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.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |