Presentation on theme: "Sedimentary rocks By Billy. Sedimentary rocks Sedimentary rocks are formed by the accumulation of sediments. There are three basic types of sedimentary."— Presentation transcript:
Sedimentary rocks Sedimentary rocks are formed by the accumulation of sediments. There are three basic types of sedimentary rocks: 1) clastic sedimentary rocks such as breccia, conglomerate, sandstone and shale, that are formed from mechanical weathering debris; 2) chemical sedimentary rocks such as rock salt and some limestones, that form when dissolved materials precipitate from solution; and, 3) organic sedimentary rocks such as coal and some limestones which form from the accumulation of plant or animal debris.
Clastic sedimentary rock Sedimentary rocks are classified on the basis of the texture (grain size) of the rock, and composition. The basic classification only concerned texture, using the Wentworth size scale. But any full rock name must specify both texture and composition. Thus, an arkose sandstone is a rock of sand sized particles, with a high percentage of those particles being feldspar. It might seem that an unlimited variety of particles could end up in a sedimentary rock. After all, there are over 6000 known minerals. In addition, any incompletely weathered piece of igneous, sedimentary, or metamorphic rock can also be found in a sedimentary rock.
A composition classification could become very complicated if all of these different particles were considered. But in most cases rock composition can be defined by four compositional components: >>> Quartz >>> Feldspar >>> Lithic fragments (including rock fragments and mineral grains other than quartz) >>> Matrix (a catchall for the silt and clay grains that cannot be easily seen by eye). Descriptions of each category are below. You will learn to recognize and identify them as you study the rocks.
Since quartz, for all practical purposes, does not weather into anything else, and will remain after everything else is weathered or sorted out, it is one of the most important of the four components of sedimentary rock composition. Pure quartz sandstones are rare. Usually quartz is mixed with one or more of the remaining three components. Pure quartz sandstones form only under great tectonic stability when the land is not high enough for rocks to be exposed to weathering, such as during Wilson Cycle Stage A and Stage I.
Chemical sedimentary rocks For example: Take a glass of water and pour some salt (halite) into it. The salt will dissolve into the water. If you set the water in a hot and dry place (like Arizona) the water, but not the salt, will evaporate away. As the water evaporates, the concentration of salt gets higher and the water will eventually become saturated and will not be able to dissolve any more salt
Sodium chloride, also known as common salt, table salt, or halite, is a chemical compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms. As the major ingredient in edible salt, it is commonly used as a condiment and food preservative.
Organic sedimentary rocks Organic sedimentary rocks are just one of three types of sedimentary rocks. This type of sedimentary rock must have organic material to be created. They are called organic because they are made from organic material such as grass or plankton that, over long periods of time, becomes a type of sedimentary rock. This organic material can be the organism itself or may be given off from the organism. An example of this is coral, which may eventually become limestone with the right pressure and temperature.
1.The United States produces about 20%, or 1.1 billion tons, of the world's coal supply—second only to China. 2.Coal generates about half of the electricity used in the United States. Coal is formed when peat is altered physically and chemically. This process is called "coalification." During coalification, peat undergoes several changes as a result of bacterial decay, compaction, heat, and time. Peat deposits are quite varied and contain everything from pristine plant parts (roots, bark, spores, etc.) to decayed plants, decay products, and even charcoal if the peat caught fire during accumulation.
How is fossil fuels form Fossil fuel was formed over hundreds of millions of years ago by decomposing plants. After a long period of time, layers and layers of rock, mud, and sand covered the dead plants thousands of feet under the earth, which fossilized them. Oil and natural gas were formed the same way, but coal was formed a slightly different way. The first two were formed by organisms - plankton and plants mostly - that lived in fresh water and they were buried under rivers and oceans. After a long period of time the water receded back. The pressure and bacteria combined to make oil and natural gas.
How oil is formed Each of the thousands of molecules that make up crude oil has particular physical and chemical properties. Hundreds of products are made by separating and sorting these molecules, then re-combining or processing them further. The range of products varies according to the particular type of crude oil and the refinery design. Processes can be altered to produce more gasoline in summer or more heating oil in winter. On average, processing light crude oil in a modern refinery yields the following range of products:
How natrual gas is formed Geologists view crude oil and natural gas as the product of compression and heating of ancient organic materials over geological time. Formation of petroleum occurs from hydrocarbon pyrolysis, in a variety of mostly endothermic reactions at high temperature and/or pressure.Today's oil formed from the preserved remains of algae which had settled to a sea or lake bottom in large quantities under anoxic conditions (the remains of prehistoric terrestrial plants, on the other hand, tended to form coal).