1. Principles of Geology
Mr. Halfen
Jan. 2017

2. Basics The geologists’ history book is called the “geologic record.”
A great example of this is the Grand Canyon.

3. Principle of Uniformitarianism
The principle of uniformitarianism states that the processes we see operating on the Earth’s surface have occurred in the past and are responsible for the geologic record.

4. Principle of Original Horizontality
The principle of original horizontality states that sediments are laid flat (horizontal).

5. Principle of Superposition
The principle of superposition states that the oldest rock are found at the bottom of the geologic record and the youngest are at the top.

6. Principle of Lateral Continuity
The principle of lateral continuity states that sediments are laid continuously in all direction within a basin.

7. Law of Cross-Cutting Relationships
The law of cross-cutting relationships states that a rock that cuts through (or intrudes) another layer is younger than the layers containing it.

8. Principle of Fossil Succession
The principle of fossil succession states that fossils can be used to date rocks since fossils of a given age are only found in rocks of that age anywhere in the world.

9. Weathering

10. Mechanical (Physical) Weathering
Weathering – the breaking apart of rocks into fragments or changing by chemical reaction
Exfoliation – breaking off of rock in sheets due to removal of overlying layers of rock.

11. Mechanical (Physical) Weathering
Gravity – breaking off rock due to stresses caused by gravity

12. Mechanical (Physical) Weathering
Tree roots – As trees grow their penetrate through cracks in the rock and break apart the rock

13. Mechanical (Physical) Weathering
Temperature Changes – constant changes in temperature can cause rocks to slowly split apart; this may also be involved with exfoliation and frost action

14. Mechanical (Physical) Weathering
Animal activity – the holes and burrows dug by animals allow other weathering mechanisms to work more efficiently.

15. Chemical Weathering
Dissolution – the dissolving of minerals by water or acids

16. Chemical Weathering
Hydrolysis – the chemical reaction of water with minerals in a rock to make new minerals

17. Chemical Weathering
Oxidation – the chemical reaction of oxygen with minerals in a rock (e.g., rusting of metals)

18. Erosion

19. Agents of Erosion
Erosion – the movement of weathered rock materials from one location to another

20. Erosion by Wind Wind erosion typically moves only small particles.
The formations usually thick are made of particles of very similar size.

21. Erosion by Water Water can move particles of almost any size.
Deposits on land in lakes and near rivers tend to be made of many different sizes of particles.
Near-shore ocean deposits tend to be sorted by size, with larger closer to shore.

22. Erosion by Ice Glaciers move particles of any size.
The deposits have particles of any size from clay to boulders.

23. Erosion by Gravity
When rock is no longer supported by underlying layers, gravity can pull down large amounts quickly.

24. Deposition

25. Deposition
Deposition – the settling out of sediments from the agents of erosion
Sediments are usually deposited in water but glaciers, wind and gravity will deposit on dry land as well.

26. Paleoenviroments
Paleoenvironments – environments where sediments were deposited in the past
Examples of paleoenvironments:
Fluvial (streams and stream banks)
Deltaic (mouth of river)
Desert
Glacial
Shallow marine (near the beach in the ocean)
Lacustrine (lakes and ponds)
Beach
Turbidite (continental slope)
Pelagic (deep ocean)

27. Compaction and Cementation

28. Compaction During compaction, three things happen:
Grains are moved closer together.
Air pockets between the grains are shrunk or eliminated.
Excess water is squeezed out.

29. Cementation
During cementation the grains of the sediment are “glued” together.
The most common cementing agents are iron oxide and calcium carbonate.