virtual_field_trip_upper-_coast_tx_f2323
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School
Texas A&M University *
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Course
1330
Subject
Geology
Date
Dec 6, 2023
Type
docx
Pages
8
Uploaded by MateBoulderPorpoise34
Virtual Field Trip to Central Texas
Physical Geology - Fall 2023
Name:
myUH ID number:
Professor’s Name:
Class Time:
Email your completed documents to
easglc@central.uh.edu
with the subject “Central TX VFT”
Academic Honesty (Acknowledgement Required)
The Virtual Field Trip to Central Texas is to be completed by yourself; you should not work with a partner
or group. Do not search for answers on the internet because 1) it is cheating; 2) answers that are posted
are incorrect, and we’ll know where you got them from, and; 3) the questions change every semester. Be
careful if you watch the videos with closed captioning because the spelling of geologic terms is often
incorrect or misinterpreted by the captioning software, so you may end up with a wrong answer. If you
are unfamiliar with a word or geologic concept, it is okay to look it up online to find the correct spelling
and definition. If you find yourself needing help, physical geology teaching assistants staff the
Geoscience Learning Center
.
By submitting this work, I,
Type Your Name Here
attest that I have not
violated the UH Academic Honesty code. I completed this assignment
by myself and did not copy any portion of my answers from another
student, a website, or any other source.
Instructions
The virtual field trip to Central TX is a Google Earth tour that will require you to watch videos of our
field trip stops, answer questions, and make interpretations on GigaPan images (very large, high quality).
In addition to this document, you will need the accompanying PowerPoint file for image
interpretations.
Head back to the field trip page if you still need the PowerPoint file. All written answer
should be in this document.
Accessing the Trip
This virtual field trip has been built in Google Earth.
Click here to access the trip
. The first thing you will
see is an overview of Texas, and the field trip stops. In the menu on the left side, click on “Present” to
begin the tour. At each location a box will appear on the right side of the screen with information about
each stop, the videos you need to watch, and links to the GigaPan images. Use the menu on the bottom
left to move between stops.
Written Answers
All answers need to be written in complete sentences to receive credit
and typed in the supplied boxes.
Your responses will appear in a green-colored font, do not change this. Any answers not written in
complete sentences will be marked as incorrect and will not receive credit.
Taking Snapshots/Screen Captures
You’ll need to take snapshots of high-resolution images from the field trip stops. Follow the directions
below according to your operating system. Paste the images into the PowerPoint answer file on their
appropriate slide. Image questions will ask you to make annotations on your snapshots to highlight items
of geologic interest. Common annotations include drawing circles and lines. Use Microsoft PowerPoint
for making these annotations.
PC Directions
for taking snapshots (Windows 10)
Mac Directions
for taking snapshots (MacOS)
Assignment Submission
Save your completed word document as “yourlastname_firstname_CentralTXVFT”you’re your
PowerPoint document as “yourlastname_firstname_CentralTXsnapshots”
Email your completed
documents to
easglc@central.uh.edu
with the subject “Central TX VFT”
. Teaching Assistants will
begin grading submissions after the deadline. After your work is graded, you will receive a confirmation
email from a TA. Submissions are graded as pass/fail. If your assignment requires resubmission because
of too many incorrect questions or missing answers, you will have 48 hours to do so.
Stop 1: Observations for the Edwards Formation
Head to Stop 1 of the virtual field trip. Watch the video at Bee Cave Road and view the GigaPan image.
Video Questions for Stop 1
1.
As you travel from Houston to Austin, the rocks are progressively older. What is the age range of
the rocks that occur along this route. Give the .
2.
Use full sentences describe the Edwards limestone, including information such as minerals
present, texture, grain size, color, weathering, size of bedding, etc.
3.
What are some of the fossils found in the Edwards Limestone?
4.
There is a small fault at this outcrop that is part of the Balcones fault system.
a.
What type of fault is this?
b.
