What are the major processes that form sedimentary rock? Weathering breaks down rock into the particles that compose siliciclastic sediments and the dissolved ions and molecules that are precipitated to form chemical and biological sediments. Erosion mobilizes the particles produced by weathering. Currents of water and air and the movement of glaciers transport the sediments to their ultimate resting place in a sedimentary basin. Deposition (also called sedimentation) is the settling out of particles or precipitation of minerals to form layers of sediments. Burial and diagenesis compress and harden the sediments into sedimentary rock.
What are the two major types of sediments and sedimentary rocks? Sediments and the sedimentary rocks that form from them can be classified as one of two types: siliciclastic sediments or chemical and biological sediments. Siliciclastic sediments form from fragmentation of parent rock by physical and chemical weathering and are transported to sedimentary basins by water, wind, or ice. Chemical and biological sediments originate from minerals dissolved in and transported by water. Through chemical and biological reactions, these minerals are precipitated from solution to form sediments.
How are the major kinds of siliciclastic sediments and chemical and biological sediments classified? Siliciclastic sediments and sedimentary rocks are classified by particle size. The three major classes, in order of descending particle size, are coarse-grained siliciclastics (gravels and conglomerates); medium-grained siliciclastics (sands and sandstones); and fine-grained siliciclastics (silts and siltstones; muds, mudstones, and shales; and clays and claystones). This classification method emphasizes the importance of the strength of the current that transported the sediments. Chemical and biological sediments and sedimentary rocks are classified on the basis of their chemical composition. The most abundant of these rocks are the carbonate rocks: limestone and dolostone. Limestone is made up largely of biologically precipitated calcite. Dolostone is formed by the diagenetic alteration of limestone. Other chemical and biological sediments include evaporites; siliceous sediments such as chert; phosphorite; iron formations; and peat and other organic matter that is transformed into coal, oil, and natural gas.
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