The product of mechanical and chemical weathering processes are the source material for the formation of sedimentary rocks. The word indicates the nature of the sedimentary sedimentary rocks derived from the Latin meaning sedimentum sediment, which is used for solid material precipitated from the fluid. Material weathering process results will steadily eroded from the parent rock, then experience transporting and deposited in lakes, river valleys, seas or any other basin. The particles on the sand dunes in the desert, mud at the bottom of the swamp, gravel in the river, is a product of the process that was held constantly. Because the process of rock weathering, transport and deposition of material weathering process continues beralangsung results, then the sediment material can be found everywhere. Once the material is deposited close to the base will experience compacting. Eventually, these deposits will tersemenkan by minerals crystallized in the pores between the grains to form sedimentary rocks.
A. Types of Sedimentary Rocks
Material accumulates as sediment has two main sources. First, the material accumulated sediments derived from the results of mechanical and chemical weathering processes that tertransportasi in the solid state. Deposition of this type are called detrital and sedimentary rocks that formed called detrital sedimentary rocks (detrital sedimentary rocks).
The second major source is a material which dissolves the result of chemical weathering processes, if the solution is experienced both by the process of precipitation of inorganic and organic material are called sedimentary rocks formed and chemical sedimentary rocks called chemical (chemical sedimentary rocks).
The second major source is a material which dissolves the result of chemical weathering processes, if the solution is experienced both by the process of precipitation of inorganic and organic material are called sedimentary rocks formed and chemical sedimentary rocks called chemical (chemical sedimentary rocks).
B. Sedimentary rocks Detrital
Detrital rocks called sedimentary rocks are also fragmentary or clastic sedimentary rocks. Although these rocks have a variety of minerals or fragments of a very large, the main composition of these rocks are quartz and clay minerals. As previously described, clay minerals are the main products of chemical weathering of silicate minerals. Clay is fine grained mineral with a crystalline structure like mica sheets. Other minerals in sedimentary rocks are quartz, because this mineral is resistant to chemical weathering processes. So at the time of igneous rock that contains quartz granite serti experienced chemical weathering, the quartz mineral grains will be released free.
Another common mineral in sedimentary rocks is feldspar and mica, both minerals are not resistant to chemical weathering. If these minerals found in sedimentary rocks may indicate that these rocks are the result of mechanical weathering processes rather than chemical weathering.
Another common mineral in sedimentary rocks is feldspar and mica, both minerals are not resistant to chemical weathering. If these minerals found in sedimentary rocks may indicate that these rocks are the result of mechanical weathering processes rather than chemical weathering.
Grain size is the main basis for distinguishing detrital sedimentary rocks. The table below illustrates the classification of detrital sediment grain size. The term clay is in the classification for grain size, not to name the mineral. Although most of the clay-sized clay minerals, but not all sized clay is clay minerals.
Table. Classification of detrital sediment grain size
Tabel. Klasifikasi ukuran butir batuan sedimen detrital
| Grain Size (Mm) | Name Of Item | Common Name Sediments | Name Sedimentary Rocks |
| > 250 64 – 256 4 – 64 2 – 4 | Border Kobel Pebel Gravel | Gravel | Conglomerate Or Breccia |
| 1/16 – 2 | Sand | Sand | Sandstones |
| 1/256 – 1/16 < 1/256 | Silt Clay | Mud | Siltstone Mudstone |
Sediment grain size can also be connected with the energy of the media transport. Water flow or wind speed will select the grain size of particles being transported. If the energy decreases, the smaller the material transported. Like for example on the river, upstream of the energy deposited coarse-sized materials, is increasingly in the downstream direction, the sand-sized material deposited. Clay-sized material and silt will be deposited with very low energy, so the accumulation of material is usually found in lakes, swamps or on a calm sea.
Shale. Sedimentary rocks are composed by silt-sized material and clay is called shale. Fine-grained sedimentary rocks that make up 70% sedimentary rocks of the earth's crust. Because of the small, rocky material can not be identified without the aid of a magnifying tool. Shale generally not experienced cementation well and easily broken, but having a small porosity. Although it is the dominant sedimentary rocks, sedimentary rocks but is the least well known. Shale outcrops rarely gives such good sandstone or other sedimentary rocks as shale susceptible to weathering and form a cover layer of rock that is still fresh. The term shale is usually used for all fine-grained sedimentary rocks, but many geologists use more limited. The term is often used for fine-grained sedimentary rocks that indicate the nature easily separated into thin layers. When the rock and form a compact block of rock called mudstone.
