Sedimentary rock forms at the surface, by deposition of detrital grains or by precipitation from solution in water. How this comes into effect is through rock cycle. This includes the erosion, transport, depostion, burial, heating, deformation, melting, cooling and exhumation of rock or rock fragments.
Turing sediments into rock
The main requirement is that it must remain buried, and not be eroded away. It is easy to forget this obvious point when looking at a sedimentary rock in the field. A 3 cm thick layer of sand may have taken less than a day to accumulate, but it may be the sole survivor of million such layers that were successively deposited and then stripped away, perhaps with every turn of the tide. Such is the fate of most sediments deposited near shorelines, in rivers and in desert dunes, and it is only in deep marine conditions that we normally find continuous deposition without erosional breaks.
Once buried, processes begin that can turn soft sediment into hard sedimentary rock. Sediments (sands) began as loose, unconsolidated deposits. However, with burial, and over time, various chemical and physical changes take place, collectively described as diagenesis. Sands are made of more equidimensional clasts, so the potential for compaction and loss of porosity is less. Compaction is achieved by a combination of rotation, bending and fracturing of grains. A sandy sediment may begin with up to 40 percent porosity and end up with only 10 percent porosity at a depth of about a kilometer. At greater depths, the points of grains resting on others may dissolve away through a process called pressure solution, reducing porosity still further.
Most of the chemical changes during diagenesis are controlled by the nature of the pore waters. Silica that has been dissolved by pressure solution may come out of solution to fill the remaining pore spaces with silica cement. This can turn loose sandy deposit into a hard rock, sandstone.
Sedimentary rocks form from sedimentation; sedimentation is the process through which minerals and organic particles collect and settle together. These particles are called sediment. Sedimentary rocks are categorized into three different main types that include many different rocks. Sedimentary rocks are found across the Earth's land masses and in the Earth's oceans.
Clastic Sedimentary
Clastic sedimentary rocks are composed of rocks that moved because of fluids and settled when the fluid stopped; for example, rocks in a river or stream that then dried up. These rocks are made up of silicate and rock fragments that have become cemented together. The materials found in clastic sedimentary rocks are quite variable, but includes: feldspar, mica, clay fragments and quartz. Clastic sedimentary rocks are further classified into groups based on the size of the fragment that makes up the rock. These three groups are breccias, sandstones and mudrocks. Breccias are made almost entirely of rock while sandstone is composed of sand and mudrocks of mud. This group is sometimes also known simply as the breccias.
Biochemical Sedimentary
Biochemical sedimentary rocks are made up of particles from air or water. These rocks are also known as organic sedimentary rocks because they form as result of something that grew. For example, coal is a biochemical sedimentary rock that comes from a plant. The plant intakes carbon as it grows and when it dies that carbon accumulation eventually creates coal. Some types of limestone are also classified as biochemical sedimentary rocks; these rocks form from the skeletons of corral, mollusks and other organisms.
Chemical Sedimentary
The final group of sedimentary rocks is the chemical rocks. These rocks form as materials evaporate. For example, over time seas and ancient oceans dried up. The salt in these seas gathered to form chemical sedimentary rocks including other types of limestone, dolomites and rock salt. The rocks are different than the other types because they don't form by energy or by current. These rocks are classified by the chemical make up of the materials that form them. The three categories are: carbonates, evaporites and chert.
Now with question and answers. Please email the answers and don't log the answers it will be deleted. THANKS. Yes, I like to see a pic.
1. When the sediment is buried a process occurs, chemical and physical, the term?
2. Through porosity and at greater depths this process forces more compaction, the term?
3. At GZ, the layers of sediments form a exposed road cut rock formation. What is the height?
A. 10' to 15'
B. 20' to 25"
C. 30' to 35'
Optional pic of your adventure
