Chapter 5 – Sediment and Sedimentary
Rocks
Sedimentary rocks are composed of sediment.
Sediment forms at or near earth’s surface
through the processes of weathering,
transportation, deposition, and lithification.
Importance of sedimentary rocks include:
Energy resources
Petroleum
Uranium
Coal
Sedimentary Resources
Importance of sedimentary rocks include:
Mineral resources
Limestone: cement
Rock salt: salt
Rock gypsum: plaster
Importance of sedimentary rocks include:
Environment of deposition
Oceans and seas
Lakes and swamps
River valleys and flood plains
Deltas
Sand dunes
Every Rock Tells a Story
Because sedimentary rocks form at earth’s
surface, they tell the geologist what was
happening on the surface when that rock was
deposited. The rocks tell the story of Earth.
For example . . .
Limestone generally only grows in sea water.
If a geologist finds limestone in Kansas, the
geologist concludes that Kansas was once
underwater.
Sedimentary Rocks
Sedimentary rocks are composed of
sediment.
Sediment can be either clastic (pieces)
or chemical.
Clastic sediment is pieces of preexisting rock like gravel,
sand, silt and clay.
Chemical sediment is chemicals
dissolved in water.
Sediment
Sediment comes in two varieties.
Sediment can be either clastic (pieces)
or chemical.
Clastic sediment is pieces of preexisting rock like gravel,
sand, silt and clay.
Chemical sediment is chemicals
dissolved in water.
Clastic Sediment
Clastic sediment forms from the
mechanical, physical and chemical
breakdown of rock.
The process of breaking rock down into
smaller pieces aids further breakdown by
chemical weathering.
Chemical Sediment
Chemical sediment forms by the chemical
dissolution and alteration of rocks at or
near earth’s surface.
Chemical sediment is transported by
stream waters to lakes and the oceans.
Weathering Chapter 15
Mechanical Weathering
Frost wedging
Alternate freezing and thawing
Temperate mountainous climates
9% expansion as water freezes
Up to 80,000 pounds per square
inch pressure
Talus Slope
Generally form a large pile of rock at the
base of mountains called talus slope.
Unloading
As the weight of overlying rock is
weathered and eroded away the rock
expands and produces fractures (or joints)
parallel to the topography. Exfoliation.
Joints
Vertical joints (cracks without
displacement) form by expansion and
contraction.
Joints from Top with Striations
Columnar joints with glacial striations.
Devils Postpile National Monument.
Thermal Expansion Joints
Results from
the daily
cycle of
temperature
changes
producing
daily expansion and
contraction.
Most
prominent in
hot deserts.
Biological Activity
Plants and
burrowing
animals cause
much joint
expansion.
Biological Activity
The greatest
mechanical
weathering is
now produced
by
catepillars.
Biological Activity
The greatest
mechanical
weathering is
now produced
by
catepillars.
Mechanical Weathering Enhances Chemical
Weathering
As mechanical weathering progresses, it
enhances chemical weathering by increasing the
surface area to volume ratio.
Comparison of Surface Area to Volume Ratio
The volume of a cube 2 cm on a side is:
2 x 2 x 2 = 8 cm3
The surface area of one side is 2 x 2 = 4 cm
There are six sides, so the total surface area is
4 cm x 6 = 24 cm2
Comparison of Surface Area to Volume Ratio
If the 2 cm cube is bisected by 3 joints how
does this affect the surface area?
Each face of the 1 cm cube has a surface area
of 1 cm x 1 cm = 1 cm2. There are six sides to
each cube so the surface area would be 6 x 1
cm2 = 6 cm2. But there are a total of 8 little
cubes so the total surface area is now
6 cm2 x 8 = 48 cm2
Compare this to the previous surface area of 24
cm2. The surface area has doubled!
Chemical Weathering
The most important chemical causing chemical
weathering is H2O-the universal solvent.
However H2O in contact with CO2 gas in the
atmosphere reacts to form carbonic acid.
H2O + CO2 = H2CO3 with a pH of about 5.7; a
weak acid.
Dissolution Weathering
When water precipitates (rains) on halite it will
dissolve. NaCl + H2O = Na+ + Cl- + H2O
Cave Formation (Karst Topography)
When carbonic acid infiltrates into limestone or
marble rock joints it begins to dissolve the
calcite. CaCO3 + H2CO3 = Ca+ + HCO3- + CO2
Solid rock dissolves into calcium ions,
bicarbonate ions and carbon dioxide gas. All
dissolved in water which carries these products
away leaving a cave.
Cave roofs collapse to form cenotes or sinkholes.
Cave
When.
Oregon Cave
When.
Hydrolysis of Granite 1
The most abundant rock in earth’s crust is
granite. The most abundant mineral in
granite is feldspar. Feldspar hydrolyses to
kaolinite clay + bicarbonate + soluble silica.
