1. Lithification and Classes
Sedimentary Rock
Lithification and Classes

2. The Rock Cycle What processes produce sediment?
What types of rocks are the sources of sediment?
What processes produce sedimentary rocks?

3. Sedimentary Rocks
Sediments are produced by the deposition of existing rocks – any type of rock - that have undergone weathering and erosion
These sediments can then be compacted and cemented into sedimentary rock

4. Deposition Deposition – settling of weathered and eroded materials
Commonly in a water environment (but not always)
Environment of deposition is related to the type of sediments that are deposited
For example – small sized sediments are deposited very slowly since they need very little energy to carry them
Therefore sediments like these will only be deposited in deep and/or still water (lakes)

5. Walther’s Law
Walther’s Law relates environment of deposition of several rock units
Can be used to correlate sea transgressions

6. Sediments Deposited sediments have porosity
Porosity measures the gaps between the particles
Large, irregular shaped particles have a higher porosity

7. Sorting
Depending on the type of erosion, sediments will be either well or poorly sorted.
Well sorted sediments all have (nearly) the same size
Poorly sorted materials have very different sized sediments
Very poor sorting is a good indication of glacially formed sediments!

8. Sorting
Poorly sorted
Well sorted

9. Compaction
After sediments have been deposited and buried for a long time, they are sometimes compacted
Compaction is due to the weight of the overlying material
Removes any trapped water from the sediment and closes the pore space

10. Cementation
Cementation occurs when minerals “cement” the sediments together into a rock
Common cements are silica, iron oxide, and carbonates
VERY LONG process – can take thousands of years!
Entire process of weathering, erosion, deposition, compaction, and cementation is referred to as Lithification

11. Classes of Sedimentary Rocks

12. Clastic Sedimentary Rocks
Clastic sedimentary rocks form from the compaction and cementation of particles that do not dissolve in water
Silica is a major component and is often the cement
Classified based on their texture (grain size) and composition (minerals)

13. Clastic Sedimentary Rocks
Textural classification compares grain sizes and is based on the Wentworth Scale of Particle Sizes
Particles over 2 mm are called “gravel”
Other categories are sand (2 mm – 1/16 mm), silt (1/16 mm – 1/256 mm) and clay (less than 1/256 mm)

14. Clastic Sedimentary Rocks
The largest grained sedimentary rocks are further divided based on the shape of the gravel
Rounded gravel – conglomerates
Angular gravel – breccia
Different shapes indicate the length of time it took for cementation
Breccias form relatively quickly – no time for gravel to become weathered

15. Clastic Sedimentary Rocks

16. Clastic Sedimentary Rocks
In order of decreasing grain size, clastic sedimentary rocks include:
Conglomerate/breccia
Sandstone
Siltstone
Shale
Clastics are then described by the composition
For example – a Red Shale contains Iron; an Arkose Sandstone contains feldspar

17. Clastic Sedimentary Rocks

18. Clastic Sedimentary Rocks
As noted earlier, the environment of deposition determines the type of rock formed
Conglomerates/breccias are formed in high-energy environments (rivers, oceans, glacier deposits)
Sandstones are formed in moderate energy environments (mature rivers, beach, desert)
Siltstone form in low energy environments (old rivers, estuaries, lakes, nearshore)
Shales form in very low energy environments (deep lakes, offshore, flood plains, deltas)

19. Clastic Sedimentary Rocks

20. Clastic Sedimentary Rocks
Geologists use the type of rock present to reconstruct the past
For example – when sandstone is present, it indicates a former beach (or desert) environment
Geologists then use other clues (fossils or sedimentary structures) to narrow the possibilities

21. Non-clastic Sedimentary Rock
Non-clastic rocks are the result of chemical or biochemical processes
Chemical processes include evaporation and chemical precipitation
Chemical precipitation is where a solid forms spontaneously in a liquid
Biochemical processes include the compaction of living materials (shells, leaves, etc)

22. Non-clastic Sedimentary Rock
Chemical sedimentary rocks include
Halite (Rock salt)
Gypsum (Rock gypsum)
Chert
Limestone
Dolostone
Biochemical sedimentary rocks include:
Chalk
Coquina
Coal

23. Non-clastic Sedimentary Rock

24. Non-clastic Sedimentary Rock

25. Sedimentary Structures
Features of the rock unit that were produced as it formed
Very useful in determining the environment of deposition!
Includes:
Layering
Surface Structures

26. Sedimentary Structures - Layering
Very obvious feature!
Thickness of the layers indicates the stability of the environment
Thinner layers are from a rapidly changing environment
Layers can be of different sized sediments, different colored sediments, or different types of sorting

27. Sedimentary Structures - Layering
Cross-Bedding occurs where there was frequent changes in wind/water movement
Common in beach, river, and dune deposits

28. Sedimentary Structures - Layering
Graded Bedding occurs when sediment size changes from large to small
Indicates a delta environment

29. Sedimentary Structures – Surface Structures
Surface structures indicate water currents, climate, and wind directions
Surface structures include:
Ripple marks
Mud cracks
Fossils
Rain drops

30. Sedimentary Structures – Surface Structures