Ch. 6, p. 154:
#3, 5, 6, 9, 11, 14
3. What do
mud cracks tell about the environment of deposition of a sedimentary
rock?
- They indicate an environment
in which sediment got wet and then dried out. Such an environment
could be a flood plain, or tidal flat.
5. List the
clastic sediment particles in order of decreasing grain size.
- boulder >256 mm
cobble 64-256 mm
pebble 2-64 mm
sand
1/16 - 2 mm
silt
1/256 - 1/16 mm
clay
< 1/256 mm
6. How does a
sedimentary breccia differ in appearance and origin from a conglomerate?
- A breccia has angular
fragments, whereas a conglomerate has rounded rounded fragments.
In each rock, the fragments are roughly the same size
("gravels"). A breccia suggests sediment that didn't travel far
from its source. A conglomerate formed from sediment that probaby
traveled far from its source, giving it the opportunity to become
rounded.
9. What is
the origin of coal?
- Coal forms from the compaction of plant material that has not
completely decayed (pg. 142). Shallow swamps and bogs are typical
environments.
11. How do
evaporites form? Name two evaporites.
- Evaporites
form from crystals that precipitate during evaporation of water (water
with dissolved material in it), such as in a drying lake bed.
Rock
gypsum and rock salt are two evaporites.
14. Explain
two ways that cross-bedding can form.
- Cross-bedding
can form in a desert environment when sand dunes migrate.
Cross-bedding can also form in river channels when sand bars or ridges
migrate downstream.
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