Act#12-Colorado River_key
pdf
keyboard_arrow_up
School
University of Colorado, Boulder *
*We aren’t endorsed by this school
Course
1040
Subject
Geology
Date
Jan 9, 2024
Type
Pages
4
Uploaded by jjc4081
1
Name ___________________________
Key
_______________________________
IC#10 – The Colorado River and its geology
GEOL 1040
Learning Goals:
1.
Examine the geological layers that have been exposed by the cutting of the Colorado River
2.
Contemplate the economic and environmental consequences of oil shale energy
development along the Colorado River corridor
3.
Calculate when and how fast the Colorado River has carved canyons in western Colorado
Background information: Between Rifle and Grand Junction the Colorado River has cut a valley
that lies about 6,000 feet below Battlement and Grand mesas (11,000 feet elevation), to the south
of the river, and 4,000 feet below the Roan Plateau (about 9,000 feet elevation), which stands to
the north of the river (see the cross-section below). 30 total points
Grand and Battlement mesas (south of the river) are higher than the Roan Plateau (north of the
river) because they are capped by erosion-resistant basalt that was erupted about 10 Ma (the
orange rock shown directly below the mesa names. More erosion has occurred on the Roan
Plateau because it lacks that resistant caprock.
1.
The Mancos Group (Late Cretaceous) is shale that contains marine fish fossils and plankton
like foraminifera and coccoliths. The yellow rock at the bottom of the Mesaverde Group (Latest
Cretaceous) is sandstone with symmetric ripple marks. The black wavy line at the top of the
Mesa Verde Group is coal. Use these rock descriptions to answer the following questions:
a.
Interpret the depositional environment of the Mancos Group and explain your evidence (2)
Shallow offshore marine because of the fish, the plankton, and the shale (small particles)
b.
Interpret the depositional environment at the beginning of the Mesaverde Group and also
at the end of the Mesaverde Group. Explain your evidence in each case (4)
2
Bottom of the Mesaverde is a beach because of sandstone with symmetric ripples, which
form due to waves washing back and forth
Top of the Mesaverde is a swamp because of the coal, which forms from the organic carbon
of trees that grow there
c.
Name the geologic process that was happening in western Colorado between the Late
Cretaceous and the Latest Cretaceous and explain how the change in depositional
environments over time allows you to deduce the activity of that process. (2)
The sea was regressing from Colorado (the Western Interior Seaway) during the Late
Cretaceous. We were offshore marine in Mancos time, a beach when the Mesaverde started
to be deposited, because the sea had retreated, and we were on land (a swamp) by the end
of Mesaverde time as the sea continued to retreat.
2.
The Wasatch Fm consists of debris eroded from the rising Laramide Rocky Mountains. The
yellow rock on the right side of the Wasatch Fm.(Paleocene) is conglomerate and the brown is
sandstone. Use these rock descriptions to answer the following questions:
a.
Were the mountains rising to the south of the modern Colorado River or the north?
Explain how you deduced their location (2)
The mountains rose to the south of the Colorado River because the conglomerate
(which is deposited at the toe of the mountain range) is found there.
b.
When did the Laramide Rocky Mountains rise (give a maximum and minimum
possible age in Ma)? How did you deduce this? (2)
The Laramide Rocky Mountains rose in Paleocene time because that is the age of the
Wasatch Fm, which is made up of the debris eroded from them. The Paleocene was
between 66-56 Ma.
3.
The Green River Fm (Eocene) has abundant oil shale that was deposited in a lake as big as
modern Lake Michigan. These lake deposits contain 4.285
trillion
barrels of oil (USGS Fact
Sheet 12-3145), making it the biggest petroleum reservoir in the world. Of that amount, an
estimated 353 billion barrels can be recovered from the “high grade” oil shale deposits (which
will be the most economical to extract). That represents about 25% of the entire world
reserve. Current United States oil consumption is 19 million barrels per day. Use these
statistics to answer:
a.
If U.S. consumption were to remain constant, how many years of supply will the
high-grade
Green River Formation oil shale provide (i.e. how long will it last)? Show
your calculations. (Hint: there are 365 days in a year) (2)
US consumption is 19 x 10
6
barrels/day x 365 days = 6.93 x10
9
barrels/year (i.e.
6.93 billion barrels per year)
353 x 10
9
barrels/(6.93 x 10
9
barrels/year) =
50.9 years
So a 51-year supply of oil
3
b.
