More than Sediment
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||grades 9 to 10
||Flesch-Kincaid grade level:
||angularity, bedding, Cross-beds, precipitate, angular, clastic, composition, finer, deposition, sandstone, sedimentary, mudflows, tremendous, geologists, organic, crystallize
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More than Sediment
By Trista L. Pollard
1 Geologists have learned that sediment composition depends on its source and that it changes as it is transported. Clastic sediments have very distinct physical characteristics. These characteristics come from the way the sediment was carried to its deposition area. As you have learned, sediment is transported by agents such as water, ice, and wind. It is also moved by the effects of gravity. Depending on the erosion rate or speed, the size of the sediment particles that can be carried and the distance they are carried will vary. Scientists have found that sediment characteristics are determined by the distance it travels and the agent that moves the sediment.
2 Sorting and angularity are two factors that affect the characteristics of sediment. As sediment is transported by currents of air or water, the sediment is separated according to size. This is called sorting. Sediment that is very well sorted has grains that are all roughly the same size. Moderately sorted sediments have grains that are roughly two different sizes. Sediment that is poorly sorted contains grains of many different sizes. Geologists have also categorized sediment as well sorted and very poorly sorted. It's the change in the speed of the agent (wind, ice, water, etc) that determines the way sediment will be sorted. Imagine what happens when fast-moving streams enter lakes. As the water from the stream combines with the water in the lake, its speed slows down sharply. Once this occurs, the larger grains of sediment become too heavy for the current to move. These are the sediment grains that are deposited out of the water first. As you may have guessed, the finer grains of sediment stay in the current for longer periods than larger grains. As a result, finer grains of sediment are usually found farther from shorelines. These finer grains also have a tendency to be deposited on coarser or heavier sediment grains.
3 Angularity describes the texture of sediment after it has traveled from its source. As sediment grains travel, they collide with other sediment particles and other objects. This action will change the shape and size of the particles. Before sediment particles are transported, when they have first broken off their source rock, their shapes tend to be angular and uneven. Sediment particles that have traveled farther from their source tend to be smoother, more rounded, and finer. Now that we have looked at sediment characteristics, let's look at the characteristics of sedimentary rocks.
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