Sedimentary rocks are made of material that has been deposited by gravitational force at the bottom of a mountain via landslide, at the bottom of a river during and after a flood, in dunes of sand blown by the wind, etc. The key similarity for all sediments (the particles that are cemented together to form sedimentary rock) is that they have moved and fallen. For the vast majority of sedimentary rocks, this will produce a layering in the rock, but even in those few that are not layered it should be possible to recognize movement of the material in the nature of the fragments themselves.

Although all sedimentary rocks are formed by falling, there is a great variety in sedimentary rocks reflecting the environment in which the sediments were deposited and the material of which they are made. Some form in the quiet waters of a swamp or deep ocean, others in active waters of a beach or stream. Some form from the deposition of organic matter -- shells or leaves, others from material carried hundreds of miles by a continental ice sheet. By applying the principle of uniformitarianism, we should be able to study sedimentary environments we see in the world today and recognize in them the processes that produced sedimentary rocks that are million or billions of years old.

I. Making a sedimentary rock

A. Sediments and gravitational force

1. Competing energy of horizontal vs. vertical movement

2. Sorting of materials

B. Burial, compaction and "cement" -- turning sand into sandstone.

A. Clastic rocks -- made of rock fragments

Conglomerate, Sandstone, Siltstone, Shale

B. Biochemical rocks -- composed primarily of organic materials

Limestone, Coal, fossiliferous shales

C. Chemical rocks -- by chemical precipitation

Evaporites (rock salt)

A. Beach

B. River deposits

C. Limestones

NOAA Photo of Belize Reef

D. Turbidites

1. Describe the processes that lead to the formation of several common sedimentary rocks.

2. Explain the process of sediment sorting.

3. Discuss the process(es) responsible for sedimentary layering and describe at least one process that might produce an unlayered sediments.

4. Relate the energy of sedimentary environment to the different kinds of clastic sedimentary rocks.

5. Explain why coal and fossiliferous shales cannot be produced in high energy environments.

6. Describe the process(es) that produce clean sandstones from beach sand but dirty sandstones and shales from turbidites.

7. Explain why breccias are likely to be very poorly sorted.

8. Discuss the importance of warm water in the production of many limestones.

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