What is consolidation diagenesis? How to distinguish metamorphism from consolidation diagenesis?

It's ablation. Erosion is a general term for weathering and denudation. Weathering: It is the effect of decomposing and loosening rocks. Denudation: It is the action of stripping weathering products or rock components away from the rock surface. The relationship between the two is mutually reinforcing. Weathering makes denudation.

Consolidation diagenesis is a kind of external force action in geological action, which refers to the process of forming sediments after weathering, erosion, transportation and sedimentation, and gradually consolidating into hard and dense sedimentary rocks under certain physical, chemical and biochemical processes under certain temperature and pressure conditions, which is the last stage in the formation of sedimentary rocks.

The process of consolidation can be divided into the following functions:

1. Compaction.

Due to the gradual thickening of the overlying sediment, the pressure also increases, and the density of the material increases, therefore, the attached water in the sediment is gradually discharged, the pores of the particles are reduced, the volume is reduced, and the connection between the particles is enhanced, which in turn makes the sediment consolidate and harden.

2. Dehydration.

As the pressure increases, the temperature also increases, and under the action of temperature and pressure, not only the attached water between the sediment particles is discharged, but also many hydrocolloids and water-containing minerals will lose water and become new minerals.

3. Cementation.

Minerals filled in the pores of the sediment stick the scattered particles together. Cementation is the main mode of diagenesis of clastic sediments, such as conglomerate and sandstone formed after conglomerate and sand cementation.

4. Recrystallization.

Sediments are affected by temperature and pressure and can dissolve or partially dissolve, resulting in a rearrangement of the material particles, turning the amorphous material into a crystalline substance and the fine-grained crystalline material into a coarse-grained crystalline substance.

Diagenesis refers to various physical processes (such as compaction), chemical (such as cementation and dissolution) and biological processes (such as bacterial sulfate reduction) that occur in the long geohistory stage of sediments from post-deposition to before metamorphism. Among these three effects, the main ones are physical and chemical, so diagenesis can be divided into chemical diagenesis and physical diagenesis.

Chemical diagenesis can be understood as a chemical reaction under stratigraphic conditions, which is a process of water-rock interaction, namely:

Methods of working on sedimentary rocks.

Formation conditions such as temperature, pressure, fluid properties, openness and closure of the system, burial history, and the degree of fracture development control of the fluid.

Physical diagenesis can be simplified into a process of change in the contact relationship between particles under stratigraphic conditions, namely:

Methods of working on sedimentary rocks.

Stratigraphic conditions such as the magnitude, nature and genesis of overlying load, confining pressure, pore pressure, temperature, tectonic factors, burial and settlement history, etc.

However, it should be noted that the above two processes are not isolated from each other, but are related and constrained by each other, for example, some cementation (especially early cementation) can inhibit compaction and preserve the intergranular pore volume.

According to the influence on the reservoir space, diagenesis can be divided into: enhanced diagenesis, which increases porosity, such as dissolution; destructive diagenesis, which reduces porosity, typically such as compaction; Retention diagenesis allows the preservation of existing pores (mainly primary pores), such as early dispersed cementation.

Answer: Both metamorphism and consolidation diagenesis are related to temperature and pressure (the sediment is buried, the overlying sediment is pressurized, and the temperature is underground), which is their similarity. Resemblance is not the same and can be distinguished.

Temperature, pressure The temperature of metamorphism is high (generally greater than 150), and the pressure is high; The temperature of consolidation diagenesis is low (less than 150) and the pressure is small.

Depth Metamorphism mainly occurs at a certain depth below the surface (below the weathering zone and cementation zone, the appearance of minerals such as turbidite, pyrophyllite, anjusite, and bluebobole is a sign); Whereas, the consolidation of diagenesis (compaction, dehydration, cementation, etc.) that is subordinate to sedimentation occurs mainly in the surface layer of the solid earth (weathering zone, cementation zone).

Factors The temperature, pressure and other factors that cause metamorphism mainly come from the earth's interior; The atmosphere, water, and organisms that cause sedimentation (including consolidation and diagenesis) come from the outside of the earth. (This article is said in passing, and it does not affect the overall situation if it is not said.) ）

Hu Shaoxiang. General Geology[M].Xuzhou:China University of Mining and Technology Press,2014:78

Internal forces are changed by the energy in the Earth's interior. Crustal movement.

