1. Formation of Sedimentary Rocks

2. Formation of Sedimentary Rocks
Sedimentary rocks account for approximately 5% of the crust. The upper 16 km of Earth.
Regardless of this low percentage, approximately 75% of all rocks exposed at the surface is sedimentary rock.
Factors leading to the formation of sedimentary rocks include;
Erosion and weathering
Transportation
Deposition
Lithification
Reference: Tarbuck and Lutgens Pages

3. Erosion and Weathering
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 happens 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

4. Mechanical weathering
Frost wedging

5. Erosion and Weathering
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. Chemical weathering oxidation hydrolysis Chemical weathering:
Processes that break rock components and
internal structures of minerals, making new
minerals
Most important processes:
dissolution
oxidation
hydrolysis
WATER: most important agent

7. Chemical weathering How? Dissolving minerals by a
Dissolution
Dissolving minerals by a
liquid agent (such as water)
How?
Many minerals are water-soluble
example: Halite (salt)
Adding acid (H+) increases corrosiveness
example: carbon dioxide and rain

8. Chemical weathering Example
Oxidation
Chemical reaction that causes loss of electrons
Example
Iron (Fe) + water (H2O)
oxygen (O) combines with Fe to form hematite (Fe2O3)
Oxidation decomposes important minerals:
mineral formula where
olivine (Mg,Fe)2SiO4 Earth’s mantle
pyroxene (Mg,Fe)SiO3 Earth’s mantle
hornblende Ca2(Fe,Mg)5Si8O22(OH)2 Continental rocks

9. Chemical weathering Decomposition of granite Hydrolysis
Granite (mainly quartz + potassium feldspar) +
carbonic acid (water + carbon dioxide)
Liberates potassium from feldspar - important plant nutrient
makes kaolinite - this left over mineral is clay
- very stable
- main inorganic part of soil
quartz - very stable, glassy appearance
- carried to sea: beach sand, sand dunes
- cements to form sandstone

10. Chemical weathering
Alterations
chemical weathering that causes physical changes to rocks
Rock corners are eroded more rapidly than sides
(more surface area at corners)

11. “ spheroidal weathering ”
Chemical weathering
Alterations
“ spheroidal weathering ”
T&L Figure 5.11

12. 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 being;
1) Water (rivers and groundwater)
2) Ice (glaciers)
3) Wind
Wind Blown Sand

13. 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.

14. 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. 1)
Shale
Sandstone
Limestone
Conglomerate
Silt and Clay
Sand
Lime (Calcite)
Round Pebbles
Compaction

15. 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. 2)
Sediment Particles
Cement
Water with dissolved minerals, (calcite or silica) pass through pore spaces