1. Earth Science Chapter 3 Section 3
Sedimentary Rocks
Earth Science Chapter 3 Section 3

2. Introduction
Most of the earth’s surface is covered by sedimentary rock.
Sedimentary rock provides geologists with a lot of information about the history of the earth.

3. Formation of Sedimentary Rock
Weathering, Erosion, and Deposition
Weathering: break down of rock
Chemical: change in composition of structure
Mechanical: physical break down or rock
Erosion: movement of sediment
water, wind, ice, and gravity
Water is the most powerful agent
Deposition: erosion stops and sediments are laid down
Larger sediments are deposited first
The larger the sediment size the more energy required to carry it

4. Compaction and Cementation
Lithification: combining of sediment into rock
Compaction: packing of sediment
Cementation or lithification takes place when dissolved minerals are bound together. This normally occurs in areas where there was once water.

5. Classification of Sedimentary Rocks
Clastic Sedimentary Rocks
Sediments from preexisting rocks
Most common minerals are feldspars and quartz
Conglomerate and breccia: larger visible sediments
Conglomerate: rounded
Breccia: angular
Sandstone: sand sized grains
Shale: small fine sediments

6. Chemical Sedimentary Rocks
Dissolved sediments that precipitate from water
Form when water evaporates
Rock salt forms from halite
Limestone forms from calcite

7. Organic Sedimentary Rocks
Biochemical rocks that form from biological processes
Form when an organism dies and their body is broken down into sediment
Organic limestone made from shells
Coal forms from the remains of swamp plants

8. Sedimentary Rock Features
Strata: layering of sedimentary rock
Each layer represents a period of deposition
Layers closer to the surface are younger than the deeper layers (law of superposition)
Determining which layer is younger or older is called relative dating
Fossils: remains or trace of ancient life
Fossils can only be found in sedimentary rock
Fossils form when organisms are quickly buried

9. Ripple marks: rock has formed in the presence of moving water
Mud cracks: rock has formed as sediments are drying.

10. Stratification of Sedimentary Rock
Ripple Marks
Mud Cracks