1. Sedimentary Rocks
Earth Science

2. Sedimentary Rocks
Sediments – pieces of solid material that have been deposited on Earth’s surface by wind, water, ice, gravity, or chemical precipitation.
When sediments become cemented together, they form sedimentary rocks
The formation of sedimentary rocks begins when weathering and erosion produce sediments

3. Sedimentary Rocks Weathering
Chemical weathering occurs when the minerals in a rock are dissolved or otherwise chemically changed.
Physical weathering occurs when fragments simply break off the solid rock along fractures or grain boundaries. During physical weathering, minerals remain chemically unchanged

4. Sedimentary Rocks Weathering
Weathering produces rock and mineral fragments known as clastic sediments.
Clastic sediments range in size from huge boulders to microscopic particles.
Clastic sediments usually have worn surfaces and rounded corners caused by physical abrasion during erosion and transport.

5. Sedimentary Rocks Particle Size Sediment Rock Conglomerate 2-0.062 mm
Classification of Clastic Sediments
Particle Size
Sediment
Rock
>256 mm mm
64-2 mm
Gravel }
Conglomerate mm
Sand
Sandstone mm
Silt
Siltstone
< mm
Clay
Mudstone or shale
Boulder
Cobble
Pebble

6. Sedimentary Rocks Erosion and Transport
Erosion - the removal and movement of surface materials from one location to another.
Four main agents of erosion: wind, moving water, gravity, and glaciers.
Eroded materials are almost always carried downhill

7. Sedimentary Rocks Erosion and Transport
Deposition – when sediments are laid down on the ground or sink to the bottoms of bodies of water
Sediments in wind and water tend to form layers when deposited – largest particles at the bottom
Glaciers and landslides, however, move all materials with equal ease

8. Sedimentary Rocks Burial
Most sediments are ultimately deposited on Earth in depressions called sedimentary basins
Some sedimentary basins can contain layers of sediment over 8 km thick
As more sediment is deposited in that area, the bottom layers are subject to increasing pressure and temperature

9. Sedimentary Rocks Lithification
The increasing temperature and pressure cause lithification.
Lithification is the physical and chemical processes that form sediments into sedimentary rocks.

10. Sedimentary Rocks Lithification
Begins with compaction. The weight of overlying sediments forces the sediment grains closer together.
For example: water is squeezed out of layers of compacted mud.
Some sediments, such as sand, resist lithification due to it being well-compacted during deposition

11. Sedimentary Rocks Cementation
Sediments that are buried 3-4 km deep experience temperatures that are high enough to start the chemical changes that cause cementation.
Cementation occurs when mineral growth cements sediments together into solid rock.

12. Sedimentary Rocks Cementation Two common types of cementation:
First type occurs when a new mineral grows between sediment grains as dissolved minerals precipitate out of groundwater. (Calcite growing between quartz grains)
Second type occurs when existing mineral grains grow larger as more of the same mineral precipitates from groundwater and crystallizes around them. (quartz crystallizing around quartz grains)

13. Sedimentary Rocks Features
Bedding – the horizontal layering of sedimentary rocks
Bedding can range from a millimeter-thick layer of shale to a sandstone deposit several meters thick
The type of bedding depends on the method of transport.

14. Sedimentary Rocks Features Graded Bedding
Bedding in which the particle sizes become progressively heavier and coarser towards the bottom layers
Often observed in marine sedimentary rocks that were deposited by underwater landslides

15. Sedimentary Rocks Features Cross-bedding
Formed as inclined layers of sediment move forward across a horizontal surface.
Small-scale cross-bedding can be observed at sandy beaches and along sandbars in streams and rivers.
Most large-scale cross-bedding is formed by migrating sand dunes

16. Sedimentary Rocks Evidence of past life
Fossils are the preserved remains, impressions, or any other evidence of once-living organisms.
When an organism dies, it may be buried before it decomposes
If its remains are further buried without being disturbed, it might be preserved as a fossil.

17. Types of Sedimentary Rocks
Classification of sedimentary rocks depends on how they were formed.
Three main types: clastic, organic, and chemical

18. Types of Sedimentary Rocks
Clastic sedimentary rocks
The most common type of sedimentary rock
Formed from the abundant deposits of loose sediments found on Earth’s surface
Clastic sedimentary rocks are further classified according to the sizes of their particles.

19. Types of Sedimentary Rocks
Coarse-grained clastics
Sedimentary rocks consisting of gravel-sized rock and mineral fragments
Conglomerates
coarse-grained sedimentary rocks that have rounded particles
Gravel is transported by high-energy flows of water.
During transport, gravel becomes abraded and rounded as the particles scrape against one another

20. Types of Sedimentary Rocks
Breccias
Coarse-grained sedimentary rocks that have angular particles
The sediments from which they formed did not have time to become rounded.
This suggests that the particles were transported only a short distance and deposited close to their source.

21. Types of Sedimentary Rocks
Medium-grained clastics
Sedimentary rocks that contain sand-sized rock and mineral fragments
When medium-sized sediments are buried and lithified, sandstone is formed.
Sandstone has relatively high porosity – the percentage of open spaces between grains in a rock
Sandstone often holds underground oil, natural gas, or groundwater deposits due to its high porosity.

22. Types of Sedimentary Rocks
Fine-grained clastics
Sedimentary rocks consisting of silt and mud
Siltstone, mudstone, and shale
Siltstone is mostly composed of silt-sized grains
Shale is mostly composed of silt and clay-sized particles
Shale has very low porosity – it usually hinders the movement of underwater liquids.

23. Types of Sedimentary Rocks
Chemical sedimentary rocks
During chemical weathering, minerals can be dissolved and carried into lakes and oceans.
As water evaporates, the minerals are left behind.

24. Types of Sedimentary Rocks
Also, when the concentration of dissolved minerals in a body of water reaches saturation, crystal grains precipitate out of solution and settle to the bottom
The layers of chemical sedimentary rocks that form as a result of this process are called evaporites
The three most common evaporites are calcite, halite, and gypsum

25. Types of Sedimentary Rocks
Organic sedimentary rocks
Formed from the remains of once-living things
The most abundant organic sedimentary rock is limestone.
Formed from the shells of ancient shell fish
Coal is also an organic sedimentary rock
Formed from the remains of ancient plants