Sandstones. Is sand-sized sediment and is most often found after the shale. Rocks make up 20% of the sedimentary rocks in the earth's crust. Quartz is a common mineral in sandstones. When this mineral is dominant, then it is called quartz sandstone. Was when the mineral feldspar dominant, called arkose. The dominance of the mineral feldspar in the sandstones indicate that these rocks are less experienced chemical weathering. Sedimentary rocks are composed by quartz and feldspar mineral called graywacke. Dark color of the rocks is caused by the content of many of the fragments are angular and clay. Because these rocks have poor sorting, it is often called a dirty sandstone.
Conglomerate. These rocks composed by particles sized coarse (gravel). Large particles is generally a rock fragments. Among the coarse fragments are finer-sized material, called the base (matrix), which consists of mud and sand. These rocks often have a good cementation, thus forming a very compact rock. If the material is rough shaped angled (angular), then the rock is called breccia.
C. Chemical Sedimentary Rocks
Unlike the detrital sedimentary rocks are composed by the weathering of solid materials, the chemical sediments formed from materials transported by dissolution. Solution containing the material results of these chemical weathering processes in the event that precipitation will form chemical sedimentary rocks. This precipitation process can take place by inorganic processes or by organic life in the water. When the precipitation process performed by the organism, then the rock is called sedimentary rocks biochemistry.
Examples of chemical sedimentary rocks are formed by inorganic processes batugaram by the evaporation of salty water. In contrast plants and animals absorb the material dissolved in water to form a framework or her home. Once the organism dies, its shell will order or accumulated on the sea floor or lake where these organisms live.
Limestone (Limestone). Prepare 10% of the total volume of sedimentary rock, limestone is a chemical sedimentary rocks the most. These rocks composed mainly by the mineral calcite (CaCO3), and can be formed either by inorganic or biochemical processes. Limestones formed by biochemical processes are more common. Approximately 90% of limestones in the world is the result of accumulated sediment biochemistry. Although most limestones formed by biochemical processes, the process is not entirely the case, because the framework or shells of animals might be changed before experiencing pembatuan. A very simple example of limestones known biochemistry is Coquina, coarse-grained rock composed of fragments of shell or case of the animals and not tersemen well. Another example is the chalk, is a rock composed almost entirely by a shell of foraminifera, a single-celled animals are very delicate. Organic limestones formed by evaporation with rising temperatures increased the concentration of calcium carbonate resulting in precipitation. Travertin is a limestone that is often found in the cave, as well as limestones oolitik. Travertin formed at the time of groundwater containing calcium carbonate having evaporation. Oolitik Limestone is a rock composed by round-shaped granules kecli called oolit. Oolit formed in shallow marine environment by a very fine grain and carried away by currents and calcium carbonate is coated by a layer by layer when rolling on the sea floor.
Limestone (Limestone). Prepare 10% of the total volume of sedimentary rock, limestone is a chemical sedimentary rocks the most. These rocks composed mainly by the mineral calcite (CaCO3), and can be formed either by inorganic or biochemical processes. Limestones formed by biochemical processes are more common. Approximately 90% of limestones in the world is the result of accumulated sediment biochemistry. Although most limestones formed by biochemical processes, the process is not entirely the case, because the framework or shells of animals might be changed before experiencing pembatuan. A very simple example of limestones known biochemistry is Coquina, coarse-grained rock composed of fragments of shell or case of the animals and not tersemen well. Another example is the chalk, is a rock composed almost entirely by a shell of foraminifera, a single-celled animals are very delicate. Organic limestones formed by evaporation with rising temperatures increased the concentration of calcium carbonate resulting in precipitation. Travertin is a limestone that is often found in the cave, as well as limestones oolitik. Travertin formed at the time of groundwater containing calcium carbonate having evaporation. Oolitik Limestone is a rock composed by round-shaped granules kecli called oolit. Oolit formed in shallow marine environment by a very fine grain and carried away by currents and calcium carbonate is coated by a layer by layer when rolling on the sea floor.
