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Detrital sedimentary rocks are formed from solid particles of pre-existing rocks or organic debris. This is the type of sedimentary rock in which you might discover a fossil.

Characteristics
Detrital sedimentary rocks are formed from pieces of existing rocks or organic debris. Thus, one of the characteristics is the presence of particles. These particles can range in size from smaller than .004 millimeters in a mudstone like shale (a rock formed from mud) to larger than an inch in a conglomerate stone (formed from large gravel).

How they are formed
Detrital sedimentary rocks are formed from particles of pre-existing rocks and organic debris, collectively called sediment. This sediment is transported in water and deposited, burying all of the previously deposited layers. When the layers are buried deep under the surface layer, they may be turned into solid sedimentary rock by the process of lithification (lithification is Greek for "to make rock").

The lithification process has two steps: compaction and cementation. During compaction, excess air and water is pressed out of the sediment and the volume of the sediment is reduced. During cementation, the sediment grains (particles) become bound together by minerals that were dissolved in the water that circulated through the sediment. These minerals "precipitate" (come out of the water) and act like glue to cement the particles together into solid rock.

Where they are found
Detrital sedimentary rocks can be found all over the world. Since sedimentary rocks, both detrital and chemical, make up 75% of the rocks on Earth's land surface, you have probably seen many of them. Some famous detrital sedimentary rocks are the sandstones in Arches National Park.


Click here to view Chemical Sedimentary Rocks

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This page was last updated on December 4, 2000
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