Geology Reference
In-Depth Information
Graded beds:
Graded beds (see Figure 7-10) occur when sediments of different
sizes settle out of water at different times: the larger grains first, followed by in-
creasingly smaller grains. This gradation indicates that the sediments were car-
ried in a flow of high energy (high enough to pick up larger grains), and then sud-
denly the water slowed or stopped so that the particles fell to the bottom — the
largest and heaviest first.
Figure 7-10:
Graded bedding.
Ripple marks:
Ripple marks (see Figure 7-11) occur in rocks created at shorelines
(like the beach) or in streambeds. You have probably seen the wavy lines of sand
created as the water moves back and forth, in and out, at the shore of a lake or
ocean. Ripple marks created by this back and forth motion are called
oscillation
ripples.
Ripples created by water moving in one direction (such as a creek bed) are
called
current ripples.
Ripples can also be created by wind moving sand.