Hydrolysis of Granite 2
Feldspar + Carbonic acid = Kaolinite clay +
Potassium + Sodium + Calcium + Soluble
Silica (SiO2)
Soluble silica is important because it
becomes the silica cement that makes sand
into a sandstone.
White Sandstone
sandstone.
Hydrolysis of Granite 3
This weathering of feldspar in granite
then releases the quartz grains to form
sand that will become sandstone. The
kaolinite clay becomes the clay mineral
that makes shale.
Shale is the most abundant sedimentary
rock.
Oxidation of Biotite
Biotite mica in granite reacts with
carbonic acid to make kaolinite clay and
releases iron that can become the
hematite cement that binds sand grains
together to form sandstone.
Red Sandstone
sandstone.
Factors that influence Weathering
Minerals present
Bowen’s Reaction Series
Available liquid water
Water is the most important
weathering agent
Tropics
Antarctica
Temperature
As temperature rises rate of
chemical reactions increases.
Bowen’s Reaction Series
Minerals present
Bowen’s Reaction Series
Available liquid water
Water is the most important
weathering agent
Tropics
Antarctica
Temperature
As temperature rises rate of
chemical reactions increases.
Liquid Water
Minerals present
Bowen’s Reaction Series
Available liquid water
Water is the most important
weathering agent
Tropics
Antarctica
Temperature
As temperature rises rate of
chemical reactions increases.
Cold and Dry Weathering
Minerals present
Bowen’s Reaction Series
Available liquid water
Water is the most important
weathering agent
Tropics
Antarctica
Temperature
As temperature rises rate of
chemical reactions increases.
Sedimentary Rock Pictures
Gravel clasts.
Chemical
sedimentary rock.
Clastic Sedimentary Rocks
Clastic sediment, composed of rock and/or
mineral fragments from pre-existing rocks.
A convenient method to classify clastic
material is by its clast (particle) size.
Clastic Sedimentary Rock Classification
Size Range (mm)
Particle Name
Rock Name
> 256 mm
Boulder
Conglomerate
64-256 mm
Cobble
4-64 mm
Pebble
2-4 mm
Granule
(rounded clasts)
Breccia
(angular clasts)
Quartz Sandstone
1/16 – 2 mm
Sand
Arkose Sandstone
Graywacke Sandstone
1/256 – 1/16 mm
Silt
Siltstone
< 1/256 mm
Clay
Claystone
A rock that is about 1/3 silt
and 2/3 clay and is fissile
(laminated)
Shale
Sedimentary Environments - Shale
Shale
Most abundant sedimentary rock
Deposition in quiet, non-turbulent water.
Particles tend to form in thin lamellae.
Deep sea environment or far away from
high energy.
Offshore and away from high-energy
surf zone.
Shale Pictures
Shale Importance
The dark colors of shale usually are
caused by the deposition of small
amounts of incompletely decayed organic
material.
Oil shale
Methane shale
Sedimentary Environments – Quartz
Sandstone
Quartz Sandstone: Quartz is highly
resistant to weathering so it is what is
left over when all the other common
minerals have weathered away. Mature.
Traveled the farthest.
Sand dunes.
Beach sand.
Sedimentary Environments – Arkose
Sandstone
Arkose Sandstone: Contains roughly
equal amounts of quartz and feldspar.
Less mature than quartz sandstone and
the presence of feldspar indicates
deposition closer to source area
(mountains).
Much of the sand size material in the
upper portions of the Santa Ana River
near the the San Gabriel and San
Bernardino Mountains is akose.
Arkose Sandstone Picture
Sedimentary Environments – Graywacke
Sandstone
Graywacke Sandstone: Usually dark
colored rock composed of quartz,
feldspar, rock fragments, mafic minerals
and a matrix of fine clays and silts. Very
immature.
Common as turbidity currents fromed
from submarine landslides associated
with the edge of the continental shelf or
trenches.
Graywacke Sandstone Picture
Sandstone textures
Two important textures in sandstones.
Rounding: the degree of rounding
determines the transportation distance
with more rounding indicating a longer
transport distance.
Sandstone Textures continued
Sorting: the range of clast sizes. Usually
determined by the means of
transportation.
Well sorted = most clasts are the
same size.
Poorly sorted = wide range of
particle sizes.
Sandstone Textures continued again
Three transporting agents.
Wind: very fine sorting. All sand
grains nearly the same size.
Water: intermediate sorting.
Ice: very poor sorting. Clay size to
boulders transported together.
Sedimentary Environments – Conglomerate
Conglomerates form in high energy
environments.
By floods
Near mountains
Steep terrains
Usually poorly sorted.
Nine foot boulder in back yard.
Angular clasts indicate deposition very
near source. Breccia.
Sedimentary Environments – Conglomerate
continued
Rock fragments (clasts) may be used to
determine the source area.
Polka-Dot Granite of Joshua Tree
National Park
Conglomerate Picture
Lithifying Agents
Conglomerates and sandstones are
lithified by cementation. Natural
cements dissolved in groundwater
precipitate minerals that end up
transforming sediment into rock.