Describe the plate tectonic setting that created this fault.
5.
Is this an active fault? How do geologists determine the age of faults?
GigaPan Questions for Stop 1
6.
Take a screenshot that highlights your description from question 3 above. Paste it onto the
PowerPoint slide.
7.
Take a new screenshot and trace three contacts between sedimentary beds.
a.
Using your observations of these contacts, how thick are the individual limestone beds?
(Hint: trees/shrubs are 5-10 ft tall).
b.
Are all the beds in the Edwards formation the same thickness? Describe what you see.
You may want to zoom out and relook at the entire GigaPan image.
8.
The Edwards formation has been affected by chemical weathering, both at the surface and
underground. Search the GigaPan image for any evidence that chemical weathering affected this
outcrop.
a.
What type of chemical weathering is prominent?
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b.
Include a screenshot with annotations that supports your answer (on the PowerPoint
slide).
c.
How do these chemical weathering features affect the Edwards aquifer, source of
drinking water for both San Antonio and Austin?
Stop 2: Observations for Slaughter Gap
This field trip stop has two different rock types: an igneous rock that students are standing on and a
sedimentary rock behind them.
Video Questions for Stop 2
9.
Describe the igneous rock the students are standing on. Include information such as color,
minerals present, texture, grain size, is it intrusive or extrusive, name of the rock, and its age.
10.
Describe the sedimentary rock located behind the students. Include information such as the type
of sedimentary rock, grain size, grain shape, minerals present, color, bedding thickness, age, and
any other features.
11.
There are no fossils at this location, but elsewhere there are reports of trilobite trackways for this
rock. What do you think was the depositional environment for this sedimentary rock?
12.
Igneous rocks form within the Earth via melting. Do you think this igneous rock formed by
decompression melting or fluid-induced melting of the mantle? What evidence would you look
for to determine this?
GigaPan Questions for Stop 2
The first image was taken at the location where the students were standing, shown at the red arrow’s tip
on the topographic map of Slaughter Gap (Figure 1). The second image is the view across the gap from
the first location, as shown by the red line on the topographic map. The base of the second GigaPan image
is parallel to the red line shown below.
Figure 1 - Topographic map of the Slaughter Gap region provided by Dr. Leon Long, University of Texas at Austin
13.
On the first GigaPan image, locate the contact between the igneous rock and the sedimentary
rock. You may have to zoom in and move around the image to look at the rock textures to help.
a.
Is the contact flat or steep?
b.
Take a snapshot and draw a line that shows the contact between these two rocks (on the
PowerPoint file).
14.
Locate this same contact on the second GigaPan image from this stop. You can zoom in to see the
rock types within the trees and look for layered rock above the break in slope. Some of these are
large boulders that have fallen down the cliff. Take a snapshot and draw a line that shows the
contact between the two rock types. The angle of the contact relative to the Earth’s surface should
be similar on both sides of Slaughter Gap.
Geochronology for Stop 2:
The Sauk marine transgression occurred during a period from the 600 to 500 million years ago when sea
level rose across North America leaving behind zircon, commonly found in sand, that contain trace
amounts of uranium and thorium within sedimentary units enabling researchers to date the sediments.
Detrital zircon geochronology is the science of
analyzing the age
of
zircon
deposited within a
specific
sedimentary unit
by examining their uranium–lead
(U-Pb)
ratios.
Researchers tested detrital
zircon samples utilizing the
U-Pb
dating method, which can be used to date rocks that formed and
crystallized, were then eroded, transported, and deposited. So, these ages may reflect different sources
for zircon as well as its age.
At this location and elsewhere throughout the Llano Uplift, a team of geologists led by J. Richard Kyle
collected samples of the Hickory Sandstone and measured the ages of detrital zircon grains (zircon found
in sedimentary rocks). Sample 13-5 is from this field trip stop location, and 13-10 is about 20 km to the
southwest. Remember, radiometric dating of minerals in sedimentary rocks gives you the age of the
igneous or metamorphic parent rock the minerals originally formed in and not the age the sediment was
deposited.
