1. Definition, Formation, Classification
Sedimentary Rocks
Definition, Formation, Classification

2. Sedimentary Rocks: Outline
Definition of a Sedimentary Rock
How sedimentary rocks “fit in” the Rock Cycle
Formation of a Sedimentary Rock
Sediments and How They’re Made
Lithification
Classification of a Sedimentary Rock
Three main types (and some subtypes)

3. Revisit the Rock Cycle

4. Sedimentary Rocks: Definition
Sedimentary rocks usually come from SEDIMENTS
E.g., mud, sand, pebbles broken from previous rocks
Sediments are pressed into layers
“strata” (singular “stratum”)

5. Sedimentary Rocks: Formation
Sediment usu. comes from two processes teaming up:
Weathering
Erosion
Weathering weakens a rock chemically or physically
Erosion tears away at a rock, starting to move sediment

6. Sedimentary Rocks: Weathering vs. Erosion

7. Sedimentary Rocks: Weathering vs. Erosion
ANOTHER JOEL BARTON ORIGINAL

8. Sedimentary Rocks: Formation Ctd.
Once sediments are settled, lithification (making a rock) begins
Can involve two main processes:
Compaction: sediments are pressed together by weight, and water is forced out
Cementation: minerals deposit out of water and “cement” together sediments
(Pictured in next slide)

9. Sedimentary Rocks: Formation Ctd.

10. Types of Sedimentary Rocks: Clastic
Clastic rocks
from broken pieces of other rock (as was just described)
Further classified according to their pieces (“clasts”)

11. Clastic Rocks ctd.
Conglomerates have large, round, pieces (see previous slide)
Poorly sorted
Breccias have large, angular pieces
Clastic rocks from smaller pieces can be sandstones, mudrocks, and more
Usu. well sorted

12. Organic Rocks Form directly or indirectly from living material
Despite our definition of minerals
Example: limestone is calcium carbonate from the shells of dead sea organisms (clams, etc.)

13. Chemical Rocks Form by chemical processes (not regular compaction)
“Evaporites” form when water evaporates, leaving just minerals
Ex: gypsum, halite, and even some limestone are from evaporating water

14. Check yourself
What are some features of a rock that might indicate it is a sedimentary rock?
In a clastic rock, why are some poorly sorted and others well sorted? (Just think on this.)
What are two ways that limestone can form?
How are chemical rocks different from other sedimentary rocks?