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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.

Sorting. Graphics: Samuele Papeschi/GW.
Example of well sorted (left) and poorly sorted (right) sandy sediment. Modified after

Compton, R. R. (1962). Manual of field geology. Soil Science93(4), 295.
Dott, R. H. (1964). Wacke, graywacke and matrix; what approach to immature sandstone classification?. Journal of Sedimentary Research34(3), 625-632.
Folk, R. L. (1980). Petrology of sedimentary rocks. Hemphill publishing company.
Lewis, D. W., & McConchie, D. (2012). Analytical sedimentology. Springer Science & Business Media.
Powers, M. C. (1953). A new roundness scale for sedimentary particles. Journal of Sedimentary Research23(2), 117-119.
Wentworth, C. K. (1922). A scale of grade and class terms for clastic sediments. The journal of geology30(5), 377-392.

Detrital and Authigenic Minerals
Sedimentary Structures
Sedimentary Rocks


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