Dolomite. Rock is very similar to the limestones and prepared by the mineral "calcium-magnesium carbonate" which is also called the mineral dolomite. To distinguish the names of minerals and rocks, some geologists refer to the name of rock dolostone are composed by the mineral dolomite. Mekipun dolomite can be formed from direct precipitation of curved, but can dolomite also formed from the substitution of magnesium contained in sea water to the calcium found in limestone. This is evident from more dolomite found in rocks older than the age-old youth, because it takes time by substituting magnesium for calcium.
Chert (chert). This name is used for hard and compact rocks are composed by microcrystalline silica (SiO2). Well-known example is the flint composed by dark-colored organic material. Jasper to variations in the red, because the content of iron oxide. The precipitate chert is generally found in one of two conditions, irregular-shaped nodules in limestone and layers of rock. Most nodules berkomposisi silica silica is precipitated directly from water. So the nodule is the result of inorganic processes. Instead chert layers is the result of direct precipitation from seawater, because the content of silica in sea water is not great. So chert layers are thought to originate from the results of biochemical processes. Some marine organisms such as radiolarians diatomae and use silica to form the frame and the house. These microorganisms can bind to silica in silica-saturated solution, the incidence is expected to form layers of chert.
Stone rock salt and gypsum. Often the process of evaporation is the mechanism of formation of chemical sedimentary rocks. Common minerals, through this process is halite (sodium chloride) that make up batugaram, and gypsum (hydro clcium sulfide) that make up gypsum.
Coal (coal). Coal is classified into biochemical sedimentary rock, but slightly different biochemical sedimentary rocks. These rocks mainly composed by organic material by the remains of plants that have experienced changes but the original structure is still visible. This shows the incidence of this coal is a long accumulation of a large accumulation of plants. Environmental conditions that allow the occurrence of this process is poor swamps oxygen content. This type of coal has several levels, the higher the temperature and pressure the smaller fouling and volatilnya content such as diagrams:
PEAT
LIGNITEANTHRACITEBITUMINOUS
LIGNITEANTHRACITEBITUMINOUSBituminous coal is the most important types of coal. Anthracite is formed from bituminous who experienced metamorphism. Although anthracite has the highest levels, but this type of distribution is not extensive and more expensive mining.
D. Being a rock Sediment Sediment Change
The process of change becomes loose sediments of sedimentary rocks called litifikasi. One process is the compaction or compaction litifikasi. At the time of sedimentary material deposited continuously in a basin, heavy sediment on top would burden the underlying sediment. As a result, sediment grain will be more meetings, and the voids between the grains will be smaller. For example, clays are buried under other sedimentary material tablanya several thousand meters, the volume of clay will experience a depreciation of 40%. Because sand and other coarse grained sediments can suffer compaction, the compaction process is a significant process for the smooth yangberbutir litifikasi sedimentary rocks such as shale.
Other processes that alter the loose sediment into sedimentary rocks is cementation. The material to be transported as cement solution by water percolating through the voids between the grains and then the solution will experience precipitation in the cavities between the grains, and will bind the grains of sediment. A common material into cement is calcite, silica and iron oxide. To find out the kinds of cement in sedimentary rocks is relatively simple. Calcite can be known with a solution of HCl. Silica cement is very hard and will produce a very hard sedimentary rock. If sedimentary rocks orange or dark red, then the sedimentary rocks are tersemenkan by iron oxide. Sometimes the cement in sedimentary rocks can provide economic value these rocks. As an example of sandstone which tersemenkan by BESA oxide can make the sandstones into iron ore (iron ore).
Although sedimentary rocks terlitifikasi by compacting process, cementation, or a combination of both, some sedimentary rocks of crystal growth terlitifikasi by mutually binding. This process often occurs in chemical sedimentary rocks.
Other processes that alter the loose sediment into sedimentary rocks is cementation. The material to be transported as cement solution by water percolating through the voids between the grains and then the solution will experience precipitation in the cavities between the grains, and will bind the grains of sediment. A common material into cement is calcite, silica and iron oxide. To find out the kinds of cement in sedimentary rocks is relatively simple. Calcite can be known with a solution of HCl. Silica cement is very hard and will produce a very hard sedimentary rock. If sedimentary rocks orange or dark red, then the sedimentary rocks are tersemenkan by iron oxide. Sometimes the cement in sedimentary rocks can provide economic value these rocks. As an example of sandstone which tersemenkan by BESA oxide can make the sandstones into iron ore (iron ore).
