Geol assignment 2
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GEOL 1011: Introduction to Geoscience 1 Yashvi Amin(t00699221)
Assignment 2: Weathering and Soil, Sedimentary and Metamorphic Rocks, and Geological Time (10%)
This assignment is worth 10% of your total course mark. There are 100 points available overall. Complete all parts of this assignment by responding to each question in the space provided.
Please type your answers directly into this document, and submit the assignment to your Open Learning Faculty Member for grading when you are finished. Do not remove the questions, or the number of points for each question, from the document.
This assignment includes two field exercises. You are expected to go out into an area
close to where you live, take some photographs, and describe what you see.
Please remember to reference concepts that you get from outside sources. Concepts from the textbook and course units do not need to be referenced, but images, tables, or
copied fragments of text longer than a few words from any
source need to have in-text
citations and references. Refer to the “TRU Citation Guides” for citing references in your assignments. If you’re not sure about what you need to reference, please see Student Academic Integrity and refer specifically to the plagiarism section (VI, 4).
Part A: Short-Answer Questions (
20 points in total
)
Answer the following questions as succinctly as you can. None of the answers should be more than a couple of sentences (100 words or less). Please type your answers into the grey boxes.
1.
Explain why the presence of carbon dioxide in the atmosphere is important to
weathering. (
2 points
)
Carbon dioxide reacts with water present in atmosphere which produces weak
carbonic acid. This reaction leads to most chemical weathering.
2.
Describe some of the ways that soil can be degraded if we don’t take care to look after it. (
2 points
) Soil can be degraded by natural factors like wind and excess flow of water, also
by tillage and human practices related to forestry and agriculture plays crucial role in soil degradation.
3.
How does the velocity of moving water affect the transportation of sedimentary particles? (
2 points
)
If velocity of water is faster, it will be able to move larger sedimentary particles. Sedimentary particles like boulders can be move by faster flow of water.
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Assignment 2: Weathering and Soil, Sedimentary and Metamorphic Rocks, and Geological Time
4.
What is chert made of what is the typical source of that material, and in what environment is it typically deposited? (
2 points
)
Chert is made from silica, which is found in hard shells of radiolarians and diatoms. They are mainly deposited in very deep marine environment in thin beds.
5.
Describe the tectonic origins of rift basins and foreland basins. (
2 points
)
Rift basin is formed when crust is being pulled apart and which results in subsiding of crust from both sides. While foreland basin is formed when mass of volcanic range is depressing the crust on either side.
6.
What is the typical origin and depositional environment of normal (i.e., fining
upward) graded bedding? (
2 points
)
Graded bedding is product of deposition from slowing current and they are deposited in submarine-fan environment.
7.
With respect to sedimentary rocks, what are the criteria for defining a “formation”? (
2 points
)
A formation can be defined as series of beds that are distinct from one another above and below and is thick enough to be presented on geological maps.
8.
Explain why mineral stability is important to metamorphism. (
2 points
)
If minerals are unstable in parent rock, then minerals start to recrystallize into new minerals when parent rock is exposed to increased temperature.
9.
Describe the nature of foliation in gneiss. (
2 points
) In gneiss, minerals may have separated into bands of different colours. Also, mica is absent in gneiss rock as it is formed under high temperature where mica is not stable.
10. Describe the rock “skarn” and the conditions under which it forms. (
2 points
)
When magnetic fluids flow through carbonate rock their chemistry changes which results in deposition in several minerals likegarnet, epidote, magnetite etc and this metamorphism is known as skarns.
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GEOL 1011: Introduction to Geoscience 3 Yashvi Amin(t00699221)
Part B: Exercises (
50 points in total
) B1: Observe and document weathering (
16 points
)
Weathering is happening all around us, although most of the time we don’t even notice it. For this exercise, you need to look around the region where you live, find some evidence of mechanical or chemical weathering, photograph it, and then describe what you see in the photo. Some examples are freeze-thaw weathering of a rock exposure, tree roots pushing rocks apart, lichen growing on a rock, or a rusty stain on a rock exposure. If you’re unable to find a natural example of weathering, acceptable alternatives would include frost heaving on a road, a crack in a building stone or sidewalk, or dissolution or other weathering of a headstone or other old monument. Make sure to show enough of the background in your photo so that it is clear what might have caused the weathering. Ask your Open Learning Faculty Member for help if you can’t think of a place to look. Include your photo with your response, and write a few sentences about the weathering effects that you can see in the photo. Provide some evidence in the photo that you were there when it was taken (e.g., a piece of paper with your name on it, or your hand with three fingers showing).
