The Size, Sorting and Roundness of Sand

Energy Levels of Water  Moving water provides a large amount of energy that is required to transport large sand grains.  In very still water there is insufficient energy to bring larger sand grains into the environment..

 The larger the size of the sand grains, the higher the energy environment. This is called a high-energy depositional environment.  The smaller the size of the sand grains, the lower the energy environment. This is called a low-energy depositional environment.

 Moving water (waves or currents) – are high-energy.  Quiet or still water – are low-energy.  Deep water has quiet water (low energy) and a wave motion at upper part of water high energy).

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Questions on Size  What would happen to the size of the sand grains in a place where there is moving water (currents or waves)?  What would happen to the size of the sand grains in a place where there is quiet or still water?

 The size of the sand grains indicates the energy level where deposited (beach, riverbed, lake, delta).  Faster-moving water is able to carry a larger sand and rocks. The larger the size of the sand grains, the higher the energy environment.  Slower-moving water is only able to carry smaller grains. Size of Grain of Sand

 What would happen to the roundness of the sand grains if they traveled a long distance and were in the depositional environment for a long time.?  What would happen to the roundness of the sand grains if they traveled a short distance and were in the depositional environment a short time? Questions about Roundness

Roundness  Roundness is a measure of the sharpness or roundness of the corners of the sand grains.  As sand grains are transported, they undergo abrasion by coming into contact with the stream bottom, sea floor, or other grains.  A well-rounded sand grain indicates that it has been transported far from the original source area, and that it has been in the depositional environment for a long time.  Angular sand grains have probably only been transported for a short distance from the source area, and it has been in the depositional environment for a short time.

Roundness  Roundness can be determined by comparing the sand grains to the following visual comparison chart.

 Sorting refers to the range in grain sizes of the sand.  Sand that is well sorted will have most of the grains roughly the same size.  Poorly sorted sand has a wide range of grain sizes. Sorting can be estimated using the following visual comparison chart. Sorting

 Well-sorted grains indicate that the sand was probably transported for a long time in a fairly high- energy environment (waves or currents).  The finer grains were probably washed away.  Good sorting implies consistent, fairly high energy levels (washing).

 Poorly sorted grains indicate that the sediment has not been transported very far from the source area.  It also suggests fluctuating energy levels,  and a fairly short time in the depositional environment.  Poor sorting implies inconsistent energy – rapid dumping (which might involve short episodes of high energy), followed by low energy conditions.

 The products of physical, chemical, and biological weathering are the raw material for sedimentary rocks.  Erosion is the transportation of these materials, usually by water, wind, ice, or gravity.  Weathered debris is eventually deposited in lakes, river valleys, seas, and oceans.  Over long periods of time these sediments are cemented together to form solid rock. Weathering & Erosional Deposition