Sedimentaryrocks are an accumulation of particulate material through physical,chemical and most importantly biological process on the earthsurface. They are formed on the earth’s surface by the accumulationof old rocks. They mainly consist of rocks that were in existencebefore and have been broken down due to various reasons mostimportantly climatic change andhuman environment. The rocks covera large percentage of what is found underneath the surface of theearth (Boggs, 2009). This paper explores key aspects of sedimentaryrocks.
TheFormation Process of
Sedimentaryrocks are in most cases formed at low temperatures with pressureemanating from beneath the earth surface. This fact is due toavailability of water and liquid which is found within water sourceslike seas and rivers bringing sediments into the main water body. Asthis happens, sedimentary rocks containing fossils are formed on theocean floor. As time proceeds, this fossils multiply due to varyingweather patterns and human activity. A rise in sea levels thenemanates thereby pushing the sea floor forward with this in turnexposing the sedimentary rocks.
Thereis then movement of particulates from the land by erosion. Thetransfer of this particulates is mostly done by water and in otherinstances wind. They are then deposited at levels perceived to bemuch lower than their previous surroundings. Liquid and solublesubstances for example water then come into contact with the rocks.This is done mostly by frequent contact which comes along in thelower reaches. When this takes place, the level of concentration isthereby dipped and subsequently a large amount of inorganic processesremoved (Boggs, 2009). Burial then takes place with layer upon layerof sediment. As temperatures and pressure upon this sediments goes anotch higher, a number of constituents are destroyed. There is thengrowth and creation of some new and other minerals with thiseventually solidifying into a sedimentary rock.
Locationof the rocks then plays a part in determining the availability ofdifferent constituents. Three major types of fundamental rocks areformed. These are mainly described as terrigenous, carbonaceous andchemical rocks (also known as biochemical). Terrigenous rocks aremostly distinguished by their texture and size of their grains. Agood example of this are sandstones which are known for theirextremely tiny pieces. Terrigenous rocks are further divided intodifferent types with this solely based on their different forms ofcomposition. Chemical and biochemical rocks are divided on the basisof components found in them. This in most cases is in the form ofcarbonates, evaporates and iron formations. Carbonaceous rocks on theother hand are separated on the basis of components such as coals andfuel. This can explain why a large amount of energy is able to bemanifested by them (Boggs, 2009). Figure 1.0 demonstrates theprocess of the formation of sedimentary rocks.
Figure1.0 Formation of
Methodsof Sediment Erosion and Transport
Thereare different modes by which sediments undergo erosion andtransportation from the surface. These movement is mostly aided byvarying components, a number of them being glaciers, wind,landslides, rivers and sea.
RiversAs rivers flow along their paths, a number of rocks are interferedwith. Those that are soft break during the process with theirfragments being carried away. Faster flowing rivers are then known tocarry away larger and more compact materials. This then movesdifferent fragments thereby crushing onto the bedrock which in mostcases is solid. Mobility then comes into the equation with fragmentsbroken down into pieces by this collision and there after becomingsmaller in both shape and size.
Winderosion happens when the gusts blow and pick up small particles.While this is happening bigger particles are sometimes uprooted androlled down particular surfaces in different directions. Blasting ofsand is a normal occurrence with the smaller rocks breaking downfurther into even smaller segments (Nyamia, 2014).
Landslidesoccur when debris is eroded from the surface and pushed downhill inlarge amounts. This is usually due to the influence of gravity whichpulls the particles from a surface normally on a higher level incomparison.(Nyamia, 2014
Erosionof glaciers normally occurs when fragments of rock are introducedinto ice on glaciers. The said fragments then continue to rub ontoeach other and against the different rocks that are found on eitherside and below the surface of the earth (Nyamia, 2014).
Distributionof Sedimentary rocks
Sedimentaryrocks range in terms of age from ancient to modern times. The oldesthave been known to be at least four billion years in age. Sedimentaryrocks began to form when oceans and the atmosphere of the earthdevelop. This ultimately leads to a decrease of gas in the earth’sinterior surface. With this developments, an increase in the area ofthe earth surface covered by sedimentary rocks is noted. This isexplained by the fact that various areas with previously covered byvolcanic rocks are presently eroded (Boggs, 2009).
