ShareRocks & Minerals - The Laying of Sedimentary Rocks Over Time
Sedimentary rock forms from bits of rocks deposited over time by wind
and or water. Rocks occur in all sizes. It is the tiny amounts of mud,
pebbles and sand grains and smaller rock particles that can form sedimentary
rock. Sediment can also contain the remains of once living things. This
may be bones, shells, droppings, leaves or stems. Wind and water carries
sediment and deposits it in layers usually in a lake or ocean bottom.
The processes that turn sediments into solid rock are compaction and cementation.
Erosion
Destructive
forces are constantly breaking up and wearing away the rocks of Earth.
The forces include grinding ice, waves, rain, and heat. Erosion occurs
when these agents loosen and carry away the fragments of rock or once
living things somewhere else.
Deposition Environments:
a place where sediments collect. Eventually,
wind or water will drop these fragments. They will accumulate in low valley
or river bottom. Deposition is the process by which wind or water sediment
settles out in layers. Furthermore, over time the remains of living things
may harden in this sediment and change into fossils. After sediment is
deposited the processes of compaction and cementation change the fragments
into sedimentary rock.
Compaction
At first the fragments of rock lie loosely together. But gradually, over
many many years these thick layers build up. This build up becomes heavy
and presses down on the layers beneath it. Compaction is the pressing
down of layers forcing the sediments to fit closer together. Over millions
of years this process can squeeze fragments tightly together. The layers
often remain visible in the rock and may be used to identify sedimentary
rock.
Cementation
During the process of compaction the minerals in the rock are dissolving.
The minerals fill in the spaces between sediment particles. Cementation
is the process of sediment being glued tightly together. The processes
of erosion, deposition, compaction and cementation may occur over millions
of years transforming rock fragments into solid rock.