Although sedimentary rocks terlitifikasi by compacting process, cementation, or a combination of both, some sedimentary rocks of crystal growth terlitifikasi by mutually binding. This process often occurs in chemical sedimentary rocks.
E. Classification of Sedimentary Rocks
Sedimentary rocks can basically be divided into two detrital and chemical sediments. Detrital sedimentary rocks then grouped again based on grain size, whereas chemical sedimentary rocks based on mineral composition.
In fact, many sedimentary rocks belonging to the chemical sedimentary rocks also contain material sediments, detrital material. For example, limestones sometimes contain sand or clay material, thus providing Pasiran or lempunga properties. Instead detriral sedimentary rocks mostly experienced cementation by minerals formed role in the water, it is actually difficult to say that is really pure detrital material is composed of.
As in igneous rocks, the texture is most important in klasifilkasi sedimentary rocks. There are two kinds of textures that are used in the classification of clastic sedimentary rocks and nonklastik. The word clastic comes from the Greek word for destruction. So clastic sedimentary rocks are sedimentary rocks composed by material destruction. As seen on the classification of sedimentary rocks, all textured detrital clastic sedimentary rocks. Coquina is a limestone composed by shells and shell fragments are klastika such as sandstones and conglomerates.
In fact, many sedimentary rocks belonging to the chemical sedimentary rocks also contain material sediments, detrital material. For example, limestones sometimes contain sand or clay material, thus providing Pasiran or lempunga properties. Instead detriral sedimentary rocks mostly experienced cementation by minerals formed role in the water, it is actually difficult to say that is really pure detrital material is composed of.
As in igneous rocks, the texture is most important in klasifilkasi sedimentary rocks. There are two kinds of textures that are used in the classification of clastic sedimentary rocks and nonklastik. The word clastic comes from the Greek word for destruction. So clastic sedimentary rocks are sedimentary rocks composed by material destruction. As seen on the classification of sedimentary rocks, all textured detrital clastic sedimentary rocks. Coquina is a limestone composed by shells and shell fragments are klastika such as sandstones and conglomerates.
Chemical sedimentary rocks mostly textured nonklastik, where each constituent minerals grow together (interloding). Therefore nonklastik appearance sedimentary rocks similar to igneous rocks. But both can be distinguished easily, since minerals that make up sedimentary rocks nonklatik different minerals that make up igneous rock.
F. Sedimentary rocks appearance
As described previously, sedimentary rocks is very important to tell the history of this earth. Rocks that formed on the surface of the earth's accumulated layer after layer. Each layer will be noted on the environmental conditions at the sediment deposited. This layer is commonly called bedding (strata, beds) is the appearance characteristic of sedimentary rocks.
Bedding thickness of sedimentary rocks varies very thin to several tens of meters. Bedding of sedimentary rocks are separated by areas of bedding (bedding planes), which is a surface barrier. Field of bedding can be formed by a change in grain size or mineral composition. In general, bedding field indicates the end of a deposition and the beginning of the next deposition.
Many of the appearance of sedimentary rocks that can diduksi by geologists. For example, conglomerates show such high energy conditions on the flow is strong, where the grain size of coarse fragments that can be deposited. Arkose sandstones indicates a dry climate, where the mineral feldspar weathering process is relatively small. "Carbonaceous shale" shows the condition of weak energy environment and rich in organic materials such as swamps and lagoons. Another appearance in sedimentary rocks can also indicate past environmental conditions. Perlapisan gelembur wave (ripple marks) is a form of surface currents generated by river or stream flowing pasangsurut above the sandy bottom or by gusts of wind over the dunes. Ripple marks may also indicate the current direction or the wind in the past.
Mudcrack (fracturing wrinkle) showed that environmental conditions in which the sedimentary rocks formed in conditions of changing between wet and dry. These conditions often occur in shallow lake environments, pasangsurut plains and basins in the desert.
Sometimes the bedding of sedimentary rocks angled towards the horizontal plane. So-called cross-bedding and bedding are characteristic for sediments of the river delta and sand dunes.
Fossils, the rest of life in the past, is an essential element that is often found in sedimentary rocks. Important fossils are used to determine the geological conditions in the past, especially to determine the paleoenvironment. Besides fossils can be used to correlate rocks of the same age that were found in different places.
Tidak ada komentar:
Posting Komentar