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Transcript
Grand Canyon Rocks
“Those who write about the Canyon
generally begin by saying that it is
indescribable; then they undertake to
describe it.” Joseph Wood Krutch
Grand Canyon: Limestone
The oldest known rocks on Earth come from
the Mackenzie District of Canada’s
Northwest Territories. They have been
dated at 4 billion years old.
It wasn’t until the later Precambrian era,
around 1.8 bya to 500 mya, that the first
carbonate sediments began to settle out of
the oceans to eventually form limestone. The
Bass Limestone, part of the GC Supergroup,
was one of the first limestones.
Grand Canyon: Limestone
The major component of all limestone is calcium
carbonate, CaCO3. This is the chemical name
for the minerals calcite and aragonite.
Calcite, aragonite, and dolomite, CaMg (CO3),
are estimated to make up 15 % of the earth’s
sediments and sedimentary rocks, and about
2 % of the earth’s crust.
Grand Canyon: Limestone
Carbonate minerals can be identified fairly
easily because they all break down in acid.
The carbon-oxygen bond in the CO3 group
becomes unstable in the presence of
hydrogen ions (H+) found in acids, and the
carbon dioxide CO2 forms. Calcite is the
most common mineral noted for fizzing.
Grand Canyon: Limestone
The reaction the occurs between hydrochloric
acid and calcite is expressed:
CaCO3 +
calcium
carbonate
2HCl
hydro
acid
CO2 + H20 + CaCl2
carbon water
calcium
dioxide
chloride
Grand Canyon: Limestone
Calcification is the process by which certain
organisms and algae extract calcium and
carbonate ions from the surrounding
seawater, oxidize the calcium, and deposit
the resulting compound as solid material,
either calcite or aragonite. Calcite is more
common than aragonite and makes up the bulk
of limestone and marble deposits on Earth.
Grand Canyon: Limestone
Calcium ions are produced through the chemical
weathering of rocks such as granite. As
mountains of granite decompose, calcium ions
are released and carried to the ocean by
rivers and streams.
Precipitation of calcium carbonate may occur by
chemical or organic means. (Limestone
created: Chem Weathering or Biological
ways.) Many marine plants and animals
extract calcium carbonate directly from
seawater for incorporation into their shells.
Grand Canyon: Limestone
Most limestones throughout the history of
Earth formed in relatively shallow, warm seas.
One ingredient all limestones have in common is
calcium carbonate. Geologists identify a
variety of different forms of limestone:
Chalk is composed of almost pure calcite. A
powdery, fine-grained rock, chalk may contain
small amounts of silt or mud.
Grand Canyon: Limestone
Reef limestones are mainly composed of the
skeletons of marine organisms, such as corals.
Today coral reefs grow in warm seas. The
beautiful blue-green waters associated with
these areas are indicators of lime-secreting
blue-green algae. Sections of the Redwall
Limestone in the GC include fossil corals and
other reef-dwelling organisms, indicating a
warm, tropical environment.
Grand Canyon: Limestone
Reef limestones are mainly composed of the skeletons of marine organisms, such
as corals. Today coral reefs grow in warm seas. The beautiful blue-green
waters associated with these areas are indicators of lime-secreting bluegreen algae. Sections of the Redwall Limestone in the GC include fossil corals
and other reef-dwelling organisms, indicating a warm, tropical environment.
Grand Canyon: Limestone
Coquina is a limestone formed almost entirely of
sorted and cemented fossil debris, mostly
small shells and shell fragments. The sorting
of the fragments and type of organisms
suggest that the material has been
transported some distance and/or sorted by
wave action.
Freshwater limestones can be identified by the
type of fossils it contains. It often includes
snail shells.
Grand Canyon: Limestone
Coquina is a limestone formed almost entirely of sorted and
cemented fossil debris, mostly small shells and shell
fragments. The sorting of the fragments and type of
organisms suggest that the material has been transported
some distance and/or sorted by wave action.
Grand Canyon: Limestone
Freshwater limestones can be identified by the
type of fossils it contains. It often includes
snail shells.
Grand Canyon: Limestone
Oöliths are small grains of sand, silt, or shells
around which concentric layers of calcium
carbonate are deposited. Oölithic limestones
usually form in warm, shallow marine
conditions where limy mud forms and in which
agitation by waves, tides, and currents takes
place.