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Assignment 2: Weathering and Soil, Sedimentary and Metamorphic Rocks, and Geological Time
I found this rock near my house (Near east village, Kamloops, British Columbia). This rock undergoes chemical weathering as it is evident by dull red stain on it. This can cause by oxidation reaction on expose part of rock under different conditions. I can surely say that its rust because when I touch stain to check, it leaves red rusty stain on my fingers (forgot to take picture of that).
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GEOL 1011: Introduction to Geoscience 5 Yashvi Amin(t00699221)
B2: Photograph and describe a depositional environment (
16 points
)
Sediments are also being deposited all around us, and for this exercise you need to find and photograph a depositional environment. Some examples might be a section of a stream, lake, wetland, beach, delta, bay of the ocean, and so on. Don’t hesitate to
ask your Open Learning Faculty Member for help. Include a photo with your response. Describe what type of sediments (clay, silt, sand, pebbles, etc.) you think are being deposited (based on what you can see or what you think should be there), and speculate about how long this particular sedimentary basin has existed. Do you think it’s likely that these sediments will be turned into rock at some time in the future, or is it more likely that they will be re-eroded and deposited elsewhere? Again, provide some evidence in the photo that you were there when it was taken. Examples of sedimentary basin photos are provided below.
Figure A2-1. Sedimentary basins. © Steven Earle. Used with permission.
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Assignment 2: Weathering and Soil, Sedimentary and Metamorphic Rocks, and Geological Time
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GEOL 1011: Introduction to Geoscience 7 Yashvi Amin(t00699221)
This picture is of Thompson River located in Kamloops. By looking at texture of soil
and size of soil grains it is evident that sediment is mostly silt and sand. This basin must be existed from approximately more than 20 million years ago. There are less chances of sediments turning into rock because of wind and flowing water will TRU Open Learning
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Assignment 2: Weathering and Soil, Sedimentary and Metamorphic Rocks, and Geological Time
relocate and erode the sediments so it is not possible for sediments to be deposited at same place for longer time.
B3: Understanding the Mt. Polley area geological map (
18 points
)
The following questions refer to the geological map of the Mt. Polley area (
Geoscience Map 2007-1: Regional Geology of the Mount Polley Area, central British Columbia. Copyright
© Province of British Columbia. All rights reserved. Reproduced with permission of the Province of British Columbia
) in central British Columbia, and are based on information in the map legend, the map symbols, the cross sections, and on the map itself:
1.
What is the unit code and approximate age range (in years) of the youngest layered unit (i.e., sedimentary or volcanic rock) in the map area? (
2 points
)
Unit code is M Cav and approximate age range is somewhere between 2-23 million years ago.
2.
Provide the unit codes, rock type names, and ages of any three of the layered units that are entirely sedimentary
in origin. (
3 points
)
MJ Dcg- Conglomerate, sandstone, graded siltstone- Middle Jurassic
EJr sn- siltstone, sandstone, and calcareous conglomerate- unnamed Sinemurian to plienscbachian
LT Nl- Limestone, ash and crystal rich sandstone and maroon siltstone- Late jurrasic
3.
Based on the map and cross-section A-A’, how would you describe the relationship between the Unnamed Cretaceous Conglomerate (Kcg) and the rocks underneath it? (You may need to refer to the “Symbols” explanations on the map.) Why is this rock called “polymictic”? (
4 points
)
Relation between Unnamed cretaceous conglomerate and underneath stone is assumed as unconformity. It is called polymictic because conglomerate in it consist of two and more i.e 5 types of rocks in it.
4.
The oldest unit shown on the map is primarily made up of metamorphic rocks.
