What are sedimentary rocks?
Sedimentary rocks are formed from pre-existing rocks or pieces of once-living organisms. They form from deposits that accumulate on the Earth's surface. Sedimentary rocks often have distinctive layering or bedding. Many of the picturesque views of the desert southwest show mesas and arches made of layered sedimentary rock. Oct 22, · Sedimentary rocks are one of three main types of rocks, along with igneous and metamorphic. They are formed on or near the Earth’s surface from the compression of ocean sediments or other processes.
An example of a sedimentary rock, which is, by definition, composed of many, smaller rocks. The most important geological processes that lead to the creation of sedimentary rocks are erosionweatheringdissolutionprecipitationand lithification.
Erosion and weathering include the effects of wind and rain, which slowly break down large rocks into smaller ones. Erosion and weathering transform boulders and even mountains into sediments, such as sand or mud. Dissolution is a form of weathering—chemical weathering. With this process, water that is slightly acidic slowly wears away stone. These three processes create the raw materials for new, sedimentary rocks. Precipitation and lithification are processes that build new rocks or minerals.
Precipitation is the formation of rocks and minerals from chemicals that precipitate from water. Finally, how to destroy cd data is the process by which clay, sand, and other sediments on the bottom of the ocean or other bodies of water are slowly compacted into rocks from the weight of overlying sediments. Sedimentary rocks can be organized into two categories. The first is detrital rockwhich comes from the erosion and accumulation of rock fragments, sedimentor other materials—categorized in total as detritus, or debris.
The other is chemical rock, produced from the dissolution and precipitation of minerals. Detritus can be either organic or inorganic. Organic detrital rocks form when parts of plants and animals decay in the ground, leaving behind biological material that is compressed and becomes rock. Coal is a sedimentary rock formed over millions of years from compressed plants. Inorganic detrital rocks, on how to password protect a word file in office 2010 other hand, are formed from broken up pieces of other rocks, not from living things.
These rocks are often called clastic sedimentary rocks. One of the best-known clastic sedimentary rocks is sandstone. Sandstone is formed from layers of sandy sediment that is compacted and lithified.
Chemical sedimentary rocks can be found in many places, from the ocean to deserts to caves. For instance, most limestone forms at the bottom of the ocean from the precipitation of calcium carbonate and the remains of marine animals with shells. If limestone is found on land, it can be assumed that the area used to be under water.
Cave formations are also sedimentary rocks, but they are produced very differently. Stalagmites and stalactites form when water passes through bedrock and picks up calcium and carbonate ions. When the chemical-rich water makes its way into a cave, the water evaporates and leaves behind calcium carbonate on the ceiling, forming a stalactiteor on the floor of the cave, creating a stalagmite.
The water drips, but the mineral remains like an icicle. The how to use an emergency eyewash station, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited. Tyson Brown, National Geographic Society.
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Any interactives on this page can only be played while you are visiting our website. You cannot download interactives. Metamorphic rocks start as one type of rock and—with pressure, heat, and time—gradually change into a new type of rock. Weathering describes the breaking down or dissolving of rocks and minerals on the surface of the Earth.
Water, ice, acids, salts, plants, animals, and changes in temperature are all agents of weathering. Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Skip to content. Image Sedimentary Rock An example of a sedimentary rock, which is, by definition, composed of many, smaller rocks. Photo courtesy of Alamy Stock Photo. Twitter Facebook Pinterest Google Classroom. Encyclopedic Entry Vocabulary. Also called rock salt.
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Sedimentary rock, rock formed at or near Earth’s surface by the accumulation and lithification of sediment or by the precipitation from solution at normal surface temperatures. Sedimentary rocks are the most common rocks exposed on Earth’s surface but are only a minor constituent of the entire crust. The use of sedimentary rock can be found in most buildings and monuments. Some uses of this type of rock are provided below. Limestone is used to make cement. Limestone and sandstone are used for building stones. Quartz is a type of sedimentary rock which is used to make glass. Rock gypsum is used to make plaster. Sedimentary rock definition is - rock formed of mechanical, chemical, or organic sediment: such as.
Sedimentary rocks are produced by the weathering of preexisting rocks and the subsequent transportation and deposition of the weathering products. These processes produce soil , unconsolidated rock detritus , and components dissolved in groundwater and runoff. Erosion is the process by which weathering products are transported away from the weathering site, either as solid material or as dissolved components, eventually to be deposited as sediment.
Any unconsolidated deposit of solid weathered material constitutes sediment. It can form as the result of deposition of grains from moving bodies of water or wind , from the melting of glacial ice , and from the downslope slumping sliding of rock and soil masses in response to gravity, as well as by precipitation of the dissolved products of weathering under the conditions of low temperature and pressure that prevail at or near the surface of Earth.
Sedimentary rocks are the lithified equivalents of sediments. They typically are produced by cementing, compacting, and otherwise solidifying preexisting unconsolidated sediments. Some varieties of sedimentary rock, however, are precipitated directly into their solid sedimentary form and exhibit no intervening existence as sediment. Organic reefs and bedded evaporites are examples of such rocks. Because the processes of physical mechanical weathering and chemical weathering are significantly different, they generate markedly distinct products and two fundamentally different kinds of sediment and sedimentary rock: 1 terrigenous clastic sedimentary rocks and 2 allochemical and orthochemical sedimentary rocks.
