Today's broadly defined concept of swamps is wetlands. Wetlands are transitional zones between land and water. According to the International Convention on Wetlands, "wetlands refer to natural or artificial marshlands, wet sources, peatlands, or areas of water (water depth< 2 m) with either static or flowing or fresh or brackish water, including waters not exceeding 6 m at low tide." Wetlands, together with oceans and forests, are the three major ecosystems of the earth, and are indispensable environments for the survival of human beings and organisms, which play an important and indispensable role in protecting biodiversity, maintaining ecological balance, reducing natural disasters (such as floods, sandstorms, etc.), controlling water quality, purifying the air, etc., so they are called "the kidneys of the earth". The world's wetlands cover an area of about 570×10 4 km 2, accounting for more than 1.1% of the total area of the earth and more than 3.8% of the land surface area. The area of the continental wetland is about 65.90×104km2, about 13% of the world's.
Geology, the concept of a swamp (in a narrow sense) refers to a place where the surface of the earth is unusually wet, where a large number of hygrophilic plants grow, and where there is a large accumulation of peat. The concept of a swamp emphasizes the presence of peat accumulation. Peat is the main source of coal. Therefore, the geological processes of the swamps in this section are mainly related to the formation process of coal.
1. Classification of swamps
(1) Classification of causes
1. Lake swamps
When the rate of detrital sedimentation of lakes exceeds the rate of decline of crustal movement, the lake will gradually silt up from the shore to the center of the lake, and swamps can be formed in the process of lake disappearance. When the groundwater level is high, it can also form around the lake.
2. Coastal marshes
It is mainly located in the supratidal zone, and is formed by the intrusion of seawater in the supratidal zone during storm surge. It can also be distributed in the intertidal or subtidal zone.
(2) Classification according to the source of water
1. Low-level swamps
The diving surface is close to the surface, and the swamp water is recharged by groundwater.
2. High marsh
It is fed by atmospheric precipitation, surface river water, and seawater, and the diving surface is lower than the surface of the swamp.
(3) According to the classification of plants
1. Moss swamps
It is found in colder boreal forest areas and grows floating plant clumps dominated by water moss.
2. Herbaceous swamps
It is mainly developed in humid climate zones, and herbaceous plants such as reeds, cattails, and grasses grow in swamps.
3. Woody swamps
It develops under humid and warm climate conditions, and grows woody plants such as pine, cedar, and cypress. One of the more special ones is the mangrove swamps that grow on tropical coasts (Figure 10-7).
(4) Classification according to the salinity of the water in the swamp
1. Freshwater swamps
The water sources are surface water, groundwater, atmospheric precipitation, and snowmelt water.
2. Saltwater swamps
The water comes mainly from the ocean.
The plants that grow in both are also different.
2. The geological process of the swamp
The marsh is dominated by clastic sedimentation and biosedimentation. Biodeposition is mainly the process of accumulation of remains after plant death to form coal. Coal is mainly derived from plants, especially higher woody plants. The formation process of humus coal is described below.
The formation process of coal is divided into two stages: the peat stage and the coalification stage.
(1) Peat stage
Mainly woody plants that grow in swamps after death, the remains are piled up and buried (covered with sediment or new biological remains), and humus is formed by biochemical and physicochemical processes with the participation of microorganisms in the reducing environment. Peat is formed when humus is further decomposed, compounded, hydrogen and oxygen content decreases, and carbon content increases. Peat is yellowish-brown or black-brown in color, and the carbon content is up to 59%. Also contains H2O and minerals. Russia has the largest peat reserves in the world, accounting for about 3/4 of the world's total.
(2) Coal stage
Under the pressure of the overlying sediment, peat is compacted and hardened to form lignite. The carbon content of lignite is higher than that of peat, which is 67%~68%. Lignite deteriorates under a certain pressure and temperature to form bituminous coal. The carbon content of bituminous coal is 75%~97%, and humus has been completely converted into coal. Bituminous coal has a wide range of uses, and can be used as thermal coal, civil coal, chemical raw materials, coking, etc. Bituminous coal becomes anthracite after further metamorphosis. Anthracite is generally only used as domestic coal.
There are three major coal-forming periods in the global geological history, namely the Carboniferous (C) to the Permian (P), the Jurassic (J) and Cretaceous (K), and the Tertiary (E-R). The mainland has the world's second largest coal reserves (the first is the United States), the world's largest production, accounting for 1/4 of the world's total output, and the world's second largest coal consumption. According to statistics, the coal stored in Shanxi Province alone on the mainland can be used by the whole world for 2,000 years.