How are sedimentary rocks formed and how are sedimentary rocks formed?

Weathered rock particles are deposited at a certain location through the atmosphere and water flow, and are subjected to high-pressure diagenesis to gradually form rocks. Sedimentary rocks retain a lot of information about the history of the earth, including fossils of ancient animals and plants, and the bedding of sedimentary rocks has information about changes in the earth's climate and environment.

Weathering and erosion: Large rocks on the banks of rivers and middle reaches gradually disintegrate into fragments or smaller sand and mud debris after years of erosion, weathering or direct cutting by river water.

Transport: Disintegrated, cut rock debris that is moved from upstream to downstream by river water.

Accumulation: The river slows down downstream and has less and less capacity to carry it, so that the debris in the river is deposited along the way. From the upstream and downstream to the seabed, they are "gravel layer", "sand layer", and "mud layer".

In addition, the "coral reef layer" is formed by the accumulation of corals, algae, and other organisms.

Compacting: As new layers are constantly piled on top of the old ones, the underlying sediments will be compacted and firm over time.

Cementation: Dense sediments still have many pores. As groundwater flows through these pores, the minerals bring in them to fill the pores one by one, while gluing the rock debris particles tightly together.

The classification of sedimentary rocks is mainly based on the conditions under which they were formed, followed by the size, structure and composition of the constituent particles. Sedimentary rocks can be formed by three different processes: mechanical sedimentation (primary), chemical sedimentation, and biological sedimentation.

The products of rock weathering or the detritus of volcanic eruptions are eroded and transported by external forces such as flowing water, wind, waves, glaciers, etc., and are deposited in new places after the kinetic energy consumption of external forces, which is called sedimentation, and the sedimentary layers formed by this form become various sedimentary rocks after diagenesis.

Under the continuous sedimentation, the loose sediment accumulates thicker and thicker, and the pressure increases The lower sediment is tightly pressed by the upper sediment, and the water in the pores is gradually discharged, the pores gradually decrease, the sediment volume shrinks and becomes compact, and finally becomes a hard rock, which is the main way of sediment diagenesis.

Chemically formed sedimentary rocks

Due to the action of water and acid, oxygen, carbon dioxide and so on dissolved in water, the rock is decomposed, and some minerals are dissolved into the water and carried to other places by the flowing water, especially in the lake and sea, under certain conditions, these substances, such as siliceous, calcareous, iron, argillaceous, etc., will fill the pores of the sediment, so that the loose particles are cemented together, or precipitated from the solution, and then the sediment is chemically formed into rocks, such as rock salt, gypsum, limestone, etc.

Biologically formed sedimentary rocks

In lakes or shallow seas, there are often a large number of biological remains accumulated, and when accumulated, accompanied by chemical reactions, under the influence of a certain temperature and pressure, recrystallization is produced, so that the density increases, forming hard sedimentary rocks, such as coal, shell limestone, coral limestone, etc.

Sedimentary rocks are formed by the accumulation, compacting, and solidification of detrital materials on the earth's surface.

Sedimentary rocks formed by biological sedimentation.

Water reacts with calcium oxide to form calcium carbonate.

Sedimentary rocks are formed by weathered detrital matter and dissolved materials through annihilation, sedimentation and diagenesis. The formation process is restricted by the geographical environment and tectonic pattern. The influence of paleogeography on the formation of sedimentary rocks is manifold.

The most obvious are the paleogeographic influences on land and sea, outside and within basins.

Stages of formation of sedimentary rocks:

1.Weathering and denudation stage: due to the long-term weathering and denudation of various rocks on the surface of the earth's crust, the original triangular rocks are gradually broken to form a new weathering product.

2.Transportation stage: Except for a part of the state silver products that have been weathered and denuded, most of the broken materials are transported to other places due to the action of flowing water, wind, glaciers and their own gravity.

3.Deposition stage: When the handling capacity is weakened or the physical and chemical environment changes, the carried material is gradually deposited. Sedimentation can generally be divided into three types: mechanical deposition, chemical deposition and biochemical deposition.

4.Hardening stage: the initial sedimentary loose material is covered by subsequent sediments, and under the action of overlying rock lamination and cemented material, the original material is gradually compacted, the pore is reduced, and the harder rock layer is formed by dehydration and consolidation or re-consolidation.

Sedimentary rocks are rocks formed by the consolidation of loose sediments deposited in layers.

The general process of its formation: when the original sediment is continuously covered by new sediments and thickened, it is isolated from the upper layer of water, and under anaerobic environmental conditions, the organic matter decays and decomposes, and various reducing gases are produced; dissolves carbonate minerals into bicarbonates; Reduction of ** oxides of certain metal elements to low-cost sulfides; At the same time, the salinity of the water in the soft mud increases, and the medium also changes from an acidic oxidation environment to an alkaline reducing environment. As a result, sediments recombine and form new secondary minerals, colloids are dehydrated and aged into solids, and detritals are compressed, cemented, etc., and consolidated into rocks.

