, but is neither a monolithic nor a granular material

clayey rocks. They are neither rocky nor granular material. They are plastic and fluid when moistened and become almost hard when dry.

Hydrogeological and engineering-geological properties of cemented clastic rocks. Cemented rocks can be either dense, impenetrable, or porous, permeable to water - it all depends on the ratio of the spaces between the fragments and the amount of cement. They can also be fractured, and if the cemented rock contains carbonate or sulfate components, karst may develop, which further increases permeability. These rocks have the usual properties of rocky and semi-rocky rocks. As a base they are quite strong and incompressible. Only sandstones and siltstones are widely used as crushing materials for crushed stone, although coarse-grained rocks can also be used. To obtain beautiful facing tiles, marble breccias are used, and sandstones and siltstones are used to obtain tiles laid on the floor. Strong, well-cemented sandstone is even used for making steps, as it provides a good rough surface. Thin-layered sandstone varieties do not need to be sawed - they produce natural tiles of irregular shape and are suitable for laying on paths.

Hydrogeological and engineering-geological properties of unconsolidated clastic rocks. All unconsolidated rocks have good permeability, water abundance, and form aquifers that are suitable and convenient for exploitation. The larger the fragments, the greater the permeability, the greater the filtration coefficients (see Part II, Table 8.1). Pebbles, crushed stone, and gravel are second only to highly porous, fractured and karst rocks in their permeability.

Sands are also permeable rock. The sizes of sand grains vary from 0.05 to 2 mm. Also, the filtration coefficient varies tenfold - it is maximum in gravelly sands and minimum in silty sands.

Sands are the most common among unconsolidated clastic rocks. They often lie on the surface, forming groundwater aquifers. Sands are often found in the section, and when overlain by clayey rocks, they form interstratal aquifers of fresh water. For the purposes of construction design, coarse soils and sands in accordance with GOST 25100-2011 are classified according to their particle size distribution, degree of water saturation, porosity and some other indicators determined in the laboratory.

The presence of clay or organic aggregate greatly reduces the permeability of unconsolidated rocks. Pebbles with clay filler essentially turn into low-permeability rocks. The permeability of clayey sands with organic matter decreases tens of times compared to similar rocks without filler. As a base and medium for structures, unconsolidated rocks usually do not present any difficulties, with the exception of dusty and fine sands that are capable of exhibiting quicksand properties and frost heaving. Boulders, blocks, pebbles, crushed stone, gravel - a weakly compressible base.

Clastics are formed by the weathering of pre-existing rocks that were transported to different areas from where they were originally and then turned into rocks. They have a clastic structure made up of clasts (large chunks like sand or gravel) and are classified by grain size. Table 7.1 lists the various clastic rocks along with their particle sizes.

Clastic rocks are composed of fragments of other rocks. These rock fragments were formed by weathering and were then carried into low areas or into crevices, where they became trapped as sediment. If the sediment is buried deep enough, it becomes compacted and cemented, forming sedimentary rock.

Clastic sedimentary rocks range in particle size from microscopic clay rocks to boulders. Their names are based on the size of their fragments or grains. Starting with the smallest grains, which are clays, then silts, then sand. Debris larger than 2 mm is called pebbles or crushed stone.

Mudstone is a rock composed mainly of clay particles, siltstone is composed of silt-sized grains, sandstone is composed of sand grains, and conglomerate is composed of pebbles covered with sand or silt.

Coarse-grained clastic rocks

Gravel (grain size greater than 2 mm; rounded fragments = conglomerate; angular fragments = breccia).

Medium-grained clastic rocks Sand (grain size from 0.05 to 2 mm).

Sandstone (mostly quartz grains = quartz sandstone or quartz arenite; mostly feldspathic grains = arkose; mostly sand-sized rock fragment grains = lithitic sandstone, litharenite, or gravuacca).

Cement (the glue that holds it all together) like calcite, iron oxides, silica.

Fine-grained clastic rocks

Silt and siltstone (grain size from 0.005 to 0.05 mm). Clay, mudstone and shale (grain size< 0,005 мм).

The deposition of these types of sedimentary rocks by different streams is what you might guess. Large gravel and pebbles are carried only by strong currents. There are rapid mountain streams, rocky shores with high waves and meltwater from glaciers. Strong glacial flows also transport sand. This is why you usually see sand between gravel and pebbles. Pebbles and small stones trip over each other and very quickly become smooth, bouncing along the ground or in the water. Beach pebbles and shards of broken glass, constantly rolled back and forth by the surf, also become smooth and round.

Coarse clastic rock, which is not so obviously smooth and washed out, is not a conglomerate, but a breccia. These sharp-angled rock fragments occur near their source, where sedimentary rocks were layered on top of each other before being transported very far away. Although some breccias are sedimentary in origin, others are formed from igneous rocks through volcanism. They were deposited on a layer of sedimentary rock after the first eruption during the eruption or were instantly crushed along a fault during an earthquake.

Clastic rocks are sedimentary rocks that arose as a result of the mechanical destruction of any rocks and the accumulation of the resulting fragments. They consist of fragments of various rocks and minerals.

