Geology Assignment Paper on Questions for the Edwards formation

Questions for the Edwards formation

Video Questions – as you watch the video at Bee Cave road answer the questions below

1) In which direction does the bed rock dip underneath Houston?

– South

2) The Edwards Plateau is the result of what type of faulting (normal/reverse/strike slip)?

Normal

3) What type of rock is the Edwards formation?

Limestone

4) In which depositional environment was the Edwards formation deposited in?

– Marine

5) What is the dominant fossil found in the Edwards formation?

Oysters

6) In what time period was the Edwards formation deposited?

Cretaceous period

7) What caused the Edwards formation to have a different color near the surface on the ends of the road cutout?

weathering

8) What makes the Edwards formation a good reservoir system?

The body of the rock can hold water and transfers water effectively. Rainwater drops down the fault zone until it fills the aquifer.

9) What geologic structure on the fault plane allows for an understanding of fault displacement?

– Fault Striae

10) Is Austin, TX in the hanging wall or footwall of the fault system?

Footwall

Gigapan Questions – Answer the following questions using the gigapan image for the Edwards formation/Bee cave road cut out

  • How thick are the individual limestone beds? (Hint: trees/shrubs are 5-10 ft. tall).

Approximately 1-2 ft; but it varies

  • Does the thickness of individual beds remain constant across the outcrop?

Yes the thickness of the beds remain constant

  • Are all the beds in the Edwards formation the same thickness?

                -No

For each of the following questions take a partial screenshot of the relevant portion of the gigapan image, creating a separate, smaller image for each. For direction on how to do this refer to the link “Directions for Interpreting Geologic structures in gigapan images”.

1) Trace three contacts between beds.

2) Circle an area where chemical weathering has taken place.

Questions for Slaughter Gap

Video Questions – as you watch the video at Slaughter Gap answer the questions below

  • What is the origin of the rock the students are standing on: sedimentary, igneous, or metamorphic?

                -Igneous Rock

  • Are the grains the students are standing on coarse or fine grained?

                   – Coarse

  • What is the mineralogy of the rock on which the students are standing? Based on the determined mineralogy, what type of rock is it?

The rock has white crystals, pink in color and clear cords. The rock is Granite

  • What is the name of the formation on which the students are standing?

                   -Town Mountain Granite

  • How old is the rock on which the students are standing and in what Eon did it form?

-The rock is 1.1 billion years old. It was formed from Precambrian- Proterozoic

  • Is the rock behind the students sedimentary, igneous or metamorphic?

Sedimentary rock

  • How large are the particles that make up the rock behind the students?

Sand and gravel size particles

  • What is the name of the rock formation behind the students? Hickory sandstone

Hickory sandstone

  • In which time period did the formation behind the students form and how old is it??

The rock was formed during the Precambrian period and is 540 million years old.

  • What type of contact is between the rock on which the students are standing and the rock that is behind the students?

Nonconformity

  • How spatially continuous was the rock the students are standing on? What geographical area did the rock on which the students are standing initially cover?

                  -Ten kilometers- Covering from Mexico all the way along Canada.

  • What are the characteristics of the rock behind the students?

-Arkose, angular clasts and feldspar- rich sandstone

  • How far did particles making up the rock behind the students travel, and where did the particles originate?

                   -Particles originated from central Texas and were not transported far.

Gigapan Questions – Answer the following questions using the gigapan image Slaughter gap 1 for the first question and Slaughter gap 2 for the second question.

For each of the following questions take a partial screenshot of the relevant portion of the gigapan image, creating a separate, smaller image for each. For direction on how to do this refer to the link “Directions for Interpreting Geologic structures in gigapan images”.

The first image was taken at a location you can easily walk up to. The second image is the view across a small stream from first location. So, you contacts should be able to be traced across the valley with a similar geometry.

  • Draw a line approximately where the contact between the Precambrian basement and Hickory sandstone is. (Hint: look for layered rock in contact with non-layered rock. You may have to zoom in and look at the rock textures to identify this.)

 

 

 

 

 

  • Draw a line where the contact between the Precambrian basement and Hickory sandstone is and label the two rock formations with text. (Hint: look for layered rock above the break in slope. Also look carefully at all rocks within the trees. Be careful as some of these have fallen down the cliff and others are in place. You may have to zoom in to identify the rock type.)

Questions for Inks Lake

Video Questions – as you watch the video of Inks Lake answer the questions below

  • Is the rock on which the students are standing near Dr. Robinson (the professor) sedimentary, igneous or Metamorphic?

-Metamorphic

  • On which type of rock are the students standing?

        -Nices

  • What is the name of the rock formation the students are standing on?

-Valley Spring Nices

  • Are the rocks the students are standing on older or younger than the rocks at Slaughter gap?

Older

  • What type of fold is in the rocks across the water?

Iceycline folds

  • Do the igneous rocks cut the metamorphic rocks, and what does this relationship tell you about which came first?

Yes, they cut the metamorphic rocks. This tells us that branites are younger than     meta- sedimentary rocks.

  • What type of igneous intrusions are there?

Still type structure

  • How old are the igneous rocks?

1.1 Billion years old

9) What is the index mineral present at Inks Lake? (Hint: it is an aluminum silicate.)

                 – Sillimanite

  • In what type of environment and tectonic setting did this index mineral form?

Relatively shallow and hot environment associated with volcanic arc

  • What supercontinent was being built when volcanism was active in Texas?

Rhodinia

Gigapan Questions – Answer the following questions using the gigapan image Inks Lake 1 for the first two questions and Inks Lake 2 for the third question.

For each of the following questions take a partial screenshot of the relevant portion of the gigapan image, creating a separate, smaller image for each. For direction on how to do this refer to the link “Directions for Interpreting Geologic structures in gigapan images”.

  • Draw a polygon around a dike.

 

 

2) Draw a polygon around a sill.

 

3) Draw a box around a fold. (Hint: look for the yellow notebook.)

 

Questions for Enchanted Rock

Enchanted Rock State Natural Area has two exfoliation domes formed by mechanical erosion of Grenville age (1, 082 million year old) Town Mountain granite similar to what you heard about at Slaughter Gap. It intruded into the Packsaddle Schist (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 above ground level.

There are two gigapan images. One is taken from the parking lot at the entrance to the Enchanted Rock State Natural Area showing two granite domes. The second gigapan image was taken from the south dome looking north at the main dome that everyone hikes up.

Gigapan Questions – Answer the following questions using the gigapan image

For each of the following questions take a partial screenshot of the relevant portion of the gigapan images, creating a separate, smaller image for each. For direction on how to do this refer to the link “Directions for Interpreting Geologic structures in gigapan images”.

  • For Enchanted Rock Gigapan 1 – draw a polygon around granite blocks on the dome that show the exfoliation process.

2) For Enchanted Rock Gigapan 1 – do you think the granite blocks will undergo either (1) further mechanical erosion, break into smaller pieces, slide down the side of the dome and be added to the granite rubble pile at the bottom of the dome or (2) be chemically eroded by rain?

Yes. The rocks will undergo further mechanization and break into smaller pieces.

  • Enchanted Rock Gigapan 2 shows black stripes running down the slope of the dome. Using a line tool, trace one of these stripes down the dome from top to bottom. These stripes are caused by what type of weathering?