Magmatic activity, metamorphism, and ** are all internal forces. The action of external forces includes weathering.

Erosion, transport, sedimentation, and consolidation are not internal processes of the Earth.

Major diagenetic phenomena.

Sedimentary rock. The main diagenesis processes include compaction, cementation (precipitation), dissolution, alteration, metasomatism and recrystallization.

1.Compaction.

Compaction refers to the action of water discharge, porosity reduction and density increase of sediment under the action of heavy load pressure of overlying sediment. According to the mechanism of compaction, compaction can be divided into two types: mechanical compaction and chemical compaction.

Mechanical compaction: It is mainly manifested in the rearrangement, plastic deformation and rupture of particles. Mechanical compaction changes the orientation of certain flaked, needle-like, and columnar particles in the sediment so that they are arranged perpendicular to the pressure direction.

For example, the shale structure of shale and the ease of cracking along the shale direction are caused by the parallel arrangement of sheet minerals due to the action of pressure.

Chemical compaction: also known as pressure dissolution. Compression refers to the selective dissolution of minerals at pressure points.

Compression can occur either in uncemented sediments or in cemented sedimentary rocks. In uncemented sediments, the sediments can slide through the surface of the particles, and when the particles are rearranged and some particles are broken to achieve a tight pack, point contact is reached between the particles. In this case, the overlying pressure is transmitted through the contact point of the particles.

As the overlying pressure increases, lattice dislocation and dissolution occur. With the strengthening of dissolution, the particles develop from point contact to linear contact, suture contact and concave and convex contact. This type of dissolution occurs mainly in quartz sandstones.

Middle. The pressure dissolution that occurs in the cemented sedimentary rocks mainly forms suture lines and pressure dissolution lines. Both the suture and the pressure line develop perpendicular to the axis of maximum stress.

This stress can be either an overlying pressure or a tectonic pressure. Sutures and pressure lines tend to occur in clay-rich carbonate rocks.

The structural contents of the rock are as follows:

Rocks of different origins have different structures and structures, and magmatic rocks often have structures formed by crystallization, such as: isogranular structure, porphyry structure, amorphous structure, etc.; It often has block-shaped, stomatal-shaped, almond-shaped and other structures.

Sedimentary rocks often have clastic structure, biological characteristic structure, and bedding structure formed by sedimentation due to weathering and sedimentation processes. Due to the metasomatism of temperature, pressure and components, the metamorphic rock Kaichong exhibits a metamorphic crystalline structure and a directional arrangement of lamellar and gneiss-like structures.

Rock is the product of a certain geological process, which is formed and stabilized in a certain geological environment. When the geological environment changes, the rocks will also change, the original rocks are destroyed and disappear, and the rocks adapted to the new environment are created. Various information on the processes of development and evolution of the earth's crust is more or less preserved in rocks, and it can be said that the main object of geological work research is rocks.

An ore is an ore if it contains an element, compound or mineral that is economically valuable and technically available. Those minerals in the ore that can be used are called ore minerals.

Key points of this chapter: 1.The mass fraction of various elements in the earth's crust is known as the Clark value.

The distribution of various chemical elements in the earth's crust is extremely uneven: O, Si, Al, Fe, Ca, Na, K, Mg, Ti, and H account for 99% of the total crust, while the sum of other elements is less than 1% of the total.

2.Minerals are elemental elements or compounds that focus on the natural production of elements, which have certain chemical composition and physical properties, and are the basic units of rock or ore. There are three main forms of minerals: needle-column, sheet (plate) and granular.

3.The optical properties of minerals include color, streaks, transparency and luster. The mechanical properties of minerals include cleavage, hardness, and density, among others. Absolute hardness is graded into 10:

1.Talc, 2Plaster, 3

Calcite, 4Fluorite, 5Apatite, 6

Feldspar, 7Quartz, 8Topaz, 9

Corundum, 10Diamond; Some minerals also have magnetic, piezoelectric and other characteristics, such as magnetite is magnetic, and some quartz is piezoelectric.

4.Rock is a naturally occurring solid aggregate composed of one or more minerals and other components, with a certain structural structure and stable shape. According to their genesis, rocks are divided into three categories: magmatic rocks, sedimentary rocks and metamorphic rocks.