Geology Cafe

Depositional Environments: Where Sediments Accumulate

Sediments are transported and deposited in a variety of depositional environments. On land, sedimentary environments include stream flood plains, swamps, dunes and desert basins. Along the coastal regions sediments accumulate in river deltas, lagoons, beaches, and barrier islands. Most sediment ultimately comes to rest in the ocean, accumulating in massive deposits that form the continental shelves, or continuing to the deep basins beyond the continental shelf margin.

In the process of migrating, sediments are sorted by currents into size fractions: cobbles, gravel, sand, silt, and clay. In route from land to sea, sediments are continuously refined by characteristics such as grain size and composition. For instance, beach sand usually consists of the most abundant durable mineral, quartz.

As sediments accumulate, the weight of overlying layers causes compaction. Dissolved minerals precipitate in pore spaces, cementing grains together. The process of lithification involves the combined effects of compaction and cementation, resulting in the formation of sedimentary rocks. Sedimentary rocks consist of pieces or fragments of rock (clasts), minerals precipitated from water, or a combination of the two sources. Sedimentary rocks are generally named after their primary clast sizes and their mineral constituents (with some exceptions).
Depositional Environments
Common depositional environments where sediments may accumulate and become sedimentary rocks. Sediments may pass through many depositional settings before coming to a resting place where they can be consolidated into rock.
Clastic depositional environments Examples of clastic depositional environments in humid and coastal regions.
Clastic depositional environments Examples of depositional environments in arid regions.
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8/28/2012