Sorting is the variability in grain size in a clastic sedimentary rock. This parameter measures how well a sediment has been ‘sorted’ by the process that transported it. A sediment can be:
– very well sorted: nearly all grains have the same size
– well sorted: most grains fall in a single grain size class with few outliers
– moderately sorted: more than one grain sizes are present but one prevails
– poorly sorted: several grain sizes are present, none of them prevails
– very poorly sorted: a wide spectrum of grain sizes of very different sizes
Sorting is linked to the type of transport experienced by the sediment. Some processes (e.g. glaciers and gravity flows) transport sediments en masse, producing poorly sorted deposits. Other processes, on the other hand, can transport only some grain sizes, efficiently selecting the sediment. Wind, for instance, can carry away the finer particles and deposit heavier sand, forming well-sorted sand dunes. Other examples of selective transports include rivers, waves, and sea currents.
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