Rock on the surface, weathered erosion become debris , and formed by transportation and sedimentation sediment ； The loose state before the sediment is compacted and hardened into rock is called sedimentary layer, or "soil". [1] Sedimentary layer can also refer to the material with inert film deposited on the periphery of quartz sand. Sedimentary layer includes Fine-grained material , dead clay and ash content It is firmly gathered on the sand to form an uneven outer layer, which reduces the flow performance of sand particles, the efficiency of energy transfer of molding sand, and the compactness of sand mold. The specific gravity of sedimentary layer is smaller than that of quartz (2.65). Therefore, it can be seen from the change of sand test whether the accumulation of sedimentary layer in molding sand has exceeded the specified limit. Sedimentary layer not only clings to sand particles, but also appears on coke particles of pulverized coal decomposition products. The deposition layer increases the water requirement of molding sand, reduces the sintering point and causes sand sticking on the casting. [2] In recent decades, Marine geology In addition to the bottom shape, the main object of study is the upper sediment. According to the data of the "Challenger" survey (1872), PeHap and other scientists studied the sedimentary (mainly Abyssal sediment ）The first classification is given. stay Abyssal sediment They divided red clay and biological sedimentary ooze—— Radiolarian ooze 、 Diatom ooze 、 Echinococcus ooze and Pteropod ooze , on Terrigenous deposit Green mud, red mud, green mud and sand are divided; Rock, pebble, gravel, sand and soft mud are divided in the nearshore terrigenous sedimentation. The terms of this classification have been used up to now. In modern literature, seafloor sedimentation is divided into two basic categories: Bathyal deposit and Abyssal sediment 。 Semi deep sea deposits are distributed at the edge of the ocean, which are mainly terrigenous clayey deposits, accompanied by pyroclastic mixtures in some areas. Deep sea sedimentation - oceanic sedimentation includes other types of sedimentation. The main difference between the two types of sediments is the accumulation rate of terrestrial materials suspended in water. Semi deep sea deposits accumulate quite quickly. Organic matter is buried in the sediment, and when microorganism decomposes organic matter, it consumes oxygen and forms the reduction conditions of the environment. For example, in the cylindrical sedimentary samples of the Sea of Japan, the boundary between the upper oxide layer and the lower reducing layer is usually located at a depth of 15-20 cm. This boundary obviously exists because it is consistent with the transition from the "warm" tone (light brown, light yellow, etc.) of the oxide layer to the "cold" tone (gray, light blue, light green) of the reduction layer, which is related to the form of iron. Deep sea sediments are acidic. Since the 19th century, according to this feature, we have traditionally divided the deep-sea and semi deep-sea sediments. For example, PeHap and other scientific circles separated the "blue ooze" around the ocean and the "red clay" of the ocean basin in 1891. [3] Sedimentary layer comes from large and small rivers soil and Bedrock Substance. During the glacial melting period, this bedrock material is carried into the sea or blown into the sea by the wind. Other sources of sedimentary layers are volcanic ash and lava, shells and biological skeletons, chemical deposits formed in seawater and cosmic dust. The thickness of the sedimentary layer covering the ocean is between 0 and 4000 meters, and it may be thicker in deep water basins. The average thickness of marine deposits in the whole world is 300 meters.
Large grained quartz and calcareous deposits are usually white and light colored. Iron or manganese bearing oozes usually have darker colors - red, sky blue, and green. In the bay with weak water exchange or seaside Black mud is often found. [4] The most important characteristics of the world ocean as a whole or its major regions' sedimentary layers have only been discussed in a few books. л. З. Liewen and B E. Hayne was the first to try to establish the thickness distribution and stratigraphic volume diagram of the world oceanic sedimentary volcanic rock series. It can be seen from the schematic diagram that the characteristics of the sedimentary layer are: thickness and Occurrence The distribution of is extremely complex, and the stratigraphic range and formation composition are variable the paleozoic era Post deposition is dominant. Only at the bottom of the Pacific Ocean sediment Only a thin cover is used to cover the oceanic crust "basalt". In the rest of the world's oceans, sediment filling was formed in different genetic types at different stages of evolution of the United Ancient Land crust sedimentary basin 。 These basins belong to five basic structural types: geosyncline depression, secondary geosyncline intermountain depression, orogenic intermountain depression, cratonic marginal depression and oceanic marginal depression. The geosyncline depressions, orogenic depressions, cratonic marginal depressions and many secondary geosyncline depressions are related to the marginal seas and inland seas of the Pacific and Mediterranean active belts. Around the Pacific Ocean (island arc) the indian ocean 、 Atlantic and arctic ocean as well as Antarctica They are either oceanic marginal depressions that belong to coastal geosynclines or transitional subtypes between typical oceanic marginal depressions and cratonic marginal depressions. The latter is found on the edge of the Arctic Ocean and Antarctica. In accordance with the overall process of crustal evolution, the thickness and volume of sedimentary layers in different regions of the world oceans are also different. [5]
Sedimentary layer can be mainly divided into the following types according to its formation reason, location, composition, etc.:
① Sedimentary layer of lake
Lakes have Freshwater lake and salt water lake Points. The sediments in the lakeshore area of the freshwater lake are mainly gravel, sandy soil or light loam; In the center of the lake, clay and silt are the main types; The general geological conditions of the lake shore are good, but for environmental protection, it is not suitable to build plants in the lake. The sediment of Chengshui Lake is mainly gypsum, rock salt and carbonate. The rock stratum is complex, with silt layer in the sediment, and the foundation condition is poor. ② Swamp deposit
The swamp sedimentary layer is mainly formed by the accumulation of decayed plants, some of which have obvious Plant fibre Generally, it is composed of silt and mucky soil as well as some clay and fine sand, with irregular bedding peat The content of organic matter is more than 60%, the moisture content of peat is more than 100%, and the compressibility is very high. It should be avoided when concentrating plants. If it is unavoidable, drainage measures shall be strengthened, or the peat layer shall be excavated, or piles shall be driven to the hard base. In short, we should find out the situation and take measures. ③ Marine sedimentary layer
The ocean is generally divided into four zones: Coastal zone , the water depth is 0 to 20 meters, which is the zone between high and low tide of seawater; continental shelf That is, shallow sea belt, with water depth of 20 to 200 meters; Sub deep sea belt on the continental slope, with water depth of 200 to 3000 meters; Deep sea belt, with water depth of 3000 to 6000 meters. Many countries have used coastal zone to build factories long ago, so here we mainly introduce the sedimentary layer of coastal zone. The sediments in the coastal zone are mainly composed of coarse debris and sand. The coarse debris is not thick and has cross bedding. The material is pure, uniform and compact. However, silt deposits are often found in the estuary of rivers. The sediment in the coastal zone varies greatly in vertical and horizontal directions, so it is required to arrange more probe points during exploration. Special attention should also be paid to the stability of the coast. When the sea waves hit the coast, the rocks should be hard and the rock stratum gradient should be gentle, preferably horizontal. If the rock stratum gradient is large or vertical, landslides and collapses are likely to occur. In order to protect the coast from waves, it can be used as a breakwater, breakwater and seawall. [6]