Three cements.
Quartz
Hematite
Calcite
How could you distinguish
these?
Chemical Sedimentary Rocks
Cemical sedimentary rocks form from
the precipitation of chemicals from
water.
Salt encrusted iguana. Ready for serving?
Oceans Salts
Ocean Ions (Salts) Abundance
Chlorine (Cl-)
Sodium (Na+)
Sulfate (SO42-)
Magnesium (Mg2+)
Bicarbonate (HCO3-)
Calcium (Ca2+)
Potassium (K+)
Precipitation of these salts governed by
chemical laws. Calcium carbonate is closest to
the solubility limit despite low abundance.
Ocean Salt Precipitation Order
Calcite (CaCO3) - 50% water evaporated
Gypsum (CaSO4  2H2O) - 80% water
evaporated
Halite (NaCl) - 90% water evaporated
What would be the order of salt
precipitation as the Mediterranean Sea
evaporated?
Limestones
Little sea organisms have evolved
protective armor against predators.
What to make shells out of?
calcium carbonate (calcite or
aragonite-a polymorph)
Many limestones are composed of the
shells of sea organisms.
Limestone Reef
Reef Limestone Requirements
Little sea organisms.
What do they require?
Warm water (>18° C 22-28 ° C
optimum) - solubility
Shallow water (bottom of food chain
are plants that require sunlight)
- <~200 ft water depth; 1% light
left
Little clastic sediment - covers
plants
Warm Water Locations
.
Great Barrier Reef
.
Great Barrier Reef
.
Limestone Types - Fossiliferous Limestone
A limestone that contains fossils.
.
Limestone Types - Coquina
A limestone that is composed of broken shell
fragments. Anastasia Formation, Florida. Beach
environment.
.
Limestone Types - Oolitic Limestone
Composed of limestone and clay spheres. Typical
of lagoons inbetween barrier island and
mainland.
.
Limestone Types - Chalk
White Cliffs of Dover.
.
Limestone Types - Chalk
Single cell coccolith shell.
.
Limestone Types - Chalkboard
Chalkboard slate. And you think you have it
tough.
.
Limestone Types - Travertine Fly Geyser
As calcium carbonate water cools at the surface
calcite precipitates as layered travertine.
.
Limestone Types - Travertine - Havasupai
Grand Canyon, Arizona.
.
Limestone Types - Travertine - Pamukkale
Turkey.
.
Limestone Types - Dolomite
Limestone rock reacts with magnesium in warm
ocean waters.
CaCO3 + Mg2+ = (Ca,Mg)CO3 + Ca2+
Since the magnesium ion is smaller than the
calcium it replaces, the volume is decreases
during dolomitization which increases porosity.
A good reservoir for petroleum. Kuwait.
.
Limestone Types - Dolomite Qatar
.
Other Biochemical Sediment
Chert - a rock composed of single cell shells of
radiolaria. Typically deep sea sediement.
.
Other Biochemical Sediment
Ribbon chert in central California.
.
Other Biochemical Sediment - Diatomite
A rock formed of diatoms.
.
Other Biochemical Sediment - Diatomite
Uses
Fuller’s Earth: Removing sheep wool grease
Swimming pool filter
Added to toothpaste and baby food
Dynamite: nitroglycerine stabilizer
Insecticide
Evaporites - Rock Salt
Uses
Food
Need some salt in our diet
Preservative - jerky
Road salt (bad - sort of)
Water softener (bad)
Mined out areas for storage
Evaporites - Camp Verde Salt Mine
.
Evaporites - Rock Gypsum
Uses
Wallboard
Plaster
Stucco
Soil Amendment
Breaks up Adobe soils
Enviornment of Deposition
Grand Canyon
Muav Limestone
Bright Angel Shale
Tapeats Sandstone
Using the Principle of Superposition, the
Sandstone was deposited first (its at the
bottom.)
.
Tapeats Sandstone
Depositional environment was a beach
.
Bright Angel Shale
Depositional environment was offshore of the
beach in quiet water.
.
Muav Limestone
Depositional environment was offshore away
from shale deposition.
.
Rising Sea Level
.
Rising Sea Level - Glaciation?
What can cause a rise in sea level?
Glaciation - If we take water out of the
oceans and place it on land as ice sea level can
change by about 600 feet. At the peak of the
last glacial cycle sea level was ~450 feet lower
than today. If all the glaciers and ice caps melt,
sea level would rise by ~150 feet. These cycles
can take place in cycles of tens of thousands of
years.
Pleistocene Glaciation
.
Rising Sea Level - Plate Tectonics?
What can cause a rise in sea level?
When the rate of plate tectonics
increases, the width of the mid-ocean ridges
increases, displacing ocean water onto
continental surfaces.
Plate Tectonics
.
Plate Tectonics
.