1. Sedimentary rocks
Geology 101

2. Making sediment
Weathering = rock breakdown into smaller rock, or minerals, or chemicals
Sediment = result of weathering of rocks
Erosion = movement of sediment

3. Physical weathering
Physical: Breaking apart of rocks by a physical force
Also called “mechanical” weathering

4. Chemical weathering
A chemical reaction alters the composition of the minerals in the rocks (e.g., dissolving halite or altering feldspars into clay minerals)
Dissolving limestone leads to karst topography and caves

5. Caves are the product of varying water tables and limestone dissolution; cave formations (speleothems) are the result of calcite precipitation

6. Or a combination
Physical weathering may break up bedrock, then chemical weathering may break down the pieces into a soil

7. A quick word on soils
Soils are the weathered material at the surface that include both organic and mineral components
Soils differ due to the parent material, time of weathering and water content

8. Charles Darwin and soils
Among other work, Darwin in 1854 determined that earthworms, through their castings, produced about an inch of soil per year.
From this rate, he realized that a great deal of geologic time was needed even to produce a fertile soil.

9. Lithification
Sedimentary rocks become lithified when they are compacted then cemented

10. Classification of sed rx
Clastic = “broken”; sed rx made of broken-up parts of other rocks
Chemical sed rx are made from the precipitation of chemicals from water (“evaporites”) or the oxidation of chemicals
Biological sed rx are “born”; that is, they derive from the remains of creatures

11. Clastic sed rx Classified by dominant grain size
Scale: “boulder”, “cobble”, “pebble”, “granule”, “sand”, “silt”, “clay”
Texture and composition are secondary considerations (e.g., “shale”)

12. Texture: Grain roundedness
The roundedness (that is, how sharply defined the “corners” of individual grains are) is used to determine the transport distance
Proximal = near; distal = far

13. Texture: Grain sorting
The variation between coarse and fine particles in the sediment is called sorting
Sorting is used to infer transport distance; well-sorted sediments have come far

14. Layering in clastic sed rx
Layers are called beds, unless they are thin, in which case they are called laminae
Beds and laminae represent distinct depositional events, like floods

15. Chemical sed rx Evaporites: limestone, rock salt
Oxidation product: taconite (iron ore)

16. Biological sed rx
Plant remains: coal
Animal remains: limestone, chert

17. Water energy
The speed of the depositing medium (usually water) can be inferred from clastic and some other sed rx
This is because coarser grains settle first in a suspension

18. Depositional environment
Is the term given to the area where the sediment was originally deposited
Must be inferred from the rock identity

19. Sedimentary structures
Macroscopic features in the rock that allow you to infer climate, current direction or other attributes of the depositional environment

20. How to make cross-beds
And notice that you can infer the wind (or water direction as well!

21. Cross-beds allow you to infer the depositional environment; meter-scale cross-beds are eolian

22. Bioturbation – trace fossils
burrows get filled in with sediment
filled burrows can tell you which
way is up in a layer!