This data table shows the percentage of zircon grains for different age ranges.
Sample
Numbe
r
480-550 Ma
600-900 Ma
1000-1300 Ma
1300-1550
Ma
1600-1800
Ma
>1800 Ma
13-05
0 %
0
89
9
1
1
13-10
5 %
2
48
44
0
1
Figure 2.
Geologic map showing locations of various basement provinces as well as the rifted margin of
the Laurentian supercontinent. The colored areas show where different belts of rock are located. The red
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box shows the location of the Slaughter Gap stop on the UH Virtual field trip.
The ages for different
basement provinces are summarized for each area. Modified after Kyle and others (2022).
15.
What is the age range for each of sample?
16.
How much of Earth’s history is recorded by zircon grains in each sample?
Hint: compare the age
of Earth (~4600 Ma) to the age range recorded by the zircon grains.
17.
The Great Unconformity at this location spans from the intrusion of granite at
~1070 Ma to the
deposition of the Hickory Sandstone at ~ 500 Ma. How much of Earth’s history is missing at this
location?
18.
For sample 13-05, describe the relationship between the detrital zircon grains compared to ages
in Figure 2.
19.
For sample 13-10, describe the relationship between the detrital zircon grains compared to ages
in Figure 2.
20.
How far from the sample location was the source area for the oldest zircon grains?
21.
How far from the sample location was the source area for the youngest zircon grains for each
sample?
22.
On Figure 2, draw an approximate location of a river that may have brought zircon grains from
their source area to the red box.
Stop 3: Observations for Inks Lake State Park
This stop has two different rock types as well, metamorphic, and igneous. The students are standing on
one type, and the other is across the stream in the GigaPan images.
Video Questions for Stop 3
23.
Describe, in detail, why the rocks here are different from most others in Texas.
24.
Describe the metamorphic rock that students are standing on. Include observations on its color,
grain size, minerals, age, and texture (terms such as granoblastic, foliated, or layered).
25.
Based on the minerals present, did the metamorphism happen deep or shallow in the Earth?
26.
Describe the cross-cutting relationships between the igneous and metamorphic rocks and which
rock came first.
27.
What was the tectonic environment of this region?
GigaPan Questions for Stop 3
28.
In the first image, locate a dike, take a snapshot, and then draw a polygon around it.
29.
In the first image, locate a sill, take a snapshot, and then draw a polygon around it.
30.
In the second GigaPan image, locate a fold, take a snapshot, and draw a box around it.
Stop 4: Observations for Enchanted Rock
Enchanted Rock State Natural Area has two exfoliation domes formed by erosion of the Grenville age
Town Mountain granite (about 1.1 billion years old), similar to what you heard about at Slaughter Gap.
See
this video
for an explanation of exfoliation domes and
watch exfoliation in action
.
The Town Mountain Granite intruded into the Packsaddle Schist (the schist is not visible in the GigaPan
image). The two granite domes are part of the second-largest batholith in the Llano Uplift. The tallest
dome is 425 ft above ground level.
There are no video questions from our Enchanted Rock stop, only observations made from images.
GigaPan Questions for Stop 4
31.
Locate the first GigaPan image for this stop.
a.
Take a screenshot and draw a polygon around the granite block on the dome to show the
exfoliation process.
b.
Do you think these blocks are hazardous to anyone who walks near them?
c.
Which of the following do you think is most likely to happen? Will the granite blocks 1)
undergo further mechanical weathering, break into smaller pieces, slide down the side of
the dome, and be added to the granite rubble pile at the bottom or 2) will the granite
blocks be chemically eroded by rain? Be sure to explain your answer.
32.
Locate the second GigaPan image for this stop.
a.
Take a snapshot and use a pen tool to trace the path of a black stripe running down the
slope of the dome.
b.
What type of weathering causes these stripes?