Clastic terrigenous sedimentary rocks consist of rock and mineral grains, or clasts, of varying size, ranging from clay-, silt-, and sand- up to pebble-, cobble-, and boulder-size materials. These clasts are transported by gravity, mudflows, running water, glaciers, and wind and eventually are deposited in various settings e. Because the agents of transportation commonly sort out discrete particles by clast size, terrigenous clastic sedimentary rocks are further subdivided on the basis of average clast diameter.
Coarse pebbles, cobbles, and boulder-size gravels lithify to form conglomerate and breccia; sand becomes sandstone; and silt and clay form siltstone , claystone , mudrock, and shale. Chemical sedimentary rocks form by chemical and organic reprecipitation of the dissolved products of chemical weathering that are removed from the weathering site. Allochemical sedimentary rocks, such as many limestones and cherts, consist of solid precipitated nondetrital fragments allochems that undergo a brief history of transport and abrasion prior to deposition as nonterrigenous clasts.
Orthochemical sedimentary rocks, on the other hand, consist of dissolved constituents that are directly precipitated as solid sedimentary rock and thus do not undergo transportation.
Orthochemical sedimentary rocks include some limestones, bedded evaporite deposits of halite , gypsum , and anhydrite , and banded iron formations. Igneous and metamorphic rocks constitute the bulk of the crust. The total volume of sediment and sedimentary rocks can be either directly measured using exposed rock sequences, drill-hole data, and seismic profiles or indirectly estimated by comparing the chemistry of major sedimentary rock types to the overall chemistry of the crust from which they are weathered.
On the other hand, the area of outcrop and exposure of sediment and sedimentary rock comprises 75 percent of the land surface and well over 90 percent of the ocean basins and continental margins. In other words, 80—90 percent of the surface area of Earth is mantled with sediment or sedimentary rocks rather than with igneous or metamorphic varieties. The sediment-sedimentary rock shell forms only a thin superficial layer.
The mean shell thickness in continental areas is 1. Rearranging this shell as a globally encircling layer and depending on the raw estimates incorporated into the model , the shell thickness would be roughly 1—3 kilometres. Despite the relatively insignificant volume of the sedimentary rock shell, not only are most rocks exposed at the terrestrial surface of the sedimentary variety, but many of the significant events in Earth history are most accurately dated and documented by analyzing and interpreting the sedimentary rock record instead of the more voluminous igneous and metamorphic rock record.
When properly understood and interpreted, sedimentary rocks provide information on ancient geography, termed paleogeography. A map of the distribution of sediments that formed in shallow oceans along alluvial fans bordering rising mountains or in deep, subsiding ocean trenches will indicate past relationships between seas and landmasses. An accurate interpretion of paleogeography and depositional settings allows conclusions to be made about the evolution of mountain systems, continental blocks, and ocean basins, as well as about the origin and evolution of the atmosphere and hydrosphere.
Sedimentary rocks contain the fossil record of ancient life-forms that enables the documentation of the evolutionary advancement from simple to complex organisms in the plant and animal kingdoms. Also, the study of the various folds or bends and breaks or faults in the strata of sedimentary rocks permits the structural geology or history of deformation to be ascertained.
Finally, it is appropriate to underscore the economic importance of sedimentary rocks. Several subdisciplines of geology deal specifically with the analysis, interpretation, and origin of sediments and sedimentary rocks. Sedimentary petrology is the study of their occurrence, composition , texture, and other overall characteristics, while sedimentology emphasizes the processes by which sediments are transported and deposited.
Sedimentary petrography involves the classification and study of sedimentary rocks using the petrographic microscope. Stratigraphy covers all aspects of sedimentary rocks, particularly from the perspective of their age and regional relationships as well as the correlation of sedimentary rocks in one region with sedimentary rock sequences elsewhere.
For further information about these fields, see geologic sciences. Sedimentary rock. Videos Images. Additional Info. Table Of Contents. While every effort has been made to follow citation style rules, there may be some discrepancies. Please refer to the appropriate style manual or other sources if you have any questions. Facebook Twitter. Give Feedback External Websites. Let us know if you have suggestions to improve this article requires login.
External Websites. The Canadian Encyclopedia - Sedimentary Rock. Articles from Britannica Encyclopedias for elementary and high school students. See Article History. Britannica Quiz. Rocks: Fact or Fiction? What is the age of the oldest rocks on earth? Are rocks and minerals the same? From fossil records to volcanoes, learn more about rocks in this quiz. Study the rock cycle as it evolves gradually from sedimentary to metamorphic and to magmatic rocks.
Geologic materials cycle through various forms. Sediments composed of weathered rock lithify to form sedimentary rock, which then becomes metamorphic rock under the pressure of Earth's crust. When tectonic forces thrust sedimentary and metamorphic rocks into the hot mantle, they may melt and be ejected as magma, which cools to form igneous, or magmatic, rock. Get a Britannica Premium subscription and gain access to exclusive content.
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