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Intro to Geology Exam 2 Review
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10/16/24, 10:37 Intro to Geology Exam 2AM Review
1
Sedimentary Rocks
Intro to Geology Lecture Notes Day
12 Intro to Geology Lecture Notes
Day 13
● Derived through the weathering and erosion of pre-existing rocks.
● Form by the transport and accumulation of fragmental materials (sediments)
or dissolved products, from a source region to a site of deposition. Can be
biogenic or inorganic.
● Sediments are constantly being produced at the Earth’s surface and
sedimentary deposits are widespread.
○ 75% of all rock outcrops on continents are sedimentary.
Different Types of Sedimentary Rocks:
● Clastic (detrital)
○ Are made from sediments that come from preexisting rocks that have been
weathered (broken down into smaller pieces), transported then <glued=
together (lithified).
○ Criteria: particle size and maturity
● Biochemical
○ Contains shells and bones/fossils
● Organic
○ Made from organic material (like coal)
● Chemical
○ Made from mineral crystals that formed from chemical or biological
precipitation from water at Earth surface temperatures.
○ Criteria: mineral composition
Weathering Processes
● Mechanical Weathering
○ Abrasion by flowing ice/water/wind
○ Pressure changes (exfoliation)
○ Frost wedging, wetting/drying
○ roots/burrows
○ Exfoliation and jointing
● Chemical Weathering
○ Reaction between minerals and water to form new minerals
and/or dissolved ions
○ Carbon dioxide dissolves in water to make a weak acid (carbonic)
○ Attacks and dissolves rocks
○ Carbonate is especially vulnerable.
Physical weathering works with chemicals to accelerate weathering by increasing
surface area. Ex: weathering granite and its structure after.
Goldich’s guide to Weathering
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,10/16/24, 10:37 Intro to Geology Exam 2
AM Review
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Basically the same list as Bowen’s Reaction Series
Temperature and Pressure Forms
Highest -> Lowest
● Olivine
● Pyroxene
● Amphibole
● Biotite
● K-feldspar
● Quartz
Stability at Surface
Highest -> Lowest
● Quartz
● K-feldspar
● Biotite
● Amphibole
● Pyroxene
● Olivine
Some minerals are more resistant to weathering than others ~ ex: green sand beaches =
weathered olivine
Lithification
Detrital (or <clastic=) Sedimentary Rocks
● Made up of fragments (clasts) of pre-existing rocks.
● In terms of composition, the most mature contain:
○ Clay minerals (weathering of feldspar)
○ Quartz (resistant to weathering)
● Presence of unstable minerals (mafics, feldspars) indicates immaturity:
○ Limited weathering
○ Rapid transport and deposition near source
● For detrital rocks, particle (clast) size:
○ Most basic distinguishing factor for naming rocks
● Classifying Clastic Sedimentary Rocks
○ Grain size and composition
○ Angularity and sphericity
○ Sorting (size of minerals)
○ Maturity (mineral grains)
○ Conglomerate (progress in lithification)
Chemical Sedimentary Rocks
● Made either by inorganic chemical or biological precipitation and lithification
1. Inorganic geochemical/crystalline
a. Evaporites
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,10/16/24, 10:37 Intro to Geology Exam 2
AM Review
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AM Review
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Review Questions
Goldich’s guide to weathering predicts that minerals formed first at depth (high T and
P) will be weatherab;e?
a. More
b. Less
Bonus: Remember we said Olivine beaches are rare because it weathers so rapidly? Is
Olivine a high or low temperature mineral?
Clastic sedimentary rocks composed of material that has been transported a long
distance (and/or a long time) will have all of the following characteristics except:
a. Rounded
b. Smaller
c. Poorly sorted
Which is an example of the chemical sedimentary rock?
a. Sandstone
b. Shale
c. Limestone
Which system is more mafic in nature?
a. Hawaiian volcanoes
b. Mt. St Helens
c. Crater lake, Oregon
Bonus: what are the names of the three types of volcanoes
~ Shield, Stratovolcano and Caldera
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