Sedimentary rocks are from sediments collected from the streams and buried beneath in a process commonly referred to as geologic. This is due to geographical effects such as the tectonic forces controlling the progression of weathering. The process leaves a complicated record thus the different kind of sediments form the deposits. (Strahler, 13) The categories include Clastic, Chemical and Biogenic. Water and wind sorts some sediment to be almost of the same size thus commonly referred to as “well-sorted”.
Conversely, there are particles of different sizes especially those sorted by the ice and huge mass wasting with a reference of “even unsorted” or “poorly sorted”. Sediments take a variety of individual shapes from rounded, sphericity or angular. Well-sorted sediments are caused by prolonged erosion or weathering.
Sedimentary rocks can also form from the biogenic deposits such as the foraminifer formed from planktons cells that covers wide area of the ocean floor or the chemical deposits such as the salts formed from magnesium, potassium or sodium chloride found near salt lakes like Lake Bonneville in Utah. The volcanic sediments form clasts, which are originally volcanic. (National Atlas of United States)
Formation of sedimentary rocks
Deposits and burring of these types of sediments in a process known as “lithification” causes the formation of new rock known as the sediment rock. (U.S. Department of Interior Survey, 2010)
The rock depends on the material or type of sediments and the process. Formation of rock beds occurs from sedimentary particles, which lay in distinct strata. The composition of the sedimentary rocks overtime changes depending in the deposition process and mineral composition. This aspect is what makes the adjacent strata different from the preceding one.
The boundary between the layers referred to as the “bedding surface” thus the origin of the term “Rock Bed”. (Strahler, 13) The presence of the bedding surface enables the geologists to be in a position of telling the ages and is the indication that the rock was once sediments thus the term “Sedimentary Rock”. Various processes are involved in the formation process: “lithification”.
They include compaction a process that reduces the pore space in the sediments because of the weight of the superimposing layer. Secondly is the cementation process where substances dissolves in pores through which water precipitates to form matter that joins the layers strongly together. Lastly is the crystallization process where new crystalline minerals bond the old ones.
The classification of sedimentary rocks falls into the following categories. Siliciclastic rocks or clastic made of sand quatz commonly referred to as resistant minerals like Lithics and fledspar mixed with clay minerals, which form from withering of iron oxides such as feldspar: orthoclase or kaolinite. Chemical and Biogenic or biochemical rocks form from liquid solutions such as calcite that reacts with hydrochloric acid to exist as either micrite; muddy line or limestone. (U.S. Department of Interior Survey, 2010)
The clastic rocks is a composition of visible grains of quartz sand and clay grains mixed together while the chemical and biochemical forms from splitting of minerals that are in solution state. Silica is made of materials that do not dissolve in water and have silica as the main component transported either as sediments at the bottom of the water or suspension. This aspect makes the clay grains and visible sand grains to mix and deposit together.
On the other hand, the minerals that are in solution state easily dissolve in water. They deposit together without traces of silica. The geologists tend to specialize on the siliciclastic rocks because of the various groupings that others have hypothetically made discovery. (Strahler, 13) The mineral deposits that are in solution form separates from the solutions through precipitation from the water thus concentrating the salts.
This helps to classify them as chemical rocks while the biochemical rocks are as a result of plants and animals remains especially those involved with marine life, which draws them from the solutions for formation of the skeletons, which eventually die to form the sediments.
Other biochemical rocks include the coal and peat but forms in the presence of clastic rocks such as sandstones or shales. The integration of minerals to form sediments makes the classification difficult due to inconsistency involved. This means that researchers have an uphill task to come up with a straightforward way of classifying them.
National Atlas of the United States. “Distribution of Sedimentary Rocks.” 2010. Web.
Strahler, Alan. H. “Introduction to physical geography” (Fifth Ed). 2009
U.S Department of the Interior survey. “U.S Geography Survey.” 2010. Retrieved from <https://www.usgs.gov/science-support/osqi/yes/resources-teachers/>