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Video: Rocks that Form on the Surface

1.    How does sediment form?

Sediment forms by the decomposition and disintegration of pre-existing rock.  This weathering can take place anywhere, but typically occurs in the mountains.

2.    Where do sedimentary rocks form?

Typically sedimentary rocks form underground.  The clastic sedimentary tocks typically form underground while the nonclastic or chemical sedimentary rocks can form at the Earth's surface.

3.    How does the sediment get from where it is formed to the site where sedimentary
       rocks are formed?

Sediment is transported, first by the mass wasting processes under the force of gravity.  Then the sediment is transported by water, ice or wind to its final depositional site, usually in the ocean.

4.    Differentiate between sediments and sedimentary rocks.

Sediment is loose grains of pre-existing rock or dissolved material.  Sedimentary rock is the compacted and lithified (cemented) form of sediment.

5.    How are sediments cemented together?  What is the most common cement?

Pre-existing rock that is soluble in water is carried into the pore spaces between grains of sediment.  There the water is removed by evaporation or heat or some combination, leaving the dissolved material behind to cement the grains in place.  The most common cement is Calcium carbonate (CaCO³).  Other cements may be SiO², NaCl, and CaSO⁴)

6.    What are the characteristics of sedimentary rocks?

Sedimentary rocks are layered.  They form by the deposition of one grain at a time.

7.    When deposited what is the orientation of the layering of sediment?

Essentially, not perfectly, horizontal.

8.    Differentiate between clastic, organic and chemical sedimentary rocks?

Clastic sedimentary rock is composed of pieces of pre-existing rock.  Both organic and chemical sedimentary rock is composed of material that was dissolved in water.  The difference between the two is that the organic sedimentary rock is composed of parts of flora and fauna, while the chemical sedimentary rock precipitated out of water chemically.

9.    If sedimentary rocks are found in a tilted position, what is the significance of
       this orientation?

Since they were deposited in a nearly horizontal position, if found in a tilted position, they have been deformed.  Frequently this is accomplished in the process of mountain building.