Unroofing of buried sandstone is accompanied by telogenesis, the third and final stage of diagenesis. Chemical compaction continues to depths of 2,000 meters (6,600 ft), and most cementation takes place at depths of 2,000–5,000 meters (6,600–16,400 ft). Mechanical compaction takes place primarily at depths less than 1,000 meters (3,300 ft). Pressure solution contributes to cementing, as the mineral dissolved from strained contact points is redeposited in the unstrained pore spaces. Lithification follows closely on compaction, as increased temperatures at depth hasten deposition of cement that binds the grains together. As a result, the contact points are dissolved away, allowing the grains to come into closer contact. Points of contact between grains are under the greatest strain, and the strained mineral is more soluble than the rest of the grain. In addition to this physical compaction, chemical compaction may take place via pressure solution.

Sediment grains move into more compact arrangements, ductile grains (such as mica grains) are deformed, and pore space is reduced. Ĭompaction takes place as the sand comes under increasing pressure from overlying sediments. Deeper burial is accompanied by mesogenesis, during which most of the compaction and lithification takes place. The red hematite that gives red bed sandstones their color is likely formed during eogenesis. Early stages of diagenesis, described as eogenesis, take place at shallow depths (a few tens of meters) and are characterized by bioturbation and mineralogical changes in the sands, with only slight compaction. This mostly consists of compaction and lithification of the sand. Īs sediments continue to accumulate in the depositional environment, older sand is buried by younger sediments, and it undergoes diagenesis. Intracontinental basins and grabens along continental margins are also common environments for deposition of sand. Forearc basins tend to accumulate sand rich in lithic grains and plagioclase.

Įroded sand is transported by rivers or by the wind from its source areas to depositional environments where tectonics has created accommodation space for sediments to accumulate. Weathering and erosion are most rapid in areas of high relief, such as volcanic arcs, areas of continental rifting, and orogenic belts. The silicate sand grains from which they form are the product of physical and chemical weathering of bedrock. Sandstones are clastic in origin (as opposed to either organic, like chalk and coal, or chemical, like gypsum and jasper). Quartz-bearing sandstone can be changed into quartzite through metamorphism, usually related to tectonic compression within orogenic belts. Rock formations that are primarily composed of sandstone usually allow the percolation of water and other fluids and are porous enough to store large quantities, making them valuable aquifers and petroleum reservoirs. Since sandstone beds often form highly visible cliffs and other topographic features, certain colors of sandstone have been strongly identified with certain regions. Like uncemented sand, sandstone may be any color due to impurities within the minerals, but the most common colors are tan, brown, yellow, red, grey, pink, white, and black. Most sandstone is composed of quartz or feldspar (both silicates) because they are the most resistant minerals to weathering processes at the Earth's surface. Sandstones comprise about 20–25% of all sedimentary rocks. Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Other minerals may be found in particularly mature sandstone. Typically quartz and feldspar lithic fragments are also common.

Oolite aragonite sand