Sedimentary Rocks
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Sedimentary rocks cover about three-quarters of the earth's surface and form more than 90 percent of Alberta's bedrock surface. Sedimentary rocks can be made up of rock fragments, called sediments, that have been eroded from one
place and moved to another by water, ice, wind, or gravity. In time, the sediments are buried, compacted and cemented together to form sedimentary rocks. Rocks that are made up of sediments are called "clastic" sedimentary rocks and include
conglomerate, sandstone, and shale. Other sedimentary rocks are of chemical or organic origin. Chemical sedimentary rocks are formed by the precipitation or evaporation of minerals from solution in an ancient seawater, and examples from Alberta
include limestone, gypsum, and halite (rock salt), and
dolostones. Even though dolostones can be formed by precipitation, it is usually formed when limestone is altered by the addition of a magnesium rich solution. Organic sedimentary rocks
are formed by the accumulation of dead plant and animal matter which is then compacted together.
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All three kinds of sedimentary rocks are found in Alberta. The
Rocky Mountains consist mostly of the chemical rocks limestone and dolostones, with some sandstones and shales. The
Plains are mainly sandstone and shale, although
there is some gypsum, limestone, and dolostones forming a rim around the
Canadian Shield in northeast Alberta. The organic rock coal is found in both the Plains and Rocky Mountains.
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