Grand Canyon: Limestone
Tufa is formed from cool freshwater sources
rich in calcium carbonate. When the water is
exposed to the atmosphere, carbon dioxide is
released, precipitating calcium carbonate. In
areas where limestone is common, tufa fills
cavities in rocks and builds stalactites and
stalagmites in caves.
Travertine is harder and denser than tufa. It is
often deposited around hot springs, such as
Yellowstone National Park. It is found in the
same places as tufa, including caves.
Grand Canyon: Limestone
Tufa is formed from cool freshwater sources
rich in calcium carbonate. When the water is
exposed to the atmosphere, carbon dioxide is
released, precipitating calcium carbonate. In
areas where limestone is common, tufa fills
cavities in rocks and builds stalactites and
stalagmites in caves.
Grand Canyon: Limestone
Travertine is harder and denser than tufa. It is
often deposited around hot springs, such as
Yellowstone National Park. It is found in the
same places as tufa, including caves.
Grand Canyon: Limestone
Stratigraphy is the study of the distribution
and sequence of sedimentary rock layers. If
two rock layers or strata contain the same
group of fossils, they must be the same age.
Lithostratigraphy is a subcategory of
Stratigraphy in which geologists describe rock
layers and their distribution.
Grand Canyon: Limestone
Lithostratigraphy : organizes rock layers:
Formations: layers with distinguishable
characteristics and sequences of sediments.
Members: smaller identifiable units that make
up formations.
Beds: the smallest distinguishable unit, often
only a few centimeters in thickness, but
different from the sediment above and below
it.
Grand Canyon: Limestone
Law (or principle) of Superposition states that
in any undisturbed sequence of layered rocks,
a particular bed must be older than any bed on
top of it.
Grand Canyon: Limestone
Law (or principle) of Superposition states that
in any undisturbed sequence of layered rocks,
a particular bed must be older than any bed on
top of it.
Law of Original Horizontality states that, when
particles of sediment settle out of water or
air, they form horizontal layers.
Grand Canyon: Limestone
Law (or principle) of Superposition states that
in any undisturbed sequence of layered rocks,
a particular bed must be older than any bed on
top of it.
Law of Original Horizontality states that, when
particles of sediment settle out of water or
air, they form horizontal layers.
An Unconformity is a gap in the geological
record during which either no rocks were
deposited or erosion of existing rocks took
place.
Grand Canyon: Rocks
Sandstone
Shale
What is the third type of rock found in the
Grand Canyon?
Making Limestone
Sandstone
Shale
What is the third type of rock found in the
Grand Canyon?
What was the property of limestone that
you observed during the “Acid Test?”
Making Limestone
Sandstone
Shale
What is the third type of rock found in the
Grand Canyon?
What was the property of limestone that
you observed during the “Acid Test?”
In your journals, list what might be found in
the seawater that would contribute to the
fizz.
Making Limestone




Double the recipe: Limestone Pg 39 binder.
You may use a total of 2 spoons of plaster of paris.
Do not change the amount of water added. Keep
30 ml.
You may use a total of 8 spoons of the following
materials
 Sand
 Oyster shells
 Powdered clay
(You may add a shell fossil to the surface of your
limestone layer.)
Making Limestone
The chemical in the water that makes it
similar to the ancient seawater is calcium
hydroxide. Calcium hydroxide dissolved in
water is called limewater (nothing to do
with lime fruit). Ancient seawater
contained many other dissolved chemicals
as well, salts, acids, but the calcium
hydroxide is the chemical of interest
today.
Making Limestone
What is a fossil?
Making Limestone
What is a fossil?
A fossil is any remains, trace, or imprint of
a plant or animal that has been preserved
in the earth’s crust since some past
geological or prehistoric time. A looser
definition is any evidence of past life.
Making Limestone
Testing for
Calcium
Carbonate/
hydroxide w/
hydrochloric
acid
Journal: Make
a table
Material
Small cup “white
stuff”
Large cup: top layer
“sedimentary”
Rock # __ from
North Canyon
Rock # __ from
Nankoweap Canyon
Fizz
No
Fizz
Biological Process
Remains of marine animals. Their
shells and skeletons are deposited
on the bottom of the ocean
 The calcite and other minerals may
harden into limestone.
 Remains of animals may also be
buried in the carbonate muds and
eventually turn into fossils.