Because the shale has to be heated in order to extract the oil, one barrel of oil is
needed to supply the energy necessary to extract 2 useable barrels of shale oil (i.e. 2
barrels of useful oil for every three barrels extracted). That means only two-thirds
of the 353 billion barrels of oil (i.e. 236 billion barrels) of oil can be used to meet U.S.
energy needs (assuming current technology). Given that fact, how many years of
supply will the high-grade oil shale provide? Show your work (2)
This is nearly the same calculation as part a):
236 x 10
9
barrels/(6.93 x 10
9
barrels/year) =
34.1 years
So a 34-year supply of oil
c.
In 2005 the RAND corporation estimated that it will cost between $70-95/barrel to
produce Colorado oil shale. More recent estimates are similar. Development of an oil
shale project will take decades to complete. In order to invest, a company will need
to be confident that the price of oil will remain above the cost of production for
several decades. Given the chart of global oil prices since 2010 from
businessinsider.com, would you invest in an oil shale project in Colorado? Explain
why or why not. The X-axis is year and the Y-axis shows price/barrel in $
(2)
The price of oil today is about $42/barrel and it has remained below $80/barrel since
2015. It got to over $140/barrel in 2008 and as high as $110-120/barrel several times
between 2011-2014, but the last two decades of price data do not suggest that it is likely to
be profitable to invest in shale oil until the price of oil gets a lot higher and/or the
technology advances enough that the price of production decreases significantly.
d.
Extraction of oil shale will require a considerable amount of water. Just the
retorting (the heating up of the shale to extract the oil) will consume five barrels of
water for every barrel of oil produced. The median estimate of water consumption
by a shale industry that produces 2.5 million barrels of oil per year is 300,000 acre-
feet (1 acre-foot=325,851 gallons) annually. Colorado’s current annual water
consumption is 5.3 million acre-feet. Calculate the percent increase of Colorado
water consumption needed to supply the shale oil industry. Show your work (2)
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
4
This calculation is done by dividing the amount of water the shale oil industry needs
by the total water consumption in Colorado and then multiplying by 100 to get
percent: (300,000 acre-feet/5.3 million acre-feet)x100 = (0.0566)x100 =5.7%
The shale oil industry would increase Colorado water consumption by about 5.7%
(this does not include the increased water demands of the increased population that
would move to the state to fill the jobs the industry will create)
e.
In 2015 the median cost of water in Colorado was $25,000/acre-foot. Given that the
shale oil industry would use 300,000 acre-feet of water each year, what would the
annual cost of water be to supply the industry? Show your work. (2)
$25,000/acre-foot x 300,000 acre-feet=(2.5 x 10
4
$/acre-foot) x (3.0 x 10
5
acre-feet)
= $7.5 x 10
9
= The cost of water to supply the industry (at today’s prices) will be
about
$7.5 billion dollars
(note that the price for water will likely rise
dramatically if there is such a large increased demand)
f.
Considering your answers to questions a-e and any other information you find
relevant (for example, your level of concern about climate change), comment on
whether or not you think that the development of shale oil in Colorado would be a
net benefit or a net drawback for the people of Colorado, the people of the U.S., and
for the world. There is no right or wrong answer to this question. You will receive
full credit for any thoughtful answer. (5)
Any thoughtful answer will receive full credit. The purpose of this question is for you to
contemplate the economic, social, and environmental consequences of developing this massive
resource that Colorado possesses.
4.
The valleys now occupied by the Colorado River and its tributary (Plateau Creek) that lies
between Grand and Battlement mesas could not have existed when the basalt erupted on top
of Grand and Battlement mesas (due to Steno’s Law of Lateral Continuity. Remember, too, that
basalt is a runny type of lava that would spill down into the valley if the valley existed at the
time. The lavas don’t spill into the valleys). So, the Colorado River must have eroded (incised)
6,000 feet (about 1,800 meters) since the lava flows were erupted 10 million years ago.
Calculate the river’s rate of incision since the lava was erupted. Show all of your work and give
your answer in both feet/million years and meters/million years. (3)
The basalt erupted 10 million years ago (10 x 10
6
years). The river has incised 6000 feet during
that time: 6000 feet/10 million years =
600 feet/million years
Using metric units: 1800 m/10 million years =
180 m/million years