What are the main rock types, and in what type of metamorphic environment did they form? Where on the map can you find this rock unit? (
4 points
)
Main rock types are gneiss, schist, quartzite, marble, and amphibolite. These rocks are formed under high pressure or shear stress and heat in regional metamorphism environment. This rock unit is found at topmost part of map between 600000m and 605000m.
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GEOL 1011: Introduction to Geoscience 9 Yashvi Amin(t00699221)
5.
The intrusive rock north of Gavin Lake has been isotopically dated. What specific dating technique was used? What is the numerical date, and to what geological period does this date correspond? (
3 points
)
The specific dating technique used for the intrusive rock north of Gavin Lake is Radiometric Dating, more specifically, Uranium-Lead (U-Pb) dating. Numerical date is 160 ± 2.3 and this correspond to Middle Jurassic period.
6.
The Gavin Lake area intrusion is depicted in Cross Section B. Describe its age relationship with the rock into which it has intruded. (
2 points
)
Relationship is described as contact approximate.
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Assignment 2: Weathering and Soil, Sedimentary and Metamorphic Rocks, and Geological Time
Part C: Longer Questions (
30 points in total
)
Please answer the following questions. Write as much as you think is necessary to answer each question, but don’t forget that someone has to read what you write, so be as concise and clear as possible. You do not need to reference the text or the material in the course units (except images and quotations), but if you use any outside sources, please provide in-text citations. Use any referencing style that you are comfortable with.
1.
Explain what sedimentary rocks can tell us about past environments, focussing
on the characteristics of sedimentary grains, the types of sedimentary structures present, and the presence and types of fossils. (
15 points
)
Grain characteristic
s
By observing sedimentary grain closely, one can determine the
about type of source rock, weathering processes (lithology), degree of rounding, and the extent to which they have been sorted by transportation and depositional processes. For example, if we study grain characteristics of stone (limestone) and if it has bicarbonates and calcium, it can be predicated that this stone was formed in marine environment and those ions are from shells and hard parts of organisms in marine water. Sedimentary structures
Sedimentary structure gives useful interference about the processes that led to deposition of rocks. For instance, if there is observable separation of sediments into layer that differ from one another (bedding) in texture, colour or composition that indicates changes in depositional processes due to seasonal difference, change in climate, change in location or tectonic changes. Also, cross- bedding can tells us direction and rate of current flows in past by observing the ripples on it.
Fossils
Fossil can help to differentiate between marine and terrestrial environment, estimating depth of water, to detect existence of currents and estimate average temperature and precipitation in past. For example, fossile found from marine environment can tell us depositional environment in past.
2.
Discuss the role of plate boundary environments and plate tectonic processes in regional metamorphism, and explain why isostasy is important to regional metamorphism. (
15 points
)
Below are listed roles of different plate boundaries and plate tectonic processes in regional metamorphism: -
1.
Subduction zone- At a subduction zone, oceanic crust is forced down into TRU Open Learning
GEOL 1011: Introduction to Geoscience 11 Yashvi Amin(t00699221)
hot mantle, but oceanic crust is relatively cool along its sea floor upper surface, and it takes time to heat up and there is temperature difference of several hundreds of degrees than surrounding mantle. This situation creates high pressure and relatively low temperature condition which produce new mineral in rock.
2.
Converging plate- When these plates collide with each other and subducts under one another, high pressure and temperature is created with leads to regional metamorphism. 3.
Divergent boundaries – At divergent boundaries, when magma rises to earth surface, it encounters other rocks and can lead to contact metamorphism.
The balance that the Earth's crust maintains in reaction to gravity's vertical pull
is known as isostasy. It is essential to the transformation of the region. Rocks can fluctuate in density as they metamorphose. Isostasy may result in the crust sinking into the mantle if metamorphism causes an increase in crustal density. On the other hand, the crust may rise if its density drops. The Earth's surface metamorphic rocks may become visible due to vertical movement of crust.
References
https://rocksminerals.flexiblelearning.auckland.ac.nz/rocks/
conglomerate.html#:~:text=Lithology%20%2D%20a%20conglomerate%20where
%20the,are%20monomictic%20(or%20oligomictic)
.
https://www.cliffsnotes.com/study-guides/geology/metamorphic-rocks/
metamorphism-and-plate-tectonics
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