Geology Reference
In-Depth Information
Lithifi cation involves compaction and cementation,
which convert sediment into sedimentary rock. Silica
and calcium carbonate are the most common chemical
cements, but iron oxide and iron hydroxide cements are
important in some rocks.
Detrital sedimentary rocks consist of solid particles
derived from preexisting rocks. Chemical sedimentary
rocks are derived from substances in solution by inor-
ganic chemical processes or the biochemical activities of
organisms. Geologists also recognize a subcategory called
biochemical sedimentary rocks.
Sedimentary facies are bodies of sediment or sedimentary
rock that are recognizably different from adjacent sedi-
ments or rocks.
Some sedimentary facies are geographically widespread
because they were deposited during marine trans-
gressions or marine regressions.
Sedimentary structures such as bedding, cross-bedding,
and ripple marks commonly form in sediments when, or
shortly after, they are deposited.
Geologists determine the depositional environments of
ancient sedimentary rocks by studying sedimentary
textures and structures, examining fossils, and
making comparisons with present-day depositional
processes.
Intense chemical weathering is responsible for the
origin of residual concentrations, many of which
contain valuable minerals such as iron, lead, copper,
and clay.
Many sediments and sedimentary rocks, including sand,
gravel, evaporites, coal, and banded iron formations, are
important resources. Most oil and natural gas are found
in sedimentary rocks.
■
■
■
■
■
■
■
■
Important Terms
bed (p. 157)
biochemical sedimentary rock
(p. 153)
carbonate rock (p. 153)
cementation (p. 149)
chemical sedimentary rock (p. 153)
chemical weathering (p. 138)
compaction (p. 149)
cross-bedding (p. 157)
depositional environment (p. 148)
detrital sedimentary rock (p. 151)
differential weathering (p. 135)
erosion (p. 134)
evaporite (p. 154)
exfoliation dome (p. 135)
fossil (p. 157)
frost action (p. 135)
graded bedding (p. 157)
hydrolysis (p. 140)
laterite (p. 144)
lithifi cation (p. 149)
marine regression (p. 157)
marine transgression (p. 156)
mechanical weathering (p. 135)
mud crack (p. 157)
oxidation (p. 140)
parent material (p. 134)
pedalfer (p. 143)
pedocal (p. 143)
pressure release (p. 137)
regolith (p. 142)
ripple mark (p. 157)
salt crystal growth (p. 135)
sediment (p. 147)
sedimentary facies (p. 156)
sedimentary rock (p. 147)
sedimentary structure (p. 157)
soil (p. 142)
soil degradation (p. 146)
soil horizon (p. 143)
solution (p. 139)
spheroidal weathering (p. 141)
strata (p. 157)
talus (p. 135)
thermal expansion and contraction
(p. 135)
weathering (p. 134)
Review Questions
1. Which one of the following is a chemical weathering
process?
a. _____ lithifi cation;
b. _____ oxidation;
c. _____ frost wedging;
d. _____ pressure release;
e. _____ compaction.
2. The type of soil found in the semiarid to arid South-
west United States is
a. _____ breccia;
b. _____ laterite;
c. _____ pedocal;
d. _____ regolith;
e. _____ detrital.
3. Which one of the following sedimentary structures
would allow you to determine ancient current directions?
a. _____ cross-beds;
b. _____ mud cracks;
c. _____ evaporites;
d. _____ wave-formed ripples;
e. _____ caliche.
4. Spheroidal weathering takes place because
a. _____ thermal expansion and contraction are so
effective;
b. _____ aluminum oxides are nearly insoluble;
c. _____ oxidation changes limestone to dolostone;
d. _____ rounding takes place rapidly during transport;
e. _____ corners and edges of stones weather faster
than fl at surfaces.
Search WWH ::
Custom Search