Sedimentary Environments

Sedimentary environments, or the conditions under which the rocks were deposited, change both horizontally and vertically.  Horizontally they reflect changes in energy and sediment supply, and vertically they reflect changes in time, because over the time the conditions as a single location can change.

The diagram below shows a number of features:

  1. Going offshore, the sediment becomes finer grained from sand to mud (sandstone to shale when it becomes rock), and then lime mud (limestone) when the supply of terrestrial sediment has all been deposited closer to shore.
  2. During times of sea level rise, such as the present, there will be a transgression as the shoreline moves inland, and the belts of different sediment also move inland.
  3. When sea level drops, a regression caused the belts of different sediment to move seaward.
  4. At a given location, the changes from one rock type to another indicate the moving positions of the shoreline.  During an ice age these cycles can repeat hundreds of times, and gave rise to the great coal swamps of the Carboniferous.  These formed in coastal swamps, but above and below will be offshore sandstone, shale, and limestone.
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Last revision 9/23/2015