Review the Unit 9 Introduction
You have reached the end of Unit 9! Double-check the list of requirements on the Unit 9 Introduction page and the Course Calendar to make sure you have completed all of the activities listed there.
Review of the main topics and ideas you encountered in Unit 9.
Nice Bryce: Stories in Sediment
- Weathering makes small pieces and salts.
- After transport, they are deposited as sediment.
- Sediment is slowly changed to sedimentary rock.
- Transformation is NOT magic:
- Hard-water deposits cement grains together;
- Squeezing compacts grains;
- Recrystallization as new minerals grow creates interlocking grains.
- Clasts make clastic rocks; dissolved salts make precipitates (rock salt, Death Valley borax).
- Limestone is both--precipitated as shells, which are clasts.
- Subclassify clastic rocks by size:
- Clay (tiny) makes claystone, also called shale;
- Silt (small) makes siltstone, sand makes sandstone;
- Cobbles make cobblestone, boulders make boulderstone, usually call both conglomerate.
Environment is Evident
- Can tell environment in which sediment or sedimentary rock was deposited:
- Sand dunes, lizard tracks? Desert
- Quiet-water muds, fish fossils? Lake
- Corals and shells? Coastal Reef
- Takes lots of study to know the rocks that different environments produce, but now is well-known.
May I Take Your Order?
- Something must exist before it can be moved or cut; clastic rocks are younger than the clasts, and faults younger than faulted rocks.
- Layers initially nearly horizontal (mass wasting flattens steep clastic layers).
- Layers on top are younger than those below (Principle of Superposition).
- After hardening, layers may be stood up or turned over, but many “up” indicators tell us this happened.
Getting Into “Up” Indicators
- Mud cracks, footprints, raindrop imprints go down into mud;
- Tops of slightly slanting sand-dune layers are eroded by wind;
- Shells on beach are flipped into stable hollow-side-down position;
- Bubbles rise toward tops of lava flows.
Nothing Succeeds Like Succession
- Can put rocks in order;
- Puts fossils in order--“Law” of Faunal Succession;
- Gives geologic time scale:
- Cenozoic=New Life, Age of Mammals
- Mesozoic=Middle Life, Age of Dinosaurs
- Paleozoic=Old Life, Age of Shellfish
- Precambrian=really old, Age of Algae
Reminder - Exercise #4 is due and Exercise #5 opens this week. See Course Calendar for specific dates and times.
Following are some supplementary materials for Unit 9. While you are not required to review these, you may find them interesting and possibly even helpful in preparing for the quiz!
Comments or Questions?
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