1. Unit: 3 Earth’s Materials
Earth Systems 3209
Unit: 3 Earth’s Materials
Reference:
Chapters 2, 3, 6, 7; Appendix A & B

2. Formation of Sedimentary Rocks
Unit 3: Topic 4.1
Formation of Sedimentary Rocks
Focus on . . .
outlining and explaining how sedimentary rocks form.

3. Formation of Sedimentary Rocks
Sedimentary rocks account for approximately 5% of the crust.
Regardless of this low percentage, approximately 75% of all rocks exposed at the surface is sedimentary rock.
Stages leading to the formation of sedimentary rocks include:
Erosion and weathering
Transportation
Deposition
Lithification
Text Reference:
Pages

4. 1) Weathering and Erosion
In reference to the Rock Cycle, the origin of sedimentary rocks begins with the processes of weathering and erosion.
Pre-existing rocks can be broken down both mechanically or chemically to produce sediment.
Mechanical weathering occurs when a material is broken into smaller pieces which still retain the characteristics of the original material.
Example: freeze – thaw action.
Water freezing cracks
fragments of rock

5. 1) Weathering and Erosion
In reference to the Rock Cycle, the origin of sedimentary rocks begins with the processes of weathering and erosion.
Pre-existing rocks can be broken down both mechanically or chemically to produce sediment.
Chemical Weathering happens when a material is altered by chemical action and a new material is produced which is chemically different than the original material.
Examples:
Oxidation reactions - Iron rusting
Decomposition of limestone (statues and headstones)

6. 2) Transportation of Sediment
Erosional agents (such as, water, wind, and ice,) influenced by gravity, transport the sediment to new locations where it is deposited.
Sediment is broken down during the transport phase. This process is called Abrasion.
Three main agents tend to transport the sediment, these agents include:
Water (rivers and groundwater)
Ice (glaciers)
Wind

7. 3) Deposition of Sediment
Eventually the sediment is deposited in lakes, river valleys, seas, and more frequently the oceans.
In dry areas of the world, sediment (sand and silt) can accumulate in areas called deserts.
Sediment size will decrease the farther it travels into a lake or ocean. This is referred to as Sorting.

8. Transportation of Clastic Sediments
Size Sorting
Coarse-grained
Medium-grained
Fine-grained
Fast
Slow
Moderate
Size Distribution Sorting
sandstone
shale
conglomerate

9. 4) Lithification of Sediment
Following deposition, sediment may become lithified, which means turned to solid rock.
Sediment is commonly lithified by two processes:
Compaction: when the sediment size is small (silt and clay), the weight from the layers of sediment above can compact the lower layers forming solid sedimentary rock.
Compaction
Silt and Clay
Sand
Lime (Calcite)
Round Pebbles
Shale
Sandstone
Limestone
Conglomerate

10. 4) Lithification of Sediment
Following deposition, sediment may become lithified, which means turned to solid rock.
Sediment is commonly lithified by two processes:
Cementation: Over long period of time mineral matter dissolved in groundwater pass through pore spaces and cement (stick) sediment particles together to form solid sedimentary rock.
Sediment Particles
Cement (in Red)
Water with dissolved minerals, (calcite or silica) pass through pore spaces

11. Example 1:
Which processes are responsible for the lithification of sediments?
cementation and compaction
faulting and folding
(C) compression and tension
(D) weathering and erosion
Which of the following is most likely to have formed farthest from the shoreline?
pebble conglomerate
quartz sandstone
shell limestone
silty shale

12. Example 2:
Which letter in the diagram below indicates where sediments is formed? A B
(C) C
(D) D

13. Your Turn . . .
Take the time and complete the following questions (Solutions to follow)
Question:
Which is the correct sequence in the formation of sedimentary rock?
compaction - deposition - weathering - cementation – erosion
deposition - erosion - cementation - weathering – compaction
erosion - weathering - deposition - cementation – compaction
weathering - erosion - deposition - compaction - cementation

14. Solutions . . .
Question:
Which is the correct sequence in the formation of sedimentary rock?
compaction - deposition - weathering - cementation – erosion
deposition - erosion - cementation - weathering – compaction
erosion – cementation – compaction - weathering – deposition
weathering - erosion - deposition - compaction - cementation

15. Summary . . . Overview of Points covered:
Four stages leading to the formation of Sedimentary rock include:
Weathering and Erosion
Transportation
Deposition
Lithification