Clastic Rock Classifications Clastic rock classifications are based on the structure of the clasts and, less commonly, on the mineral composition. More often, classifications are used that are based on structural features - the size and shape of the fragments.

The lower boundary of clastic rocks is drawn by the size of 0.005 mm, since below this particular size interval most clastic particles lose the signs of the primary rocks and minerals from which they are formed. And having a large total surface area of particles relative to volume, they are subject to oxidation, hydration, hydrolysis and replacement by newly formed minerals, mainly layered silicates-clay minerals and chlorites. These particles, lying beyond the size of 0.005 mm, form sediments and rocks, the structures of which are defined as pelitic, and the sediments and rocks themselves are called pelites through their structural name. Taking into account the newly formed, predominantly clay minerals, pelitolites are also called clay rocks.

Clastic sediments and rocks made of particles larger than 0.005 mm are divided into three groups according to the size of the fragments. The smallest ones from the term “silt” are called silts and siltstones: the next largest ones are from the term “psammit”, introduced by A.T. Brongniar in 1813 are psammites and psammitolites, most often called sands and sandstones. And the largest from the term “psephyte”, proposed by A.T. Bronyar in the same 1813, are psephites and psephytolites, also called coarse, coarse clastic rocks.

The basis of coarse clastic rocks is made up of rock fragments of different mineral composition and genesis: igneous, metamorphic and sedimentary. Smaller ones (sands and silts) are represented by fragments of individual minerals.

According to the mineral composition, they are distinguished: monomictic rocks - in which one mineral makes up at least 95%, oligomictic rocks - the predominant mineral is 75-95%, and polymictic rocks - none of the minerals makes up 75%.

Decisive evidence of the existence of real units within clastic sediments and rocks, the presence of boundaries between them and the position of the latter is the distribution of clastic rocks of different sizes in the lithosphere.

According to the size of the fragments, they are distinguished:

1) coarse clastic rocks (psephites), consisting mainly of fragments with a diameter of more than 2.0 mm;

2) medium-clastic (psammites), consisting of fragments with a diameter of 2.0 to 0.05 mm;

3) fine-clastic (siltstones), consisting of fragments with a diameter of 0.05 to 0.005 mm;

4) clayey rocks (pelites), consisting mainly of particles with a diameter of less than 0.005 mm (see table).

Table 1 - Classification of clastic rocks

debris,	Structure	Loose structure	Cemented structure
coal	Rounded	coal	Rounded
Breed name
	Psephytic (coarse clastic)
		Pebble
			Dresvyanyk	Gravelite
	Psammitovaya (medium clastic)		Sandstone
	Siltstone (fine clastic)		Siltstone
	Pelitovy (fine clastic)	Pelit (clay)	Argillite

Coarse clastic rocks. These include rocks consisting of fragments ranging in size from 2.0 mm to several meters in diameter. Depending on the structure and texture, the following types of rocks are distinguished.

Blocks are angular fragments measuring over 200 mm, crushed stone is angular fragments measuring from 200 to 40 mm and debris - from 40 to 2.0 mm. If the fragments of the indicated sizes are rounded, then they are respectively called boulders, pebbles and gravel (see Appendix A).

Cemented crushed stone and debris are called breccia. Ore breccias deserve special attention, the cement of which often contains industrial accumulations of copper, lead, zinc and other metals, and cemented pebbles and gravel are conglomerates.

Conglomerates are widespread among ancient marine sediments. Conglomerates contain industrial concentrations of gold and uranium (Figure 1.2).

Figure 1.2 Glacial conglomerate and sandstone. Volozhin district near ag. Rakov (photo by the author)

Medium clastic rocks. These include sands and sandstones that are widespread in nature. Sands are loose accumulations of fragments ranging in size from 2.0 to 0.05 mm, and sandstones are fragments of the same size cemented together (see Appendix A).

Fine clastic rocks. Fine clastic rocks include rocks consisting of fragments ranging in size from 0.05 to 0.005 mm. Loose accumulations of such fragments are called siltstones, and cemented ones are called siltstones.

One of the widespread representatives of silts is loess, a light yellow rock consisting of fragments of quartz and feldspars.

Siltstones are cemented rocks of various colors and often have a thin-layered platy structure (see Appendix B).

Mixed rocks. These include sandy loams, which contain, along with sand, up to 20-30% clay particles, and loams, in which the number of clay particles increases to 40-50%. Accordingly, the properties of the rocks change, which, first of all, is expressed in a decrease in plasticity when wet from clays to sands (see Appendix B).

Clay rocks. The most common sedimentary rocks are clay rocks, which account for more than 50% of the volume of all sedimentary rocks.

Clay rocks are mainly composed of tiny (less than 0.02 mm) crystalline grains of clay minerals. In addition, they contain equally small grains of chlorites, oxides and hydroxides of aluminum, glauconite, opal and other minerals, which are products of the chemical destruction of various rocks and partly clay minerals. The third component of clayey rocks is various fragments measuring less than 0.01 mm.

Clay rocks are formed as a result of chemical processes leading to the accumulation of clay minerals, and the simultaneous introduction of tiny clastic particles.

According to the degree of lithification among clayey rocks, clays are distinguished, and mudstones are highly compacted clays (see Appendix D).