Typesof sedimentary rocks
Sedimentary rocks can be differentiated from other rocks largely inpart by their composition and organization. In most cases, they areexplicitly divided into various groups with their places of originbeing the number one factor considered. In this process compositionis highly acknowledged. Sedimentary rocks can therefore beclassified varyingly, the major aspect being availability ofdifferent biological components. These rocks are recognized on thebasis of their composition, with only three major types taken intoconsideration. This include:
Limestoneis in most cases classified into two. This is wholly dependent on theformation of the rock itself. After deposition, the rock forms itselfand there after defined as chemical or organic sediment. Limestone isin most cases made up of the chemical calcium carbonate and can formin two major ways. This can either be organically or chemically fromthe precipitation of calcium carbonate accumulated from differentwater bodies. Limestone is used in many ways dependant on theactivity in question. In most cases it is used in the production ofcement, a vital material used in the building industry
Conglomerateis a form of sedimentary rock mainly made up of large andwell-rounded particles. Most cases, these are large in size andgreater than two millimeters in diameter. In conglomerate rocks, aspace exists between the pebbles. The rocks in question are in mostcases filled with smaller particles which pale in comparison to otherrocks. Binding and joining of this rocks is thereby done courtesy ofchemical cement. (Nyamia, 2014).
Sandstoneis a primarily clastic sedimentary rock. This is made up of mainlysand-size grain which measure close to two millimeters in diameter.Sandstone is created mainly as a result of weathering of differentdebris. Sandstone is found in various environments with large chunksof this including beaches, deserts, flood, plains and deltas (Nyamia,2014).
Thisis rock that is formed in most cases from plant debris. This debrismostly accumulates in swampy or waterlogged enviroments.In all but afew cases, coal is mainly used as a fuel (Nyamia, 2014).
Structuresin sedimentary rocks
Oneof the structures in sedimentary rocks is bedding. This is the mostdistinctive structure of sedimentary rocks and consists of the bedsseparated by each other in form of planes. The thickness of the saidplanes varies from one to the next with very thin ones the directopposite of thick. Different beds show different types of depositionwith the upper most bed showing latest time of deposit with thelowest showing the earliest time with which it was deposited (Mibei,2014).
Beddingis mainly divided into two categories. These are broadly described asgraded bedding and cross bedding. Grade bedding occurs usually when asingle bed varies largely in size from the bottom to the top mostsegment. Cross bedding on the other hand occurs when a slope likecreation forms a range of parallel lines inclined at differentangles. This are produced by different deposits of sediments createdunder water by subsequent movement of both water and wind indifferent directions (Mibei, 2014).
Ripple marks occur on top of water beds. This is a result of movementof water during their formation. An example of this are formation ofbeaches (Mibei, 2014).
Otherformations include mud cracks. This are formed when cracks areformed on the top of beds when sediments begin to dry up are mostlyfound on top of river beds and dried up lakes(Mibei, 2014).
Sedimentary rocks have a variety of different features due to theirstructures, textures and fossil content. This distinctive featuresplay a part in revealing past life forms on earth and the nature ofvarious surfaces. This contributes in a large way to the reasongeologists and anthropologists carry out their research on this rockstoday (Carlson, et al, 2008).
Differentattributes of sedimentary rocks include availability of fossil fuelsand minerals that have economic significance. Petroleum, natural gas,sulfur, iron, uranium, coal and salt are the economic products thatcan be derived from sedimentary rocks (Boggs, 2009).
Itis therefore wise to say that sediments are loose and weatheredparticles brought together by different forces of nature to formwhole some rocks. There forms depend on the conditions in which therewere deposited with wind and water being the major componentsinvolved in this. Natural features play a part in sediment creationin the form of marine features and gaseous organisms. This being thecase, both human and natural habitat live concurrently due to the fewmain elements involved in this geographical phenomenon.
Boggs,S. (2009). Petrologyof .Cambridge University Press.
Carlson,D, Hammersley, L and Plummer, C. (2008). Physicalgeology, earth revealed.
McGraw-Hill. New York, NY.
Nyamia,C. (2014). Natureand Classification of .UNO.
Mibei,G. (2014). Introductionto types and classification of rocks. Geothermal Development Company.