Under the condition of deep burial, due to the increase of temperature and pressure and the influence of deep moisture, it can also produce the effects of pressure dissolution, metasomatism and recrystallization, so that the sedimentary rock mass is further compacted and the grain is coarse.

The ** of sediments are the products of weathering of pregenetic rocks on the earth's surface, the sediment of volcanic eruptions, various organic matter of biotic origin, and a small number of landfall from the universe. According to the origin and nature of sediments, they can be divided into the following categories:

1.mechanical (detrital) deposits.

2.Chemical deposits.

3.Organic sediments.

a) Basic characteristics of sedimentary rocks.

The material composition of sedimentary rocks is most different from magmatic rocks in that they are rich in secondary minerals and organic matter and the presence of fossils. The occurrence of sedimentary rocks is characterized by layered production.

Sedimentary rocks have a variety of structures, the most prominent of which are bedding and layering.

Bedding can be generally divided into: 1) horizontal bedding, 2) wavy bedding, and 3) cross-bedding.

Horizontal tectonics refers to the impressions and traces left in the upper and lower layers that are related to the origin of the rocks.

The main structural types of sedimentary rocks are: clastic structure, slow filial piety disadvantage argillaceous disturbance structure, chemical structure and biological structure.

b) The main types of sedimentary rocks.

Among the three major rock types, sedimentary rocks have the most extensive distribution area on the surface (about 70). Sedimentary rocks can be divided into the following categories according to their genesis, material composition and structure:

1.Clastic rocks.

According to the genesis, it can be divided into two types: volcaniclastic rocks and normal clastic rocks.

2.Clay rocks.

3.Biochemical rocks.

Conglomerate, breccia, sandstone,DolomitesShale.

Sedimentary rock. There are: 1. Conglomerate is a kind of gravel composed of round muddy.

Cemented rocks are clastic rocks with round and subcircular gravels accounting for more than 30% of the total rocks. The clastic components in the conglomerate are mainly cuttings, with only a small amount of mineral debris, and the gap fillers are sand, silt, clay and chemical precipitates.

2. Brecciate, like conglomerate, is also a kind of clastic rock, which is sold by those who are broken down from the parent rock, and the debris with a particle diameter of more than 2 mm is a rock formed by handling, sedimentation, compaction and cementation, and the average diameter of the gravel is fine gravel if it is 1 to 10 mm, 10 to 100 mm is called coarse gravel, and more than 100 mm is a boulder.

3. Sandstone is a kind of sedimentary rock, mainly cemented by various sand grains, with a particle diameter of up to 2mm, of which the sand content is greater than 50%, with a stable structure, usually light brown or red and comatose, mainly containing silicon, calcium, clay and iron oxide.

4. Dolomite is a sedimentary carbonate rock. Mainly composed of dolomite.

Composition, often mixed with quartz, feldspar, calcite.

and clay minerals. It is grayish-white, brittle, hard, and easy to scratch with iron. In case of dilute hydrochloric acid, it bubbles slowly or does not bubble, and its appearance is very similar to limestone.

5. Closed shale is a rock formed by dehydration and cementation of clay. It is dominated by clay minerals (kaolinite, hydromica, etc.), and has an obvious thin-bedded structure. According to different compositions, it is divided into carbonaceous shale, calcareous shale, sandy shale, siliceous shale, etc.

The formation process of sedimentary rocks: formed by weathered detritals and dissolved materials through transport, sedimentation and diagenesis.

The rock has undergone a very complex weathering process, and the result of the weathering of the surface rock of the earth's crust has become the main sedimentary rock. Weathering refers to the whole process of physical and chemical changes in the contact between hard rocks and minerals on or near the surface of the earth and the atmosphere, water and organisms, resulting in the formation of loose deposits in situ.

Characteristics of sedimentary rocks

Sedimentary rocks have two significant characteristics, one is with bedding structure, the so-called bedding structure refers to the long formation process of sedimentary rocks, due to the influence of various factors, usually there are layers between sediments, that is, a layer of empty layers is very distinct, the interface between layers is called a layer, generally speaking, the rock layer located below is older than the rock layer above, and the bedding structure is an important basis for judging sedimentary rock.

The second is that sedimentary rocks often contain fossils, because sedimentary rocks are formed by the sediment and other materials carried by external forces, so it is very likely that a large number of biological remains are carried in these materials, and finally enter the sedimentary rock layer to form fossils.

Sedimentary rocks are formed by weathered detrital and dissolved materials through transport, sedimentation and diagenesis. The formation process is constrained by the geographical environment and the tectonic pattern of the Yinqing land, the most obvious is the paleogeographic influence of land and sea, outside and within the basin. Sedimentary rocks are formed by weathered detrital and dissolved materials through transport, sedimentation and diagenesis.

The formation process is affected by the geographical environment and tectonic patterns'The most obvious constraints are paleogeographic influences on land and sea, outside and within basins.