1.Formation of Sedimentary Rocks

Sedimentary rocks tend to form close or on the surface of the earth from organic debris or remains of weathered pre-existing rocks. Sedimentary implies both lithified or consolidated sediments and unconsolidated sediments. Most sedimentary rocks belong to chemical, clastic or organic groups.

 2.Significance of Sedimentary Rocks Origin and Composition

Organic rocks are classified according to their composition by Geologists. Sedimentary rocks origin and composition help geologists in getting insights about the environment around the areas where they are deposited. This information helps in interpreting an area’s geologic history and aids in searching for minerals and rocks that have economic importance.

 3.Composition of Sedimentary Rocks

Since sedimentary rocks result from sediment deposit that happens over time mostly as layers in ocean and lake bottom, they may be composed of tiny plant pieces, minerals and any other organic particles.  Once the sediment compresses over long periods of time, they consolidate to form layers of solid rock.

 4.The Earth’s Rocky Surface comprises Sedimentary Rocks

Sedimentary rocks are in stratas that appear like exposed cliffs. These rocks cover most of the rocky surface on Earth but only comprise a small portion of Earth’s crust as opposed to igneous and metamorphic rocks. Sedimentary rocks include sandstone, limestone, greywacke, mudstone, coal, chalk, flint and claystone.

 5.Oldest Layers form at the Bottom

As sedimentary rocks form, the oldest layers tend to be at the bottom while newer layers appear at the top. An important feature in these rocks is the grain size that forms them. Grain names vary depending on size and they provide information about the current’s energy level in the deposition environment.

 6.Grain Depositing Patterns

Large grains tend to be deposited by fast, strong currents occurring on stream channels, beaches and windy deserts. Sandstones reflect high energy environments because they are heavy. Finer clay and silt size particles in mudstones tend to be deposited in waters that are quiet such as lakes, swamps and deep oceans.

 7.Sedimentary Rocks Resistance

Sandstones are much resistant and harder than mudstones and usually form ledges and cliffs. On the other hand, mudstones result to formation of crumbly, soft covered slopes. Sedimentary rocks are the only rocks that have fossils which provide a wide range of information to geologists. For instance, coral fossils found in sedimentary rocks will indicate deposits by sea water since corals are found in marine environments.

8.Cementation and Lithification

Cementation refers to the process through which minerals dissolve and hold particles in sedimentary rocks.  On the other hand, lithification is the process through which the sediments hard in order to create sedimentary rocks.

9.Uses of Sedimentary Rocks

Since time immemorial, sedimentary rocks such as sand stone have been used to craft housewares. Organic sedimentary rocks, which have high levels of organic material are a source of tar and petroleum.

 10.Rocks of Devils Tower

Sedimentary rocks are the oldest rocks on the Rocks of Devils Tower in South Dakota. They are called the Spearfish formation, after the Spearfish town. These rocks feature bright red layers on their lower elevation close to the Belle Fourche River Valley. Sediments for this formation were deposited about 240 million years back during the Triassic time when South America, Africa and North America were adjoined. The Appalachian Mountains found on the eastern U.S. were still young and the Gulf of Mexico and Atlantic Ocean were yet to form. Fossils of the oldest dinosaur have been found in these rocks.  The Spearfish Formation is formed from fine-grained sandstones and mudstones in a slow energy environment under hot flat desert plains close to the ocean.