Sedimentary Rocks Introduction: Common, Clastic, Chemical and Organic Sedimentary Rocks

Sedimentary rocks introduction is coming in the follows. Then we will continue with a short review on different types of sedimentary rocks. Let’s start.

Sedimentary Rocks Introduction

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.

Common Sedimentary Rocks

Common sedimentary rocks include sandstone, limestone, and shale. These rocks often start as sediments carried in rivers and deposited in lakes and oceans. When buried, the sediments lose water and become cemented to form rock. Tuffaceous sandstones contain volcanic ash.

Clastic Sedimentary Rocks

Sedimentary clastic rocks are the group of rocks most people think of when they think of sedimentary rocks. Clastic sedimentary rocks are made up of pieces or clasts of pre-existing rocks. Pieces of rock are loosened by weathering, then transported to some basin or depression where sediment is trapped. If the sediment is buried deeply, it becomes compacted and cemented, forming sedimentary rock.

Clastic sedimentary rocks may have particles ranging in size from microscopic clay to huge boulders. Their names are based on their clast or grain size. The smallest grains are called clay, then silt, then sand. Grains larger than 2 millimeters are called pebbles. Shale is a rock made mostly of clay, siltstone is made up of silt-sized grains, sandstone is made of sand-sized clasts, and conglomerate is made of pebbles surrounded by a matrix of sand or mud.

Biologic Sedimentary Rocks

Biologic sedimentary rocks form when large numbers of living things die. Chert is an example for this type of rock, and this is one of the ways limestone can form. Limestone can also form by precipitating out of the water.

More Information on Sedimentary Rocks

Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at the Earth’s surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles to settle in place. The particles that form a sedimentary rock are called sediment, and may be composed of geological detritus called minerals or biological detritus called organic matter.

Geological and Biological Detritus

The geological detritus originated from weathering and erosion of existing rocks, or from the solidification of molten lava blobs erupted by volcanoes. The geological detritus is transported to the place of deposition by water, wind, ice or mass movement, which are called agents of denudation. Biological detritus was formed by bodies and parts mainly shells of dead aquatic organisms, as well as their fecal mass, suspended in water and slowly piling up on the floor of water bodies. Sedimentation may also occur as dissolved minerals precipitate from water solution.

Sedimentary Rock in Earth Crust

The sedimentary rock cover of the continents of the Earth’s crust is extensive. that is about 73% of the Earth’s current land surface. But sedimentary rock is estimated to be only 8% of the volume of the crust. Sedimentary rocks are only a thin veneer over a crust consisting mainly of igneous and metamorphic rocks. These rocks are deposited in layers as strata, forming a structure called bedding. They are often deposited in large structures called sedimentary basins. Sedimentary rocks have also been found on Mars.

Sedimentary Rocks Studies

The study of sedimentary rocks and rock strata provides information about the subsurface that is useful for civil engineering, for example in the construction of roads, houses, tunnels, canals or other structures. Sedimentary rocks are also important sources of natural resources including coal, fossil fuels, drinking water and ores.

Palaeogeography, Paleoclimatology, Sedimentology

The study of the sequence of sedimentary rock strata is the main source for an understanding of the Earth’s history, including palaeogeography, paleoclimatology and the history of life. The scientific discipline that studies the properties and origin of sedimentary rocks is called sedimentology. Sedimentology is part of both geology and physical geography and overlaps partly with other disciplines in the Earth sciences, such as pedology, geomorphology, geochemistry and structural geology.

Sedimentary Rocks Formation

Sedimentary rocks are formed when sediment is deposited out of air, ice, wind, gravity, or water flows carrying the particles in suspension. This sediment is often formed when weathering and erosion break down a rock into loose material in a source area. The material is then transported from the source area to the deposition area. The type of sediment transported depends on the geology of the hinterland and the source area of the sediment. However, some sedimentary rocks, such as evaporites, are composed of material that form at the place of deposition. The nature of a sedimentary rock, therefore, not only depends on the sediment supply, but also on the sedimentary depositional environment in which it formed.

Final Statement

Sedimentary rocks are formed by the accumulation of sediments. There are three basic types of sedimentary rocks. Clastic sedimentary rocks form from the accumulation and lithification of mechanical weathering debris. Examples include: breccia, conglomerate, sandstone, siltstone, and shale.

Chemical and Organic Sedimentary Rocks 

Chemical sedimentary rocks form when dissolved materials precipitate from solution. Examples include: chert, some dolomites, flint, iron ore, limestones, and rock salt. Organic sedimentary rocks form from the accumulation of plant or animal debris. Examples include: chalk, coal, diatomite, some dolomites, and some limestones.

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Sources

en.wikipedia.org/wiki/Sedimentary_rock

www.usgs.gov/faqs/what-are-sedimentary-rocks-0?qt-news_science_products=0#qt-news_science_products

geology.com/rocks/sedimentary-rocks.shtml